Meet the Scientists who won the 2025 Nobel Prize in Medicine

Every day, our immune system protects us from thousands of different microbes trying to invade our bodies. These all have different appearances, and many have developed similarities with human cells as a form of camouflage. So how does the immune system determine what it should attack and what it should defend?

Mary Brunkow, Fred Ramsdell and Shimon Sakaguchi are awarded the Nobel Prize in Physiology or Medicine 2025 for their fundamental discoveries relating to peripheral immune tolerance. The laureates identified the immune system’s security guards, regulatory T cells, which prevent immune cells from attacking our own body, the press release stated.

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“Their discoveries have been decisive for our understanding of how the immune system functions and why we do not all develop serious autoimmune diseases,” says Olle Kämpe, chair of the Nobel Committee.

Nobel Prize Winners 2025: Who They Are

Mary E. Brunkow, born in 1961, was awarded the 2025 Nobel Prize in Physiology or Medicine for her groundbreaking discoveries concerning peripheral immune tolerance. At the time of the award, she was affiliated with the Institute for Systems Biology in Seattle, Washington, USA. 

Frederick J. Ramsdell, born on 4 December 1960 in Elmhurst, Illinois, USA, was awarded the 2025 Nobel Prize in Physiology or Medicine for his seminal contributions to the understanding of peripheral immune tolerance. At the time of receiving the award, he was affiliated with Sonoma Biotherapeutics in San Francisco, California, USA.

Shimon Sakaguchi, born on 19 January 1951 in Nagahama, Shiga, Japan, was awarded the 2025 Nobel Prize in Physiology or Medicine for his pioneering discoveries related to peripheral immune tolerance. At the time of the award, he was affiliated with Osaka University in Osaka, Japan.

Shimon Sakaguchi was swimming against the tide in 1995 when he made the first key discovery. At the time, many researchers were convinced that immune tolerance only developed due to potentially harmful immune cells being eliminated in the thymus, through a process called central tolerance. Sakaguchi showed that the immune system is more complex and discovered a previously unknown class of immune cells, which protect the body from autoimmune diseases.

The press release further stated that Mary Brunkow and Fred Ramsdell made the other key discovery in 2001, when they presented the explanation for why a specific mouse strain was particularly vulnerable to autoimmune diseases. They had discovered that the mice have a mutation in a gene that they named Foxp3. They also showed that mutations in the human equivalent of this gene cause a serious autoimmune disease, IPEX.

Two years after this, Shimon Sakaguchi was able to link these discoveries. He proved that the Foxp3 gene governs the development of the cells he identified in 1995. These cells, now known as regulatory T cells, monitor other immune cells and ensure that our immune system tolerates our own tissues.

The laureates’ discoveries launched the field of peripheral tolerance, spurring the development of medical treatments for cancer and autoimmune diseases. This may also lead to more successful transplantations. Several of these treatments are now undergoing clinical trials.

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