We found that the baseline frequencies of circulating CD4+PD-1+ and CD8+PD-1+ T cells in HCC patients were 6.85% and 6.08%, respectively, whereas in patients treated with PD-1 inhibitors, we detected significantly reduced values of 0.30% and 0.21%, respectively, thereby indicating that PD-1 inhibitors can effectively block PD-1 receptors on the surface of T cells. Here, CD4 is linked to hepatocellular carcinoma.