Slide 1: SER-155 Phase 1b Cohort 1 Day 100 Data
SER-155 Phase 1b Cohort 1 Day 100 Data May 2023 Exhibit 99.3
Slide 2: SER-155 May Represent a Novel Solution to Reduce GI Pathogen Abundance and Infection & GvHD
SER-155 May Represent a Novel Solution to Reduce GI Pathogen Abundance and Infection & GvHD in Allogeneic HSCT Enrollment ongoing in SER-155 Phase 1b Cohort 2 a randomized, double-blind, placebo-controlled study Expect to release topline results in mid-2024 SER-155 is an oral, cultivated consortium,
Slide 3: Beneficial Bacteria Protect the GI Tract from Potential Microbial Pathogens
Beneficial Bacteria Protect the GI Tract from Potential Microbial Pathogens A healthy, diverse microbiome is essential to preventing colonization and infection with pathogens Antibiotics and other insults can drive the loss of beneficial microbes, enabling pathogens and drug-resistant bacteria to ra
Slide 4: Microbiome Therapeutics are a Potential Novel Approach to Address Infections, Antimicrobial Resistance
Microbiome Therapeutics are a Potential Novel Approach to Address Infections, Antimicrobial Resistance, & Associated Complications Antibiotic resistant pathogens can dominate the GI microbiome Compromised epithelial layer Bacterial translocation/blood stream infections and GI inflammation Lamina pro
Slide 5: Designed to Modulate Targets that Address Leading Causes of Mortality Following Allo-HSCT
SER-155 Designed to Modulate Targets that Address Leading Causes of Mortality Following Allogeneic HSCT (allo-HSCT) Consortium of unique, human commensal bacterial strains Cultivated and encapsulated for oral delivery Strain selection based on broad pre-clinical screening for defined functions and i
Slide 6: Phase 1b: Two-Cohort Study to Evaluate SER-155 in Allogeneic HSCT Patients
SER-155 Phase 1b: Two-Cohort Study to Evaluate SER-155 in Allogeneic HSCT Patients Evaluate safety, tolerability of SER-155 dosed before and after allogeneic HSCT Evaluate the engraftment (PK) of SER-155 strains in the GI microbiome Assess the impact of SER-155 engraftment on gastrointestinal microb
Slide 7: Cohort Enrollment Summary: Majority of Subjects Retained Post Transplant
SER-155 Cohort 1 Enrollment Summary: Majority of Subjects Retained Post Transplant 15 enrolled 13 received study drug 11 received allogeneic stem cell transplant 10 reached Day 100 (*9 subjects with evaluable samples for PK/PD) 2 enrolled but untreated due to disease progression/withdrawal of consen
Slide 8: SER-155 Was Generally Well-Tolerated in Cohort 1 (Day 100 Data)
SER-155 Was Generally Well-Tolerated in Cohort 1 (Day 100 Data) TEAE: treatment-emergent adverse event; SAE: serious adverse event; AESI: adverse event of special interest; SUSAR: suspected unexpected serious adverse reaction TEAEs observed as expected in this patient population All subjects experie
Slide 9: GI Microbiome Pathogen Domination as a Driver of Infection & GvHD in Allo-HSCT
GI Microbiome Pathogen Domination as a Driver of Infection & GvHD in Allo-HSCT has been Reported in Peer-Reviewed Literature Seres ongoing 7-year partnership with Memorial Sloan Kettering Cancer Center (MSKCC) to elucidate role of microbiome in HSCT: Gastrointestinal (GI) microbiome domination, a st
Slide 10: GI Microbiome Pathogen Domination is Associated with Worse Clinical Outcomes in Allo-HSCT Recipients
GI Microbiome Pathogen Domination is Associated with Worse Clinical Outcomes in Allo-HSCT Recipients * Taur et al, Clin Inf Dis 2012; extended in Tamburini et al Nat Med, 2018 ** Stein-Thoringer et al Science 2019; also supported by Jenq et al Bio BMT 2015 Dominated Not dominated Dominated Not domin
Slide 11: ESKAPE Pathogen Domination was Rare and Transient in Cohort 1
ESKAPE pathogen domination* in SER-155 administered subjects observed at rates substantially lower than reference cohort ESKAPE Pathogen Domination was Rare and Transient in Cohort 1 SER-155 Cohort 1 From HSCT Day 0-30, 11% of patients (1 subject, Fig.1 blue line) From HSCT day 0-100, 22% of patient
Slide 12: Bacterial Strains Engrafted in Cohort 1 Patients
SER-155 Bacterial Strains Engrafted in Cohort 1 Patients Engraftment magnitude and kinetics were consistent with our expectations Engraftment is the colonization of the GI tract by metabolically active drug product strains; assessed throughout the study period via proprietary genomic technologies. M
Slide 13: Phase 1b Cohort 2: What We Expect to Learn
SER-155 Phase 1b Cohort 2: What We Expect to Learn SER-155 safety, strain engraftment (PK) and pathogen abundance (PD) in the context of placebo comparator arm Further elucidate mechanism of action of SER-155 Explore impact of SER-155 on clinical outcomes, including the incidence of enteric infectio
Slide 14: SER-155 Could Become Core Part of Allogeneic HSCT Treatment Regimen
SER-155 Could Become Core Part of Allogeneic HSCT Treatment Regimen Unique potential clinical and economic value for allogeneic HSCT patients Double benefit of reducing infections and GvHD, 2 of 3 leading causes of mortality at 1 year Avoids costs of post-transplant complications: $181K average addi