Mary E. Brunkow, Fred Ramsdell, and Dr. Shimon Sakaguchi have been awarded the 2025 Nobel Prize in Medicine for their pioneering discoveries on peripheral immune tolerance — the body’s mechanism for preventing harmful immune overreactions that can cause autoimmune diseases.
The Nobel Committee announced the award on Monday, October 6, at the Karolinska Institute in Stockholm, describing the trio’s work as a “decisive advancement in understanding how the immune system functions and why we do not all develop serious autoimmune diseases.”
Sakaguchi, 74, is a distinguished professor at the Immunology Frontier Research Center at Osaka University in Japan. Brunkow, 64, serves as a senior program manager at the Institute for Systems Biology in Seattle, while Ramsdell, 64, is a scientific adviser at Sonoma Biotherapeutics in San Francisco.
The foundation of their joint recognition dates back to 1995, when Sakaguchi discovered a previously unknown type of T cell — now known as regulatory T cells or T-regs — which help control immune responses. Later, in 2001, Brunkow and Ramsdell identified a mutation in a gene called Foxp3, linked to a rare autoimmune disorder in humans. Two years after, Sakaguchi established that the Foxp3 gene regulates the development of T-regs, acting as the immune system’s safeguard against overactive T cells.
Speaking from Osaka, Sakaguchi said, “It was a nice surprise. I hope research into this area will further progress so that our findings can be used in treatment, and I hope we can contribute to that as well.”
Brunkow, who learned about her award from a visiting photographer after ignoring an early call from Sweden, recalled the moment with amusement. “My phone rang and I saw a number from Sweden and thought: ‘That’s just spam,’” she said, while her husband, Ross Colquhoun, added that she initially dismissed the news as “ridiculous.”
The Nobel Committee said their discoveries have opened a new frontier in immunology, paving the way for potential therapies targeting autoimmune diseases and certain cancers.
Professor Marie Wahren-Herlenius of the Karolinska Institute noted that “researchers around the world are now working to harness regulatory T cells to treat autoimmune diseases and cancer,” underscoring the long-term global impact of their work.
This marks the first Nobel Prize announcement of 2025, setting the tone for a week of awards honouring outstanding contributions in physics, chemistry, literature, peace, and economics.