PRF1 and neoplasm: Superantigens use several mechanisms to induce tumor cell cytotoxicity in vitro and in vivo. In superantigen dependent cellular cytotoxicity (SDCC) SAgs efficiently bind MHC class II-positive tumor cells which then initiate human T cell proliferation and differentiation into cytotoxic T cells that lyse tumor cells in a perforin/granzyme dependent manner (Dohlsten et al., 1995).