SER-155

SER-155 is an investigational, orally administered, live biotherapeutic product being developed by Seres Therapeutics. [3, 13] It is a rationally designed, cultivated consortium of 16 commensal bacterial strains, including both spores and vegetative bacteria. [9, 11, 12] The therapeutic is designed to prevent bloodstream infections, including those from antimicrobial-resistant bacteria, and graft-versus-host disease (GvHD) in immunocompromised patients, particularly those undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT). [3, 8] The proposed mechanism of action involves restoring colonization resistance in the gastrointestinal (GI) tract to decolonize pathogens, improving the integrity of the gut's epithelial barrier to reduce bacterial translocation, and modulating the host immune system to promote tolerance. [3, 7, 9] A Phase 1b study demonstrated a significant reduction in bloodstream infections compared to placebo. [2, 5, 7] SER-155 has received both Breakthrough Therapy and Fast Track designations from the U.S. FDA for the allo-HSCT indication. [1, 3] An investigator-sponsored trial is also evaluating its potential in immune checkpoint inhibitor-related enterocolitis (irEC). [1] Early development was supported by funding from CARB-X. [1, 10]