STOCKHOLM (AP) — Three scientists won Nobel Prize in Medicine Monday is a discovery about how the immune system knows to attack germs rather than our own bodies.
Research by Mary E. Brankow, Fred Ramsdell, and Dr. Shimon Sakaguchi has uncovered an important pathway the body uses to suppress the immune system, called peripheral immune tolerance. Experts call the discovery crucial for understanding autoimmune diseases such as type 1 diabetes, rheumatoid arthritis and lupus.
In separate projects spanning several years, three scientists, two in the United States and one in Japan, identified the importance of cells now called regulatory T cells. Scientists are currently using these discoveries in a variety of ways. For example, finding better treatments for autoimmune diseases, increasing the success rate of organ transplants, and strengthening the body’s own fight against cancer.
“Their findings are decisive in our understanding of how the immune system works and why we do not all develop serious autoimmune diseases,” said Nobel Committee Chairman Ole Kampe.
Brankow, 64, is currently a senior program manager at the Systems Biology Institute in Seattle. Ramsdell, 64, is a scientific advisor to San Francisco-based Sonoma Biotherapeutics. Mr. Sakaguchi, 74, is a distinguished professor at the Osaka University Immunology Frontier Research Center in Japan.
Mary E. Brunkow is thrilled to hear that she has won the Nobel Prize in Medicine for part of her research on peripheral immune tolerance, Monday, Oct. 6, 2025, in Seattle. (AP Photo/Lindsay Wasson)
The award, officially known as the Nobel Prize in Physiology or Medicine, is 2025 Nobel Prize Announcement Published by a panel at the Karolinska Institute in Stockholm.
of physics award It will be announced on Tuesday, chemistry Wednesday and literature on Thursday. nobel peace prize Announced on Friday, the Nobel Memorial Prize is economy October 13th.
2025 Nobel Prize Winners in Medicine
The immune system has redundant ways to detect and fight bacteria, viruses, and other invaders. However, sometimes certain immune cells can go out of control and mistakenly attack your own cells and tissues, causing autoimmune diseases.
Scientists once thought that the body controlled this system only in a focused way. Key immune soldiers, such as T cells, are trained to spot villains, and the thymus eliminates those that go wrong in ways that can cause autoimmunity.
nobel prize winners The research team later uncovered additional ways the body suppresses the system when immune cells become confused and mistake human cells for invaders. This happens when a person has an autoimmune disease.
Sakaguchi said, “I was interested in the mechanism of the immune response, which is supposed to protect itself, but instead reacts and attacks itself.”
His experiments in mice showed that the thymic pathway alone could not explain it. In 1995, he discovered a previously unknown T cell subtype: regulatory T cells. This subtype can also suppress overreacting immune cells like a biological guard.
And in 2001, Brankow and Ramsdell were working together at a biotechnology company, studying mice with autoimmune diseases. In painstaking research at a time when genetic mapping was still a developing field, they pinpointed the culprit as a specific mutation in a gene called Foxp3, and soon realized that it may also play a major role in human health.
“From a DNA level, it was really small changes that caused big changes in how the immune system worked,” Brunkow told The Associated Press.
When Dr. Sakaguchi returned to Japan, he realized, “Although this gene had attracted a lot of attention as a gene that could explain multiple autoimmune diseases, it was still a mystery why this gene caused the disease.”
Two years later, Sakaguchi combined this discovery to show that the Foxp3 gene can control the development of regulatory T cells and suppress other hyperreactive cells.
A screen displays photos of Nobel Prize winners Mary E. Brankow, Fred Ramsdell, and Shimon Sakaguchi at the Nobel General Assembly at the Karolinska Institutet in Stockholm, Sweden, Monday, Oct. 6, 2025. (Claudio Bresciani/TT News Agency, via AP)
Why is this work important?
Marie Warren Helenius, professor of rheumatology at Karolinska Institutet, said the study opened up a new field of immunology.
Until the authors’ work, immunologists had not understood the intricacies of how the human body distinguishes between foreign cells and its own cells, said Dr. Jonathan Schneck, an expert in cellular immunology at Johns Hopkins University.
One goal now is to find ways to increase the number of regulatory T cells (also known as T-regs) to help fight autoimmune diseases, Schneck said. This would reduce the need for current treatments that instead suppress the immune system, leaving patients vulnerable to infection.
The American Association of Immunologists said the laureate’s work “fundamentally changed our understanding of immune balance.”
Schneck cautioned that this discovery has not yet led to new treatments. But “I want to emphasize that this research started in 1995, and we are benefiting from it, but there is much more to come.”Scientists are building on the research.
Reactions from Mary E. Brunkow, Fred Ramsdell, and Dr. Shimon Sakaguchi
Thomas Perlman, secretary general of the Nobel committee, said he reached Sakaguchi by phone in his lab on Monday morning. “He seemed incredibly grateful and said it was a great honor. He was very surprised by the news.”
At a press conference hours later (interrupted by a congratulatory phone call from Japan’s prime minister), Sakaguchi called his victory a “pleasant surprise.”
“There are many diseases that require further research and treatment. We hope that further progress will be made in the field and that our discoveries will lead to disease prevention. That is the purpose of our research,” he added.
Meanwhile, Brankow learned of the award from an Associated Press photographer who visited her home in Seattle early in the morning.
She said she had ignored earlier calls from the Nobel committee. “My phone rang, I saw the number from Sweden, and I thought, ‘This is some kind of spam.'”
“When I told Mary I had won, she said, ‘Don’t be ridiculous,'” said her husband, Ross Colquhoun.
Ramsdell could not immediately be reached by the Associated Press or his employer, believing he may be on a backpacking trip.
Sonoma Biotherapeutics CEO Jeff Bluestone told The Associated Press that Ramsdell is “one of the most humble people I’ve ever met.” “It would be great if we could honk the horn for him.”
The award ceremony will be held on December 10th, the anniversary of Alfred Nobel’s death. The person who created the award. Nobel was a wealthy Swedish businessman and the inventor of dynamite. He died in 1896.
Osaka University professor Dr. Shimon Sakaguchi (right) receives a bouquet of flowers at a press conference in Suita, near Osaka, after receiving the Nobel Prize in Medicine on Monday, October 6, 2025. (Shohei Miyano/Kyodo News AP)
The trio will share the prize money of 11 million Swedish krona (approximately $1.2 million).
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Mr. Wasson reported from Seattle and Mr. Neergaard from Washington. Mari Yamaguchi in Tokyo, Stephanie Dazio and David Keaton in Berlin, and Aditi Ramakrishnan in New York contributed.
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