Seres Therapeutics is a clinical-stage biopharmaceutical company developing live biotherapeutic products (LBPs) — drugs made from defined consortia of living bacteria — to treat serious diseases in immunocompromised patients. Seres' lead program, SER-155, is an oral LBP designed to reduce bloodstream infections in patients undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT), a procedure used to treat blood cancers that leaves patients highly vulnerable to life-threatening infections. In a Phase 1b trial, SER-155 was associated with a 77% relative risk reduction in bloodstream infections versus placebo, and the FDA has granted SER-155 Breakthrough Therapy designation. Seres is also evaluating SER-155 in immune checkpoint inhibitor-related enterocolitis and ICU patients. Earlier-stage pipeline assets include SER-603 for inflammatory bowel disease and SER-147 for patients with chronic liver disease, both preclinical. Seres previously developed VOWST, the first FDA-approved oral microbiome therapeutic (for recurrent C. difficile infection), which was sold to Nestlé Health Science in 2024. Seres funds operations through asset sales, non-dilutive grants, and partnerships, and is actively seeking collaborators or licensees for its pipeline. Seres' underlying technology platform, MbTx, combines a proprietary bacterial strain library with genomic and metabolomic databases and machine learning to design therapeutic bacterial consortia, manufactured via cultivation-based processes at its Cambridge, MA facility.