classified HCC patients into three subtypes based on immune cell infiltration: S1 is characterized by a “hot tumor” with high infiltration of immune cells and the best prognosis; S2 is characterized by a “cold tumor” due to its low immune infiltration rate; and S3 is characterized by an “immunosuppressive tumor” with high expression of immunosuppressive genes (CTLA4 and TIGIT) and the worst prognosis (61). Here, CTLA4 is linked to hepatocellular carcinoma.