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 	  
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	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*
UBS Oncology Impact 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		2,421,775	A	(1)	2,421,775	D(2)(3) 		
Common Stock	02/19/2019		C		282,540	A	(1)	2,704,315	D(2)(3) 		
Common Stock	02/19/2019		P		666,667	A	$15 	3,370,982	D(2)(3) 		
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			15,000,000	(1) 	(1) 	Common Stock	2,421,775	$0.00 	0	D		
Series B Preferred Stock	(1)	02/19/2019		C			1,750,000	(1) 	(1) 	Common Stock	282,540	$0.00 	0	D		
1. Name and Address of Reporting Person*
UBS Oncology Impact 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*
Oncology Impact Fund (Cayman) Management 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 Oncology Impact Management LP	

(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 Oncology Impact Management GP LLC	

(Last)	(First)	(Middle)	
C/O 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 reported securities are held in the account of UBS Oncology Impact Fund L.P. ("UBS Oncology"). MPM Oncology Impact Management GP LLC ("Oncology GP LLC") is the General Partner of MPM Oncology Impact Management LP, the General Partner of Oncology Impact Fund (Cayman) Management L.P., the General Partner of UBS Oncology. Ansbert Gadicke is the managing director of Oncology GP LLC.	
3. The Reporting Persons disclaim beneficial ownership of the securities except to the extent of their respective pecuniary interests therein.	
Remarks:	
	
	/s/ Ansbert Gadicke, managing director of MPM Oncology Impact Management GP LLC, the general partner of MPM Oncology Impact Management LP, the general partner of Oncology Impact Fund (Cayman) Management L.P., the GP of UBS Oncology Impact Fund L.P.	02/21/2019	
	/s/ Ansbert Gadicke, managing director of MPM Oncology Impact Management GP LLC, the general partner of MPM Oncology Impact Management LP, the general partner of Oncology Impact Fund (Cayman) Management L.P.	02/21/2019	
	/s/ Ansbert Gadicke, managing director of MPM Oncology Impact Management GP LLC, the general partner of MPM Oncology Impact Management LP	02/21/2019	
	/s/ Ansbert Gadicke, managing director of MPM Oncology Impact Management GP LLC	02/21/2019	
	** 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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