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*
Third Rock Ventures II, L.P.	

(Last)	(First)	(Middle)	
C/O THIRD ROCK VENTURES, LLC	
29 NEWBURY STREET, 3RD FLOOR	

(Street) 
BOSTON	MA	02116	

(City)	(State)	(Zip)	
	2. Issuer Name and Ticker or Trading Symbol 
Blueprint Medicines Corp [ BPMC ] 	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)
04/14/2016 		
	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	04/14/2016		J(1) 		1,200,000	D	(1)	5,453,753	D(2) 		
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					
1. Name and Address of Reporting Person*
Third Rock Ventures II, L.P.	

(Last)	(First)	(Middle)	
C/O THIRD ROCK VENTURES, LLC	
29 NEWBURY STREET, 3RD FLOOR	

(Street) 
BOSTON	MA	02116	

(City)	(State)	(Zip)	
	
1. Name and Address of Reporting Person*
Third Rock Ventures GP II, L.P.	

(Last)	(First)	(Middle)	
29 NEWBURY STREET, 3RD FLOOR	

(Street) 
BOSTON	MA	02116	

(City)	(State)	(Zip)	
	
1. Name and Address of Reporting Person*
TRV GP II, LLC	

(Last)	(First)	(Middle)	
29 NEWBURY STREET, 3RD FLOOR	

(Street) 
BOSTON	MA	02116	

(City)	(State)	(Zip)	
	
1. Name and Address of Reporting Person*
LEVIN MARK J	

(Last)	(First)	(Middle)	
C/O THIRD ROCK VENTURES, LLC	
29 NEWBURY STREET, 3RD FLOOR	

(Street) 
BOSTON	MA	02116	

(City)	(State)	(Zip)	
	
1. Name and Address of Reporting Person*
STARR KEVIN P	

(Last)	(First)	(Middle)	
C/O THIRD ROCK VENTURES, LLC	
29 NEWBURY STREET, 3RD FLOOR	

(Street) 
BOSTON	MA	02116	

(City)	(State)	(Zip)	
	
1. Name and Address of Reporting Person*
TEPPER ROBERT I	

(Last)	(First)	(Middle)	
C/O THIRD ROCK VENTURES, LLC	
29 NEWBURY STREET, 3RD FLOOR	

(Street) 
BOSTON	MA	02116	

(City)	(State)	(Zip)	
	
Explanation of Responses:	
1. On April 14, 2016, Third Rock Ventures II, L.P. ("TRV II") distributed, for no consideration, 1,200,000 shares of Common Stock of the Issuer (the "Shares") to its limited partners and to Third Rock Ventures GP II, L.P. ("TRV GP II"), the general partner of TRV II, representing each such partner's pro rata interest in such Shares. On the same date, TRV GP II distributed, for no consideration, the Shares it received in the distribution by TRV II to its limited partners and to its general partner, TRV GP II, LLC ("TRV GP II LLC"), representing each such partner's pro rata interest in such Shares. On the same date, TRV GP II LLC, distributed, for no consideration, the Shares it received in the distribution by TRV GP II to its members in an amount equal to each such member's respective pro rata interest in such Shares. All of the aforementioned distributions were made in accordance with the exemptions afforded by Rules 16a-13 and 16a-9 of the Securities Exchange Act of 1934, as amended.	
2. These shares are directly held by TRV II. The general partner of TRV II is TRV GP II. The general partner of TRV GP II is TRV GP II LLC. The individual managers of TRV GP II LLC are Mark Levin ("Levin"), Kevin Starr ("Starr") and Dr. Robert Tepper ("Tepper"). Each of TRV GP II, TRV GP II LLC, Levin, Starr and Tepper disclaims beneficial ownership of the shares except to the extent of its or his pecuniary interest therein, if any, and this report shall not be deemed an admission that it or he is the beneficial owner of such shares.	
Remarks:	
	
	/s/ Kevin Gillis, Chief Financial Officer of TRV GP II, LLC, general partner of Third Rock Ventures GP II, L.P., general partner of Third Rock Ventures II, L.P.	04/15/2016	
	/s/ Kevin Gillis, Chief Financial Officer of TRV GP II, LLC, general partner of Third Rock Ventures GP II, L.P.	04/15/2016	
	/s/ Kevin Gillis, Chief Financial Officer of TRV GP II, LLC	04/15/2016	
	/s/ Kevin Gillis by power of attorney for Mark Levin	04/15/2016	
	/s/ Kevin Gillis by power of attorney for Kevin Starr	04/15/2016	
	/s/ Kevin Gillis by power of attorney for Dr. Robert Tepper	04/15/2016	
	** 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).	
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.	
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