Goodwin Procter LLP
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Boston, MA 02210
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May 11, 2021

CONFIDENTIAL SUBMISSION VIA EDGAR

U.S. Securities and Exchange Commission

Division of Corporation Finance

100 F. Street, N.E.

Washington, D.C.  20549

Re:       2seventy bio, Inc.

Draft Registration Statement on Form 10

Ladies and Gentlemen:

On behalf of 2seventy bio, Inc. (the “Company”), we are confidentially submitting a draft Registration Statement on Form 10 to the staff of the Securities and Exchange Commission for confidential nonpublic review.  The Company confirms that as of the date of this letter it is an “emerging growth company,” as defined in Section 3(a)(80) of the Securities Exchange Act of 1934, as amended.  In addition, the Company confirms that it will publicly file its Registration Statement on Form 10 and all nonpublic draft submissions at least 15 days prior to the anticipated effective date of such registration statement.

If you have any questions regarding this filing, please call me at (617) 570-1406.

Best regards,

/s/ Gregg L. Katz

Gregg L. Katz

Goodwin Procter LLP