Programmed death-ligand 1 (PD-L1) (found on the surfaces of cancer cells and stromal cells) and programmed cell death protein 1 (PD-1) and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) (found on the surface of T cells) have been shown to play particularly important roles in the suppression of T-cell activation by cancer cells. The gene discussed is PDCD1; the disease is cancer.