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                <filerCredentials>
                    <cik>0001791742</cik>
                    <ccc>XXXXXXXX</ccc>
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            <liveTestFlag>LIVE</liveTestFlag>



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            <issuerCik>0001759138</issuerCik>
            <issuerName>CABALETTA BIO INC</issuerName>
            <secFileNumber>001-39103</secFileNumber>
            <issuerAddress>
                <ns2:street1>2929 Arch Street,  Suite 600</ns2:street1>
                <ns2:city>Philadelphia</ns2:city>
                <ns2:stateOrCountry>PA</ns2:stateOrCountry>
                <ns2:zipCode>19104</ns2:zipCode>
            </issuerAddress>
            <issuerContactPhone>2677593100</issuerContactPhone>
            <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>GWENDOLYN BINDER</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
            <relationshipsToIssuer>
                <relationshipToIssuer>Officer</relationshipToIssuer>
            </relationshipsToIssuer>
        </issuerInfo>
        <securitiesInformation>
            <securitiesClassTitle>COMMON</securitiesClassTitle>
            <brokerOrMarketmakerDetails>
                <name>Morgan Stanley Smith Barney LLC Executive Financial Services</name>
                <address>
                    <ns2:street1>1 New York Plaza</ns2:street1>
                    <ns2:street2>38th Fl.</ns2:street2>
                    <ns2:city>New York</ns2:city>
                    <ns2:stateOrCountry>NY</ns2:stateOrCountry>
                    <ns2:zipCode>10004</ns2:zipCode>
                </address>
            </brokerOrMarketmakerDetails>
            <noOfUnitsSold>11000</noOfUnitsSold>
            <aggregateMarketValue>139480.00</aggregateMarketValue>
            <noOfUnitsOutstanding>39805032</noOfUnitsOutstanding>
            <approxSaleDate>08/21/2023</approxSaleDate>
            <securitiesExchangeName>NASDAQ</securitiesExchangeName>
        </securitiesInformation>
        <securitiesToBeSold>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <acquiredDate>08/21/2023</acquiredDate>
            <natureOfAcquisitionTransaction>Exercise of Stock Options</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>11000</amountOfSecuritiesAcquired>
            <paymentDate>08/21/2023</paymentDate>
            <natureOfPayment>Cash</natureOfPayment>
        </securitiesToBeSold>
        <nothingToReportFlagOnSecuritiesSoldInPast3Months>N</nothingToReportFlagOnSecuritiesSoldInPast3Months>
        <securitiesSoldInPast3Months>
            <sellerDetails>
                <name>10b5-1 Sales for GWENDOLYN BINDER</name>
                <address>
                    <ns2:street1>2929 Arch Street,  Suite 600</ns2:street1>
                    <ns2:city>Philadelphia</ns2:city>
                    <ns2:stateOrCountry>PA</ns2:stateOrCountry>
                    <ns2:zipCode>19104</ns2:zipCode>
                </address>
            </sellerDetails>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <saleDate>07/19/2023</saleDate>
            <amountOfSecuritiesSold>11000</amountOfSecuritiesSold>
            <grossProceeds>152022.20</grossProceeds>
        </securitiesSoldInPast3Months>
        <securitiesSoldInPast3Months>
            <sellerDetails>
                <name>10b5-1 Sales for GWENDOLYN BINDER</name>
                <address>
                    <ns2:street1>2929 Arch Street,  Suite 600</ns2:street1>
                    <ns2:city>Philadelphia</ns2:city>
                    <ns2:stateOrCountry>PA</ns2:stateOrCountry>
                    <ns2:zipCode>19104</ns2:zipCode>
                </address>
            </sellerDetails>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <saleDate>06/20/2023</saleDate>
            <amountOfSecuritiesSold>11000</amountOfSecuritiesSold>
            <grossProceeds>142925.20</grossProceeds>
        </securitiesSoldInPast3Months>
        <noticeSignature>
            <noticeDate>08/21/2023</noticeDate>
            <planAdoptionDates>
                <planAdoptionDate>01/20/2023</planAdoptionDate>
            </planAdoptionDates>
            <signature>/s/ Gwendolyn Binder</signature>
        </noticeSignature>
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144
0001791742
XXXXXXXX
LIVE
0001759138
CABALETTA BIO INC
001-39103
2929 Arch Street,  Suite 600
Philadelphia
PA
19104
2677593100
GWENDOLYN BINDER
Officer
COMMON
Morgan Stanley Smith Barney LLC Executive Financial Services
1 New York Plaza
38th Fl.
New York
NY
10004
11000
139480.00
39805032
08/21/2023
NASDAQ
Common
08/21/2023
Exercise of Stock Options
Issuer
N
11000
08/21/2023
Cash
N
10b5-1 Sales for GWENDOLYN BINDER
2929 Arch Street,  Suite 600
Philadelphia
PA
19104
Common
07/19/2023
11000
152022.20
10b5-1 Sales for GWENDOLYN BINDER
2929 Arch Street,  Suite 600
Philadelphia
PA
19104
Common
06/20/2023
11000
142925.20
08/21/2023
01/20/2023
/s/ Gwendolyn Binder