Seres reported a Q1 net loss of $19.9 million on $358,000 revenue, compared to a $32.7 million profit in Q1 2025 after a $50 million payment from Nestlé. Operating expenses declined by $6 million year-over-year, while research and development spending rose to $13.2 million driven by higher facilities and manufacturing costs.

Enrollment of 15 patients in an investigator-sponsored SER-155 trial for immune checkpoint inhibitor-related enterocolitis is complete, with clinical data expected shortly. The company has achieved Phase 2 readiness for SER-155 in allogeneic hematopoietic stem cell transplant infection prevention and is designing a Phase 1b liquid‐formulation study for ICU patients.

Seres is conducting IND-enabling studies for its SER-603 live biotherapeutic candidate targeting inflammatory bowel disease, presenting new preclinical data at a major gastroenterology conference. The data emphasize rational microbial strain selection and biomarker-driven patient stratification to support clinical advancement.