Thomas A. Coll
+1 858 550 6013
collta@cooley.com
February 23, 2024
Equillium, Inc.
2223 Avenida de la Playa, Suite 105
La Jolla, CA 92037
Ladies and Gentlemen:
We have acted as counsel to
Equillium, Inc., a Delaware corporation (the Company), in connection with the offering by the Company of shares (the Shares) of its common stock, par value $0.0001 per share (the Common
Stock), having aggregate offering price of up to $21,950,000 pursuant to the Registration Statement on Form S-3 (File No. 333-269153) (the
Registration Statement) filed with the Securities and Exchange Commission (the Commission) under the Securities Act of 1933, as amended (the Securities Act), the
prospectus included in the Registration Statement (the Base Prospectus) and the prospectus supplements relating to the Shares dated October 5, 2023, and February 23, 2024, filed with the Commission pursuant to
Rule 424(b) under the Securities Act (together with the Base Prospectus, the Prospectus). The Shares are to be sold by the Company in accordance with that certain Open Market Sale AgreementSM, dated October 5, 2023, by and between the Company and Jefferies LLC (the Agreement), as described in the Prospectus.
In connection with this opinion, we have examined and relied upon (a) the Registration Statement and the Prospectus, (b) the Agreement,
(c) the Companys certificate of incorporation and bylaws, each as currently in effect, and (d) such other records, documents, opinions, certificates, memoranda and 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; 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 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.
We have assumed (i) that each sale of Shares will be duly authorized by the Board of Directors of the Company, a duly authorized committee thereof
or a person or body pursuant to an authorization granted in accordance with Section 152 of the General Corporation Law of the State of Delaware (the DGCL), (ii) that no more than $21,950,000 Shares will be sold under
the Agreement pursuant to the Prospectus and (iii) that the price at which the Shares are sold will equal or exceed the par value of the Shares. We express no opinion to the extent that future issuances of securities of the Company,
anti-dilution adjustments to outstanding securities of the Company or other matters cause the number of shares of Common Stock issuable under the Agreement to exceed the number of shares of Common Stock available for issuance by the Company.
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