Alpha-melanocyte stimulating hormone can reduce T-cell interaction with melanoma cells in vitro.

This study was undertaken to investigate whether alpha-melanocyte stimulating hormone (alphaMSH) influences the interaction of melanoma cells with T-lymphocytes in the light of previous work from our laboratories showing that alphaMSH can reduce tumour necrosis factor-alpha (TNFalpha) stimulated ICAM-1 upregulation in both normal and transformed melanocytes. Two cutaneous melanoma cell lines--A375-SM and HBL--were examined initially. A375-SM cells gave only a two-fold increase in T-cell proliferation, which was not much improved by the pretreatment of the melanoma cells with cytokines. HBL cells induced a three-fold increase in T-cell proliferation, which was slightly enhanced by the addition of cytokines. Neither cell line expressed B7(1), HBL cells expressed a low level of B7(2), whereas A375-SM cells had little, if any, B7(2) expression. Addition of alphaMSH reduced the interaction between these cutaneous melanoma cells and T-lymphocytes in some, but not all, conditions. An ocular melanoma cell line transfected with B7 showed a modest interaction with T-cells (in two out of three donors) and this response was reduced by the addition of alphaMSH. Pretreatment of the transfected line with cytokines markedly enhanced stimulation of T-cell proliferation by these tumour cells, and alphaMSH reduced the interaction between melanoma cells and T-cells for two out of three donors. In summary, under experimental conditions where melanoma cell stimulation of T-cells occurred (generally pretreatment of the cells with interferon-gamma gave the most convincing response), alphaMSH reduced this response in the majority of experiments, providing preliminary evidence to confirm the hypothesis that MSH may assist melanoma cells to evade interaction with immune cells.