Form SC 13G Blueprint Medicines Corp Filed by: FMR LLC

SCHEDULE 13G
 
Amendment No. 0
BLUEPRINT MEDICINES CORP
COMMON STOCK
Cusip #09627Y109
Check the appropriate box to designate the rule pursuant to which this 
Schedule is filed:
[ ] 	  Rule 13d-1(b)
[x] 	  Rule 13d-1(c)
[ ] 	  Rule 13d-1(d)
Cusip #09627Y109
Item 1: 	   	Reporting Person - FMR LLC
Item 2: 	   	(a)  	[ ]
   	   	(b)  	[ ]
Item 4: 	   	Delaware
Item 5: 	   	2,505,611
Item 6: 	   	0
Item 7: 	   	2,520,454
Item 8: 	   	0
Item 9: 	   	2,520,454
Item 11: 	   	9.757%
Item 12: 	   	HC
Cusip #09627Y109
Item 1: 	   	Reporting Person - Edward C. Johnson 3d
Item 2: 	   	(a)  	[ ]
   	   	(b)  	[ ]
Item 4: 	   	United States of America
Item 5: 	   	0
Item 6: 	   	0
Item 7: 	   	2,520,454
Item 8: 	   	0
Item 9: 	   	2,520,454
Item 11: 	   	9.757%
Item 12: 	   	IN
Cusip #09627Y109
Item 1: 	   	Reporting Person - Abigail P. Johnson
Item 2: 	   	(a)  	[ ]
   	   	(b)  	[ ]
Item 4: 	   	United States of America
Item 5: 	   	0
Item 6: 	   	0
Item 7: 	   	2,520,454
Item 8: 	   	0
Item 9: 	   	2,520,454
Item 11: 	   	9.757%
Item 12: 	   	IN
 
Item 1(a). 	    	Name of Issuer:
 
  	  	          	BLUEPRINT MEDICINES CORP
 
Item 1(b). 	    	Address of Issuer's Principal Executive Offices:
 
  	  	          	215 First Street
  	  	          	Cambridge, MA 02142
  	  	          	USA
 
Item 2(a). 	     	 Name of Person Filing:
 
  	   	               	 FMR LLC
 
Item 2(b). 	     	 Address or Principal Business Office or, if None, 
Residence:
 
  	   	               	 245 Summer Street, Boston, Massachusetts 02210
 
Item 2(c). 	     	 Citizenship:
 
  	   	               	 Not applicable
 
Item 2(d). 	     	 Title of Class of Securities:
 
  	   	               	 COMMON STOCK
 
Item 2(e). 	     	 CUSIP Number:
 
  	   	               	 09627Y109
 
Item 3. 	    	Not Applicable
 
Item 4. 	    	Ownership
 
  	  	     	(a)    Amount Beneficially Owned: 	2,520,454
 
  	  	     	(b)    Percent of Class: 	9.757%
 
  	  	     	(c)    Number of shares as to which such person has:
 
  	  	     	       (i)    sole power to vote or to direct the vote: 	
2,505,611
 
  	  	     	       (ii)    shared power to vote or to direct the vote: 	0
 
  	  	     	       (iii)    sole power to dispose or to direct the 
disposition of: 	2,520,454
 
  	  	     	       (iv)    shared power to dispose or to direct the 
disposition of: 	0
 
Item 5. 	    	Ownership of Five Percent or Less of a Class.
 
  	    	     	Not applicable.
 
Item 6. 	    	Ownership of More than Five Percent on Behalf of Another 
Person.
 
  	 Various persons have the right to receive or the power to direct the 
receipt of dividends from, or the proceeds from the sale of, the COMMON 
STOCK of BLUEPRINT MEDICINES CORP.
  	 
  	 The interest of one person, Beacon Bioventures Advisors Fund III Limited
Partnership, in the COMMON STOCK of BLUEPRINT MEDICINES CORP, amounted to
2,500,711 shares or 9.680% of the total outstanding COMMON STOCK at May 5, 2015.
 
Item 7. 	    	Identification and Classification of the Subsidiary Which 
Acquired the Security Being Reported on By the Parent Holding Company.
 
  	    	     	See attached Exhibit A.
 
Item 8. 	    	Identification and Classification of Members of the Group.
 
  	    	     	Not applicable.
 
Item 9. 	    	Notice of Dissolution of Group.
 
  	    	  	Not applicable.
 
Item 10. 	    	Certifications.
 
  	    	     	

By signing below I certify that, to the best of my knowledge and belief, 
the securities referred to above were not acquired and are not held for the 
purpose of or with the effect of changing or influencing the control of the 
issuer of the securities and were not acquired and are not held in 
connection with or as a participant in any transaction having that purpose 
or effect.

 
Signature
 
  	    	     	

After reasonable inquiry and to the best of my knowledge and belief, I 
certify that the information set forth in this statement is true, complete 
and correct.

  	May 7, 2015
  	Date
 
  	/s/ Scott C. Goebel
  	Signature
 
  	Scott C. Goebel
  	 Duly authorized under Power of Attorney effective as of June 1, 2008, 
by and on behalf of FMR LLC and its direct and indirect subsidiaries*


* This power of attorney is incorporated herein by reference to Exhibit B 
to the Schedule 13G filed by FMR LLC on June 10, 2014, accession number: 
0000315066-14-003512.


Exhibit A
 

                 Pursuant to the instructions in Item 7 of Schedule 13G, 
the following table lists the identity and Item 3 classification, if 
applicable, of each relevant entity that beneficially owns shares of the 
security class being reported on this Schedule 13G.

 
Entity 	ITEM 3 Classification
FMR CO., INC 	IA
IMPRESA MANAGEMENT LLC * 	IA
PYRAMIS GLOBAL ADVISORS TRUST COMPANY 	BK
PYRAMIS GLOBAL ADVISORS, LLC 	IA
  	 
  	 
* Entity beneficially owns 5% or greater of the outstanding shares of the 
security class being reported on this Schedule 13G.
 
 

                Edward C. Johnson 3d is a Director and the Chairman of FMR 
LLC and Abigail P. Johnson is a Director, the Vice Chairman, the Chief 
Executive Officer and the President of FMR LLC.

 

                Members of the family of Edward C. Johnson 3d, including 
Abigail P. Johnson, are the predominant owners, directly or through trusts, 
of Series B voting common shares of FMR LLC, representing 49% of the voting 
power of FMR LLC. The Johnson family group and all other Series B 
shareholders have entered into a shareholders' voting agreement under which 
all Series B voting common shares will be voted in accordance with the 
majority vote of Series B voting common shares. Accordingly, through their 
ownership of voting common shares and the execution of the shareholders' 
voting agreement, members of the Johnson family may be deemed, under the 
Investment Company Act of 1940, to form a controlling group with respect to 
FMR LLC.

 

                Neither FMR LLC nor Edward C. Johnson 3d nor Abigail P. 
Johnson has the sole power to vote or direct the voting of the shares owned 
directly by the various investment companies registered under the 
Investment Company Act ("Fidelity Funds") advised by Fidelity Management & 
Research Company ("FMR Co"), a wholly owned subsidiary of FMR LLC, which 
power resides with the Fidelity Funds' Boards of Trustees. Fidelity 
Management & Research Company carries out the voting of the shares under 
written guidelines established by the Fidelity Funds' Boards of Trustees.

 

                This filing reflects the securities beneficially owned, or 
that may be deemed to be beneficially owned, by FMR LLC, certain of its 
subsidiaries and affiliates, and other companies (collectively, the "FMR 
Reporters"). This filing does not reflect securities, if any, beneficially 
owned by certain other companies whose beneficial ownership of securities 
is disaggregated from that of the FMR Reporters in accordance with 
Securities and Exchange Commission Release No. 34-39538 (January 12, 1998).

 
RULE 13d-1(k)(1) AGREEMENT
 

                The undersigned persons, on May 7, 2015, agree and consent 
to the joint filing on their behalf of this Schedule 13G in connection with 
their beneficial ownership of the COMMON STOCK of BLUEPRINT MEDICINES CORP 
at May 5, 2015.

 
  	FMR LLC
 
  	By /s/ Scott C. Goebel
  	Scott C. Goebel
  	Duly authorized under Power of Attorney effective as of June 1, 2008, by 
and on behalf of FMR LLC and its direct and indirect subsidiaries*
 
  	Edward C. Johnson 3d
 
  	By /s/ Scott C. Goebel
  	Scott C. Goebel
  	Duly authorized under Power of Attorney effective as of June 1, 2008, by 
and on behalf of Edward C. Johnson 3d*
 
  	Abigail P. Johnson
 
  	By /s/ Scott C. Goebel
  	Scott C. Goebel
  	Duly authorized under Power of Attorney effective as of April 24, 2014, 
by and on behalf of Abigail P. Johnson*


* This power of attorney is incorporated herein by reference to Exhibit B 
to the Schedule 13G filed by FMR LLC on June 10, 2014, accession number: 
0000315066-14-003512.

   

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