CERTAIN IDENTIFIED INFORMATION HAS BEEN EXCLUDED FROM THE EXHIBIT BECAUSE IT IS BOTH (I) NOT MATERIAL AND (II) WOULD BE COMPETITIVELY HARMFUL IF PUBLICLY DISCLOSED. SUCH EXCLUDED INFORMATION HAS BEEN MARKED WITH [***]. A

CERTAIN IDENTIFIED INFORMATION HAS BEEN EXCLUDED FROM THE

EXHIBIT BECAUSE IT IS BOTH (I) NOT MATERIAL AND (II) WOULD BE

COMPETITIVELY HARMFUL IF PUBLICLY DISCLOSED. SUCH EXCLUDED

INFORMATION HAS BEEN MARKED WITH [***].

ASSET PURCHASE AGREEMENT

CATALYST BIOSCIENCES, INC.

VERTEX PHARMACEUTICALS INCORPORATED

Index of Defined Terms

ASSET PURCHASE AGREEMENT

This ASSET PURCHASE AGREEMENT, dated as of May 19, 2022 (this Agreement ), is by and between Catalyst Biosciences,

Inc., a Delaware corporation ( Seller ), and Vertex Pharmaceuticals Incorporated, a Massachusetts corporation ( Purchaser ). Capitalized terms are defined on the pages of this Agreement set forth opposite such

capitalized terms listed in the Index of Defined Terms.

WHEREAS, Seller desires to sell, transfer, assign, convey, and deliver to

Purchaser, and Purchaser desires to purchase, acquire, and accept from Seller, the Transferred Assets and assume the Assumed Liabilities upon the terms and conditions of this Agreement.

WHEREAS, Purchaser and Seller desire to make certain representations, warranties, covenants, and agreements in connection with the Transaction

and prescribe various conditions to the Transaction.

NOW, THEREFORE, in consideration of the foregoing premises, the mutual covenants,

promises, and agreements set forth in this Agreement, the mutual benefits to be gained by the performance thereof, and for other good and valuable consideration, the receipt and sufficiency of which is acknowledged and accepted, the parties,

intending to be legally bound, agree as follows:

ARTICLE 1. DEFINITIONS

Section 1.1 Defined Terms. The following terms have the following meanings:

Action means any claim, action, suit or proceeding, investigation, governmental inquiry, or criminal prosecution.

Affiliate means, when used with respect to a specified Person, another Person that either directly or indirectly, through

one or more intermediaries, controls, is controlled by, or is under common control with, the specified Person. For purposes of this Agreement, control means the possession, directly or indirectly, of the power to direct, or cause

the direction of, the management and policies of a Person, whether through ownership of voting securities, contract or otherwise, and controlled and controlling will have correlative meanings.

Ancillary Agreements means (a) a bill of sale providing for the transfer of the Transferred Assets in the form of

Exhibit A, (b) an assignment and assumption agreement for the assumption of the Assumed Liabilities in the form of Exhibit B, (c) the Patent Assignment Agreement, (d) the Trademark Assignment

Agreement, and (e) each document, certificate, or other instrument required to be delivered under this Agreement or under any other Ancillary Agreement.

Day means a day, other than a Saturday or a Sunday, on which commercial banks are not required or authorized to close in New York City, New York.

Closing Consideration means the Purchase Price minus the Holdback Amount.

Code means the U.S. Internal Revenue Code of 1986.

Consulting Agreement means each of the consulting agreements in a form to be agreed by Purchaser and each individual set

forth on Section 7.1(c) of the Disclosure Schedule following the Closing.

contract, agreement, indenture, note, bond, loan, instrument, lease, conditional sales contract, mortgage, license, or other commitment or arrangement, whether oral or written, that is binding on any Person or any of its property under applicable

Damages means the amount of any loss, claim, tax, demand, damage, deficiency, liability, judgment, royalty, fine,

penalty, cost, or expense (including costs of investigation and out-of-pocket, reasonable attorneys , consultants and experts fees and expenses and

interest and penalties awarded or imposed by a Governmental Entity) incurred, paid, accrued, or sustained by the applicable Purchaser Indemnified Parties; provided, however, that Damages will not include (a) any punitive damages

unless such damages are awarded to a third party, or (b) incidental, special, exemplary, or consequential damages, lost profits, or diminution in value.

Disclosure Schedule means the disclosure letter in respect of this Agreement delivered by one party to the other party

concurrently with the execution and delivery of this Agreement.

Excluded Taxes means any Taxes (a) imposed by any

applicable Law on Seller for any Tax period, other than Property Taxes that are not attributable to a Pre-Closing Tax Period (as determined pursuant to Section 6.1(a)),

(b) imposed on or with respect to the ownership or operation of the Excluded Assets or Retained Liabilities for any Tax period, (c) imposed on or with respect to the acquisition, ownership, or operation of the Transferred Assets for any Pre-Closing Tax Period, (d) that are Property Taxes that are attributable to a Pre-Closing Tax Period (as determined pursuant to

Section 6.1(a)), (e) for which the Purchaser or any of its Affiliates is liable (i) as a transferee or successor to Seller or its Affiliates or (ii) pursuant to any contract entered into by Seller or its

Affiliates prior to the Closing, other than Taxes of another Person owed pursuant to a contract that constitutes a Transferred Asset or Assumed Liability or that is entered into in the ordinary course of business, the purpose of which is not

primarily related to Taxes, and (f) that are Transfer Taxes, in each case other than any Taxes for which Purchaser is liable under the terms of this Agreement including Section 6.1(c).

Exploit means to research, develop, design, test, manufacture, have made, use, sell, offer for sale, import, export,

promote, market, distribute, or otherwise commercialize.

FDA means the United States Food and Drug

Fraud means, with respect to any Person, intentional (and not constructive) misrepresentation in

making of the representations and warranties in Article 4 or Article 5 (as applicable) with the actual knowledge (as opposed to imputed or constructive knowledge or knowledge that could have been obtained after inquiry, or recklessness

or negligence) of such Person that such representation was false when made and upon which the Person to whom such representation was made (the Recipient ) has reasonably relied to its detriment.

GAAP means United States generally accepted accounting principles.

Governmental Entity means any government, any governmental entity,

commission, board, agency, or instrumentality, and any court, tribunal, or judicial body, whether federal, state, county, local, or foreign.

Holdback Amount means $5,000,000.

Intellectual Property Rights means any and all (a) Patents, (b) copyrights, copyright registrations, and

applications therefor and all other rights corresponding thereto, rights in data and databases, moral and economic rights of authors and inventors, however denominated and any similar or equivalent rights to any of the foregoing, (c) trade

names, logos, trade dress, trademarks and service marks, trademark and service mark registrations, trademark and service mark applications, and any and all goodwill associated with and symbolized by the foregoing items, (d) rights associated

with trade secrets, confidential and proprietary information and know-how (including inventions, proprietary processes, formulae, models, and methodologies), industrial designs, and any registrations and

applications therefor, (e) rights of privacy and publicity, (f) social media identifiers and account information and Internet domain names, and (g) other proprietary rights arising under Law, Contract, or otherwise and any other

intellectual property rights or proprietary rights recognized by the Law of each applicable jurisdiction, in each case whether registered or unregistered and including all applications for, and renewals, extensions or reversions of, such rights, and

all similar or equivalent rights or forms of protection in any part of the world.

Inventory means all inventory or

tangible personal property of Seller used, held for use or otherwise consumed in the research, development, or manufacturing of the Products that, as of the Closing, are in the possession or control of Seller, including all raw materials, work-in-process, inventories, compounds, cell lines, assays, reagents, ingredients, and samples, in each case to the extent owned or controlled by Seller or its Affiliates.

Know-How means all existing and available technical information, know-how, and data including inventions (whether patentable or not), discoveries, trade secrets, specifications, information, instructions, processes, formulae, materials, and other technology, in each case as are

used, held for use or otherwise relate to the Products or the Platforms or to their Exploitation, and including all biological, chemical, pharmacological, biochemical, toxicological, pharmaceutical, physical, safety, quality control, preclinical,

and clinical data relating to the Products or the Platforms in the Territory, and that is in existence and owned or controlled by, Seller and/or its Affiliates on the Closing Date.

Knowledge of Seller means the actual knowledge, after due inquiry, of [***].

Law means any and all federal, state, provincial, regional, territorial, and local (a) laws, statutes, statutory

instruments, ordinances, regulations of or by any Governmental Entity, (b) rules, executive orders, consent orders, supervisory requirements, directives, circulars, opinions, interpretive letters, and other office releases, guidelines, and

policies, in each case, with the force of Law, of or by any Governmental Entity, and (c) Orders.

Liabilities means all debts, losses, damages, adverse claims,

obligations, liabilities, or commitments of any nature or kind, in each case whether (a) known or unknown, express or implied, primary or secondary, direct or indirect, liquidated or unliquidated, absolute or contingent, accrued or unaccrued,

due or to become due, matured or unmatured, fixed, disputed, liquidated, executory, determined or determinable, (b) in contract, tort, strict liability, or otherwise (including all costs and expenses related to such Liabilities), or

(c) required to be recorded or reflected on a balance sheet prepared in accordance with GAAP.

security interest, pledge, mortgage, lien, charge, adverse claim of ownership or use, restriction on transfer (such as a right of first refusal or other similar rights), defect of title, or other similar encumbrance.

Order means any order, judgment, injunction, or decree issued, promulgated, or entered by or with any Governmental Entity

of competent jurisdiction.

Patent Assignment Agreement means the Patent assignment agreement in the form of

Patents means the rights and interests in and to issued patents and pending

patent applications in any country, jurisdiction or region (including inventor s certificates and utility models), including all provisionals, non-provisionals, substitutions, continuations, continuations-in-part, divisionals, renewals and all patents granted thereon, and all reissues, reexaminations, extensions, confirmations, revalidations, registrations, and

patents of addition thereof, including patent term extensions and supplementary protection certificates, international patent applications filed under the Patent Cooperation Treaty (PCT) and any foreign equivalents to any of the foregoing.

Permit means any license, franchise, or permit with any Governmental Entity required by Law for the development,

manufacturing, marketing, commercialization, distribution, or sale of the Products, and/or the ownership or use of the Transferred Assets.

Permitted Liens means (a) mechanics , carriers , workmen s, repairmen s or other similar Liens

arising or incurred in the ordinary course of business, and (b) Liens for Taxes and other governmental charges that are not due and payable, or that are being contested in good faith through appropriate proceedings.

Person means any individual, firm, corporation, partnership, limited liability company, trust, joint venture, Governmental

Entity, or other entity.

Platforms means those degrader platforms identified as of the Closing Date as ProTUNE C3b/C4b degrader, ImmunoTune C3a/C5a, and the protease molecular evolution platform, as further described in the Patents set forth on

Section 1.1 of the Disclosure Schedule.

Period means any taxable period (or portion thereof) ending on or before the Closing Date.

(a) CB 4332, [], (b) CB 2782-PEG, a C3 degrader product, (c) [], [], and (d) [].

Property Taxes means real, personal, ad valorem, and intangible property

Taxes and any similar Taxes.