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            <filer>
                <filerCredentials>
                    <cik>0002009134</cik>
                    <ccc>XXXXXXXX</ccc>
                </filerCredentials>
            </filer>
            <liveTestFlag>LIVE</liveTestFlag>



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        <issuerInfo>
            <issuerCik>0001860782</issuerCik>
            <issuerName>2SEVENTY BIO, INC.</issuerName>
            <secFileNumber>001-40791</secFileNumber>
            <issuerAddress>
                <ns2:street1>60 Binney Street</ns2:street1>
                <ns2:city>Cambridge</ns2:city>
                <ns2:stateOrCountry>MA</ns2:stateOrCountry>
                <ns2:zipCode>02142</ns2:zipCode>
            </issuerAddress>
            <issuerContactPhone>(617) 675-7270</issuerContactPhone>
            <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>JESSICA SNOW</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>8th Floor</ns2:street2>
                    <ns2:city>New York</ns2:city>
                    <ns2:stateOrCountry>NY</ns2:stateOrCountry>
                    <ns2:zipCode>10004</ns2:zipCode>
                </address>
            </brokerOrMarketmakerDetails>
            <noOfUnitsSold>7816</noOfUnitsSold>
            <aggregateMarketValue>33760.22</aggregateMarketValue>
            <noOfUnitsOutstanding>51405419</noOfUnitsOutstanding>
            <approxSaleDate>08/14/2024</approxSaleDate>
            <securitiesExchangeName>NASDAQ</securitiesExchangeName>
        </securitiesInformation>
        <securitiesToBeSold>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <acquiredDate>06/02/2024</acquiredDate>
            <natureOfAcquisitionTransaction>Restricted Stock</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>1639</amountOfSecuritiesAcquired>
            <paymentDate>06/02/2024</paymentDate>
            <natureOfPayment>Not Applicable</natureOfPayment>
        </securitiesToBeSold>
        <securitiesToBeSold>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <acquiredDate>07/01/2024</acquiredDate>
            <natureOfAcquisitionTransaction>Restricted Stock</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>25</amountOfSecuritiesAcquired>
            <paymentDate>07/01/2024</paymentDate>
            <natureOfPayment>Not Applicable</natureOfPayment>
        </securitiesToBeSold>
        <securitiesToBeSold>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <acquiredDate>05/01/2024</acquiredDate>
            <natureOfAcquisitionTransaction>Restricted Stock</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>23</amountOfSecuritiesAcquired>
            <paymentDate>05/01/2024</paymentDate>
            <natureOfPayment>Not Applicable</natureOfPayment>
        </securitiesToBeSold>
        <securitiesToBeSold>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <acquiredDate>03/29/2024</acquiredDate>
            <natureOfAcquisitionTransaction>Employee Stock Purchase Plan</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>6129</amountOfSecuritiesAcquired>
            <paymentDate>03/29/2024</paymentDate>
            <natureOfPayment>Cash</natureOfPayment>
        </securitiesToBeSold>
        <nothingToReportFlagOnSecuritiesSoldInPast3Months>N</nothingToReportFlagOnSecuritiesSoldInPast3Months>
        <securitiesSoldInPast3Months>
            <sellerDetails>
                <name>JESSICA SNOW</name>
                <address>
                    <ns2:street1>60 Binney Street</ns2:street1>
                    <ns2:city>Cambridge</ns2:city>
                    <ns2:stateOrCountry>MA</ns2:stateOrCountry>
                    <ns2:zipCode>02142</ns2:zipCode>
                </address>
            </sellerDetails>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <saleDate>07/02/2024</saleDate>
            <amountOfSecuritiesSold>14</amountOfSecuritiesSold>
            <grossProceeds>56.25</grossProceeds>
        </securitiesSoldInPast3Months>
        <securitiesSoldInPast3Months>
            <sellerDetails>
                <name>JESSICA SNOW</name>
                <address>
                    <ns2:street1>60 Binney Street</ns2:street1>
                    <ns2:city>Cambridge</ns2:city>
                    <ns2:stateOrCountry>MA</ns2:stateOrCountry>
                    <ns2:zipCode>02142</ns2:zipCode>
                </address>
            </sellerDetails>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <saleDate>06/03/2024</saleDate>
            <amountOfSecuritiesSold>649</amountOfSecuritiesSold>
            <grossProceeds>2714.31</grossProceeds>
        </securitiesSoldInPast3Months>
        <noticeSignature>
            <noticeDate>08/14/2024</noticeDate>
            <planAdoptionDates/>
            <signature>/s/ Jessica Condon Snow</signature>
        </noticeSignature>
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144
0002009134
XXXXXXXX
LIVE
0001860782
2SEVENTY BIO, INC.
001-40791
60 Binney Street
Cambridge
MA
02142
(617) 675-7270
JESSICA SNOW
Officer
Common
Morgan Stanley Smith Barney LLC Executive Financial Services
1 New York Plaza
8th Floor
New York
NY
10004
7816
33760.22
51405419
08/14/2024
NASDAQ
Common
06/02/2024
Restricted Stock
Issuer
N
1639
06/02/2024
Not Applicable
Common
07/01/2024
Restricted Stock
Issuer
N
25
07/01/2024
Not Applicable
Common
05/01/2024
Restricted Stock
Issuer
N
23
05/01/2024
Not Applicable
Common
03/29/2024
Employee Stock Purchase Plan
Issuer
N
6129
03/29/2024
Cash
N
JESSICA SNOW
60 Binney Street
Cambridge
MA
02142
Common
07/02/2024
14
56.25
JESSICA SNOW
60 Binney Street
Cambridge
MA
02142
Common
06/03/2024
649
2714.31
08/14/2024
/s/ Jessica Condon Snow