So far, six immune checkpoint inhibitors targeting PD-1 or PD-L1 have already been approved for clinical therapy in cancer patients, including PD-1 inhibitors like pembrolizumab, nivolumab, cemiplimab, and PD-L1 inhibitors like atezolizumab, avelumab, and durvalumab [319] (Table 1). This evidence concerns the gene PDCD1 and cancer.