IL35 Hinders Endogenous Antitumor T-cell Immunity and Responsiveness to Immunotherapy in Pancreatic Cancer.

Although successes in cancer immunotherapy have generated considerable excitement, this form of treatment has been largely ineffective in patients with pancreatic ductal adenocarcinoma (PDA). Mechanisms that contribute to the poor antitumor immune response in PDA are not well understood. Here, we demonstrated that cytokine IL35 is a major immunosuppressive driver in PDA and potentiates tumor growth via the suppression of endogenous antitumor T-cell responses. The growth of pancreatic tumors in mice deficient for IL35 was significantly reduced. An analysis of tumor-infiltrating immune cells revealed a role for IL35 in the expansion of regulatory T cells and the suppression of CD4+ effector T cells. We also detected a robust increase in both the infiltration and activation of cytotoxic CD8+ T cells, suggesting that targeting IL35 may be an effective strategy to convert PDA from an immunologically "cold" to "hot" tumor. Although PDA is typically resistant to anti-PD-1 immunotherapy, we demonstrated robust synergistic reduction in tumor growth when IL35 deficiency was combined with anti-PD-1 treatment. These findings provide new insight into the function of IL35 in the pathogenesis of pancreatic cancer and underscore the potential significance of IL35 as a therapeutic target for use in combination immunotherapy approaches in this deadly malignancy. Cancer Immunol Res; 6(9); 1014-24. ©2018 AACR.