Nobel Prize in Physiology or Medicine 2025 awarded to immune system researchers

Press release Navigate to: Summary - Mary E. Brunkow - Fred Ramsdell - Shimon Sakaguchi Prize announcement Press release Advanced information Popular information English English (pdf) Swedish Swedish (pdf) 6 October 2025 The Nobel Assembly at Karolinska Institutet has decided to award the 2025 Nobel Prize in Physiology or Medicine to: Mary E. Brunkow Institute for Systems Biology, Seattle, USA Fred Ramsdell Sonoma Biotherapeutics, San Francisco, USA Shimon Sakaguchi Osaka University, Osaka, Japan “for their discoveries concerning peripheral immune tolerance” They discovered how the immune system is kept in check The body’s powerful immune system must be regulated, or it may attack our own organs. Mary E. Brunkow, Fred Ramsdell and Shimon Sakaguchi are awarded the Nobel Prize in Physiology or Medicine 2025 for their groundbreaking discoveries concerning peripheral immune tolerance that prevents the immune system from harming the body. Every day, our immune system protects us from thousands of different microbes trying to invade our bodies. These all have different appearances, and many have developed similarities with human cells as a form of camouflage. So how does the immune system determine what it should attack and what it should defend? Mary Brunkow, Fred Ramsdell and Shimon Sakaguchi are awarded the Nobel Prize in Physiology or Medicine 2025 for their fundamental discoveries relating to peripheral immune tolerance. The laureates identified the immune system’s security guards, regulatory T cells, which prevent immune cells from attacking our own body. “Their discoveries have been decisive for our understanding of how the immune system functions and why we do not all develop serious autoimmune diseases,” says Olle Kämpe, chair of the Nobel Committee. Shimon Sakaguchi was swimming against the tide in 1995, when he made the first key discovery. At the time, many researchers were convinced that immune tolerance only developed due to potentially harmful immune cells being eliminated in the thymus, through a process called central tolerance. Sakaguchi showed that the immune system is more complex and discovered a previously unknown class of immune cells, which protect the body from autoimmune diseases. Mary Brunkow and Fred Ramsdell made the other key discovery in 2001, when they presented the explanation for why a specific mouse strain was particularly vulnerable to autoimmune diseases. They had discovered that the mice have a mutation in a gene that they named Foxp3. They also showed that mutations in the human equivalent of this gene cause a serious autoimmune disease, IPEX. Two years after this, Shimon Sakaguchi was able to link these discoveries. He proved that the Foxp3 gene governs the development of the cells he identified in 1995. These cells, now known as regulatory T cells, monitor other immune cells and ensure that our immune system tolerates our own tissues. The laureates’ discoveries launched the field of peripheral tolerance, spurring the development of medical treatments for cancer and autoimmune diseases. This may also lead to more successful transplantations. Several of these treatments are now undergoing clinical trials. Illustrations The illustrations are free to use for non-commercial purposes. Attribute “© The Nobel Committee for Physiology or Medicine. Ill. Mattias Karlén” Illustration: The Nobel Prize in Physiology or Medicine 2025 Illustration: How T cells discover a virus Illustration: How harmful T cells are eliminated Illustration: The experiment that inspired Sakaguchi Illustration: Sakaguchi defines a new class of T cells Illustration: Brunkow and Ramsdell find the scurfy mutation Illustration: How regulatory T cells protect us Read more about this year’s prize Popular science background: They understood how the immune system is kept in check (pdf) Scientific background to the Nobel Prize in Physiology or Medicine 2025 (pdf) Mary E. Brunkow, born 1961. Ph.D. from Princeton University, Princeton, USA. Senior Program Manager at the Institute for Systems Biology, Seattle, USA. Fred Ramsdell, born 1960. Ph.D. 1987 from the University of California, Los Angeles, USA. Scientific Advisor, Sonoma Biotherapeutics, San Francisco, USA. Shimon Sakaguchi, born 1951. M.D. 1976 and Ph.D. 1983 from Kyoto University, Japan. Distinguished Professor at the Immunology Frontier Research Center, Osaka University, Japan. Prize amount: 11 million Swedish kronor, to be shared equally between the laureates. Press contact: Pernilla Witte, +46 8 524 86 107, [email protected] or Thomas Perlmann, [email protected], Secretary-General, The Nobel Assembly at Karolinska Institutet. Illustrations: © The Nobel Committee for Physiology or Medicine. The Nobel Assembly, consisting of 50 professors at Karolinska Institutet, awards the Nobel Prize in Physiology or Medicine. Its Nobel Committee evaluates the nominations. Since 1901 the Nobel Prize has been awarded to scientists who have made the most important discoveries for the benefit of humankind. Nobel Prize® is the registered trademark of the Nobel Foundation To cite this section MLA style: Press release. NobelPrize.org. Nobel Prize Outreach 2025. Mon. 6 Oct 2025.