Stockholm, 6 October 2025 (dpa/MIA) - The 2025 Nobel Prize in Medicine has been awarded to Mary E Brunkow, Fred Ramsdell and Shimon Sakaguchi for their groundbreaking research on the immune system, Sweden's Karolinska Institute said on Monday.

The Nobel Prize for Physiology or Medicine was awarded to Brunkow and Ramsdell of the United States and Japan's Sakaguchi "for their discoveries concerning 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 institute said in a statement.

"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 Kämpe, chair of the Nobel Committee.

According to the institute, the laureates' work has laid the foundation for a new field of research and has advanced the development of treatments for diseases such as cancer and autoimmune disorders.

The prize amount of 11 million Swedish kronor ($1.17 million) is to be shared equally between the three laureates.

Research in Japan and the US

Brunkow, born in 1961, completed her doctorate at Princeton University in the United States and now works at the Institute for Systems Biology in Seattle.

The 64-year-old Ramsdell comes from the US state of Illinois and completed his doctorate at the University of California in Los Angeles. He is a scientific advisor at Sonoma Biotherapeutics in San Francisco.

Shimon Sakaguchi, 74, completed his doctorate in Kyoto in 1983 and is a professor at Osaka University.

Sakaguchi's research laid the groundwork in the mid-1990s by identifying a previously unknown group of immune cells - regulatory T cells - which control the immune system's response and prevent autoimmune reactions.

A few years later, Brunkow and Ramsdell discovered that a specific mutation in the Foxp3 gene makes mice susceptible to autoimmune diseases.

Shortly thereafter, Sakaguchi demonstrated that this gene is essential for the development and function of regulatory T cells.

Two Nobel laureates unreachable at time of announcement

Only Japanese laureate Sakaguchi could be reached in his laboratory, Secretary of the Nobel Assembly Thomas Perlmann said during the announcement.

He asked the two US researchers to call him back, adding that their phones were probably on silent mode because of the time difference on the US West Coast.

"[Sakaguchi] sounded incredibly grateful and expressed that it was a fantastic honour," Perlmann said. "Unfortunately I wasn't able to reach any of the other two ... I asked them to call back."

Historical context

Since 1901, a total of 229 people have received the Nobel Prize in Medicine, including 13 women.

Thirty years ago, German developmental biologist Christiane Nüsslein-Volhard became the first and only German woman to win the prize for her work on the genetic control of early embryonic development.

Last year, US geneticists Victor Ambros and Gary Ruvkun were honoured for discovering microRNA, revealing a previously unknown mechanism of gene regulation.

The Medicine or Physiology prize traditionally opens the annual week of Nobel announcements. In the following days, winners in Physics, Chemistry, Literature, Peace and Economics will be revealed.

The Nobel Prizes will be formally presented on December 10, the anniversary of the death of Alfred Nobel (1833–96), the inventor of dynamite and founder of the prizes.

Photo: epa