Cancer cells hijack the regular mechanisms by which the immune system limits cytotoxic T cell activity in inflammation, autoimmune response74,75 and tolerance,76 which is normally mediated by programmed cell death protein 1 (PD-1; also known as CD279).76 Expression of this integral membrane protein is inducible in T cells, B cells and activated peripheral monocytes. Here, PDCD1 is linked to cancer.