STOCKHOLM – The 2025 Nobel Prize in Physiology or Medicine has been jointly awarded to American scientists Mary E. Brunkow and Fred Ramsdell, and Japanese scientist Shimon Sakaguchi for their fundamental discoveries related to how the immune system learns not to attack the body's own tissues.

The Nobel Assembly announced on monday that the trio won for their breakthroughs in understanding “peripheral immune tolerance.” Their research identified a specific type of immune cell, known as regulatory T-cells (T-regs), which are crucial for maintaining order within the immune system.

This discovery has been heralded as a cornerstone of modern immunology. It explains a critical mechanism that prevents the body from launching a self-destructive assault, which is the cause of autoimmune diseases such as multiple sclerosis and rheumatoid arthritis. The laureates' work has fundamentally changed our understanding of immune control.

Before their discoveries, the concept of cells actively suppressing the immune system was highly debated. Sakaguchi's pioneering experiments in Japan, along with the parallel work by Brunkow and Ramsdell in the United States, provided definitive proof of the existence and function of these regulatory T-cells. They act as the immune system’s “security guards,” ensuring that other immune cells do not mistake the body’s own healthy tissues for foreign invaders.

The implications of their findings extend far beyond autoimmune conditions. This research has paved the way for innovative treatments for a wide range of diseases. By manipulating these regulatory T-cells, scientists can either boost the immune response to fight cancer or suppress it to treat autoimmune disorders and prevent organ transplant rejection.

The Nobel committee stated that the laureates' discoveries have “paved the way for developing new treatments for various conditions.”

The three scientists will share the prize money of 11 million Swedish kronor (approximately $1.2 million). The formal award ceremony will be held in Stockholm on December 10, the anniversary of the death of Alfred Nobel, the benefactor of the prize. Their work provides a profound example of how basic scientific inquiry can lead to revolutionary advances in medicine.