Fig. 1

PD-1/PD-L pathway and therapeutic targeting. PD-1 contains an extracellular domain, transmembrane region, and cytoplasmic tail with ITIM and ITSM. During T cell activation through TCR crosslinking with antigen presented by MHC, PD-L1, and PD-L2 expressed on cancer cells downregulate T cell activity by binding to PD-1, unless blocked by anti-PD-1/PD-L1/PD-L2. Red arrows indicate inhibitory signals, and green lines indicate stimulatory signals