The 2025 Nobel Prize in Physiology or Medicine has been awarded to Mary E. Brunkow, Fred Ramsdell, and Shimon Sakaguchi for their “groundbreaking discoveries concerning peripheral immune tolerance that prevents the immune system from harming the body,” the Nobel Assembly at Karolinska Institutet announced on Monday.
The trio’s research has fundamentally advanced the understanding of how the body’s immune system maintains balance — ensuring that while it attacks harmful invaders such as bacteria and viruses, it does not turn against the body’s own tissues.
Mary E. Brunkow (64) is a Senior Programme Manager at the Institute for Systems Biology in Seattle; Fred Ramsdell (64) serves as a Scientific Adviser for Sonoma Biotherapeutics in San Francisco; and Shimon Sakaguchi (74) is a Distinguished Professor at the Immunology Frontier Research Centre at Osaka University, Japan.
The immune system employs multiple mechanisms to identify and combat pathogens. T cells, one of its key defenders, are trained to distinguish between harmful agents and the body’s own cells. Those that mistakenly react against the body are typically eliminated in the thymus, a process known as central tolerance.
However, the 2025 Nobel laureates uncovered an additional layer of protection — peripheral immune tolerance — which ensures that any self-reactive T cells that escape the thymus are kept under control, thereby preventing autoimmune diseases.
The Nobel Prize in Physiology or Medicine has been awarded 115 times to 229 laureates between 1901 and 2024. Last year’s prize went to Victor Ambros and Gary Ruvkun, both from the United States, for discovering microRNA — tiny genetic regulators that act as cellular “on and off switches,” controlling key biological functions.
The 2025 Nobel announcements continue through the week, with Physics on Tuesday, Chemistry on Wednesday, and Literature on Thursday. The Nobel Peace Prize will be announced on Friday, followed by the Nobel Memorial Prize in Economic Sciences next Monday.
The award ceremony will take place on 10 December, marking the anniversary of Alfred Nobel’s death. Nobel, the Swedish industrialist and inventor of dynamite, established the prizes in his will before his passing in 1896.