Characterization and augmentation of CD4⁺ cytotoxic T cell lines against melanoma

Abstract

Cytotoxic T cells have been implicated in the control of the progression of human melanoma. Most studies on human tumor T cell immunity have focused on the CD3⁺CD8⁺ cytotoxic T lymphocyte (CTL) phenotype; however, CD3⁺CD4⁺ CTL are important effector cells in other diseases and may also contribute to antimelanoma immunity. In this study we compared the functional activity of CD3⁺CD4⁺ and CD3⁺CD8⁺ CTL lines generated against autologous melanoma cells. CD8⁺ CTL had twofold higher cytotoxicity and serine esterase activity than CD4⁺ CTL. CD8⁺ CTL also were better binders to autologous melanoma cells. Binding of both CD4⁺ and CD8⁺ CTL to melanoma cells was significantly inhibited by ICAM-1 mAb. Interleukin-2 (IL-2) and IL-4 secretion was induced in both CD4⁺ and CD8⁺ CTL after stimulation by melanoma cells. A reverse transcriptase polymerase chain reaction performed on specific messenger RNA showed that both CD4⁺ and CD8⁺ CTL expressed IL-1, IL-2 and IL-4; CD4⁺ CTL also expressed interferon γ (IFN). Both CTL phenotypes expressed receptors for IL-2 and IFN, but only CD4⁺ CTL expressed the receptor for IL-4. Methods to augment CD4⁺ CTL growth were assessed using different combinations of cytokines. The combination of IL-2, IL-4 and IFN provided the optimal stimulation. Treatment of melanoma target cells with IL-4 and IFN enhanced CD4⁺ CTL recognition activity. CD4⁺ T cells are associated with antigen memory response and helper function, therefore activation of CD4⁺ CTL may be more beneficial with respect to long-term protective antimelanoma immunity.