Stockholm: American researchers Mary Brunkow and Fred Ramsdell, alongside Japan’s Shimon Sakaguchi, have been awarded the 2025 Nobel Prize in Physiology or Medicine for groundbreaking discoveries that explain how the immune system spares healthy cells.
The Nobel Assembly at Sweden’s Karolinska Institute said the trio was honoured for their pioneering work on peripheral immune tolerance, the process that prevents the body’s defences from turning against its own tissues.
“Their discoveries have laid the foundation for a new field of research and spurred the development of therapies targeting cancer and autoimmune disorders,” the institute said in its citation.
BREAKING NEWS
The 2025 #NobelPrize in Physiology or Medicine has been awarded to Mary E. Brunkow, Fred Ramsdell and Shimon Sakaguchi “for their discoveries concerning peripheral immune tolerance.” pic.twitter.com/nhjxJSoZEr— The Nobel Prize (@NobelPrize) October 6, 2025
Sakaguchi, a professor at Osaka University, first identified regulatory T cells, the immune system’s ‘security guards’ that stop immune attacks on healthy cells. Brunkow, now senior programme manager at the Institute for Systems Biology in Seattle, and Ramsdell, scientific adviser at Sonoma Biotherapeutics in San Francisco, helped uncover how these cells function and can be harnessed to restore immune balance.
“This work shows how we can fight infections while avoiding autoimmune disease,” said Marie Wahren-Herlenius, professor of rheumatology at the Karolinska Institute. Speaking to reporters outside his Osaka lab, Sakaguchi said he felt tremendous honour at receiving the prize.
Each laureate will receive 11 million Swedish crowns (about $1.2 million) and a gold medal from Sweden’s King Carl XVI Gustaf at a ceremony in December.
Our immune system is an evolutionary masterpiece. Every day it protects us from the thousands of different viruses, bacteria and other microbes that attempt to invade our bodies. Without a functioning immune system, we would not survive.
One of the immune system’s marvels is its… pic.twitter.com/TzBWuIrTgn
— The Nobel Prize (@NobelPrize) October 6, 2025
More than 200 clinical trials involving regulatory T cells are currently underway, according to Thomas Perlmann, secretary of the Nobel Committee. Companies such as Sonoma Biotherapeutics, co-founded by Ramsdell and backed by Regeneron, are exploring therapies for conditions including inflammatory bowel disease. Other firms like Quell Therapeutics, in partnership with AstraZeneca, and Bayer’s BlueRock Therapeutics, are also pursuing similar research avenues.
The Medicine Prize traditionally opens the annual Nobel season, which continues this week with announcements in physics, chemistry, literature, peace, and economics. Established through the will of Alfred Nobel, the Swedish inventor of dynamite, the prizes have been awarded since 1901 for extraordinary contributions to humanity.
Over the decades, the Nobel Prize in Medicine has honoured some of science’s greatest breakthroughs, from Alexander Fleming’s discovery of penicillin in 1945 to the 2023 recognition of microRNA research that reshaped understanding of cellular function.
