Sharing the 2025 Nobel Prize in Physiology or Medicine with Mary E. Brunkow and Fred Ramsdell, Shimon Sakaguchi was honored “for their discoveries concerning peripheral immune tolerance,” a fundamental mechanism that prevents the immune system from attacking the body’s own tissues. The trio identified and characterized regulatory T cells (Tregs)—immune cells that act as key brakes on immune responses—and elucidated the central role of the FOXP3 gene in their development and function.

Sakaguchi first demonstrated the existence of these cells in 1995, challenging the belief that self-tolerance was mediated solely in the thymus, while Brunkow and Ramsdell linked Treg dysfunction to autoimmune disease through FOXP3 mutations. Their work reshaped modern immunology, enabling new therapeutic approaches for autoimmune diseases, transplantation and cancer.

(Photo: The University of Osaka)