This morning, the Nobel Prize committee awarded the 2018 Nobel Prize in physiology or medicine to two scientists who, separately, discovered proteins that “brake” the immune system — work that paved the way for what the committee calls “an entirely new principle for cancer therapy.” The winners are James P. Allison of the United States and Tasuku Honjo of Japan.

Working in the 1990s, both scientists studied proteins that regulate the immune system and keep it in check. For Allison, this protein was CTLA-4 protein, while Honjo studied a protein called PD-1. Both CTLA-4 and PD-1 regulate the immune system and keep it from being too aggressive. Therefore, it’s possible to use an antibody to target these proteins and shut them down. When these proteins are shut down, and the brakes “released,” our body’s immune system can go on the attack against cancerous tumors, a form of treatment today called immunotherapy. (Both proteins brake the immune system, just in different ways.)

In later experiments, Allison found that blocking CTLA proteins in mice cured them of cancer. In 2011, the US Food and Drug Administration approved this method to treat metastatic melanoma. Three years later, the FDA approved Keytruda and Opdivo, two treatments for melanoma that were based on Honjo’s work. The Nobel citation notes that a combination therapy targeting both proteins could work even better.

Dr. Allison, 70, is the chairman of immunology at the University of Texas MD Anderson Cancer Center. Dr. Honjo, 76, is a longtime professor at Kyoto University. The two will share the roughly $1.01 million prize money.