SL9 is presented by the major histocompatibility complex class I molecules on matured dendritic cells (DCs) to T lymphocytes for stimulating antigen-specific CTLs, i.e., antigen-specific CD8+ T cells, which mediate antigen-specific lysis of cancer cells by releasing cytolytic granule proteins, such as granzymes and perforin [11]. Here, PRF1 is linked to cancer.