Medicine Nobel Prize Goes to Researchers Who Made Autoimmune Breakthrough

The Nobel Prize in Physiology or Medicine 2025 has been awarded to Mary E. Brunkow, Ph.D., a molecular biologist at the Institute for Systems Biology in Seattle; Fred Ramsdell, Ph.D., a scientific adviser for Sonoma Biotherapeutics in San Francisco; and Shimon Sakaguchi, M.D., an immunologist at Osaka University in Japan, for their discoveries related to peripheral immune tolerance, according to a news release published today.

The combined discoveries of Brunkow, Ramsdell and Sakaguchi explain how the immune system is regulated. In other words, how it discerns between what it should attack and what it should defend.

These discoveries have led to the development of more than 200 clinical trials for cancer and autoimmune diseases and to improve organ transplantation.

The three winners will share the prize amount of 11 million Swedish kronor, the equivalent of approximately $1.2 million in USD.

“Their discoveries have been decisive for our understanding of how the immune system functions and why we do not all develop serious autoimmune diseases,” Olle Kämpe, chair of the Nobel Committee, said in the news release.

The prize-winning research began in 1995, when Sakaguchi discovered a subtype of T cells, called regulatory T cells, which protect the body from diseases by monitoring immune cell activity. Scientists previously thought that immune tolerance was built through a process called central tolerance, in which potentially harmful immune cells were eliminated in the thymus gland, the part of the lymphatic system that produces and matures T cells. Despite their impact, regulatory T cells only make up approximately 1 to 2% of all T cells.

In 2001, Brunkow and Ramsdell discovered a gene mutation in mice that they named Foxp3. Brunkow and Ramsdell also showed that mutations in the human equivalent of the gene were the cause of the autoimmune disease called IPEX.

Two years later, Sakaguchi connected these two discoveries by proving the Foxp3 gene controls the development of the regulatory T cells that monitor immune cell activity.

The immune system is a complex system of cells and organs that identifies and removes foreign substances such as bacteria, viruses, toxins, parasites and even cancer, using antibodies, inflammation or immune cells such as T cells and B cells. In people with an autoimmune disorder, their immune system attacks the healthy cells in their body instead of defending them, leading to symptoms like inflammation, joint pain, and, in severe cases, death. There are currently more than 100 diagnosable autoimmune diseases that affect approximately 1 in 10 people, the most common being rheumatoid arthritis, multiple sclerosis and type 1 diabetes.

“The history behind the identification of regulatory T cells and FOXP3 and their role in immune tolerance by this year’s Nobel Laureates is a testament to the power of scientific perseverance and the importance of integrating,” Gunilla Karlsson Hedestam, Ph.D., member of the Nobel Committee, and Kämpe write in their explanation of the award. “As our understanding of Treg cells deepens, so does the potential to harness their power for therapeutic benefit—protecting us from the twin perils of autoimmunity and immunopathology, while ensuring immune system homeostasis.”