3 scientists win Nobel Prize in medicine for work on human immune system

• American scientists Mary E. Brunkow and Fred Ramsdell and Shimon Sakaguchi from Japan won the 2025 Nobel Prize in Physiology or Medicine on October 6.

• They were awarded for their discoveries concerning peripheral immune tolerance that prevents the immune system from harming the body. 

This year’s winners:

a) Mary E. Brunkow was born in 1961. She is a senior program manager at the Institute for Systems Biology, Seattle.

b) Fred Ramsdell was born in 1960. He is a scientific adviser for Sonoma Biotherapeutics, San Francisco.

c) Shimon Sakaguchi was born in 1951. He is a distinguished professor at the Immunology Frontier Research Center, Osaka University, Japan.

• The winners of the prize for physiology or medicine are selected by the Nobel Assembly of Sweden’s Karolinska Institute medical university and receive a prize sum of 11 million Swedish crowns ($1.2 million).

• Created in the will of Swedish dynamite inventor and businessman Alfred Nobel, the prizes have been awarded for breakthroughs in science, literature and peace since 1901, while economics is a later addition.

They discovered how the immune system is kept in check

• 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.

• The trio identified the immune system’s security guards, regulatory T cells, which prevent immune cells from attacking our own body.

• Their discoveries have been decisive for our understanding of how the immune system functions and why we do not all develop serious autoimmune diseases.

• 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.

• 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.

• Their discoveries launched the field of peripheral tolerance, spurring the development of medical treatments for cancer and autoimmune diseases that are now being evaluated in clinical trials. 

• The hope is to be able to treat or cure autoimmune diseases, provide more effective cancer treatments and prevent serious complications after stem cell transplants.