MCRB

EX-99.1

2 d124829dex991.htm

EX-99.1

EX-99.1

Exhibit 99.1

SERES THERAPEUTICS REPORTS SECOND QUARTER 2026 FINANCIAL RESULTS AND PROVIDES BUSINESS UPDATES, INCLUDING

FURTHER ACTION TO REDUCE ONGOING FACILITIES COSTS

Recently announced 80% of SER-155 recipients achieved immunosuppressive-free clinical response at day 15 for immune checkpoint inhibitor-related enterocolitis (irEC) in the investigator-sponsored trial (IST) conducted by Memorial Sloan Kettering Cancer Center (MSK)

IST data support SER-155 as a potential treatment for irEC that may allow patients to continue

cancer therapy; Company evaluating irEC clinical development strategy in consultation with KOLs

Seres engaging potential partners, seeking capital to advance its SER-155 programs, including for the prevention of bloodstream infections in patients undergoing allo-HCT and those experiencing irEC

Seres announces agreement to exit additional leased space early, further reducing ongoing facility-related cash costs, which follows announcement of balance sheet strengthening and facilities cost reduction transactions in June 2026

CAMBRIDGE, Mass.- August 5, 2026 — Seres Therapeutics, Inc. (Nasdaq: MCRB), (Seres or the Company), a leading live biotherapeutics company, today reported second quarter 2026 financial results and provided business updates.

“We are very pleased with the recent progress at Seres, including the positive topline data from the investigator-sponsored trial of SER-155 in irEC conducted by MSK, announced last month,” said Richard Kender, Executive Chairman and Interim Chief Executive Officer of Seres. “The study demonstrated that 80% of participants achieved an immunosuppressive-free clinical response at day 15, and the accompanying pharmacology data reinforced that our live biotherapeutic operated as designed, including by repairing the mucosal epithelial barrier. SER-155 to treat irEC, a frequent and often severe side effect of widely used immune checkpoint inhibitor (ICI) cancer treatment, represents a meaningful therapeutic and commercial opportunity, as many patients who experience irEC are required to halt their ICI therapy and begin immunosuppressive corticosteroid treatment. We are engaging potential partners, including companies with ICI franchises, as we evaluate the clinical development pathway in this indication and consider sources of financing. In parallel, we continue to pursue partnerships and other financing sources to support development of SER-155 in allo-HCT, and to advance our broader inflammatory and immune portfolio, including SER-603 for inflammatory bowel disease.”

Marella Thorell, Chief Financial Officer of Seres, added, “Terminating our Sidney Street lease will substantially reduce our future lease obligations and will further lower our ongoing annual fixed costs beginning in 2027. Together with the lease restructuring we announced in June, this transaction reflects our continued focus on rigorous financial discipline, while we maintain the operational infrastructure needed to advance our live biotherapeutic pipeline, including our Phase 2-ready SER-155 program in allo-HCT.”

Recent Highlights

SER-155 in immune checkpoint inhibitor-related enterocolitis (irEC)

•

In July, Seres announced positive topline results from the IST of SER-155 in irEC (NCT06801067) conducted at MSK. The open-label study evaluated SER-155 in 15 participants with moderate-to-severe (Grade 2-3) irEC who were naïve to immunosuppressive therapy. irEC is among the most frequent and severe immune-related adverse reactions in recipients of ICI therapy and, at the moderate-to-severe grade, affects approximately 25% of ICI recipients in the US.

•

In the study, 12 of 15 participants (80%) achieved an immunosuppressive-free clinical response at day 15, the primary efficacy endpoint, defined as at least a 1-grade improvement in diarrhea symptoms without immunosuppressive therapy. SER-155 was generally well tolerated with no safety concerns identified and no serious adverse events assessed as related to SER-155.

•

Participants in the study were on a wide range of ICI types, including PD-1 inhibitors (Keytruda®, Opdivo®, Zynyz®), PD-L1 inhibitors (Imfinzi®, Bavencio®), CTLA-4 inhibitors (Yervoy®, Imjudo®), LAG-3 inhibitor (Opdualag®), and combinations thereof. The promising study results support continued development of SER-155 to treat irEC and the Company is engaging potential partners, including companies with ICI franchises, as it evaluates next steps for the development of SER-155 in irEC.

Broader pipeline and portfolio

•

SER-155 remains Phase 2 ready for the prevention of bloodstream

infections in patients undergoing allogeneic hematopoietic stem cell transplant (allo-HCT) for the treatment of blood cancer. SER-155 has received Breakthrough Therapy and Fast Track designations for this indication. Efforts to secure funding to advance clinical development for this program continue.

•

The Company continues to advance IND-e

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8-K

false 0001609809 0001609809 2026-03-12 2026-03-12

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): March 12, 2026

SERES THERAPEUTICS, INC.

(Exact name of Registrant as Specified in Its Charter)

Delaware

001-37465

27-4326290

(State or other jurisdiction of incorporation)

(Commission File Number)

(IRS Employer Identification No.)

101 Cambridgepark Drive

Cambridge, MA

02140

(Address of principal executive offices)

(Zip Code) Registrant’s telephone number, including area code: (617) 945-9626 Not Applicable (Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

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

Title of each class

Trading Symbol(s)

Name of each exchange on which registered

Common stock, par value $0.001 per share

MCRB

The Nasdaq Stock Market LLC

(Nasdaq Global Select Market) Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter). Emerging growth company ☐ 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. ☐

Item 2.02. Results of Operations and Financial Condition.

On March 12, 2026, Seres Therapeutics, Inc. (the “Company”) announced its financial results for the quarter and year ended December 31, 2025 and provided operational updates. The full text of the press release issued in connection with the announcement is furnished as Exhibit 99.1 to this Current Report on Form 8-K (the “Current Report”).

Item 7.01. Regulation FD Disclosure.

On March 12, 2026, the Company posted an updated corporate presentation in the “Investors and News” portion of its website at www.serestherapeutics.com. A copy of the slide presentation is attached as Exhibit 99.2 to this Current Report and incorporated herein by reference. The information in Items 2.02 and 7.01 of this Current Report, including Exhibits 99.1 and 99.2 attached hereto, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such filing.

Item 9.01. Financial Statements and Exhibits.

(d) Exhibits The following Exhibits 99.1 and 99.2 relate to Items 2.02 and 7.01, respectively, and shall be deemed to be furnished, and not filed:

Exhibit No.

Description

99.1

Seres Therapeutics, Inc. Press Release issued March 12, 2026

99.2

Seres Therapeutics, Inc. Corporate Presentation as of March 2026

104

Cover Page Interactive Data File (embedded within the Inline XBRL document)

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

SERES THERAPEUTICS, INC.

Date: March 12, 2026

By:

/s/ Thomas J. DesRosier

Name:

Thomas J. DesRosier

Title:

Executive Vice President and Chief Legal Officer