TNFRSF9 and hepatocellular carcinoma: Recognizing the pivotal role that Treg cells play in the immune microenvironment and immunotherapy of HCC, we selected 8 Treg cell marker genes: FOXP3, CCR8, TNFRSF8, LAYN, TNFRSF9, IKZF2, RTKN2, CTLA4, BATF, and IL21R [21].