Published: September 9, 2015Updated: April 5, 2022Medically Reviewed By: Gordon J. Freeman, PhDAn immune checkpoint inhibitor is a drug that unleashes an immune system attack on cancer cells. Often made of antibodies, checkpoint inhibitors act on the immune system, therefore such drugs are known as immunotherapies. How do checkpoint inhibitors work? Checkpoint inhibitors seek to … Continue reading What is a Checkpoint Inhibitor? Immune Checkpoint Inhibitor Definition