US-Japanese Trio Wins 2025 Nobel Prize in Medicine for Immune System ‘Security Guard’ Discovery

A US-Japanese team — Mary Brunkow, Fred Ramsdell, and Shimon Sakaguchi — has been awarded the 2025 Nobel Prize in Medicine for groundbreaking research that revealed how the immune system is regulated by its own “security guards,” known as regulatory T-cells.

The Nobel Committee said their discoveries have been “decisive for understanding how the immune system functions and why we do not all develop serious autoimmune diseases.”

Sakaguchi, a professor at Osaka University, expressed hope that the recognition would “serve as an opportunity for this field to develop further… in a direction where it can be applied in actual bedside and clinical settings.”

The committee noted that it had been unable to reach the two US laureates before the public announcement. “If you hear this, call me,” joked Nobel Committee Secretary General Thomas Perlmann during the press briefing.

Their collective research into “peripheral immune tolerance” — the body’s ability to prevent its immune system from attacking itself — has laid the foundation for potential treatments for autoimmune diseases, cancer, and complications following stem cell transplants.

Sakaguchi first made a breakthrough in 1995, discovering a new class of immune cells that protect against autoimmune reactions, challenging the long-held belief that immune tolerance was controlled solely by processes in the thymus.

In 2001, Brunkow and Ramsdell identified the Foxp3 gene, showing that mutations in its human equivalent cause IPEX, a severe autoimmune disorder. Sakaguchi later linked this discovery to his earlier findings, completing the picture of immune regulation.

The trio will share a $1.2 million cash award, along with Nobel medals and diplomas, at the official ceremony in Stockholm on December 10.

The Nobel Committee noted that while US researchers have long dominated the sciences due to strong investment in basic research, budget cuts under President Donald Trump may threaten that lead.

Meanwhile, speculation continues over possible Nobel Peace Prize contenders, with names like Yulia Navalnaya, Sudan’s Emergency Response Rooms, and press freedom groups such as Reporters Without Borders and the Committee to Protect Journalists among those being discussed.