The 2025 Nobel Prize in Physiology or Medicine has been awarded to three scientists — Mary E. Brunkow, Fred Ramsdell, and Shimon Sakaguchi — for their pioneering discoveries that revealed how the body’s immune system prevents itself from attacking its own cells. Their work uncovered the existence and function of regulatory T cells, a special class of immune cells that act as the body’s “security guards,” maintaining balance in the immune system and protecting against autoimmune diseases.
Announced in Stockholm, Sweden, the Nobel Committee praised the trio’s research for transforming our understanding of peripheral immune tolerance, the mechanism by which the immune system distinguishes between harmful invaders and the body’s own tissues. “Their discoveries have been decisive for understanding why we do not all develop serious autoimmune diseases,” said Professor Olle Kämpe, chair of the Nobel Committee.
The team’s findings have opened up new frontiers in medicine, leading to potential therapies that could treat autoimmune disorders, improve cancer immunotherapy, and reduce transplant rejection. Autoimmune diseases such as lupus, rheumatoid arthritis, and multiple sclerosis affect millions worldwide, often causing lifelong suffering. As immunologist Daniel Kastner of the U.S. National Institutes of Health noted, “T regulatory cells play an absolutely vital role in preventing or ameliorating their impact.”
The roots of this discovery trace back to 1995, when Shimon Sakaguchi, a Japanese immunologist at Osaka University, identified a mysterious group of T cells that suppressed harmful immune reactions. His work suggested that the immune system had built-in mechanisms to prevent “friendly fire” — the self-destructive attacks that cause autoimmune disease. He named these protective cells regulatory T cells.
Years later, American scientists Mary E. Brunkow and Fred Ramsdell built upon Sakaguchi’s work. Studying mice prone to severe autoimmune disorders, they spent years mapping their genetic code — an arduous process before modern sequencing tools existed. Their efforts led to the discovery of the Foxp3 gene, a master regulator responsible for developing and controlling regulatory T cells. Mutations in this gene, they found, cause IPEX syndrome, a rare but devastating autoimmune condition in humans.
In 2003, Sakaguchi connected these findings, confirming that Foxp3 governs the regulatory T cells he had discovered a decade earlier. Together, their research reshaped immunology, bridging fundamental science and clinical application.
Reacting to the news, Sakaguchi said he was “pleasantly surprised” and hoped the award would inspire future research using regulatory T cells to treat immune disorders. Brunkow, now a program manager at the Institute for Systems Biology in Seattle, and Ramsdell, co-founder of Sonoma Biotherapeutics in San Francisco, were also recognised for their enduring impact on biomedical science.
Experts hailed the award as richly deserved. Professor Annette Dolphin, president of the UK’s Physiological Society, called their discoveries “vital insights into the regulation of the immune system,” highlighting their implications for autoimmune therapy, cancer treatment, and transplantation medicine.
This year’s prize continues the Nobel tradition of celebrating breakthroughs with profound implications for human health. Recent laureates have included Victor Ambros and Gary Ruvkun for the discovery of microRNA in 2024, and Katalin Karikó and Drew Weissman in 2023 for their groundbreaking work on mRNA vaccines, which helped combat the COVID-19 pandemic.
The 2025 Nobel Prize in Medicine comes with a cash award of 11 million Swedish kronor (approximately US$1 million) — but its greater legacy lies in advancing a deeper understanding of the human immune system, offering new hope for millions living with autoimmune diseases and immune-related disorders.
