PDCD1 and neoplasm: Conversely, PD-L1 formed on the surface of HCC cells can not only bind to PD-1, but also bind to B7.1 on dendritic cells (DCs) to prevent the interaction of B7.1/CD28 to inhibit the activation of anti-tumor T cells, thereby evading T encirclement and suppression of cells (20, 21).