Data highlight both SER-603's rational design that targets microbial functions linked to mucosal healing and gastrointestinal inflammation in IBD, as well as the advancement of microbiome-based biomarkers that inform response to biologics and patient stratification

Presentation selected for DDW ‘Poster of Distinction' recognition

CAMBRIDGE, Mass., May 04, 2026 (GLOBE NEWSWIRE) -- Seres Therapeutics, Inc. (NASDAQ:MCRB) (Seres or the Company), a leading live biotherapeutics company, today announced new preclinical data supporting the design and potential of SER-603, a next-generation cultivated live biotherapeutic candidate for inflammatory bowel disease (IBD), being presented at Digestive Disease Week (DDW) 2026, taking place May 2–5, 2026, in Chicago, IL. The poster, titled "The Rational Design of SER-603: A Next Generation Cultivated Microbial Consortia to Treat IBD," which has been selected as a DDW ‘Poster of Distinction,' highlights Seres' integrated approach to the design of microbiome therapeutics, combining rational strain selection and a novel biomarker-driven patient stratification.

"We are advancing next-generation live biotherapeutics through a rational, data-driven design strategy to address underlying drivers of IBD that current therapeutics do not," said Matthew Henn, Ph.D., President and Chief Scientific Officer of Seres. "SER-603 is designed to enable more precise modulation of inflammatory pathways relevant to IBD by combining the targeting of microbial functions linked to epithelial barrier integrity and mucosal healing with a biomarker-based approach to patient stratification. By leveraging insights from clinical datasets and translational models, we have developed a consortium intended to achieve durable drug strain engraftment and targeted modulation of disease-relevant inflammatory pathways. We are advancing SER-603 through IND-enabling activities and have engaged potential collaborators to support clinical development, including evaluation as both a monotherapy and in combination with existing treatment approaches."

Current therapies for IBD focus primarily on the downstream consequences of inflammation, specifically suppressing cytokine-induced inflammation by broadly suppressing the immune system, and do not address two additional drivers of disease: mucosal barrier compromise and inflammation inducing bacteria in the gastrointestinal (GI) tract. SER-603 is optimized to modulate the GI microbiome to reduce microbial inflammatory stimuli, induce mucosal healing and reduce barrier damage that can allow translocation of inflammatory bacteria and molecules. The mechanisms of action of SER-603 are complementary to existing therapeutics, providing the opportunity for both mono- and combination therapy, potentially without added toxicities given live biotherapeutics historical favorable safety profile. SER-603 incorporates strains selected for engraftment and delivery of clinically relevant metabolites, including short-chain fatty acids, secondary bile acids, and tryptophan-derived molecules, with a therapeutic goal of inducing mucosal healing and regulating inflammatory pathways central to IBD pathophysiology, without immunosuppression. Its design integrates insights from human clinical datasets and reverse translational approaches to identify strains linked to key functional outputs, enabling targeted modulation of inflammatory microbiome features, and is complemented by microbiome-based biomarkers associated with GI inflammation, to support patient stratification and to enrich for those most likely to benefit. In the MiGUT in vitro gut model, which recapitulates patient-derived IBD microbiomes, SER-603 reduced inflammatory cytokine production across multiple samples, supporting its potential to impact disease-relevant biology and providing translational support for its mechanism of action.

Presentations Details

Poster Presentation (Su1462)

Title: The Rational Design of SER-603: A Next Generation Cultivated Microbial Consortia to Treat IBD

Session: 7165

Date and Time: May 3 at 12:30-1:30 pm

Presenter: Nicholas Beauchemin

About Seres Therapeutics

Seres Therapeutics, Inc. (NASDAQ:MCRB) is a clinical-stage biotechnology company developing novel live biotherapeutics, with a focus on 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 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 is ongoing in immune checkpoint inhibitor–related enterocolitis (irEC) to further evaluate the potential breadth of the Company's live biotherapeutic platform. SER-603, in development for irritable Inflammatory bowel disease, is designed to modulate the gastrointestinal microbiome and support mucosal barrier integrity by targeting inflammatory bacteria and associated metabolites. 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 presentations and conferences; the design, timing and results of our pre-clinical and clinical studies and data readouts; current or future product candidates and their potential impacts and outcomes; clinical development plans and commercial opportunities; our efforts to create a strategic, R&D, or other partnership; the advancement of IND-enabling activities; our ability to operationalize a study upon receipt of any financing; our planned strategic focus; 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) the expected payments from the VOWST sale are subject to risks and uncertainties; (7) 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; (8) 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; (9) our novel approach to therapeutic intervention; (10) our reliance on third parties to conduct our clinical trials and manufacture our product candidates; (11) our ability to achieve market acceptance necessary for commercial success; (12) the competition we will face; (13) our ability to protect our intellectual property; (14) impact of our recent management transitions and appointments and our ability, to retain key personnel; and (15) disruptions at the FDA or other government agencies. These and other important factors discussed under the caption "Risk Factors" in our Annual Report on Form 10-K for the fiscal year ended December 31, 2025 filed with the Securities and Exchange Commission (SEC) , 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, we disclaim any obligation to do so, even if subsequent events cause our views to change except as required by law. 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:

IR@serestherapeutics.com

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Seres Therapeutics Presents Preclinical Data at Digestive Disease Week (DDW) 2026 Supporting SER-603, a Next-Generation Cultivated Live Biotherapeutic Candidate, for Inflammatory Bowel Disease