Slide 1: Topline Results: SER-155 in Immune Checkpoint Inhibitor-Related Enterocolitis (irEC)
Topline Results: SER-155 in Immune Checkpoint Inhibitor-Related Enterocolitis (irEC) --- An Alternative To Immunosuppression That May Preserve Checkpoint Therapy Memorial Sloan Kettering Cancer Center (NCT 06801067) July 8, 2026
Slide 2: Disclaimers
Disclaimers Forward Looking Statements This communication contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. All statements contained in this communication that do not relate to matters of historical fact should be considered forward-looki
Slide 3: What is Immune Checkpoint Inhibitor-Related Enterocolitis (irEC)?
What is Immune Checkpoint Inhibitor-Related Enterocolitis (irEC)? irEC is a serious, frequent complication of rapidly growing immune checkpoint inhibitor therapy that requires immunosuppressive treatment and often disrupts life-extending cancer treatment • Immune Checkpoint inhibitors (ICIs) activat
Slide 4: A significant unmet need exists for new therapies that treat irEC without immunosuppression
A significant unmet need exists for new therapies that treat irEC without immunosuppression and that preserve life-extending checkpoint inhibitor therapy Oral treatment that resolves irEC without systemic immunosuppression and without a negative impact on immune checkpoint inhibitor therapy Enables
Slide 5: Top-Line Results Summary: SER-155 resulted in immunosuppressive-free clinical response
Top-Line Results Summary: SER-155 resulted in immunosuppressive-free clinical response with mechanistic biomarker data supporting efficacy outcomes Memorial Sloan Kettering Cancer Center (MSK) investigator sponsored trial in 15 cancer patients with immune checkpoint inhibitor-related enterocolitis (
Slide 6: MSK initiated trial to evaluate safety and efficacy of SER-155
MSK initiated trial to evaluate safety and efficacy of SER-155, an investigational biotherapeutic optimized to specifically target the type of damage caused by ICIs Memorial Sloan Kettering Cancer Center (MSK) Trial Summary -- NCT06801067 • 15 participants who had not yet received immunosuppressive
Slide 7: SER-155 efficacy response occurred in a representative cancer patient population
SER-155 efficacy response occurred in a cancer patient population representative of current clinical practice, spanned multiple ICI and cancer types Profile of 15 participants enrolled Multiple cancer types • Majority with stage 3-4 Multiple ICI types used on study: • PD-1 inhibitors (Keytruda, Opdi
Slide 8: irEC is a significant side effect which can interrupt ICI cancer therapy
Immune checkpoint inhibitor-related enterocolitis (irEC) is a significant side effect which can cause interruption of ICI cancer therapy and use of immunosuppressives irEC increasing severity; patient population is substantial and growing Moderate-to-Severe Population Grade 1 Grade 2 Grade 3 Grade 4
Slide 9: SER-155 Top Line Efficacy: 80% achieved immunosuppressive-free response at Day 15
SER-155 Top Line Efficacy: 80% of participants achieved immunosuppressive-free response at Day 15, with 33% of participants achieving complete clinical remission Day 15 Immunosuppressive-Free Response (Primary Endpoint; n=15) 80% of all participants achieved Response 80% 33% of all participants achi
Slide 10: At Day 43, patients with a Day 15 response had same grade or better
At Day 43, patients with a primary endpoint response at Day 15, had same grade or better The 12 of 15 participants who achieved Grade 0 or Grade 1 without immunosuppressives at Day 15 following SER-155 dosing achieved the same grade or better at Day 43 Secondary Endpoint: 5 of 15 participants mainta
Slide 11: SER-155 Safety through Day 43: Generally well-tolerated with no treatment-related SAEs
SER-155 Safety through Day 43: Generally well-tolerated with no treatment-related severe adverse events (SAEs) • Majority of participants (73.3%) experienced a TEAE, most mild to moderate Treatment-Emergent Adverse Events • Most common: diarrhea (26.7%), though diarrhea is the primary symptom associ
Slide 12: irEC is a disease of the mucosal epithelial barrier-immune interface
irEC is a disease of the mucosal epithelial barrier-immune interface Activation and amplification of T cells and macrophages by ICI – intended to kill tumor cells – have off-target effects causing injury to the gastrointestinal mucosal barrier and severe inflammation Gastrointestinal Mucosal Epithel
Slide 13: Pharmacology: Biomarkers support SER-155 repaired mucosal epithelial barrier
Pharmacology: Biomarkers support SER-155 repaired mucosal epithelial barrier & reduced GI inflammation consistent with drug’s design & clinical results Pharmacokinetics SER-155 strains colonized participants' GI tracts, i.e., engrafted, with the majority of strains observed across the study particip
Slide 14: Seres has pioneered a new drug modality targeting the mucosal barrier-immune interface
Seres has pioneered a new drug modality and accessed the vast functional potential of microbes to target the mucosal barrier-immune interface and treat disease Track-record of realizing ambitious, 2023 impactful therapeutic goals: First company to go from novel concept FDA approval through clinical
Slide 15: Disruption of the mucosal epithelial barrier-immune interface is broadly linked to many diseases
Disruption of the mucosal epithelial barrier-immune interface is broadly linked to many diseases Inflammatory & Immune (I&I) • Immune-checkpoint related enterocolitis (irEC) • Inflammatory Bowel Disease (UC & Crohn’s) • Rheumatoid Arthritis (RA) • Systemic lupus erythematosus (SLE) • Type 1 Diabetes
Slide 16: SER-155 irEC study results are clinically meaningful and represent an additional oncology indication
SER-155 irEC study results are clinically meaningful and represent an additional valuable oncology indication Immune checkpoint inhibitors Immune checkpoint inhibitors SER-155 has the potential to have revolutionized cancer can cause irEC that can become a critical component treatment and represent
Slide 17: Jonathan Peled, M.D., Ph.D.
Jonathan Peled, M.D., Ph.D. Bone Marrow Transplant Specialist and Cellular Therapist Memorial Sloan Kettering Cancer Center 17 - Seres Therapeutics ©2026
Slide 18: Q&A
Q&A 18 - Seres Therapeutics ©2026
Slide 19: Thank You
Thank You 19 - Seres Therapeutics ©2026