Checkpoint inhibitors are antibodies which are intended to prevent manipulation of the immune system by tumour cells.
To prevent over-reactions of the immune system (T-lymphocytes), the immune system has a number of mechanisms. Tumours misuse these immune control points or checkpoints in order to override the immune defence against them.
The activation of PD-1 (“programmed cell death”) triggers apoptosis in T-lymphocytes. The PD-1 receptor, which sits on the surface of the T cells, is activated by the binding of the ligands PD-L1 and PD-L2 (“programmed cell death ligand”) on tumour cells and thereupon suppress the immune cells which attack cancer cells. The cancer cell thus escapes the cytotoxic immune reaction.
With antibody therapies these bonds are to be prevented so that the immune cells can attack the cancer cells.