The 2025 Nobel Prize in Physiology or Medicine was awarded to Mary E. Brunkow, Fred Ramsdell, and Shimon Sakaguchi for their work on how immune systems work in determining what should be attacked or protected. The prize was announced at the Nobel Assembly at Karolinska Institutet in Stockholm, Sweden, on Monday (October 6, 2025).

What is the research about?

The 2025 winner of the Nobel Prize in Physiology or Medicine concerns the peripheral immune tolerance.

The peripheral immune system of the body includes the components of the immune system outside the central nervous system, which is made up of the brain and the spinal cord. The prize-winning research identifies regulatory T (Treg) cells, which prevent immune cells from attacking the host body itself.

Shimon Sakaguchi

The primary work that led to this discovery was done by Japanese immunologist Shimon Sakaguchi. Currently at the Osaka University in Japan, 74-year-old Sakaguchi earned his Doctor of Medicine degree from Kyoto University in 1983, although he reportedly began researching Treg cells first in 1979.

T-cells, in general, help the immune system fight hostile bodies and keep people disease-free. There are different kinds of these cells, specialised to perform different tasks. These cells are identified by proteins on their surfaces.

Sakaguchi identified the Treg cells in 1995. Instead of attacking foreign bodies, these cells help calm the immune system so that it doesn’t end up attacking the host itself or causing autoimmune diseases.

Other researchers in the field, however, wanted more proof of the existence of Treg cells.

Sakaguchi also won the Canada Gairdner Award in 2015 for the same discovery. He was previously also a Lucille P. Marky scholar which allowed him to pursue biomedical research in the US.

Mary Brunkow and Fred Ramsdell

Mary Brunkow holds a PhD in molecular biology from Princeton University. She is currently a senior program manager at the Institute for Systems Biology in Seattle, US.

Fred Ramsdell is a scientific advisor at Sonoma Biotherapeutics in Bainbridge island, Washington. He holds a PhD in immunology from the University of California, Los Angeles.

After Sakaguchi’s initial work in the field of Treg cells, Brunkow and Ramsdell got interested in a mutation in the male scurfy mouse strain, which was being attacked by T-cells, thus destroying its own tissues. Both Brunkow and Ramsdell worked at the Celltech Chiroscience biotech company in Bothell, Washington, at the time, and tried to find the cause of this disease with the idea of studying how autoimmune diseases arise.

The 2025 Nobel Prize in Physiology or Medicine was awarded to Mary E. Brunkow, Fred Ramsdell, and Shimon Sakaguchi for their work on how immune systems work in determining what should be attacked or protected. The prize was announced at the Nobel Assembly at Karolinska Institutet in Stockholm, Sweden, on Monday (October 6, 2025).

What is the research about?

The 2025 winner of the Nobel Prize in Physiology or Medicine concerns the peripheral immune tolerance.

The peripheral immune system of the body includes the components of the immune system outside the central nervous system, which is made up of the brain and the spinal cord. The prize-winning research identifies regulatory T (Treg) cells, which prevent immune cells from attacking the host body itself.

Shimon Sakaguchi

The primary work that led to this discovery was done by Japanese immunologist Shimon Sakaguchi. Currently at the Osaka University in Japan, 74-year-old Sakaguchi earned his Doctor of Medicine degree from Kyoto University in 1983, although he reportedly began researching Treg cells first in 1979.

T-cells, in general, help the immune system fight hostile bodies and keep people disease-free. There are different kinds of these cells, specialised to perform different tasks. These cells are identified by proteins on their surfaces.

Sakaguchi identified the Treg cells in 1995. Instead of attacking foreign bodies, these cells help calm the immune system so that it doesn’t end up attacking the host itself or causing autoimmune diseases.

Other researchers in the field, however, wanted more proof of the existence of Treg cells.

Sakaguchi also won the Canada Gairdner Award in 2015 for the same discovery. He was previously also a Lucille P. Marky scholar which allowed him to pursue biomedical research in the US.

Mary Brunkow and Fred Ramsdell

Mary Brunkow holds a PhD in molecular biology from Princeton University. She is currently a senior program manager at the Institute for Systems Biology in Seattle, US.

Fred Ramsdell is a scientific advisor at Sonoma Biotherapeutics in Bainbridge island, Washington. He holds a PhD in immunology from the University of California, Los Angeles.

After Sakaguchi’s initial work in the field of Treg cells, Brunkow and Ramsdell got interested in a mutation in the male scurfy mouse strain, which was being attacked by T-cells, thus destroying its own tissues. Both Brunkow and Ramsdell worked at the Celltech Chiroscience biotech company in Bothell, Washington, at the time, and tried to find the cause of this disease with the idea of studying how autoimmune diseases arise.

The Nobel Prize for 2025 in Physiology or Medicine goes to Mary E. Brunkow, Fred Ramsdell and Shimon Sakaguchi “for their discoveries concerning peripheral immune tolerance,” the Royal Swedish Academy of Sciences announced on Monday (October 6, 2025).

The laureates identified the immune system’s security guards, regulatory T cells, which prevent immune cells from attacking our own body.

Last year, the Medicine Nobel was jointly awarded to Victor Ambros and Gary Ruvkun for the discovery of microRNA and its role in post-transcriptional gene regulation.

The Prize for Physiology or Medicine kicks off a week of Nobel Prize announcements. The winners for Physics will be announced tomorrow (October 7), followed by Chemistry on October 8. The winners of the Literature, Peace and Economic Sciences Prize will be declared on October 9, October 10, and October 13 respectively.

The prizes carry a cash award of 10 million Swedish kronor (nearly $900,000) and will be awarded on December 10.

The Nobel Prize was created by Swedish inventor Alfred Nobel, who in his will dictated that his estate should be used to fund “prizes to those who, during the preceding year, have conferred the greatest benefit to humankind”.