Harvard Health Letter

What is immunotherapy?

Ask the doctor

Q. A friend has melanoma, and his doctor wants to use a new kind of treatment that boosts the immune system. Can you tell me more?

A. The immune system exists to attack foreign things that enter the body, such as germs. Certain cells of the immune system recognize and attack foreign things. Cancerous cells make chemicals that are not made by normal cells, chemicals the immune system should recognize as foreign. Unfortunately, eight million people around the globe die of cancer each year after their immune systems fail to destroy the cancer. Why do their immune systems fail?

About 20 years ago, two scientists — one in the United States and one in Japan — were studying T cells, immune system cells that attack foreign things. They weren’t studying cancer. They were just trying to figure out how T cells work. Each of the scientists found a chemical on the surface of T cells that had not previously been discovered. One chemical was called PD-1, and the other CTLA-4. What did they do? When stimulated, the chemicals kept the T cells from attacking things: they applied the brakes.

The scientists wondered: what if we could figure out a way to disable these chemicals? Would disabling them release the brakes and make the T cell attack more effective? Over several years of trial and error, they finally found drugs that disabled the chemicals. Then came the acid test: would giving these drugs to mice with cancer help the T cells to attack the cancer? The answer was a robust “yes”!

But treatments that work in mice don’t always work in people. And a century of trying had made many scientists skeptical that the human immune system could ever be stimulated to fight cancer. The scientists struggled to interest pharmaceutical companies, and finally succeeded. In certain people, with certain types of cancer, the immune-boosting treatment produced startling results.

Perhaps the best known example is former president Jimmy Carter. In 2015, he was diagnosed with melanoma that had spread to his brain, and was given months to live. His doctors tried one of these immune-boosting drugs, and the brain metastases melted away. In 2018, at age 94, President Carter published his latest book. For some people, the treatments appear to have cured their cancer. While it’s very unlikely that this approach will cure all kinds of cancer, it is helping a growing number of people.

For me, there is an important message in this story. These scientists, whose work was honored in 2018 with the Nobel Prize, were not trying to cure cancer. They were just trying to figure out how living things work. A society that supports such curiosity benefits in ways that it never could have predicted.

— by Anthony L. Komaroff, M.D.Editor in Chief, Harvard Health Letter

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