Sec Form 4 Filing - LYNCH DANIEL @ 2seventy bio, Inc. - 2021-11-11

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

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, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person LYNCH DANIEL 2. Issuer Name and Ticker or Trading Symbol 2seventy bio, Inc. [ TSVT] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 2SEVENTY BIO, INC., 60 BINNEY STREET 3. Date of Earliest Transaction (MM/DD/YY) 11/11/2021 (Street) CAMBRIDGE, MA02142 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 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( 1 )( 2 )( 3 ) 11/11/2021 A 2,803 A $ 0 5,453( 4 ) D

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 (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 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 (MM/DD/YY) 7. Title and Amount of Underlying Securities (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 of Derivative Security: 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 Option (right to buy) $ 8.55 11/11/2021 A( 5 ) 7,660 ( 6 ) 01/16/2023 Common Stock 7,660 $ 0 7,660 D Stock Option (right to buy) $ 39.07 11/11/2021 A( 5 ) 3,445 ( 6 ) 06/11/2024 Common Stock 3,445 $ 0 3,445 D Stock Option (right to buy) $ 287.25 11/11/2021 A( 5 ) 3,445 ( 6 ) 06/04/2025 Common Stock 3,445 $ 0 3,445 D Stock Option (right to buy) $ 74.34 11/11/2021 A( 5 ) 1,837 ( 6 ) 06/02/2026 Common Stock 1,837 $ 0 1,837 D Stock Option (right to buy) $ 172.37 11/11/2021 A( 5 ) 1,837 ( 6 ) 06/08/2027 Common Stock 1,837 $ 0 1,837 D Stock Option (right to buy) $ 284.33 11/11/2021 A( 5 ) 1,837 ( 6 ) 06/20/2028 Common Stock 1,837 $ 0 1,837 D Stock Option (right to buy) $ 189.47 11/11/2021 A( 5 ) 1,837 ( 6 ) 06/06/2029 Common Stock 1,837 $ 0 1,837 D Stock Option (right to buy) $ 99.53 11/11/2021 A( 5 ) 1,378 ( 6 ) 06/18/2030 Common Stock 1,378 $ 0 1,378 D Stock Option (right to buy) $ 50.98 11/11/2021 A( 5 ) 4,507 ( 7 ) 06/15/2031 Common Stock 4,507 $ 0 4,507 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other LYNCH DANIEL 2SEVENTY BIO, INC. 60 BINNEY STREET CAMBRIDGE, MA02142 X Signatures /s/ Teresa Jurgensen, Attorney-in-Fact 11/16/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )In connection with the separation (the "Separation") of seventy bio, Inc. ("2seventy") from bluebird bio, Inc. ("bluebird"), the reporting person received restricted stock units, each representing the right to receive a share of 2seventy's common stock, as a result of the adjustment of existing bluebird restricted stock units prior to the Separation (see footnotes 2 and 3). This restricted stock unit award vests 100% on the earlier of June 15, 2022 or the date of the next annual meeting of stockholders. ( 2 )bluebird equity awards granted prior to January 1, 2021 were converted into equity awards of both bluebird and 2seventy. The number of shares underlying the converted bluebird equity awards was determined by multiplying the number of shares underlying the existing bluebird equity award by a fraction, the numerator of which is the volume-weighted average trading price of bluebird common stock (trading "regular way") on the five trading days immediately prior to the distribution date (the "bluebird Pre-Distribution VWAP"), the denominator of which is the sum of (1) the volume-weighted average trading price of 2seventy common stock (trading "regular way") on the five trading days immediately following the distribution date (the "2seventy VWAP") multiplied by the distribution ratio and (2) the volume-weighted average trading price of bluebird common stock (trading "regular way") on the five trading days immediately following the distribution date (the "bluebird Post-Distribution VWAP"). ( 3 )The number of shares underlying the converted 2seventy equity awards was determined by multiplying the number of shares underlying the existing bluebird equity awards by a fraction, the numerator of which is the bluebird Pre-Distribution VWAP and the denominator of which is the sum of (1) the 2seventy VWAP multiplied by the distribution ratio and (2) the quotient obtained by dividing the bluebird Post-Distribution VWAP by the distribution ratio. bluebird equity awards granted on or after January 1, 2021, such equity awards were converted into 2seventy equity awards. The number of shares of 2seventy common stock underlying such converted equity awards is equal to the number of shares of bluebird common stock subject to the equity award immediately prior to the distribution multiplied by a fraction, the numerator of which is the bluebird Pre-Distribution VWAP and the denominator of which is the 2seventy VWAP. ( 4 )Includes 2,650 shares of 2seve nty's common stock received in a pro rata distribution by bluebird as a result of the Separation. ( 5 )Represents options to purchase shares of 2seventy's common stock granted to the reporting person in connection with the Separation (see footnotes 2 and 3). ( 6 )This option is fully vested and exercisable as of the date hereof (see footnotes 2 and 3). ( 7 )This option vests 100% on the earlier of June 15, 2022 or the date of the next annual meeting of stockholders (see footnotes 2 and 3).

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).

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