Adage Capital discloses 7.25% Equillium (EQ) stake via Schedule 13G/A filing

Rhea-AI Filing Summary

Adage Capital Management, L.P. and affiliates report a 7.25% beneficial ownership stake in Equillium, Inc. The group, including Adage Capital Management, Robert Atchinson, and Phillip Gross, reports beneficial ownership of 4,832,767 shares of Equillium common stock, including 3,442,514 shares issuable upon exercise of warrants held by Adage Capital Partners, L.P. The ownership percentage is calculated based on 63,226,556 shares outstanding as of May 8, 2026, as disclosed in Equillium’s Form 10-Q for the quarter ended March 31, 2026. All reported shares are subject to shared voting and shared dispositive power among the reporting persons.

Key Figures

Beneficially owned shares: 4,832,767 shares Ownership percentage: 7.25% Warrant-related shares: 3,442,514 shares +1 more

4 metrics

Beneficially owned shares 4,832,767 shares Shares of Equillium common stock beneficially owned by the reporting persons

Ownership percentage 7.25% Percent of Equillium common stock class beneficially owned by the reporting persons

Warrant-related shares 3,442,514 shares Shares of common stock issuable upon exercise of warrants held by Adage Capital Partners, L.P.

Shares outstanding baseline 63,226,556 shares Equillium common shares outstanding as of May 8, 2026, used to compute ownership percentage

Key Terms

beneficial ownership, shared voting power, shared dispositive power, Schedule 13G/A, +1 more

5 terms

beneficial ownership financial

"The filing of this statement should not be construed in and of itself as an admission by any Reporting Person as to beneficial ownership of the securities reported herein."

Beneficial ownership means the person or entity that actually enjoys the benefits of owning shares or other assets — such as receiving dividends, voting rights, or price gains — even if the legal title is held in another name. For investors it matters because knowing who truly controls and profits from a company reveals who can influence decisions, exposes potential conflicts of interest or hidden concentration of power, and affects transparency and risk in the stock.

shared voting power financial

"Shared Voting Power 4,832,767.00"

Shared voting power occurs when two or more parties jointly have the right to vote or decide how a block of company shares is cast, like co-owners who must agree before moving a piece of furniture. Investors care because who controls voting rights affects board elections, major corporate decisions and takeover outcomes, and shared control can alter regulatory disclosures and the practical influence any holder has over a company’s direction and value.

shared dispositive power financial

"Shared Dispositive Power 4,832,767.00"

Schedule 13G/A regulatory

"The percentage set forth in this is calculated based upon an aggregate of 63,226,556 shares of Common Stock outstanding..."

A Schedule 13G/A is an amended public filing with the U.S. securities regulator that updates a previous Schedule 13G, disclosing when an individual or group holds a substantial (typically over 5%) stake in a company and is claiming a passive, non‑controlling intent. Investors monitor these updates because rising or falling holdings can signal changing confidence, potential future moves, or shifts in voting power — like watching a public ledger where large shareholders quietly adjust their positions.

warrants financial

"Includes 3,442,514 shares of Common Stock issuable upon exercise of warrants."

Warrants are special documents that give you the right to buy a company's stock at a set price before a certain date. They are often used as a way for companies to attract investors or raise money, and their value can increase if the company's stock price goes up.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Available on EDGAR 08/12/2026 - 12:12 PM Accepted by SEC EDGAR 08/12/2026 - 12:11 PM Learn about SEC filing dates

FAQ

What ownership stake in Equillium, Inc. (EQ) does Adage Capital report?

Adage Capital and related reporting persons report beneficial ownership of 4,832,767 shares of Equillium common stock, representing 7.25% of the class, including shares issuable upon exercise of warrants held by Adage Capital Partners, L.P.

How is the 7.25% beneficial ownership in Equillium (EQ) calculated?

The 7.25% ownership is calculated using 63,226,556 shares of Equillium common stock outstanding as of May 8, 2026, as reported in Equillium’s Form 10-Q for the quarter ended March 31, 2026.

How many Equillium (EQ) shares held by Adage are tied to warrants?

The reporting persons state that their position includes 3,442,514 shares of Equillium common stock issuable upon exercise of warrants directly held by Adage Capital Partners, L.P., forming a substantial portion of the reported beneficial ownership.

Do Adage and its principals have shared voting power over their Equillium (EQ) stake?

Yes. The reporting persons disclose 4,832,767 shares subject to shared voting power and shared dispositive power, with no shares reported under sole voting or sole dispositive power for any of the reporting persons.

Who are the reporting persons on this Schedule 13G/A for Equillium (EQ)?

The filing is made by Adage Capital Management, L.P., and by its associated principals Robert Atchinson and Phillip Gross, each reporting indirect beneficial ownership of Equillium common stock through Adage Capital Partners, L.P. and related entities.

Where is Adage Capital’s business office for this Equillium (EQ) holding?

The business office for each reporting person is listed as 200 Clarendon Street, 52nd Floor, Boston, Massachusetts 02116, which serves as the address for Adage Capital Management and its principals regarding this ownership.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 1)

Equillium, Inc.

(Name of Issuer)

Common Stock, par value $0.0001 per share

(Title of Class of Securities)

29446K106

(CUSIP Number)

06/30/2026

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

Rule 13d-1(b)

Rule 13d-1(c)

Rule 13d-1(d)

schemaVersion:

SCHEDULE 13G

CUSIP Number(s): 29446K106

1

Names of Reporting Persons

Adage Capital Management, L.P.

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 4,832,767.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 4,832,767.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

4,832,767.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

7.25 %

12

Type of Reporting Person (See Instructions)

IA, PN

Comment for Type of Reporting Person: Includes 3,442,514 shares of Common Stock (as defined in Item 2(a)) issuable upon exercise of warrants.

SCHEDULE 13G

CUSIP Number(s): 29446K106

1

Names of Reporting Persons

Robert Atchinson

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 4,832,767.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 4,832,767.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

4,832,767.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

7.25 %

12

Type of Reporting Person (See Instructions)

HC, IN

Comment for Type of Reporting Person: Includes 3,442,514 shares of Common Stock issuable upon exercise of warrants.

SCHEDULE 13G

CUSIP Number(s): 29446K106

1

Names of Reporting Persons

Phillip Gross

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 4,832,767.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 4,832,767.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

4,832,767.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

7.25 %

12

Type of Reporting Person (See Instructions)

HC, IN

Comment for Type of Reporting Person: Includes 3,442,514 shares of Common Stock issuable upon exercise of warrants.

SCHEDULE 13G

Item 1.
(a)	Name of issuer: Equillium, Inc.
(b)	Address of issuer's principal executive offices: 2223 Avenida De La Playa, Suite 105, La Jolla, California 92037
Item 2.
(a)	Name of person filing: This statement is filed by: (i) Adage Capital Management, L.P., a Delaware limited partnership ("ACM"), as the investment manager of Adage Capital Partners, L.P., a Delaware limited partnership ("ACP"), with respect to the common stock, par value $0.0001 per share ("Common Stock") of Equillium, Inc., a Delaware corporation (the "Company"), and shares of Common Stock issuable upon exercise of warrants directly held by ACP; (ii) Robert Atchinson ("Mr. Atchinson"), as (1) managing member of Adage Capital Advisors, L.L.C., a limited liability company organized under the laws of the State of Delaware ("ACA"), managing member of Adage Capital Partners GP, L.L.C., a limited liability company organized under the laws of the State of Delaware ("ACPGP"), general partner of ACP, and (2) managing member of Adage Capital Partners, L.L.C., a Delaware limited liability company ("ACPLLC"), general partner of ACM, with respect to the Common Stock and shares of Common Stock issuable upon exercise of warrants directly held by ACP; and (iii) Phillip Gross ("Mr. Gross"), as (1) managing member of ACA, managing member of ACPGP, and (2) managing member of ACPLLC, general partner of ACM, with respect to the Common Stock and shares of Common Stock issuable upon exercise of warrants directly held by ACP. The foregoing persons are hereinafter sometimes collectively referred to as the "Reporting Persons." Any disclosures herein with respect to persons other than the Reporting Persons are made on information and belief after making inquiry to the appropriate party. The filing of this statement should not be construed in and of itself as an admission by any Reporting Person as to beneficial ownership of the securities reported herein.
(b)	Address or principal business office or, if none, residence: The address of the business office of each of the Reporting Persons is 200 Clarendon Street, 52nd Floor, Boston, Massachusetts 02116.
(c)	Citizenship: ACM is a limited partnership organized under the laws of the State of Delaware. Messrs. Gross and Atchinson are citizens of the United States.
(d)	Title of class of securities: Common Stock, par value $0.0001 per share
(e)	CUSIP No.: 29446K106
Item 3.	If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)	Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)	Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)	Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)	Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)	An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)	An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)	A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)	A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)	A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)	A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J), please specify the type of institution:
(k)	Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.	Ownership
(a)	Amount beneficially owned: The information required by Item 4(a) is set forth in Row 9 of the cover page for each of the Reporting Persons and is incorporated herein by reference. The percentage set forth in this Schedule 13G is calculated based upon an aggregate of 63,226,556 shares of Common Stock outstanding as of May 8, 2026, as reported in the Company's Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2026 filed with the Securities and Exchange Commission on May 13, 2026, and assumes the exercise of the warrants held by ACP.
(b)	Percent of class: 7.25%
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: The information required by Item 4(c)(i) is set forth in Row 5 of the cover page for each of the Reporting Persons and is incorporated herein by reference.
	(ii) Shared power to vote or to direct the vote: The information required by Item 4(c)(ii) is set forth in Row 6 of the cover page for each of the Reporting Persons and is incorporated herein by reference.
	(iii) Sole power to dispose or to direct the disposition of: The information required by Item 4(c)(iii) is set forth in Row 7 of the cover page for each of the Reporting Persons and is incorporated herein by reference.
	(iv) Shared power to dispose or to direct the disposition of: The information required by Item 4(c)(iv) is set forth in Row 8 of the cover page for each of the Reporting Persons and is incorporated herein by reference.
Item 5.	Ownership of 5 Percent or Less of a Class.
	Not Applicable
Item 6.	Ownership of more than 5 Percent on Behalf of Another Person.
	If any other person is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, such securities, a statement to that effect should be included in response to this item and, if such interest relates to more than 5 percent of the class, such person should be identified. A listing of the shareholders of an investment company registered under the Investment Company Act of 1940 or the beneficiaries of employee benefit plan, pension fund or endowment fund is not required. See Item 2(a).
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
	Not Applicable
Item 8.	Identification and Classification of Members of the Group.
	Not Applicable
Item 9.	Notice of Dissolution of Group.
	Not Applicable

Item 10.

Certifications:

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Adage Capital Management, L.P.

Signature:	/s/ Robert Atchinson
Name/Title:	By: Adage Capital Partners, L.L.C., its General Partner, By: Robert Atchinson, its Managing Member
Date:	08/12/2026

Robert Atchinson

Signature:	/s/ Robert Atchinson
Name/Title:	Robert Atchinson, individually
Date:	08/12/2026

Phillip Gross

Signature:	/s/ Phillip Gross
Name/Title:	Phillip Gross, individually
Date:	08/12/2026