The 2025 Nobel Prize in Physiology or Medicine has been jointly awarded to three outstanding scientists: Mary E. Brunkow, Fred Ramsdell, and Shimon Sakaguchi. Their groundbreaking research illuminates how our intricate immune system intelligently distinguishes between harmful invaders and the body’s own healthy tissues, a crucial process for maintaining health. The prestigious announcement was made on Monday, October 6, 2025, by the Nobel Assembly at Karolinska Institutet in Stockholm, Sweden.
Unpacking the Core Research
At the heart of this year’s Nobel win lies the concept of peripheral immune tolerance. This refers to the immune system’s ability to avoid attacking the body’s own cells and tissues in areas outside the brain and spinal cord – essentially, preventing self-destruction.
The trio’s award-winning work meticulously identified and characterized regulatory T (Treg) cells. These remarkable cells act as peacekeepers within the immune system, actively suppressing immune responses and thus preventing immune cells from launching damaging attacks against the body itself, which is the root cause of autoimmune diseases.
Shimon Sakaguchi: The Pioneer
Japanese immunologist Shimon Sakaguchi is credited with the foundational discoveries in this field. Now a distinguished figure at Osaka University in Japan, Sakaguchi, 74, began his pioneering investigations into Treg cells as early as 1979, earning his Doctor of Medicine degree from Kyoto University in 1983.
To understand Treg cells, it helps to know about T-cells in general. T-cells are vital soldiers in our immune system, specialized to combat various threats and keep us healthy. Different types of T-cells, distinguished by unique surface proteins, perform specific roles. In 1995, Sakaguchi precisely identified Treg cells. Unlike other T-cells that aggressively target foreign bodies, Treg cells possess a calming influence, preventing the immune system from overreacting and mistakenly attacking the host, thereby averting autoimmune conditions.
Initially, Sakaguchi’s groundbreaking findings required further validation from the broader scientific community. His profound contributions have been recognized previously, including the Canada Gairdner Award in 2015 for the same discovery. He also benefited from being a Lucille P. Markey scholar, which facilitated his biomedical research in the United States.
Mary Brunkow and Fred Ramsdell: Expanding the Horizon
Dr. Mary Brunkow holds a PhD in molecular biology from Princeton University and currently serves as a senior program manager at the Institute for Systems Biology in Seattle, US.
Dr. Fred Ramsdell, an immunologist with a PhD from the University of California, Los Angeles, is a scientific advisor at Sonoma Biotherapeutics in Bainbridge Island, Washington.
Following Sakaguchi’s initial revelations, Brunkow and Ramsdell embarked on their own critical research. Their interest was piqued by a genetic mutation found in a specific strain of male mice, known as scurfy mice. These mice suffered from T-cells relentlessly attacking and destroying their own tissues – a clear manifestation of an autoimmune disorder. While working together at Celltech Chiroscience, a biotech company in Bothell, Washington, Brunkow and Ramsdell focused on unraveling the genetic underpinnings of this disease, aiming to understand the fundamental mechanisms behind autoimmune conditions.