LIMITED POWER OF ATTORNEY

      The  undersigned  hereby  constitutes  and appoints each of Tracey McCain,
Christopher  Frankenfield,  Xing  Yan,  Ariel Hurley and Michael Landsittel, and
each   of   them   individually,  and  with  full  power  of  substitution,  the
undersigned's true and lawful attorney-in-fact to:

      (1)   Complete  and  execute  for and on behalf of the undersigned, in the
            undersigned's  capacity  as  an officer, director and/or ten percent
            (10%)  shareholder  of  Blueprint  Medicines Corporation, a Delaware
            corporation  (the  "Company"), any and all instruments, certificates
            and  documents  required to be executed on behalf of the undersigned
            as  an  individual  or  on  behalf  of  the undersigned's company or
            partnership,  as the case may be, pursuant to Section 13 and Section
            16 of the Securities Exchange Act of 1934, as amended (the "Exchange
            Act") or the rules and regulations thereunder;

      (2)   Do and perform any and all acts for and on behalf of the undersigned
            which may be necessary or desirable to complete and execute any such
            instruments, certificates or documents required to be filed pursuant
            to  Sections  13  and  16  of  the  Exchange  Act  or  the  rules or
            regulations  thereunder  and  timely file such forms with the United
            States  Securities and Exchange Commission and any stock exchange or
            similar authority; and

      (3)   Take  any other action of any type whatsoever in connection with the
            foregoing  which, in the opinion of such attorney-in-fact, may be of
            benefit  to,  in  the  best interest of, or legally required by, the
            undersigned,  it being understood that the documents executed by any
            such  attorney-in-fact on behalf of the undersigned pursuant to this
            Power of Attorney shall be in such form and shall contain such terms
            and   conditions  as  such  attorney-in-fact  may  approve  in  such
            attorney-in-fact's discretion.

      The  undersigned  hereby  grants  to  each  such  attorney-in-fact, acting
singly,  full  power  and authority to do and perform any and every act which is
necessary,  proper  or desirable to be done in the exercise of any of the rights
and  powers  herein  granted,  as  fully  to  all  intents  and  purposes as the
undersigned  might  or  could  do  if  personally  present,  with  full power of
substitution  or  revocation,  hereby ratifying and confirming all that any such
attorney-in-fact,  or  any  such  attorney-in-fact's  substitute or substitutes,
shall  lawfully  do  or cause to be done by virtue of this Power of Attorney and
the rights and powers herein granted.

      The undersigned acknowledges that each of the foregoing attorneys-in-fact,
in serving in such capacity at the request of the undersigned, are not assuming,
nor is the Company assuming, any of the undersigned's responsibilities to comply
with  Section  13  or Section 16 of the Exchange Act or the rules or regulations
thereunder. The undersigned hereby agrees to indemnify each attorney-in-fact and
the  Company  from and against any demand, damage, loss, cost or expense arising
from  any  false  or  misleading information provided by the undersigned to such
attorney-in fact.

      This  Power  of  Attorney  shall remain in full force and effect until the
undersigned  is  no  longer  required  to file any instruments, certificates and
documents  pursuant  to  Section  13  and 16 of the Exchange Act or the rules or
regulations  thereunder  with  respect  to  the  undersigned's  holdings  of and
transactions  in securities issued by the Company, unless earlier revoked by the
undersigned in a signed writing delivered to the foregoing attorneys-in-fact.

      IN  WITNESS  WHEREOF, the undersigned has caused this Power of Attorney to
be executed as of January 11, 2021.


                                   By:   /s/ Becker Hewes
                                         ---------------------------------------
                                   Name: L. Becker Hewes