Background: Monotherapy with immune checkpoint inhibitors (ICIs) is not effective in metastatic pancreatic adenocarcinoma (PDAC), likely due to the unique immunosuppressive tumor microenvironment (TME) of PDAC, thus safe and novel strategies to overcome resistance and facilitate adaptive immune responses are a major unmet need. Preclinical and clinical studies demonstrated that antibody blockade of semaphorin 4D (SEMA4D) promotes tumoral infiltration and activation of DCs and CD8+ T cells and reverses immunosuppression, including attenuation of MDSC recruitment and function, leading to enhanced efficacy of ICIs without increasing toxicity. Pepinemab, a SEMA4D blocking antibody, in combination (combo) with avelumab provided clinical benefit in some patients with ICI-resistant and PD-L1-low NSCLC (NCT03268057). Pepinemab is also being evaluated in combo with pembrolizumab in patients with metastatic squamous cell carcinoma of the head and neck (NCT04815720). The principal goals of this proof-of-concept study are to investigate the safety, efficacy, and TME biomarker changes of treatment with the combo of pepinemab plus avelumab in patients with metastatic PDAC. Methods: This single-arm, open-label study (NCT05102721) is evaluating the safety, tolerability, and efficacy of pepinemab in combo with avelumab in patients diagnosed with metastatic PDAC who have either progressed on or are otherwise intolerant to first line chemotherapy. Patients must have received 5FU or gemcitabine-based first line therapy with evidence of intolerance or treatment failure, including progression both during or after completing first-line treatment. Accrual for the Phase 1b portion follows a Bayesian Optimal Interval Design (BOIN), beginning at the highest dose combo; 20 mg/kg pepinemab and 800 mg avelumab Q2W. Phase 2 begins after 16 subjects are enrolled at MTD, permitting a Simon’s two stage assessment of futility prior to closing the Phase 1b period. The primary objective for Phase 1b is tolerability, and the primary objective for Phase 2 is therapeutic efficacy compared to historical second-line systemic chemotherapy. The trial anticipates a total evaluable cohort of 40 subjects and is powered to detect a response rate of 23% or greater, with alpha set at 0.1 and 80% power. Exploratory objectives include robust correlative analysis of immune, stromal, and genomic profiling of baseline and on-treatment tumor biopsies to ascertain mechanisms of treatment response and failure. Patient reported outcomes are incorporated throughout the trial to assess disease specific symptoms associated with pancreatic cancer and cancer cachexia. One patient has been enrolled as of Feb 14, 2023. Clinical trial information: NCT05102721.