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 SARTI(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)‐γ, or to some extent with IFN‐α, 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‐γ ‐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‐γ, 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‐γ 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.