Blog about 2025 Nobel Prize of Physiology and Medicine
The 2025 Nobel Prize in Medicine: How the Immune System Learns to Protect the Body Without Turning Against It
Every day, the immune system works as a powerful defense network, identifying and eliminating viruses, bacteria, and other pathogens that threaten our health. But this defense must be carefully regulated. If the immune system becomes overactive or loses its sense of “self,” it can begin to attack the body’s own cells, leading to autoimmune diseases.
The 2025 Nobel Prize in Physiology or Medicine honors three scientists who uncovered the key mechanisms that prevent such self-destruction. Their discoveries revealed how the immune system maintains peripheral immune tolerance and how specialized immune cells keep it under control.
The 2025 Nobel Laureates
This year’s Nobel Prize in Physiology or Medicine has been awarded to
- Mary E. Brunkow, Institute for Systems Biology, Seattle, USA
- Fred Ramsdell, Sonoma Biotherapeutics, San Francisco, USA
- Shimon Sakaguchi, Osaka University, Osaka, Japan
Brunkow, Ramsdell, and Sakaguchi showed that a healthy immune system needs not only strong defenses but also restraint. Their work helps us understand how balance, even in our immune cells, maintains our health and well-being.
The Discovery
In the 1990s, most scientists believed immune tolerance was controlled only in the thymus, where harmful T cells are removed. But in 1995, Shimon Sakaguchi showed that the story is more complex. He discovered a special group of T cells that prevents autoimmunity. These are now known as regulatory T cells, or Tregs, which act as peacekeepers that calm the immune system when it becomes overly active.
In 2001, Mary Brunkow and Fred Ramsdell discovered a key gene, Foxp3, which is essential for the creation of these regulatory T cells. They also discovered that defects in this gene lead to severe autoimmune diseases in both mice and humans. Later, Sakaguchi proved that Foxp3 is the master switch that enables Tregs to function.
Why It Matters
These discoveries transformed immunology. They revealed how the body maintains self-tolerance and opened the door to new treatments for autoimmune diseases, cancer, and organ transplant rejection. Many therapies inspired by this work are now being tested in clinical trials.
Read more about this year’s prize
Popular science background: They understood how the immune system is kept in check (pdf)
Scientific background to the Nobel Prize in Physiology or Medicine 2025 (pdf)
Read the entire Press Release here: Click Here