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Anti-PD-1 and PD-L1 monoclonal antibodies are a type of targeted immunotherapy called an immune checkpoint inhibitor. Checkpoint inhibitors don't kill cancer cells directly, instead, they target specific proteins on T-cells (a type of immune cell), one of which is called PD-1.

In healthy people, PD-1 acts as a “set of brakes” to stop the T-cells from attacking other cells in the body. It does this by attaching to PD-L1, a protein on some normal (and cancer) cells. When PD-1 is bound to PD-L1, the T-cell will not attack the other cell. This helps our immune system tell the difference between foreign invaders and healthy tissue.

But some cancer cells have large amounts of PD-L1, which allows them to bind to PD-1 on the T-cell, and avoid being attacked. When the T-cells are bound to the cancer cells, it puts the "brakes" on, and the T-cell can't fight the cancer.

Monoclonal antibodies that target either PD-1 or PD-L1 can block this binding and put the T-cell "brakes" in the “off” position, which means the T-cells are now active to find and kill the cancer cells, wherever they are in the body.

Other types of immune checkpoint inhibitors include those that target other checkpoint proteins such as CTLA-4 and LAG-3. These are typically used in combination with a PD-1 or PD-L1 inhibitor to treat several types of cancer.

All of these drugs are given as an infusion into a vein (IV).

PD-1 inhibitors

Examples of drugs that target PD-1 include:

• Cemiplimab (Libtayo)
• Nivolumab (Opdivo)
• Pembrolizumab (Keytruda).

PD-L1 inhibitors

Examples of drugs that target PD-L1 include:

• Atezolizumab (Tecentriq)
• Avelumab (Bavencio)
• Durvalumab (Imfinzi).