Stockholm: Mary E. Brunkow, Fred Ramsdell, and Dr. Shimon Sakaguchi were on Monday awarded the 2025 Nobel Prize in Medicine for their pioneering discoveries on how the human immune system prevents itself from attacking the body — a mechanism known as peripheral immune tolerance.

Brunkow, 64, serves as senior program manager at the Institute for Systems Biology in Seattle; Ramsdell, 64, is a scientific adviser at Sonoma Biotherapeutics in San Francisco; and Sakaguchi, 74, is a distinguished professor at Osaka University's Immunology Frontier Research Centre in Japan.

Their research unveiled critical insights into how the immune system regulates itself to avoid autoimmune diseases. Sakaguchi's 1995 discovery of regulatory T cells (T-regs) revealed a new subset of T cells that suppress overactive immune responses. In 2001, Brunkow and Ramsdell identified mutations in the Foxp3 gene, linked to a rare autoimmune disorder, and two years later, Sakaguchi established that Foxp3 governs T-reg development.

The Nobel Committee said their combined work laid the foundation for a new field of immunology, transforming understanding of autoimmune diseases and opening potential pathways for therapies targeting cancer and immune disorders.

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

The three laureates will share the prize money of 11 million Swedish kronor (about USD 1.2 million).

This year's Nobel Prize announcements will continue with physics on Tuesday, chemistry on Wednesday, literature on Thursday, the peace prize on Friday, and economics on October 13. The award ceremony will take place on December 10 in Stockholm, marking the anniversary of Alfred Nobel's death.