CONTINGENT VALUE RIGHTS AGREEMENT By and between AVENTIS INC. and CONTINENTAL STOCK TRANSFER & TRUST COMPANY as Rights Agent Dated as of

CONTINGENT VALUE RIGHTS AGREEMENT

TRANSFER & TRUST COMPANY

Dated as of July 15, 2025

Annex A - Form of Assignment and Assumption Agreement

CONTINGENT VALUE RIGHTS AGREEMENT

This CONTINGENT VALUE RIGHTS AGREEMENT, dated as of July 15, 2025 (this Agreement ), by and between Aventis Inc., a

Pennsylvania corporation ( Parent ), and Continental Stock Transfer & Trust Company, a New York corporation (the Rights Agent ), is made in favor of each person who from time to time holds one or more

contingent value rights to receive up to two (2) contingent cash payments (each such contingent value right, a CVR ), subject to the terms and conditions set forth herein.

WHEREAS, this Agreement is entered into pursuant to the Agreement and Plan of Merger, dated June 2, 2025 (as amended, restated,

supplemented, waived or otherwise modified from time to time, the Merger Agreement ), by and among Blueprint Medicines Corporation, a Delaware corporation (the Company ), SANOFI, a French

soci t anonyme ( Ultimate Parent ), Parent and Rothko Merger Sub, Inc., a Delaware corporation wholly owned by Parent ( Merger Sub ), pursuant to which

(i) Merger Sub has made a tender offer (as it may be extended and amended from time to time as permitted under the Merger Agreement, the Offer ) to acquire all of the issued and outstanding shares of common stock, par value

$0.001 per share, of the Company (such shares, collectively, the Common Shares ) and (ii) following consummation of the Offer, Merger Sub will be merged with and into the Company (the Merger ), with the

Company continuing as the surviving corporation in the merger and as a wholly owned Subsidiary of Parent (the Surviving Corporation ) in accordance with Section 251(h) of the DGCL and on the terms and subject to the conditions

set forth in the Merger Agreement;

WHEREAS, pursuant to the terms of the Merger Agreement, as a result of the consummation of the Offer

and the Merger, the holders of Common Shares and holders of Company Equity Awards will become entitled to receive the Milestone Payments contingent upon the achievement of the applicable Milestones during each Milestone Period, subject to the terms

and conditions of this Agreement; and

WHEREAS, pursuant to this Agreement, the maximum amount payable per CVR is $6.00 in cash, without

NOW, THEREFORE, in consideration of the foregoing and the consummation of the transactions referred to above, Parent and the

Rights Agent agree, for the equal and proportionate benefit of all Holders (as hereinafter defined), as follows:

Section 1.1 Definitions. Capitalized terms used in this Agreement and not otherwise defined shall have the meanings assigned to

them in the Merger Agreement. For purposes of this Agreement, the following terms shall have the following meanings:

Holders means, at the time of determination, the Holders of at least 35% of the outstanding CVRs as set forth in the CVR Register.

Affiliate means, with respect to any Person, any other Person that, now

or in the future, directly, or indirectly through one or more intermediaries, Controls, is Controlled by, or is under common Control with, the first Person specified, but only for so long as such Control exists. For the purposes of this definition,

Controls, Controlled and Control mean the possession, directly or indirectly, of the power to direct or cause the direction of the management and policies of a Person, whether through the ownership of voting

securities or partnership or other ownership interests, by Contract or otherwise.

Assignment Transaction means any

transaction (including a sale of assets, spinoff, split-off or licensing transaction), other than a Change in Control, pursuant to which rights in and to the Product are sold, licensed, assigned or transferred

to or acquired by any Person other than Ultimate Parent or any of Ultimate Parent s Subsidiaries or controlled Affiliates. For purposes of clarification, an Assignment Transaction shall not apply to sales of the Product made

by Ultimate Parent or its Subsidiaries or controlled Affiliates or ordinary course licensing arrangements between Ultimate Parent and its Subsidiaries or controlled Affiliates, on the one hand, and third party licensees, distributors and contract

manufacturers, on the other hand, entered into in the ordinary course of business for purposes of developing, manufacturing, distributing or selling the Product.

Business Day means a day except a Saturday, a Sunday or any other day on which commercial banks in New York, New York USA

or in Paris, France are authorized or required by Law to be closed.

Change in Control means (i) a merger or

consolidation in which Parent is a constituent party and is not the surviving entity, other than any merger or consolidation between or among Parent and any of Ultimate Parent s wholly-owned Subsidiaries pursuant to which the surviving entity

assumes all the obligations of Parent under this Agreement (an Internal Transaction ), (ii) any merger or consolidation in which Parent is the surviving entity but in which the stockholders of Parent immediately prior to such

transaction own less than fifty percent (50%) of the voting power of Parent immediately after such transaction, other than an Internal Transaction, or (iii) any other transaction pursuant to which rights in and to the Product are transferred or

acquired by any Person, by operation of law, other than by Ultimate Parent or any of Ultimate Parent s Subsidiaries or controlled Affiliates.

Company Equity Award means, collectively, all Company Stock Options, Company RSUs and Company PSUs outstanding under any

Company Equity Plan as of immediately prior to the Effective Time.

Company Equity Plan means, collectively,

(i) the Company s 2015 Stock Option and Incentive Plan, (ii) the Company s 2020 Inducement Plan, and (iii) the Company s 2024 Stock Incentive Plan, each as amended.

Diligent Efforts means, with respect to the Product and Parent s obligations hereunder, the efforts of a Person to

carry out its obligations or tasks in a diligent and sustained manner without undue pause, interruption or delay, which level of efforts is consistent with the level of efforts devoted by Parent and its Affiliates to the development and seeking of

regulatory approval (including Regulatory Approval) of its other pharmaceutical compounds, products or

therapies owned by Parent and its Affiliates, or to which Parent and its Affiliates have exclusive rights, which are of similar commercial and market potential as the Product, and at a similar

stage in their development or product life as the Product, taking into account all relevant factors, including issues of safety, tolerability and efficacy, benefit/risk product profile, difficulty in developing or manufacturing the Product, market

exclusivity, the competitiveness of alternate products in the marketplace or under development, the availability of existing forms or dosages of the Product or other indication(s), the launch or sales of a generic or compounding pharmacy product,

the patent or other proprietary position of the Product, other issues of market exclusivity and the regulatory environment and the profitability of the Product (including pricing and reimbursement status achieved), Ultimate Parent s portfolio

at the time of consideration and other technical, commercial, legal, scientific and/or medical factors for the Product. For the avoidance of doubt, the Diligent Efforts definition is subject to Section 4.5 and

shall not be deemed to require Parent to take steps to pursue the Product for more than two (2) indications in parallel.

Equity Award Holder means a Holder of a CVR that was granted, in accordance with the terms of the Merger Agreement, with

respect to a Company Equity Award.

FDA means the U.S. Food and Drug Administration.

Governmental Authority means any court, nation, government, any state or other political subdivision thereof and any entity

exercising executive, legislative, judicial, regulatory or administrative functions of, or pertaining to or on behalf of, government.

Holder means a Person in whose name a CVR is registered in the CVR Register at the applicable time.

Law means any applicable domestic, federal, state, municipal, local, national, supranational, foreign or other statute, law

(whether statutory or common law), constitution, code, ordinance, rule, administrative interpretation, regulation, order, writ, judgment, decree, license, permit or any other enforceable requirement of any Governmental Authority.

Milestone means each of Milestone One and Milestone Two, as the context requires. For clarity, the plural form

Milestones shall mean both Milestone One and Milestone Two collectively.

Milestone Achievement

Notice means each of the Milestone One Achievement Notice or the Milestone Two Achievement Notice, as the context requires.

Milestone Payment means each of the Milestone One Payment or Milestone Two Payment, as the context requires. For clarity,

the plural form Milestone Payments shall mean both the Milestone One Payment and the Milestone Two Payment collectively.

Milestone Payment Amount means, for a given Holder, with respect to the achievement of the applicable Milestone, a one-time payment equal to the product of (a) the applicable Milestone Payment and (b) the number of CVRs held by such Holder as reflected on the CVR Register as of the close of business on the date of the

applicable Milestone Achievement Notice.

Milestone Payment Date means each of the Milestone One Payment Date or

Milestone Two Payment Date, as the context requires. For clarity, the plural form Milestone Payment Dates shall mean both the Milestone One Payment Date and the Milestone Two Payment Date, collectively.

Milestone One means the dosing of the fifth patient in the first Phase 2b Study or the first Phase 3 Study (whichever

occurs first) for the Product in any indication.

Milestone One Payment means an amount per CVR equal to $2.00, which

shall become payable upon the achievement of Milestone One.

Milestone One Payment Date means the date that is selected

by Parent not more than ten (10) Business Days following the end of the quarter in which the applicable Milestone Payment Amounts can be determined following the occurrence of Milestone One.

Milestone One Period means the period commencing as of the Effective Time and ending on December 31, 2028.

Milestone Period means each of the Milestone One Period or the Milestone Two Period, as the context requires.

Milestone Two means receipt from the FDA by Parent or its Affiliates (including the Surviving Corporation) or their

(sub)licensees of Regulatory Approval for the Product.

Milestone Two Payment means an amount per CVR equal to $4.00,

which shall become payable upon the achievement of Milestone Two.

Milestone Two Payment Date means the date that is

selected by Parent not more than ten (10) Business Days following the end of the quarter in which the applicable Milestone Payment Amounts can be determined following the occurrence of Milestone Two.

Milestone Two Period means the period commencing as of the Effective Time and ending on June 30, 2032.

Officer s Certificate means a certificate signed by the chief executive officer, chief financial

officer, any vice president, the controller, the treasurer or the secretary, in each case of Parent, in his or her capacity as such an officer (and not in any individual capacity), and delivered to the Rights Agent or any other Person authorized to

act on behalf of Parent.

Opinion of Counsel means a written opinion of counsel, who may be counsel for Parent or its

Subsidiaries and who shall be reasonably acceptable to the Rights Agent.

Party shall mean the Rights Agent and Parent.

Permitted Transfer means a transfer of a CVR: (i) upon the death of a Holder by will or intestacy, (ii) by

instrument to an inter vivos or testamentary trust in which the CVRs are to be passed to beneficiaries upon the death of the trustee, (iii) pursuant to a court order, (iv) by operation of law (including by consolidation or merger)

or without consideration in connection

with the dissolution, liquidation or termination of any corporation, limited liability company, partnership or other entity, (v) in the case of CVRs payable to a nominee, from a nominee to a

beneficial owner (and, if applicable, through an intermediary) or from such nominee to another nominee for the same beneficial owner, in each case to the extent allowable by DTC, or (vi) as permitted by Section 2.7.

Phase 2b Study means a human clinical trial of the Product that is: (i) generally consistent with 21 C.F.R.