EX-5.1

Exhibit 5.1

LOGO

Chadwick L. Mills

+1 650 843 5654

cmills@cooley.com

August 4, 2022

Cerus Corporation

1220 Concord Ave., Suite 600

Concord, California 94520

Re:

Registration on Form S-8

Ladies and Gentlemen:

We have acted as counsel to Cerus Corporation, a Delaware corporation (the “Company”), in connection with the filing of a registration statement on Form S-8 (the “Registration Statement”) with the Securities and Exchange Commission covering the offering of up to 12,000,000 shares of the Company’s Common Stock, $0.001 par value per share, to be issued pursuant to the Company’s Amended and Restated 2008 Equity Incentive Plan (the “Plan”).

In connection with this opinion, we have examined and relied upon (a) the Registration Statement and related prospectus, (b) the Plan, (c) the Company’s Amended and Restated Certificate of Incorporation and Amended and Restated Bylaws, as currently in effect, and (d) originals or copies certified to our satisfaction of such records, documents, certificates, memoranda and other instruments as in our judgment are necessary or appropriate to enable us to render the opinion expressed below. We have assumed the genuineness of all signatures, the authenticity of all documents submitted to us as originals and the conformity to originals of all documents submitted to us as copies, the accuracy, completeness and authenticity of certificates of public officials, and the due authorization, execution and delivery, by all persons other than by the Company, of all documents where authorization, execution and delivery are prerequisites to the effectiveness thereof. As to certain factual matters, we have relied upon a certificate of an officer of the Company and have not independently verified such matters.

Our opinion is expressed only with respect to the General Corporation Law of the State of Delaware. We express no opinion to the extent that any other laws are applicable to the subject matter hereof and express no opinion and provide no assurance as to compliance with any federal or state securities law, rule or regulation.

On the basis of the foregoing, and in reliance thereon, we are of the opinion that the Shares, when sold and issued in accordance with the Plan, and the Registration Statement and related prospectuses, will be validly issued, fully paid and nonassessable (except as to Shares issued pursuant to deferred payment arrangements, which will be fully paid and nonassessable when such deferred payments are made in full).