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  <xsd:element name="DocumentAndEntityInformationAbstract" id="cldx_DocumentAndEntityInformationAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <element id="cldx_RevenueFromProductDevelopmentAndLicensingAgreements" name="RevenueFromProductDevelopmentAndLicensingAgreements" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="credit" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_RevenueFromContractsAndGrants" name="RevenueFromContractsAndGrants" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="credit" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_SignificantRevenueArrangementsDisclosureAbstract" name="SignificantRevenueArrangementsDisclosureAbstract" nillable="true" type="xbrli:stringItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_SignificantRevenueArrangementsDisclosureTextBlock" name="SignificantRevenueArrangementsDisclosureTextBlock" nillable="true" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xmlns="http://www.w3.org/2001/XMLSchema" />
  <xsd:element name="FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassTable" id="cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassLineItems" id="cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="DeferredIncomeFromSaleOfTaxBenefits" id="cldx_DeferredIncomeFromSaleOfTaxBenefits" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element name="PeriodForWhichBaseOfOperationsMustBeMaintained" id="cldx_PeriodForWhichBaseOfOperationsMustBeMaintained" type="xbrli:durationItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract" id="cldx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="StockholdersEquityTable" id="cldx_StockholdersEquityTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="StockholdersEquityLineItems" id="cldx_StockholdersEquityLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element name="AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsAmortizedCost" id="cldx_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsAmortizedCost" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:balance="debit" xbrli:periodType="instant" />
  <element id="cldx_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearGrossUnrealizedGain" name="AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearGrossUnrealizedGain" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="credit" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsGrossUnrealizedGain" name="AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsGrossUnrealizedGain" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="credit" xmlns="http://www.w3.org/2001/XMLSchema" />
  <xsd:element name="AvailableForSaleSecuritiesGrossUnrealizedLossesAbstract" id="cldx_AvailableForSaleSecuritiesGrossUnrealizedLossesAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <element id="cldx_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearGrossUnrealizedLosses" name="AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearGrossUnrealizedLosses" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="debit" xmlns="http://www.w3.org/2001/XMLSchema" />
  <xsd:element name="AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsFairValue" id="cldx_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsFairValue" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element name="EmployeeConsultantAndNonEmployeeDirectorStockOptionMember" id="cldx_EmployeeConsultantAndNonEmployeeDirectorStockOptionMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <element id="cldx_CollaborativeArrangementAgreementTerm" name="CollaborativeArrangementAgreementTerm" nillable="true" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_DeferredTaxAssetsInProcessResearchAndDevelopmentIntangibleAssets" name="DeferredTaxAssetsInProcessResearchAndDevelopmentIntangibleAssets" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="credit" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_AccumulatedOtherComprehensiveIncomeLossRollForward" name="AccumulatedOtherComprehensiveIncomeLossRollForward" nillable="true" type="xbrli:stringItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_ReimbursementOfExternalCostsIncurredPercentage" name="ReimbursementOfExternalCostsIncurredPercentage" nillable="true" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_ScheduleOfOtherLongTermLiabilitiesTableTextBlock" name="ScheduleOfOtherLongTermLiabilitiesTableTextBlock" nillable="true" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_BristolMeyersSquibbCompanyMember" name="BristolMeyersSquibbCompanyMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_StockIssuedAuthorizedAmount" name="StockIssuedAuthorizedAmount" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="credit" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_StockIssuedRemainingAuthorizedAmount" name="StockIssuedRemainingAuthorizedAmount" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="credit" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_KolltanPharmaceuticalsMember" name="KolltanPharmaceuticalsMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_BusinessAcquisitionStockIssuedInLieuOfSeverance" name="BusinessAcquisitionStockIssuedInLieuOfSeverance" nillable="true" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherCurrentAndLongTermAssets" name="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherCurrentAndLongTermAssets" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="debit" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherLiabilities" name="BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherLiabilities" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="credit" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_BusinessAcquisitionProFormaEarningsPerShareBasicAndDiluted" name="BusinessAcquisitionProFormaEarningsPerShareBasicAndDiluted" nillable="true" type="num:perShareItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_BusinessAcquisitionStockIssuableInLieuOfSeverance" name="BusinessAcquisitionStockIssuableInLieuOfSeverance" nillable="true" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_SharesIssuedToFormerKolltanExecutiveForSettlementOfSeverance" name="SharesIssuedToFormerKolltanExecutiveForSettlementOfSeverance" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="credit" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_AccountingStandardsUpdateMember" name="AccountingStandardsUpdateMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_GrossDeferredTaxAssetsAndCorrespondingValuation" name="GrossDeferredTaxAssetsAndCorrespondingValuation" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="debit" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_BusinessAcquisitionRemainingStockObligation" name="BusinessAcquisitionRemainingStockObligation" nillable="true" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_NewlyAdoptedAccountingPronouncementsPolicyPolicyTextBlock" name="NewlyAdoptedAccountingPronouncementsPolicyPolicyTextBlock" nillable="true" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_InternationalAidsVaccineInitiativeMember" name="InternationalAidsVaccineInitiativeMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_ProceedsFromSaleOfOperatingLossesAndTaxCredits" name="ProceedsFromSaleOfOperatingLossesAndTaxCredits" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="debit" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_NeedhamMassachusettsExpansionSpaceMember" name="NeedhamMassachusettsExpansionSpaceMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_ControlledEquityOfferingSalesAgreementMember" name="ControlledEquityOfferingSalesAgreementMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_ContingentMilestoneMember" name="ContingentMilestoneMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_LongTermSeveranceAccrual" name="LongTermSeveranceAccrual" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="credit" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_RockefellerMember" name="RockefellerMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_FrontierBiotechnologiesIncMember" name="FrontierBiotechnologiesIncMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xmlns="http://www.w3.org/2001/XMLSchema" />
</xsd:schema>
