American scientists Mary Brunkow and Fred Ramsdell, along with Japan’s Shimon Sakaguchi, have been awarded the 2025 Nobel Prize in Medicine for groundbreaking research into how the immune system protects healthy cells from attack. Their discovery paves the way for new treatments targeting autoimmune diseases and cancer.
The Nobel Assembly at Sweden’s Karolinska Institute awarded the prize for their work on peripheral immune tolerance, which explains how the body maintains balance, fighting harmful microbes without harming its own tissues. Professor Marie Wahren-Herlenius of the Karolinska Institute described it as a major step in understanding “how we keep our immune system under control.”
Sakaguchi, speaking to reporters outside his Osaka University lab, said, “I feel it is a tremendous honour,” according to Kyodo News.
The 2025 Nobel Prize in Medicine comes with a reward of 11 million Swedish crowns (approximately $1.2 million) and a gold medal, which will be presented by Sweden’s king later this year.
Brunkow currently serves as senior program manager at the Institute for Systems Biology in Seattle, while Ramsdell works as a scientific adviser at Sonoma Biotherapeutics in San Francisco. Sakaguchi is a professor at Osaka University in Japan.
In its statement, the Nobel committee said the trio’s discoveries “laid the foundation for a new field of research and spurred the development of new treatments, for example, for cancer and autoimmune diseases.” Their work identified regulatory T cells (immune system) “security guards” that prevent immune cells from mistakenly attacking the body’s own tissues.