The PD-1 is co-expressed with other ICPs, including T-cell immunoglobulin and ITIM domain (TIGIT; also called Vstm3, WUCAM, VSIG9), lymphocyte activation gene 3 (LAG-3), DNAX accessory molecule-1 (DNAM-1; CD226) and T-cell immunoglobulin and mucin domain-containing molecule-3 (TIM-3) in human cancers [29,43,44]. The gene discussed is PDCD1; the disease is cancer.