The failure to mount effective immunity against melanoma cells likely results from a combination of attenuated priming of naïve CD4+ T cells due to suppression of antigen presentation by dendritic cells coupled to selection for loss of class I major histocompatibility complex (MHC) expression in proliferating melanoma cells, negative regulation by surface CTLA4 in CD4+ and CD8+ effector T cells and the direct suppression of these cells by Treg cells, among other factors [22]. This evidence concerns the gene CTLA4 and melanoma.