Seres Therapeutics, Inc. announced preliminary microbiome data analyses from the Phase 2b ECO-RESET study evaluating SER-287 in patients with mild-to-moderate ulcerative colitis (UC). Following the topline clinical data readout in July, which noted that the SER-287 Phase 2b study did not achieve its primary endpoints, analysis of the microbiome data demonstrated the successful engraftment of SER-287 bacterial species. The Company continues to conduct analyses on its SER-287 and SER-301 UC clinical stage programs to inform next steps for further development. Based on the SER-287 Phase 2b microbiome data analyses, engraftment of SER-287 bacteria was statistically significant in patients receiving SER-287 versus placebo (p = 0.001 at all timepoints). The magnitude and kinetics of engraftment were comparable to Seres’ Phase 1b study. However, unlike the Phase 1b study, anticipated changes in disease-relevant metabolites post-administration with SER-287 in the Phase 2b study were not observed. Analysis of the genomic and metabolomic data characterizing the microbiome of SER-287 study participants at baseline and post dosing suggest potential biomarkers for inclusion in future development efforts. UC is a biologically and clinically heterogeneous disease and the Company believes that a biomarker-based patient selection approach may enable future development to focus on individuals most amenable to a microbiome-based therapeutic intervention.