The 2025 Nobel Prize in Physiology or Medicine honors Mary Brunkow, Fred Ramsdell, and Shimon Sakaguchi for elucidating regulatory T cells (Tregs), a subset of CD4+ T lymphocytes critical for peripheral immune tolerance. Their pioneering work revealed Tregs’ role in preventing autoimmune attacks and maintaining immune homeostasis, transforming understanding of immune regulation. These insights underpin therapeutic strategies targeting autoimmune diseases, transplantation, and cancer immunotherapy.