2025 Nobel Prize in Medicine Awarded to US–Japanese Researchers for Immune System Breakthrough

The Nobel Assembly at the Karolinska Institute announced that Mary E. Brunkow and Fred Ramsdell of the United States, together with Shimon Sakaguchi of Japan, have won the Nobel Prize in Physiology or Medicine for their pioneering discoveries in peripheral immune tolerance.


The laureates were honoured “for their discoveries concerning peripheral immune tolerance,” a fundamental mechanism by which the body prevents the immune system from attacking its own tissues. They identified the so-called regulatory T cells, often described as immune system “security guards,” which restrain harmful immune reactions that might damage healthy cells.


According to the official press release, Shimon Sakaguchi first made the key discovery in 1995, demonstrating that immune tolerance extends beyond the thymus to peripheral tissues. Brunkow and Ramsdell later revealed how a mutation in the Foxp3 gene disrupts regulatory T cell function, a finding linked to serious autoimmune conditions in mice and humans.


The prize carries a total award of 11 million Swedish kronor, which will be shared equally among the three scientists. This discovery is hailed as a milestone in immunology, opening new avenues for therapies targeting autoimmune diseases, cancer, and transplant rejection.

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