Mastering Immunity: The 2025 Nobel Prize in Medicine

Courtesy of the Economic Times

On October 6, 2025, the Nobel Assembly awarded the Nobel Prize in Physiology or Medicine to Dr. Mary E. Brunkow (Institute for Systems Biology),  Dr. Shimon Sakaguchi (Osaka University), and Dr. Fred Ramsdell (Sonoma Biotherapeutics) for their groundbreaking achievements in understanding peripheral immune tolerance. Their collaborative work, culminating in the identification of regulatory T cells and the FOXP3 gene, has transformed immunology and paved the way for new treatments across a myriad of medical disciplines. 

Peripheral immune tolerance is the mechanism by which the immune system prevents its own cells from attacking the body's tissues and organs. This concept challenges previous models of immune function and fills critical gaps in the understanding of self-tolerance; a question that had long perplexed immunologists and genetic researchers. 

The pathway toward this historic scientific milestone began in 1995 when Dr. Shimon Sakaguchi published his discovery of a subset of T cells responsible for suppressing immune responses. At the time, the commonly held view was that immune tolerance arose mostly through central tolerance – a process in the thymus where self-reactive T cells are deleted before they enter circulation. 

However, Dr. Sakaguchi’s experiments, specifically those involving the removal of the thymus in mice, revealed a secondary peripheral mechanism. In the absence of the thymus, a small organ responsible for defending against infection and disease, mice developed debilitating autoimmune conditions. Dr. Sakaguchi identified cells that could prevent this autoimmune disease, called CD25+ cells, a key marker for identifying regulatory T cells. This identification suggested that the immune system is equipped with a secondary regulatory system that lives outside of the thymus, ensuring tolerance after T cell intervention in the bloodstream. 

This breakthrough led to a shift in immunity research: tolerance was not solely contained within the function of the thymus, rather, it is maintained throughout the body. 

While Dr. Sakaguchi’s discovery identified regulatory T cells phenotypically, the genetic mechanisms that code their function and formation remained unknown until he joined forces with Dr. Mary E. Brynkow and Dr. Fred Ramsdell. 

Their focus while conducting research at Celltech Chiroscience was on a mutant mouse model with a detrimental autoimmune disease similar to IPEX Syndrome in humans. These mice lacked a crucial regulatory mechanism, leading to a rapid fatality rate as their immune system attacked their own organs. Through genetic mapping and molecular analysis, Dr. Brunkow and Dr. Ramsdell identified the FOXP3 gene as the missing piece to Dr. Sakaguchi's nearly solved puzzle. 

FOXP3 functions as the ruling regulatory gene for the development and stability of regulatory T cells. Without FOXP3, the immune system fails to produce functional regulatory T cells, leading to a breakdown of self-tolerance. Their discovery not only confirmed the existence of a genetic foundation for regulatory T cells but also established FOXP3 as a key component in immune homeostasis. 

One of the greatest things to come from the identification of regulatory T cells and the FOXP3 gene is its potential strides within the medical world. It has opened new doors for clinical trials for new treatments for cancer and autoimmune diseases, as well as leading to developments in organ transplantation.