A possible role of the immune system in the etiology of HCC is suggested by the increased presence of immunological factors favoring immunosuppression such as augmented numbers of Tregs, myeloid-derived suppressor cells (MDSC), PD-1+exhausted T cells, and increased levels of immunosuppressive cytokines in patients with HCC, compared with normal controls [14]. The gene discussed is PDCD1; the disease is hepatocellular carcinoma.