The 2025 Nobel Prize in Physiology or Medicine was awarded to U.S. scientists Mary E. Brunkow and Fred Ramsdell, along with Japanese immunologist Shimon Sakaguchi, for their groundbreaking discoveries about the immune system’s “peacekeepers” regulatory T cells. Their work revealed how the immune system learns to distinguish between harmful invaders and the body’s own cells, preventing autoimmune diseases like Type 1 diabetes and rheumatoid arthritis. Sakaguchi first discovered these crucial cells in 1995, and Brunkow and Ramsdell later identified the FOXP3 gene that governs their development. Their discoveries have transformed immunology and paved the way for potential therapies in autoimmune diseases, cancer, and transplant medicine.