2025 Nobel Prize in Physiology or Medicine Awarded for Discoveries Key to Treating Autoimmune Disease

2025 Nobel Prize in Physiology or Medicine Awarded for Discoveries of How the Body Puts the Brakes on the Immune System 

By Lauren J. Young edited by Tanya Lewis

This story will be updated. 

The human immune system is our body’s primary line of defense against harmful microbes, viruses and other invaders—but that defense line can sometimes run amok and attack healthy cells. This is the basis of many autoimmune diseases, from cancer to rheumatoid arthritis to type 1 diabetes. The 2025 Nobel Prize in Physiology or Medicine was awarded to the scientists who conducted fundamental research on peripheral immune tolerance, a system that pumps the brakes on the immune system and keeps it from harming the body. 

Mary E. Brunkow, Fred Ramsdell and Shimon Sakaguchi jointly won the prize, which was announced on Monday in Stockholm. The Nobel committee recognized the awardees’ body of work for spurring clinical trials on potential new treatments, such as therapies that may propagate immune cells called regulatory T cells that can suppress overreactive immune responses in an autoimmune disease or organ transplant. More than 200 clinical trials on therapies investigating such peripheral immune tolerance are in the works, according to committee members. 

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“This year’s Nobel Prize in Physiology or Medicine relates to how we keep our immune system under control so we can fight all imaginable microbes and still avoid autoimmune disease,” said Marie Wahren-Herlenius, a member of the 2025 Nobel Committee for Physiology or Medicine, at a livestreamed press conference today in Stockholm. 

Sakaguchi is a distinguished professor at the Immunology Frontier Research Center at Osaka University, in Japan. His initial work investigating an organ called the thymus in mice in the 1980s and 1990s at Aichi Cancer Center Research Institute in Nagoya, Japan, eventually led to the discovery of a novel surface protein, CD25, that helped him establish the new class of T cells: regulatory T cells.  

Brunkow and Ramsdell had both been researchers at Celltech Chiroscience, a biotech company focused on autoimmune disease therapies in Washington state, where they looked into the genetic basis of peripheral immune tolerance. Using scurfy mice—a strain of mice unexpectedly born with scaly, crusty skin, swollen lymph nodes, and that lived for just a few weeks—Ramsdell and Brunkow pinpointed a mutant gene called Foxp3, the key gene that controls T regulatory cells. Brunkow is now a senior program manager at the Institute for Systems Biology in Seattle and Ramsdell is a scientific advisor for Sonoma Biotherapeutics in San Francisco. 

“It’s a fundamental discovery about the principle that keeps our immune system in check,” said Rickard Sandberg, a member of the 2025 Nobel Committee for Physiology or Medicine, in an interview with press at the livestreamed announcement. The system is “very important for not having us all develop autoimmune disorders.”  

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