Pancreatic ductal adenocarcinoma (PDAC) has an immunosuppressed, apoptosis-resistant phenotype. TLY012 is pegylated recombinant Tumor necrosis factor-Related Apoptosis-Inducing Ligand (TRAIL), an orphan drug for chronic pancreatitis and systemic sclerosis. Innate immune TRAIL signaling suppresses cancer. We hypothesized that the combination of immune checkpoint-blocking anti-PD-1 antibody and TLY012 would have synergistic anti-tumor efficacy in immune-competent PDAC-bearing mice. PDAC tumor-bearing C57Bl/6 mice treated with 10 mg/kg anti-mouse PD-1 antibody twice weekly and 10 mg/kg TLY012 three times weekly had reduced tumor growth and tumor volume at 70 days compared to either drug alone (all P <
0.005). B-cell activating factor (BAFF), which promotes PDAC tumors, decreased to 44% of control mice with dual treatment at 7 days and remained decreased at 3 months. Long-term dual treatment showed the highest plasma levels of proinflammatory cytokines interferon-gamma (average 5.6 times control level, P=0.046), CCL5 (average 14.1 times control level, P=0.048), and interleukin-3 (IL-3, average 71.1 times control level, P=0.0053). Flow cytometry showed trends toward decreased circulating regulatory T cells, increased NK cells, and a higher proportion of CD8+ T cells within tumors in the dual treatment group. In summary, the combination of anti-PD-1 and TLY012 prevented the growth of PDAC in an immunocompetent mouse model while increasing tumor-infiltrating CD8+ T cells, decreasing circulating T-regulatory cells and altering plasma cytokine expression of CCL5, interferon-gamma, and IL-3 to promote proinflammatory, antitumor effects. Combining TLY012 and anti-mouse PD-1 modifies immune cell and cytokine levels to induce a more proinflammatory immune environment that contributes to decreased PDAC tumor growth.