Seres Therapeutics Reports Third Quarter 2025 Financial Results and Provides Business Updates

Following constructive FDA feedback, Seres is finalizing its SER-155 Phase 2 study protocol for the prevention of bloodstream infections in adults undergoing allogeneic hematopoietic stem cell transplant for the treatment of hematological malignancies

Efforts are ongoing to obtain capital and other resources to support SER-155 Phase 2 study; pending securing funding, interim clinical results anticipated within 12 months of study initiation

Ongoing investigator-sponsored study in immune checkpoint related enterocolitis expected to inform broader SER-155 opportunity; initial study results anticipated in early 2026

Seres recently implemented actions to reduce operating costs; based on these actions and current operating plans, Seres expects to fund operations through Q2 2026

CAMBRIDGE, Mass., Nov. 05, 2025 (GLOBE NEWSWIRE) -- Seres Therapeutics, Inc. (Nasdaq: MCRB), (Seres or the Company), a leading live biotherapeutics company, today reported third quarter 2025 financial results and provided business updates.

“Following constructive feedback from the FDA, we are working to finalize our SER-155 Phase 2 study protocol for the prevention of bloodstream infections in adults undergoing allogeneic hematopoietic stem cell transplant (allo-HSCT) for hematological malignancies,” said Thomas DesRosier and Marella Thorell, co-Chief Executive Officers of Seres. “As we prepare for the next phase of SER-155 development, we continue our efforts aimed at securing the funding needed to conduct the Phase 2 study. We expect to be ready to rapidly operationalize the study once financing is in place, and we expect to obtain interim efficacy and safety results within 12 months of the study start. If these results are consistent with our prior successful Phase 1b study, and supportive of continued development, we believe this milestone should be a significant value-creating event for the Company and shareholders. Based on our on-going engagement with the medical community and assessment of the commercial landscape, we remain highly enthusiastic about the broad potential for SER-155—in allo-HSCT and other medically vulnerable populations.”

Mr. DesRosier and Ms. Thorell continued, “In addition to SER-155 development in allo-HSCT, we are expanding our understanding of the broader SER-155 therapeutic opportunity through an ongoing investigator-sponsored study in immune checkpoint related enterocolitis, initiated by the investigator at Memorial Sloan Kettering Cancer Center, and we look forward to obtaining initial efficacy results in early 2026. Additionally, during the third quarter, we implemented cost-reduction measures, including decreasing our workforce. Considering these actions and our current operating plans, we expect to fund operations through the second quarter of 2026, providing flexibility to advance our strategic priorities.”

Recent Highlights

SER-155 and Bloodstream Infection (BSI) Prevention

Development of Biotherapeutics for the Treatment of Inflammatory and Immune Diseases

Financial Results

The Company has classified all historical operating results for the VOWST business within discontinued operations in the consolidated statements of operations for the comparative periods presented (three and nine months ended September 30, 2024). There is no activity in the current period related to discontinued operations.

Cash Runway

As of September 30, 2025, Seres had $47.6 million in cash and cash equivalents. Based on the Company’s current cash position, VOWST transaction-related obligations, and current operating plans, the Company expects to fund operations through the second quarter of 2026. The Company continues to evaluate further opportunities to extend its cash runway.

Conference Call Information

Seres’ management will host a conference call today, November 5, 2025, at 8:30 a.m. ET. The conference call may be accessed by calling 1-800-715-9871 (international callers dial 1-646-307-1963) and referencing the conference ID number 8471287. To join the live webcast, please visit the “Investors and News” section of the Seres website at www.serestherapeutics.com. A webcast replay will be available on the Seres website shortly after the event and will be archived for at least 21 days.

About SER-155

SER-155 is an investigational, oral, live biotherapeutic designed to decolonize gastrointestinal (GI) pathogens, improve epithelial barrier integrity, and induce immune homeostasis, to prevent bacterial bloodstream infections, including those that can harbor antimicrobial resistance (AMR), as well as other pathogen associated negative clinical outcomes, in patients undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT).

SER-155 has been evaluated in a Phase 1b placebo-controlled study in patients undergoing allo-HSCT, which demonstrated a significant reduction in both bacterial bloodstream infections (BSIs) (77% relative risk reduction) and systemic antibiotic exposure, as well as lower incidence of febrile neutropenia. SER-155 has received Breakthrough Therapy designation for the reduction of bloodstream infections in adults undergoing allo-HCST and Fast Track designation for reducing the risk of infection and graft-versus-host disease in patients undergoing allo-HCST. The early development of the program was supported by Combating Antibiotic-Resistant Bacteria Biopharmaceutical Accelerator (CARB-X), a global non-profit partnership accelerating antibacterial products to address drug-resistant bacteria.

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, 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 design, timing and results of our clinical studies and data readouts; current or future product candidates and their potential benefits; clinical development plans and commercial opportunities; communications with, feedback from, or submissions to the FDA; operating plans; cost reduction actions and their anticipated benefits; our cash runway; our ability to secure a strategic, R&D, or other partnership and/or generate or obtain additional capital, financing or other resources; 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 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; (14) our ability to manage our recent CEO transition, to retain key personnel and to manage our growth; and (15) 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 10-Q filed with the Securities and Exchange Commission (SEC) on August 6, 2025 and our Quarterly Report on Form 10-Q to be filed with the 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