Slide 1: SER-155 Phase 1b Readout
Exhibit 99.1 SER-155 Phase 1b Readout September 12, 2024
Slide 2: Disclaimers: Forward Looking Statements
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: Disclaimers: Important Information About the Transaction
Disclaimers Important Information About the Transaction and Where to Find it In connection with the proposed transaction involving Seres Therapeutics, Inc. (“Seres”) and Société des Produits Nestlé S.A. (“SPN”), Seres filed a definitive proxy statement with the Securities and Exchange Commission (th
Slide 4: SER-155 is designed to reduce life-threatening complications of allo-HSCT
SER-155 is designed to reduce life-threatening complications of allo-HSCT • Investigational live oral biotherapeutic cultivated from clonal master cell banks SER-155 • Designed to prevent GI-derived bacterial bloodstream infections (BSIs) and other pathogen-associated complications Allo-HSCT treatme
Slide 5: SER-155 Phase 1b study evaluated safety, pharmacology, and efficacy in adult allo-HSCT recipients
SER-155 Phase 1b study evaluated safety, pharmacology, and efficacy in adult allo-HSCT recipients COHORT 1 COHORT 2 Open-label (n=15 enrolled) Placebo-controlled 1:1 (n=45 enrolled) SER-155 SER-155 Placebo results reported May 2023 results announced Sept. 2024 Primary Endpoints: Key Secondary Endpoi
Slide 6: Cohort patient disposition
Cohort 2 patient disposition ITT Safety mITT-1 SER-155 n = 23 n = 21 n = 20 -2 randomized untreated -1 consent withdrawal mITT-1 population studied for efficacy Safety mITT-1 ITT Placebo n = 19 n = 14 n = 22 -3 randomized untreated -3 disease progression -1 transplant delay -1 consent withdrawal ITT
Slide 7: Cohort demographics: Representative of the allo-HSCT population
Cohort 2 demographics: Representative of the allo-HSCT population • Median age: 63 years Demographics • Gender: 50% male, 50% female • Ethnicity: 88% white • Most common diagnosis: acute myeloid leukemia (AML): 38% Cancer Diagnosis • Other common diagnoses: acute lymphocytic leukemia (ALL), myelodys
Slide 8: Patient Safety: SER-155 was generally well tolerated with no treatment-related SAEs
Patient Safety: Cohort 2 SER-155 was generally well tolerated with no treatment-related SAEs • All but one subject in the placebo arm experienced at least 1 TEAE • Most common for SER-155 treated subjects (≥50% and with Δ ≥5% greater than placebo): Treatment-emergent diarrhea (86% vs. 74% placebo),
Slide 9: Efficacy: significant reduction in bacterial BSIs and systemic antibiotic exposure
Efficacy: SER-155 administration favorable with significant* reduction in both bacterial BSIs and systemic antibiotic exposure; lower febrile neutropenia Significant decrease in bacterial bloodstream infections in SER-155-treated Bloodstream infections subjects vs. placebo Numerically lower incidenc
Slide 10: Bloodstream infections from HSCT Day 0 to Day 100
Bloodstream infections from HSCT Day 0 to Day 100: Lower incidence in SER-155 treated subjects vs. placebo Bloodstream infections from Day 0 SER-155 Placebo to Day 100 n=20 n=14 (# patients) n (%) n (%) Subjects with confirmed BSI 2 (10.0%) 6 (42.9%) 95% confidence interval (1.2, 31.7) (17.7, 71.1)
Slide 11: Febrile neutropenia from HSCT Day 0 to Day 100
Febrile neutropenia from HSCT Day 0 to Day 100: Lower incidence in SER-155 treated subjects vs. placebo Febrile neutropenia from Day 0 to SER-155 Placebo Day 100 n=20 n=14 (# patients) n (%) n (%) Subjects with FN 13 (65.0) 11 (78.6) 95% confidence interval (40.8, 84.6) (49.2, 95.3) mITT-1 populatio
Slide 12: Cumulative exposure to systemic antibacterials / antimycotics through HSCT Day 100
Cumulative exposure to systemic antibacterials / antimycotics through HSCT Day 100: Lower incidence in SER-155 treated subjects vs. placebo Cumulative Antibacterial or SER-155 Placebo Antimycotic Exposure n=20 n=14 (HSCT Days) n (%) n (%) Mean (SD) 9.2 (5.44) 21.1 (20.31) Median 9.0 14.0 Min, Max 0,
Slide 13: Cumulative exposure rate to systemic antibacterials / antimycotics through HSCT Day 100
Cumulative exposure rate to systemic antibacterials / antimycotics through HSCT Day 100: Lower incidence in SER-155 treated subjects vs. placebo Cumulative Antibacterial or SER-155 Placebo Antimycotic Exposure Rate n=20 n=14 (% of days) n (%) n (%) Mean (SD) 0.090 (0.0530) 0.305 (0.2898) Median 0.08
Slide 14: SER-155 Strain Engraftment: Primary objective achieved
SER-155 Strain Engraftment: Primary objective achieved - drug bacteria strain engraftment was robust and as expected • The majority of SER-155 strains were present at start of HSCT conditioning and durable through chemotherapy exposure • Engraftment decreased but was detectable post- neutrophil reco
Slide 15: Pathogen Domination: Prevalence lower relative to Historical Control Cohort
Pathogen Domination: Prevalence in SER-155 Cohort 2 was substantially lower relative to Historical Control Cohort • SER-155 was designed to reduce pathogen domination that has been associated with risk of BSIs and other negative 1 clinical outcomes 2 • In Cohort 2, the ability to detect pathogen dom
Slide 16: Summary and Next Steps
Summary and Next Steps Seres to engage with FDA on advancement Phase 1 results support Seres’ strategy to of SER-155 allo-HSCT program pursue SER-155 and other live biotherapeutics for prevention of serious bacterial infections • Intend to evaluate SER-155 in additional patient • Seek Breakthrough T