CD4 and hepatocellular carcinoma: Although we found that DKK1 increased the expression of PD-L1 and decreased the expression of CD4 and CD8 in HCC mouse models (Supplementary Fig. 5A and B), the effects of DKK1 inhibitors on immuno-oncological therapeutics, such as anti-PD-L1 antibodies, should be further investigated in the future.