UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE TO

Tender Offer Statement under Section 14(d)(1) or 13(e)(1)

of the Securities Exchange Act of 1934

Blueprint Medicines Corporation

(Name of Subject Company (Issuer))

ROTHKO MERGER SUB, INC.

AVENTIS INC.

SANOFI

(Names of Filing Persons — Offerors)

Common Stock, Par Value $0.001 Per Share

(Title of Class of Securities)

09627Y109

(Cusip Number of Class of Securities)

Roy Papatheodorou

Executive Vice President, General Counsel, Head of Legal Ethics & Business Integrity

Sanofi

46, avenue de la Grande Armée, 75017

Paris, France

Telephone: 011 + 33 1 53 77 40 00

(Name, Address and Telephone Number of Person Authorized to Receive Notices and

Communications on Behalf of Filing Persons)

Copies to:

Michael J. Aiello, Esq.

Sachin Kohli, Esq.

Weil, Gotshal & Manges LLP

767 Fifth Avenue

New York, New York 10153

(212) 310-8000

☐ Check the box if any part of the fee is offset as provided by Rule 0-11(a)(2) and identify the filing with which the offsetting fee was previously paid. Identify the previous filing by registration statement number, or the form or schedule and the date of its filing.

Amount Previously Paid: N/A.	Filing Party: N/A
Form or Registration No.: N/A	Date Filed: N/A

☐ Check the box if the filing relates solely to preliminary communications made before the commencement of a tender offer.

Check the appropriate boxes below to designate any transactions to which the statement relates:

☒ Third-party tender offer subject to Rule 14d-1.

☐ Issuer tender offer subject to Rule 13e-4.

☐ Going-private transaction subject to Rule 13e-3.

☐ Amendment to Schedule 13D under Rule 13d-2.

Check the following box if the filing is a final amendment reporting the results of the tender offer: ☐

If applicable, check the appropriate box(es) below to designate the appropriate rule provision(s) relied upon:

☐ Rule 13e-4(i) (Cross-Border Issuer Tender Offer)

☐ Rule 14d-1(d) (Cross-Border Third-Party Tender Offer)

This Tender Offer Statement on Schedule TO (together with any amendments and supplements hereto, this “Schedule TO”) is filed by (i) Rothko Merger Sub, Inc., a Delaware corporation (“Purchaser”) and an indirect wholly owned subsidiary of SANOFI, a French société anonyme (“Parent”), (ii) Parent and (iii) Aventis Inc., a Pennsylvania corporation and wholly owned subsidiary of Parent and direct parent of Purchaser (“Aventis”). This Schedule TO relates to the offer by Purchaser to purchase all of the outstanding shares of common stock, par value, $0.001 per share (the “Shares”), of Blueprint Medicines Corporation, a Delaware corporation (the “Company”), for $129.00 per Share in cash, without interest (the “Cash Offer Price”) and subject to any withholding of taxes required by applicable legal requirements, plus one (1) non-transferable contractual contingent value right (each, a “CVR”) per Share, representing the right to receive contingent payments of up to an aggregate amount of $6.00 per Share in cash, without interest, upon the achievement of one or both of the milestones on or prior to the expiration of the applicable milestone period set forth in the Contingent Value Rights Agreement (the “CVR Agreement”) to be entered into with a rights agent (the “Rights Agent”) mutually agreeable to Aventis and the Company (the CVR, together with the Cash Offer Price, or any other amount paid pursuant to the Offer to the extent permitted under the Merger Agreement (as defined below), the “Offer Consideration”). Such offer is being made upon the terms and subject to the conditions set forth in the Offer to Purchase, dated June 17, 2025 (together with any amendments or supplements thereto, the “Offer to Purchase”) and in the accompanying Letter of Transmittal, which are annexed to and filed with this Schedule TO as Exhibits (a)(1)(A) and (a)(1)(B), respectively.

All information contained in the Offer to Purchase (including Schedule I to the Offer to Purchase) and the accompanying Letter of Transmittal is hereby expressly incorporated herein by reference in response to Items 1 through 9 and Item 11 of this Schedule TO.

The Agreement and Plan of Merger, dated as of June 2, 2025 (as it may be amended from time to time, the “Merger Agreement”), by and among the Company, Parent, Aventis and Purchaser, a copy of which is attached as Exhibit (d)(1) hereto, is incorporated herein by reference with respect to Items 4 through 9 and 11 of this Schedule TO.

Item 1. Summary Term Sheet.

The information set forth in the “Summary Term Sheet” of the Offer to Purchase is incorporated herein by reference.

Item 2. Subject Company Information.

(a) The name of the subject company and the issuer of the securities to which this Schedule TO relates is Blueprint Medicines Corporation, a Delaware corporation. The Company’s principal executive offices are located at 45 Sidney Street, Cambridge, Massachusetts 02139. The Company’s telephone number is (617) 374-7580.

(b) This Schedule TO relates to the outstanding Shares. The Company has advised Purchaser and Parent that, as of the close of business on June 12, 2025 (the most recent practicable date) 64,733,629 Shares were issued and outstanding.

(c) The information concerning the principal market, if any, in which the Shares are traded and certain high and low sales prices for Shares in the principal market in which the Shares are traded are set forth in Section 6 (entitled “Price Range of Shares; Dividends on the Shares”) of the Offer to Purchase is incorporated herein by reference.

Item 3. Identity and Background of the Filing Person.

(a) – (c) This Schedule TO is filed by Purchaser, Parent and Aventis. The information set forth in Section 8 (entitled “Certain Information Concerning Parent, Aventis, Purchaser and Certain Related Persons”) of the Offer to Purchase and Schedule I to the Offer to Purchase is incorporated herein by reference.

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Item 4. Terms of the Transaction.

(a)(1)(i) – (viii), (x), (xii), (a)(2)(i) – (iv), (vii) The information set forth in the following sections of the Offer to Purchase is incorporated herein by reference:

• the “Summary Term Sheet”

• the “Introduction”

• Section 1 – “Terms of the Offer”

• Section 2 – “Acceptance for Payment and Payment for Shares”

• Section 3 – “Procedures for Accepting the Offer and Tendering Shares”

• Section 4 – “Withdrawal Rights”

• Section 5 – “Certain U.S. Federal Income Tax Consequences of the Offer”

• Section 11 – “The Merger Agreement; The CVR Agreement; Other Agreements”

• Section 12 – “Purpose of the Offer; Plans for the Company”

• Section 13 – “Certain Effects of the Offer”

• Section 15 – “Conditions of the Offer”

• Section 16 – “Certain Legal Matters; Regulatory Approvals”

• Section 17 – “Appraisal Rights”

• Section 19 – “Miscellaneous”

(a)(1)(ix) and (xi), (a)(2)(v) – (vi) Not applicable.

Item 5. Past Contacts, Transactions, Negotiations and Agreements.

(a), (b) The information set forth in the following sections of the Offer to Purchase is incorporated herein by reference:

• the “Summary Term Sheet”

• the “Introduction”

• Section 7 – “Certain Information Concerning the Company”

• Section 8 – “Certain Information Concerning Parent, Aventis, Purchaser and Certain Related Persons”

• Section 10 – “Background of the Offer; Past Contacts or Negotiations with the Company”

• Section 11 – “The Merger Agreement; The CVR Agreement; Other Agreements”

• Section 12 – “Purpose of the Offer; Plans for the Company”

• Schedule I

Item 6. Purposes of the Transaction and Plans or Proposals.

(a), (c)(1) – (7) The information set forth in the following sections of the Offer to Purchase is incorporated herein by reference:

• the “Summary Term Sheet”

• the “Introduction”

• Section 6 – “Price Range of Shares; Dividends on the Shares”

• Section 10 – “Background of the Offer; Past Contacts or Negotiations with the Company”

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• Section 11 – “The Merger Agreement; The CVR Agreement; Other Agreements”

• Section 12 – “Purpose of the Offer; Plans for the Company”

• Section 13 – “Certain Effects of the Offer”

• Schedule I

Item 7. Source and Amount of Funds or Other Consideration.

(a), (b) The information set forth in the following sections of the Offer to Purchase is incorporated herein by reference:

• the “Summary Term Sheet”

• the “Introduction”

• Section 9 – “Source and Amount of Funds”

(d) Not applicable.

Item 8. Interest in Securities of the Subject Company.

(a) The information set forth in the following sections of the Offer to Purchase is incorporated herein by reference:

• the “Summary Term Sheet”

• Section 8 – “Certain Information Concerning Parent, Aventis, Purchaser and Certain Related Persons”

• Section 11 – “The Merger Agreement; The CVR Agreement; Other Agreements”

• Section 12 – “Purpose of the Offer; Plans for the Company”

• Schedule I

(b) The information set forth in the following sections of the Offer to Purchase is incorporated herein by reference:

• Section 8 – “Certain Information Concerning Parent, Aventis, Purchaser and Certain Related Persons”

• Schedule I

Item 9. Persons/Assets, Retained, Employed, Compensated or Used.

(a) The information set forth in the following sections of the Offer to Purchase is incorporated herein by reference:

• the “Summary Term Sheet”

• Section 3 – “Procedures for Accepting the Offer and Tendering Shares”

• Section 10 – “Background of the Offer; Past Contacts or Negotiations with the Company”

• Section 18 – “Fees and Expenses”

Item 10. Financial Statements.

(a), (b) Not applicable.

Item 11. Additional Information.

(a)(1) The information set forth in the following sections of the Offer to Purchase is incorporated herein by reference:

• Section 8 – “Certain Information Concerning Parent, Aventis, Purchaser and Certain Related Persons”

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• Section 10 – “Background of the Offer; Past Contacts or Negotiations with the Company”

• Section 11 – “The Merger Agreement; The CVR Agreement; Other Agreements”

• Section 12 – “Purpose of the Offer; Plans for the Company”

(a)(2) The information set forth in the following sections of the Offer to Purchase is incorporated herein by reference:

• Section 12 – “Purpose of the Offer; Plans for the Company”

• Section 15 – “Conditions of the Offer”

• Section 16 – “Certain Legal Matters; Regulatory Approvals”

(a)(3) The information set forth in the following sections of the Offer to Purchase is incorporated herein by reference:

• Section 15 – “Conditions of the Offer”

• Section 16 – “Certain Legal Matters; Regulatory Approvals”

(a)(4) The information set forth in the following sections of the Offer to Purchase is incorporated herein by reference:

• Section 13 – “Certain Effects of the Offer”

(a)(5) The information set forth in the following sections of the Offer to Purchase is incorporated herein by reference:

• Section 16 – “Certain Legal Matters; Regulatory Approvals”

(c) The information set forth in the Offer to Purchase is incorporated herein by reference.

Item 12. Exhibits.

Exhibit No.	Description
(a)(1)(A)	Offer to Purchase, dated June 17, 2025.*
(a)(1)(B)	Letter of Transmittal (including Guidelines for Certification of Taxpayer Identification Number on IRS Form W-9).*
(a)(1)(C)	Letter to Brokers, Dealers, Commercial Banks, Trust Companies and Other Nominees.*
(a)(1)(D)	Letter to Clients for use by Brokers, Dealers, Commercial Banks, Trust Companies and Other Nominees.*
(a)(1)(E)	Form of Notice of Guaranteed Delivery.*
(a)(1)(F)	Summary Advertisement as published in the New York Times, dated June 17, 2025.*
(a)(5)(A)	Joint Press Release of Sanofi and Blueprint Medicines Corporation, dated June  2, 2025 (incorporated herein by reference to Exhibit 99.1 to the Schedule TO-C filed by Parent on June 2, 2025).
(a)(5)(B)	Post on employee portal to certain Sanofi employees from Brian Foard, dated June  2, 2025 (incorporated herein by reference to Exhibit 99.1 to the Schedule TO-C filed by Parent on June 2, 2025).

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Exhibit No.	Description
(a)(5)(C)	Post on employee portal to Sanofi research and development organization from Houman Ashrafian, dated June  2, 2025 (incorporated herein by reference to Exhibit 99.2 to the Schedule TO-C filed by Parent on June 2, 2025).
(a)(5)(D)	Social media posts on Sanofi’s LinkedIn and X accounts, dated June  2, 2025 (incorporated herein by reference to Exhibit 99.3 to the Schedule TO-C filed by Parent on June 2, 2025).
(a)(5)(E)	Slide deck presented on investor relations call, dated June  2, 2025 (incorporated herein by reference to Exhibit 99.4 to the Schedule TO-C filed by Parent on June 2, 2025).
(a)(5)(F)	Post on employee portal to Sanofi employees, dated June 2, 2025 (incorporated herein by reference to Exhibit 99.5 to the Schedule TO-C filed by Parent on June 2, 2025).
(a)(5)(G)	Investor Relations call transcript, dated June 2, 2025 (incorporated herein by reference to Exhibit 99.6 to the Schedule TO-C filed by Parent on June 2, 2025).
(a)(5)(H)	Social media post on Sanofi CEO Paul Hudson’s LinkedIn account, dated June  3, 2025 (incorporated herein by reference to Exhibit 99.1 to the Schedule TO-C filed by Parent on June 2, 2025).
(d)(1)	Agreement and Plan of Merger, dated as of June  2, 2025, by and among Parent, Purchaser, Aventis and the Company (incorporated herein by reference to Exhibit 2.1 to the Form 8-K filed by the Company on June 2, 2025).
(d)(2)	Confidentiality Agreement between the Company and Parent dated as of May 17, 2024.*
(d)(3)	Amendment No. 1 to the Confidentiality Agreement between the Company and Parent dated as of November 5, 2024.*
(d)(4)	Amendment No. 2 to the Confidentiality Agreement between the Company and Parent dated as of May 17, 2025.*
(d)(5)	Exclusivity Agreement between the Company and Parent dated as of May 18, 2025.*
(d)(6)	Form of Contingent Value Rights Agreement (incorporated herein by reference to Exhibit 2.1 to the Form 8-K filed by the Company on June 2, 2025).
(g)	Not applicable.
(h)	Not applicable.
107	Filing Fee Table.*

* Filed herewith

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SIGNATURES

After due inquiry and to the best knowledge and belief of the undersigned, each of the undersigned certifies that the information set forth in this statement is true, complete and correct.

Date: June 17, 2025

Rothko Merger Sub, Inc.
By:	/s/ Michael J. Tolpa
	Name: Michael J. Tolpa
	Title: President

SANOFI
By:	/s/ Roy Papatheodorou
	Name: Roy Papatheodorou
	Title: Executive Vice President, General Counsel

Aventis Inc.
By:	/s/ Jamie Haney
	Name: Jamie Haney
	Title: Vice President, General Counsel, Secretary