United States securities and exchange commission logo

                            June 7, 2021

       Nick Leschly
       Chief Executive Officer
       2seventy bio, Inc.
       60 Binney Street
       Cambridge, MA 02142

                                                        Re: 2seventy bio, Inc.
                                                            Draft Registration
Statement on Form 10
                                                            Submitted May 11,
                                                            CIK No. 0001860782

       Dear Mr. Leschly:

              We have reviewed your draft registration statement and have the
following comments. In
       some of our comments, we may ask you to provide us with information so
we may better
       understand your disclosure.

              Please respond to this letter by providing the requested
information and either submitting
       an amended draft registration statement or publicly filing your
registration statement on
       EDGAR. If you do not believe our comments apply to your facts and
circumstances or do not
       believe an amendment is appropriate, please tell us why in your

             After reviewing the information you provide in response to these
comments and your
       amended draft registration statement or filed registration statement, we
may have additional

       Draft Registration Statement on Form 10

       Information Statement Summary
       Overview, page 10

   1.                                                   We note your disclosure
that you are delivering Abecma to multiple myeloma patients in
                                                        the United States
together with your partner Bristol-Myers Squibb. Please revise to
                                                        disclose when in 2021
you and Bristol-Myers Squibb began delivering Abecma to
                                                        patients. Please also
briefly describe Bristol-Myers Squibb's and your obligations under
                                                        your co-development and
co-promotion arrangement.
   2.                                                   With reference to your
disclosure on page 107, please specify that Abecma was approved
                                                        for the treatment of
adults with multiple myeloma who have received at least four prior
 Nick Leschly
FirstName  LastNameNick  Leschly
2seventy bio, Inc.
June 7, 2021Name2seventy bio, Inc.
June 7,
Page 2 2021 Page 2
FirstName LastName
         lines of therapy, including an immunomodulatory agent, a proteasome
inhibitor, and an
         anti-CD38 monoclonal antibody.
Our Approach, page 98

3.       We note your statement on page 100 that you believe that certain
technologies will enable
         bbT369 to drive rapid tumor clearance, a hallmark of the CD19 CAR T
cell patients who
         proceed to achieve complete responses. Please revise this statement to
remove any
         suggestion that your product candidate will be effective as findings
of efficacy are solely
         within the authority of the FDA or comparable foreign regulators.
Multiple Myeloma, page 106

4.       We note your disclosure regarding an ongoing Phase 1 CRB-402 study for
         that clinical endpoints were "promising" across the study and the
estimated median
         duration of response was "promising" at 17.0 months across doses.
Please revise these and
         any similar statements to remove any implication of forthcoming
regulatory approval or
         the efficacy of your product candidate, as these determinations are
solely within the
         authority of the FDA or comparable foreign regulators. You may present
clinical trial end
         points and objective data resulting from trials without including
conclusions related to
Strategic Collaborations, page 108

5.       With respect to each of the agreements discussed in this section,
please revise to disclose
         the nature and scope of intellectual property transferred if the
agreement involves a
         license, each parties    rights and obligations, the duration of the
agreement, the royalty
         term, the termination provisions, and the following payment

             Up-front or execution payments received or paid;
             Aggregate amounts paid or received to date under the agreement;
             Aggregate future potential milestone payments to be paid or
             Royalty rates or a royalty range;
             Profit or revenue-sharing provisions; and
             Minimum purchase requirements if the agreement involves

         Please also file these agreements as exhibits or tell us why you
believe that you are not
         required to file them. Refer to Item 601(b)(10) of Regulation S-K.
Intellectual Property, page 111

6.       Please revise to disclose the material foreign jurisdictions where you
own or license
         patents or have pending patent applications.
7.       We note your disclosure that certain patents will expire during 2021 -
2024. Please revise
         to disclose what effect you expect the expiration of these patents to
have on your patent
 Nick Leschly
2seventy bio, Inc.
June 7, 2021
Page 3
       portfolio and your business, if any, and if you intend to take any
action to mitigate such
Management, page 134

8.     Please revise to briefly discuss the specific experience,
qualifications, attributes or skills
       that led to the conclusion that Mr. Leschly should serve as a director
of your company, in
       light of your business and structure. Refer to Item 401(e) of Regulation
Executive Compensation
Agreements with our Named Executive Officers, page 143

9.     We note your disclosure that you intend to enter into new employment
agreements with
       your named executive officers that will be effective upon completion of
the separation.
       Please tell us whether you intend to file such agreements in a
subsequent amendment.
Financial Statements
Report of Independent Registered Public Accounting Firm, page F-2

10.    Please have your auditor explain how they determined 2021, and not 2012,
to be the
       appropriate year they began serving consecutively as your auditor, for
the purpose of AS
       3101.10 (b) and the included note.
       You may contact Michael Fay at 202-551-3812 or Lynn Dicker at
202-551-3616 if you
have questions regarding comments on the financial statements and related
matters. Please
contact Ada D. Sarmento at 202-551-3798 or Irene Paik at 202-551-6553 with any

FirstName LastNameNick Leschly
                                                               Division of
Corporation Finance
Comapany Name2seventy bio, Inc.
                                                               Office of Life
June 7, 2021 Page 3
cc:       Gregg L. Katz, Esq.
FirstName LastName