The 2025 Nobel Prize in Medicine has been awarded for one of the most important discoveries in immunology: the biological system that keeps your immune system from turning on you.
Your immune cells are trained to destroy viruses, bacteria, and other foreign invaders. But that power has to be kept in check – or it can misfire, attacking your own organs. The process that prevents this is called peripheral immune tolerance, and it’s largely controlled by a type of cell called the regulatory T cell.
This year’s Nobel went to Mary E. Brunkow, Fred Ramsdell, and Shimon Sakaguchi for uncovering the genetic and cellular systems that make this immune self-regulation possible.
Back in 1995, Sakaguchi identified a previously unknown class of T cells that seemed to hold back the immune system from attacking the body. A few years later, Brunkow and Ramsdell discovered the gene that controlled them – FOXP3 – after studying a rare, fatal autoimmune disease in children. They found that when this gene is mutated, the immune system becomes unregulated and begins destroying healthy tissue.
Two years after that, Sakaguchi made the connection: FOXP3 was the master switch for the same immune-regulating cells he had identified earlier.
These discoveries launched a new field of research. Regulatory T cells are now being investigated in therapies to suppress autoimmunity, improve transplant success, and even enhance cancer treatment by modulating immune suppression around tumors.
