Immune checkpoint inhibitors (ICIs) are cancer immunotherapies that are categorized under mAbs.Some checkpoint proteins help tell T cells to become active, for example when an infection is present.But if T cells are active for too long, or react to things they shouldn't, they can start to destroy healthy cells and tissues.Drugs that block checkpoint proteins are called checkpoint inhibitors.How do checkpoint inhibitors work?T cells have proteins on them that turn on an immune response and other proteins that turn it off.These are called checkpoint proteins.Some cancer cells make high levels of proteins.One main type of immune cell that does this is called a T cell.So other checkpoints help tell T cells to switch off.These can switch off T cells, when they should really be attacking the cancer cells.So the cancer cells are pushing a stop button on the immune system.And the T cells can no longer recognise and kill cancer cells.They stop the proteins on the cancer cells from pushing the stop button.