TCRR TCR2 Therapeutics Inc

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 OF SECURITIES	OMB APPROVAL OMB Number: 3235-0287 Estimated average burden hours per response... 0.5
	Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940

1. Name and Address of Reporting Person * MPM ASSET MANAGEMENT LLC	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/YYYY) 5/22/2023
(Street) BOSTON, MA 02116	4. If Amendment, Date Original Filed (MM/DD/YYYY)	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)	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. Trans. Date	2A. Deemed Execution Date, if any	3. Trans. 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	5/22/2023		X(1)		178269	A	$0.74	374171	D
Common Stock	5/22/2023		S(1)		70170	D	$1.88	304001	D
Common Stock								3370977	I	See Footnote (2)

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivate Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Trans. Date	3A. Deemed Execution Date, if any	4. Trans. 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		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 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
Common Stock Warrant (Right To Buy)	$0.74	5/22/2023		X (1)			42761	12/13/2016	12/12/2026	Common Stock	42761	$0.00	0	D
Common Stock Warrant (Right to Buy)	$0.74	5/22/2023		X (1)			135508	12/6/2017	12/5/2027	Common Stock	135508	$0.00	0	D

Explanation of Responses:
(1)	On May 22, 2023, MPM Asset Management LLC ("AM LLC") exercised warrants to purchase 178,269 shares of the Issuer's common stock for $0.74 a share. AM LLC paid the exercise price on a cashless basis, resulting in the Issuer's withholding of 70,170 of the warrant shares to satisfy the exercise price and issuing to AM LLC the remaining 108,099 shares.
(2)	The shares are 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)") and 110,859 by MPM Asset Management Investors BV2014 LLC ("AM BV2014"). 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 BV 2014. Luke Evnin is a managing director of BV LLC and disclaims beneficial ownership of the reported securities except to the extent of his pecuniary interest therein.

Reporting Owners
Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
MPM ASSET MANAGEMENT LLC C/O MPM CAPITAL 399 BOYLSTON STREET, SUITE 1100 BOSTON, MA 02116		X
EVNIN LUKE C/O MPM CAPITAL 399 BOYLSTON STREET, SUITE 1100 BOSTON, MA 02116		X

Signatures
/s/ Luke Evnin, member of MPM Asset Management LLC		5/24/2023
**Signature of Reporting Person		Date
/s/ Luke Evnin		5/24/2023
**Signature of Reporting Person		Date

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