Seres Therapeutics, Inc. (Nasdaq: MCRB), a leading microbiome therapeutics company, announced today that preliminary clinical data from a currently enrolling Phase 1b study of SER-155 study in adult patients undergoing allogeneic hematopoietic cell transplantation (allo-HCT) will be presented at the 65th American Society of Hematology (ASH) Annual Meeting held from December 9-12, 2023, in San Diego, California, USA. SER-155 is an oral, cultivated live bacterial consortia investigational therapeutic designed to prevent enteric-derived infections and resulting blood stream infections, as well as reduce the incidence of graft-versus-host disease (GvHD) by modulating immune responses in the gastrointestinal tract.

Poster Presentation Details:

Poster Title: Impact of Investigational Microbiome Therapeutic SER-155 on Pathogen Domination: Initial Results from a Phase 1b Study in Adults Undergoing Allogeneic Hematopoietic Cell Transplantation (HCT)

Poster number: 2198

Presenter: Jonathan Peled, MD, PhD, Memorial Sloan Kettering Cancer Center, New York, NY

Session: 722. Allogeneic Transplantation: Acute and Chronic GVHD, Immune Reconstitution: Poster I

Session Date/Time: Saturday, December 9, 2023: 5:30pm - 7:30pm EST

Location: San Diego Convention Center, Halls G-H

About SER-155

SER-155 is a consortium of bacterial strains selected using Seres’ reverse translation discovery and development platform technologies. SER-155 design incorporated microbiome biomarker data from human clinical data and preclinical data from human cell-based assays and in vivo disease models. SER-155 is intended to restructure the gastrointestinal microbiome by decreasing the abundance of bacterial pathogens that can harbor antibiotic resistance, and introducing bacteria that provide immunomodulatory metabolites that can improve mucosal barrier integrity and reduce local GI inflammation. These effects are hypothesized to reduce the likelihood of pathogen translocation and subsequent bloodstream infection and GvHD.

About Seres Therapeutics

Seres Therapeutics, Inc. (Nasdaq: MCRB) is a commercial-stage company developing novel microbiome therapeutics for serious diseases. Seres’ lead program, VOWST™, obtained U.S. FDA approval in April 2023 as the first orally administered microbiome therapeutic to prevent recurrence of C. difficile infection (CDI) in adults following antibacterial treatment for recurrent CDI and is being commercialized in collaboration with Nestlé Health Science. Seres is evaluating SER-155 in a Phase 1b study in patients receiving allogeneic hematopoietic stem cell transplantation. 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 the timing and success of the SER-155 Phase 1b study, and other statements which 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: we have incurred significant losses, are not currently profitable and may never become profitable; our need for additional funding; our limited operating history; the impact of the COVID-19 pandemic; our unproven approach to therapeutic intervention; our reliance on third parties and collaborators to conduct our clinical trials, manufacture our product candidates and develop and commercialize our product candidates, if approved; the unknown degree and competing factors of market acceptance for VOWST; the competition we will face; our ability to protect our intellectual property; and our ability 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 2, 2023, and 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.

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