The 2025 Nobel Prize in Medicine: How the Body Keeps the Immune System Under Control

The human immune system is our primary line of defense—working against harmful germs, viruses, and various invaders. However, sometimes this defense system backfires, starting to attack healthy cells. At the root of autoimmune diseases like cancer, rheumatoid arthritis, or type 1 diabetes lies this very imbalance. The 2025 Nobel Prize in Physiology or Medicine has been awarded to three scientists for their groundbreaking research on “peripheral immune tolerance.” This mechanism essentially prevents the immune system from harming the body, and has opened new horizons for organ transplantation and autoimmune disease treatment.

Announced in Stockholm on Monday, the prize was awarded to Mary E. Brankow, Fred Ramsdell, and Shimon Sakaguchi. Sakaguchi is currently a distinguished professor at the Immunology Frontier Research Center at Osaka University in Japan. Brankow is Senior Program Manager at the Institute for Systems Biology in Seattle, USA, while Ramsdell is a Scientific Advisor at Sonoma Biotherapeutics in California. The Nobel Committee recognized their work because it paved the way for clinical trials of new therapies—especially involving regulatory T cells, which can suppress overactive immune responses.

Mary Vahren-Harrison, a member of the Nobel Committee, said at a press conference,

“This year’s Nobel Prize mainly recognizes the mechanisms by which our body keeps the immune system under control. In this way, we are able to fight off germs while also avoiding autoimmune diseases.”

Maria-Luisa Alegre, Professor of Medicine at the University of Chicago, said,

“Although the Nobel Prize can only recognize three people, many pioneers contributed to this field. This recognition will bring new impetus to treatments for organ transplantation and autoimmune diseases.”

From Suppressor Cells to Regulatory T Cells

In the 1970s, scientists suggested that there might be certain T cells in the immune system that suppress other immune responses. These were initially called “suppressor T cells.” However, due to lack of conclusive evidence from early research, this idea gradually fell out of favor.

Later, while researching at the Aichi Cancer Center in Nagoya, Japan, Sakaguchi revived this concept. He was searching for a molecular marker that could be used to identify these special cells. Sakaguchi and his team conducted experiments using mice and found that cells containing a specific protein called CD25 are essential for preventing the body from attacking itself. In an important study published in 1995, he redefined this class of cells, which are now known as regulatory T cells.

Peter Savage, Professor at the University of Chicago, said,

“The idea of suppressor cells was unpopular at the time. But Sakaguchi, through thorough and meticulous experimentation, proved that such powerful ‘peacekeeper’ cells do exist.”

The FOXP3 Gene and a New Chapter in Immunology Research

In Washington State, Brankow and Ramsdell went even deeper, uncovering the genetic basis of regulatory T cells. They conducted research on a special strain of mice known as scurfy mice, which showed symptoms like skin peeling and swollen lymph nodes, and had a short lifespan. Their studies revealed that a gene called FOXP3 was responsible for this autoimmune disease. Later, it was found that mutations in this gene in humans cause a severe illness called IPEX syndrome (immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome).

These discoveries laid a new foundation for Sakaguchi and other researchers, including Alexander Rudensky, who now directs the Immunology Program at Memorial Sloan Kettering Cancer Center.

Conclusion

The 2025 Nobel Prize again demonstrates that fundamental research opens new horizons for medicine. The work of Sakaguchi, Brankow, and Ramsdell is not just limited to scientific theory; it is paving the way to save millions of lives in practice. In the future, there is no doubt that their discoveries will be directly applied in the treatment of autoimmune diseases and organ transplantation.