Nobel Prize in Medicine Awarded to Mary E. Brunkow, Fred Ramsdell, and Dr. Shimon Sakaguchi

Introduction to the Nobel Prize Winners

STOCKHOLM — Mary E. Brunkow, Fred Ramsdell, and Dr. Shimon Sakaguchi won the Nobel Prize in medicine Monday for their discoveries concerning peripheral immune tolerance.

Brunkow, 64, is a senior program manager at the Institute for Systems Biology in Seattle. Ramsdell, 64, is a scientific adviser for Sonoma Biotherapeutics in San Francisco. Sakaguchi, 74, is a distinguished professor at the Immunology Frontier Research Center at Osaka University in Japan.

“Their discoveries have been decisive for our understanding of how the immune system functions and why we do not all develop serious autoimmune diseases,” Olle Kämpe, chair of the Nobel Committee, said.

The award, officially known as the Nobel Prize in Physiology or Medicine, is the first of the 2025 Nobel Prize announcements and was announced by a panel at the Karolinska Institute in Stockholm.

The physics prize will be announced on Tuesday, chemistry on Wednesday and literature on Thursday. The Nobel Peace Prize will be announced Friday and the Nobel Memorial Prize in economics Oct. 13.

The award ceremony will be Dec. 10, the anniversary of the death of Alfred Nobel, who founded the prizes. Nobel was a wealthy Swedish industrialist and the inventor of dynamite. He died in 1896.

Mary E. Brunkow smiles after hearing about winning a Nobel Prize in medicine for part of her work on peripheral immune tolerance, in Seattle, Monday, Oct. 6, 2025. (AP Photo/Lindsey Wasson)

The trio will share prize money of nearly $1.2 million.

The Work That Won the 2025 Nobel Prize in Medicine

The immune system has many overlapping systems to detect and fight bacteria, viruses, and other intruders. Key immune warriors such as T cells get trained on how to spot bad actors. If some instead go awry in a way that might trigger autoimmune diseases, they’re supposed to be eliminated in the thymus — a process called central tolerance.

The Nobel winners unraveled an additional way the body keeps the system in check.

The Nobel Committee said it started with Sakaguchi’s discovery in 1995 of a previously unknown T cell subtype now known as regulatory T cells or T-regs. Then in 2001, Brunkow and Ramsdell discovered a culprit mutation in a gene named Foxp3, a gene that also plays a role in a rare human autoimmune disease.

Osaka University professor Dr. Shimon Sakaguchi, right, receives flowers at a news conference in Suita, near Osaka, western Japan, Monday, Oct. 6, 2025, after he won the Nobel Prize in medicine. (Mizuki Sakai/Kyodo News via AP)

Brunkow said she and Ramsdell were working together at a biotech company, investigating why a particular strain of mice had an over-active immune system. They had to work with brand-new techniques to find the mouse gene behind the problem — but quickly realized it could be a major player in human health, too.

“From a DNA level, it was a really small alteration that caused this massive change to how the immune system works,” she told AP.

Two years later, Sakaguchi linked the discoveries to show that the Foxp3 gene controls the development of those T-regs — which in turn act as a security guard to find and curb other forms of T cells that overreact.

Why This Work Matters

The work opened a new field of immunology, said Karolinska Institute rheumatology professor Marie Wahren-Herlenius. Researchers around the world now are working to use regulatory T cells to develop treatments for autoimmune diseases and cancer.

Dr. Jonathan Schneck, a pathology professor at Johns Hopkins University, is among those who study T cells. He said that until the trio’s research published, immunologists didn’t understand the complexity of how the body differentiates foreign cells from its own and how it can tamp down an overreaction.

The discoveries haven’t yet led to new therapies, Schneck cautioned. But “it’s incredibly important to emphasize, this work started back in 1995 and we’re reaping the benefits but yet have many more benefits we can reap” as scientists build on their work.

How Mary E. Brunkow, Fred Ramsdell, and Dr. Shimon Sakaguchi Reacted

Thomas Perlmann, secretary-general of the Nobel Committee, said he was only able to reach Sakaguchi by phone Monday morning.

“I got hold of him at his lab and he sounded incredibly