Although pre-mNK cells (IKDC) were first described for their role in antitumor immunity, they have also been observed to control tolerance to self-antigens.30 Interestingly, melanoma licenses NK1.1+B220+CD11c+MHC class II++ pre-mNK cells to present antigen.50,52 Activated pre-mNK cells express the inhibitory PD-1 ligand, PD-L1, and produce the immunosuppressive cytokine, IL-10,30 both of which have been demonstrated to suppress antitumor immunity. This evidence concerns the gene PTPRC and melanoma.