PDCD1 and hepatocellular carcinoma: The high pre-treatment level of exosomal PD-L1 may reflect the fact that T cells will not be reinvigorated by anti-PD-1 therapy, and the high on-treatment level of exosomal PD-L1 may reflect that anti-PD-1 therapy successfully elicits anti-tumor immunity, which must be validated in HCC patients [89].