13G Filing: Biotechnology Value Fund LP and Blueprint Medicines Corp (BPMC)

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Item 2(d). Title of Class of Securities:

Common Stock, $0.001 par value (the “Common Stock”)

Item 2(e). CUSIP Number:

09627Y109

Item 3. If This Statement is Filed Pursuant to Rule 13d-1(b), or 13d-2(b) or (c), Check Whether the Person
Filing is a:
/x/ Not applicable.
(a) / / Broker or dealer registered under Section 15 of the Exchange Act.
(b) / / Bank as defined in Section 3(a)(6) of the Exchange Act.
(c) / / Insurance company as defined in Section 3(a)(19) of the Exchange Act.
(d) / / Investment company registered under Section 8 of the Investment Company Act.
(e) / / An investment adviser in accordance with Rule 13d-1(b)(1)(ii)(E).
(f) / / An employee benefit plan or endowment fund in accordance with Rule 13d-1(b)(1)(ii)(F).
(g) / / A parent holding company or control person in accordance with Rule 13d-1(b)(1)(ii)(G).
(h) / / A savings association as defined in Section 3(b) of the Federal Deposit Insurance Act.
(i) / / A church plan that is excluded from the definition of an investment company under Section 3(c)(14) of the Investment Company Act.
(j) / / Group, in accordance with Rule 13d-1(b)(1)(ii)(J).
(k) / / Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K). If filing as a non-U.S. institution in accordance with Rule 240.13d-1(b)(1)(ii)(J), please specify the type of institution: ____
Item 4. Ownership
(a) Amount beneficially owned:

As of the close of business on May
3, 2017 (i) BVF beneficially owned 945,674 shares of Common Stock, (ii) BVF2 beneficially owned 568,797 shares of Common Stock,
and (iii) Trading Fund OS beneficially owned 111,366 shares of Common Stock.

Partners OS as the general partner
of Trading Fund OS may be deemed to beneficially own the 111,366 shares of Common Stock beneficially owned by Trading Fund OS.

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