Trio of Researchers Awarded Nobel Prize for Groundbreaking Discovery of Immune Cells That Prevent Autoimmune Disease

Mary Brunkow, Fred Ramsdell and Shimon Sakaguchi’s research revealed a new class of cells shaking up scientists’ understanding of the human immune system

Marta Hill | Freelance contributor

October 6, 2025

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Three researchers were awarded the 2025 Nobel Prize in Physiology or Medicine on October 6 for their fundamental discoveries about the cells that keep humans’ immune systems in check and prevent autoimmune diseases.

Mary Brunkow, Frederick Ramsdell and Shimon Sakaguchi’s work to identify regulatory T cells launched the field of peripheral tolerance, which is spurring development of new treatments for cancer and autoimmune diseases.

Just as in 2024, the Nobel was awarded for fundamental science research, not the discovery of a specific clinical treatment.

The trio’s work has laid the foundation for a variety of possible clinical applications, Olle Kämpe, chair of the Nobel Committee, says in a statement. “Their discoveries have been decisive for our understanding of how the immune system functions and why we do not all develop serious autoimmune diseases.”

The immune system is a powerful defense against malicious microbes and pathogenic particles, but under normal circumstances, it does not attack the body’s own cells and organs. When it does, it can lead to autoimmune diseases like Type 1 diabetes and rheumatoid arthritis.

Two primary mechanisms protect us from our own immune systems: central and peripheral tolerance. Central tolerance develops early in life through a process in the thymus gland. Immune cells, including T cells, are screened by the small organ, and any self-reactive cells are eliminated before being sent out into the rest of the body.

But some of the harmful cells get by the thymus’ defenses. That’s where the cells in this year’s Nobel Prize work come in. Brunkow, Ramsdell and Sakaguchi’s work identified cells, called regulatory T cells, that work as the immune system’s security guards, patrolling the body for rogue immune cells—what’s known as peripheral tolerance.

“It opens a completely new dimension of how to think about this important immune system’s balance [and] checks,” Nobel Committee member Rickard Sandberg said at a press conference. “By knowing about the existence of these regulatory T cells, we also have the ability to start thinking about how we can increase their activity or decrease their activity.”

“If you control the brakes to the immune system, it gives you the ability to turn the immune response up or to tone it down,” Adrian Liston, an immunologist at the University of Cambridge in England, tells Science’s Catherine Offord.

In autoimmune diseases, the regulatory T cells aren’t doing enough. By understanding the mechanisms at play, new treatments could ramp up the responses of these cells and help alleviate such conditions. Other possible applications include dampening the immune system’s ability to reject organ transplants or increasing its ability to attack malicious cancer cells.

More than 200 clinical tests are currently ongoing, Sandberg noted at the conference.

When Thomas Perlmann, secretary-general of the Nobel Committee, called to give the new laureates the news, he originally reached only Sakaguchi. “I got hold of him at his lab and he sounded incredibly grateful, expressed that it was a fantastic honor. He was quite taken by the news,” Perlmann said at the conference. He left messages with Brunkow and Ramsdell asking them to call him back.

Brunkow learned the news from an Associated Press photographer, the news outlet reports, after ignoring the earlier call from the Nobel committee. “My phone rang, and I saw a number from Sweden and thought: ‘That’s just ... spam of some sort,’” Brunkow tells the Associated Press’ Kostya Manenkov, Lauran Neergaard and Lindsey Wasson.

“It’s amazing news,” Holm Uhlig, a pediatrician at the University of Oxford in England who studies inflammatory bowel diseases and has previously collaborated with Ramsdell, tells Science. “It just shows the contribution that the field has made. ... These are brilliant, brilliant people.”

The Nobel committee will continue revealing winners in its various award categories this week. Each prize comes with an 11 million Swedish kronor (about $1.2 million) prize that is split between laureates.

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Marta Hill is a science journalist based in New York City and a former intern at Smithsonian magazine. She is a part of the 2025 class of New York University’s Science, Health and Environmental Reporting Program. Her work has appeared in the Transmitter, Eos, Boston.com and more.