Evelo Biosciences, Inc. announced that it has dosed the first patient in its Phase 1/2 clinical trial of EDP1503 in combination with KEYTRUDA® (pembrolizumab), Merck’s anti-PD-1 therapy. EDP1503 is an orally delivered monoclonal microbial product candidate being developed for the treatment of cancer. This open-label clinical trial will evaluate the safety, tolerability, immune response markers, and overall response rates achieved with EDP1503 in combination with KEYTRUDA® in up to 120 patients across three groups: microsatellite stable colorectal cancer; triple-negative breast cancer; and patients across multiple tumor types who have relapsed on prior PD-1/L1 inhibitor treatment. Patients will receive daily EDP1503 monotherapy for two weeks followed by treatment with daily EDP1503 in combination with KEYTRUDA®. The study will evaluate biomarkers identified from paired biopsies taken before and after the two-week run-in, as well as clinical outcomes observed over the course of the trial. Evelo expects to report initial clinical data from the trial in the first half of 2020. In preclinical studies orally delivered EDP1503 shows activation of multiple clinically validated systemic immune pathways which are complementary to and potentially synergistic with checkpoint inhibitors. Effects include increased CXCL9 and CXCL10 production in the tumor microenvironment, augmentation of NK and T cell infiltration to the tumor site as well as upregulation of MHC Class I expression in tumors.