PRF1 and neoplasm: Specifically, pancreatic cancer cells inhibit the cytotoxic action of T cells by multiple mechanisms including inhibition of perforin and granzyme secretion, lack of expression of major histocompatibility complex (MHC) class I molecules, and expression of the programmed death-ligand 1 (PD-L1) by tumor cells that bind to the programmed cell death-1 (PD-1) to suppress the function of CD8+T cells (Dong et al., 2002; Ryschich et al., 2005; Thomas and Massague, 2005).