As one of the most important immune checkpoint protein, PD-1 expresses on activated T cells, B cells, natural killer cells, monocytes, and dendritic cells [20, 21], and plays a critical role in inhibiting immune responses and promoting self-tolerance by suppressing the activity of T cells; therefore, anti-PD-1 therapies have significantly evolved for cancer treatment in the era of immunotherapy [22–24]. The gene discussed is PDCD1; the disease is cancer.