Fig. 1.

The interactions between PD-1, PD-L1 and CTLA-4 and B7 inhibits T cell proliferation, clonal expansion, cytokine production and consequently tumour cell killing. The blocking of CTLA-4, PD-1 and PD-L1 results in T cell activation and T cell mediated killing of tumour cells. Majority of tumour cells over-express a ligand e.g., PD-L1. ICIs include antibodies against for example PD-1 (nivolumab, pembrolizumab) or PD-L1 (Atezolizumab) which prevents these interactions and cause a T-cell reaction against these tumours.