Disrupting the interaction between PD-1, expressed on activated cytotoxic CD8+ T cells, and PD-L1, expressed on tumor cells, T regulatory (TREG) cells, and tumor-associated macrophages, results in activation and proliferation of antigen-experienced cytotoxic T cells present in the tumor microenvironment (4, 5). The gene discussed is CD8A; the disease is neoplasm.