Fig. 1

Mechanisms of immune effects of PD-1/PD-L1 inhibitors in the tumour microenvironment. DC: Dendritic cells; MDSC: Myeloid-Derived Suppressor Cells; M1/M2: Macrophages 1/2 CTL: Cytotoxic T Lymphocyte; TCR: T-cell Receptor; MHC I: Major Histocompatibility Complex Class I; Treg cell: Regulatory T cells. CTL activates cytotoxicity through TCR recognition of MHC-1-like molecule-tumour antigen peptide complexes on the surface of tumour cells. PD-L1 on the surface of tumour cells binds to PD-1 on CTL cells, inhibiting CTL activation and facilitating tumour cell immune escape. PD-1/PD-L1 inhibitors can block PD-1 and PD-L1 binding, lift CTL activation restriction, and restore the anti-tumour immune effect