<?xml version="1.0" encoding="us-ascii"?>
<!-- Created by Merrill Corporation -->
<!--Generated by IRIS XBRL Generation Engine-->
<link:linkbase xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" />
  <link:roleRef roleURI="http://www.celldextherapeutics.com/role/DisclosureStockBasedCompensationDetails2" xlink:type="simple" xlink:href="cldx-20131231.xsd#DisclosureStockBasedCompensationDetails2" />
  <link:roleRef roleURI="http://www.celldextherapeutics.com/role/DisclosureIncomeTaxesDetails2" xlink:type="simple" xlink:href="cldx-20131231.xsd#DisclosureIncomeTaxesDetails2" />
  <link:roleRef roleURI="http://www.celldextherapeutics.com/role/DisclosureStockBasedCompensationDetails" xlink:type="simple" xlink:href="cldx-20131231.xsd#DisclosureStockBasedCompensationDetails" />
  <link:roleRef roleURI="http://www.celldextherapeutics.com/role/DisclosureOtherLongTermLiabilitiesDetails2" xlink:type="simple" xlink:href="cldx-20131231.xsd#DisclosureOtherLongTermLiabilitiesDetails2" />
  <link:roleRef roleURI="http://www.celldextherapeutics.com/role/DisclosureTermLoanDetails" xlink:type="simple" xlink:href="cldx-20131231.xsd#DisclosureTermLoanDetails" />
  <link:roleRef roleURI="http://www.celldextherapeutics.com/role/DisclosureRevenueDetails" xlink:type="simple" xlink:href="cldx-20131231.xsd#DisclosureRevenueDetails" />
  <link:roleRef roleURI="http://www.celldextherapeutics.com/role/DisclosureCollaborationAgreementsDetails" xlink:type="simple" xlink:href="cldx-20131231.xsd#DisclosureCollaborationAgreementsDetails" />
  <link:roleRef roleURI="http://www.celldextherapeutics.com/role/DisclosureNatureOfBusinessAndOverviewDetails" xlink:type="simple" xlink:href="cldx-20131231.xsd#DisclosureNatureOfBusinessAndOverviewDetails" />
  <link:roleRef roleURI="http://www.celldextherapeutics.com/role/DisclosureStockholdersEquityDetails" xlink:type="simple" xlink:href="cldx-20131231.xsd#DisclosureStockholdersEquityDetails" />
  <link:roleRef roleURI="http://www.celldextherapeutics.com/role/DisclosureSummaryOfSignificantAccountingPoliciesDetails3" xlink:type="simple" xlink:href="cldx-20131231.xsd#DisclosureSummaryOfSignificantAccountingPoliciesDetails3" />
  <link:roleRef roleURI="http://www.celldextherapeutics.com/role/DisclosureSummaryOfSignificantAccountingPoliciesDetails2" xlink:type="simple" xlink:href="cldx-20131231.xsd#DisclosureSummaryOfSignificantAccountingPoliciesDetails2" />
  <link:roleRef roleURI="http://www.celldextherapeutics.com/role/DisclosureIntangibleAssetsAndGoodwillDetails" xlink:type="simple" xlink:href="cldx-20131231.xsd#DisclosureIntangibleAssetsAndGoodwillDetails" />
  <link:roleRef roleURI="http://www.celldextherapeutics.com/role/DisclosureNetLossPerShareDetails" xlink:type="simple" xlink:href="cldx-20131231.xsd#DisclosureNetLossPerShareDetails" />
  <link:roleRef roleURI="http://www.celldextherapeutics.com/role/DisclosureSummaryOfSignificantAccountingPoliciesDetails4" xlink:type="simple" xlink:href="cldx-20131231.xsd#DisclosureSummaryOfSignificantAccountingPoliciesDetails4" />
  <link:roleRef roleURI="http://www.celldextherapeutics.com/role/DisclosureSummaryOfSignificantAccountingPoliciesDetails" xlink:type="simple" xlink:href="cldx-20131231.xsd#DisclosureSummaryOfSignificantAccountingPoliciesDetails" />
  <link:roleRef roleURI="http://www.celldextherapeutics.com/role/DisclosurePropertyAndEquipmentNetDetails" xlink:type="simple" xlink:href="cldx-20131231.xsd#DisclosurePropertyAndEquipmentNetDetails" />
  <link:roleRef roleURI="http://www.celldextherapeutics.com/role/DisclosureMarketableSecuritiesDetails" xlink:type="simple" xlink:href="cldx-20131231.xsd#DisclosureMarketableSecuritiesDetails" />
  <link:roleRef roleURI="http://www.celldextherapeutics.com/role/DisclosureOtherLongTermLiabilitiesDetails3" xlink:type="simple" xlink:href="cldx-20131231.xsd#DisclosureOtherLongTermLiabilitiesDetails3" />
  <link:roleRef roleURI="http://www.celldextherapeutics.com/role/DisclosureFairValueMeasurementsDetails" xlink:type="simple" xlink:href="cldx-20131231.xsd#DisclosureFairValueMeasurementsDetails" />
  <link:roleRef roleURI="http://www.celldextherapeutics.com/role/DisclosureComprehensiveLossDetails" xlink:type="simple" xlink:href="cldx-20131231.xsd#DisclosureComprehensiveLossDetails" />
  <link:roleRef roleURI="http://www.celldextherapeutics.com/role/DisclosureCommitmentsAndContingenciesDetails2" xlink:type="simple" xlink:href="cldx-20131231.xsd#DisclosureCommitmentsAndContingenciesDetails2" />
  <link:roleRef roleURI="http://www.celldextherapeutics.com/role/DisclosureRockefellerUniversityDetails" xlink:type="simple" xlink:href="cldx-20131231.xsd#DisclosureRockefellerUniversityDetails" />
  <link:roleRef roleURI="http://www.celldextherapeutics.com/role/StatementOfStockholdersEquity" xlink:type="simple" xlink:href="cldx-20131231.xsd#StatementOfStockholdersEquity" />
  <link:roleRef roleURI="http://www.celldextherapeutics.com/role/DisclosureOtherLongTermLiabilitiesTables" xlink:type="simple" xlink:href="cldx-20131231.xsd#DisclosureOtherLongTermLiabilitiesTables" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.celldextherapeutics.com/role/DisclosureStockBasedCompensationDetails2">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:title="EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:title="ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:title="Definition : loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems to loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:type="arc" use="optional" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="loc_us-gaap_IncomeStatementLocationAxis" xlink:title="IncomeStatementLocationAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain" xlink:title="IncomeStatementLocationDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis" xlink:to="loc_us-gaap_IncomeStatementLocationDomain" xlink:title="Definition : loc_us-gaap_IncomeStatementLocationAxis to loc_us-gaap_IncomeStatementLocationDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis" xlink:title="AwardTypeAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="Definition : loc_us-gaap_AwardTypeAxis to loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ResearchAndDevelopmentExpenseMember" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember" xlink:title="ResearchAndDevelopmentExpenseMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember" xlink:title="Definition : loc_us-gaap_IncomeStatementLocationDomain to loc_us-gaap_ResearchAndDevelopmentExpenseMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_EmployeeConsultantAndNonEmployeeDirectorStockOptionMember" xlink:label="loc_cldx_EmployeeConsultantAndNonEmployeeDirectorStockOptionMember" xlink:title="EmployeeConsultantAndNonEmployeeDirectorStockOptionMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_cldx_EmployeeConsultantAndNonEmployeeDirectorStockOptionMember" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain to loc_cldx_EmployeeConsultantAndNonEmployeeDirectorStockOptionMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum" xlink:type="arc" use="optional" order="1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:to="loc_us-gaap_IncomeStatementLocationAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable to loc_us-gaap_IncomeStatementLocationAxis" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="IncomeStatementLocationDomain_1" xlink:title="IncomeStatementLocationDomain_1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis" xlink:to="IncomeStatementLocationDomain_1" xlink:title="Definition : loc_us-gaap_IncomeStatementLocationAxis to loc_us-gaap_IncomeStatementLocationDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_GeneralAndAdministrativeExpenseMember" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember" xlink:title="GeneralAndAdministrativeExpenseMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember" xlink:title="Definition : loc_us-gaap_IncomeStatementLocationDomain to loc_us-gaap_GeneralAndAdministrativeExpenseMember" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense" xlink:title="AllocatedShareBasedCompensationExpense" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense" xlink:title="Definition : loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems to loc_us-gaap_AllocatedShareBasedCompensationExpense" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum" xlink:type="arc" use="optional" order="2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:to="loc_us-gaap_AwardTypeAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable to loc_us-gaap_AwardTypeAxis" xlink:type="arc" use="optional" order="2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" xlink:title="Definition : loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:title="SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract to loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis" xlink:title="RangeAxis" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:to="loc_us-gaap_RangeAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable to loc_us-gaap_RangeAxis" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum" xlink:type="arc" use="optional" order="5" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:type="arc" use="optional" order="6" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember" xlink:title="RangeMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis" xlink:to="loc_us-gaap_RangeMember" xlink:title="Definition : loc_us-gaap_RangeAxis to loc_us-gaap_RangeMember" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember" xlink:title="MinimumMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember" xlink:to="loc_us-gaap_MinimumMember" xlink:title="Definition : loc_us-gaap_RangeMember to loc_us-gaap_MinimumMember" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" xlink:type="arc" use="optional" order="8001" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember" xlink:title="MaximumMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember" xlink:to="loc_us-gaap_MaximumMember" xlink:title="Definition : loc_us-gaap_RangeMember to loc_us-gaap_MaximumMember" xlink:type="arc" use="optional" order="8001" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://www.celldextherapeutics.com/role/DisclosureIncomeTaxesDetails2">
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_OperatingLossAndTaxCreditCarryforwardsLineItems" xlink:label="loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems" xlink:title="OperatingLossAndTaxCreditCarryforwardsLineItems" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_OperatingLossAndTaxCreditCarryforwardsTable" xlink:label="loc_cldx_OperatingLossAndTaxCreditCarryforwardsTable" xlink:title="OperatingLossAndTaxCreditCarryforwardsTable" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems" xlink:to="loc_cldx_OperatingLossAndTaxCreditCarryforwardsTable" xlink:title="Definition : loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems to loc_cldx_OperatingLossAndTaxCreditCarryforwardsTable" xlink:type="arc" use="optional" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeTaxAuthorityAxis" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis" xlink:title="IncomeTaxAuthorityAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain" xlink:title="IncomeTaxAuthorityDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain" xlink:title="Definition : loc_us-gaap_IncomeTaxAuthorityAxis to loc_us-gaap_IncomeTaxAuthorityDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="loc_us-gaap_BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain" xlink:title="Definition : loc_us-gaap_BusinessAcquisitionAxis to loc_us-gaap_BusinessAcquisitionAcquireeDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_StatusOfMergerAndAcquisitionAxis" xlink:label="loc_cldx_StatusOfMergerAndAcquisitionAxis" xlink:title="StatusOfMergerAndAcquisitionAxis" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_StatusOfMergerAndAcquisitionDomain" xlink:label="loc_cldx_StatusOfMergerAndAcquisitionDomain" xlink:title="StatusOfMergerAndAcquisitionDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_cldx_StatusOfMergerAndAcquisitionAxis" xlink:to="loc_cldx_StatusOfMergerAndAcquisitionDomain" xlink:title="Definition : loc_cldx_StatusOfMergerAndAcquisitionAxis to loc_cldx_StatusOfMergerAndAcquisitionDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_OwnershipChangeAxis" xlink:label="loc_cldx_OwnershipChangeAxis" xlink:title="OwnershipChangeAxis" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_OwnershipChangeDomain" xlink:label="loc_cldx_OwnershipChangeDomain" xlink:title="OwnershipChangeDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_cldx_OwnershipChangeAxis" xlink:to="loc_cldx_OwnershipChangeDomain" xlink:title="Definition : loc_cldx_OwnershipChangeAxis to loc_cldx_OwnershipChangeDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TaxCreditCarryforwardAxis" xlink:label="loc_us-gaap_TaxCreditCarryforwardAxis" xlink:title="TaxCreditCarryforwardAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TaxCreditCarryforwardNameDomain" xlink:label="loc_us-gaap_TaxCreditCarryforwardNameDomain" xlink:title="TaxCreditCarryforwardNameDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TaxCreditCarryforwardAxis" xlink:to="loc_us-gaap_TaxCreditCarryforwardNameDomain" xlink:title="Definition : loc_us-gaap_TaxCreditCarryforwardAxis to loc_us-gaap_TaxCreditCarryforwardNameDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InternalRevenueServiceIRSMember" xlink:label="loc_us-gaap_InternalRevenueServiceIRSMember" xlink:title="InternalRevenueServiceIRSMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain" xlink:to="loc_us-gaap_InternalRevenueServiceIRSMember" xlink:title="Definition : loc_us-gaap_IncomeTaxAuthorityDomain to loc_us-gaap_InternalRevenueServiceIRSMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_CuraGenCorporationMember" xlink:label="loc_cldx_CuraGenCorporationMember" xlink:title="CuraGenCorporationMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="loc_cldx_CuraGenCorporationMember" xlink:title="Definition : loc_us-gaap_BusinessAcquisitionAcquireeDomain to loc_cldx_CuraGenCorporationMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_OwnershipChangeInOctober2007Member" xlink:label="loc_cldx_OwnershipChangeInOctober2007Member" xlink:title="OwnershipChangeInOctober2007Member" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_OwnershipChangeDomain" xlink:to="loc_cldx_OwnershipChangeInOctober2007Member" xlink:title="Definition : loc_cldx_OwnershipChangeDomain to loc_cldx_OwnershipChangeInOctober2007Member" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ResearchMember" xlink:label="loc_us-gaap_ResearchMember" xlink:title="ResearchMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardNameDomain" xlink:to="loc_us-gaap_ResearchMember" xlink:title="Definition : loc_us-gaap_TaxCreditCarryforwardNameDomain to loc_us-gaap_ResearchMember" xlink:type="arc" use="optional" order="1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cldx_OperatingLossAndTaxCreditCarryforwardsTable" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis" xlink:title="Definition : loc_cldx_OperatingLossAndTaxCreditCarryforwardsTable to loc_us-gaap_IncomeTaxAuthorityAxis" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:label="IncomeTaxAuthorityDomain_1" xlink:title="IncomeTaxAuthorityDomain_1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis" xlink:to="IncomeTaxAuthorityDomain_1" xlink:title="Definition : loc_us-gaap_IncomeTaxAuthorityAxis to loc_us-gaap_IncomeTaxAuthorityDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain_2" xlink:title="BusinessAcquisitionAcquireeDomain_2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain_2" xlink:title="Definition : loc_us-gaap_BusinessAcquisitionAxis to loc_us-gaap_BusinessAcquisitionAcquireeDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_StatusOfMergerAndAcquisitionDomain" xlink:label="StatusOfMergerAndAcquisitionDomain_3" xlink:title="StatusOfMergerAndAcquisitionDomain_3" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_cldx_StatusOfMergerAndAcquisitionAxis" xlink:to="StatusOfMergerAndAcquisitionDomain_3" xlink:title="Definition : loc_cldx_StatusOfMergerAndAcquisitionAxis to loc_cldx_StatusOfMergerAndAcquisitionDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_OwnershipChangeDomain" xlink:label="OwnershipChangeDomain_4" xlink:title="OwnershipChangeDomain_4" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_cldx_OwnershipChangeAxis" xlink:to="OwnershipChangeDomain_4" xlink:title="Definition : loc_cldx_OwnershipChangeAxis to loc_cldx_OwnershipChangeDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TaxCreditCarryforwardNameDomain" xlink:label="TaxCreditCarryforwardNameDomain_5" xlink:title="TaxCreditCarryforwardNameDomain_5" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TaxCreditCarryforwardAxis" xlink:to="TaxCreditCarryforwardNameDomain_5" xlink:title="Definition : loc_us-gaap_TaxCreditCarryforwardAxis to loc_us-gaap_TaxCreditCarryforwardNameDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StateAndLocalJurisdictionMember" xlink:label="loc_us-gaap_StateAndLocalJurisdictionMember" xlink:title="StateAndLocalJurisdictionMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain" xlink:to="loc_us-gaap_StateAndLocalJurisdictionMember" xlink:title="Definition : loc_us-gaap_IncomeTaxAuthorityDomain to loc_us-gaap_StateAndLocalJurisdictionMember" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_OwnershipChangesInJune2009AndDecember2009Member" xlink:label="loc_cldx_OwnershipChangesInJune2009AndDecember2009Member" xlink:title="OwnershipChangesInJune2009AndDecember2009Member" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_OwnershipChangeDomain" xlink:to="loc_cldx_OwnershipChangesInJune2009AndDecember2009Member" xlink:title="Definition : loc_cldx_OwnershipChangeDomain to loc_cldx_OwnershipChangesInJune2009AndDecember2009Member" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OperatingLossCarryforwards" xlink:label="loc_us-gaap_OperatingLossCarryforwards" xlink:title="OperatingLossCarryforwards" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems" xlink:to="loc_us-gaap_OperatingLossCarryforwards" xlink:title="Definition : loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems to loc_us-gaap_OperatingLossCarryforwards" xlink:type="arc" use="optional" order="2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cldx_OperatingLossAndTaxCreditCarryforwardsTable" xlink:to="loc_us-gaap_BusinessAcquisitionAxis" xlink:title="Definition : loc_cldx_OperatingLossAndTaxCreditCarryforwardsTable to loc_us-gaap_BusinessAcquisitionAxis" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_OperatingLossCarryforwardsNetOfExpirationsAndUtilization" xlink:label="loc_cldx_OperatingLossCarryforwardsNetOfExpirationsAndUtilization" xlink:title="OperatingLossCarryforwardsNetOfExpirationsAndUtilization" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems" xlink:to="loc_cldx_OperatingLossCarryforwardsNetOfExpirationsAndUtilization" xlink:title="Definition : loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems to loc_cldx_OperatingLossCarryforwardsNetOfExpirationsAndUtilization" xlink:type="arc" use="optional" order="3" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cldx_OperatingLossAndTaxCreditCarryforwardsTable" xlink:to="loc_cldx_StatusOfMergerAndAcquisitionAxis" xlink:title="Definition : loc_cldx_OperatingLossAndTaxCreditCarryforwardsTable to loc_cldx_StatusOfMergerAndAcquisitionAxis" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_OperatingLossCarryforwardsExpired" xlink:label="loc_cldx_OperatingLossCarryforwardsExpired" xlink:title="OperatingLossCarryforwardsExpired" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems" xlink:to="loc_cldx_OperatingLossCarryforwardsExpired" xlink:title="Definition : loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems to loc_cldx_OperatingLossCarryforwardsExpired" xlink:type="arc" use="optional" order="4" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cldx_OperatingLossAndTaxCreditCarryforwardsTable" xlink:to="loc_cldx_OwnershipChangeAxis" xlink:title="Definition : loc_cldx_OperatingLossAndTaxCreditCarryforwardsTable to loc_cldx_OwnershipChangeAxis" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_OperatingLossCarryforwardsWithLimitationsOnUse" xlink:label="loc_cldx_OperatingLossCarryforwardsWithLimitationsOnUse" xlink:title="OperatingLossCarryforwardsWithLimitationsOnUse" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems" xlink:to="loc_cldx_OperatingLossCarryforwardsWithLimitationsOnUse" xlink:title="Definition : loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems to loc_cldx_OperatingLossCarryforwardsWithLimitationsOnUse" xlink:type="arc" use="optional" order="5" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cldx_OperatingLossAndTaxCreditCarryforwardsTable" xlink:to="loc_us-gaap_TaxCreditCarryforwardAxis" xlink:title="Definition : loc_cldx_OperatingLossAndTaxCreditCarryforwardsTable to loc_us-gaap_TaxCreditCarryforwardAxis" xlink:type="arc" use="optional" order="5" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_DeferredTaxAssetsOperatingLossCarryforwardsNotYetUtilized" xlink:label="loc_cldx_DeferredTaxAssetsOperatingLossCarryforwardsNotYetUtilized" xlink:title="DeferredTaxAssetsOperatingLossCarryforwardsNotYetUtilized" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems" xlink:to="loc_cldx_DeferredTaxAssetsOperatingLossCarryforwardsNotYetUtilized" xlink:title="Definition : loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems to loc_cldx_DeferredTaxAssetsOperatingLossCarryforwardsNotYetUtilized" xlink:type="arc" use="optional" order="6" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_OperatingLossCarryforwardsRemotelyLikelyToBeUtilized" xlink:label="loc_cldx_OperatingLossCarryforwardsRemotelyLikelyToBeUtilized" xlink:title="OperatingLossCarryforwardsRemotelyLikelyToBeUtilized" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems" xlink:to="loc_cldx_OperatingLossCarryforwardsRemotelyLikelyToBeUtilized" xlink:title="Definition : loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems to loc_cldx_OperatingLossCarryforwardsRemotelyLikelyToBeUtilized" xlink:type="arc" use="optional" order="7" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_OperatingLossCarryforwardsAnnualLimitationAmount" xlink:label="loc_cldx_OperatingLossCarryforwardsAnnualLimitationAmount" xlink:title="OperatingLossCarryforwardsAnnualLimitationAmount" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems" xlink:to="loc_cldx_OperatingLossCarryforwardsAnnualLimitationAmount" xlink:title="Definition : loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems to loc_cldx_OperatingLossCarryforwardsAnnualLimitationAmount" xlink:type="arc" use="optional" order="8" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_PeriodOfRecognitionOfUnrealizedGainLossAfterOwnershipChange" xlink:label="loc_cldx_PeriodOfRecognitionOfUnrealizedGainLossAfterOwnershipChange" xlink:title="PeriodOfRecognitionOfUnrealizedGainLossAfterOwnershipChange" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems" xlink:to="loc_cldx_PeriodOfRecognitionOfUnrealizedGainLossAfterOwnershipChange" xlink:title="Definition : loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems to loc_cldx_PeriodOfRecognitionOfUnrealizedGainLossAfterOwnershipChange" xlink:type="arc" use="optional" order="9" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TaxCreditCarryforwardAmount" xlink:label="loc_us-gaap_TaxCreditCarryforwardAmount" xlink:title="TaxCreditCarryforwardAmount" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems" xlink:to="loc_us-gaap_TaxCreditCarryforwardAmount" xlink:title="Definition : loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems to loc_us-gaap_TaxCreditCarryforwardAmount" xlink:type="arc" use="optional" order="10" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_TaxCreditCarryforwardAmountWithSubstantialLimitationsOnUse" xlink:label="loc_cldx_TaxCreditCarryforwardAmountWithSubstantialLimitationsOnUse" xlink:title="TaxCreditCarryforwardAmountWithSubstantialLimitationsOnUse" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems" xlink:to="loc_cldx_TaxCreditCarryforwardAmountWithSubstantialLimitationsOnUse" xlink:title="Definition : loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems to loc_cldx_TaxCreditCarryforwardAmountWithSubstantialLimitationsOnUse" xlink:type="arc" use="optional" order="11" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NumberOfStatesInWhichEntityOperates" xlink:label="loc_us-gaap_NumberOfStatesInWhichEntityOperates" xlink:title="NumberOfStatesInWhichEntityOperates" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems" xlink:to="loc_us-gaap_NumberOfStatesInWhichEntityOperates" xlink:title="Definition : loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems to loc_us-gaap_NumberOfStatesInWhichEntityOperates" xlink:type="arc" use="optional" order="12" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_UnrecognizedTaxBenefits" xlink:label="loc_us-gaap_UnrecognizedTaxBenefits" xlink:title="UnrecognizedTaxBenefits" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems" xlink:to="loc_us-gaap_UnrecognizedTaxBenefits" xlink:title="Definition : loc_cldx_OperatingLossAndTaxCreditCarryforwardsLineItems to loc_us-gaap_UnrecognizedTaxBenefits" xlink:type="arc" use="optional" order="13" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_AVANTMember" xlink:label="loc_cldx_AVANTMember" xlink:title="AVANTMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="loc_cldx_AVANTMember" xlink:title="Definition : loc_us-gaap_BusinessAcquisitionAcquireeDomain to loc_cldx_AVANTMember" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_PriorToMergerMember" xlink:label="loc_cldx_PriorToMergerMember" xlink:title="PriorToMergerMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_StatusOfMergerAndAcquisitionDomain" xlink:to="loc_cldx_PriorToMergerMember" xlink:title="Definition : loc_cldx_StatusOfMergerAndAcquisitionDomain to loc_cldx_PriorToMergerMember" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_PriorToAcquisitionMember" xlink:label="loc_cldx_PriorToAcquisitionMember" xlink:title="PriorToAcquisitionMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_StatusOfMergerAndAcquisitionDomain" xlink:to="loc_cldx_PriorToAcquisitionMember" xlink:title="Definition : loc_cldx_StatusOfMergerAndAcquisitionDomain to loc_cldx_PriorToAcquisitionMember" xlink:type="arc" use="optional" order="8001" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://www.celldextherapeutics.com/role/DisclosureStockBasedCompensationDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:title="ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:type="arc" use="optional" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis" xlink:title="AwardTypeAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="Definition : loc_us-gaap_AwardTypeAxis to loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis" xlink:title="RangeAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember" xlink:title="RangeMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis" xlink:to="loc_us-gaap_RangeMember" xlink:title="Definition : loc_us-gaap_RangeAxis to loc_us-gaap_RangeMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="loc_us-gaap_PlanNameAxis" xlink:title="PlanNameAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain" xlink:title="PlanNameDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis" xlink:to="loc_us-gaap_PlanNameDomain" xlink:title="Definition : loc_us-gaap_PlanNameAxis to loc_us-gaap_PlanNameDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_EmployeeConsultantAndNonEmployeeDirectorStockOptionMember" xlink:label="loc_cldx_EmployeeConsultantAndNonEmployeeDirectorStockOptionMember" xlink:title="EmployeeConsultantAndNonEmployeeDirectorStockOptionMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_cldx_EmployeeConsultantAndNonEmployeeDirectorStockOptionMember" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain to loc_cldx_EmployeeConsultantAndNonEmployeeDirectorStockOptionMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember" xlink:title="MaximumMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember" xlink:to="loc_us-gaap_MaximumMember" xlink:title="Definition : loc_us-gaap_RangeMember to loc_us-gaap_MaximumMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_CelldexResearchEquityIncentivePlan2005AndCuraGenStockPlan2007Member" xlink:label="loc_cldx_CelldexResearchEquityIncentivePlan2005AndCuraGenStockPlan2007Member" xlink:title="CelldexResearchEquityIncentivePlan2005AndCuraGenStockPlan2007Member" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain" xlink:to="loc_cldx_CelldexResearchEquityIncentivePlan2005AndCuraGenStockPlan2007Member" xlink:title="Definition : loc_us-gaap_PlanNameDomain to loc_cldx_CelldexResearchEquityIncentivePlan2005AndCuraGenStockPlan2007Member" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract" xlink:label="loc_cldx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" xlink:title="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" xlink:title="Definition : loc_cldx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract to loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:type="arc" use="optional" order="1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="loc_us-gaap_PlanNameAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to loc_us-gaap_PlanNameAxis" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1" xlink:title="Definition : loc_us-gaap_AwardTypeAxis to loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="PlanNameDomain_2" xlink:title="PlanNameDomain_2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis" xlink:to="PlanNameDomain_2" xlink:title="Definition : loc_us-gaap_PlanNameAxis to loc_us-gaap_PlanNameDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward to loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="loc_us-gaap_RestrictedStockMember" xlink:title="RestrictedStockMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaap_RestrictedStockMember" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain to loc_us-gaap_RestrictedStockMember" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EmployeeStockMember" xlink:label="loc_us-gaap_EmployeeStockMember" xlink:title="EmployeeStockMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain" xlink:to="loc_us-gaap_EmployeeStockMember" xlink:title="Definition : loc_us-gaap_PlanNameDomain to loc_us-gaap_EmployeeStockMember" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:title="CommonStockCapitalSharesReservedForFutureIssuance" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageRemainingContractualTerm1" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageRemainingContractualTerm1" xlink:title="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageRemainingContractualTerm1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageRemainingContractualTerm1" xlink:title="Definition : loc_cldx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract to loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageRemainingContractualTerm1" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:type="arc" use="optional" order="2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="loc_us-gaap_AwardTypeAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to loc_us-gaap_AwardTypeAxis" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_StockOptionAndIncentivePlan2008Member" xlink:label="loc_cldx_StockOptionAndIncentivePlan2008Member" xlink:title="StockOptionAndIncentivePlan2008Member" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain" xlink:to="loc_cldx_StockOptionAndIncentivePlan2008Member" xlink:title="Definition : loc_us-gaap_PlanNameDomain to loc_cldx_StockOptionAndIncentivePlan2008Member" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent" xlink:title="SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:title="StockIssuedDuringPeriodSharesStockOptionsExercised" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward to loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward to loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1" xlink:title="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1" xlink:title="Definition : loc_cldx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract to loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1" xlink:title="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract to loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" xlink:type="arc" use="optional" order="3" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="loc_us-gaap_RangeAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable to loc_us-gaap_RangeAxis" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward to loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" xlink:title="StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:type="arc" use="optional" order="5" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" xlink:type="arc" use="optional" order="5" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" xlink:type="arc" use="optional" order="5" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableAggregateIntrinsicValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableAggregateIntrinsicValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableAggregateIntrinsicValue" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableAggregateIntrinsicValue" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableAggregateIntrinsicValue" xlink:type="arc" use="optional" order="5" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" xlink:type="arc" use="optional" order="6" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" xlink:type="arc" use="optional" order="6" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:type="arc" use="optional" order="6" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" xlink:title="EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract to loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" xlink:type="arc" use="optional" order="6" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:type="arc" use="optional" order="7" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:title="EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract to loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:type="arc" use="optional" order="7" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationTerm" xlink:label="loc_cldx_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationTerm" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationTerm" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_cldx_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationTerm" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to loc_cldx_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationTerm" xlink:type="arc" use="optional" order="8" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationTermForHoldersOfMoreThanTenPercentOfVotingStock" xlink:label="loc_cldx_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationTermForHoldersOfMoreThanTenPercentOfVotingStock" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationTermForHoldersOfMoreThanTenPercentOfVotingStock" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_cldx_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationTermForHoldersOfMoreThanTenPercentOfVotingStock" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to loc_cldx_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationTermForHoldersOfMoreThanTenPercentOfVotingStock" xlink:type="arc" use="optional" order="9" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsThresholdPercentageOfVotingStock" xlink:label="loc_cldx_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsThresholdPercentageOfVotingStock" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsThresholdPercentageOfVotingStock" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_cldx_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsThresholdPercentageOfVotingStock" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to loc_cldx_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsThresholdPercentageOfVotingStock" xlink:type="arc" use="optional" order="10" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisePriceAsPercentageOfFairMarketValueForHoldersOfMoreThanTenPercentOfVotingStock" xlink:label="loc_cldx_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisePriceAsPercentageOfFairMarketValueForHoldersOfMoreThanTenPercentOfVotingStock" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisePriceAsPercentageOfFairMarketValueForHoldersOfMoreThanTenPercentOfVotingStock" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_cldx_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisePriceAsPercentageOfFairMarketValueForHoldersOfMoreThanTenPercentOfVotingStock" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to loc_cldx_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisePriceAsPercentageOfFairMarketValueForHoldersOfMoreThanTenPercentOfVotingStock" xlink:type="arc" use="optional" order="11" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:type="arc" use="optional" order="12" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:type="arc" use="optional" order="13" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_cldx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to loc_cldx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract" xlink:type="arc" use="optional" order="14" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract" xlink:type="arc" use="optional" order="15" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:type="arc" use="optional" order="16" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:type="arc" use="optional" order="17" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesPerEmployee" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesPerEmployee" xlink:title="ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesPerEmployee" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesPerEmployee" xlink:title="Definition : loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems to loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesPerEmployee" xlink:type="arc" use="optional" order="8000" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://www.celldextherapeutics.com/role/DisclosureOtherLongTermLiabilitiesDetails2">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:label="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:title="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:label="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="Definition : loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:type="arc" use="optional" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="loc_us-gaap_TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:title="Definition : loc_us-gaap_TypeOfArrangementAxis to loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_ProductDevelopmentAndLicensingAgreementMember" xlink:label="loc_cldx_ProductDevelopmentAndLicensingAgreementMember" xlink:title="ProductDevelopmentAndLicensingAgreementMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:to="loc_cldx_ProductDevelopmentAndLicensingAgreementMember" xlink:title="Definition : loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember to loc_cldx_ProductDevelopmentAndLicensingAgreementMember" xlink:type="arc" use="optional" order="1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="loc_us-gaap_TypeOfArrangementAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to loc_us-gaap_TypeOfArrangementAxis" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_CollaborativeArrangementEstimatedCostForDevelopmentServices" xlink:label="loc_cldx_CollaborativeArrangementEstimatedCostForDevelopmentServices" xlink:title="CollaborativeArrangementEstimatedCostForDevelopmentServices" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="loc_cldx_CollaborativeArrangementEstimatedCostForDevelopmentServices" xlink:title="Definition : loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to loc_cldx_CollaborativeArrangementEstimatedCostForDevelopmentServices" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_CollaborativeArrangementAgreementTerm" xlink:label="loc_cldx_CollaborativeArrangementAgreementTerm" xlink:title="CollaborativeArrangementAgreementTerm" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="loc_cldx_CollaborativeArrangementAgreementTerm" xlink:title="Definition : loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to loc_cldx_CollaborativeArrangementAgreementTerm" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_CollaborativeArrangementUpfrontPaymentAmount" xlink:label="loc_cldx_CollaborativeArrangementUpfrontPaymentAmount" xlink:title="CollaborativeArrangementUpfrontPaymentAmount" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="loc_cldx_CollaborativeArrangementUpfrontPaymentAmount" xlink:title="Definition : loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to loc_cldx_CollaborativeArrangementUpfrontPaymentAmount" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_RevenueFromContractsAndGrants" xlink:label="loc_cldx_RevenueFromContractsAndGrants" xlink:title="RevenueFromContractsAndGrants" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="loc_cldx_RevenueFromContractsAndGrants" xlink:title="Definition : loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to loc_cldx_RevenueFromContractsAndGrants" xlink:type="arc" order="5" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://www.celldextherapeutics.com/role/DisclosureTermLoanDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentLineItems" xlink:label="loc_us-gaap_DebtInstrumentLineItems" xlink:title="DebtInstrumentLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentTable" xlink:label="loc_us-gaap_DebtInstrumentTable" xlink:title="DebtInstrumentTable" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems" xlink:to="loc_us-gaap_DebtInstrumentTable" xlink:title="Definition : loc_us-gaap_DebtInstrumentLineItems to loc_us-gaap_DebtInstrumentTable" xlink:type="arc" use="optional" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongtermDebtTypeAxis" xlink:label="loc_us-gaap_LongtermDebtTypeAxis" xlink:title="LongtermDebtTypeAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaap_LongtermDebtTypeDomain" xlink:title="LongtermDebtTypeDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis" xlink:to="loc_us-gaap_LongtermDebtTypeDomain" xlink:title="Definition : loc_us-gaap_LongtermDebtTypeAxis to loc_us-gaap_LongtermDebtTypeDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_DebtInstrumentLenderAxis" xlink:label="loc_cldx_DebtInstrumentLenderAxis" xlink:title="DebtInstrumentLenderAxis" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_DebtInstrumentLenderDomain" xlink:label="loc_cldx_DebtInstrumentLenderDomain" xlink:title="DebtInstrumentLenderDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_cldx_DebtInstrumentLenderAxis" xlink:to="loc_cldx_DebtInstrumentLenderDomain" xlink:title="Definition : loc_cldx_DebtInstrumentLenderAxis to loc_cldx_DebtInstrumentLenderDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SecuredDebtMember" xlink:label="loc_us-gaap_SecuredDebtMember" xlink:title="SecuredDebtMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain" xlink:to="loc_us-gaap_SecuredDebtMember" xlink:title="Definition : loc_us-gaap_LongtermDebtTypeDomain to loc_us-gaap_SecuredDebtMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_MidCapFinancialLLCMember" xlink:label="loc_cldx_MidCapFinancialLLCMember" xlink:title="MidCapFinancialLLCMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_DebtInstrumentLenderDomain" xlink:to="loc_cldx_MidCapFinancialLLCMember" xlink:title="Definition : loc_cldx_DebtInstrumentLenderDomain to loc_cldx_MidCapFinancialLLCMember" xlink:type="arc" use="optional" order="1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable" xlink:to="loc_cldx_DebtInstrumentLenderAxis" xlink:title="Definition : loc_us-gaap_DebtInstrumentTable to loc_cldx_DebtInstrumentLenderAxis" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="LongtermDebtTypeDomain_1" xlink:title="LongtermDebtTypeDomain_1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis" xlink:to="LongtermDebtTypeDomain_1" xlink:title="Definition : loc_us-gaap_LongtermDebtTypeAxis to loc_us-gaap_LongtermDebtTypeDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_DebtInstrumentLenderDomain" xlink:label="DebtInstrumentLenderDomain_2" xlink:title="DebtInstrumentLenderDomain_2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_cldx_DebtInstrumentLenderAxis" xlink:to="DebtInstrumentLenderDomain_2" xlink:title="Definition : loc_cldx_DebtInstrumentLenderAxis to loc_cldx_DebtInstrumentLenderDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_GeneralElectricCapitalCorporationMember" xlink:label="loc_cldx_GeneralElectricCapitalCorporationMember" xlink:title="GeneralElectricCapitalCorporationMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_DebtInstrumentLenderDomain" xlink:to="loc_cldx_GeneralElectricCapitalCorporationMember" xlink:title="Definition : loc_cldx_DebtInstrumentLenderDomain to loc_cldx_GeneralElectricCapitalCorporationMember" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromIssuanceOfDebt" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfDebt" xlink:title="ProceedsFromIssuanceOfDebt" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfDebt" xlink:title="Definition : loc_us-gaap_DebtInstrumentLineItems to loc_us-gaap_ProceedsFromIssuanceOfDebt" xlink:type="arc" use="optional" order="2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable" xlink:to="loc_us-gaap_LongtermDebtTypeAxis" xlink:title="Definition : loc_us-gaap_DebtInstrumentTable to loc_us-gaap_LongtermDebtTypeAxis" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SecuredDebt" xlink:label="loc_us-gaap_SecuredDebt" xlink:title="SecuredDebt" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems" xlink:to="loc_us-gaap_SecuredDebt" xlink:title="Definition : loc_us-gaap_DebtInstrumentLineItems to loc_us-gaap_SecuredDebt" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis" xlink:title="RangeAxis" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable" xlink:to="loc_us-gaap_RangeAxis" xlink:title="Definition : loc_us-gaap_DebtInstrumentTable to loc_us-gaap_RangeAxis" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_RepaymentOfLongTermDebtPrincipalAmount" xlink:label="loc_cldx_RepaymentOfLongTermDebtPrincipalAmount" xlink:title="RepaymentOfLongTermDebtPrincipalAmount" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems" xlink:to="loc_cldx_RepaymentOfLongTermDebtPrincipalAmount" xlink:title="Definition : loc_us-gaap_DebtInstrumentLineItems to loc_cldx_RepaymentOfLongTermDebtPrincipalAmount" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_DebtInstrumentInterestAndPrepaymentFees" xlink:label="loc_cldx_DebtInstrumentInterestAndPrepaymentFees" xlink:title="DebtInstrumentInterestAndPrepaymentFees" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems" xlink:to="loc_cldx_DebtInstrumentInterestAndPrepaymentFees" xlink:title="Definition : loc_us-gaap_DebtInstrumentLineItems to loc_cldx_DebtInstrumentInterestAndPrepaymentFees" xlink:type="arc" use="optional" order="5" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InterestExpenseLongTermDebt" xlink:label="loc_us-gaap_InterestExpenseLongTermDebt" xlink:title="InterestExpenseLongTermDebt" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems" xlink:to="loc_us-gaap_InterestExpenseLongTermDebt" xlink:title="Definition : loc_us-gaap_DebtInstrumentLineItems to loc_us-gaap_InterestExpenseLongTermDebt" xlink:type="arc" use="optional" order="6" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember" xlink:title="RangeMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis" xlink:to="loc_us-gaap_RangeMember" xlink:title="Definition : loc_us-gaap_RangeAxis to loc_us-gaap_RangeMember" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember" xlink:title="MinimumMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember" xlink:to="loc_us-gaap_MinimumMember" xlink:title="Definition : loc_us-gaap_RangeMember to loc_us-gaap_MinimumMember" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:title="DebtInstrumentBasisSpreadOnVariableRate1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:title="Definition : loc_us-gaap_DebtInstrumentLineItems to loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_DebtInstrumentUpFrontFeeDueUponRepaymentForExtensionOfMaturityPeriodOfDebt" xlink:label="loc_cldx_DebtInstrumentUpFrontFeeDueUponRepaymentForExtensionOfMaturityPeriodOfDebt" xlink:title="DebtInstrumentUpFrontFeeDueUponRepaymentForExtensionOfMaturityPeriodOfDebt" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems" xlink:to="loc_cldx_DebtInstrumentUpFrontFeeDueUponRepaymentForExtensionOfMaturityPeriodOfDebt" xlink:title="Definition : loc_us-gaap_DebtInstrumentLineItems to loc_cldx_DebtInstrumentUpFrontFeeDueUponRepaymentForExtensionOfMaturityPeriodOfDebt" xlink:type="arc" use="optional" order="8001" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_DebtInstrumentAdditionalFeeDueOnRepaymentForExtensionOfMaturityPeriodOfDebt" xlink:label="loc_cldx_DebtInstrumentAdditionalFeeDueOnRepaymentForExtensionOfMaturityPeriodOfDebt" xlink:title="DebtInstrumentAdditionalFeeDueOnRepaymentForExtensionOfMaturityPeriodOfDebt" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems" xlink:to="loc_cldx_DebtInstrumentAdditionalFeeDueOnRepaymentForExtensionOfMaturityPeriodOfDebt" xlink:title="Definition : loc_us-gaap_DebtInstrumentLineItems to loc_cldx_DebtInstrumentAdditionalFeeDueOnRepaymentForExtensionOfMaturityPeriodOfDebt" xlink:type="arc" use="optional" order="8002" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_DebtInstrumentCovenantRateOfPrepaymentPremiumInYearThree" xlink:label="loc_cldx_DebtInstrumentCovenantRateOfPrepaymentPremiumInYearThree" xlink:title="DebtInstrumentCovenantRateOfPrepaymentPremiumInYearThree" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems" xlink:to="loc_cldx_DebtInstrumentCovenantRateOfPrepaymentPremiumInYearThree" xlink:title="Definition : loc_us-gaap_DebtInstrumentLineItems to loc_cldx_DebtInstrumentCovenantRateOfPrepaymentPremiumInYearThree" xlink:type="arc" use="optional" order="8003" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_DebtInstrumentCovenantRateOfPrepaymentPremiumInYearFour" xlink:label="loc_cldx_DebtInstrumentCovenantRateOfPrepaymentPremiumInYearFour" xlink:title="DebtInstrumentCovenantRateOfPrepaymentPremiumInYearFour" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems" xlink:to="loc_cldx_DebtInstrumentCovenantRateOfPrepaymentPremiumInYearFour" xlink:title="Definition : loc_us-gaap_DebtInstrumentLineItems to loc_cldx_DebtInstrumentCovenantRateOfPrepaymentPremiumInYearFour" xlink:type="arc" use="optional" order="8004" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_DebtInstrumentPaymentFeePayableOnRepayment" xlink:label="loc_cldx_DebtInstrumentPaymentFeePayableOnRepayment" xlink:title="DebtInstrumentPaymentFeePayableOnRepayment" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems" xlink:to="loc_cldx_DebtInstrumentPaymentFeePayableOnRepayment" xlink:title="Definition : loc_us-gaap_DebtInstrumentLineItems to loc_cldx_DebtInstrumentPaymentFeePayableOnRepayment" xlink:type="arc" use="optional" order="8005" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_DebtInstrumentInterestOnlyPeriodOfExtension" xlink:label="loc_cldx_DebtInstrumentInterestOnlyPeriodOfExtension" xlink:title="DebtInstrumentInterestOnlyPeriodOfExtension" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems" xlink:to="loc_cldx_DebtInstrumentInterestOnlyPeriodOfExtension" xlink:title="Definition : loc_us-gaap_DebtInstrumentLineItems to loc_cldx_DebtInstrumentInterestOnlyPeriodOfExtension" xlink:type="arc" use="optional" order="8006" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_DebtInstrumentNumberOfEqualConsecutiveMonthlyInstallments" xlink:label="loc_cldx_DebtInstrumentNumberOfEqualConsecutiveMonthlyInstallments" xlink:title="DebtInstrumentNumberOfEqualConsecutiveMonthlyInstallments" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems" xlink:to="loc_cldx_DebtInstrumentNumberOfEqualConsecutiveMonthlyInstallments" xlink:title="Definition : loc_us-gaap_DebtInstrumentLineItems to loc_cldx_DebtInstrumentNumberOfEqualConsecutiveMonthlyInstallments" xlink:type="arc" use="optional" order="8007" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtByMaturityAbstract" xlink:label="loc_us-gaap_LongTermDebtByMaturityAbstract" xlink:title="LongTermDebtByMaturityAbstract" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems" xlink:to="loc_us-gaap_LongTermDebtByMaturityAbstract" xlink:title="Definition : loc_us-gaap_DebtInstrumentLineItems to loc_us-gaap_LongTermDebtByMaturityAbstract" xlink:type="arc" use="optional" order="8008" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentDescriptionOfVariableRateBasis" xlink:label="loc_us-gaap_DebtInstrumentDescriptionOfVariableRateBasis" xlink:title="DebtInstrumentDescriptionOfVariableRateBasis" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems" xlink:to="loc_us-gaap_DebtInstrumentDescriptionOfVariableRateBasis" xlink:title="Definition : loc_us-gaap_DebtInstrumentLineItems to loc_us-gaap_DebtInstrumentDescriptionOfVariableRateBasis" xlink:type="arc" use="optional" order="8009" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://www.celldextherapeutics.com/role/DisclosureRevenueDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:label="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:title="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:label="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="Definition : loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:type="arc" use="optional" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="loc_us-gaap_TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:title="Definition : loc_us-gaap_TypeOfArrangementAxis to loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CounterpartyNameAxis" xlink:label="loc_us-gaap_CounterpartyNameAxis" xlink:title="CounterpartyNameAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:label="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:title="RepurchaseAgreementCounterpartyNameDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CounterpartyNameAxis" xlink:to="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:title="Definition : loc_us-gaap_CounterpartyNameAxis to loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProductOrServiceAxis" xlink:label="loc_us-gaap_ProductOrServiceAxis" xlink:title="ProductOrServiceAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProductsAndServicesDomain" xlink:label="loc_us-gaap_ProductsAndServicesDomain" xlink:title="ProductsAndServicesDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ProductOrServiceAxis" xlink:to="loc_us-gaap_ProductsAndServicesDomain" xlink:title="Definition : loc_us-gaap_ProductOrServiceAxis to loc_us-gaap_ProductsAndServicesDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_CollaborativeArrangementForDevelopmentAndCommercializationOfProductMember" xlink:label="loc_cldx_CollaborativeArrangementForDevelopmentAndCommercializationOfProductMember" xlink:title="CollaborativeArrangementForDevelopmentAndCommercializationOfProductMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:to="loc_cldx_CollaborativeArrangementForDevelopmentAndCommercializationOfProductMember" xlink:title="Definition : loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember to loc_cldx_CollaborativeArrangementForDevelopmentAndCommercializationOfProductMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_GlaxoSmithKlinePlcMember" xlink:label="loc_cldx_GlaxoSmithKlinePlcMember" xlink:title="GlaxoSmithKlinePlcMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:to="loc_cldx_GlaxoSmithKlinePlcMember" xlink:title="Definition : loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain to loc_cldx_GlaxoSmithKlinePlcMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_RotarixRotavirusVaccineMember" xlink:label="loc_cldx_RotarixRotavirusVaccineMember" xlink:title="RotarixRotavirusVaccineMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain" xlink:to="loc_cldx_RotarixRotavirusVaccineMember" xlink:title="Definition : loc_us-gaap_ProductsAndServicesDomain to loc_cldx_RotarixRotavirusVaccineMember" xlink:type="arc" use="optional" order="1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="loc_us-gaap_TypeOfArrangementAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to loc_us-gaap_TypeOfArrangementAxis" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember_1" xlink:title="ArrangementsAndNonarrangementTransactionsMember_1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember_1" xlink:title="Definition : loc_us-gaap_TypeOfArrangementAxis to loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:label="RepurchaseAgreementCounterpartyNameDomain_2" xlink:title="RepurchaseAgreementCounterpartyNameDomain_2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CounterpartyNameAxis" xlink:to="RepurchaseAgreementCounterpartyNameDomain_2" xlink:title="Definition : loc_us-gaap_CounterpartyNameAxis to loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProductsAndServicesDomain" xlink:label="ProductsAndServicesDomain_3" xlink:title="ProductsAndServicesDomain_3" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ProductOrServiceAxis" xlink:to="ProductsAndServicesDomain_3" xlink:title="Definition : loc_us-gaap_ProductOrServiceAxis to loc_us-gaap_ProductsAndServicesDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_LicenseAgreementsMember" xlink:label="loc_cldx_LicenseAgreementsMember" xlink:title="LicenseAgreementsMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:to="loc_cldx_LicenseAgreementsMember" xlink:title="Definition : loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember to loc_cldx_LicenseAgreementsMember" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_CincinnatiChildrensHospitalMedicalCenterMember" xlink:label="loc_cldx_CincinnatiChildrensHospitalMedicalCenterMember" xlink:title="CincinnatiChildrensHospitalMedicalCenterMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:to="loc_cldx_CincinnatiChildrensHospitalMedicalCenterMember" xlink:title="Definition : loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain to loc_cldx_CincinnatiChildrensHospitalMedicalCenterMember" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_PercentageOfLicenseFeeDueOnNetRoyaltiesReceived" xlink:label="loc_cldx_PercentageOfLicenseFeeDueOnNetRoyaltiesReceived" xlink:title="PercentageOfLicenseFeeDueOnNetRoyaltiesReceived" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="loc_cldx_PercentageOfLicenseFeeDueOnNetRoyaltiesReceived" xlink:title="Definition : loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to loc_cldx_PercentageOfLicenseFeeDueOnNetRoyaltiesReceived" xlink:type="arc" use="optional" order="2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="loc_us-gaap_CounterpartyNameAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to loc_us-gaap_CounterpartyNameAxis" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_RoyaltyAgreementMember" xlink:label="loc_cldx_RoyaltyAgreementMember" xlink:title="RoyaltyAgreementMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:to="loc_cldx_RoyaltyAgreementMember" xlink:title="Definition : loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember to loc_cldx_RoyaltyAgreementMember" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_PRFAgreementMember" xlink:label="loc_cldx_PRFAgreementMember" xlink:title="PRFAgreementMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:to="loc_cldx_PRFAgreementMember" xlink:title="Definition : loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain to loc_cldx_PRFAgreementMember" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_PercentageOfInterestInNetRoyaltiesSold" xlink:label="loc_cldx_PercentageOfInterestInNetRoyaltiesSold" xlink:title="PercentageOfInterestInNetRoyaltiesSold" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="loc_cldx_PercentageOfInterestInNetRoyaltiesSold" xlink:title="Definition : loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to loc_cldx_PercentageOfInterestInNetRoyaltiesSold" xlink:type="arc" use="optional" order="3" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="loc_us-gaap_ProductOrServiceAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to loc_us-gaap_ProductOrServiceAxis" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RoyaltyExpense" xlink:label="loc_us-gaap_RoyaltyExpense" xlink:title="RoyaltyExpense" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="loc_us-gaap_RoyaltyExpense" xlink:title="Definition : loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to loc_us-gaap_RoyaltyExpense" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="loc_us-gaap_SubsequentEventTypeAxis" xlink:title="SubsequentEventTypeAxis" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="loc_us-gaap_SubsequentEventTypeAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to loc_us-gaap_SubsequentEventTypeAxis" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain" xlink:title="SubsequentEventTypeDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis" xlink:to="loc_us-gaap_SubsequentEventTypeDomain" xlink:title="Definition : loc_us-gaap_SubsequentEventTypeAxis to loc_us-gaap_SubsequentEventTypeDomain" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_PfizerIncMember" xlink:label="loc_cldx_PfizerIncMember" xlink:title="PfizerIncMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:to="loc_cldx_PfizerIncMember" xlink:title="Definition : loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain to loc_cldx_PfizerIncMember" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_RindopepimutMember" xlink:label="loc_cldx_RindopepimutMember" xlink:title="RindopepimutMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductsAndServicesDomain" xlink:to="loc_cldx_RindopepimutMember" xlink:title="Definition : loc_us-gaap_ProductsAndServicesDomain to loc_cldx_RindopepimutMember" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SubsequentEventMember" xlink:label="loc_us-gaap_SubsequentEventMember" xlink:title="SubsequentEventMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain" xlink:to="loc_us-gaap_SubsequentEventMember" xlink:title="Definition : loc_us-gaap_SubsequentEventTypeDomain to loc_us-gaap_SubsequentEventMember" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_PeriodForRightToNegotiateForExtensionOfAgreementTermUnderCertainCircumstances" xlink:label="loc_cldx_PeriodForRightToNegotiateForExtensionOfAgreementTermUnderCertainCircumstances" xlink:title="PeriodForRightToNegotiateForExtensionOfAgreementTermUnderCertainCircumstances" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="loc_cldx_PeriodForRightToNegotiateForExtensionOfAgreementTermUnderCertainCircumstances" xlink:title="Definition : loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to loc_cldx_PeriodForRightToNegotiateForExtensionOfAgreementTermUnderCertainCircumstances" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_DukeUniversityAndThomasJeffersonUniversityMember" xlink:label="loc_cldx_DukeUniversityAndThomasJeffersonUniversityMember" xlink:title="DukeUniversityAndThomasJeffersonUniversityMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:to="loc_cldx_DukeUniversityAndThomasJeffersonUniversityMember" xlink:title="Definition : loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain to loc_cldx_DukeUniversityAndThomasJeffersonUniversityMember" xlink:type="arc" use="optional" order="8001" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_AmountReceivedForRightToParticipateInCollaborativeArrangement" xlink:label="loc_cldx_AmountReceivedForRightToParticipateInCollaborativeArrangement" xlink:title="AmountReceivedForRightToParticipateInCollaborativeArrangement" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="loc_cldx_AmountReceivedForRightToParticipateInCollaborativeArrangement" xlink:title="Definition : loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to loc_cldx_AmountReceivedForRightToParticipateInCollaborativeArrangement" xlink:type="arc" use="optional" order="8001" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_StockIssuedDuringPeriodValueIssuedForCollaborativeArrangement" xlink:label="loc_cldx_StockIssuedDuringPeriodValueIssuedForCollaborativeArrangement" xlink:title="StockIssuedDuringPeriodValueIssuedForCollaborativeArrangement" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="loc_cldx_StockIssuedDuringPeriodValueIssuedForCollaborativeArrangement" xlink:title="Definition : loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to loc_cldx_StockIssuedDuringPeriodValueIssuedForCollaborativeArrangement" xlink:type="arc" use="optional" order="8002" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CostOfReimbursableExpense" xlink:label="loc_us-gaap_CostOfReimbursableExpense" xlink:title="CostOfReimbursableExpense" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="loc_us-gaap_CostOfReimbursableExpense" xlink:title="Definition : loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to loc_us-gaap_CostOfReimbursableExpense" xlink:type="arc" use="optional" order="8003" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LicenseCosts" xlink:label="loc_us-gaap_LicenseCosts" xlink:title="LicenseCosts" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="loc_us-gaap_LicenseCosts" xlink:title="Definition : loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to loc_us-gaap_LicenseCosts" xlink:type="arc" use="optional" order="8004" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://www.celldextherapeutics.com/role/DisclosureCollaborationAgreementsDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:label="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:title="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:label="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="Definition : loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:type="arc" use="optional" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis" xlink:title="RangeAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember" xlink:title="RangeMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis" xlink:to="loc_us-gaap_RangeMember" xlink:title="Definition : loc_us-gaap_RangeAxis to loc_us-gaap_RangeMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="loc_us-gaap_BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain" xlink:title="Definition : loc_us-gaap_BusinessAcquisitionAxis to loc_us-gaap_BusinessAcquisitionAcquireeDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="loc_us-gaap_TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:title="Definition : loc_us-gaap_TypeOfArrangementAxis to loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CounterpartyNameAxis" xlink:label="loc_us-gaap_CounterpartyNameAxis" xlink:title="CounterpartyNameAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:label="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:title="RepurchaseAgreementCounterpartyNameDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CounterpartyNameAxis" xlink:to="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:title="Definition : loc_us-gaap_CounterpartyNameAxis to loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="loc_us-gaap_SubsequentEventTypeAxis" xlink:title="SubsequentEventTypeAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain" xlink:title="SubsequentEventTypeDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis" xlink:to="loc_us-gaap_SubsequentEventTypeDomain" xlink:title="Definition : loc_us-gaap_SubsequentEventTypeAxis to loc_us-gaap_SubsequentEventTypeDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember" xlink:title="MaximumMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember" xlink:to="loc_us-gaap_MaximumMember" xlink:title="Definition : loc_us-gaap_RangeMember to loc_us-gaap_MaximumMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_CuraGenCorporationMember" xlink:label="loc_cldx_CuraGenCorporationMember" xlink:title="CuraGenCorporationMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="loc_cldx_CuraGenCorporationMember" xlink:title="Definition : loc_us-gaap_BusinessAcquisitionAcquireeDomain to loc_cldx_CuraGenCorporationMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_LicenseAgreementsMember" xlink:label="loc_cldx_LicenseAgreementsMember" xlink:title="LicenseAgreementsMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:to="loc_cldx_LicenseAgreementsMember" xlink:title="Definition : loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember to loc_cldx_LicenseAgreementsMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_MedarexIncMember" xlink:label="loc_cldx_MedarexIncMember" xlink:title="MedarexIncMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:to="loc_cldx_MedarexIncMember" xlink:title="Definition : loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain to loc_cldx_MedarexIncMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SubsequentEventMember" xlink:label="loc_us-gaap_SubsequentEventMember" xlink:title="SubsequentEventMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain" xlink:to="loc_us-gaap_SubsequentEventMember" xlink:title="Definition : loc_us-gaap_SubsequentEventTypeDomain to loc_us-gaap_SubsequentEventMember" xlink:type="arc" use="optional" order="1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="loc_us-gaap_TypeOfArrangementAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to loc_us-gaap_TypeOfArrangementAxis" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_NonRefundableLicenseFee" xlink:label="loc_cldx_NonRefundableLicenseFee" xlink:title="NonRefundableLicenseFee" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="loc_cldx_NonRefundableLicenseFee" xlink:title="Definition : loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to loc_cldx_NonRefundableLicenseFee" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_RockefellerUniversityMember" xlink:label="loc_cldx_RockefellerUniversityMember" xlink:title="RockefellerUniversityMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:to="loc_cldx_RockefellerUniversityMember" xlink:title="Definition : loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain to loc_cldx_RockefellerUniversityMember" xlink:type="arc" use="optional" order="2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="loc_us-gaap_CounterpartyNameAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to loc_us-gaap_CounterpartyNameAxis" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_DukeUniversityBrainTumorCancerCenterMember" xlink:label="loc_cldx_DukeUniversityBrainTumorCancerCenterMember" xlink:title="DukeUniversityBrainTumorCancerCenterMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:to="loc_cldx_DukeUniversityBrainTumorCancerCenterMember" xlink:title="Definition : loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain to loc_cldx_DukeUniversityBrainTumorCancerCenterMember" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_CollaborativeArrangementRoyaltyPaymentPeriodFromFirstCommercialSaleOfLicensedProduct" xlink:label="loc_cldx_CollaborativeArrangementRoyaltyPaymentPeriodFromFirstCommercialSaleOfLicensedProduct" xlink:title="CollaborativeArrangementRoyaltyPaymentPeriodFromFirstCommercialSaleOfLicensedProduct" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="loc_cldx_CollaborativeArrangementRoyaltyPaymentPeriodFromFirstCommercialSaleOfLicensedProduct" xlink:title="Definition : loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to loc_cldx_CollaborativeArrangementRoyaltyPaymentPeriodFromFirstCommercialSaleOfLicensedProduct" xlink:type="arc" use="optional" order="3" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="loc_us-gaap_BusinessAcquisitionAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to loc_us-gaap_BusinessAcquisitionAxis" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_LudwigInstituteForCancerResearchMember" xlink:label="loc_cldx_LudwigInstituteForCancerResearchMember" xlink:title="LudwigInstituteForCancerResearchMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:to="loc_cldx_LudwigInstituteForCancerResearchMember" xlink:title="Definition : loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain to loc_cldx_LudwigInstituteForCancerResearchMember" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_CollaborativeArrangementTotalPotentialMilestonePayments" xlink:label="loc_cldx_CollaborativeArrangementTotalPotentialMilestonePayments" xlink:title="CollaborativeArrangementTotalPotentialMilestonePayments" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="loc_cldx_CollaborativeArrangementTotalPotentialMilestonePayments" xlink:title="Definition : loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to loc_cldx_CollaborativeArrangementTotalPotentialMilestonePayments" xlink:type="arc" use="optional" order="4" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="loc_us-gaap_RangeAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to loc_us-gaap_RangeAxis" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_AlterisTherapeuticsIncMember" xlink:label="loc_cldx_AlterisTherapeuticsIncMember" xlink:title="AlterisTherapeuticsIncMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:to="loc_cldx_AlterisTherapeuticsIncMember" xlink:title="Definition : loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain to loc_cldx_AlterisTherapeuticsIncMember" xlink:type="arc" use="optional" order="5" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_CollaborativeArrangementMilestonePaymentsMadeInConnectionWithInitiationOfMetric" xlink:label="loc_cldx_CollaborativeArrangementMilestonePaymentsMadeInConnectionWithInitiationOfMetric" xlink:title="CollaborativeArrangementMilestonePaymentsMadeInConnectionWithInitiationOfMetric" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="loc_cldx_CollaborativeArrangementMilestonePaymentsMadeInConnectionWithInitiationOfMetric" xlink:title="Definition : loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to loc_cldx_CollaborativeArrangementMilestonePaymentsMadeInConnectionWithInitiationOfMetric" xlink:type="arc" use="optional" order="5" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="loc_us-gaap_SubsequentEventTypeAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to loc_us-gaap_SubsequentEventTypeAxis" xlink:type="arc" use="optional" order="5" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_CollaborativeArrangementAgreementTerm" xlink:label="loc_cldx_CollaborativeArrangementAgreementTerm" xlink:title="CollaborativeArrangementAgreementTerm" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="loc_cldx_CollaborativeArrangementAgreementTerm" xlink:title="Definition : loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to loc_cldx_CollaborativeArrangementAgreementTerm" xlink:type="arc" use="optional" order="6" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_UniversityOfSouthamptonUKMember" xlink:label="loc_cldx_UniversityOfSouthamptonUKMember" xlink:title="UniversityOfSouthamptonUKMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:to="loc_cldx_UniversityOfSouthamptonUKMember" xlink:title="Definition : loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain to loc_cldx_UniversityOfSouthamptonUKMember" xlink:type="arc" use="optional" order="6" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_AmgenIncMember" xlink:label="loc_cldx_AmgenIncMember" xlink:title="AmgenIncMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:to="loc_cldx_AmgenIncMember" xlink:title="Definition : loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain to loc_cldx_AmgenIncMember" xlink:type="arc" use="optional" order="7" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_SeattleGeneticIncMember" xlink:label="loc_cldx_SeattleGeneticIncMember" xlink:title="SeattleGeneticIncMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:to="loc_cldx_SeattleGeneticIncMember" xlink:title="Definition : loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain to loc_cldx_SeattleGeneticIncMember" xlink:type="arc" use="optional" order="8" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_CollaborativeArrangementNumberOfAgreements" xlink:label="loc_cldx_CollaborativeArrangementNumberOfAgreements" xlink:title="CollaborativeArrangementNumberOfAgreements" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="loc_cldx_CollaborativeArrangementNumberOfAgreements" xlink:title="Definition : loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to loc_cldx_CollaborativeArrangementNumberOfAgreements" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_ThomasJeffersonUniversityMember" xlink:label="loc_cldx_ThomasJeffersonUniversityMember" xlink:title="ThomasJeffersonUniversityMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:to="loc_cldx_ThomasJeffersonUniversityMember" xlink:title="Definition : loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain to loc_cldx_ThomasJeffersonUniversityMember" xlink:type="arc" use="optional" order="8000" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://www.celldextherapeutics.com/role/DisclosureNatureOfBusinessAndOverviewDetails">
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_NatureOfBusinessAndOverviewLineItems" xlink:label="loc_cldx_NatureOfBusinessAndOverviewLineItems" xlink:title="NatureOfBusinessAndOverviewLineItems" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_ScheduleOfNatureOfBusinessAndOverviewTable" xlink:label="loc_cldx_ScheduleOfNatureOfBusinessAndOverviewTable" xlink:title="ScheduleOfNatureOfBusinessAndOverviewTable" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_cldx_NatureOfBusinessAndOverviewLineItems" xlink:to="loc_cldx_ScheduleOfNatureOfBusinessAndOverviewTable" xlink:title="Definition : loc_cldx_NatureOfBusinessAndOverviewLineItems to loc_cldx_ScheduleOfNatureOfBusinessAndOverviewTable" xlink:type="arc" use="optional" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="loc_us-gaap_SubsequentEventTypeAxis" xlink:title="SubsequentEventTypeAxis" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cldx_ScheduleOfNatureOfBusinessAndOverviewTable" xlink:to="loc_us-gaap_SubsequentEventTypeAxis" xlink:title="Definition : loc_cldx_ScheduleOfNatureOfBusinessAndOverviewTable to loc_us-gaap_SubsequentEventTypeAxis" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InvestmentsAndCash" xlink:label="loc_us-gaap_InvestmentsAndCash" xlink:title="InvestmentsAndCash" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_NatureOfBusinessAndOverviewLineItems" xlink:to="loc_us-gaap_InvestmentsAndCash" xlink:title="Definition : loc_cldx_NatureOfBusinessAndOverviewLineItems to loc_us-gaap_InvestmentsAndCash" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:title="NetIncomeLossAvailableToCommonStockholdersBasic" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_NatureOfBusinessAndOverviewLineItems" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:title="Definition : loc_cldx_NatureOfBusinessAndOverviewLineItems to loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations" xlink:title="NetCashProvidedByUsedInOperatingActivitiesContinuingOperations" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_NatureOfBusinessAndOverviewLineItems" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations" xlink:title="Definition : loc_cldx_NatureOfBusinessAndOverviewLineItems to loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain" xlink:title="SubsequentEventTypeDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis" xlink:to="loc_us-gaap_SubsequentEventTypeDomain" xlink:title="Definition : loc_us-gaap_SubsequentEventTypeAxis to loc_us-gaap_SubsequentEventTypeDomain" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_WorkingCapital" xlink:label="loc_cldx_WorkingCapital" xlink:title="WorkingCapital" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_NatureOfBusinessAndOverviewLineItems" xlink:to="loc_cldx_WorkingCapital" xlink:title="Definition : loc_cldx_NatureOfBusinessAndOverviewLineItems to loc_cldx_WorkingCapital" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SubsequentEventMember" xlink:label="loc_us-gaap_SubsequentEventMember" xlink:title="SubsequentEventMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain" xlink:to="loc_us-gaap_SubsequentEventMember" xlink:title="Definition : loc_us-gaap_SubsequentEventTypeDomain to loc_us-gaap_SubsequentEventMember" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="SubsequentEventTypeDomain_1" xlink:title="SubsequentEventTypeDomain_1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis" xlink:to="SubsequentEventTypeDomain_1" xlink:title="Definition : loc_us-gaap_SubsequentEventTypeAxis to loc_us-gaap_SubsequentEventTypeDomain" xlink:type="arc" use="optional" order="8001" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://www.celldextherapeutics.com/role/DisclosureStockholdersEquityDetails">
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_StockholdersEquityLineItems" xlink:label="loc_cldx_StockholdersEquityLineItems" xlink:title="StockholdersEquityLineItems" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_StockholdersEquityTable" xlink:label="loc_cldx_StockholdersEquityTable" xlink:title="StockholdersEquityTable" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_cldx_StockholdersEquityLineItems" xlink:to="loc_cldx_StockholdersEquityTable" xlink:title="Definition : loc_cldx_StockholdersEquityLineItems to loc_cldx_StockholdersEquityTable" xlink:type="arc" use="optional" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis" xlink:title="RangeAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember" xlink:title="RangeMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis" xlink:to="loc_us-gaap_RangeMember" xlink:title="Definition : loc_us-gaap_RangeAxis to loc_us-gaap_RangeMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_StockIssuedByTypeOfProgramAxis" xlink:label="loc_cldx_StockIssuedByTypeOfProgramAxis" xlink:title="StockIssuedByTypeOfProgramAxis" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_StockIssuedByTypeOfProgramDomain" xlink:label="loc_cldx_StockIssuedByTypeOfProgramDomain" xlink:title="StockIssuedByTypeOfProgramDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_cldx_StockIssuedByTypeOfProgramAxis" xlink:to="loc_cldx_StockIssuedByTypeOfProgramDomain" xlink:title="Definition : loc_cldx_StockIssuedByTypeOfProgramAxis to loc_cldx_StockIssuedByTypeOfProgramDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis" xlink:title="StatementClassOfStockAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain" xlink:title="ClassOfStockDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis" xlink:to="loc_us-gaap_ClassOfStockDomain" xlink:title="Definition : loc_us-gaap_StatementClassOfStockAxis to loc_us-gaap_ClassOfStockDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember" xlink:title="MinimumMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember" xlink:to="loc_us-gaap_MinimumMember" xlink:title="Definition : loc_us-gaap_RangeMember to loc_us-gaap_MinimumMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_ControlledEquityOfferingProgramMember" xlink:label="loc_cldx_ControlledEquityOfferingProgramMember" xlink:title="ControlledEquityOfferingProgramMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_StockIssuedByTypeOfProgramDomain" xlink:to="loc_cldx_ControlledEquityOfferingProgramMember" xlink:title="Definition : loc_cldx_StockIssuedByTypeOfProgramDomain to loc_cldx_ControlledEquityOfferingProgramMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SeriesCPreferredStockMember" xlink:label="loc_us-gaap_SeriesCPreferredStockMember" xlink:title="SeriesCPreferredStockMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain" xlink:to="loc_us-gaap_SeriesCPreferredStockMember" xlink:title="Definition : loc_us-gaap_ClassOfStockDomain to loc_us-gaap_SeriesCPreferredStockMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CumulativePreferredStockMember" xlink:label="loc_us-gaap_CumulativePreferredStockMember" xlink:title="CumulativePreferredStockMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SeriesCPreferredStockMember" xlink:to="loc_us-gaap_CumulativePreferredStockMember" xlink:title="Definition : loc_us-gaap_SeriesCPreferredStockMember to loc_us-gaap_CumulativePreferredStockMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_WarrantsAndRightsNoteDisclosureAbstract" xlink:label="loc_us-gaap_WarrantsAndRightsNoteDisclosureAbstract" xlink:title="WarrantsAndRightsNoteDisclosureAbstract" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_ClassOfWarrantOrRightNumberOfRightsPerCommonStockShare" xlink:label="loc_cldx_ClassOfWarrantOrRightNumberOfRightsPerCommonStockShare" xlink:title="ClassOfWarrantOrRightNumberOfRightsPerCommonStockShare" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WarrantsAndRightsNoteDisclosureAbstract" xlink:to="loc_cldx_ClassOfWarrantOrRightNumberOfRightsPerCommonStockShare" xlink:title="Definition : loc_us-gaap_WarrantsAndRightsNoteDisclosureAbstract to loc_cldx_ClassOfWarrantOrRightNumberOfRightsPerCommonStockShare" xlink:type="arc" use="optional" order="1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cldx_StockholdersEquityTable" xlink:to="loc_cldx_StockIssuedByTypeOfProgramAxis" xlink:title="Definition : loc_cldx_StockholdersEquityTable to loc_cldx_StockIssuedByTypeOfProgramAxis" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeMember" xlink:label="RangeMember_1" xlink:title="RangeMember_1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis" xlink:to="RangeMember_1" xlink:title="Definition : loc_us-gaap_RangeAxis to loc_us-gaap_RangeMember" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_StockIssuedByTypeOfProgramDomain" xlink:label="StockIssuedByTypeOfProgramDomain_2" xlink:title="StockIssuedByTypeOfProgramDomain_2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_cldx_StockIssuedByTypeOfProgramAxis" xlink:to="StockIssuedByTypeOfProgramDomain_2" xlink:title="Definition : loc_cldx_StockIssuedByTypeOfProgramAxis to loc_cldx_StockIssuedByTypeOfProgramDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="ClassOfStockDomain_3" xlink:title="ClassOfStockDomain_3" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis" xlink:to="ClassOfStockDomain_3" xlink:title="Definition : loc_us-gaap_StatementClassOfStockAxis to loc_us-gaap_ClassOfStockDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_ControlledEquityOfferingProgramAmendedMember" xlink:label="loc_cldx_ControlledEquityOfferingProgramAmendedMember" xlink:title="ControlledEquityOfferingProgramAmendedMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_StockIssuedByTypeOfProgramDomain" xlink:to="loc_cldx_ControlledEquityOfferingProgramAmendedMember" xlink:title="Definition : loc_cldx_StockIssuedByTypeOfProgramDomain to loc_cldx_ControlledEquityOfferingProgramAmendedMember" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_ShelfRegistrationStatementAmount" xlink:label="loc_cldx_ShelfRegistrationStatementAmount" xlink:title="ShelfRegistrationStatementAmount" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_StockholdersEquityLineItems" xlink:to="loc_cldx_ShelfRegistrationStatementAmount" xlink:title="Definition : loc_cldx_StockholdersEquityLineItems to loc_cldx_ShelfRegistrationStatementAmount" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:title="ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WarrantsAndRightsNoteDisclosureAbstract" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:title="Definition : loc_us-gaap_WarrantsAndRightsNoteDisclosureAbstract to loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:type="arc" use="optional" order="2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cldx_StockholdersEquityTable" xlink:to="loc_us-gaap_StatementClassOfStockAxis" xlink:title="Definition : loc_cldx_StockholdersEquityTable to loc_us-gaap_StatementClassOfStockAxis" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_ShareholderRightsPlanMember" xlink:label="loc_cldx_ShareholderRightsPlanMember" xlink:title="ShareholderRightsPlanMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_StockIssuedByTypeOfProgramDomain" xlink:to="loc_cldx_ShareholderRightsPlanMember" xlink:title="Definition : loc_cldx_StockIssuedByTypeOfProgramDomain to loc_cldx_ShareholderRightsPlanMember" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights" xlink:title="ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WarrantsAndRightsNoteDisclosureAbstract" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights" xlink:title="Definition : loc_us-gaap_WarrantsAndRightsNoteDisclosureAbstract to loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:title="StockIssuedDuringPeriodSharesNewIssues" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_StockholdersEquityLineItems" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:title="Definition : loc_cldx_StockholdersEquityLineItems to loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:type="arc" use="optional" order="3" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cldx_StockholdersEquityTable" xlink:to="loc_us-gaap_RangeAxis" xlink:title="Definition : loc_cldx_StockholdersEquityTable to loc_us-gaap_RangeAxis" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_ClassOfWarrantOrRightConditionOnExerciseOfRightsPercentageOfCommonStockAcquired" xlink:label="loc_cldx_ClassOfWarrantOrRightConditionOnExerciseOfRightsPercentageOfCommonStockAcquired" xlink:title="ClassOfWarrantOrRightConditionOnExerciseOfRightsPercentageOfCommonStockAcquired" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WarrantsAndRightsNoteDisclosureAbstract" xlink:to="loc_cldx_ClassOfWarrantOrRightConditionOnExerciseOfRightsPercentageOfCommonStockAcquired" xlink:title="Definition : loc_us-gaap_WarrantsAndRightsNoteDisclosureAbstract to loc_cldx_ClassOfWarrantOrRightConditionOnExerciseOfRightsPercentageOfCommonStockAcquired" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:title="ProceedsFromIssuanceOfCommonStock" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_StockholdersEquityLineItems" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:title="Definition : loc_cldx_StockholdersEquityLineItems to loc_us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="loc_us-gaap_SubsequentEventTypeAxis" xlink:title="SubsequentEventTypeAxis" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cldx_StockholdersEquityTable" xlink:to="loc_us-gaap_SubsequentEventTypeAxis" xlink:title="Definition : loc_cldx_StockholdersEquityTable to loc_us-gaap_SubsequentEventTypeAxis" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_ClassOfWarrantOrRightConditionOnExerciseOfRightsPercentageOfCommonStockAcquiredThroughTender" xlink:label="loc_cldx_ClassOfWarrantOrRightConditionOnExerciseOfRightsPercentageOfCommonStockAcquiredThroughTender" xlink:title="ClassOfWarrantOrRightConditionOnExerciseOfRightsPercentageOfCommonStockAcquiredThroughTender" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WarrantsAndRightsNoteDisclosureAbstract" xlink:to="loc_cldx_ClassOfWarrantOrRightConditionOnExerciseOfRightsPercentageOfCommonStockAcquiredThroughTender" xlink:title="Definition : loc_us-gaap_WarrantsAndRightsNoteDisclosureAbstract to loc_cldx_ClassOfWarrantOrRightConditionOnExerciseOfRightsPercentageOfCommonStockAcquiredThroughTender" xlink:type="arc" use="optional" order="5" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:title="StockIssuedDuringPeriodValueNewIssues" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_StockholdersEquityLineItems" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:title="Definition : loc_cldx_StockholdersEquityLineItems to loc_us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:type="arc" use="optional" order="5" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_NumberOfMultiplesClassOfWarrantOrRightConditionOnExerciseOfRightsOfExercisePriceHolderCanReceiveInValueIfFifteenPercentOrMoreOfCommonStockIsAcquired" xlink:label="loc_cldx_NumberOfMultiplesClassOfWarrantOrRightConditionOnExerciseOfRightsOfExercisePriceHolderCanReceiveInValueIfFifteenPercentOrMoreOfCommonStockIsAcquired" xlink:title="NumberOfMultiplesClassOfWarrantOrRightConditionOnExerciseOfRightsOfExercisePriceHolderCanReceiveInValueIfFifteenPercentOrMoreOfCommonStockIsAcquired" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WarrantsAndRightsNoteDisclosureAbstract" xlink:to="loc_cldx_NumberOfMultiplesClassOfWarrantOrRightConditionOnExerciseOfRightsOfExercisePriceHolderCanReceiveInValueIfFifteenPercentOrMoreOfCommonStockIsAcquired" xlink:title="Definition : loc_us-gaap_WarrantsAndRightsNoteDisclosureAbstract to loc_cldx_NumberOfMultiplesClassOfWarrantOrRightConditionOnExerciseOfRightsOfExercisePriceHolderCanReceiveInValueIfFifteenPercentOrMoreOfCommonStockIsAcquired" xlink:type="arc" use="optional" order="6" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized" xlink:title="PreferredStockSharesAuthorized" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_StockholdersEquityLineItems" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized" xlink:title="Definition : loc_cldx_StockholdersEquityLineItems to loc_us-gaap_PreferredStockSharesAuthorized" xlink:type="arc" use="optional" order="6" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_ClassOfWarrantOrRightConditionOnExerciseOfRightsPercentageOfAssetsOrEarningPowerSoldForHolderRightToReceiveCommonStockOfAcquiringCompany" xlink:label="loc_cldx_ClassOfWarrantOrRightConditionOnExerciseOfRightsPercentageOfAssetsOrEarningPowerSoldForHolderRightToReceiveCommonStockOfAcquiringCompany" xlink:title="ClassOfWarrantOrRightConditionOnExerciseOfRightsPercentageOfAssetsOrEarningPowerSoldForHolderRightToReceiveCommonStockOfAcquiringCompany" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WarrantsAndRightsNoteDisclosureAbstract" xlink:to="loc_cldx_ClassOfWarrantOrRightConditionOnExerciseOfRightsPercentageOfAssetsOrEarningPowerSoldForHolderRightToReceiveCommonStockOfAcquiringCompany" xlink:title="Definition : loc_us-gaap_WarrantsAndRightsNoteDisclosureAbstract to loc_cldx_ClassOfWarrantOrRightConditionOnExerciseOfRightsPercentageOfAssetsOrEarningPowerSoldForHolderRightToReceiveCommonStockOfAcquiringCompany" xlink:type="arc" use="optional" order="7" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_StockholdersEquityLineItems" xlink:to="loc_us-gaap_WarrantsAndRightsNoteDisclosureAbstract" xlink:title="Definition : loc_cldx_StockholdersEquityLineItems to loc_us-gaap_WarrantsAndRightsNoteDisclosureAbstract" xlink:type="arc" use="optional" order="7" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_NumberOfMultiplesClassOfWarrantOrRightConditionOnExerciseOfRightsOfExercisePriceHolderCanReceiveInCommonStockValueOfAcquiringCompany" xlink:label="loc_cldx_NumberOfMultiplesClassOfWarrantOrRightConditionOnExerciseOfRightsOfExercisePriceHolderCanReceiveInCommonStockValueOfAcquiringCompany" xlink:title="NumberOfMultiplesClassOfWarrantOrRightConditionOnExerciseOfRightsOfExercisePriceHolderCanReceiveInCommonStockValueOfAcquiringCompany" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WarrantsAndRightsNoteDisclosureAbstract" xlink:to="loc_cldx_NumberOfMultiplesClassOfWarrantOrRightConditionOnExerciseOfRightsOfExercisePriceHolderCanReceiveInCommonStockValueOfAcquiringCompany" xlink:title="Definition : loc_us-gaap_WarrantsAndRightsNoteDisclosureAbstract to loc_cldx_NumberOfMultiplesClassOfWarrantOrRightConditionOnExerciseOfRightsOfExercisePriceHolderCanReceiveInCommonStockValueOfAcquiringCompany" xlink:type="arc" use="optional" order="8" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain" xlink:title="SubsequentEventTypeDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis" xlink:to="loc_us-gaap_SubsequentEventTypeDomain" xlink:title="Definition : loc_us-gaap_SubsequentEventTypeAxis to loc_us-gaap_SubsequentEventTypeDomain" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_CommonStockExerciseOfFullOverAllotmentOptionToPurchaseAdditionalSharesByUnderwriter" xlink:label="loc_cldx_CommonStockExerciseOfFullOverAllotmentOptionToPurchaseAdditionalSharesByUnderwriter" xlink:title="CommonStockExerciseOfFullOverAllotmentOptionToPurchaseAdditionalSharesByUnderwriter" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_StockholdersEquityLineItems" xlink:to="loc_cldx_CommonStockExerciseOfFullOverAllotmentOptionToPurchaseAdditionalSharesByUnderwriter" xlink:title="Definition : loc_cldx_StockholdersEquityLineItems to loc_cldx_CommonStockExerciseOfFullOverAllotmentOptionToPurchaseAdditionalSharesByUnderwriter" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember" xlink:title="MaximumMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember" xlink:to="loc_us-gaap_MaximumMember" xlink:title="Definition : loc_us-gaap_RangeMember to loc_us-gaap_MaximumMember" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SubsequentEventMember" xlink:label="loc_us-gaap_SubsequentEventMember" xlink:title="SubsequentEventMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain" xlink:to="loc_us-gaap_SubsequentEventMember" xlink:title="Definition : loc_us-gaap_SubsequentEventTypeDomain to loc_us-gaap_SubsequentEventMember" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_CommonStockSharesAvailableForSale" xlink:label="loc_cldx_CommonStockSharesAvailableForSale" xlink:title="CommonStockSharesAvailableForSale" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_StockholdersEquityLineItems" xlink:to="loc_cldx_CommonStockSharesAvailableForSale" xlink:title="Definition : loc_cldx_StockholdersEquityLineItems to loc_cldx_CommonStockSharesAvailableForSale" xlink:type="arc" use="optional" order="8001" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_CommonStockIssuanceOfAdditionalSharesAggregateOfferingPrice" xlink:label="loc_cldx_CommonStockIssuanceOfAdditionalSharesAggregateOfferingPrice" xlink:title="CommonStockIssuanceOfAdditionalSharesAggregateOfferingPrice" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_StockholdersEquityLineItems" xlink:to="loc_cldx_CommonStockIssuanceOfAdditionalSharesAggregateOfferingPrice" xlink:title="Definition : loc_cldx_StockholdersEquityLineItems to loc_cldx_CommonStockIssuanceOfAdditionalSharesAggregateOfferingPrice" xlink:type="arc" use="optional" order="8002" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_FixedRateOfCommissionOnSaleOfStock" xlink:label="loc_cldx_FixedRateOfCommissionOnSaleOfStock" xlink:title="FixedRateOfCommissionOnSaleOfStock" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_StockholdersEquityLineItems" xlink:to="loc_cldx_FixedRateOfCommissionOnSaleOfStock" xlink:title="Definition : loc_cldx_StockholdersEquityLineItems to loc_cldx_FixedRateOfCommissionOnSaleOfStock" xlink:type="arc" use="optional" order="8003" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_NoticePeriodForTerminationOfAgreement" xlink:label="loc_cldx_NoticePeriodForTerminationOfAgreement" xlink:title="NoticePeriodForTerminationOfAgreement" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_StockholdersEquityLineItems" xlink:to="loc_cldx_NoticePeriodForTerminationOfAgreement" xlink:title="Definition : loc_cldx_StockholdersEquityLineItems to loc_cldx_NoticePeriodForTerminationOfAgreement" xlink:type="arc" use="optional" order="8004" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_CommonStockAvailableForSaleLockUpPeriodToBeWaivedByUnderwriters" xlink:label="loc_cldx_CommonStockAvailableForSaleLockUpPeriodToBeWaivedByUnderwriters" xlink:title="CommonStockAvailableForSaleLockUpPeriodToBeWaivedByUnderwriters" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_StockholdersEquityLineItems" xlink:to="loc_cldx_CommonStockAvailableForSaleLockUpPeriodToBeWaivedByUnderwriters" xlink:title="Definition : loc_cldx_StockholdersEquityLineItems to loc_cldx_CommonStockAvailableForSaleLockUpPeriodToBeWaivedByUnderwriters" xlink:type="arc" use="optional" order="8005" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://www.celldextherapeutics.com/role/DisclosureSummaryOfSignificantAccountingPoliciesDetails3">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems" xlink:title="BusinessAcquisitionLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:title="ScheduleOfBusinessAcquisitionsByAcquisitionTable" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:title="Definition : loc_us-gaap_BusinessAcquisitionLineItems to loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:type="arc" use="optional" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="loc_us-gaap_BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain" xlink:title="Definition : loc_us-gaap_BusinessAcquisitionAxis to loc_us-gaap_BusinessAcquisitionAcquireeDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentAxis" xlink:label="loc_us-gaap_DebtInstrumentAxis" xlink:title="DebtInstrumentAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain" xlink:title="DebtInstrumentNameDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis" xlink:to="loc_us-gaap_DebtInstrumentNameDomain" xlink:title="Definition : loc_us-gaap_DebtInstrumentAxis to loc_us-gaap_DebtInstrumentNameDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_CuraGenCorporationMember" xlink:label="loc_cldx_CuraGenCorporationMember" xlink:title="CuraGenCorporationMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="loc_cldx_CuraGenCorporationMember" xlink:title="Definition : loc_us-gaap_BusinessAcquisitionAcquireeDomain to loc_cldx_CuraGenCorporationMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConvertibleSubordinatedDebtMember" xlink:label="loc_us-gaap_ConvertibleSubordinatedDebtMember" xlink:title="ConvertibleSubordinatedDebtMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain" xlink:to="loc_us-gaap_ConvertibleSubordinatedDebtMember" xlink:title="Definition : loc_us-gaap_DebtInstrumentNameDomain to loc_us-gaap_ConvertibleSubordinatedDebtMember" xlink:type="arc" use="optional" order="1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="loc_us-gaap_BusinessAcquisitionAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable to loc_us-gaap_BusinessAcquisitionAxis" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="DebtInstrumentNameDomain_1" xlink:title="DebtInstrumentNameDomain_1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis" xlink:to="DebtInstrumentNameDomain_1" xlink:title="Definition : loc_us-gaap_DebtInstrumentAxis to loc_us-gaap_DebtInstrumentNameDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConvertibleSubordinatedDebt" xlink:label="loc_us-gaap_ConvertibleSubordinatedDebt" xlink:title="ConvertibleSubordinatedDebt" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems" xlink:to="loc_us-gaap_ConvertibleSubordinatedDebt" xlink:title="Definition : loc_us-gaap_BusinessAcquisitionLineItems to loc_us-gaap_ConvertibleSubordinatedDebt" xlink:type="arc" use="optional" order="2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="loc_us-gaap_DebtInstrumentAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable to loc_us-gaap_DebtInstrumentAxis" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:title="DebtInstrumentInterestRateStatedPercentage" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:title="Definition : loc_us-gaap_BusinessAcquisitionLineItems to loc_us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RepaymentsOfDebt" xlink:label="loc_us-gaap_RepaymentsOfDebt" xlink:title="RepaymentsOfDebt" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems" xlink:to="loc_us-gaap_RepaymentsOfDebt" xlink:title="Definition : loc_us-gaap_BusinessAcquisitionLineItems to loc_us-gaap_RepaymentsOfDebt" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentConvertibleNumberOfEquityInstruments" xlink:label="loc_us-gaap_DebtInstrumentConvertibleNumberOfEquityInstruments" xlink:title="DebtInstrumentConvertibleNumberOfEquityInstruments" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems" xlink:to="loc_us-gaap_DebtInstrumentConvertibleNumberOfEquityInstruments" xlink:title="Definition : loc_us-gaap_BusinessAcquisitionLineItems to loc_us-gaap_DebtInstrumentConvertibleNumberOfEquityInstruments" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentConvertibleConversionRatio1" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1" xlink:title="DebtInstrumentConvertibleConversionRatio1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1" xlink:title="Definition : loc_us-gaap_BusinessAcquisitionLineItems to loc_us-gaap_DebtInstrumentConvertibleConversionRatio1" xlink:type="arc" use="optional" order="8001" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_DebtInstrumentPrincipalAmountDenominationForConversionIntoCommonStock" xlink:label="loc_cldx_DebtInstrumentPrincipalAmountDenominationForConversionIntoCommonStock" xlink:title="DebtInstrumentPrincipalAmountDenominationForConversionIntoCommonStock" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems" xlink:to="loc_cldx_DebtInstrumentPrincipalAmountDenominationForConversionIntoCommonStock" xlink:title="Definition : loc_us-gaap_BusinessAcquisitionLineItems to loc_cldx_DebtInstrumentPrincipalAmountDenominationForConversionIntoCommonStock" xlink:type="arc" use="optional" order="8002" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1" xlink:title="DebtInstrumentConvertibleConversionPrice1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1" xlink:title="Definition : loc_us-gaap_BusinessAcquisitionLineItems to loc_us-gaap_DebtInstrumentConvertibleConversionPrice1" xlink:type="arc" use="optional" order="8003" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InterestExpenseDebt" xlink:label="loc_us-gaap_InterestExpenseDebt" xlink:title="InterestExpenseDebt" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems" xlink:to="loc_us-gaap_InterestExpenseDebt" xlink:title="Definition : loc_us-gaap_BusinessAcquisitionLineItems to loc_us-gaap_InterestExpenseDebt" xlink:type="arc" use="optional" order="8004" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://www.celldextherapeutics.com/role/DisclosureSummaryOfSignificantAccountingPoliciesDetails2">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems" xlink:title="PropertyPlantAndEquipmentLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:title="ScheduleOfPropertyPlantAndEquipmentTable" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:title="Definition : loc_us-gaap_PropertyPlantAndEquipmentLineItems to loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:type="arc" use="optional" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis" xlink:title="RangeAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember" xlink:title="RangeMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis" xlink:to="loc_us-gaap_RangeMember" xlink:title="Definition : loc_us-gaap_RangeAxis to loc_us-gaap_RangeMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:title="PropertyPlantAndEquipmentByTypeAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:title="PropertyPlantAndEquipmentTypeDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:title="Definition : loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis to loc_us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember" xlink:title="MinimumMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember" xlink:to="loc_us-gaap_MinimumMember" xlink:title="Definition : loc_us-gaap_RangeMember to loc_us-gaap_MinimumMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_LaboratoryEquipmentMember" xlink:label="loc_cldx_LaboratoryEquipmentMember" xlink:title="LaboratoryEquipmentMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="loc_cldx_LaboratoryEquipmentMember" xlink:title="Definition : loc_us-gaap_PropertyPlantAndEquipmentTypeDomain to loc_cldx_LaboratoryEquipmentMember" xlink:type="arc" use="optional" order="1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable to loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="PropertyPlantAndEquipmentTypeDomain_1" xlink:title="PropertyPlantAndEquipmentTypeDomain_1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="PropertyPlantAndEquipmentTypeDomain_1" xlink:title="Definition : loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis to loc_us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember" xlink:title="MaximumMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember" xlink:to="loc_us-gaap_MaximumMember" xlink:title="Definition : loc_us-gaap_RangeMember to loc_us-gaap_MaximumMember" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FurnitureAndFixturesMember" xlink:label="loc_us-gaap_FurnitureAndFixturesMember" xlink:title="FurnitureAndFixturesMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="loc_us-gaap_FurnitureAndFixturesMember" xlink:title="Definition : loc_us-gaap_PropertyPlantAndEquipmentTypeDomain to loc_us-gaap_FurnitureAndFixturesMember" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife" xlink:title="PropertyPlantAndEquipmentUsefulLife" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife" xlink:title="Definition : loc_us-gaap_PropertyPlantAndEquipmentLineItems to loc_us-gaap_PropertyPlantAndEquipmentUsefulLife" xlink:type="arc" use="optional" order="2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:to="loc_us-gaap_RangeAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable to loc_us-gaap_RangeAxis" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ComputerEquipmentMember" xlink:label="loc_us-gaap_ComputerEquipmentMember" xlink:title="ComputerEquipmentMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="loc_us-gaap_ComputerEquipmentMember" xlink:title="Definition : loc_us-gaap_PropertyPlantAndEquipmentTypeDomain to loc_us-gaap_ComputerEquipmentMember" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_ManufacturingEquipmentMember" xlink:label="loc_cldx_ManufacturingEquipmentMember" xlink:title="ManufacturingEquipmentMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="loc_cldx_ManufacturingEquipmentMember" xlink:title="Definition : loc_us-gaap_PropertyPlantAndEquipmentTypeDomain to loc_cldx_ManufacturingEquipmentMember" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RevenueRecognitionAbstract" xlink:label="loc_us-gaap_RevenueRecognitionAbstract" xlink:title="RevenueRecognitionAbstract" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="loc_us-gaap_RevenueRecognitionAbstract" xlink:title="Definition : loc_us-gaap_PropertyPlantAndEquipmentLineItems to loc_us-gaap_RevenueRecognitionAbstract" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_CollaborativeArrangementMilestonePaymentsReceived" xlink:label="loc_cldx_CollaborativeArrangementMilestonePaymentsReceived" xlink:title="CollaborativeArrangementMilestonePaymentsReceived" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRecognitionAbstract" xlink:to="loc_cldx_CollaborativeArrangementMilestonePaymentsReceived" xlink:title="Definition : loc_us-gaap_RevenueRecognitionAbstract to loc_cldx_CollaborativeArrangementMilestonePaymentsReceived" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherNonoperatingIncome" xlink:label="loc_us-gaap_OtherNonoperatingIncome" xlink:title="OtherNonoperatingIncome" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRecognitionAbstract" xlink:to="loc_us-gaap_OtherNonoperatingIncome" xlink:title="Definition : loc_us-gaap_RevenueRecognitionAbstract to loc_us-gaap_OtherNonoperatingIncome" xlink:type="arc" use="optional" order="8001" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://www.celldextherapeutics.com/role/DisclosureIntangibleAssetsAndGoodwillDetails">
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassLineItems" xlink:label="loc_cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassLineItems" xlink:title="FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassLineItems" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassTable" xlink:label="loc_cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassTable" xlink:title="FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassTable" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassLineItems" xlink:to="loc_cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassTable" xlink:title="Definition : loc_cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassLineItems to loc_cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassTable" xlink:type="arc" use="optional" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis" xlink:title="IndefiniteLivedIntangibleAssetsByMajorClassAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:title="IndefiniteLivedIntangibleAssetsMajorClassNameDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:title="Definition : loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis to loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:title="FiniteLivedIntangibleAssetsByMajorClassAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:title="FiniteLivedIntangibleAssetsMajorClassNameDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:title="Definition : loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis to loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InProcessResearchAndDevelopmentMember" xlink:label="loc_us-gaap_InProcessResearchAndDevelopmentMember" xlink:title="InProcessResearchAndDevelopmentMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="loc_us-gaap_InProcessResearchAndDevelopmentMember" xlink:title="Definition : loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain to loc_us-gaap_InProcessResearchAndDevelopmentMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_AmgenAmendmentMember" xlink:label="loc_cldx_AmgenAmendmentMember" xlink:title="AmgenAmendmentMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="loc_cldx_AmgenAmendmentMember" xlink:title="Definition : loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain to loc_cldx_AmgenAmendmentMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillAbstract" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillAbstract" xlink:title="IndefiniteLivedIntangibleAssetsExcludingGoodwillAbstract" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill" xlink:title="IndefiniteLivedIntangibleAssetsExcludingGoodwill" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillAbstract" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill" xlink:title="Definition : loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillAbstract to loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:title="FiniteLivedIntangibleAssetsNetAbstract" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:title="FiniteLivedIntangibleAssetUsefulLife" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:title="Definition : loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract to loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwillAbstract" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwillAbstract" xlink:title="IntangibleAssetsNetExcludingGoodwillAbstract" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IntangibleAssetsGrossExcludingGoodwill" xlink:label="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill" xlink:title="IntangibleAssetsGrossExcludingGoodwill" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IntangibleAssetsNetExcludingGoodwillAbstract" xlink:to="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill" xlink:title="Definition : loc_us-gaap_IntangibleAssetsNetExcludingGoodwillAbstract to loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:title="FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths" xlink:title="FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths" xlink:title="Definition : loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract to loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths" xlink:type="arc" use="optional" order="1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassTable" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis" xlink:title="Definition : loc_cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassTable to loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="IndefiniteLivedIntangibleAssetsMajorClassNameDomain_1" xlink:title="IndefiniteLivedIntangibleAssetsMajorClassNameDomain_1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="IndefiniteLivedIntangibleAssetsMajorClassNameDomain_1" xlink:title="Definition : loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis to loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="FiniteLivedIntangibleAssetsMajorClassNameDomain_2" xlink:title="FiniteLivedIntangibleAssetsMajorClassNameDomain_2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="FiniteLivedIntangibleAssetsMajorClassNameDomain_2" xlink:title="Definition : loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis to loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_CoreTechnologyMember" xlink:label="loc_cldx_CoreTechnologyMember" xlink:title="CoreTechnologyMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="loc_cldx_CoreTechnologyMember" xlink:title="Definition : loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain to loc_cldx_CoreTechnologyMember" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Goodwill" xlink:label="loc_us-gaap_Goodwill" xlink:title="Goodwill" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassLineItems" xlink:to="loc_us-gaap_Goodwill" xlink:title="Definition : loc_cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassLineItems to loc_us-gaap_Goodwill" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsGross" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross" xlink:title="FiniteLivedIntangibleAssetsGross" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross" xlink:title="Definition : loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract to loc_us-gaap_FiniteLivedIntangibleAssetsGross" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill" xlink:title="IntangibleAssetsNetExcludingGoodwill" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IntangibleAssetsNetExcludingGoodwillAbstract" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill" xlink:title="Definition : loc_us-gaap_IntangibleAssetsNetExcludingGoodwillAbstract to loc_us-gaap_IntangibleAssetsNetExcludingGoodwill" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo" xlink:title="FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo" xlink:title="Definition : loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract to loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo" xlink:type="arc" use="optional" order="2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassTable" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:title="Definition : loc_cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassTable to loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:type="arc" use="optional" order="2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassLineItems" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillAbstract" xlink:title="Definition : loc_cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassLineItems to loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillAbstract" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:title="FiniteLivedIntangibleAssetsAccumulatedAmortization" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:title="Definition : loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract to loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree" xlink:title="FiniteLivedIntangibleAssetsAmortizationExpenseYearThree" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree" xlink:title="Definition : loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract to loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis" xlink:title="RangeAxis" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassTable" xlink:to="loc_us-gaap_RangeAxis" xlink:title="Definition : loc_cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassTable to loc_us-gaap_RangeAxis" xlink:type="arc" use="optional" order="3" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassLineItems" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:title="Definition : loc_cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassLineItems to loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNet" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet" xlink:title="FiniteLivedIntangibleAssetsNet" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet" xlink:title="Definition : loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract to loc_us-gaap_FiniteLivedIntangibleAssetsNet" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour" xlink:title="FiniteLivedIntangibleAssetsAmortizationExpenseYearFour" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour" xlink:title="Definition : loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract to loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour" xlink:type="arc" use="optional" order="4" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassLineItems" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwillAbstract" xlink:title="Definition : loc_cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassLineItems to loc_us-gaap_IntangibleAssetsNetExcludingGoodwillAbstract" xlink:type="arc" use="optional" order="5" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive" xlink:title="FiniteLivedIntangibleAssetsAmortizationExpenseYearFive" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive" xlink:title="Definition : loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract to loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive" xlink:type="arc" use="optional" order="5" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AmortizationOfIntangibleAssets" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets" xlink:title="AmortizationOfIntangibleAssets" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassLineItems" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets" xlink:title="Definition : loc_cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassLineItems to loc_us-gaap_AmortizationOfIntangibleAssets" xlink:type="arc" use="optional" order="6" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassLineItems" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:title="Definition : loc_cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassLineItems to loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:type="arc" use="optional" order="7" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember" xlink:title="RangeMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis" xlink:to="loc_us-gaap_RangeMember" xlink:title="Definition : loc_us-gaap_RangeAxis to loc_us-gaap_RangeMember" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember" xlink:title="MinimumMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember" xlink:to="loc_us-gaap_MinimumMember" xlink:title="Definition : loc_us-gaap_RangeMember to loc_us-gaap_MinimumMember" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember" xlink:title="MaximumMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember" xlink:to="loc_us-gaap_MaximumMember" xlink:title="Definition : loc_us-gaap_RangeMember to loc_us-gaap_MaximumMember" xlink:type="arc" use="optional" order="8001" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://www.celldextherapeutics.com/role/DisclosureNetLossPerShareDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:title="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:title="ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:title="Definition : loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems to loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:type="arc" use="optional" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:title="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain" xlink:title="AntidilutiveSecuritiesNameDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain" xlink:title="Definition : loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis to loc_us-gaap_AntidilutiveSecuritiesNameDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_EmployeeConsultantAndNonEmployeeDirectorStockOptionMember" xlink:label="loc_cldx_EmployeeConsultantAndNonEmployeeDirectorStockOptionMember" xlink:title="EmployeeConsultantAndNonEmployeeDirectorStockOptionMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain" xlink:to="loc_cldx_EmployeeConsultantAndNonEmployeeDirectorStockOptionMember" xlink:title="Definition : loc_us-gaap_AntidilutiveSecuritiesNameDomain to loc_cldx_EmployeeConsultantAndNonEmployeeDirectorStockOptionMember" xlink:type="arc" use="optional" order="1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable to loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="AntidilutiveSecuritiesNameDomain_1" xlink:title="AntidilutiveSecuritiesNameDomain_1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="AntidilutiveSecuritiesNameDomain_1" xlink:title="Definition : loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis to loc_us-gaap_AntidilutiveSecuritiesNameDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="loc_us-gaap_RestrictedStockMember" xlink:title="RestrictedStockMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain" xlink:to="loc_us-gaap_RestrictedStockMember" xlink:title="Definition : loc_us-gaap_AntidilutiveSecuritiesNameDomain to loc_us-gaap_RestrictedStockMember" xlink:type="arc" use="optional" order="2" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://www.celldextherapeutics.com/role/DisclosureSummaryOfSignificantAccountingPoliciesDetails4">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:title="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:title="ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:title="Definition : loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems to loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:type="arc" use="optional" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:title="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain" xlink:title="AntidilutiveSecuritiesNameDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain" xlink:title="Definition : loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis to loc_us-gaap_AntidilutiveSecuritiesNameDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_EmployeeConsultantAndNonEmployeeDirectorStockOptionMember" xlink:label="loc_cldx_EmployeeConsultantAndNonEmployeeDirectorStockOptionMember" xlink:title="EmployeeConsultantAndNonEmployeeDirectorStockOptionMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain" xlink:to="loc_cldx_EmployeeConsultantAndNonEmployeeDirectorStockOptionMember" xlink:title="Definition : loc_us-gaap_AntidilutiveSecuritiesNameDomain to loc_cldx_EmployeeConsultantAndNonEmployeeDirectorStockOptionMember" xlink:type="arc" use="optional" order="1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable to loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="loc_us-gaap_RestrictedStockMember" xlink:title="RestrictedStockMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain" xlink:to="loc_us-gaap_RestrictedStockMember" xlink:title="Definition : loc_us-gaap_AntidilutiveSecuritiesNameDomain to loc_us-gaap_RestrictedStockMember" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:title="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:title="Definition : loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems to loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConvertibleSubordinatedDebtMember" xlink:label="loc_us-gaap_ConvertibleSubordinatedDebtMember" xlink:title="ConvertibleSubordinatedDebtMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain" xlink:to="loc_us-gaap_ConvertibleSubordinatedDebtMember" xlink:title="Definition : loc_us-gaap_AntidilutiveSecuritiesNameDomain to loc_us-gaap_ConvertibleSubordinatedDebtMember" xlink:type="arc" use="optional" order="8000" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://www.celldextherapeutics.com/role/DisclosureSummaryOfSignificantAccountingPoliciesDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConcentrationRiskLineItems" xlink:label="loc_us-gaap_ConcentrationRiskLineItems" xlink:title="ConcentrationRiskLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConcentrationRiskTable" xlink:label="loc_us-gaap_ConcentrationRiskTable" xlink:title="ConcentrationRiskTable" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems" xlink:to="loc_us-gaap_ConcentrationRiskTable" xlink:title="Definition : loc_us-gaap_ConcentrationRiskLineItems to loc_us-gaap_ConcentrationRiskTable" xlink:type="arc" use="optional" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:title="ConcentrationRiskByBenchmarkAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain" xlink:title="ConcentrationRiskBenchmarkDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain" xlink:title="Definition : loc_us-gaap_ConcentrationRiskByBenchmarkAxis to loc_us-gaap_ConcentrationRiskBenchmarkDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConcentrationRiskByTypeAxis" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis" xlink:title="ConcentrationRiskByTypeAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain" xlink:title="ConcentrationRiskTypeDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain" xlink:title="Definition : loc_us-gaap_ConcentrationRiskByTypeAxis to loc_us-gaap_ConcentrationRiskTypeDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorCustomersAxis" xlink:label="loc_us-gaap_MajorCustomersAxis" xlink:title="MajorCustomersAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NameOfMajorCustomerDomain" xlink:label="loc_us-gaap_NameOfMajorCustomerDomain" xlink:title="NameOfMajorCustomerDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorCustomersAxis" xlink:to="loc_us-gaap_NameOfMajorCustomerDomain" xlink:title="Definition : loc_us-gaap_MajorCustomersAxis to loc_us-gaap_NameOfMajorCustomerDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SalesMember" xlink:label="loc_us-gaap_SalesMember" xlink:title="SalesMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain" xlink:to="loc_us-gaap_SalesMember" xlink:title="Definition : loc_us-gaap_ConcentrationRiskBenchmarkDomain to loc_us-gaap_SalesMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CustomerConcentrationRiskMember" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember" xlink:title="CustomerConcentrationRiskMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember" xlink:title="Definition : loc_us-gaap_ConcentrationRiskTypeDomain to loc_us-gaap_CustomerConcentrationRiskMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_GlaxoSmithKlinePlcMember" xlink:label="loc_cldx_GlaxoSmithKlinePlcMember" xlink:title="GlaxoSmithKlinePlcMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NameOfMajorCustomerDomain" xlink:to="loc_cldx_GlaxoSmithKlinePlcMember" xlink:title="Definition : loc_us-gaap_NameOfMajorCustomerDomain to loc_cldx_GlaxoSmithKlinePlcMember" xlink:type="arc" use="optional" order="1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:title="Definition : loc_us-gaap_ConcentrationRiskTable to loc_us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="ConcentrationRiskBenchmarkDomain_1" xlink:title="ConcentrationRiskBenchmarkDomain_1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:to="ConcentrationRiskBenchmarkDomain_1" xlink:title="Definition : loc_us-gaap_ConcentrationRiskByBenchmarkAxis to loc_us-gaap_ConcentrationRiskBenchmarkDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="ConcentrationRiskTypeDomain_2" xlink:title="ConcentrationRiskTypeDomain_2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis" xlink:to="ConcentrationRiskTypeDomain_2" xlink:title="Definition : loc_us-gaap_ConcentrationRiskByTypeAxis to loc_us-gaap_ConcentrationRiskTypeDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NameOfMajorCustomerDomain" xlink:label="NameOfMajorCustomerDomain_3" xlink:title="NameOfMajorCustomerDomain_3" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorCustomersAxis" xlink:to="NameOfMajorCustomerDomain_3" xlink:title="Definition : loc_us-gaap_MajorCustomersAxis to loc_us-gaap_NameOfMajorCustomerDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConcentrationRiskPercentage1" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1" xlink:title="ConcentrationRiskPercentage1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1" xlink:title="Definition : loc_us-gaap_ConcentrationRiskLineItems to loc_us-gaap_ConcentrationRiskPercentage1" xlink:type="arc" use="optional" order="2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis" xlink:title="Definition : loc_us-gaap_ConcentrationRiskTable to loc_us-gaap_ConcentrationRiskByTypeAxis" xlink:type="arc" use="optional" order="2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable" xlink:to="loc_us-gaap_MajorCustomersAxis" xlink:title="Definition : loc_us-gaap_ConcentrationRiskTable to loc_us-gaap_MajorCustomersAxis" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_PfizerIncMember" xlink:label="loc_cldx_PfizerIncMember" xlink:title="PfizerIncMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NameOfMajorCustomerDomain" xlink:to="loc_cldx_PfizerIncMember" xlink:title="Definition : loc_us-gaap_NameOfMajorCustomerDomain to loc_cldx_PfizerIncMember" xlink:type="arc" use="optional" order="8000" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://www.celldextherapeutics.com/role/DisclosurePropertyAndEquipmentNetDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems" xlink:title="PropertyPlantAndEquipmentLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:title="ScheduleOfPropertyPlantAndEquipmentTable" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:title="Definition : loc_us-gaap_PropertyPlantAndEquipmentLineItems to loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:type="arc" use="optional" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:title="PropertyPlantAndEquipmentByTypeAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:title="PropertyPlantAndEquipmentTypeDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:title="Definition : loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis to loc_us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_LaboratoryEquipmentMember" xlink:label="loc_cldx_LaboratoryEquipmentMember" xlink:title="LaboratoryEquipmentMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="loc_cldx_LaboratoryEquipmentMember" xlink:title="Definition : loc_us-gaap_PropertyPlantAndEquipmentTypeDomain to loc_cldx_LaboratoryEquipmentMember" xlink:type="arc" use="optional" order="1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable to loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_ManufacturingEquipmentMember" xlink:label="loc_cldx_ManufacturingEquipmentMember" xlink:title="ManufacturingEquipmentMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="loc_cldx_ManufacturingEquipmentMember" xlink:title="Definition : loc_us-gaap_PropertyPlantAndEquipmentTypeDomain to loc_cldx_ManufacturingEquipmentMember" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross" xlink:title="PropertyPlantAndEquipmentGross" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross" xlink:title="Definition : loc_us-gaap_PropertyPlantAndEquipmentLineItems to loc_us-gaap_PropertyPlantAndEquipmentGross" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FurnitureAndFixturesMember" xlink:label="loc_us-gaap_FurnitureAndFixturesMember" xlink:title="FurnitureAndFixturesMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="loc_us-gaap_FurnitureAndFixturesMember" xlink:title="Definition : loc_us-gaap_PropertyPlantAndEquipmentTypeDomain to loc_us-gaap_FurnitureAndFixturesMember" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:title="AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:title="Definition : loc_us-gaap_PropertyPlantAndEquipmentLineItems to loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LeaseholdImprovementsMember" xlink:label="loc_us-gaap_LeaseholdImprovementsMember" xlink:title="LeaseholdImprovementsMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="loc_us-gaap_LeaseholdImprovementsMember" xlink:title="Definition : loc_us-gaap_PropertyPlantAndEquipmentTypeDomain to loc_us-gaap_LeaseholdImprovementsMember" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet" xlink:title="PropertyPlantAndEquipmentNet" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet" xlink:title="Definition : loc_us-gaap_PropertyPlantAndEquipmentLineItems to loc_us-gaap_PropertyPlantAndEquipmentNet" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConstructionInProgressMember" xlink:label="loc_us-gaap_ConstructionInProgressMember" xlink:title="ConstructionInProgressMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="loc_us-gaap_ConstructionInProgressMember" xlink:title="Definition : loc_us-gaap_PropertyPlantAndEquipmentTypeDomain to loc_us-gaap_ConstructionInProgressMember" xlink:type="arc" use="optional" order="5" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DepreciationDepletionAndAmortization" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization" xlink:title="DepreciationDepletionAndAmortization" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization" xlink:title="Definition : loc_us-gaap_PropertyPlantAndEquipmentLineItems to loc_us-gaap_DepreciationDepletionAndAmortization" xlink:type="arc" use="optional" order="5" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://www.celldextherapeutics.com/role/DisclosureMarketableSecuritiesDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:title="ScheduleOfAvailableForSaleSecuritiesLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesTable" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesTable" xlink:title="ScheduleOfAvailableForSaleSecuritiesTable" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesTable" xlink:title="Definition : loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems to loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesTable" xlink:type="arc" use="optional" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:title="MajorTypesOfDebtAndEquitySecuritiesAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:title="MajorTypesOfDebtAndEquitySecuritiesDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:title="Definition : loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis to loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_USGovernmentAndMunicipalObligationsMember" xlink:label="loc_cldx_USGovernmentAndMunicipalObligationsMember" xlink:title="USGovernmentAndMunicipalObligationsMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:to="loc_cldx_USGovernmentAndMunicipalObligationsMember" xlink:title="Definition : loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain to loc_cldx_USGovernmentAndMunicipalObligationsMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract" xlink:title="AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost" xlink:title="AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost" xlink:title="Definition : loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract to loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGainAbstract" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGainAbstract" xlink:title="AvailableForSaleSecuritiesGrossUnrealizedGainAbstract" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearGrossUnrealizedGain" xlink:label="loc_cldx_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearGrossUnrealizedGain" xlink:title="AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearGrossUnrealizedGain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGainAbstract" xlink:to="loc_cldx_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearGrossUnrealizedGain" xlink:title="Definition : loc_us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGainAbstract to loc_cldx_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearGrossUnrealizedGain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_AvailableForSaleSecuritiesGrossUnrealizedLossesAbstract" xlink:label="loc_cldx_AvailableForSaleSecuritiesGrossUnrealizedLossesAbstract" xlink:title="AvailableForSaleSecuritiesGrossUnrealizedLossesAbstract" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearGrossUnrealizedLosses" xlink:label="loc_cldx_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearGrossUnrealizedLosses" xlink:title="AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearGrossUnrealizedLosses" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_AvailableForSaleSecuritiesGrossUnrealizedLossesAbstract" xlink:to="loc_cldx_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearGrossUnrealizedLosses" xlink:title="Definition : loc_cldx_AvailableForSaleSecuritiesGrossUnrealizedLossesAbstract to loc_cldx_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearGrossUnrealizedLosses" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract" xlink:title="AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue" xlink:title="AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue" xlink:title="Definition : loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract to loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue" xlink:type="arc" use="optional" order="1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesTable" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesTable to loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="MajorTypesOfDebtAndEquitySecuritiesDomain_1" xlink:title="MajorTypesOfDebtAndEquitySecuritiesDomain_1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:to="MajorTypesOfDebtAndEquitySecuritiesDomain_1" xlink:title="Definition : loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis to loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CorporateDebtSecuritiesMember" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember" xlink:title="CorporateDebtSecuritiesMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember" xlink:title="Definition : loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain to loc_us-gaap_CorporateDebtSecuritiesMember" xlink:type="arc" use="optional" order="2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract" xlink:title="Definition : loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems to loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsAmortizedCost" xlink:label="loc_cldx_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsAmortizedCost" xlink:title="AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsAmortizedCost" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract" xlink:to="loc_cldx_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsAmortizedCost" xlink:title="Definition : loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract to loc_cldx_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsAmortizedCost" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsGrossUnrealizedGain" xlink:label="loc_cldx_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsGrossUnrealizedGain" xlink:title="AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsGrossUnrealizedGain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGainAbstract" xlink:to="loc_cldx_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsGrossUnrealizedGain" xlink:title="Definition : loc_us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGainAbstract to loc_cldx_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsGrossUnrealizedGain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsGrossUnrealizedLosses" xlink:label="loc_cldx_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsGrossUnrealizedLosses" xlink:title="AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsGrossUnrealizedLosses" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_AvailableForSaleSecuritiesGrossUnrealizedLossesAbstract" xlink:to="loc_cldx_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsGrossUnrealizedLosses" xlink:title="Definition : loc_cldx_AvailableForSaleSecuritiesGrossUnrealizedLossesAbstract to loc_cldx_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsGrossUnrealizedLosses" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsFairValue" xlink:label="loc_cldx_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsFairValue" xlink:title="AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsFairValue" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract" xlink:to="loc_cldx_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsFairValue" xlink:title="Definition : loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract to loc_cldx_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsFairValue" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCost" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCost" xlink:title="AvailableForSaleSecuritiesDebtMaturitiesAmortizedCost" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCost" xlink:title="Definition : loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract to loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCost" xlink:type="arc" use="optional" order="3" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGainAbstract" xlink:title="Definition : loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems to loc_us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGainAbstract" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInInvestments" xlink:label="loc_cldx_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInInvestments" xlink:title="AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInInvestments" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGainAbstract" xlink:to="loc_cldx_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInInvestments" xlink:title="Definition : loc_us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGainAbstract to loc_cldx_AvailableForSaleSecuritiesGrossUnrealizedGainAccumulatedInInvestments" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments" xlink:label="loc_cldx_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments" xlink:title="AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_AvailableForSaleSecuritiesGrossUnrealizedLossesAbstract" xlink:to="loc_cldx_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments" xlink:title="Definition : loc_cldx_AvailableForSaleSecuritiesGrossUnrealizedLossesAbstract to loc_cldx_AvailableForSaleSecuritiesGrossUnrealizedLossAccumulatedInInvestments" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent" xlink:title="AvailableForSaleSecuritiesDebtSecuritiesCurrent" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent" xlink:title="Definition : loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract to loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent" xlink:type="arc" use="optional" order="3" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="loc_cldx_AvailableForSaleSecuritiesGrossUnrealizedLossesAbstract" xlink:title="Definition : loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems to loc_cldx_AvailableForSaleSecuritiesGrossUnrealizedLossesAbstract" xlink:type="arc" use="optional" order="4" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract" xlink:title="Definition : loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems to loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract" xlink:type="arc" use="optional" order="5" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_AvailableForSaleSecuritiesConsideredToBeOtherThanTemporarilyImpaired" xlink:label="loc_cldx_AvailableForSaleSecuritiesConsideredToBeOtherThanTemporarilyImpaired" xlink:title="AvailableForSaleSecuritiesConsideredToBeOtherThanTemporarilyImpaired" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:to="loc_cldx_AvailableForSaleSecuritiesConsideredToBeOtherThanTemporarilyImpaired" xlink:title="Definition : loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems to loc_cldx_AvailableForSaleSecuritiesConsideredToBeOtherThanTemporarilyImpaired" xlink:type="arc" use="optional" order="6" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://www.celldextherapeutics.com/role/DisclosureOtherLongTermLiabilitiesDetails3">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentLineItems" xlink:label="loc_us-gaap_DebtInstrumentLineItems" xlink:title="DebtInstrumentLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentTable" xlink:label="loc_us-gaap_DebtInstrumentTable" xlink:title="DebtInstrumentTable" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems" xlink:to="loc_us-gaap_DebtInstrumentTable" xlink:title="Definition : loc_us-gaap_DebtInstrumentLineItems to loc_us-gaap_DebtInstrumentTable" xlink:type="arc" use="optional" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongtermDebtTypeAxis" xlink:label="loc_us-gaap_LongtermDebtTypeAxis" xlink:title="LongtermDebtTypeAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaap_LongtermDebtTypeDomain" xlink:title="LongtermDebtTypeDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis" xlink:to="loc_us-gaap_LongtermDebtTypeDomain" xlink:title="Definition : loc_us-gaap_LongtermDebtTypeAxis to loc_us-gaap_LongtermDebtTypeDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LoansPayableMember" xlink:label="loc_us-gaap_LoansPayableMember" xlink:title="LoansPayableMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain" xlink:to="loc_us-gaap_LoansPayableMember" xlink:title="Definition : loc_us-gaap_LongtermDebtTypeDomain to loc_us-gaap_LoansPayableMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtByMaturityAbstract" xlink:label="loc_us-gaap_LongTermDebtByMaturityAbstract" xlink:title="LongTermDebtByMaturityAbstract" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths" xlink:title="LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths" xlink:title="Definition : loc_us-gaap_LongTermDebtByMaturityAbstract to loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths" xlink:type="arc" use="optional" order="1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable" xlink:to="loc_us-gaap_LongtermDebtTypeAxis" xlink:title="Definition : loc_us-gaap_DebtInstrumentTable to loc_us-gaap_LongtermDebtTypeAxis" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo" xlink:title="LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo" xlink:title="Definition : loc_us-gaap_LongTermDebtByMaturityAbstract to loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_DebtInstrumentAmortizationPeriod" xlink:label="loc_cldx_DebtInstrumentAmortizationPeriod" xlink:title="DebtInstrumentAmortizationPeriod" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems" xlink:to="loc_cldx_DebtInstrumentAmortizationPeriod" xlink:title="Definition : loc_us-gaap_DebtInstrumentLineItems to loc_cldx_DebtInstrumentAmortizationPeriod" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree" xlink:title="LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree" xlink:title="Definition : loc_us-gaap_LongTermDebtByMaturityAbstract to loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentInterestRateAtPeriodEnd" xlink:label="loc_us-gaap_DebtInstrumentInterestRateAtPeriodEnd" xlink:title="DebtInstrumentInterestRateAtPeriodEnd" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems" xlink:to="loc_us-gaap_DebtInstrumentInterestRateAtPeriodEnd" xlink:title="Definition : loc_us-gaap_DebtInstrumentLineItems to loc_us-gaap_DebtInstrumentInterestRateAtPeriodEnd" xlink:type="arc" use="optional" order="3" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems" xlink:to="loc_us-gaap_LongTermDebtByMaturityAbstract" xlink:title="Definition : loc_us-gaap_DebtInstrumentLineItems to loc_us-gaap_LongTermDebtByMaturityAbstract" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour" xlink:title="LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour" xlink:title="Definition : loc_us-gaap_LongTermDebtByMaturityAbstract to loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive" xlink:title="LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive" xlink:title="Definition : loc_us-gaap_LongTermDebtByMaturityAbstract to loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive" xlink:type="arc" use="optional" order="5" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive" xlink:title="LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtByMaturityAbstract" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive" xlink:title="Definition : loc_us-gaap_LongTermDebtByMaturityAbstract to loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive" xlink:type="arc" use="optional" order="6" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://www.celldextherapeutics.com/role/DisclosureFairValueMeasurementsDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:title="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:title="FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:title="Definition : loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:type="arc" use="optional" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis" xlink:title="FairValueByMeasurementFrequencyAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain" xlink:title="FairValueMeasurementFrequencyDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain" xlink:title="Definition : loc_us-gaap_FairValueByMeasurementFrequencyAxis to loc_us-gaap_FairValueMeasurementFrequencyDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:title="FairValueByFairValueHierarchyLevelAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:title="FairValueMeasurementsFairValueHierarchyDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:title="Definition : loc_us-gaap_FairValueByFairValueHierarchyLevelAxis to loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember" xlink:title="FairValueMeasurementsRecurringMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember" xlink:title="Definition : loc_us-gaap_FairValueMeasurementFrequencyDomain to loc_us-gaap_FairValueMeasurementsRecurringMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:title="EstimateOfFairValueFairValueDisclosureMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:title="Definition : loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain to loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:type="arc" use="optional" order="1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis" xlink:title="Definition : loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable to loc_us-gaap_FairValueByMeasurementFrequencyAxis" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="FairValueMeasurementFrequencyDomain_1" xlink:title="FairValueMeasurementFrequencyDomain_1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="FairValueMeasurementFrequencyDomain_1" xlink:title="Definition : loc_us-gaap_FairValueByMeasurementFrequencyAxis to loc_us-gaap_FairValueMeasurementFrequencyDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="FairValueMeasurementsFairValueHierarchyDomain_2" xlink:title="FairValueMeasurementsFairValueHierarchyDomain_2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="FairValueMeasurementsFairValueHierarchyDomain_2" xlink:title="Definition : loc_us-gaap_FairValueByFairValueHierarchyLevelAxis to loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="loc_us-gaap_FairValueInputsLevel1Member" xlink:title="FairValueInputsLevel1Member" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="loc_us-gaap_FairValueInputsLevel1Member" xlink:title="Definition : loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain to loc_us-gaap_FairValueInputsLevel1Member" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure" xlink:title="CashAndCashEquivalentsFairValueDisclosure" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure" xlink:title="Definition : loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure" xlink:type="arc" use="optional" order="2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:title="Definition : loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable to loc_us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="loc_us-gaap_FairValueInputsLevel2Member" xlink:title="FairValueInputsLevel2Member" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="loc_us-gaap_FairValueInputsLevel2Member" xlink:title="Definition : loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain to loc_us-gaap_FairValueInputsLevel2Member" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AvailableForSaleSecurities" xlink:label="loc_us-gaap_AvailableForSaleSecurities" xlink:title="AvailableForSaleSecurities" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="loc_us-gaap_AvailableForSaleSecurities" xlink:title="Definition : loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to loc_us-gaap_AvailableForSaleSecurities" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AssetsFairValueDisclosure" xlink:label="loc_us-gaap_AssetsFairValueDisclosure" xlink:title="AssetsFairValueDisclosure" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="loc_us-gaap_AssetsFairValueDisclosure" xlink:title="Definition : loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to loc_us-gaap_AssetsFairValueDisclosure" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_FairValueAssetsAmountTransfersBetweenMeasurementLevels" xlink:label="loc_cldx_FairValueAssetsAmountTransfersBetweenMeasurementLevels" xlink:title="FairValueAssetsAmountTransfersBetweenMeasurementLevels" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="loc_cldx_FairValueAssetsAmountTransfersBetweenMeasurementLevels" xlink:title="Definition : loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to loc_cldx_FairValueAssetsAmountTransfersBetweenMeasurementLevels" xlink:type="arc" use="optional" order="5" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_FairValueLiabilitiesAmountTransfersBetweenMeasurementLevels" xlink:label="loc_cldx_FairValueLiabilitiesAmountTransfersBetweenMeasurementLevels" xlink:title="FairValueLiabilitiesAmountTransfersBetweenMeasurementLevels" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="loc_cldx_FairValueLiabilitiesAmountTransfersBetweenMeasurementLevels" xlink:title="Definition : loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems to loc_cldx_FairValueLiabilitiesAmountTransfersBetweenMeasurementLevels" xlink:type="arc" use="optional" order="6" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://www.celldextherapeutics.com/role/DisclosureComprehensiveLossDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems" xlink:title="AccumulatedOtherComprehensiveIncomeLossLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable" xlink:title="AccumulatedOtherComprehensiveIncomeLossTable" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable" xlink:title="Definition : loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems to loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable" xlink:type="arc" use="optional" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis" xlink:title="StatementEquityComponentsAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis" xlink:to="loc_us-gaap_EquityComponentDomain" xlink:title="Definition : loc_us-gaap_StatementEquityComponentsAxis to loc_us-gaap_EquityComponentDomain" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember" xlink:label="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember" xlink:title="AccumulatedNetUnrealizedInvestmentGainLossMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain" xlink:to="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember" xlink:title="Definition : loc_us-gaap_EquityComponentDomain to loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_AccumulatedOtherComprehensiveIncomeLossRollForward" xlink:label="loc_cldx_AccumulatedOtherComprehensiveIncomeLossRollForward" xlink:title="AccumulatedOtherComprehensiveIncomeLossRollForward" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:title="AccumulatedOtherComprehensiveIncomeLossNetOfTax" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_AccumulatedOtherComprehensiveIncomeLossRollForward" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:title="Definition : loc_cldx_AccumulatedOtherComprehensiveIncomeLossRollForward to loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:type="arc" use="optional" order="1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable" xlink:to="loc_us-gaap_StatementEquityComponentsAxis" xlink:title="Definition : loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable to loc_us-gaap_StatementEquityComponentsAxis" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain_1" xlink:title="EquityComponentDomain_1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis" xlink:to="EquityComponentDomain_1" xlink:title="Definition : loc_us-gaap_StatementEquityComponentsAxis to loc_us-gaap_EquityComponentDomain" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccumulatedTranslationAdjustmentMember" xlink:label="loc_us-gaap_AccumulatedTranslationAdjustmentMember" xlink:title="AccumulatedTranslationAdjustmentMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain" xlink:to="loc_us-gaap_AccumulatedTranslationAdjustmentMember" xlink:title="Definition : loc_us-gaap_EquityComponentDomain to loc_us-gaap_AccumulatedTranslationAdjustmentMember" xlink:type="arc" use="optional" order="2" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_cldx_AccumulatedOtherComprehensiveIncomeLossRollForward" xlink:title="Definition : loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems to loc_cldx_AccumulatedOtherComprehensiveIncomeLossRollForward" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax" xlink:title="OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_AccumulatedOtherComprehensiveIncomeLossRollForward" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax" xlink:title="Definition : loc_cldx_AccumulatedOtherComprehensiveIncomeLossRollForward to loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax" xlink:title="OtherComprehensiveIncomeLossNetOfTax" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cldx_AccumulatedOtherComprehensiveIncomeLossRollForward" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax" xlink:title="Definition : loc_cldx_AccumulatedOtherComprehensiveIncomeLossRollForward to loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax" xlink:type="arc" use="optional" order="3" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://www.celldextherapeutics.com/role/DisclosureCommitmentsAndContingenciesDetails2">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OperatingLeasedAssetsLineItems" xlink:label="loc_us-gaap_OperatingLeasedAssetsLineItems" xlink:title="OperatingLeasedAssetsLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfOperatingLeasedAssetsTable" xlink:label="loc_us-gaap_ScheduleOfOperatingLeasedAssetsTable" xlink:title="ScheduleOfOperatingLeasedAssetsTable" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems" xlink:to="loc_us-gaap_ScheduleOfOperatingLeasedAssetsTable" xlink:title="Definition : loc_us-gaap_OperatingLeasedAssetsLineItems to loc_us-gaap_ScheduleOfOperatingLeasedAssetsTable" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="loc_us-gaap_SubsequentEventTypeAxis" xlink:title="SubsequentEventTypeAxis" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfOperatingLeasedAssetsTable" xlink:to="loc_us-gaap_SubsequentEventTypeAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfOperatingLeasedAssetsTable to loc_us-gaap_SubsequentEventTypeAxis" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AreaOfRealEstateProperty" xlink:label="loc_us-gaap_AreaOfRealEstateProperty" xlink:title="AreaOfRealEstateProperty" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems" xlink:to="loc_us-gaap_AreaOfRealEstateProperty" xlink:title="Definition : loc_us-gaap_OperatingLeasedAssetsLineItems to loc_us-gaap_AreaOfRealEstateProperty" xlink:type="arc" use="optional" order="2" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_OperatingLeasesTermOfLease" xlink:label="loc_cldx_OperatingLeasesTermOfLease" xlink:title="OperatingLeasesTermOfLease" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems" xlink:to="loc_cldx_OperatingLeasesTermOfLease" xlink:title="Definition : loc_us-gaap_OperatingLeasedAssetsLineItems to loc_cldx_OperatingLeasesTermOfLease" xlink:type="arc" use="optional" order="3" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_OperatingLeasesCommencementPeriodOfRentalObligations" xlink:label="loc_cldx_OperatingLeasesCommencementPeriodOfRentalObligations" xlink:title="OperatingLeasesCommencementPeriodOfRentalObligations" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems" xlink:to="loc_cldx_OperatingLeasesCommencementPeriodOfRentalObligations" xlink:title="Definition : loc_us-gaap_OperatingLeasedAssetsLineItems to loc_cldx_OperatingLeasesCommencementPeriodOfRentalObligations" xlink:type="arc" use="optional" order="4" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_OperatingLeasesNumberOfRenewalOptions" xlink:label="loc_cldx_OperatingLeasesNumberOfRenewalOptions" xlink:title="OperatingLeasesNumberOfRenewalOptions" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems" xlink:to="loc_cldx_OperatingLeasesNumberOfRenewalOptions" xlink:title="Definition : loc_us-gaap_OperatingLeasedAssetsLineItems to loc_cldx_OperatingLeasesNumberOfRenewalOptions" xlink:type="arc" use="optional" order="7" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_OperatingLeasesPeriodOfRenewalOptions" xlink:label="loc_cldx_OperatingLeasesPeriodOfRenewalOptions" xlink:title="OperatingLeasesPeriodOfRenewalOptions" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems" xlink:to="loc_cldx_OperatingLeasesPeriodOfRenewalOptions" xlink:title="Definition : loc_us-gaap_OperatingLeasedAssetsLineItems to loc_cldx_OperatingLeasesPeriodOfRenewalOptions" xlink:type="arc" use="optional" order="8" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain" xlink:title="SubsequentEventTypeDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis" xlink:to="loc_us-gaap_SubsequentEventTypeDomain" xlink:title="Definition : loc_us-gaap_SubsequentEventTypeAxis to loc_us-gaap_SubsequentEventTypeDomain" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SubsequentEventMember" xlink:label="loc_us-gaap_SubsequentEventMember" xlink:title="SubsequentEventMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain" xlink:to="loc_us-gaap_SubsequentEventMember" xlink:title="Definition : loc_us-gaap_SubsequentEventTypeDomain to loc_us-gaap_SubsequentEventMember" xlink:type="arc" use="optional" order="8000" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://www.celldextherapeutics.com/role/DisclosureRockefellerUniversityDetails">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:label="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:title="CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:label="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:title="Definition : loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:type="arc" use="optional" order="1" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="loc_us-gaap_TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:title="Definition : loc_us-gaap_TypeOfArrangementAxis to loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_ProductDevelopmentAndLicensingAgreementMember" xlink:label="loc_cldx_ProductDevelopmentAndLicensingAgreementMember" xlink:title="ProductDevelopmentAndLicensingAgreementMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:to="loc_cldx_ProductDevelopmentAndLicensingAgreementMember" xlink:title="Definition : loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember to loc_cldx_ProductDevelopmentAndLicensingAgreementMember" xlink:type="arc" use="optional" order="1" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable" xlink:to="loc_us-gaap_TypeOfArrangementAxis" xlink:title="Definition : loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable to loc_us-gaap_TypeOfArrangementAxis" xlink:type="arc" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="cldx-20131231.xsd#cldx_CollaborativeArrangementNumberOfAntiHIVAntibodies" xlink:label="loc_cldx_CollaborativeArrangementNumberOfAntiHIVAntibodies" xlink:title="CollaborativeArrangementNumberOfAntiHIVAntibodies" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:to="loc_cldx_CollaborativeArrangementNumberOfAntiHIVAntibodies" xlink:title="Definition : loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems to loc_cldx_CollaborativeArrangementNumberOfAntiHIVAntibodies" xlink:type="arc" use="optional" order="2" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://www.celldextherapeutics.com/role/StatementOfStockholdersEquity">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems" xlink:title="StatementLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable" xlink:title="StatementTable" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems" xlink:to="loc_us-gaap_StatementTable" xlink:title="Definition : loc_us-gaap_StatementLineItems to loc_us-gaap_StatementTable" xlink:type="arc" use="optional" order="10" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis" xlink:title="StatementEquityComponentsAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis" xlink:to="loc_us-gaap_EquityComponentDomain" xlink:title="Definition : loc_us-gaap_StatementEquityComponentsAxis to loc_us-gaap_EquityComponentDomain" xlink:type="arc" use="optional" order="10" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:title="StockIssuedDuringPeriodValueNewIssues" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:title="StockIssuedDuringPeriodSharesNewIssues" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:title="Definition : loc_us-gaap_StockIssuedDuringPeriodValueNewIssues to loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:type="arc" use="optional" order="10" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember" xlink:title="CommonStockMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain" xlink:to="loc_us-gaap_CommonStockMember" xlink:title="Definition : loc_us-gaap_EquityComponentDomain to loc_us-gaap_CommonStockMember" xlink:type="arc" use="optional" order="10" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:title="IncreaseDecreaseInStockholdersEquityRollForward" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="loc_us-gaap_StockholdersEquity" xlink:title="StockholdersEquity" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="loc_us-gaap_StockholdersEquity" xlink:title="Definition : loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward to loc_us-gaap_StockholdersEquity" xlink:type="arc" use="optional" order="10" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" xlink:title="StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" xlink:title="StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" xlink:title="Definition : loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan to loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" xlink:type="arc" use="optional" order="10" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueOther" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueOther" xlink:title="StockIssuedDuringPeriodValueOther" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesOther" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesOther" xlink:title="StockIssuedDuringPeriodSharesOther" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockIssuedDuringPeriodValueOther" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesOther" xlink:title="Definition : loc_us-gaap_StockIssuedDuringPeriodValueOther to loc_us-gaap_StockIssuedDuringPeriodSharesOther" xlink:type="arc" use="optional" order="10" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockholdersEquityPeriodIncreaseDecrease" xlink:label="loc_us-gaap_StockholdersEquityPeriodIncreaseDecrease" xlink:title="StockholdersEquityPeriodIncreaseDecrease" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesPeriodIncreaseDecrease" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesPeriodIncreaseDecrease" xlink:title="StockIssuedDuringPeriodSharesPeriodIncreaseDecrease" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityPeriodIncreaseDecrease" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesPeriodIncreaseDecrease" xlink:title="Definition : loc_us-gaap_StockholdersEquityPeriodIncreaseDecrease to loc_us-gaap_StockIssuedDuringPeriodSharesPeriodIncreaseDecrease" xlink:type="arc" use="optional" order="10" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable" xlink:to="loc_us-gaap_StatementEquityComponentsAxis" xlink:title="Definition : loc_us-gaap_StatementTable to loc_us-gaap_StatementEquityComponentsAxis" xlink:type="arc" use="optional" order="10" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember" xlink:title="AdditionalPaidInCapitalMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember" xlink:title="Definition : loc_us-gaap_EquityComponentDomain to loc_us-gaap_AdditionalPaidInCapitalMember" xlink:type="arc" use="optional" order="20" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:title="Definition : loc_us-gaap_StatementLineItems to loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:type="arc" use="optional" order="20" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStockSharesIssued" xlink:label="loc_us-gaap_CommonStockSharesIssued" xlink:title="CommonStockSharesIssued" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="loc_us-gaap_CommonStockSharesIssued" xlink:title="Definition : loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward to loc_us-gaap_CommonStockSharesIssued" xlink:type="arc" use="optional" order="20" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:title="AccumulatedOtherComprehensiveIncomeMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:title="Definition : loc_us-gaap_EquityComponentDomain to loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:type="arc" use="optional" order="30" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" xlink:title="Definition : loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward to loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" xlink:type="arc" use="optional" order="30" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RetainedEarningsMember" xlink:label="loc_us-gaap_RetainedEarningsMember" xlink:title="RetainedEarningsMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain" xlink:to="loc_us-gaap_RetainedEarningsMember" xlink:title="Definition : loc_us-gaap_EquityComponentDomain to loc_us-gaap_RetainedEarningsMember" xlink:type="arc" use="optional" order="40" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueOther" xlink:title="Definition : loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward to loc_us-gaap_StockIssuedDuringPeriodValueOther" xlink:type="arc" use="optional" order="40" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:title="Definition : loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward to loc_us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:type="arc" use="optional" order="50" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:title="AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:title="Definition : loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward to loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:type="arc" use="optional" order="60" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent" xlink:label="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent" xlink:title="OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent" xlink:title="Definition : loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward to loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent" xlink:type="arc" use="optional" order="70" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" xlink:title="OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" xlink:title="Definition : loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward to loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" xlink:type="arc" use="optional" order="80" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:title="NetIncomeLossAvailableToCommonStockholdersBasic" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:title="Definition : loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward to loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:type="arc" use="optional" order="90" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="loc_us-gaap_StockholdersEquityPeriodIncreaseDecrease" xlink:title="Definition : loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward to loc_us-gaap_StockholdersEquityPeriodIncreaseDecrease" xlink:type="arc" use="optional" order="100" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueAcquisitions" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions" xlink:title="StockIssuedDuringPeriodValueAcquisitions" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions" xlink:title="Definition : loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward to loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesAcquisitions" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions" xlink:title="StockIssuedDuringPeriodSharesAcquisitions" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions" xlink:title="Definition : loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions to loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions" xlink:type="arc" use="optional" order="8000" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://www.celldextherapeutics.com/role/DisclosureOtherLongTermLiabilitiesTables">
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentLineItems" xlink:label="loc_us-gaap_DebtInstrumentLineItems" xlink:title="DebtInstrumentLineItems" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentTable" xlink:label="loc_us-gaap_DebtInstrumentTable" xlink:title="DebtInstrumentTable" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems" xlink:to="loc_us-gaap_DebtInstrumentTable" xlink:title="Definition : loc_us-gaap_DebtInstrumentLineItems to loc_us-gaap_DebtInstrumentTable" xlink:type="arc" use="optional" order="8000" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongtermDebtTypeAxis" xlink:label="loc_us-gaap_LongtermDebtTypeAxis" xlink:title="LongtermDebtTypeAxis" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaap_LongtermDebtTypeDomain" xlink:title="LongtermDebtTypeDomain" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis" xlink:to="loc_us-gaap_LongtermDebtTypeDomain" xlink:title="Definition : loc_us-gaap_LongtermDebtTypeAxis to loc_us-gaap_LongtermDebtTypeDomain" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LoansPayableMember" xlink:label="loc_us-gaap_LoansPayableMember" xlink:title="LoansPayableMember" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain" xlink:to="loc_us-gaap_LoansPayableMember" xlink:title="Definition : loc_us-gaap_LongtermDebtTypeDomain to loc_us-gaap_LoansPayableMember" xlink:type="arc" use="optional" order="8000" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable" xlink:to="loc_us-gaap_LongtermDebtTypeAxis" xlink:title="Definition : loc_us-gaap_DebtInstrumentTable to loc_us-gaap_LongtermDebtTypeAxis" xlink:type="arc" use="optional" order="8000" />
    <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfMaturitiesOfLongTermDebtTableTextBlock" xlink:label="loc_us-gaap_ScheduleOfMaturitiesOfLongTermDebtTableTextBlock" xlink:title="ScheduleOfMaturitiesOfLongTermDebtTableTextBlock" />
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems" xlink:to="loc_us-gaap_ScheduleOfMaturitiesOfLongTermDebtTableTextBlock" xlink:title="Definition : loc_us-gaap_DebtInstrumentLineItems to loc_us-gaap_ScheduleOfMaturitiesOfLongTermDebtTableTextBlock" xlink:type="arc" use="optional" order="8001" />
  </link:definitionLink>
</link:linkbase>
