Figure 2.

Mechanisms of PD-1/PD-L1 axis in HCC. (A) Cancer antigen is released from HCC cells and recognized by APCs (B) APCs that capture antigens migrate to lymph nodes (C) APC presents antigen to immature T cells through TCR and activates T cells, which can be inhibited by PD-1/PD-L1 axis (D, E) T cells infiltrate to the tumor. Activated T cells secrete IFN γ and stimulate cancer cells to express PD-L1 and protect themselves. By binding its ligand PD-L1 or PD-L2, it can prevent the stimulation signal of TCR, reduce the activity of T cells and prevent autoimmune damage during the immune response. MDSCS inhibits the activation of T cells by binding to PD-1 on T cells. Tregs also inhibits the proliferation and activation of T cells.