PDCD1 and liver cancer: In human liver cancer tissues, PD-L1 expression was mainly expressed in Kupffer cells, and PD-L1+Kupffer cells interacted with PD-1+CD8+ T cells, resulting in hepatocellular carcinoma effector T cell dysfunction, suggesting that PD-L1/PD-1 immune checkpoints could be used as targets for the treatment of HCC (35, 36).