Finding immune cells that stop a body from attacking itself wins medicine Nobel

Work on peacemakers in the immune system won the 2025 Nobel Prize in physiology or medicine.

The peacemakers are regulatory T cells, a type of immune cell that calms the immune system after it has finished fighting infection or healing a wound. These special T cells also prevent the immune system from attacking the body. If they fail in this mission, autoimmune disorders or damaging inflammation can result. These cells are also important to prevent rejection of the fetus during pregnancy.

Shimon Sakaguchi of Osaka University in Japan first discovered these important cells, also known as T-regs, in 1995. Sakaguchi shares the prize, worth 11 million Swedish krona (over $1.1 million), with Mary Brunkow of the Institute for Systems Biology in Seattle and Fred Ramsdell, a cofounder of Sonoma Biotherapeutics, a company based in San Francisco and Seattle. The Nobel Assembly at the Karolinska Institute in Stockholm announced the prize October 6.

Brunkow and Ramsdell tracked down a mutation that caused a fatal autoimmune disease in male mouse pups while working at Celltech Chiroscience in Bothell, Wash., in the 1990s. The mutation turned out to disable a gene called FOXP3. That gene is important for T-reg development, Sakaguchi later discovered. Without it, there aren’t enough T-regs to stop wayward immune cells from causing harm in the body. Mutations in FOXP3 are also responsible for an autoimmune disease called IPEX in people, the American duo revealed in 2001.

Scientists are learning to harness T-regs to prevent rejection of transplanted organs and treat autoimmune disorders, food allergies, cancer and other conditions in which the immune system is overactive or directed against the wrong thing.