Adage Capital Management, L.P., along with managing members Robert Atchinson and Phillip Gross, filed an amended Schedule 13G with the SEC on November 12, 2026, disclosing a 5.93% beneficial ownership position in Equillium, Inc. as of September 30, 2026.

Key Highlights

  • Aggregate beneficial ownership: Adage Capital Management, Robert Atchinson, and Phillip Gross each report 3,966,917 shares of Equillium common stock beneficially owned.
  • Ownership percentage: The 3,966,917 shares represent 5.93% of Equillium's outstanding common stock, according to the filing.
  • Warrants included: Of the 3,966,917 shares, 3,442,514 are shares of common stock issuable upon exercise of warrants directly held by Adage Capital Partners, L.P.
  • Voting structure: All three reporting persons report zero sole voting power and zero sole dispositive power, with shared voting and dispositive power each reported as 3,966,917 shares.
  • Share count basis: The 5.93% figure is calculated against 63,408,082 shares outstanding as of August 7, 2026, as reported in Equillium's quarterly report for the period ended June 30, 2026.
  • Event date: The date of the event requiring this filing is stated as September 30, 2026.

Adage Capital's Position in Equillium and the Structure of the Filing

According to the amended Schedule 13G, Adage Capital Management, L.P. ("ACM") acts as the investment manager of Adage Capital Partners, L.P. ("ACP"), the entity that directly holds the common stock and warrants of Equillium, Inc. (NASDAQ:EQ). Equillium is a Delaware corporation headquartered at 2223 Avenida De La Playa, Suite 105, La Jolla, California 92037. The filing is designated Amendment No. 2, indicating this is a revised version of a previously submitted ownership statement.

Robert Atchinson and Phillip Gross are each identified in the filing as managing members of Adage Capital Advisors, L.L.C. and related general partner entities that sit within the Adage organizational structure. As a result, both individuals share in the voting and dispositive power attributed to the 3,966,917 shares held through ACP. The filing notes that 3,442,514 of those shares are not currently outstanding common stock but are instead issuable upon exercise of warrants held by ACP, a detail that the filing explicitly incorporates into the total beneficial ownership count and the resulting 5.93% class percentage.

The filing states that the securities "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 Equillium, reproducing the standard certification language included in Schedule 13G filings. All three reporting persons list their business address as 200 Clarendon Street, 52nd Floor, Boston, Massachusetts 02116. ACM is classified as an investment adviser and limited partnership; Atchinson and Gross are classified as holding company persons and individuals.

What Was Disclosed

Adage Capital Management, L.P., Robert Atchinson, and Phillip Gross filed an amended beneficial ownership report covering 3,966,917 shares, including 3,442,514 warrant-linked shares, representing 5.93% of Equillium, Inc. common stock as of September 30, 2026.