The PD-1/PD-L1 axis is well-known to perform as a powerful IC—it limits T lymphocyte proliferation and toxicity effects, induces apoptosis of T cells, and promotes the differentiation of CD4+ T cells into Foxp3+ regulatory T cells and resistance of tumor cells to cytotoxic T-lymphocyte (CTL) attack (55). The gene discussed is PDCD1; the disease is neoplasm.