The 2025 Nobel Prize in Physiology or Medicine has been awarded on 6th October 2025 to three scientists , Mary E. Brunkow, Fred Ramsdell, and Shimon Sakaguchi, for their groundbreaking discoveries on how the immune system avoids attacking the body it is meant to protect.
These researchers’ work on peripheral immune tolerance has redefined modern immunology and opened new frontiers in the treatment of autoimmune diseases, cancer, and organ transplantation.
The Discovery That Changed Immunology
The journey toward this breakthrough began in 1995 when Japanese immunologist Shimon Sakaguchi questioned long-held scientific assumptions.
At that time, most researchers believed that the body maintained immune tolerance, the ability to tell the difference between its own cells and foreign invaders, only by removing potentially harmful immune cells in the thymus, a mechanism known as central tolerance.
Sakaguchi, who is now a distinguished Professor at Osaka University, demonstrated that the immune system possesses an additional safeguard known as peripheral tolerance.
This process is controlled by a previously unidentified group of immune cells that he named regulatory T cells. These cells act as moderators of the immune response, preventing self-destruction and ensuring that the body’s defense system remains in balance.
A few years later, in 2001, Mary Brunkow and Fred Ramsdell independently uncovered the genetic key behind these cells.
While studying a mouse strain that suffered severe autoimmune symptoms, they discovered a mutation in a gene they named FOXP3. Their research revealed that the human equivalent of this gene, when mutated, causes a rare and life-threatening condition known as IPEX syndrome. This connection demonstrated that FOXP3 was crucial to immune regulation.
Together, their discoveries connected the dots between genetics and immune regulation, establishing the foundation of what is now known as peripheral immune tolerance, a concept that reshaped immunology and medicine alike.
Who Are These Researchers?
Mary E. Brunkow, born in 1961, works at the Institute for Systems Biology in Seattle, Washington. Her scientific curiosity and precision helped decode how genes control immune regulation. Her work on FOXP3 illuminated how the immune system can go from harmony to chaos with a single mutation.
Fred Ramsdell, born on December 4, 1960, in Elmhurst, Illinois, is a molecular immunologist whose research has always bridged science and therapy. Now at Sonoma Biotherapeutics in San Francisco, Ramsdell’s efforts are focused on transforming discoveries about Tregs into real-world treatments for autoimmune diseases such as type 1 diabetes and rheumatoid arthritis.
Shimon Sakaguchi, born on January 19, 1951, in Nagahama, Shiga, Japan, is regarded as a pioneer in the field of immunoregulation. His early skepticism of established dogma led him to identify the body’s ‘immune brakes.’ His decades-long pursuit of understanding immune tolerance has inspired generations of scientists worldwide.