immunotherapy

Immunotherapy is treatment that uses substances to stimulate or suppress the immune system so that the body can fight cancer, infection and other diseases. Some immunotherapies act only on particular cells of the immune system; others affect it in a general way. The US National Cancer Institute lists cytokines, vaccines, bacillus Calmette-Guerin and some monoclonal antibodies among the types in use, and groups the main approaches used against cancer as nonspecific immune stimulation, T-cell transfer therapy and immune checkpoint inhibitors.

The distinction that matters when reading a cancer trial is what the drug acts on. An immunotherapy does not attack the tumour directly. It changes how the patient's own immune cells behave, which is how a checkpoint inhibitor such as pembrolizumab works: it binds to a receptor called PD-1 on activated T cells and blocks the signal that would otherwise hold those cells back from attacking a tumour. The same mechanism explains the risks. Because the treatment alters immune behaviour, its side effects can take the form of the immune system attacking healthy organs, and the prescribing information for these medicines carries warnings about immune-mediated reactions.