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Mary Brunkow, Fred Ramsdell, Shimon Sakaguchi receive Nobel Prize in Medicine for revealing body’s immune balance

Statesman News Service

Illustrations: The Nobel Committee for Physiology or Medicine.


  • The Nobel Prize in Physiology or Medicine for 2025 has been awarded to three scientists who made path-breaking discoveries about how our immune system avoids attacking its own body.

This year’s winners are Mary E Brunkow from the Institute for Systems Biology in Seattle, Fred Ramsdell from Sonoma Biotherapeutics in San Francisco, and Shimon Sakaguchi from Osaka University in Japan. They have been honored “for their discoveries concerning peripheral immune tolerance.”

The work of Brunkow, Ramsdell, and Sakaguchi showed how the body avoids dangerous self-attacks. They uncovered special “peacekeeping” cells of the immune system, known as regulatory T cells, that act like security guards. These cells keep the rest of the immune army in check and prevent it from harming healthy tissues.

Back in 1995, Japanese researcher Shimon Sakaguchi challenged the common belief of the time. Most scientists thought that immune tolerance, the ability to avoid attacking the body’s own cells, was under full control of the thymus, a small organ in the chest. They call it “central tolerance.”

But Sakaguchi showed something new. He discovered a separate group of immune cells that lived outside the thymus and acted as protectors against autoimmune diseases. This was the first glimpse of what we now have started to call regulatory T cells. His work opened a new chapter in immunology.

Also Read: Complete Nobel Prize in Physiology or Medicine winners list (1901–2025) and their discoveries

A few years later, in 2001, American scientists Mary Brunkow and Fred Ramsdell made a breakthrough that explained the genetic basis of these cells. They studied a special strain of mice suffering from severe autoimmune diseases. The team discovered that these mice carried a mutation in a gene they named Foxp3.

Their work didn’t stop with mice. They proved that mutations in the human version of the Foxp3 gene cause a life-threatening autoimmune condition called IPEX syndrome. This discovery gave a clear genetic link between immune tolerance and disease.

By 2003, Sakaguchi tied the discoveries together. He demonstrated that the Foxp3 gene is essential for the development of regulatory T cells. Without this gene, the peacekeeping cells cannot form. Then the immune system spirals out of control.

This knowledge is already shaping new therapies. Drugs and treatments that drew inspiration from their discoveries are under development for both autoimmune diseases and cancer.

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