PRF1 and neoplasm: CD8+ cytotoxic T lymphocytes (CTLs) facilitate immunosurveillance by T cell receptor (TCR) recognition of antigens bound to major histocompatibility complex (MHC)-I on antigen presenting cells and when activated, produce interferon gamma (IFN-γ), perforin and granzyme B that contribute to tumor cell cytolysis [46].