The 2025 Nobel Prize in physiology or medicine has been awarded to a trio of scientists—two American and one Japanese—for unraveling the critical mechanism that ensures the immune system protects the body without attacking its own cells.
Mary E. Brunkow, Fred Ramsdell, and Shimon Sakaguchi will share the prize “for their fundamental discoveries relating to peripheral immune tolerance,” the Nobel Committee announced Monday during a ceremony in Stockholm.
The recognition is a reminder that for all the problems in the American healthcare system, the country continues to produce world-class scientists making discoveries that can make a huge impact on progress in diagnosis and treatment.
The laureates are credited with identifying “regulatory T cells” (Tregs), which act as the immune system’s security guards. These cells prevent the immune system from launching attacks against the body’s own tissues, a failure that results in autoimmune diseases.
Olle Kämpe, chair of the Nobel Committee, emphasized that their discoveries are “decisive for our understanding of how the immune system functions and why we do not all develop serious autoimmune diseases”.
The fundamental physiological research holds profound implications for human health. The findings have already paved the way for the development of potential medical treatments aimed at curing autoimmune diseases like lupus, rheumatoid arthritis, and multiple sclerosis.
Furthermore, the work is expected to provide more effective cancer treatments and reduce complications following stem cell and organ transplants. Daniel Kastner, a distinguished investigator at the National Institutes of Health, affirmed that T regulatory cells play an “absolutely vital role in preventing or ameliorating” the impact of these conditions.
The immune system, dubbed an “evolutionary masterpiece” by the committee, continuously works to differentiate invading pathogens from the body’s own cells. However, microbes often attempt to evade detection by developing similarities to human cells, a form of camouflage that can lead to “biological friendly fire” if the immune system attacks its own cells.
The scientific breakthrough began with Shimon Sakaguchi, a Japanese immunologist, who made a groundbreaking discovery in 1995. After examining mice and the role of the thymus, he determined the need for a mechanism—a “security guard”—to prevent self-attack, leading to his identification of regulatory T cells.
Americans Brunkow and Ramsdell subsequently built upon Sakaguchi’s work in the early 2000s. Through years of difficult experimentation, they identified a mutation in the Foxp3 gene in mice prone to autoimmune diseases. They later showed that mutations in the human equivalent of Foxp3 cause IPEX syndrome, a serious autoimmune disease. Sakaguchi then confirmed their link in 2003, proving that the Foxp3 gene governs the development of the regulatory T cells.
Sakaguchi, who was “pleasantly surprised” by the news, believes the award will encourage immunologists and physicians to apply T regulatory cells to treat various immunological diseases. The trio will share a cash prize of 11 million Swedish kronor, equivalent to $1 million.