OncoMed Pharmaceuticals Inc. announced that the first patient has been dosed in the company’s Phase 1b portion of the Phase 1a/1b clinical trial of anti-TIGIT (OMP-313M32) in combination with anti-PD1 (nivolumab). TIGIT (T-cell immunoreceptor with Ig and ITIM domains) is a next generation checkpoint receptor, and upon activation by the PVR ligand, a protein broadly expressed on tumor cells, it blocks T-cell activation. Company’s anti-TIGIT candidate is an IgG1 monoclonal antibody checkpoint inhibitor which binds to the human TIGIT receptor on T-cells with a goal of improving the activation and effectiveness of T-cell and NK cell tumor-killing activity. The Phase 1b portion of the open-label Phase 1a/1b clinical trial is designed to assess safety, tolerability, preliminary efficacy, and biomarkers with escalating doses of anti-TIGIT in combination with anti-PD1 in the treatment of patients with selected advanced or metastatic solid tumors who have progressed after treatment with anti-PD1 or anti-PD-L1. The Phase 1a/1b trial is being conducted at 5 centers in the U.S., and company currently plans to enroll approximately 12 patients in the Phase 1b portion of the study. The trial will define a dosing regimen that could provide the basis for expanded studies of anti-TIGIT in combination with anti-PD1. TIGIT blocks T-cells from attacking tumor cells and is similar in structure and function to the inhibitory protein PD-1. Company's anti-TIGIT antibody (OMP-313M32) is intended to activate the immune system through multiple mechanisms and enable anti-tumor activity. At the 2018 AACR Annual Meeting, company presented preclinical data (Abstract 5627) which demonstrated that anti-TIGIT treatment reduced the abundance of regulatory T-cells (Tregs) within tumors in animal models. Mechanistic studies demonstrated an important contribution of effector function for anti-tumor efficacy. Using a surrogate anti-TIGIT antibody, potent single-agent dose-dependent anti-tumor efficacy was demonstrated on large established CT26 WT tumors. Anti-TIGIT efficacy was shown to require effector function for tumor growth inhibition and biomarker analysis demonstrated reduction of Treg frequency and activation of T-cells and NK cells as part of the mechanism of action of anti-TIGIT. CD226, a co-receptor for TIGIT’s ligands PVR and PVRL2, was significantly upregulated in T-cells, Tregs and NK cells, reflecting a feedback loop activated by the inhibition of TIGIT activity. Additionally in a human tissue study, TIGIT expression on Tregs was found to be considerably higher than on CD8+ T-cells in multiplexed IHC panels across a panel of multiple solid tumors types. This program is part of company's Celgene collaboration.