The 2025 Nobel Prize in Physiology or Medicine has been awarded to Shimon Sakaguchi from Japan, and Mary Brunkow and Fred Ramsdell from the United States, for their groundbreaking discovery revealing how the immune system targets harmful foreign organisms while avoiding attacks on the body’s own cells.
The three researchers will share 11 million Swedish kronor (£870,000) for their discovery of regulatory T cells, often referred to as the security guards of the body, since they ensure that the immune cells do not attack healthy tissue. Their findings have revolutionized the concept of immune tolerance and led to new ways of treating autoimmune diseases and cancer.
Olle Kämpe, chair of the Nobel Committee, has indicated that their discoveries have been decisive in our understanding of how the immune system functions and why not everyone develops a serious autoimmune disease.
Their findings describe how the white blood cells can identify and destroy billions of foreign invaders while sparing the body’s own tissues. The receptors used by white blood cells can recognize an immense variety of infectious agents.
Nevertheless, this process also generates certain cells capable of attacking the body’s own tissues. It was already known that some of these harmful cells are destroyed in the thymus, where immune cells develop. The discovery leading to the Nobel Prize revealed the second layer of protection in the form of regulatory T cells that circulate throughout the body to prevent attack by the immune system on healthy tissue.
When this system fails, it can lead to autoimmune diseases such as rheumatoid arthritis, multiple sclerosis, and type 1 diabetes as autoimmune diseases. Whereas in cancer, the regulatory T cells are able to suppress the immune response to kill tumors. Scientists are currently considering ways to modulate these cells in order to treat diseases.
Osaka University researcher Shimon Sakaguchi demonstrated through experiments on mice that the deletion of the thymus caused autoimmune disease. He also demonstrated that this condition could be prevented by transferring immune cells from healthy mice, which provided evidence of a system that controls immune attacks. Embryos’ research on inherited autoimmune diseases in mice and humans, as well as the work of Mary Brunkow of the Institute of Systems Biology in Seattle and Fred Ramsdell of Sonoma Biotherapeutics in San Francisco, later identified a gene essential for the function of regulatory T cells.
Professor Annette Dolphin, the president of the UK Physiological Society, stated, “Their breakthrough work has shown how the immune system is regulated by the regulatory T cells to ensure it does not attack its own body tissues. It is a striking example of how basic physiological studies can be translated into advances that improve the overall human well-being.
References: BBC. Scientists win Nobel Prize for discovering why the immune system does not destroy the body. Published October 6, 2025. Accessed October 8, 2025. Scientists win Nobel Prize for discovering why immune system does not destroy the body
