The 2025 Nobel Prize in Physiology or Medicine was jointly awarded to Mary Brunkow, Fred Ramsdell, and Shimon Sakaguchi for their seminal work elucidating regulatory T cells (T-regs), a class of immune cells critical in preventing autoimmunity by maintaining peripheral immune tolerance. Their discoveries underpin novel approaches in treating autoimmune disorders, cancer, and improving organ transplant outcomes. This recognition highlights decades of foundational immunology research redefining immune system modulation.