Key Points:
The 2025 Nobel Prize in Physiology or Medicine has been awarded to Mary E. Brunkow, Fred Ramsdell, and Shimon Sakaguchi.
Their discoveries have helped us understand "how the immune system functions and why we do not all develop serious autoimmune diseases.”
Sakaguchi first discovered regulatory T cells in 1995. In 2001, Brunkow and Ramsdell discovered how a particular gene mutation leads to the development of autoimmune diseases.
The 2025 Nobel Prize in Physiology or Medicine has been awarded to Mary E. Brunkow, Fred Ramsdell, and Shimon Sakaguchi “for their discoveries concerning peripheral immune tolerance.” The announcement was made by the Royal Swedish Academy of Sciences on Monday, 6 October 2025.
The Nobel Committee recognized the trio for their work in immunology. According to Olle Kämpe, chair of the committee, “Their discoveries have been decisive for our understanding of how the immune system functions and why we do not all develop serious autoimmune diseases.”
Their work stretches back as far back as 1995, when Sakaguchi made his first key discovery – the regulatory T cell. This is a class of cells that monitor other immune cells – normal T cells – thereby preventing autoimmune diseases. This class of cells was previously undiscovered, showing that the immune system was more complex than understood at the time. The discovery upended the dominant theory at the time that immunity developed due to a process called ‘central tolerance’.
Then in 2001, Brunkow and Ramsdell discovered why a particular mouse strain was exceptionally susceptible to autoimmune diseases. They showed that the mice from the strain had a mutation in the Foxp3 gene and that mutations in the human equivalent of this gene led to the development of IPEX, a serious autoimmune disease.
Two years after this, Sakaguchi linked the two discoveries by proving that the Foxp3 gene governs the development of regulatory T cells.
See Also: 2024 Nobel Prize in Physiology or Medicine: Victor Ambros and Gary Ruvkun for MicroRNA Discovery
According to the Nobel Prize website, “The laureates’ discoveries launched the field of peripheral tolerance, spurring the development of medical treatments for cancer and autoimmune diseases.”
Mary E. Brunkown is a Senior Program Manager at the Institute for Systems Biology in Seattle, Fred Ramsdell is a Scientific Advisor at Sonoma Biotherapeutics in San Francisco, and Shimon Sakaguchi is a Distinguished Professor at the Immunology Frontier Research Center in Osaka University.
The award will be conferred to the three later this year in December, along with three gold medals, and a million-dollar prize, which will be split evenly between them.
Sakaguchi was reached by phone at his laboratory shortly after the announcement and expressed his surprise and gratitude for the honour. Nobel official Thomas Perlmann said voicemails were left for the other laureates.
The announcement of the prize marks the start of ‘Nobel Week’ – with winners for Physics, Chemistry, Literature, Peace, and Economic Sciences to be declared over the coming days. The formal Nobel ceremony is scheduled for 10 December 2025, the anniversary of Alfred Nobel’s death. [Rh/DS]
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