Fig. 2: Mechanism of action of anti-PD-1 and anti-PD-L1 antibodies.

a In a PD-L1 negative tumour, tumour neoantigens presented on the surface of tumour cells or APCs are detected by T cells, which are then activated to destroy the tumour cell. b Tumour cell or APC expression of PD-L1 prevents T cell activation and allows immune evasion. c Anti-PD-I antibodies can bind to PD-1 on T cells, preventing the interaction between PD-1 and PD-L1 and therefore enabling tumour cell destruction. d Anti-PD-L1 antibodies can bind to PD-L1 on tumour cells and APCs, preventing the interaction between PD-1 and PD-L1 and enabling tumour cell destruction.