Nobel Prize in Medicine 2025 Awarded for Discovery in Immune System Regulation

Three scientists — Mary Brunkow, Fred Ramsdell (both from the United States), and Shimon Sakaguchi (from Japan) — have been jointly awarded the 2025 Nobel Prize in Physiology or Medicine for their pioneering discoveries that revealed key mechanisms of the human immune system.

Discovery of Peripheral Immune Tolerance

The Nobel Committee recognised their work for uncovering the mechanism of “peripheral immune tolerance,” a process that prevents the immune system from attacking the body’s own healthy cells.

Their research identified regulatory T cells (Tregs) — often described as the immune system’s “security guards” — which suppress overactive immune responses and maintain internal balance.

Shimon Sakaguchi’s Breakthrough (1995)

In 1995, Shimon Sakaguchi made the first landmark discovery by showing that immune tolerance isn’t limited to the destruction of self-reactive immune cells (a process called central tolerance).
He identified a new class of immune cells, now known as regulatory T cells, which play a vital role in preventing autoimmune diseases by actively controlling immune reactions.

Brunkow and Ramsdell’s Contribution (2001)

In 2001, Mary Brunkow and Fred Ramsdell discovered that a mutation in a gene called Foxp3 made certain mice highly susceptible to autoimmune diseases.
They later demonstrated that mutations in the human Foxp3 gene cause a severe autoimmune disorder known as IPEX (Immune dysregulation, Polyendocrinopathy, Enteropathy, X-linked syndrome).

Connecting the Dots (2003)

By 2003, Sakaguchi linked the findings, proving that the Foxp3 gene is essential for the development and functioning of regulatory T cells. These cells act as the immune system’s moderators — ensuring it attacks pathogens but spares the body’s own tissues.

Medical Impact

This discovery has transformed modern medicine, paving the way for new immunotherapies in cancer treatment, autoimmune disorders, and organ transplantation.
By understanding and manipulating regulatory T cells, scientists can now explore targeted treatments that fine-tune immune responses — a major leap in both immunology and clinical therapeutics.

Nobel Committee’s Statement

The Nobel Assembly stated that the laureates’ discoveries “unlocked the mysteries of immune self-tolerance,” offering profound insights into how the immune system distinguishes between friend and foe — a cornerstone of human health.