PIK3CA in KrasG12D/Trp53R172H Tumor Cells Promotes Immune Evasion by Limiting Infiltration of T Cells in a Model of Pancreatic Cancer

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 immunotherapies. Here we show using a syngeneic orthotopic implantation model of pancreatic cancer that Pik3ca regulates tumor immunogenicity. Genetic silencing of Pik3ca in Kras G12D /Trp53 R172H -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 all of the animals. Adoptive transfer of tumor antigen-experienced T cells eliminates Pik3ca-null tumors in immunodeficient mice. Loss of PIK3CA or inhibition of its effector, AKT, increases the expression of MHC Class I and CD80 on tumor cells. These changes contribute to the increased susceptibility of Pik3ca-null tumors to T cell surveillance. These results indicate that tumor cell PIK3CA-AKT signaling limits T cell recognition and clearance of pancreatic cancer cells. Strategies that target this pathway may yield an effective immunotherapy for this cancer.