Chronic exposure to low IFN-γ levels in H22 hepatoma, MA782/5S mammary adenocarcinoma and B16 melanoma led to tumor development and induction of PD-L1, PD-L2, CTLA-4 and Foxp3 molecules which at least partially mediated tumor immune evasion [138]. This evidence concerns the gene CTLA4 and neoplasm.