Tejura, Bindu

6554 Background: Acute graft- versus-host disease (aGvHD) is a life-threatening complication following allo-HCT. Microbiome dysfunction and associated GI barrier disruption may contribute to aGvHD via activation of inflammatory immune responses. Circulating biomarkers in the peri-transplant period are correlated with risk of severe aGvHD, including suppression of tumorigenicity 2 (ST2), regenerating islet-derived 3-alpha (Reg3a) and inflammatory cytokines (IL6, IFNϒγ & TNFα). SER-155 is an investigational cultivated oral microbiome therapeutic designed to restructure the GI microbiome, improve GI barrier integrity and reduce GI inflammation and is being assessed in a 2-part Phase 1b study in adults undergoing allo-HCT. We present preliminary safety, GvHD, PK, and exploratory biomarker data from the completed open-label Cohort 1 through Day 100 post-HCT. Methods: Adult recipients of allo-HCT were eligible. HCT conditioning and aGvHD prophylaxis were per investigator discretion. Patients received 2 courses of SER-155 (pre-HCT and post-neutrophil engraftment, each comprised of 4 days of microbiome conditioning with oral vancomycin followed by 10 days oral SER-155. The primary endpoint was safety. Strain engraftment (PK) and biomarkers were assessed in stool and plasma samples. Results: Fifteen adults enrolled; 13 received at least 1 course of study drug (median age 67; 54% male), and 11 underwent allo-HCT. Following each course, the majority of the 16 SER-155 strains were detected in stool. Treatment-emergent adverse events (AEs) were reported in all patients with GI AEs the most common. No serious AEs (SAEs) were deemed related to SER-155. Most SAEs and AEs of special interest (ie, BSIs, invasive or GI infections) occurred between HCT and the 2nd SER-155 course. There were no deaths before Day 100. No BSIs were attributable to SER-155 strains. The rate of grade 2-4 aGvHD based on MAGIC criteria through Day 100 was 45.5%; no severe grade 3-4 aGvHD was observed. Median levels of plasma biomarkers REG3α, ST2 and inflammatory cytokines were not elevated relative to a reference range (Table). Conclusions: In this small open-label cohort, SER-155 was generally well-tolerated through Day 100 without drug-related SAEs and no severe aGvHD. Plasma biomarkers were not elevated at HCT Day 0 or neutrophil recovery. These preliminary observations align with the design and preclinical evaluation of SER-155. Clinical trial information: NCT04995653 . [Table: see text]

TPS7080 Background: In patients undergoing allogeneic hematopoietic cell transplantation (HCT), loss of gastrointestinal microbial diversity is associated with risk of bloodstream infections (BSI), acute graft-versus-host disease (aGvHD), and death. SER-155 is a rationally designed investigational cultivated microbiome therapeutic, hypothesized to improve clinical outcomes in HCT by restoring colonization resistance to potential pathogens, promoting epithelial barrier integrity, and reducing colonic inflammation. SER-155-001 is a Phase 1b study evaluating the efficacy, safety, and pharmacokinetics (PK) of SER-155 in adults undergoing HCT. Methods: This study will enroll approximately 70 subjects ≥18 years in an open-label Cohort 1 (n = 10) followed by a double-blind, placebo-controlled Cohort 2 (n = 60) randomized 1:1 to SER-155 or placebo. A variety of conditioning regimens, donor types, and GVHD-prophylaxis regimens are included. Exclusion criteria include history of severe colitis or active inflammatory bowel disease or total colectomy, umbilical cord blood or ex vivo T-cell depletion, exposure to fecal microbiota transplant or any live microbial therapeutic within 3 months prior to screening, and evidence of relapse or progression of hematologic malignancy (minimal residual disease is allowed). Following screening, participants in both cohorts receive 2 treatment courses (one before and one after HCT), each comprised of microbiome conditioning with oral vancomycin or placebo followed by SER-155 or placebo, plus a conditional 3rd treatment course if the subject receives antibiotics. Safety outcomes are followed through 52 weeks post HCT. The primary endpoint is the incidence and severity of adverse events, serious adverse events, and adverse events of special interest. Secondary endpoints include rates of BSI, gastrointestinal infections, aGvHD, febrile neutropenia and overall survival. Microbiome related endpoints include engraftment of SER-155 bacterial strains in the gastrointestinal tract (PK endpoint) and fecal microbiome diversity, composition and metabolites. Results: Cohort 1 enrollment is complete, with 13 participants receiving SER-155. In December 2022, the Data and Safety Monitoring Committee supported continuation to Cohort 2 enrollment following review of safety data from Cohort 1. Enrollment in Cohort 2 is underway. Conclusions: This Phase 1b study is designed to assess the safety, and clinical efficacy of SER-155 in allogeneic HCT, expanding the clinical experience of microbiome- directed interventions in allogeneic HCT recipients. Clinical trial information: NCT04995653 .