Murine models have shown that blocking any of PD-1 [99,100], PD-L1 [100,101], or PD-L2 [101] has beneficial effects in inhibiting the growth and spread of tumors; conversely, constitutive expression of PD-L1 by tumor cells leads to enhanced resistance to CD8+ T cell-mediated cytolysis [102]. This evidence concerns the gene CD274 and neoplasm.