Mary E Brunkow, Fred Ramsdell, and Shimon Sakaguchi have been jointly awarded the Nobel Prize in Medicine for their significant discoveries concerning peripheral immune tolerance.
Ms Brunkow, 64, is a senior programme manager at the Institute for Systems Biology in Seattle. Mr Ramsdell, also 64, serves as a scientific adviser for Sonoma Biotherapeutics in San Francisco.
Professor Sakaguchi, 74, is a distinguished professor at the Immunology Frontier Research Centre at Osaka University in Japan.
Their pioneering work focused on the immune system, which uses multiple overlapping mechanisms to detect and combat bacteria, viruses, and other harmful agents and trains vital T cells to recognise these ‘bad actors’.
If some instead go awry in a way that might trigger autoimmune diseases, they are supposed to be eliminated in the thymus – a process called central tolerance.
The Nobel winners unravelled an additional way the body keeps the system in check.
The Nobel Committee said it started with Mr Sakaguchi’s discovery in 1995 of a previously unknown T cell subtype now known as regulatory T cells or T-regs.
Then in 2001, Ms Brunkow and Mr Ramsdell discovered a culprit mutation in a gene named Foxp3, a gene that also plays a role in a rare human autoimmune disease.
The Nobel Committee said that two years later, Mr Sakaguchi linked the discoveries to show that the Foxp3 gene controls the development of those T-regs – which in turn act as a security guard to find and curb other forms of T cells that overreact.
The work opened a new field of immunology, said Karolinska Institute rheumatology professor Marie Wahren-Herlenius.
Researchers around the world are now working to use regulatory T cells to develop treatments for autoimmune diseases and cancer.
“Their discoveries have been decisive for our understanding of how the immune system functions and why we do not all develop serious autoimmune diseases,” said Olle Kampe, chairman of the Nobel Committee.
Thomas Perlmann, secretary-general of the Nobel Committee, said he was only able to reach Mr Sakaguchi by phone on Monday morning.
“I got hold of him at his lab and he sounded incredibly grateful, expressed that it was a fantastic honour. He was quite taken by the news,” Mr Perlmann said. He added that he left voicemails for Ms Brunkow and Mr Ramsdell.
The trio will share the prize money of 11 million Swedish kronor (£870,000).
The award is the first of the 2025 Nobel Prize announcements and was announced by a panel at the Karolinska Institute in Stockholm.
Nobel announcements continue with the physics prize on Tuesday, chemistry on Wednesday and literature on Thursday.
The Nobel Peace Prize will be announced on Friday and the Nobel Memorial Prize in economics on October 13.
The award ceremony will be held on December 10, the anniversary of the death of Alfred Nobel, who founded the prizes.
Nobel was a wealthy Swedish industrialist and the inventor of dynamite. He died in 1896.
