American scientists Mary E. Brunkow and Fred Ramsdell, along with Japan’s Shimon Sakaguchi, have been awarded the 2025 Nobel Prize in Physiology or Medicine for their pioneering research into how the immune system is regulated to prevent self-destruction.

The Nobel Assembly at Karolinska Institutet announced the prize on Monday, honouring the trio “for their discoveries concerning peripheral immune tolerance”—a crucial mechanism that stops the immune system from attacking the body’s own tissues.

“Their work has been decisive in understanding how the immune system functions and why most people do not develop severe autoimmune diseases,” the jury said. “These discoveries have laid the foundation for a new field of research and spurred the development of novel therapies—for cancer, autoimmune disorders, and potentially more successful organ transplantations.”

Sakaguchi, 74, made the first major breakthrough in 1995. At the time, the prevailing scientific view held that immune tolerance arose solely through the elimination of harmful immune cells in the thymus—a process known as “central tolerance.” Sakaguchi challenged this notion by identifying a previously unknown class of immune cells—now known as regulatory T cells—that actively suppress autoimmune responses in the body’s periphery.

In 2001, Brunkow (born 1961) and Ramsdell (64) uncovered why certain mice were unusually prone to autoimmune conditions. They discovered a mutation in a gene they named Foxp3. Crucially, they later demonstrated that mutations in the human counterpart of this gene cause IPEX syndrome—a rare but life-threatening autoimmune disorder.

Two years after their discovery, Sakaguchi connected the dots, showing that Foxp3 is essential for the development and function of regulatory T cells, thereby unifying the findings into a coherent biological framework.

The laureates will receive the Nobel Prize—a diploma, a gold medal, and a cash award of $1.2 million—at a formal ceremony in Stockholm on 10 December, the anniversary of Alfred Nobel’s death in 1896.

Concerns over US leadership in science

Historically, researchers from major US institutions have dominated the Nobel science prizes, thanks to sustained investment in basic research and academic freedom. However, that dominance may be at risk.

Since January, the US National Institutes of Health (NIH) has terminated 2,100 research grants—worth approximately $9.5 billion—and cut $2.6 billion in contracts, according to the independent tracking database Grant Watch. These cuts follow sweeping budget reductions announced by President Donald Trump.

Thomas Perlmann, Secretary General of the Nobel Committee for Physiology or Medicine, told AFP: “It’s no coincidence that the US has by far the most Nobel laureates. But there is now a creeping sense of uncertainty about America’s willingness to maintain its leading role in scientific research.”

Calling the United States “the very engine of global scientific discovery,” Perlmann warned: “There would be very serious consequences for research worldwide if that engine starts to falter. It doesn’t take many years of deep cuts to cause irreversible damage.”

Trump’s Nobel ambitions meet skepticism

President Trump has openly expressed his desire to win a Nobel Peace Prize. Yet experts remain unconvinced.

“Trump is, in many ways, the opposite of the ideals the Nobel Prize represents,” said Øyvind Stenersen, a historian and co-author of a book on the Nobel Peace Prize. “The prize honours multilateral cooperation—through institutions like the UN—and Trump consistently rejects that principle in favour of unilateral action.”

This year’s Peace Prize is widely expected to go to humanitarian or press freedom efforts. Leading contenders include Sudan’s Emergency Response Rooms (ERR)—volunteer networks providing aid amid war and famine—as well as media watchdogs such as the Committee to Protect Journalists and Reporters Without Borders. Yulia Navalnaya, widow of Russian opposition leader Alexei Navalny, is also among bookmakers’ favourites.

The Nobel announcements continue this week:

Physics: Tuesday

Chemistry: Wednesday

Literature: Thursday

Peace: Friday

Economic Sciences: Monday, October 13