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<!--Created on: 8/6/2018 7:48:12 AM-->
<!--Modified on: 8/6/2018 7:48:12 AM-->
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  <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" />
  <element id="cldx_CommonStockSharesAvailableForSale" name="CommonStockSharesAvailableForSale" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="credit" 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_GlembatumumabVedotinMember" name="GlembatumumabVedotinMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" 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_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_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_NewlyAdoptedAccountingPronouncementsPolicyPolicyTextBlock" name="NewlyAdoptedAccountingPronouncementsPolicyPolicyTextBlock" nillable="true" type="nonnum:textBlockItemType" substitutionGroup="xbrli:item" 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_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_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_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassTable" name="FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassTable" nillable="true" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" abstract="true" xbrli:periodType="duration" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassLineItems" name="FiniteLivedAndIndefiniteLivedIntangibleAssetsByMajorClassLineItems" nillable="true" type="xbrli:stringItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_AdditionalSaleOfCommonStockMaximumAmount" name="AdditionalSaleOfCommonStockMaximumAmount" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" 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_TaxCutsAndJobsActOf2017IncomeTaxExpenseBenefit" name="TaxCutsAndJobsActOf2017IncomeTaxExpenseBenefit" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" xbrli:balance="debit" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_EmployeeConsultantAndNonEmployeeDirectorStockOptionMember" name="EmployeeConsultantAndNonEmployeeDirectorStockOptionMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_ProductDevelopmentAndLicensingAgreementsMember" name="ProductDevelopmentAndLicensingAgreementsMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_ContractsAndGrantsMember" name="ContractsAndGrantsMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_InternationalAidsVaccineInitiativeAndFrontierBiotechnologiesIncMember" name="InternationalAidsVaccineInitiativeAndFrontierBiotechnologiesIncMember" nillable="true" type="nonnum:domainItemType" substitutionGroup="xbrli:item" abstract="true" xbrli:periodType="duration" xmlns="http://www.w3.org/2001/XMLSchema" />
  <element id="cldx_ReportingUnitCarryingAmountInExcessOfFairValueAmount" name="ReportingUnitCarryingAmountInExcessOfFairValueAmount" nillable="true" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" xbrli:balance="debit" xmlns="http://www.w3.org/2001/XMLSchema" />
</xsd:schema>
