Checkpoint inhibitor therapies are a demonstrably successful approach to cancer immunotherapy. They suppress a mechanism that normally restrains immune cells from attacking other cells. This mechanism is abused by cancers, alongside a variety of other ways in which the immune system can be subverted or quieted. Any advanced tumor tends to have evolved into a state in which it is ignored or even helped by the immune system. Checkpoint inhibitor therapies are an improvement on chemotherapy when it comes to the trade-off between harming the cancer and harming the patient, as well as in the odds of success, but still present risks to patients. Immune checkpoints exist to prevent autoimmunity, and rampant autoimmunity can be just as deadly as any cancer.
Our usual defence against disease is our immune system. It does an excellent job of sorting out what doesn’t belong in the body and attacking it – except when it comes to cancer. The checkpoint inhibitor breakthrough was the realisation that the immune system wasn’t ignoring cancer. Instead, cancer was taking advantage of tricks that shut down the immune system. When stimulated, the T cell protein CTLA-4 acted like a circuit breaker on immune response.
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