Background: There is a high unmet medical need for the treatment (tx) of patients (pt) who are refractory to or relapse following tx with checkpoint inhibitors. Newer checkpoint therapies with novel mechanisms of action that can activate T cells and demonstrate antitumor activity in this pre-tx pt population are urgently needed. COM701 is a novel first-in-class humanized IgG4 monoclonal antibody that binds with high affinity to PVRIG (poliovirus receptor related immunoglobulin domain containing) blocking its interaction with its ligand, PVRL2. Both PVRIG and PVRL2 are part of the DNAM axis as are TIGIT and PD1. Inhibition of PVRIG leads to enhanced activation of T and NK cells, and PVRIG results in tumor growth inhibition in mouse tumor models. We hypothesize that COM701 will demonstrate antitumor activity in pts who are checkpoint inhibitor pre-tx. Methods: NCT03667716 is an ongoing open-label first-in-human phase 1 study in pts with advanced solid tumors. The initial part of this study (Arm A) will evaluate escalating doses of COM701 monotherapy IV Q3 weekly with single pt cohorts for the initial 4 and then 3+3 design. Key Inclusion Criteria: Age ≥18 yrs, histologically confirmed locally advanced/ metastatic solid malignancy and has exhausted available standard therapy, ECOG 0-1, prior anti-PD-1, anti-PD-L1, anti-CTLA-4, OX-40, CD137 permissible. Key Exclusion Criteria: Active autoimmune disease requiring systemic therapy in the last 2 years, symptomatic interstitial or inflammatory lung disease, untx or symptomatic central nervous system metastases. Primary objectives are safety and tolerability of COM701 as measured by the incidence of adverse events (AEs) and dose-limiting toxicities (21-day DLT window), pharmacokinetics of COM701, and to identify the maximum tolerated dose and/or the recommended dose for expansion. Secondary objectives are to characterize the immunogenicity and preliminary antitumor activity of COM701. Statistical Considerations: AEs graded as per CTCAE v4.03, responses as per RECIST v1.1. The analyses of all study objectives will be descriptive and hypothesis generating. No DLTs have been observed in the single pt cohorts. Assessment of pts enrolled into cohort 5 is ongoing at the time of this submission. Clinical trial information: NCT03667716