Seres Therapeutics to Host Webcast on July 8, 2026, to Discuss Results of Investigator-Sponsored Trial of Seres’ SER-155 in Immune Checkpoint Inhibitor-Related Enterocolitis

CAMBRIDGE, Mass., June 25, 2026 (GLOBE NEWSWIRE) -- Seres Therapeutics, Inc. (Nasdaq: MCRB), a leading live biotherapeutics company, today announced that it will host a webcast to discuss top-line results from an investigator-sponsored trial (IST) evaluating SER-155 in patients with immune checkpoint inhibitor-related enterocolitis, a serious and frequent side effect of immune checkpoint inhibitor cancer therapy. The IST was conducted at Memorial Sloan Kettering Cancer Center, with which Seres has a long history of collaboration, by Principal Investigator David Faleck, M.D., Director of Inflammatory and Immune-Related Bowel Diseases. The webcast will occur on July 8, 2026, at 8:30 am ET.

To access the conference call, please dial 800-715-9871 (domestic) or 646-307-1963 (international) and reference the conference ID number 3327556. To join the live webcast, please visit the "Events and Presentations" tab within the "Investors and News" section of the Seres website at https://www.serestherapeutics.com. The webcast will be available for replay following the event.

About Immune Checkpoint Inhibitors and the Investigator-Sponsored Trial (NCT06801067)
Immune checkpoint inhibitors (ICI) have transformed cancer treatment across multiple tumor types, but they frequently trigger immune-mediated adverse events, including enterocolitis. ICIs now represent one of the largest and fastest-growing segments of the oncology market. Immune checkpoint inhibitor-related enterocolitis (irEC) is among the most frequent and severe immune-related adverse events in ICI recipients. Current standard of care for those who suffer from moderate to severe irEC (in the US this approximates 25% of all ICI recipients) requires halting their ICI cancer therapy and initiating an immunosuppressive corticosteroid, further compromising the patient's immune system. A significant unmet need remains for immunosuppressive-free therapeutic approaches that reduce gastrointestinal inflammation and diarrhea and may allow patients that develop irEC to avoid disruption of their ICI therapy.

This investigator-sponsored, open-label trial (IST) (NCT06801067) evaluated SER-155 in 15 participants with Grade 2-3 (moderate to severe) irEC who were naïve to immunosuppressive therapy. The primary efficacy endpoint is the proportion of participants achieving an immunosuppressive-free clinical response on Day 15, defined as at least a 1-grade improvement in diarrhea symptoms, without the need for toxic immunosuppressive therapy such as corticosteroids. The study is also evaluating the safety, tolerability and drug pharmacology of SER-155. The IST is designed to inform if SER-155 may provide an alternate treatment for irEC with the potential to prevent interruption of the patient's ICI cancer treatment.

About Seres Therapeutics
Seres Therapeutics, Inc. (Nasdaq: MCRB) is a clinical-stage biotechnology company developing novel live biotherapeutics, with a focus on therapies that allow patients to maintain their cancer care, and that treat inflammatory and immune diseases. The Company led the development and FDA approval of VOWST™, the first orally administered microbiome therapeutic, which was subsequently divested to Nestlé Health Science. SER-155, which has received Breakthrough Therapy and Fast Track designations, is being advanced for the prevention of bloodstream infections in patients undergoing allogeneic hematopoietic stem cell transplant (allo-HSCT), and is Phase 2 ready, pending receipt of funding. An investigator-sponsored trial of SER-155 in immune checkpoint inhibitor-related enterocolitis (irEC) to further evaluate the potential breadth of the Company's live biotherapeutic platform is ongoing. The Company is advancing IND-enabling studies for SER-603, which is in development for inflammatory bowel disease. Mechanistically, Seres' biotherapeutics target the mucosal epithelial barrier-immune interface and are optimized to modulate host function to increase epithelium integrity, induce immune homeostasis, and prevent the colonization and overgrowth of harmful bacteria in the gastrointestinal tract. For more information, please visit www.serestherapeutics.com.

Forward-Looking Statements
This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. All statements contained in this press release that do not relate to matters of historical fact should be considered forward-looking statements, including statements about: the anticipated content and timing of upcoming webcasts, conference calls and data readouts; SER-155 and its intended uses and benefits in irEC and other indications; potential accessibility for patients; clinical development plans for SER-155; the timing and results of our clinical studies; the anticipated timing of any of the foregoing; and other statements that are not historical fact.
These forward-looking statements are based on management's current expectations. These statements are neither promises nor guarantees, but involve known and unknown risks, uncertainties and other important factors that 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, including, but not limited to, the following: (1) our need for additional funding; (2) our ability to continue as a going concern; (3) we have incurred significant losses, are not currently profitable and may never become profitable; (4) our cost reduction actions may not achieve their intended benefits, including an extended cash runway; (5) our limited operating history;(6) we may not be able to realize the anticipated benefits of the VOWST sale, and may face new challenges as a smaller, less diversified company; (7) we have in the past and may in the future receive notice of the failure to satisfy a continued listing rule from The Nasdaq Stock Market LLC; (8) our novel approach to therapeutic intervention; (9) our reliance on third parties to conduct our clinical trials and manufacture our product candidates; (10) our ability to achieve market acceptance necessary for commercial success; (11) the competition we will face; (12) our ability to protect our intellectual property; (13) impact of our recent management transitions and appointments and our ability, to retain key personnel; and (14) disruptions at the FDA or other government agencies. These and other important factors discussed under the caption "Risk Factors" in our Quarterly Report on Form 10Q for the quarterly period ended May 5, 2026, as well as our other reports filed with the SEC, could cause actual results to differ materially from those indicated by the forward-looking statements made in this press release. Any such forward-looking statements represent management's estimates as of the date of this press release. While we may elect to update such forward-looking statements at some point in the future, except as required by law, we disclaim any obligation to do so, even if subsequent events cause our views to change. These forward-looking statements should not be relied upon as representing our views as of any date subsequent to the date of this press release.

Investor and Media Contacts:[email protected]

Carlo Tanzi, Ph.D.Kendall Investor [email protected]