A milestone in cancer immunotherapy was the Food and Drug Administration (FDA) approval of the checkpoint inhibitor ipilimumab, a monoclonal antibody targeting cytotoxic T lymphocyte antigen 4 (CTLA-4) in 2011 [2], which paved the way for other immunotherapeutic strategies, such as the use of monoclonal antibodies targeting programmed cell death 1 (PD-1) or PD-1 ligand 1 (PD-L1) [3]. The gene discussed is PDCD1; the disease is cancer.