SEC Form 4

FORM 4		UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940	OMB APPROVAL OMB Number: 3235-0287 Estimated average burden hours per response: 0.5
	Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

1. Name and Address of Reporting Person* Casdin Capital, LLC (Last) (First) (Middle) 1350 AVENUE OF THE AMERICAS SUITE 2600 (Street) NEW YORK NY 10019 (City) (State) (Zip)	2. Issuer Name and Ticker or Trading Symbol 2seventy bio, Inc. [ TSVT ]	5. Relationship of Reporting Person(s) to Issuer (Check all applicable) Director 10% Owner Officer (give title below) Other (specify below)
	3. Date of Earliest Transaction (Month/Day/Year) 06/10/2024
	4. If Amendment, Date of Original Filed (Month/Day/Year)	6. Individual or Joint/Group Filing (Check Applicable Line) Form filed by One Reporting Person Form filed by More than One Reporting Person
	Rule 10b5-1(c) Transaction Indication Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock, par value $0.0001 per share	06/10/2024		A		6,025	A	(1)	22,625(2)	D(3)
Common Stock, par value $0.0001 per share								2,000,000	I	See footnote(4)

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Stock Options (Right to buy)	$3.93	06/10/2024		A		12,050		(5)	(5)	Common Stock, par value $0.0001 per share	12,050	$3.93	12,050	D(3)
Stock Options (Right to buy)	$4.54							(6)	03/20/2034	Common Stock, par value $0.0001 per share	33,400		33,400	D(3)
Total Return Swap	(7)							(7)	(7)	Common Stock, par value $0.0001 per share	536,784		536,784	I	See footnote(4)

1. Name and Address of Reporting Person* Casdin Capital, LLC (Last) (First) (Middle) 1350 AVENUE OF THE AMERICAS SUITE 2600 (Street) NEW YORK NY 10019 (City) (State) (Zip)

1. Name and Address of Reporting Person* Casdin Eli (Last) (First) (Middle) 1350 AVENUE OF THE AMERICAS SUITE 2600 (Street) NEW YORK NY 10019 (City) (State) (Zip)

1. Name and Address of Reporting Person* Casdin Partners Master Fund, L.P. (Last) (First) (Middle) 1350 AVENUE OF THE AMERICAS SUITE 2600 (Street) NEW YORK NY 10019 (City) (State) (Zip)

1. Name and Address of Reporting Person* Casdin Partners GP, LLC (Last) (First) (Middle) 1350 AVENUE OF THE AMERICAS SUITE 2600 (Street) NEW YORK NY 10019 (City) (State) (Zip)

Explanation of Responses:

1. Each restricted stock unit represents the right to receive one share of the Issuer's common Stock, par value $0.0001 per share.

2. These shares are comprised of (i) 16,000 restricted stock units that vest ratable over three years in annual installments with the first installment vesting on March 20, 2025, subject to the Reporting Person's continued service through the applicable vesting date and (ii) 6,025 restricted stock units that vest on the earlier of (a) June 10, 2025 or (b) the date of the next annual meeting of stockholders of the Issuer.

3. The securities are owned directly by Eli Casdin.

4. The securities are owned directly by Casdin Partners Master Fund, L.P. (the "Master Fund") and may be deemed to be indirectly beneficially owned by (i) Casdin Capital, LLC, the investment adviser to the Master Fund ("Casdin"), (ii) Casdin Partners GP, LLC, the general partner of the Master Fund (the "GP"), and (iii) Eli Casdin, the managing member of Casdin and the GP.

5. This stock option vests on the earlier of (a) June 10, 2025 or (b) the date of the next annual meeting of stockholders of the Issuer.

6. This stock option vests ratably over three years in annual installments with the first installment vesting on March 20, 2025, subject to the Reporting Person's continued service through the applicable vesting date.

7. The Master Fund has entered into certain cash-settled total return swap agreements (the "Swap Agreements"), which represent, after the transaction reported herein, economic exposure to an aggregate of 536,784.15 notional shares of the Issuer's Common Stock, par value $0.0001 per share. The Swap Agreements provide the Master Fund with economic results that are comparable to the economic results of ownership but do not provide it with the power to vote or direct the voting or dispose of or direct the disposition of the securities that are referenced by the Swap Agreements.

Remarks:

Eli Casdin has been deputized to represent the Reporting Persons on the board of directors of the Issuer. By virtue of Mr. Casdin's representation, for purposes of Section 16 of the Securities Exchange Act of 1934 (the "Exchange Act"), each of the Reporting Persons may be deemed directors by deputization of the Issuer. Each Reporting Person disclaims beneficial ownership in the securities reported on this Form 4 except to the extent of its pecuniary interest, if any, therein, and this report shall not be deemed to be an admission that such Reporting Person is the beneficial owner of such securities for purposes of Section 16 or for any other purpose.

	Casdin Capital LLC, By: /s/ Eli Casdin, Managing Member	06/12/2024
	/s/ Eli Casdin, Eli Casdin	06/12/2024
	Casdin Partners Master Fund, LP, By: Casdin Partners GP, LLC, its General Partner, By: /s/ Eli Casdin, Managing Member	06/12/2024
	Casdin Partners GP LLC, By: /s/ Eli Casdin, Managing Member	06/12/2024
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
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