The existence of CD8+ CTLs that are capable of recognizing MHC class I-bound, human tumor-associated peptide antigens is now unequivocally documented in cancer patients. Thus far, the role of CD8+ T cells in tumor immunity has been predominantly viewed in terms of cytolytic ability as the prime mode of their function. Interestingly, it is increasingly evident that CD8+ T cells are capable of synthesizing both type I and type II cytokines. Thus, it is conceivable that tumor antigen-specific but non-cytolytic CD8+ T cells might play an important role in antitumor immune response by synthesizing type I cytokine. Through such cytokines, they could provide “help” for the process of generating as well as in maintaining an effective CD8+ CTL response. In addition, they might recruit other types of effector cells (such as natural killer cells, macrophages, and others) locally at the tumor site. Either way, they could exert a profoundly positive role in cell-mediated antitumor immune response, particularly because the great majority of tumor cells express only MHC class I molecules that present peptide epitopes to CD8+ T cells. Unfortunately, tumor antigen-specific, noncytolytic but type I cytokine-secreting CD8+ T cells have not received much investigative attention. Here we show that CD8+ T cells, isolated from the tumor-infiltrating lymphocytes from human melanoma, synthesize type I cytokine (IFN-γ and tumor necrosis factor α) in a MHC class I-restricted and tumor-specific noncytolytic interaction with the autologous melanoma cells.
The work was supported by USPHS Grant CA 61398 and in part by the Lavery Memorial Resarch Fund.