Equillium, Inc.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K

(Mark One)

☒ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the fiscal year ended December 31, 2025

OR

☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 FOR THE TRANSITION PERIOD FROM TO

Commission File Number 001-38692

EQUILLIUM, INC.

(Exact name of registrant as specified in its Charter)

Registrant’s telephone number, including area code: (858)240-1200

Securities registered pursuant to Section 12(b) of the Act:

Securities registered pursuant to 12(g) of the Act: None

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes ☐No ☒

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or 15(d) of the Act. Yes ☐No ☒

Indicate by check mark whether the registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes ☒ No ☐

Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files). Yes ☒ No ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Indicate by check mark whether the registrant has filed a report on and attestation to its management’s assessment of the effectiveness of its internal control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act (15 U.S.C. 7262(b)) by the registered public accounting firm that prepared or issued its audit report.☐

If securities are registered pursuant to Section 12(b) of the Act, indicate by check mark whether the financial statements of the registrant included in the filing reflect the correction of an error to previously issued financial statements.☐

Indicate by check mark whether any of those error corrections are restatements that required a recovery analysis of incentive-based compensation received by any of the registrant’s executive officers during the relevant recovery period pursuant to § 240.10D-1(b). ☐

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). Yes ☐ No☒

The aggregate market value of the voting and non-voting common equity held by non-affiliates of the registrant as of June 30, 2025 (the last business day of the registrant’s most recently completed second fiscal quarter) was approximately $7.1 million based on the closing price of the registrant’s common stock on June 30, 2025 of $0.32 per share, as reported by the Nasdaq Capital Market. Shares of the registrant's common stock held by executive officers, directors and registrant's affiliates have been excluded from this calculation. This determination of affiliate status is not necessarily a conclusive determination for other purposes.

As of March 20, 2026, there were 63,226,556 shares of the registrant’s common stock outstanding.

DOCUMENTS INCORPORATED BY REFERENCE

Part III of this Annual Report on Form 10-K incorporates by reference certain information from the registrant’s definitive Proxy Statement for its 2026 annual meeting of stockholders, which the registrant intends to file pursuant to Regulation 14A with the Securities and Exchange Commission not later than 120 days after the registrant’s fiscal year end of December 31, 2025. Except with respect to information specifically incorporated by reference in this Form 10-K, the Proxy Statement is not deemed to be filed as part of this Form 10-K.

Table of Contents

SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This Annual Report on Form 10-K contains forward-looking statements. The forward-looking statements are contained principally in the sections entitled “Risk Factors,” “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and “Business.” These statements relate to future events or to our future financial performance and involve known and unknown risks, uncertainties and other factors which may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements. Forward-looking statements include, but are not limited to, statements about:

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our ability to obtain funding for our operations, including funding necessary to commence and complete the preclinical and clinical studies of our product candidates;

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our plans to research, develop and commercialize our product candidates and any future product candidates;

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our ability to obtain and maintain regulatory approval for our product candidates in any of the indications for which we plan to develop them;

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our estimated timeline for announcing data from our clinical studies, for interacting with regulatory authorities, and for initiating preclinical and clinical studies;

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the success, cost, and timing of our product development activities, including our ongoing and planned preclinical and clinical studies;

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the beneficial characteristics, safety, efficacy, and therapeutic effects of our product candidates;

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the size of the markets for our product candidates, and our ability to serve those markets;

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the rate and degree of market acceptance of any of our product candidates;

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our ability to develop and maintain sales and marketing capabilities, whether alone or with potential future collaborators;

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existing regulations and regulatory developments in the United States and in other territories where we may conduct business, including the clinical development and potential commercialization of our product candidates;

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the performance of our contract service providers, including suppliers and manufacturers;

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the safety, efficacy and market success of competing therapies that are or become available;

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our ability to attract and retain key scientific or management personnel;

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our ability to attract and retain collaborators with development, regulatory and commercialization expertise;

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the accuracy of our estimates regarding expenses, future revenues, capital requirements and needs for additional financing; and

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our expectations regarding our ability to obtain and maintain intellectual property protection for our product candidates and our ability to operate our business without infringing on the intellectual property rights of others.

In some cases, you can identify these statements by terms such as “anticipate,” “believe,” “could,” “estimate,” “expects,” “intend,” “may,” “plan,” “potential,” “predict,” “project,” “should,” “will,” “would” or the negative of those terms, and similar expressions that convey uncertainty of future events or outcomes. These forward-looking statements reflect our management’s beliefs, opinions and views with respect to future events and are based on estimates, assumptions and information available to us as of the date of this Annual Report on Form 10-K, and while we believe such information forms a reasonable basis for such statements, such information may be limited or incomplete and our statements should not be read to indicate that we have conducted an exhaustive inquiry into, or review of, all potentially available relevant information. These statements are inherently uncertain and are subject to risks and uncertainties. We discuss many of these risks in greater detail under the heading “Risk Factors.” Moreover, we operate in a very competitive and rapidly changing environment. New risks emerge from time to time. It is not possible for our management to predict all risks, nor can we assess the impact of all factors on our business or the extent to which any factor, or combination of factors, may cause actual results to differ materially from those contained in any forward-looking statements we may make. Given these uncertainties, you should not place undue reliance on these forward-looking statements.

You should carefully read this Annual Report on Form 10-K and the documents that we reference herein and have filed as exhibits to the Annual Report on Form 10-K completely and with the understanding that our actual future results may be materially different from what we expect. We qualify all of the forward-looking statements in this Annual Report on Form 10-K by these cautionary statements.

Except as required by law, we assume no obligation to update these forward-looking statements publicly, or to update the reasons actual results could differ materially from those anticipated in any forward-looking statements, whether as a result of new information, future events or otherwise.

RISK FACTORS SUMMARY

We face many risks and uncertainties, as more fully described in this section under the heading “Risk Factors.” Some of these risks and uncertainties are summarized below. The summary below does not contain all of the information that may be important to you, and you should read this summary together with the more detailed discussion of these risks and uncertainties contained in “Risk Factors.”

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We have incurred significant losses since our inception, expect to incur significant losses for the foreseeable future and may never achieve or maintain profitability;

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We will require substantial additional funding to complete the planned or future development and any commercialization of EQ504, EQ302 and any future product candidates. If we are unable to raise this capital when needed, we may be forced to delay, reduce or eliminate our research and development programs or other operations;

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Raising additional equity capital may cause dilution to our stockholders, and raising additional equity or debt capital may restrict our operations or require us to relinquish rights to our technologies or product candidates;

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We are highly dependent on the successful planned or future development of our current product candidates, EQ504 and EQ302, and we may not be able to obtain regulatory or marketing approval of, or successfully commercialize, these product candidates in any of the indications for which we plan to develop them;

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Any delays in the commencement and completion, or any termination or suspension, of our planned or future clinical studies could result in increased costs to us, and delay or limit our ability to raise capital or generate revenue and adversely affect our commercial prospects;

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Interim, topline or preliminary data from our planned or future clinical studies that we announce or publish from time to time may change as more patient data become available and are subject to audit and verification procedures that could result in material changes in the final data;

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We currently have no marketing and sales organization and have no experience as a company in commercializing products and we may have to invest significant resources to develop these capabilities. If we are unable to establish marketing and sales capabilities or enter into agreements with contracted third parties to market and sell any of our products if and when approved, we may not be able to generate product revenue;

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The manufacture of pharmaceutical products is complex and we may encounter difficulties in production, distribution and delivery of our product candidates. If CMOs encounter such difficulties, our ability to provide supply of our product candidates for our planned or future clinical studies, our ability to obtain marketing approval, or our ability to obtain commercial supply of our products, if approved, could be delayed or stopped;

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International trade policies, including tariffs, sanctions and trade barriers may adversely affect our business, financial condition, results of operations and prospects;

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We rely, and intend to continue to rely, on CROs to conduct our planned or future clinical studies and perform some of our planned or future research and nonclinical studies. If these third parties do not satisfactorily carry out their contractual duties, fail to comply with applicable regulatory requirements or meet expected deadlines, our development programs may be delayed or subject to increased costs or we may be unable to obtain regulatory approval, each of which may have an adverse effect on our business, financial condition, results of operations and prospects;

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If we are unable to obtain or protect intellectual property rights covering our product candidates, or if the scope of the intellectual property protection is not sufficiently broad, our competitors could develop and commercialize products similar or identical to our product candidates, and we may not be able to compete effectively in our market;

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Even if our product candidates receive marketing approval in any indication, they may fail to achieve the degree of market acceptance by physicians, patients, hospitals, healthcare payors and others in the medical community necessary for commercial success; and

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We have in the past and may in the future fail to maintain compliance with the listing requirements of the Nasdaq Capital Market, and as a result, our common stock may be delisted from the Nasdaq Capital Market which could have a material adverse effect on our financial condition and could make it difficult for you to sell your shares.