The 2025 Nobel Prize in Physiology or Medicine has been awarded jointly to Mary E. Brunkow and Fred Ramsdell of the United States, and Shimon Sakaguchi of Japan, for their pioneering discoveries on how the immune system maintains balance and prevents autoimmune diseases.
Announcing the award on Monday, the Nobel Assembly at the Karolinska Institute said the trio were honoured “for their discoveries concerning peripheral immune tolerance.”
According to the jury, their work has been “decisive for understanding how the immune system functions and why we do not all develop serious autoimmune diseases.”
The Nobel Committee noted that the findings of Brunkow, Ramsdell, and Sakaguchi have “laid the foundation for a new field of research and spurred the development of new treatments, for example, for cancer and autoimmune diseases.” The discoveries could also lead to improved outcomes in organ transplantation.
Shimon Sakaguchi, 74, first identified a previously unknown class of immune cells in 1995 — a finding that transformed the understanding of immune tolerance. Before his breakthrough, scientists believed tolerance was achieved only by eliminating harmful immune cells in the thymus through a process called central tolerance. Sakaguchi’s research revealed a more complex system involving regulatory immune cells that protect the body from attacking itself.
Six years later, Mary E. Brunkow (born 1961) and Fred Ramsdell (64) made another major discovery when studying mice highly prone to autoimmune diseases. They found that these mice had a mutation in a gene they named Foxp3, a finding later linked to a severe autoimmune condition in humans known as IPEX syndrome.
By 2003, Sakaguchi was able to connect these discoveries, establishing how Foxp3 plays a vital role in maintaining immune balance.
The laureates will receive their awards ,a gold medal, a diploma, and a $1.2 million cash prize from King Carl XVI Gustaf of Sweden during the Nobel Prize ceremony in Stockholm on December 10, marking the anniversary of Alfred Nobel’s death in 1896.
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