Abstract 522: PI3K/Akt signaling in tumor cells promotes immune evasion by limiting infiltration, recognition and killing by T cells

The presence of tumor-infiltrating T cells is associated with favorable patient outcomes, yet most pancreatic cancers are immunologically silent and resistant to currently available immunotherapy. In this study, a syngeneic orthotopic implantation model of pancreatic cancer was used to show that PI3K/Akt signaling in tumor cells down-regulate immunogenicity to evade T cell surveillance. Genetic silencing of PI3K catalytic isoform Pik3ca in KrasG12D/Trp53R172H-driven pancreatic tumors leads to infiltration of T cells, complete tumor regression, and 100% survival of immunocompetent host mice. By contrast, Pik3ca-null tumors implanted in T cell-deficient mice progress and kill 100% of the animals. Adoptive transfer of tumor antigen-experienced T cells eliminates Pik3ca-null tumors in immunodeficient mice. Pik3ca silencing or inhibition of its effector, Akt, increases the expression of MHC Class I and CD80 on the surface of murine and human pancreatic cancer cells. Down-regulating MHC Class I and CD80 expression, or increasing Akt activity, in Pik3ca-null tumors increases their susceptibility to T cell-mediated regression in vivo. These results indicate that PI3K/Akt signaling in tumor cells limits T cell recognition and clearance of pancreatic cancer. Strategies that selectively target the PI3K/Akt signaling pathway in tumor cells may improve immunotherapy for pancreatic cancer. Citation Format: Nithya Sivaram, Patrick McLaughlin, Ya-Ping Jiang, Lisa Ballou, Kien Pham, Chen Liu, Adrianus van der Velden, Richard Lin. PI3K/Akt signaling in tumor cells promotes immune evasion by limiting infiltration, recognition and killing by T cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 522.