<?xml version="1.0" encoding="US-ASCII" ?>
    <!-- Field: Doc-Info; Name: Generator; Value: GoFiler Complete; Version: 5.13a -->
    <!-- Field: Doc-Info; Name: VendorURI; Value: https://www.novaworks.com -->
    <!-- Field: Doc-Info; Name: Status; Value: 0x00000000 -->
    <!-- Field: Doc-Info; Name: Misc; Value: 96Mps7xRiXgen8uDanwsWamN+bP9z5Z8KekhvWBzbZmazyUrnqsxDifloFzm0QoK -->
<schema xmlns="http://www.w3.org/2001/XMLSchema" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xbrldi="http://xbrl.org/2006/xbrldi" xmlns:dei="http://xbrl.sec.gov/dei/2021q4" xmlns:us-gaap="http://fasb.org/us-gaap/2021-01-31" xmlns:srt="http://fasb.org/srt/2021-01-31" xmlns:srt-types="http://fasb.org/srt-types/2021-01-31" xmlns:dtr-types="http://www.xbrl.org/dtr/type/2020-01-21" xmlns:CLSN="http://celsion.com/20211231" elementFormDefault="qualified" targetNamespace="http://celsion.com/20211231">
    <annotation>
      <appinfo>
	<link:roleType roleURI="http://celsion.com/role/Cover" id="Cover">
	  <link:definition>00000001 - Document - Cover</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/BalanceSheets" id="BalanceSheets">
	  <link:definition>00000002 - Statement - Consolidated Balance Sheets</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/BalanceSheetsParenthetical" id="BalanceSheetsParenthetical">
	  <link:definition>00000003 - Statement - Consolidated Balance Sheets (Parenthetical)</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/StatementsOfOperations" id="StatementsOfOperations">
	  <link:definition>00000004 - Statement - Consolidated Statements of Operations</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/StatementsOfComprehensiveLoss" id="StatementsOfComprehensiveLoss">
	  <link:definition>00000005 - Statement - Consolidated Statements of Comprehensive loss</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/StatementsOfCashFlows" id="StatementsOfCashFlows">
	  <link:definition>00000006 - Statement - Consolidated Statements of Cash Flows</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/StatementsOfChangesInStockholdersEquity" id="StatementsOfChangesInStockholdersEquity">
	  <link:definition>00000007 - Statement - Consolidated Statements of Changes in Stockholders' Equity</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/SummaryOfSignificantAccountingPolicies" id="SummaryOfSignificantAccountingPolicies">
	  <link:definition>00000008 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES</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/FinancialCondition" id="FinancialCondition">
	  <link:definition>00000009 - Disclosure - FINANCIAL CONDITION</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/InvestmentsInDebtSecuritiesAvailableForSale" id="InvestmentsInDebtSecuritiesAvailableForSale">
	  <link:definition>00000010 - Disclosure - INVESTMENTS IN DEBT SECURITIES AVAILABLE FOR SALE</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/FairValuesOfFinancialInstruments" id="FairValuesOfFinancialInstruments">
	  <link:definition>00000011 - Disclosure - FAIR VALUES OF FINANCIAL INSTRUMENTS</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/IntangibleAssets" id="IntangibleAssets">
	  <link:definition>00000012 - Disclosure - INTANGIBLE ASSETS</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/PropertyAndEquipment" id="PropertyAndEquipment">
	  <link:definition>00000013 - Disclosure - PROPERTY AND EQUIPMENT</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/OtherAccruedLiabilities" id="OtherAccruedLiabilities">
	  <link:definition>00000014 - Disclosure - OTHER ACCRUED LIABILITIES</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/NotesPayable" id="NotesPayable">
	  <link:definition>00000015 - Disclosure - NOTES PAYABLE</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/IncomeTaxes" id="IncomeTaxes">
	  <link:definition>00000016 - Disclosure - INCOME TAXES</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/StockholdersEquity" id="StockholdersEquity">
	  <link:definition>00000017 - Disclosure - STOCKHOLDERS&#8217; EQUITY</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/Stock-basedCompensation" id="Stock-basedCompensation">
	  <link:definition>00000018 - Disclosure - STOCK-BASED COMPENSATION</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/Earn-outMilestoneLiability" id="Earn-outMilestoneLiability">
	  <link:definition>00000019 - Disclosure - EARN-OUT MILESTONE LIABILITY</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" id="Warrants">
	  <link:definition>00000020 - Disclosure - WARRANTS</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/CelsionEmployeeBenefitPlans" id="CelsionEmployeeBenefitPlans">
	  <link:definition>00000021 - Disclosure - CELSION EMPLOYEE BENEFIT PLANS</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" id="Leases">
	  <link:definition>00000022 - Disclosure - LEASES</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/CommitmentsAndContingencies" id="CommitmentsAndContingencies">
	  <link:definition>00000023 - Disclosure - COMMITMENTS AND CONTINGENCIES</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/LicensesOfIntellectualPropertyAndPatents" id="LicensesOfIntellectualPropertyAndPatents">
	  <link:definition>00000024 - Disclosure - LICENSES OF INTELLECTUAL PROPERTY AND PATENTS</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/TechnologyDevelopmentAndLicensingAgreements" id="TechnologyDevelopmentAndLicensingAgreements">
	  <link:definition>00000025 - Disclosure - TECHNOLOGY DEVELOPMENT AND LICENSING AGREEMENTS</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/SubsequentEvents" id="SubsequentEvents">
	  <link:definition>00000026 - Disclosure - SUBSEQUENT EVENTS</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/SummaryOfSignificantAccountingPoliciesPolicies" id="SummaryOfSignificantAccountingPoliciesPolicies">
	  <link:definition>00000027 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)</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/InvestmentsInDebtSecuritiesAvailableForSaleTables" id="InvestmentsInDebtSecuritiesAvailableForSaleTables">
	  <link:definition>00000028 - Disclosure - INVESTMENTS IN DEBT SECURITIES AVAILABLE FOR SALE (Tables)</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/FairValuesOfFinancialInstrumentsTables" id="FairValuesOfFinancialInstrumentsTables">
	  <link:definition>00000029 - Disclosure - FAIR VALUES OF FINANCIAL INSTRUMENTS (Tables)</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/IntangibleAssetsTables" id="IntangibleAssetsTables">
	  <link:definition>00000030 - Disclosure - INTANGIBLE ASSETS (Tables)</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/PropertyAndEquipmentTables" id="PropertyAndEquipmentTables">
	  <link:definition>00000031 - Disclosure - PROPERTY AND EQUIPMENT (Tables)</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/OtherAccruedLiabilitiesTables" id="OtherAccruedLiabilitiesTables">
	  <link:definition>00000032 - Disclosure - OTHER ACCRUED LIABILITIES (Tables)</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/NotesPayableTables" id="NotesPayableTables">
	  <link:definition>00000033 - Disclosure - NOTES PAYABLE (Tables)</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/IncomeTaxesTables" id="IncomeTaxesTables">
	  <link:definition>00000034 - Disclosure - INCOME TAXES (Tables)</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/Stock-basedCompensationTables" id="Stock-basedCompensationTables">
	  <link:definition>00000035 - Disclosure - STOCK-BASED COMPENSATION (Tables)</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/Earn-outMilestoneLiabilityTables" id="Earn-outMilestoneLiabilityTables">
	  <link:definition>00000036 - Disclosure - EARN-OUT MILESTONE LIABILITY (Tables)</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/WarrantsTables" id="WarrantsTables">
	  <link:definition>00000037 - Disclosure - WARRANTS (Tables)</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/LeasesTables" id="LeasesTables">
	  <link:definition>00000038 - Disclosure - LEASES (Tables)</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/SummaryOfSignificantAccountingPoliciesDetailsNarrative" id="SummaryOfSignificantAccountingPoliciesDetailsNarrative">
	  <link:definition>00000039 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (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/FinancialConditionDetailsNarrative" id="FinancialConditionDetailsNarrative">
	  <link:definition>00000040 - Disclosure - FINANCIAL CONDITION (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/ScheduleOfCostFairValueAndMaturitiesOfShortTermInvestmentsDetails" id="ScheduleOfCostFairValueAndMaturitiesOfShortTermInvestmentsDetails">
	  <link:definition>00000041 - Disclosure - SCHEDULE OF COST, FAIR VALUE AND MATURITIES OF SHORT TERM INVESTMENTS (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/SummaryOfInvestmentSecuritiesGrossUnrealizedGainsLossesDetails" id="SummaryOfInvestmentSecuritiesGrossUnrealizedGainsLossesDetails">
	  <link:definition>00000042 - Disclosure - SUMMARY OF INVESTMENT SECURITIES GROSS UNREALIZED GAINS (LOSSES) (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/SummaryOfNetRealizedLossesOnSalesOfAvailableForSaleSecuritiesAndInvestmentIncomeInterestAndDividendsDetails" id="SummaryOfNetRealizedLossesOnSalesOfAvailableForSaleSecuritiesAndInvestmentIncomeInterestAndDividendsDetails">
	  <link:definition>00000043 - Disclosure - SUMMARY OF NET REALIZED LOSSES ON SALES OF AVAILABLE FOR SALE SECURITIES AND INVESTMENT INCOME INTEREST AND DIVIDENDS (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/InvestmentsInDebtSecuritiesAvailableForSaleDetailsNarrative" id="InvestmentsInDebtSecuritiesAvailableForSaleDetailsNarrative">
	  <link:definition>00000044 - Disclosure - INVESTMENTS IN DEBT SECURITIES AVAILABLE FOR SALE (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/ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisDetails" id="ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisDetails">
	  <link:definition>00000045 - Disclosure - SCHEDULE OF FAIR VALUE, ASSETS AND LIABILITIES MEASURED ON RECURRING BASIS (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/ScheduleOfFairValueOfAssetsAcquiredDetails" id="ScheduleOfFairValueOfAssetsAcquiredDetails">
	  <link:definition>00000046 - Disclosure - SCHEDULE OF FAIR VALUE OF ASSETS ACQUIRED (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/IntangibleAssetsDetailsNarrative" id="IntangibleAssetsDetailsNarrative">
	  <link:definition>00000047 - Disclosure - INTANGIBLE ASSETS (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/SummaryOfPropertyAndEquipmentDetails" id="SummaryOfPropertyAndEquipmentDetails">
	  <link:definition>00000048 - Disclosure - SUMMARY OF PROPERTY AND EQUIPMENT (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/SummaryOfPropertyAndEquipmentDetailsParenthetical" id="SummaryOfPropertyAndEquipmentDetailsParenthetical">
	  <link:definition>00000049 - Disclosure - SUMMARY OF PROPERTY AND EQUIPMENT (Details) (Parenthetical)</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/ScheduleOfOtherAccruedLiabilitiesDetails" id="ScheduleOfOtherAccruedLiabilitiesDetails">
	  <link:definition>00000050 - Disclosure - SCHEDULE OF OTHER ACCRUED 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/ScheduleOfFuturePrinciplePaymentsNetOfUnamortizedDebtDiscountsDetails" id="ScheduleOfFuturePrinciplePaymentsNetOfUnamortizedDebtDiscountsDetails">
	  <link:definition>00000051 - Disclosure - SCHEDULE OF FUTURE PRINCIPLE PAYMENTS, NET OF UNAMORTIZED DEBT DISCOUNTS (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/ScheduleOfDebtDetails" id="ScheduleOfDebtDetails">
	  <link:definition>00000052 - Disclosure - SCHEDULE OF DEBT (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/NotesPayableDetailsNarrative" id="NotesPayableDetailsNarrative">
	  <link:definition>00000053 - Disclosure - NOTES PAYABLE (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/ScheduleOfIncomeTaxProvisionBenefitDetails" id="ScheduleOfIncomeTaxProvisionBenefitDetails">
	  <link:definition>00000054 - Disclosure - SCHEDULE OF INCOME TAX PROVISION (BENEFIT) (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/ScheduleOfEffectiveIncomeTaxRateReconciliationDetails" id="ScheduleOfEffectiveIncomeTaxRateReconciliationDetails">
	  <link:definition>00000055 - Disclosure - SCHEDULE OF EFFECTIVE INCOME TAX RATE RECONCILIATION (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/ScheduleOfDeferredTaxAssetsAndLiabilitiesDetails" id="ScheduleOfDeferredTaxAssetsAndLiabilitiesDetails">
	  <link:definition>00000056 - Disclosure - SCHEDULE OF DEFERRED TAX ASSETS AND 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/IncomeTaxesDetailsNarrative" id="IncomeTaxesDetailsNarrative">
	  <link:definition>00000057 - Disclosure - INCOME TAXES (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/StockholdersEquityDetailsNarrative" id="StockholdersEquityDetailsNarrative">
	  <link:definition>00000058 - Disclosure - STOCKHOLDERS&#8217; EQUITY (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/SummaryOfStockOptionsDetails" id="SummaryOfStockOptionsDetails">
	  <link:definition>00000059 - Disclosure - SUMMARY OF STOCK OPTIONS (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/SummaryOfNon-vestedRestrictedStockAwardsDetails" id="SummaryOfNon-vestedRestrictedStockAwardsDetails">
	  <link:definition>00000060 - Disclosure - SUMMARY OF NON-VESTED RESTRICTED STOCK AWARDS (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/SummaryOfStockOptionsOutstandingDetails" id="SummaryOfStockOptionsOutstandingDetails">
	  <link:definition>00000061 - Disclosure - SUMMARY OF STOCK OPTIONS OUTSTANDING (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/ScheduleOfAssumptionsUsedToDetermineFairValueOfOptionsGrantedDetails" id="ScheduleOfAssumptionsUsedToDetermineFairValueOfOptionsGrantedDetails">
	  <link:definition>00000062 - Disclosure - SCHEDULE OF ASSUMPTIONS USED TO DETERMINE FAIR VALUE OF OPTIONS GRANTED (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/Stock-basedCompensationDetailsNarrative" id="Stock-basedCompensationDetailsNarrative">
	  <link:definition>00000063 - Disclosure - STOCK-BASED COMPENSATION (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/ScheduleOfChangesInEarn-outMilestoneLiabilityDetails" id="ScheduleOfChangesInEarn-outMilestoneLiabilityDetails">
	  <link:definition>00000064 - Disclosure - SCHEDULE OF CHANGES IN EARN-OUT MILESTONE LIABILITY (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/Earn-outMilestoneLiabilityDetailsNarrative" id="Earn-outMilestoneLiabilityDetailsNarrative">
	  <link:definition>00000065 - Disclosure - EARN-OUT MILESTONE LIABILITY (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/SummaryOfWarrantActivityDetails" id="SummaryOfWarrantActivityDetails">
	  <link:definition>00000066 - Disclosure - 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/SummaryOfWarrantActivityDetailsParenthetical" id="SummaryOfWarrantActivityDetailsParenthetical">
	  <link:definition>00000067 - Disclosure - SUMMARY OF WARRANT ACTIVITY (Details) (Parenthetical)</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/WarrantsDetailsNarrative" id="WarrantsDetailsNarrative">
	  <link:definition>00000068 - Disclosure - WARRANTS (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/CelsionEmployeeBenefitPlansDetailsNarrative" id="CelsionEmployeeBenefitPlansDetailsNarrative">
	  <link:definition>00000069 - Disclosure - CELSION EMPLOYEE BENEFIT PLANS (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/ScheduleOfLeasePaymentsAndMaturityOfOperatingLeaseLiabilitiesDetails" id="ScheduleOfLeasePaymentsAndMaturityOfOperatingLeaseLiabilitiesDetails">
	  <link:definition>00000070 - Disclosure - 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/LeasesDetailsNarrative" id="LeasesDetailsNarrative">
	  <link:definition>00000071 - 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/LicensesOfIntellectualPropertyAndPatentsDetailsNarrative" id="LicensesOfIntellectualPropertyAndPatentsDetailsNarrative">
	  <link:definition>00000072 - Disclosure - LICENSES OF INTELLECTUAL PROPERTY AND PATENTS (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/TechnologyDevelopmentAndLicensingAgreementsDetailsNarrative" id="TechnologyDevelopmentAndLicensingAgreementsDetailsNarrative">
	  <link:definition>00000073 - 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/SubsequentEventsDetailsNarrative" id="SubsequentEventsDetailsNarrative">
	  <link:definition>00000074 - 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-20211231_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-20211231_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-20211231_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-20211231_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" />
      </appinfo>
    </annotation>
    <import namespace="http://www.xbrl.org/2003/instance" schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd" />
    <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/2021q4" schemaLocation="https://xbrl.sec.gov/dei/2021q4/dei-2021q4.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" />
    <import namespace="http://fasb.org/us-types/2021-01-31" schemaLocation="https://xbrl.fasb.org/us-gaap/2021/elts/us-types-2021-01-31.xsd" />
    <import namespace="http://www.xbrl.org/dtr/type/2020-01-21" schemaLocation="https://www.xbrl.org/dtr/type/2020-01-21/types.xsd" />
    <import namespace="http://xbrl.sec.gov/country/2021" schemaLocation="https://xbrl.sec.gov/country/2021/country-2021.xsd" />
    <import namespace="http://fasb.org/srt/2021-01-31" schemaLocation="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd" />
    <import namespace="http://fasb.org/srt-types/2021-01-31" schemaLocation="https://xbrl.fasb.org/srt/2021/elts/srt-types-2021-01-31.xsd" />
    <element id="CLSN_HisunAgreementMember" name="HisunAgreementMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_NJMember" name="NJMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_HorizonCreditAgreementMember" name="HorizonCreditAgreementMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_HorizonTechnologyFinanceCorporationMember" name="HorizonTechnologyFinanceCorporationMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_SVBLoanFacilityMember" name="SVBLoanFacilityMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_AmendmentToHorizonCreditAgreementMember" name="AmendmentToHorizonCreditAgreementMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_SiliconValleyBankMember" name="SiliconValleyBankMember" 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_EGENIncMember" name="EGENIncMember" 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" />
    <element id="CLSN_OvarianCancerMember" name="OvarianCancerMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_GlioblastomaMultiformeBrainCancerMember" name="GlioblastomaMultiformeBrainCancerMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_PurchaseAgreementMember" name="PurchaseAgreementMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_AspirePurchaseAgreementsMember" name="AspirePurchaseAgreementsMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_IPRAndDMember" name="IPRAndDMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_InitialHorizonCreditAgreementMember" name="InitialHorizonCreditAgreementMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_InitialHorizonCreditAgreementAmendmentMember" name="InitialHorizonCreditAgreementAmendmentMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_FederalIncomeTaxMember" name="FederalIncomeTaxMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_NoExpirationMember" name="NoExpirationMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_CapitalOnDemandTMSalesAgreementMember" name="CapitalOnDemandTMSalesAgreementMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_CapitalOnDemandAgreementMember" name="CapitalOnDemandAgreementMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <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_LPCPurchaseAgreementMember" name="LPCPurchaseAgreementMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_LincolnParkCapitalFundLLCMember" name="LincolnParkCapitalFundLLCMember" 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_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_SeriesAConvertibleRedeemablePreferredStockMember" name="SeriesAConvertibleRedeemablePreferredStockMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_SeriesBConvertibleRedeemablePreferredStockMember" name="SeriesBConvertibleRedeemablePreferredStockMember" 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_ExercisePriceOneMember" name="ExercisePriceOneMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_ExercisePriceTwoMember" name="ExercisePriceTwoMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_ExercisePriceThreeMember" name="ExercisePriceThreeMember" 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_EGWCMember" name="EGWCMember" 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_FairValueEarnoutMilestoneLiabilityMember" name="FairValueEarnoutMilestoneLiabilityMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_HorizonCreditAgreementAmendmentMember" name="HorizonCreditAgreementAmendmentMember" 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_EGENAssetPurchaseAgreementMember" name="EGENAssetPurchaseAgreementMember" 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_OperatingLeasesMember" name="OperatingLeasesMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_LicenseAgreementMember" name="LicenseAgreementMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_DukeUniversityMember" name="DukeUniversityMember" 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_GainLossFromChangeInEarnoutMilestoneLiability" name="GainLossFromChangeInEarnoutMilestoneLiability" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_ImpairmentOfGoodwillAndInprocessResearchAndDevelopment" name="ImpairmentOfGoodwillAndInprocessResearchAndDevelopment" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_FairValueOfWarrantsIssuedInExchangeForServices" name="FairValueOfWarrantsIssuedInExchangeForServices" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_ImpairmentOfInprocessResearchAndDevelopment" name="ImpairmentOfInprocessResearchAndDevelopment" nillable="true" xbrli:periodType="duration" 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_ProceedsFromIssuanceOfCommonStockUponExerciseOfStockOptions" name="ProceedsFromIssuanceOfCommonStockUponExerciseOfStockOptions" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_PaymentsOnNotesPayableIncludingEndoftermFees" name="PaymentsOnNotesPayableIncludingEndoftermFees" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_FairValueOfWarrantsIssuedInConnectionWithDebtFacilityNetOfCancelledWarrants" name="FairValueOfWarrantsIssuedInConnectionWithDebtFacilityNetOfCancelledWarrants" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" 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_IssuanceOfCommonStockUponExerciseOfOptions" name="IssuanceOfCommonStockUponExerciseOfOptions" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_IssuanceOfCommonStockUponExerciseOfOptionsShares" name="IssuanceOfCommonStockUponExerciseOfOptionsShares" nillable="true" xbrli:periodType="duration" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_StockIssuedDuringPeriodValueIssuanceOfCommonStockUponExerciseOfCommonStockWarrants" name="StockIssuedDuringPeriodValueIssuanceOfCommonStockUponExerciseOfCommonStockWarrants" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_StockIssuedDuringPeriodSharesIssuanceOfCommonStockUponExerciseOfCommonStockWarrants" name="StockIssuedDuringPeriodSharesIssuanceOfCommonStockUponExerciseOfCommonStockWarrants" nillable="true" xbrli:periodType="duration" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_CommonStockIssuanceToSettleAccruedBonuses" name="CommonStockIssuanceToSettleAccruedBonuses" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_CommonStockIssuedToSettleAccruedBonusesShares" name="CommonStockIssuedToSettleAccruedBonusesShares" nillable="true" xbrli:periodType="duration" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_AdjustmentsToAdditionalPaidInCapitaCommonStockWarrantsIssuedInExchangeForServices" name="AdjustmentsToAdditionalPaidInCapitaCommonStockWarrantsIssuedInExchangeForServices" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_DisclosureFairValuesOfFinancialInstrumentsAbstract" name="DisclosureFairValuesOfFinancialInstrumentsAbstract" abstract="true" nillable="true" xbrli:periodType="duration" type="xbrli:stringItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_DisclosureEarnoutMilestoneLiabilityAbstract" name="DisclosureEarnoutMilestoneLiabilityAbstract" abstract="true" nillable="true" xbrli:periodType="duration" type="xbrli:stringItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_EarnoutMilestoneLiabilityDisclosureTextBlock" name="EarnoutMilestoneLiabilityDisclosureTextBlock" nillable="true" xbrli:periodType="duration" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_DisclosureWarrantsAbstract" name="DisclosureWarrantsAbstract" abstract="true" nillable="true" xbrli:periodType="duration" type="xbrli:stringItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_WarrantsTextBlock" name="WarrantsTextBlock" nillable="true" xbrli:periodType="duration" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_DisclosureLeasesAbstract" name="DisclosureLeasesAbstract" abstract="true" nillable="true" xbrli:periodType="duration" type="xbrli:stringItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_DisclosureLicensesOfIntellectualPropertyAndPatentsAbstract" name="DisclosureLicensesOfIntellectualPropertyAndPatentsAbstract" abstract="true" nillable="true" xbrli:periodType="duration" type="xbrli:stringItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_LicensesOfIntellectualPropertyAndPatentsTextBlock" name="LicensesOfIntellectualPropertyAndPatentsTextBlock" nillable="true" xbrli:periodType="duration" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_DisclosureTechnologyDevelopmentAndLicensingAgreementsAbstract" name="DisclosureTechnologyDevelopmentAndLicensingAgreementsAbstract" abstract="true" nillable="true" xbrli:periodType="duration" type="xbrli:stringItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_LicensingTransactionTextBlock" name="LicensingTransactionTextBlock" nillable="true" xbrli:periodType="duration" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_DescriptionOfBusinessPolicyTextBlock" name="DescriptionOfBusinessPolicyTextBlock" nillable="true" xbrli:periodType="duration" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_DepositsPolicyTextBlock" name="DepositsPolicyTextBlock" nillable="true" xbrli:periodType="duration" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_ScheduleOfChangesInEarnOutMilestoneLiabilitiesTableTextBlock" name="ScheduleOfChangesInEarnOutMilestoneLiabilitiesTableTextBlock" nillable="true" xbrli:periodType="duration" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_NumberOfSharesOfCommonStockIssuableUponExerciseOfWarrantsAndEquityAwards" name="NumberOfSharesOfCommonStockIssuableUponExerciseOfWarrantsAndEquityAwards" nillable="true" xbrli:periodType="duration" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_ProceedFromNetOperatingLossesGross" name="ProceedFromNetOperatingLossesGross" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" 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_TaxBenefitsOfEarningsBeforeDepreciationAndAmortization" name="TaxBenefitsOfEarningsBeforeDepreciationAndAmortization" 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_PaymentOfDebtEndTermCharges" name="PaymentOfDebtEndTermCharges" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_RepaymentOfOutstandingIndebtednessAmount" name="RepaymentOfOutstandingIndebtednessAmount" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" type="xbrli:monetaryItemType" 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_DebtSecuritiesAvailableforsaleMaturityAllocatedAndSingleMaturityDateRollingWithinThreeMonthsFairValue" name="DebtSecuritiesAvailableforsaleMaturityAllocatedAndSingleMaturityDateRollingWithinThreeMonthsFairValue" 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_DebtSecuritiesAvailableforsaleMaturityAllocatedAndSingleMaturityDateRollingBetweenThreeAndTwelveMonthsFairValue" name="DebtSecuritiesAvailableforsaleMaturityAllocatedAndSingleMaturityDateRollingBetweenThreeAndTwelveMonthsFairValue" 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_AvailableForSaleSecuritiesUnrealizedGainsFairValue" name="AvailableForSaleSecuritiesUnrealizedGainsFairValue" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_AvailableForSaleSecuritiesUnrealizedHoldingGainsLessThanTwelveMonths" name="AvailableForSaleSecuritiesUnrealizedHoldingGainsLessThanTwelveMonths" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_AvailableForSaleSecuritiesUnrealizedLossFairValue" name="AvailableForSaleSecuritiesUnrealizedLossFairValue" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_AvailableForSaleSecuritiesUnrealizedHoldingLossesLessThanTwelveMonths" name="AvailableForSaleSecuritiesUnrealizedHoldingLossesLessThanTwelveMonths" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_AvailableForSaleSecuritiesUnrealizedHoldingGainsLossesLessThanTwelveMonths" name="AvailableForSaleSecuritiesUnrealizedHoldingGainsLossesLessThanTwelveMonths" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_InvestmentIncomeLossNonoperating" name="InvestmentIncomeLossNonoperating" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_NoncashCharge" name="NoncashCharge" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" type="xbrli:monetaryItemType" 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_EarlyTerminationFee" name="EarlyTerminationFee" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_EndOfTermCharges" name="EndOfTermCharges" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_FinalPaymentPercentage" name="FinalPaymentPercentage" nillable="true" xbrli:periodType="instant" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_EndOfTermChargePercentage" name="EndOfTermChargePercentage" nillable="true" xbrli:periodType="duration" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_ClassOfWarrantOrRightWarrantsOrRightsCancelled" name="ClassOfWarrantOrRightWarrantsOrRightsCancelled" nillable="true" xbrli:periodType="instant" type="xbrli:sharesItemType" 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_EffectiveIncomeTaxRateReconciliationPermanentDifferences" name="EffectiveIncomeTaxRateReconciliationPermanentDifferences" nillable="true" xbrli:periodType="duration" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_ProceedsFromSaleOfNetOperatingLosses" name="ProceedsFromSaleOfNetOperatingLosses" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_NetOperatingLossesUnused" name="NetOperatingLossesUnused" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_NetOperatingLossesCarryforwardLimitsDescription" name="NetOperatingLossesCarryforwardLimitsDescription" nillable="true" xbrli:periodType="duration" type="xbrli:stringItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_NetOperatingLossesExpirationDescription" name="NetOperatingLossesExpirationDescription" nillable="true" xbrli:periodType="duration" type="xbrli:stringItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_OperatingLossCarryForwardsLimitationOnUse" name="OperatingLossCarryForwardsLimitationOnUse" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_ShelfRegistrationStatementAmount" name="ShelfRegistrationStatementAmount" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_AggregateOfferingPrices" name="AggregateOfferingPrices" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_UnderwritingDiscountPricePerShare" name="UnderwritingDiscountPricePerShare" nillable="true" xbrli:periodType="duration" type="dtr-types:perShareItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_PercentageOfUnderwritingDiscountOnPublicOfferingPrice" name="PercentageOfUnderwritingDiscountOnPublicOfferingPrice" nillable="true" xbrli:periodType="duration" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_PlacementAgentFeeDescription" name="PlacementAgentFeeDescription" nillable="true" xbrli:periodType="duration" type="xbrli:stringItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_StockOptionsStrikePriceDescription" name="StockOptionsStrikePriceDescription" nillable="true" xbrli:periodType="duration" type="xbrli:stringItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_EarnoutMilestoneLiability" name="EarnoutMilestoneLiability" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_GainLossFromChangeInFairValueOfEarnOutMilestoneLiability" name="GainLossFromChangeInFairValueOfEarnOutMilestoneLiability" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_EarnoutMilestoneLiability1" name="EarnoutMilestoneLiability1" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" 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_NoncashChargeOnEarnoutMilestoneLiability" name="NoncashChargeOnEarnoutMilestoneLiability" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingWeightedAverageExercisePrice" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingWeightedAverageExercisePrice" nillable="true" xbrli:periodType="instant" type="dtr-types:perShareItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantsInPeriodWeightedAverageExercisePrice" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantsInPeriodWeightedAverageExercisePrice" nillable="true" xbrli:periodType="duration" 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeituresWeightedAverageExercisePrice" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeituresWeightedAverageExercisePrice" nillable="true" xbrli:periodType="duration" type="dtr-types:perShareItemType" 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_SharebasedCompensationArrangementBySharebasedPaymentAwardNonOptionsOutstandingWeightedAverageRemainingContractualTerm2" name="SharebasedCompensationArrangementBySharebasedPaymentAwardNonOptionsOutstandingWeightedAverageRemainingContractualTerm2" nillable="true" xbrli:periodType="duration" type="xbrli:durationItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_DefinedContributionPlanEmployerDiscretionaryContributionPercent" name="DefinedContributionPlanEmployerDiscretionaryContributionPercent" nillable="true" xbrli:periodType="duration" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_NumberOfDaysBeforeIssuanceFactoringIntoAverageClosingPrice" name="NumberOfDaysBeforeIssuanceFactoringIntoAverageClosingPrice" nillable="true" xbrli:periodType="duration" type="xbrli:stringItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_DeferredRevenueAmortizationPeriod" name="DeferredRevenueAmortizationPeriod" nillable="true" xbrli:periodType="duration" type="xbrli:durationItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_GovernmentBackedDebtSecuritiesMember" name="GovernmentBackedDebtSecuritiesMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="CLSN_GrossProceedsFromSaleOfNetOperatingLosses" name="GrossProceedsFromSaleOfNetOperatingLosses" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
</schema>
