Cancer immunotherapy employs different strategies to stimulate, improve or reactivate the patient’s immune system to destroy cancer cells. There are several types of immunotherapy amongst which immune checkpoint inhibitors are the most promising. Immune checkpoints refer to a plethora of signalling pathways that regulate the immune response. Therefore, many of the immune checkpoint inhibitors are based on monoclonal antibodies or fusion proteins that bind to immune checkpoints. In some cases, they can also be based on molecules that bind to immune-inhibitory enzymes and deactivates them. The utilization of the immune checkpoint inhibitors shifts the signalling pathways responsible for regulating the immune response. CTLA-4 and PD-1/PD-L1 axis are the most researched immune checkpoints, with inhibitory effects on the cell-mediated immune response. CTLA-4 downregulates the activation of T cells in the early stages of the immune response, while the PD-1/PD-L1 axis downregulates the effector phase of the immune response. There are 7 different FDA approved immune checkpoint inhibitors to treat many different types of cancer. Due to their durable responses in a significant percentage of cancer patients and low toxicity new immune checkpoints such as LAG-3, IDO-enzyme, TIM-3, ICOS, 4-1BB, OX40, CD27, GITR, and CD4 are being extensively researched. At the same time, researchers are testing existing immune checkpoints in combination with other cancer therapies.
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