Stockholm, October 6, 2025 — The 2025 Nobel Prize in Physiology or Medicine has been awarded to Mary E. Brunkow, Fred Ramsdell, and Shimon Sakaguchi. The trio discovered how the immune system prevents attacks on the body’s own cells, a breakthrough in understanding autoimmune diseases.
Regulatory T Cells: The Immune System’s Security Guards
The Nobel Committee recognized the scientists “for their fundamental discoveries relating to peripheral immune tolerance.” Their work revealed regulatory T cells, which act like the body’s internal security system, stopping immune cells from harming healthy tissue.
Shimon Sakaguchi, a Japanese immunologist, first discovered this class of T cells in 1995. Brunkow and Ramsdell, both Americans, later identified the Foxp3 gene, explaining why certain mice were prone to autoimmune diseases. They also linked mutations in this gene to IPEX, a severe autoimmune condition in humans.
By 2003, Sakaguchi confirmed that Foxp3 governs the development of regulatory T cells, connecting the findings of all three scientists. Their research has since guided new treatments for cancer, autoimmune disorders, and therapies that enhance immune regulation.
Global Recognition and Careers
Mary Brunkow serves as a program manager at the Institute for Systems Biology in Seattle. Fred Ramsdell co-founded Sonoma Biotherapeutics in San Francisco. Shimon Sakaguchi is a professor at Osaka University in Japan.
Thomas Perlmann, secretary of the Nobel Committee for Medicine, highlighted Sakaguchi’s gratitude during a call ahead of the announcement. Brunkow and Ramsdell were also expected to respond after adjusting for time differences between Sweden and the United States.
Prize Context and Legacy
The award carries a cash prize of 11 million Swedish kronor ($1 million). Last year, the Nobel went to Victor Ambros and Gary Ruvkun for microRNA research, while in 2023 it honored Katalin Karikó and Drew Weissman for mRNA vaccine development.
Experts note that the work of this trio remains a foundational reference for immunology. Their discoveries help scientists develop new therapies that balance immune responses — often described in ABC terms: Activation, Balance, Control of immune function.
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