Seres announces 80% response rate for SER-155 in immune checkpoint inhibitor-related enterocolitis trial

Key facts

• 12 of 15 participants (80%) achieved immunosuppressive-free clinical response at Day 15, the primary endpoint
• 5 of 15 participants (33%) achieved immunosuppressive-free complete clinical remission (Grade 0) at Day 15
• SER-155 was generally well tolerated with no serious adverse events assessed as related to SER-155; no bloodstream infections reported through Day 43
• Study conducted at Memorial Sloan Kettering Cancer Center by Principal Investigator David Faleck, M.D.
• Study evaluated SER-155 in patients with Grade 2–3 (moderate-to-severe) irEC, which affects approximately 25% of all immune checkpoint inhibitor therapy recipients in the US
• irEC affects approximately 25% of all immune checkpoint inhibitor (ICI) therapy recipients in the US
• Participants were on a wide range of ICI types: PD-1 inhibitors (Keytruda, Opdivo, Zynz), PD-L1 inhibitors (Imfinzi, Bavencio), CTLA-4 inhibitors (Yervoy, Imjudo), LAG-3 inhibitor (Opdualag), and combinations thereof
• At Day 43, 5 of 15 participants (33%) maintained immunosuppressive-free clinical response, with 2 of 15 participants (13%) maintaining immunosuppressive-free complete clinical remission
• Fecal calprotectin and fecal albumin biomarkers showed statistically significant reductions by Day 43, reflecting improvement in gastrointestinal inflammation and mucosal epithelial barrier integrity
• SER-155 bacterial strain engraftment was robust, with kinetics, magnitude, and durability comparable to prior Seres clinical studies

Why it matters

The trial results support potential development of SER-155 as a non-immunosuppressive treatment for irEC, a serious adverse event that often forces cancer patients to halt immune checkpoint inhibitor therapy; the company is now evaluating next steps and engaging with potential partners including companies with ICI franchises.

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