Cytokines required for induction of histocompatibility leukocyte antigen-class I-restricted and tumor-specific cytotoxic T lymphocytes by a SART1-derived peptide.

Although there have been several reports on peptides of human tumor-rejection antigens capable of inducing histocompatibility leukocyte antigen (HLA)-class I-restricted and tumor-specific cytotoxic T lymphocytes (CTLs), it is not yet clear which cytokines are required for CTL induction. This study has investigated the cytokine combinations required for optimal induction of CTLs by SART1(690-698) peptide, which is capable of inducing HLA-A24-restricted and tumor-specific CTLs in peripheral blood mononuclear cells (PBMCs). Pretreatment of PBMCs as a source of antigen-presenting cells (APCs) with interferon (IFN)-gamma, or to some extent with IFN-alpha, but not with any of the other cytokines tested, augmented the peptide-induced CTL activity in HLA-A24 heterozygotes, but not in HLA-A24 homozygotes. This IFN-gamma-mediated augmentation was inhibited by either interleukin (IL)-4 or IL-10. IL-2 alone in culture, along with weekly stimulation by peptide-pulsed APCs, was sufficient for the differentiation and proliferation of CTLs for the initial several weeks of culture. This IL-2-mediated activation of CTLs was inhibited by the addition of IFN-gamma, IL-4, or IL-10 to the IL-2 culture. For further expansion of the CTLs, dendritic cells (DCs) induced from PBMCs with IL-4 and granulocyte macrophage colony-stimulating factor (GM-CSF) were required as APCs. These results indicate that IFN-gamma and IL-2 are important in the activation of APCs and CTLs, respectively, while GM-CSF and IL-4 are needed for the induction of DCs, which in turn are required for further expansion of mature CTLs. These results are important in allowing for a better understanding of the cellular and molecular basis of tumor-specific immunity, and also for the development of peptide-based specific immunotherapy.