US, Japan scientists win Nobel Prize for breakthroughs in immune system control
(L-R) The portraits of Mary E Brunkow, Fred Ramsdell and Shimon Sakaguchi are displayed during a press conference where the winners of the 2025 Nobel Prize in Physiology or Medicine are being announced at the Karolinska Institute in Stockholm, Sweden, on October 6, 2025. Mary E. Brunkow and Fred Ramsdell of the United States and Japan's Shimon Sakaguchi won the Nobel Prize in Medicine on Monday for research into how the immune system is kept in check, the Nobel jury said.PHOTO:AFP
American scientists Mary Brunkow and Fred Ramsdell, together with Shimon Sakaguchi of Japan, won the 2025 Nobel Prize in Physiology or Medicine on Monday for discoveries explaining how the immune system spares healthy cells — paving the way for potential new treatments for autoimmune diseases and cancer.
Their discoveries shed light on peripheral immune tolerance, or “how we keep our immune system under control so we can fight all imaginable microbes and still avoid autoimmune disease,” said Marie Wahren-Herlenius, rheumatology professor at Sweden’s Karolinska Institute, which awards the prize.
The institute said all three laureates highlighted the role of regulatory T cells — white blood cells that act as “security guards” preventing immune cells from attacking the body’s own tissues.
Research into what stops the immune system attacking itself
Brunkow, who learned of her win after her dog barked at a photographer on her Seattle porch, said she and Ramsdell had identified a gene called FOXP3, a marker for regulatory T cells.
“They’re rare, but powerful, and they’re critical for dampening an immune response,” she told Reuters, describing the cells as “a braking system that prevents the immune system from tipping over into attacking itself.”
In Osaka, Sakaguchi said he was surprised by the timing of the award.
“I used to think that some sort of reward may be forthcoming if what we have been doing will advance a little further and it will become more beneficial to people in clinical settings,” he said calmly, occasionally smiling.
During the press conference, Sakaguchi received a call from Japanese Prime Minister Shigeru Ishiba, who asked about the future of cancer immunotherapy.
“I believe the time will come when cancer is no longer a scary disease, but a curable one,” Sakaguchi replied.
The laureates will share a prize of 11 million Swedish crowns ($1.2 million) and gold medals presented by Sweden’s king.
Brunkow is senior programme manager at the Institute for Systems Biology in Seattle, Ramsdell is scientific adviser at Sonoma Biotherapeutics in San Francisco, and Sakaguchi is professor at Osaka University.
More than 200 human trials in progress
Jeffrey Bluestone, a longtime collaborator of Ramsdell and co-founder of Sonoma Biotherapeutics, said Ramsdell’s key contribution was identifying the FOXP3 gene in mice, which controls regulatory T cell development. Their findings were first published in 2001.
“Those cells were the master regulators of the tolerance of the immune system,” Bluestone said.
Ramsdell could not be reached for comment — nor could Brunkow or Bluestone — with Bluestone suggesting Ramsdell might be on a hiking trip without phone reception.
After announcing the winners, Thomas Perlmann of the Karolinska Institute said no regulatory T-cell therapies had yet reached market, but over 200 clinical trials were ongoing.
Among early movers, Sonoma Biotherapeutics is working with Regeneron on treatments for inflammatory bowel disease. Quell Therapeutics, in partnership with AstraZeneca, is targeting similar conditions, while Bayer’s BlueRock is also exploring T-cell therapies.
Medicine kicks off 2025 Nobel season
The Nobel Prizes, established by Alfred Nobel, the Swedish inventor of dynamite, have been awarded since 1901 for exceptional achievements in science, literature, and peace. The economics prize was added later, funded by Sweden’s central bank.
All Nobel Prizes are awarded in Stockholm, except the Peace Prize, which is presented in Oslo.
Past medicine laureates include Alexander Fleming, who won in 1945 for discovering penicillin. In recent years, the prize has recognized advances that led to COVID-19 vaccines.
Last year’s award went to US scientists Victor Ambros and Gary Ruvkun for their discovery of microRNA and its crucial role in the growth of multicellular organisms.
Medicine traditionally opens the annual Nobel season. The Physics Prize will be announced on Tuesday, followed by other categories.
The awards culminate in December 10 ceremonies attended by Sweden’s and Norway’s royal families, marking the anniversary of Alfred Nobel’s death.