<SUBMISSION>
<ACCESSION-NUMBER>0001179110-04-000156
<TYPE>5
<PUBLIC-DOCUMENT-COUNT>1
<PERIOD>20031231
<FILING-DATE>20040105
<REPORTING-OWNER>
<OWNER-DATA>
<CONFORMED-NAME>HELSTOSKY ANTHONY
<CIK>0001260289
</OWNER-DATA>
<FILING-VALUES>
<FORM-TYPE>5
<ACT>34
<FILE-NUMBER>000-15006
<FILM-NUMBER>04504379
</FILING-VALUES>
<MAIL-ADDRESS>
<STREET1>5 GIBBON RD
<CITY>HOPKINTON
<STATE>MA
<ZIP>01748
</MAIL-ADDRESS>
</REPORTING-OWNER>
<ISSUER>
<COMPANY-DATA>
<CONFORMED-NAME>AVANT IMMUNOTHERAPEUTICS INC
<CIK>0000744218
<ASSIGNED-SIC>2835
<IRS-NUMBER>133191702
<STATE-OF-INCORPORATION>DE
<FISCAL-YEAR-END>1231
</COMPANY-DATA>
<BUSINESS-ADDRESS>
<STREET1>119 FOURTH AVE
<CITY>NEEDHAM
<STATE>MA
<ZIP>02494
<PHONE>7814330771
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>119 FOURTH AVE
<CITY>NEEDHAM
<STATE>MA
<ZIP>021942725
</MAIL-ADDRESS>
<FORMER-COMPANY>
<FORMER-CONFORMED-NAME>T CELL SCIENCES INC
<DATE-CHANGED>19920703
</FORMER-COMPANY>
</ISSUER>
<DOCUMENT>
<TYPE>5
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>FORM 5 -
<TEXT>
<XML>
<ownershipDocument>
    <schemaVersion>X0201</schemaVersion>

    <documentType>5</documentType>
<periodOfReport>2003-12-31</periodOfReport>
<notSubjectToSection16>0</notSubjectToSection16>
    <form3HoldingsReported>0</form3HoldingsReported>

    <form4TransactionsReported>0</form4TransactionsReported>

    <issuer>
        <issuerCik>0000744218</issuerCik>
        <issuerName>AVANT IMMUNOTHERAPEUTICS INC</issuerName>
        <issuerTradingSymbol>AVAN</issuerTradingSymbol>
</issuer>
<reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001260289</rptOwnerCik>
            <rptOwnerName>HELSTOSKY ANTHONY</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>5 GIBBON ROAD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>HOPKINTON</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>01748</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>0</isDirector>
<isOfficer>0</isOfficer>
<isTenPercentOwner>0</isTenPercentOwner>
<isOther>1</isOther>
<officerTitle></officerTitle>
<otherText>Sr.Dir Reg Affairs</otherText>
</reportingOwnerRelationship>
</reportingOwner>
<nonDerivativeTable><nonDerivativeTransaction><securityTitle><value>Non-Derviative Security</value>
</securityTitle>
<transactionDate><value>2003-07-23</value>
</transactionDate>
<transactionCoding><transactionFormType>5</transactionFormType>
<transactionCode>L</transactionCode>
<equitySwapInvolved>0</equitySwapInvolved>
</transactionCoding>
<transactionAmounts><transactionShares><value>500</value>
</transactionShares>
<transactionPricePerShare><value>.969</value>
</transactionPricePerShare>
<transactionAcquiredDisposedCode><value>A</value>
</transactionAcquiredDisposedCode>
</transactionAmounts>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>3000</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>D</value>
</directOrIndirectOwnership>
</ownershipNature>
</nonDerivativeTransaction>
</nonDerivativeTable>
<derivativeTable></derivativeTable>
<footnotes></footnotes>
<ownerSignature><signatureName>Anthony Helstosky</signatureName>
<signatureDate>2004-01-05</signatureDate>
</ownerSignature>
</ownershipDocument>

</XML>
</TEXT>
</DOCUMENT>
</SUBMISSION>
