Fig. 1.

The extrinsic function of the PD-1/PD-L1 signaling axis in cancer and the mechanisms of PD-1/PD-L1 inhibitors in cancer therapy. A When the overexpressed PD-L1 of tumors bind to the PD-1 expressed on the T cells, it will lead to T cells anergy or apoptosis and ultimately immune evasion. B PD-1/PD-L1 inhibitors can block this pathway to promote T cell activation [11]. Copyright © 2020 Hudson, Cross, Jordan-Mahy, and Leyland