Seres Therapeutics (Nasdaq: MCRB) released early clinical data from an investigator-sponsored trial evaluating SER-155 in patients with immune checkpoint inhibitor-related enterocolitis (irEC), a side effect that affects approximately 25% of immune checkpoint inhibitor (ICI) therapy recipients in the U.S.

The trial, conducted at Memorial Sloan Kettering Cancer Center (MSK) and led by principal investigator David Faleck, M.D., enrolled 15 patients with moderate-to-severe irEC. At Day 15, 12 of 15 participants (80%) achieved an immunosuppressive-free clinical response, defined as at least a one-grade improvement in diarrhea symptoms without the use of immunosuppressive therapy. Five of 15 participants (33%) achieved complete resolution of diarrhea symptoms without immunosuppressive therapy at Day 15.

At Day 43, five participants (33%) maintained immunosuppressive-free clinical response, and two (13%) maintained complete remission without immunosuppressive therapy. The remaining seven participants who had responded at Day 15 were treated with gastrointestinal-targeted, non-systemic immunosuppressives after Day 15.

No serious adverse events related to SER-155 were reported through Day 43. Two participants experienced moderate non-serious adverse events assessed as possibly related to vancomycin and SER-155, all of which resolved.

Pharmacology data showed reductions in biomarkers of gastrointestinal inflammation and mucosal barrier dysfunction following SER-155 treatment, with statistically significant reductions observed by Day 43.

"These results suggest SER-155 may offer a promising, novel approach to managing irEC, with the potential to reduce reliance on systemic immunosuppressive therapies, while also helping patients continue ICI treatment," said Dr. Faleck.

Richard Kender, Executive Chairman and Interim CEO of Seres, said the company is engaging with potential partners, including companies with ICI franchises, as it evaluates next steps for SER-155 development in irEC. The company is also seeking funding to advance a Phase 2 study of SER-155 in allogeneic hematopoietic cell transplantation.

MSK intends to present the full trial results at a future medical conference. The information is based on a company press release.