Business Description

1. Nature of the Business and Basis of Presentation Seres Therapeutics, Inc. (the “Company”) was incorporated under the laws of the State of Delaware in October 2010 under the name Newco LS21, Inc. In October 2011, the Company changed its name to Seres Health, Inc., and in May 2015, the Company changed its name to Seres Therapeutics, Inc. The Company is a clinical-stage company focused on improving patient outcomes in medically vulnerable populations through discovery and development of novel live biotherapeutics. The Company led the successful development and approval of VOWST (previously referred to as SER-109), the first FDA-approved orally administered microbiome therapeutic and a Breakthrough Therapy designated drug, which was sold to Nestlé Health Science (as defined below) in September 2024. The Company's live biotherapeutic product ( “ LBP ” ) candidates, including SER-155, SER-603, SER-147, and other potential candidates in earlier development, are consortia of bacteria designed to optimize specific, targeted pharmacological properties, and are formulated for oral delivery. The Company is designing LBP candidates to target the prevention and treatment of a broad swath of infections, and to treat inflammatory and immune ( “ I&I ” ) diseases by modulating host function to increase epithelium integrity and to induce immune homeostasis and tolerance, as well as to prevent the colonization and overgrowth of pathogens in the gastrointestinal ( “ GI ” ) tract. SER-155, the Company's most advanced LBP candidate, is an investigational, oral, live biotherapeutic designed to decolonize GI pathogens, improve GI epithelial barrier integrity, and induce immune homeostasis to prevent bacterial bloodstream infections ( “ BSIs ” ), 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 ” ). In the Company's placebo-controlled Phase 1b study of SER-155 in allo-HSCT, SER-155 was associated with a 77% relative risk reduction in bacterial BSIs and a significant reduction in systemic antibiotic exposure as well as a lower incidence of febrile neutropenia, as compared to placebo through day 100 post HSCT. SER-155 was generally well tolerated, with no observed treatment-related serious adverse events. Following advancement of key startup activities for the SER-155 Phase 2 study in allo-HSCT, including the submission of a final protocol to the FDA in January 2026, study site evaluation and qualification with its CRO, and manufacturing of drug substance, the Company has paused additional investment in that program while continuing to seek funding for the Phase 2 study. The clinical data from the SER-155 Phase 1b study in allo-HSCT, along with the Company's extensive preclinical and translational clinical data compiled over the past decade support and inform the advancement of the Company's earlier stage programs targeting I&I diseases. The Company is evaluating SER-155 in immune checkpoint-related enterocolitis, or irEC, and the Company is developing SER-603, broadly in inflammatory bowel disease, or IBD, including ulcerative colitis, or UC, and Crohn's disease. The Company is currently exploring potential collaborations related to those I&I disease programs. The Company has built and deploys a reverse translational platform and knowledge base for the discovery and development of live biotherapeutics, and maintains extensive proprietary know-how that may be used to support future research and development efforts. This platform incorporates high-resolution analysis of human clinical data to identify microbiome biomarkers associated with disease and non-disease states; preclinical screening using human cell-based assays and in vitro/ex vivo and in vivo disease models customized for live biotherapeutics; and a strain library and associated microbiological capabilities that spans broad biological and functional breadth. This platform and knowledge base are integrated through a proprietary knowledge graph and agentic artificial intelligence, enabling rapid identification of specific microbes, microbial genes, and microbial metabolites/peptides associated with disease and the design of therapeutic consortia of bacteria for specific pharmacological properties to restructure the gut microbiome and modulate functional pathways associated with disease.…