The 2025 Nobel Prize in Physiology or Medicine has been awarded to Mary E. Brunkow, Fred Ramsdell, and Shimon Sakaguchi for their paradigm-shifting contributions to understanding how the immune system maintains balance without attacking the body’s own tissues.

Their discoveries centre on a process known as peripheral immune tolerance, and a class of immune cells called regulatory T cells (Tregs). Sakaguchi first demonstrated that these cells play a critical suppressive role in the immune system. Brunkow and Ramsdell later revealed that mutation of a gene called FOXP3 disrupts Treg development and leads to autoimmune diseases, linking molecular mechanisms to systemic outcomes.

The Nobel Assembly at the Karolinska Institute cited their work as foundational to a new field of research, opening pathways for therapies targeting autoimmunity, organ transplantation, and cancer. The laureates will share a monetary award of 11 million Swedish kronor and a gold medal, to be conferred on December 10.

In public remarks, Sakaguchi expressed his gratitude and humility at the recognition. The trio’s findings are already influencing over two hundred clinical investigations into manipulating regulatory T cells for therapeutic use. The announcement marks the start of the 2025 Nobel season, with further awards in physics, chemistry, literature, peace, and economics to follow.