Fig. 1.

Schematic of T cell interactions. a Major histocompatibility complex (MHC) on antigen presenting cell (APC) binding to T cell receptor (TCR) along with the costimulatory B7-CD28 interaction. b CTLA-4 competitively inhibits the binding of B7 to CD28 and results in dampened T cell activation and proliferation. c PD-1 on a T cell binding to PD-L1 expressed on a cancer cell to decrease T cell activation. d Anti-PD-1 antibody binding to PD-1 and eliminating the negative effect of the PD-1/PD-L1 axis on T cell function