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* MPM SunStates Fund, L.P. (Last) (First) (Middle) C/O MPM CAPITAL 450 KENDALL STREET (Street) CAMBRIDGE MA 02142 (City) (State) (Zip)	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)
	3. Date of Earliest Transaction (Month/Day/Year) 02/19/2019
	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 X Form filed by More than One Reporting Person

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	02/19/2019		C		2,825,396	A	(1)	3,021,298	I	See Footnote(2)(3)
Common Stock	02/19/2019		C		322,901	A	(1)	3,344,199	I	See Footnote(2)(4)
Common Stock	02/19/2019		P		706,666	A	$15	4,050,865	I	See Footnote(2)(5)

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
Series A Preferred Stock	(1)	02/19/2019		C			17,500,000	(1)	(1)	Common Stock	2,825,396	$0.00	0	I	See Footnote(6)
Series B Preferred Stock	(1)	02/19/2019		C			2,000,000	(1)	(1)	Common Stock	322,901	$0.00	0	I	See Footnote(6)

1. Name and Address of Reporting Person* MPM SunStates Fund, L.P. (Last) (First) (Middle) C/O MPM CAPITAL 450 KENDALL STREET (Street) CAMBRIDGE MA 02142 (City) (State) (Zip)

1. Name and Address of Reporting Person* MPM Asset Management Investors SunStates Fund LLC (Last) (First) (Middle) C/O MPM CAPITAL 450 KENDALL STREET (Street) CAMBRIDGE MA 02142 (City) (State) (Zip)

1. Name and Address of Reporting Person* MPM SunStates Fund GP LLC (Last) (First) (Middle) C/O MPM CAPITAL 450 KENDALL STREET (Street) CAMBRIDGE MA 02142 (City) (State) (Zip)

1. Name and Address of Reporting Person* MPM SunStates GP Managing Member LLC (Last) (First) (Middle) MPM CAPITAL 450 KENDALL STREET (Street) CAMBRIDGE MA 02142 (City) (State) (Zip)

Explanation of Responses:

1. All shares of Series A Preferred Stock and Series B Preferred Stock automatically converted into the number of shares of the Issuer's common stock on a 6.1938:1 basis, for no additional consideration, immediately prior to the closing of the Issuer's initial public offering and had no expiration date.

2. The Reporting Persons disclaim beneficial ownership of the securities except to the extent of their respective pecuniary interests therein.

3. The shares are held as follows: 2,195,681 by MPM BioVentures 2014, L.P. ("BV 2014"), 146,447 by MPM BioVentures 2014(B), L.P. ("BV 2014(B)"), 79,644 by MPM Asset Management Investors BV2014 LLC ("AM BV2014"), 195,902 by MPM Asset Management LLC ("AM LLC"), 351,155 by MPM SunStates Fund, L.P. ("MPM SunStates") and 52,469 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). MPM SunStates Fund GP LLC and MPM SunStates GP Managing Member LLC ("SunStates GP") are the direct and indirect general partners of MPM 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.

4. The shares are held as follows: 2,451,844 by BV 2014, 163,532 by BV 2014(B), 88,935 by AM BV2014, 195,902 by AM LLC, 386,270 by MPM SunStates and 57,716 by AM SunStates.

5. The shares are held as follows: 3,056,272 by BV 2014, 203,846 by BV 2014(B), 110,859 by AM BV2014, 195,902 by AM LLC, 421,070 by MPM SunStates and 62,916 by AM SunStates.

6. No securities held by the Reporting Persons.

Remarks:

See Form 4 for MPM BioVentures 2014, L.P. for additional members of this joint filing.

	/s/ Ansbert Gadicke, member of MPM Sunstates GP Managing Member LLC, the managing member of MPM SunStates Fund GP LLC, the general partner of MPM SunStates Fund, L.P.	02/21/2019
	/s/ Howard Rubin, director of MPM Asset Management Investors SunStates Fund LLC	02/21/2019
	/s/ Ansbert Gadicke, member of MPM SunStates GP Managing Member LLC, the managing member of MPM SunStates Fund GP LLC	02/21/2019
	/s/ Ansbert Gadicke, member of MPM SunStates GP Managing Member LLC	02/21/2019
	** Signature of Reporting Person	Date
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