Seres Therapeutics Announces Completion of Patient Enrollment for SER-155 Phase 1B Cohort 2 Clinical Trial in Allogenic HSCT

Seres Therapeutics, Inc. (Nasdaq: MCRB), a leading microbiome therapeutics company, announced today that enrollment is complete in the placebo-controlled Cohort 2 of its Phase 1b trial of SER-155 in patients who received Allogeneic Hematopoietic Stem Cell Transplantation (Allo HSCT). SER-155 is an orally administered, consortium of bacteria, cultivated from cell banks and designed to reduce the incidence and severity of enteric-derived infections and resulting bloodstream infections, including those that may harbor antibiotic resistance. Infections are a leading cause of mortality and morbidity in this immunocompromised patient population. SER-155 is also designed to induce immune tolerance responses to reduce the incidence of GvHD.

“We are pleased to complete enrollment in Cohort 2 of our SER-155 Phase 1b study and are looking forward to a robust dataset late in the third quarter of this year,” said Eric Shaff, President and Chief Executive Officer of Seres. “The initial study data will include safety, drug pharmacology, and efficacy-related measures through day 100 following HSCT, a period in which many patients experience infections. There are an estimated 40,000 Allo HSCT procedures annually worldwide and infection is one of the most common causes of mortality in these patients. Our pending clinical results could validate the promise of microbiome therapeutics to prevent poor outcomes associated with pathogens in the GI tract. We intend to evaluate SER-155 and other microbiome therapeutic candidates in several other high prevalence, medically vulnerable patient populations, including chronic liver disease, cancer neutropenia, and solid organ transplants. We envision a future where Seres is pioneering a new standard of care, potentially protecting millions of immunocompromised patients from life-threatening infections.”

The SER-155 Phase 1b study (NCT04995653) is being conducted across 13 clinical centers in the US, including Memorial Sloan Kettering. Study Cohort 1, which included 13 participants, was designed to assess safety and drug pharmacology, including the engraftment of drug bacteria in the gastrointestinal tract. Cohort 1 clinical data, announced in May 2023, showed favorable tolerability, successful drug bacteria engraftment, and a substantial reduction in pathogen domination in the gastrointestinal microbiome. Study Cohort 2, which includes 45 participants, incorporates a randomized, double-blinded placebo-controlled 1:1 design to further evaluate safety and engraftment, as well as clinical outcomes.