Immune checkpoint inhibitors (ICIs) trigger antitumor activity by blocking intrinsic downregulating factors of the immune system such as programmed cell death 1 (PD-1), programmed cell death ligand 1 (PD-L1), and cytotoxic T-lymphocyte antigen 4 (CTLA-4), have shown significant breakthroughs in treating different types of cancer, including melanoma, gastric carcinoma, and non-small cell lung cancer [5–7]. The gene discussed is PDCD1; the disease is cancer.