Seres Therapeutics to Present New Post Hoc Data From SER-155 Phase 1b Trial at IDWeek 2025, Highlighting Potential to Improve Outcomes in Adults Undergoing Allogeneic Hematopoietic Stem Cell Transplant

CAMBRIDGE, Mass., Oct. 14, 2025 (GLOBE NEWSWIRE) -- Seres Therapeutics, Inc. (Nasdaq: MCRB), (Seres or the Company), a leading live biotherapeutics company, today announced that new post hoc data from its SER-155 Phase 1b trial will be featured in an oral presentation at IDWeek 2025, taking place October 19–22 in Atlanta, Georgia.

Presentation Details

Abstract ID: 2106936

Title: Clinical and Microbiology Outcomes of Bloodstream Infections (BSI) in Adults Undergoing Allogeneic Hematopoietic Stem Cell Transplant (allo-HCT) in a Randomized, Double-blind, Placebo-controlled Cohort 2 of a Phase 1b Study of SER-155, an Investigation Live Biotherapeutic

Presenter: Tessa Andermann, MD, MPH; Associate Professor of Medicine, Division of Infectious Diseases, University of North Carolina at Chapel Hill School of Medicine

Session: Blood and Guts – Microbiome Discoveries

Date and Time: October 20, 10:30-10:42am EDT

Location: B207-B208, Georgia World Congress Center

The presentation will include new data describing differences between the SER-155 and placebo groups in the bacterial and fungal organisms causing BSIs, including BSI event clinical outcomes, antibacterial prophylaxis use, and patterns of antimicrobial resistance (AMR) among the bacterial BSI organisms.

In a randomized, placebo-controlled Phase 1b study evaluating SER-155 in patients receiving allo-HSCT, SER-155 reduced BSIs by 77% and lowered systemic treatment antibiotic use and febrile neutropenia. Exploratory biomarker data presented at recent medical meetings have supported the intended mechanisms of SER-155 and demonstrated the broader potential of live biotherapeutics in inflammatory and immune-mediated diseases.

The Company recently received constructive FDA feedback on the design of a well-powered, placebo-controlled Phase 2 study of SER-155 in patients receiving allo-HSCT and is finalizing the clinical protocol. Seres is also engaged in discussions with multiple parties to secure capital and additional resources to advance SER-155 and its broader live biotherapeutics portfolio.

IDWeek is an annual meeting organized by a collaboration of professional organizations, including the Infectious Diseases Society of America (IDSA), the Society for Healthcare Epidemiology of America (SHEA), the HIV Medicine Association (HIVMA), the Pediatric Infectious Diseases Society (PIDS), and the Society of Infectious Diseases Pharmacists (SIDP).

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 .

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 our presentation at IDWeek 2025; timing and results of our clinical studies and data readouts, including the interpretation and potential implications of new post hoc data from the SER-155 Phase 1b trial; current or future product candidates and their potential benefits; clinical development plans and commercial opportunities; communications with, feedback from, or submissions to, the FDA; our plans and expectations regarding the design and finalization of a Phase 2 study of SER-155; our clinical development plans for SER-155 and other cultivated live biotherapeutic candidates across medically vulnerable populations; our ability to secure capital and additional resources; 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; 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 August 6, 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:  

Carlo Tanzi, Ph.D.

Kendall Investor Relations