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    <element id="CLSN_SeriesBBBWarrantsMember" name="SeriesBBBWarrantsMember" nillable="true" xbrli:periodType="duration" type="nonnum:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_SeriesDDDWarrantsMember" name="SeriesDDDWarrantsMember" nillable="true" xbrli:periodType="duration" type="nonnum:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_February142017PublicOfferingMember" name="February142017PublicOfferingMember" nillable="true" xbrli:periodType="duration" type="nonnum:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_SeriesAAWarrantMember" name="SeriesAAWarrantMember" nillable="true" xbrli:periodType="duration" type="nonnum:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_PreFundedSeriesBBWarrantMember" name="PreFundedSeriesBBWarrantMember" nillable="true" xbrli:periodType="duration" type="nonnum:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_TwoThousandThirteenWarrants2014WarrantsAndJune2016WarrantsMember" name="TwoThousandThirteenWarrants2014WarrantsAndJune2016WarrantsMember" nillable="true" xbrli:periodType="duration" type="nonnum:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_TwoThousandFifteenWarrantsMember" name="TwoThousandFifteenWarrantsMember" nillable="true" xbrli:periodType="duration" type="nonnum:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_May2015CommonStockOfferingMember" name="May2015CommonStockOfferingMember" nillable="true" xbrli:periodType="duration" type="nonnum:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_ATMAgreementMember" name="ATMAgreementMember" nillable="true" xbrli:periodType="duration" type="nonnum:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_ReverseStockSplitMember" name="ReverseStockSplitMember" nillable="true" xbrli:periodType="duration" type="nonnum:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_JuneTwoThousandAndSixrteenWarrantsMember" name="JuneTwoThousandAndSixrteenWarrantsMember" nillable="true" xbrli:periodType="duration" type="nonnum:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_NewJerseyMember" name="NewJerseyMember" nillable="true" xbrli:periodType="duration" type="nonnum:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_HorizonTechnologyFinanceCorporationMember" name="HorizonTechnologyFinanceCorporationMember" nillable="true" xbrli:periodType="duration" type="nonnum:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_HorizonCreditAgreementMember" name="HorizonCreditAgreementMember" nillable="true" xbrli:periodType="duration" type="nonnum:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_HorizonWarrantMember" name="HorizonWarrantMember" nillable="true" xbrli:periodType="duration" type="nonnum:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_HorizonMember" name="HorizonMember" nillable="true" xbrli:periodType="duration" type="nonnum:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_AspirePurchaseAgreementMember" name="AspirePurchaseAgreementMember" nillable="true" xbrli:periodType="duration" type="nonnum:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_InducementOptionGrantsMember" name="InducementOptionGrantsMember" nillable="true" xbrli:periodType="duration" type="nonnum:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_ThreeNewEmployeesMember" name="ThreeNewEmployeesMember" nillable="true" xbrli:periodType="duration" type="nonnum:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_OctoberTwentynineTwoThousandEighteenMember" name="OctoberTwentynineTwoThousandEighteenMember" nillable="true" xbrli:periodType="duration" type="nonnum:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_DocumentAndEntityInformationAbstract" name="DocumentAndEntityInformationAbstract" abstract="true" nillable="true" xbrli:periodType="duration" type="xbrli:stringItemType" 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_WarrantAbstract" name="WarrantAbstract" 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" />
    <element id="CLSN_ClassOfWarrantOrRightExercisablePeriod" name="ClassOfWarrantOrRightExercisablePeriod" nillable="true" xbrli:periodType="duration" type="xbrli:durationItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_CommissionOnProceedsFromAtmSharesPercent" name="CommissionOnProceedsFromAtmSharesPercent" nillable="true" xbrli:periodType="duration" type="num:percentItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_AggregateOfferingPriceRemainingAmounts" name="AggregateOfferingPriceRemainingAmounts" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
</schema>
