The success of CTLA4 and PD-1/PD-L1 blockade in cancer treatment results in the discovery of novel inhibitory regulators of T cell activation, including Lymphocyte activation gene 3 (LAG3), T cell immunoglobulin 3 (TIM3), V-domain immunoglobulin suppressor of T cell activation (VISTA) and B7-H3 (121). Here, PDCD1 is linked to cancer.