Abstract: Background and purpose: Cytotoxic T lymphocyte (CTL) plays a vital role in the process of antitumor immunology. The aim of this study was to investigate whether changes in concentration of IL-2 (50, 200 and 1 000 U/mL) would affect the sub-population and cytotoxic function of cells cultivated by peptide-specific CTL induction system in vitro and also observe whether using the concentration of IL-2 at a range of 50-1 000 U/mL is beneficial to regulatory cells (Tregs) enrichment. Methods: Peripheral blood from 10 healthy donors and 10 cancer patients that were HLA-A2 positive, were collected in the study. HLA-A2 restricted CTL epitope P321 (ILIGETIKI) derived from COX-2 pulsed with different concentrations of IL-2 were used to induce peptides-specific CTL in vitro. Flow cytometry was performed to analyze the proliferative capability, the proportion of different T-cell subsets, and secretion of perforin, granzyme B and IFN-γ. IFN-γ secretion was assessed by ELISpot assay. Results: High concentration of IL-2 increased the proliferative activity. The percentage of CD4+ T cells of cancer patient group was significantly higher than that of healthy donor group, while the percentage of CD8+ T cells of cancer patient group was significantly lower than that of healthy donor group. And there was no significant difference in the percentages of CD4+ T cells, CD8+ T cells and Tregs among groups with different IL-2 concentrations. No difference was seen in cytokine (perforin, granzyme B, IFN-γ) secretion capacity of CD8+ T cells. ELISpot study revealed that high-dose IL-2 resulted in the increasing of IFN-γ secretion. Conclusion: The sub-population and the function of cells cultured by peptide-specific CTL induction system in vitro are not affected by different concentrations of IL-2. Furthermore, high concentrations of IL-2 (50-1 000 U/mL) do not provide the enrichment for Tregs. Higher concentration of IL-2 is likely to cause high secretion of IFN-γ in ELISpot assay. In order to exclude the distraction of NK cells or NKT cells, the concentration of 50 U/mL is better choice.

Key words: IL-2, CTL, Polypeptide vaccine, Treg, Cytotoxicity