The 2025 Nobel Prize in Physiology or Medicine was awarded to Mary Brunkow, Fred Ramsdell, and Shimon Sakaguchi for seminal discoveries concerning regulatory T cells (Tregs) and their role in peripheral immune tolerance. Their research identified CD4+CD25+FOXP3+ Tregs as critical mediators that prevent autoimmune attacks, expanding understanding beyond central tolerance mechanisms in the thymus. This breakthrough has profound implications for autoimmune disease treatment, organ transplant success, and cancer immunology development.