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  <xsd:import namespace="http://fasb.org/us-roles/2024" schemaLocation="https://xbrl.fasb.org/us-gaap/2024/elts/us-roles-2024.xsd" />
  <xsd:import namespace="http://www.xbrl.org/2003/instance" schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd" />
  <xsd:import namespace="http://xbrl.org/2005/xbrldt" schemaLocation="http://www.xbrl.org/2005/xbrldt-2005.xsd" />
  <xsd:import namespace="http://fasb.org/us-gaap/2024" schemaLocation="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd" />
  <xsd:import namespace="http://fasb.org/srt/2024" schemaLocation="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd" />
  <xsd:import namespace="http://xbrl.sec.gov/ecd-sub/2024" schemaLocation="https://xbrl.sec.gov/ecd/2024/ecd-sub-2024.xsd" />
  <xsd:element id="cldx_DeferredIncomeFromSaleOfTaxBenefits" name="DeferredIncomeFromSaleOfTaxBenefits" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="credit" />
  <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 id="cldx_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsAmortizedCost" name="AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsAmortizedCost" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="debit" />
  <xsd:element id="cldx_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearGrossUnrealizedGain" name="AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearGrossUnrealizedGain" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="credit" />
  <xsd:element id="cldx_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsGrossUnrealizedGain" name="AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsGrossUnrealizedGain" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="credit" />
  <xsd:element name="AvailableForSaleSecuritiesGrossUnrealizedLossesAbstract" id="cldx_AvailableForSaleSecuritiesGrossUnrealizedLossesAbstract" type="xbrli:stringItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration" />
  <xsd:element id="cldx_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearGrossUnrealizedLosses" name="AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearGrossUnrealizedLosses" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="debit" />
  <xsd:element id="cldx_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsGrossUnrealizedLosses" name="AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsGrossUnrealizedLosses" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="debit" />
  <xsd:element id="cldx_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsFairValue" name="AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughThreeYearsFairValue" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="debit" />
  <xsd:element id="cldx_ProceedsFromSaleOfOperatingLossesAndTaxCredits" name="ProceedsFromSaleOfOperatingLossesAndTaxCredits" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="debit" />
  <xsd:element id="cldx_UnderwrittenPublicOfferingMember" name="UnderwrittenPublicOfferingMember" nillable="true" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <xsd:element id="cldx_KolltanPharmaceuticalsMember" name="KolltanPharmaceuticalsMember" nillable="true" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <xsd:element id="cldx_ContingentMilestoneMember" name="ContingentMilestoneMember" nillable="true" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" />
  <xsd:element name="BusinessCombinationContingentConsiderationSettlementAgreementAmountPaid" id="cldx_BusinessCombinationContingentConsiderationSettlementAgreementAmountPaid" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" xbrli:balance="credit" />
  <xsd:element name="BusinessCombinationContingentConsiderationSettlementAgreementAmountPayable" id="cldx_BusinessCombinationContingentConsiderationSettlementAgreementAmountPayable" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" xbrli:balance="credit" />
  <xsd:element name="IncomeTaxesTable" id="cldx_IncomeTaxesTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="IncomeTaxesLineItem" id="cldx_IncomeTaxesLineItem" type="xbrli:stringItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="NewJerseyEconomicDevelopmentAuthorityMember" id="cldx_NewJerseyEconomicDevelopmentAuthorityMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="RockefellerUniversityMember" id="cldx_RockefellerUniversityMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="CashOutflowForMilestonePaymentsMadeUponSuccessfulCompletionOfClinicalTrial" id="cldx_CashOutflowForMilestonePaymentsMadeUponSuccessfulCompletionOfClinicalTrial" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="false" xbrli:balance="credit" />
  <xsd:element name="OtherNonCurrentLiabilitiesTable" id="cldx_OtherNonCurrentLiabilitiesTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="OtherNonCurrentLiabilitiesLineItems" id="cldx_OtherNonCurrentLiabilitiesLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
  <xsd:element name="CommonStockAmountReservedForFutureIssuance" id="cldx_CommonStockAmountReservedForFutureIssuance" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="instant" abstract="false" xbrli:balance="credit" />
  <xsd:element name="EquityOfferingSalesAgreementMember" id="cldx_EquityOfferingSalesAgreementMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" nillable="true" xbrli:periodType="duration" abstract="true" />
</xsd:schema>
