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	<link:roleType roleURI="http://celsion.com/role/Earn-outMilestoneLiability-ScheduleOfRiskAdjustmentAssessmentDetails" id="Earn-outMilestoneLiability-ScheduleOfRiskAdjustmentAssessmentDetails">
	  <link:definition>00000054 - Disclosure - Earn-out Milestone Liability - Schedule of Risk Adjustment Assessment (Details)</link:definition>
	  <link:usedOn>link:presentationLink</link:usedOn>
	  <link:usedOn>link:calculationLink</link:usedOn>
	  <link:usedOn>link:definitionLink</link:usedOn>
	</link:roleType>
	<link:roleType roleURI="http://celsion.com/role/Warrants-SummaryOfWarrantActivityDetails" id="Warrants-SummaryOfWarrantActivityDetails">
	  <link:definition>00000055 - Disclosure - Warrants - Summary of Warrant Activity (Details)</link:definition>
	  <link:usedOn>link:presentationLink</link:usedOn>
	  <link:usedOn>link:calculationLink</link:usedOn>
	  <link:usedOn>link:definitionLink</link:usedOn>
	</link:roleType>
	<link:roleType roleURI="http://celsion.com/role/LeasesDetailsNarrative" id="LeasesDetailsNarrative">
	  <link:definition>00000056 - Disclosure - Leases (Details Narrative)</link:definition>
	  <link:usedOn>link:presentationLink</link:usedOn>
	  <link:usedOn>link:calculationLink</link:usedOn>
	  <link:usedOn>link:definitionLink</link:usedOn>
	</link:roleType>
	<link:roleType roleURI="http://celsion.com/role/Leases-ScheduleOfLeasePaymentsAndMaturityOfOperatingLeaseLiabilitiesDetails" id="Leases-ScheduleOfLeasePaymentsAndMaturityOfOperatingLeaseLiabilitiesDetails">
	  <link:definition>00000057 - Disclosure - Leases - Schedule of Lease Payments and Maturity of Operating Lease Liabilities (Details)</link:definition>
	  <link:usedOn>link:presentationLink</link:usedOn>
	  <link:usedOn>link:calculationLink</link:usedOn>
	  <link:usedOn>link:definitionLink</link:usedOn>
	</link:roleType>
	<link:roleType roleURI="http://celsion.com/role/TechnologyDevelopmentAndLicensingAgreementsDetailsNarrative" id="TechnologyDevelopmentAndLicensingAgreementsDetailsNarrative">
	  <link:definition>00000058 - Disclosure - Technology Development and Licensing Agreements (Details Narrative)</link:definition>
	  <link:usedOn>link:presentationLink</link:usedOn>
	  <link:usedOn>link:calculationLink</link:usedOn>
	  <link:usedOn>link:definitionLink</link:usedOn>
	</link:roleType>
	<link:roleType roleURI="http://celsion.com/role/CommitmentsAndContingenciesDetailsNarrative" id="CommitmentsAndContingenciesDetailsNarrative">
	  <link:definition>00000059 - Disclosure - Commitments and Contingencies (Details Narrative)</link:definition>
	  <link:usedOn>link:presentationLink</link:usedOn>
	  <link:usedOn>link:calculationLink</link:usedOn>
	  <link:usedOn>link:definitionLink</link:usedOn>
	</link:roleType>
	<link:roleType roleURI="http://celsion.com/role/SubsequentEventsDetailsNarrative" id="SubsequentEventsDetailsNarrative">
	  <link:definition>00000060 - Disclosure - Subsequent Events (Details Narrative)</link:definition>
	  <link:usedOn>link:presentationLink</link:usedOn>
	  <link:usedOn>link:calculationLink</link:usedOn>
	  <link:usedOn>link:definitionLink</link:usedOn>
	</link:roleType>
	<link:linkbaseRef xlink:type="simple" xlink:href="clsn-20210331_pre.xml" xlink:role="http://www.xbrl.org/2003/role/presentationLinkbaseRef" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:title="Presentation Links" />
	<link:linkbaseRef xlink:type="simple" xlink:href="clsn-20210331_lab.xml" xlink:role="http://www.xbrl.org/2003/role/labelLinkbaseRef" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:title="Label Links" />
	<link:linkbaseRef xlink:type="simple" xlink:href="clsn-20210331_cal.xml" xlink:role="http://www.xbrl.org/2003/role/calculationLinkbaseRef" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:title="Calculation Links" />
	<link:linkbaseRef xlink:type="simple" xlink:href="clsn-20210331_def.xml" xlink:role="http://www.xbrl.org/2003/role/definitionLinkbaseRef" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:title="Definition Links" />
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    <import namespace="http://www.xbrl.org/2003/linkbase" schemaLocation="http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" />
    <import namespace="http://xbrl.sec.gov/dei/2021" schemaLocation="https://xbrl.sec.gov/dei/2021/dei-2021.xsd" />
    <import namespace="http://fasb.org/us-gaap/2021-01-31" schemaLocation="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd" />
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    <import namespace="http://xbrl.sec.gov/country/2021" schemaLocation="https://xbrl.sec.gov/country/2021/country-2021.xsd" />
    <import namespace="http://xbrl.sec.gov/stpr/2021" schemaLocation="https://xbrl.sec.gov/stpr/2021/stpr-2021.xsd" />
    <import namespace="http://fasb.org/srt/2021-01-31" schemaLocation="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd" />
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    <element id="CLSN_ClassOfWarrantOrRightWarrantsOrRightsCancelled" name="ClassOfWarrantOrRightWarrantsOrRightsCancelled" nillable="true" xbrli:periodType="instant" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_EndOfTermChargePercentage" name="EndOfTermChargePercentage" nillable="true" xbrli:periodType="duration" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_EndOfTermFees" name="EndOfTermFees" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_ReceivableOnSaleOfNetOperatingLosses" name="ReceivableOnSaleOfNetOperatingLosses" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_AmortizationOfDeferredFinanceChargesAndDebtDiscountAssociatedWithNotePayable" name="AmortizationOfDeferredFinanceChargesAndDebtDiscountAssociatedWithNotePayable" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_FairValueOfWarrantsIssuedInConnectionWithAmendmentToModifyEarnoutMilestonePayments" name="FairValueOfWarrantsIssuedInConnectionWithAmendmentToModifyEarnoutMilestonePayments" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_RealizedAndUnrealizedGainsAndLossesNetOnInvestmentInDebtSecurities" name="RealizedAndUnrealizedGainsAndLossesNetOnInvestmentInDebtSecurities" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_StockIssuedUponExerciseOfCommonStockWarrants" name="StockIssuedUponExerciseOfCommonStockWarrants" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_StockIssuedUponExerciseOfCommonStockWarrantsShares" name="StockIssuedUponExerciseOfCommonStockWarrantsShares" nillable="true" xbrli:periodType="duration" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_LongTermDebtMaturitiesRepaymentsOfPrincipalYearFourAndThereAfter" name="LongTermDebtMaturitiesRepaymentsOfPrincipalYearFourAndThereAfter" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_NetProceedsFromSaleOfNetOperatingLosses" name="NetProceedsFromSaleOfNetOperatingLosses" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_NumberOfSharesOfCommonStockIssuableUponExerciseOfWarrantsAndEquityAwards" name="NumberOfSharesOfCommonStockIssuableUponExerciseOfWarrantsAndEquityAwards" nillable="true" xbrli:periodType="duration" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_NumberOfSharesOfCommonStockIssuedInCalculationBasicLossPerShare" name="NumberOfSharesOfCommonStockIssuedInCalculationBasicLossPerShare" nillable="true" xbrli:periodType="duration" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_DebtSecuritiesAvailableforsaleMaturityAllocatedAndSingleMaturityDateRollingWithinThreeMonthsAmortizedCost" name="DebtSecuritiesAvailableforsaleMaturityAllocatedAndSingleMaturityDateRollingWithinThreeMonthsAmortizedCost" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_DebtSecuritiesAvailableforsaleMaturityAllocatedAndSingleMaturityDateRollingBetweenThreeAndTwelveMonthsAmortizedCost" name="DebtSecuritiesAvailableforsaleMaturityAllocatedAndSingleMaturityDateRollingBetweenThreeAndTwelveMonthsAmortizedCost" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_AvailableForSaleDebtSecuritiesAmortizedCostBasisCurrent" name="AvailableForSaleDebtSecuritiesAmortizedCostBasisCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_DebtSecuritiesAvailableforsaleMaturityAllocatedAndSingleMaturityDateRollingWithinThreeMonthsFairValue" name="DebtSecuritiesAvailableforsaleMaturityAllocatedAndSingleMaturityDateRollingWithinThreeMonthsFairValue" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_DebtSecuritiesAvailableforsaleMaturityAllocatedAndSingleMaturityDateRollingBetweenThreeAndTwelveMonthsFairValue" name="DebtSecuritiesAvailableforsaleMaturityAllocatedAndSingleMaturityDateRollingBetweenThreeAndTwelveMonthsFairValue" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_DebtSecuritiesAvailableforsaleContinuousUnrealizedGainPositionLessThan12Months" name="DebtSecuritiesAvailableforsaleContinuousUnrealizedGainPositionLessThan12Months" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
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    <element id="CLSN_AvailableforsaleSecuritiesDebtSecuritiesCurrentAccumulatedUnrealizedGainLoss" name="AvailableforsaleSecuritiesDebtSecuritiesCurrentAccumulatedUnrealizedGainLoss" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
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    <element id="CLSN_PercentageOfUnderwritingDiscountOnPublicOfferingPrice" name="PercentageOfUnderwritingDiscountOnPublicOfferingPrice" nillable="true" xbrli:periodType="duration" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" />
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    <element id="CLSN_StockOptionsStrikePriceDescription" name="StockOptionsStrikePriceDescription" nillable="true" xbrli:periodType="duration" type="xbrli:stringItemType" substitutionGroup="xbrli:item" />
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    <element id="CLSN_GainLossFromChangeInFairValueOfEarnOutMilestoneLiability" name="GainLossFromChangeInFairValueOfEarnOutMilestoneLiability" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_EarnoutMilestoneLiability" name="EarnoutMilestoneLiability" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_EarnoutPaymentOptionsDescription" name="EarnoutPaymentOptionsDescription" nillable="true" xbrli:periodType="duration" type="xbrli:stringItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_NoncashChargeOnEarnourMilestoneLiability" name="NoncashChargeOnEarnourMilestoneLiability" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_EstimatedTimeToAchieveMileStone" name="EstimatedTimeToAchieveMileStone" nillable="true" xbrli:periodType="duration" type="xbrli:durationItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingWeightedAverageExercisePrice" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingWeightedAverageExercisePrice" nillable="true" xbrli:periodType="instant" type="dtr-types:perShareItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExerciseInPeriodWeightedAverageExercisePrice" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExerciseInPeriodWeightedAverageExercisePrice" nillable="true" xbrli:periodType="duration" type="dtr-types:perShareItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_SharebasedCompensationArrangementBySharebasedPaymentAwardNonOptionsOutstandingWeightedAverageRemainingContractualTerm2" name="SharebasedCompensationArrangementBySharebasedPaymentAwardNonOptionsOutstandingWeightedAverageRemainingContractualTerm2" nillable="true" xbrli:periodType="duration" type="xbrli:durationItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionsOutstandingIntrinsicValue" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionsOutstandingIntrinsicValue" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_LesseeOperatingLeaseLiabilityPaymentsDueAfterYearThreeAndThereAfter" name="LesseeOperatingLeaseLiabilityPaymentsDueAfterYearThreeAndThereAfter" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_DeferredRevenueAmortizationPeriod" name="DeferredRevenueAmortizationPeriod" nillable="true" xbrli:periodType="duration" type="xbrli:durationItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_UpfrontPaymentBeingRecognized" name="UpfrontPaymentBeingRecognized" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_RiskadjustmentAssessmentOfAchievingMilestone" name="RiskadjustmentAssessmentOfAchievingMilestone" nillable="true" xbrli:periodType="duration" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_DiscountRatesOnMileStoneLiabilities" name="DiscountRatesOnMileStoneLiabilities" nillable="true" xbrli:periodType="duration" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_SummaryOfStockOptionAndRestrictedStockAwardsTableTextBlock" name="SummaryOfStockOptionAndRestrictedStockAwardsTableTextBlock" nillable="true" xbrli:periodType="duration" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_LicensingTransactionTextBlock" name="LicensingTransactionTextBlock" nillable="true" xbrli:periodType="duration" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" />
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    <element id="CLSN_ScheduleOfChangesInEarnOutMilestoneLiabilitiesTableTextBlock" name="ScheduleOfChangesInEarnOutMilestoneLiabilitiesTableTextBlock" nillable="true" xbrli:periodType="duration" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" />
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    <element id="CLSN_IncreaseDecreaseInReceivableOnSaleOfNetOperatingLosses" name="IncreaseDecreaseInReceivableOnSaleOfNetOperatingLosses" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_CashAndCashEquivalentsShorttermInvestmentsAndReceivableOnSaleOfNetOperatingLosses" name="CashAndCashEquivalentsShorttermInvestmentsAndReceivableOnSaleOfNetOperatingLosses" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
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    <element id="CLSN_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwoAndAfter" name="FiniteLivedIntangibleAssetsAmortizationExpenseYearTwoAndAfter" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_GainLossFromChangeInEarnoutMilestoneLiability" name="GainLossFromChangeInEarnoutMilestoneLiability" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
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    <element id="CLSN_GlioblastomaMultiformeBrainCancerMember" name="GlioblastomaMultiformeBrainCancerMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
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    <element id="CLSN_AspirePurchaseAgreementsMember" name="AspirePurchaseAgreementsMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_IPRAndDDrugTechnologyPlatformsMember" name="IPRAndDDrugTechnologyPlatformsMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
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    <element id="CLSN_PurchaseAgreementMember" name="PurchaseAgreementMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
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    <element id="CLSN_JonesTradingInstitutionalServicesLLCMember" name="JonesTradingInstitutionalServicesLLCMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
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    <element id="CLSN_LincolnParkCapitalFundLLCMember" name="LincolnParkCapitalFundLLCMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
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    <element id="CLSN_SecuritiesPurchaseAgreementMember" name="SecuritiesPurchaseAgreementMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_OriginalWarrantsMember" name="OriginalWarrantsMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_ExchangeAgreementsMember" name="ExchangeAgreementsMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_UnderwritingAgreementMember" name="UnderwritingAgreementMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_UnderwrittenOfferingMember" name="UnderwrittenOfferingMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_RegularPurchaseShareLimitMember" name="RegularPurchaseShareLimitMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_ExchangeCapOfCommonStockMember" name="ExchangeCapOfCommonStockMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_LPCCommitmentSharesMember" name="LPCCommitmentSharesMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_TwoThousandNineteenAspirePurchaseAgreementsMember" name="TwoThousandNineteenAspirePurchaseAgreementsMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_TwoThousandEighteenAspirePurchaseAgreementsMember" name="TwoThousandEighteenAspirePurchaseAgreementsMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_JanuaryRegisteredDirectOfferingMember" name="JanuaryRegisteredDirectOfferingMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_MarchRegisteredDirectOfferingMember" name="MarchRegisteredDirectOfferingMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_TwoThousandAndEighteenStockIncentivePlanMember" name="TwoThousandAndEighteenStockIncentivePlanMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_TwoThousandSevenStockIncentivePlanMember" name="TwoThousandSevenStockIncentivePlanMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_InducementOptionGrantsMember" name="InducementOptionGrantsMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_FiveNewEmployeesMember" name="FiveNewEmployeesMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_EquityStockAwardsMember" name="EquityStockAwardsMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_GrantedUnderTwoThousandEighteenPlanAndTwoThousandSevenPlanMember" name="GrantedUnderTwoThousandEighteenPlanAndTwoThousandSevenPlanMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_TwoThousandAndEighteenPlanMember" name="TwoThousandAndEighteenPlanMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_InducementAwardsMember" name="InducementAwardsMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_EmployeeStockOptionAndRestrictedStockAwardsMember" name="EmployeeStockOptionAndRestrictedStockAwardsMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_TwoThousandNineteenBonusProgramMember" name="TwoThousandNineteenBonusProgramMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_StockOptionsMember" name="StockOptionsMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_AmendedAssetPurchaseAgreementMember" name="AmendedAssetPurchaseAgreementMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_AchievingMilestoneWithInOneYearMember" name="AchievingMilestoneWithInOneYearMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_CertainBusinessDaysOfAchievingMilestoneMember" name="CertainBusinessDaysOfAchievingMilestoneMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_EGWUIncMember" name="EGWUIncMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_FairValueEarnoutMilestoneLiabilityMember" name="FairValueEarnoutMilestoneLiabilityMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_AmendedAssetPurchaseAgreementOptionPaymentOneMember" name="AmendedAssetPurchaseAgreementOptionPaymentOneMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_AmendedAssetPurchaseAgreementOptionPaymentTwoMember" name="AmendedAssetPurchaseAgreementOptionPaymentTwoMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_EGWCMember" name="EGWCMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_FirstLeaseAmendmentMember" name="FirstLeaseAmendmentMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_FirstYearMember" name="FirstYearMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_FinalYearMember" name="FinalYearMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_SecondLeaseAmendmentMember" name="SecondLeaseAmendmentMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_HuntsvilleAlabamaMember" name="HuntsvilleAlabamaMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_EGENAssetPurchaseAgreementMember" name="EGENAssetPurchaseAgreementMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_OperatingLeasesMember" name="OperatingLeasesMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_HisunMember" name="HisunMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_InprocessRandDMember" name="InprocessRandDMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_EarnoutMilestoneLiabilityAbstract" name="EarnoutMilestoneLiabilityAbstract" abstract="true" nillable="true" xbrli:periodType="duration" type="xbrli:stringItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_TechnologyDevelopmentAndLicensingAgreementsAbstract" name="TechnologyDevelopmentAndLicensingAgreementsAbstract" abstract="true" nillable="true" xbrli:periodType="duration" type="xbrli:stringItemType" substitutionGroup="xbrli:item" />
</schema>
