EX-5.1

Exhibit 5.1

LOGO

Chadwick L. Mills

+1 650 843 5654

cmills@cooley.com

January 30, 2020

Cerus Corporation

1220 Concord Avenue, Suite 660

Concord, CA 94520

Ladies and Gentlemen:

You have requested our opinion, as counsel to Cerus Corporation, a Delaware corporation (the “Company”), with respect to certain matters in connection with the offering by the Company of up to 16,866,667 shares of its common stock, par value $0.001 (the “Shares”), including up to 2,200,000 Shares that may be sold pursuant to the exercise of an option to purchase additional Shares, pursuant to a Registration Statement on Form S-3 (Registration Statement No. 333-219727) (the “Registration Statement”), filed with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended (the “Act”), the prospectus included within the Registration Statement (the “Base Prospectus”), and the prospectus supplement, dated January 28, 2020, and filed with the Commission pursuant to Rule 424(b) under the Act (together with the Base Prospectus, the “Prospectus”).

In connection with this opinion, we have examined and relied upon the Registration Statement, the Prospectus, the Company’s Amended and Restated Certificate of Incorporation, the Company’s Amended and Restated Bylaws and 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. In rendering this opinion, we have assumed the genuineness and authenticity of all signatures on signed documents; the authenticity of all documents submitted to us as originals; 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 of all documents by all persons other than the Company where due authorization, execution and delivery are a prerequisite to the effectiveness thereof. As to certain factual matters, we have relied upon a certificate of an officer of the Company and have not sought to independently verify such matters.

Our opinion herein is expressed solely 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 Registration Statement and the Prospectus, will be validly issued, fully paid and nonassessable.

COOLEY LLP 101 CALIFORNIA STREET 5TH FLOOR SAN FRANCISCO, CA 94111-5800

T: (415) 693-2000 F: (415) 693-2222 COOLEY.COM


Sincerely,

COOLEY LLP

By:		/s/ Chadwick L. Mills
		Chadwick L. Mills