LIMITED POWER OF ATTORNEY

       The undersigned hereby constitutes and appoints each of William D.
Baird III and Iya Kessler, signing singly, and with full power of substitution,
the undersigned's true and lawful attorney-in-fact to:

	(1)	execute for and on behalf of the undersigned, in the
undersigned's capacity as officer and/or director of 2seventy bio, Inc., a
Delaware corporation (the "Company"), from time to time the following U.S.
Securities and Exchange Commission ("SEC") forms: (i) Form ID, including any
attached documents (such as Update Passphrase Authentication), to effect the
assignment of codes to the undersigned to be used in the transmission of
information to the SEC using the EDGAR System; (ii) Form 3, Initial Statement
of Beneficial Ownership of Securities, including any attached documents;
(iii) Form 4, Statement of Changes in Beneficial Ownership of Securities,
including any attached documents; (iv) Form 5, Annual Statement of Beneficial
Ownership of Securities in accordance with Section 16(a) of the Securities
Exchange Act of 1934, as amended, and the rules thereunder, including
any attached documents; (v) Schedules 13D and 13G; and (vi) amendments of each
thereof, in accordance with the Securities Exchange Act of 1934, as amended,
and the rules thereunder, including any attached documents;

	(2)	do and perform any and all acts for and on behalf of the
undersigned which may be necessary or desirable to complete and execute any
such Form 3, 4 or 5, Schedule 13D or 13G, or any amendment(s) thereto and
timely file such form(s) with the SEC and any securities exchange, national
association or similar authority; and

	(3)	take any other action of any type whatsoever in connection
with the foregoing which, in the opinion of such attorney-in-fact, may be
of benefit to, in the best interest of, or legally required by, the
undersigned, it being understood that the documents executed by such
attorney-in-fact on behalf of the undersigned pursuant to this Power of
Attorney shall be in such form and shall contain such terms and conditions
as such attorney-in-fact may approve in such attorney-in-fact's discretion.

	The undersigned hereby grants to each such attorney-in-fact, acting
singly, full power and authority to do and perform any and every act and
thing whatsoever requisite, necessary or proper to be done in the exercise
of any of the rights and powers herein granted, as fully to all intents and
purposes as the undersigned might or could do if personally present, with
full power of substitution or revocation, hereby ratifying and confirming
all that such attorney-in-fact, or such attorney-in-fact's substitute or
substitutes, shall lawfully do or cause to be done by virtue of this power
of attorney and the rights and powers herein granted. The undersigned
acknowledges that the foregoing attorneys-in-fact, in serving in such
capacity at the request of the undersigned, are not assuming, nor is the
Company assuming, any of the undersigned's responsibilities to comply with
Section 16 or Regulation 13D-G of the Securities Exchange Act of 1934, as
amended. The undersigned hereby agrees to indemnify the attorneys-in-fact
and the Company from and against any demand, damage, loss, cost or expense
arising from any false or misleading information provided by the
undersigned to the attorneys-in-fact.

	This Power of Attorney shall remain in full force and effect until
the undersigned is no longer required to file such forms with respect to
the undersigned's holdings of and transactions in securities issued by the
Company, unless earlier revoked by the undersigned in a signed writing
delivered to the foregoing attorneys-in-fact.  This Power of Attorney
supersedes any prior power of attorney in connection with the undersigned's
capacity as an officer and/or director of the Company.  This Power of
Attorney shall expire as to any individual attorney-in-fact if such
attorney-in-fact ceases to be an employee of the Company.

	IN WITNESS WHEREOF, the undersigned has caused this Power of
Attorney to be executed as of March 20, 2024.

					/s/ Jessica Snow
					Signature

					Jessica Snow
					Print Name