Sec Form 4 Filing - MPM BioVentures 2014, L.P. @ TCR2 THERAPEUTICS INC. - 2023-06-01

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 MPM BioVentures 2014, L.P. 2. Issuer Name and Ticker or Trading Symbol TCR2 THERAPEUTICS INC. [ TCRR] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O MPM CAPITAL, 399 BOYLSTON STREET, SUITE 1100 3. Date of Earliest Transaction (MM/DD/YY) 06/01/2023 (Street) BOSTON, MA02116 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ 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 06/01/2023 J( 1 ) 4,158,964 D $ 0 ( 2 ) 0 I See Footnote ( 3 ) ( 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 (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

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other MPM BioVentures 2014, L.P. C/O MPM CAPITAL 399 BOYLSTON STREET, SUITE 1100 BOSTON, MA02116 X Foley Todd C/O MPM CAPITAL 399 BOYLSTON STREET, 1100 BOSTON, MA02116 X EVNIN LUKE C/O MPM CAPITAL 399 BOYLSTON STREET, SUITE 1100 BOSTON, MA02116 X MPM BioVentures 2014 (B), L.P. C/O MPM CAPITAL 399 BOYLSTON STREET, SUITE 1100 BOSTON, MA02116 X MPM Asset Management Investors BV2014 LLC C/O MPM CAPITAL 399 BOYLSTON STREET, 1100 BOSTON, MA02116 X MPM BioVentures 2014 LLC C/O MPM CAPITAL 399 BOYLSTON STREET, SUITE 1100 BOSTON, MA02116 X MPM BioVentures 2014 GP LLC C/O MPM CAPITAL 399 BOYLSTON STREET, SUITE 1100 BOSTON, MA02116 X MPM ASSET MANAGEMENT LLC C/O MPM CAPITAL 399 BOYLSTON STREET, SUITE 1100 BOSTON, MA02116 X Signatures /s/ Ansbert Gadicke, managing director of MPM BioVentures 2014 LLC, the managing member of MPM BioVentures 2014 GP LLC, the general partner of MPM BioVentures 2014, L.P. 06/05/2023 Signature of Reporting Person Date /s/ Todd Foley 06/05/2023 Signature of Reporting Person Date /s/ Luke Evnin 06/05/2023 Signature of Reporting Person Date /s/ Ansbert Gadicke, managing director of MPM BioVentures 2014 LLC, the managing member of MPM BioVentures 2014 GP LLC, the general partner of MPM BioVentures 2014 (B), L.P. 06/05/2023 Signature of Reporting Person Date /s/ Ansbert Gadicke, managing director of MPM BioVentures 2014 LLC, manager of MPM Asset Management Investors BV2014 LLC 06/05/2023 Signature of Reporting Person Date /s/ Ansbert Gadicke, managing director of MPM BioVentures 2014 LLC 06/05/2023 Signature of Reporting Person Date /s/ Ansbert Gadicke, managing director of MPM BioVentures 2014 LLC, the managing member of MPM BioVentures 2014 GP LLC 06/05/2023 Signature of Reporting Person Date /s/ Ansbert Gadicke, member of MPM Asset Management LLC 06/05/2023 Signature of Reporting Person Date

Explanation of Responses:

( 1 )This Form 4 reports securities disposed of pursuant to the terms of the Agreement and Plan of Merger, dated as of March 5, 2023, by and among TCR2 Therapeutics Inc. (the "Company"), Adaptimmune Therapeutics plc ("Parent") and CM Merger Sub, Inc., an indirect wholly-owned subsidiary of Parent ("Merger Sub"), as amended by that certain Amendment No. 1 to the Agreement and Plan of Merger, dated April 5, 2023, by and among the Company, Parent and Merger Sub (the "Merger Agreement"), pursuant to which Merger Sub merged with and into the Company (the "Merger") with the Company surviving the Merger as an indirect wholly-owned subsidiary of Parent effective as of June 1, 2023 (the "Effective Time"). ( 2 )At the Effective Time, each issued and outstanding share of common stock of the Company (each, a "Share") (excluding any Shares held in treasury of the Company or owned, directly or indirectly, by Parent or Merger Sub immediately prior to the Effective Time) was cancelled and converted into the right to receive 1.5117 (the "Exchange Ratio") American Depositary Shares of Parent ("Parent ADS") representing six ordinary shares of Parent ("Parent Ordinary Shares"). ( 3 )The Reporting Persons disclaim beneficial ownership of the securities except to the extent of their respective pecuniary interests therein. ( 4 )The shares were held as follows: 3,056,272 by MPM BioVentures 2014, L.P. ("BV 2014"), 203,846 by MPM BioVentures 2014(B), L.P. ("BV 2014(B)"), 110,859 by MPM Asset Management Investors BV2014 LLC ("AM BV2014"), 304,001 by MPM Asset Management LLC ("AM LLC"), 421,070 by MPM SunStates Fund, L.P. ("MPM SunStates") and 62,916 by MPM Asset Management Investors Sunstates Fund LLC ("AM SunStates"). MPM BioVentures 2014 GP LLC and MPM BioVentures 2014 LLC ("BV LLC") are the direct and indirect general partners of BV 2014 and BV 2014(B) and BV LLC is the manager of AM BV2014. MPM SunStates Fund GP LLC and MPM SunStates GP Managing Member LLC ("SunStates GP") are the direct and indirect general partners of MPM SunStates and SunStates GP is the manager of AM SunStates. Luke Evnin, Ansbert Gadicke and Todd Foley are the managing directors of BV LLC, Ansbert Gadicke is a member of SunStates GP and Luke Evnin and Anbsert Gadicke are the members of AM LLC.

Remarks: See Form 4 for MPM SunStates Fund, L.P for additional members of this joint filing.

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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