Japanese scientist awarded Nobel Prize for immune tolerance discovery

Japanese immunologist Shimon Sakaguchi was named one of three laureates for the 2025 Nobel Prize in Physiology or Medicine on Monday. He shares the recognition with U.S. scientists Mary Brunkow and Fred Ramsdell for discovering how specialized immune cells, known as regulatory T cells, prevent the body from attacking its own tissues. The discovery established a foundation for therapies that modulate the immune system in conditions such as type 1 diabetes and multiple sclerosis.

Sakaguchi first identified a unique class of immune cells in 1995 that act as suppressors, keeping the body’s defenses from turning against itself. Years later, Brunkow and Ramsdell pinpointed the FOXP3 gene as essential to these cells’ function, explaining why mutations in the gene trigger fatal autoimmune disorders in both mice and humans. By 2003, Sakaguchi confirmed that FOXP3 was critical for the development and stability of regulatory T cells, linking two independent lines of research that transformed the field of immunology.

The Nobel Assembly at the Karolinska Institute said the trio’s work “has been decisive for our understanding of how the immune system functions and why we do not all develop serious autoimmune diseases.” Their findings now underpin clinical efforts to fine-tune immune responses for treating chronic inflammation, organ rejection and cancer. More than 200 clinical trials involving regulatory T cells are currently underway worldwide, testing ways to apply these insights to human medicine.

At a news conference in Osaka, Sakaguchi, 74, expressed surprise at the honor, saying, “I used to think that some sort of reward may be forthcoming if what we have been doing will advance a little further and it will become more beneficial to people in clinical settings.” The Nobel award ceremony will take place in Stockholm on Dec. 10, where each laureate will receive an equal share of the 11 million Swedish kronor ($1,160,000) prize.