Data demonstrate clinical translation of VOWST mechanisms of action in both first and multiply recurrent CDI patients

Seres MbTx® platform provides high-resolution functional biological understanding of live biotherapeutics and supports the advancement of Seres’ portfolio, including Phase 2-ready lead candidate SER-155

CAMBRIDGE, Mass., Jan. 06, 2026 (GLOBE NEWSWIRE) -- Seres Therapeutics, Inc. (Nasdaq: MCRB), a leading live biotherapeutics company, today announced the publication of two manuscripts in Nature Medicine and the Journal of Infectious Diseases highlighting new insights into the functional mechanism and clinical impact of VOWST™. Together, these publications provide further validation of the Company’s Live Biotherapeutics Products (LBPs) approach and inform the continued development of Seres’ pipeline of next-generation LBPs, including its lead investigational candidate, SER-155.

Seres led the development and FDA approval of VOWST™, a rationally selected consortia of bacteria in oral capsules that was designed to have specific functional pharmacological properties with clinical translation of these MoAs observed in the ECOSPOR III and IV Phase 3 trials. VOWST was the first-ever oral microbiome biotherapeutic licensed by the FDA, with approval in April 2023 for the prevention of recurrent Clostridioides difficile (rCDI) infection. VOWST was sold to Nestlé Health Science in September 2024.

The Nature Medicine article, titled “The impact of an oral purified microbiome therapeutic on the gastrointestinal microbiome”, confirmed Seres pharmacological hypotheses from earlier VOWST studies, with higher VOWST dosing associated with enhanced pharmacokinetics, as assessed by faster and more robust therapeutic species engraftment in the gut. Treatment also significantly altered the composition of the intestinal microbiome and microbe-associated metabolites, including decreased primary and increased secondary bile acids, as well as elevated short- and medium-chain fatty acids, functional changes that inhibit C. difficile spore germination and vegetative growth. Further, in vitro analyses confirmed that VOWST batches induced production of these metabolites that disrupt C. difficile life cycle and growth. Collectively, these findings support VOWST’s role in restoring microbe-associated metabolic functions critical to preventing CDI recurrence.

A complementary publication in the Journal of Infectious Diseases, titled “Comparability of Gastrointestinal Microbiome and Bile Acid Profiles in Patients With First or Multiply Recurrent Clostridioides difficile Infection”, reported a post hoc analysis of the ECOSPOR IV Phase 3 trial, evaluating differences in gastrointestinal microbiome and bile acid profiles between patients experiencing a first recurrence C. difficile infection (frCDI) versus multiply recurrence infection (mrCDI). These data demonstrate that the underlying functional disease etiology is consistent in both first and multiply recurrent CDI patient populations, with VOWST demonstrating similar efficacy and drug pharmacology across the broad patient population.

“We are thrilled to see these high-impact publications highlighting the important role biotherapeutics that comprise commensal bacteria may have in treating human disease,” said Matthew Henn, Ph.D., Chief Scientific Officer at Seres Therapeutics. “These data provide important clinical translation and further demonstrate the promise of live biotherapeutics to target specific microbiome functions that are linked to serious disease, including those that are not effectively treated with other drug modalities. The body of evidence from our clinical trials provides additional momentum for our current pipeline, including our lead candidate SER-155, which we believe has the potential to transform care for allogeneic hematopoietic stem cell transplant (allo-HSCT) recipients and other high-risk patients vulnerable to bloodstream infections.”

The underlying data supporting these publications was developed using Seres MbTx platform, which provides high-resolution assessment of drug pharmacology and functional mechanism of action. These data on bacterial function and pharmacology anchored the preclinical development of SER-155. In a randomized, placebo-controlled Phase 1b study evaluating SER-155 in patients undergoing allo-HSCT, SER-155 reduced bacterial bloodstream infections by 77% and significantly lowered systemic antibiotic use and febrile neutropenia. Exploratory biomarker data presented at medical meetings has further supported the therapy’s intended mechanisms and demonstrate the broader potential of live biotherapeutics in inflammatory and immune-mediated diseases.

About Seres Therapeutics
Seres Therapeutics, Inc. (Nasdaq: MCRB) is a clinical-stage company focused on improving patient outcomes in medically vulnerable populations through novel live biotherapeutics. Seres led the successful development and approval of VOWST™, the first FDA-approved orally administered microbiome therapeutic, which was sold to Nestlé Health Science in September 2024. The Company is developing SER-155, which has received Breakthrough Therapy designation for the reduction of bloodstream infections in adults undergoing allo-HSCT and Fast Track designation for reducing the risk of infection and graft-versus-host disease in adults undergoing allo-HSCT, and which has demonstrated a significant reduction in bloodstream infections and related complications (as compared to placebo) in a Phase 1b clinical study in patients undergoing allo-HSCT. SER-155 and the Company's other pipeline programs are designed to target multiple disease-relevant pathways and are manufactured from standard clonal cell banks via cultivation, rather than from the donor-sourced production process used for VOWST. In addition to allo-HSCT, the Company intends to evaluate SER-155 and other cultivated live biotherapeutic candidates in other medically vulnerable patient populations including autologous-HSCT patients, cancer patients with neutropenia, CAR-T recipients, individuals with chronic liver disease, solid organ transplant recipients, as well as patients in the intensive care unit and long-term acute care facilities. 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: timing and results of our clinical studies and data readouts; past, current or future products or product candidates and their potential benefits; clinical development plans and commercial opportunities; our clinical development plans for SER-155 and other cultivated live biotherapeutic candidates across medically vulnerable populations; 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 VOSWT 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; and (14) our ability to manage our recent CEO transition, to retain key personnel and to manage our growth. These and other important factors discussed under the caption “Risk Factors” in our Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission (SEC) on November 5, 2025, 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. 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 Contact:  
IR@serestherapeutics.com

Carlo Tanzi, Ph.D.
Kendall Investor Relations
ctanzi@kendallir.com

Source: Seres Therapeutics, Inc.