Breakthrough

Three scientists won the 2025 Nobel Prize in Physiology or Medicine for their research that led to the discovery of how the immune system avoids attacking the body’s healthy cells.

Context

The immune system must perform a delicate balancing act: It needs to fight off thousands of different infections while leaving the body’s own tissues unharmed. Scientists already knew that the thymus – an organ where white blood cells mature – routinely destroys some problematic immune cells. However, this process, called central tolerance, didn’t explain the complete picture of how the body prevents autoimmune diseases.

The Discovery

On Monday, Shimon Sakaguchi from Japan, alongside American researchers Mary Brunkow and Fred Ramsdell, received the first award in the 2025 Nobel Prizes for discovering regulatory T cells through their research in the late 90s and early 2000s.

These cells act as the immune system’s security guards, traveling throughout the body to shut down any immune cells that mistakenly attack healthy tissues. The researchers also identified the gene that controls these regulatory T cells, called FOXP3.

How It Works

The immune system creates white blood cells with receptors in quadrillions of random combinations, giving it the ability to recognize and fight countless different infections. However, this randomness inevitably produces some cells that could attack the body itself. While the thymus eliminates many of these dangerous cells, regulatory T cells provide a crucial backup system by patrolling the body and disarming any remaining threats.

Medical Applications

The discovery opened up new approaches for treating disease. In cancer, regulatory T cells can prevent the immune system from attacking tumors, so researchers are developing treatments to reduce their numbers.

For autoimmune diseases like type 1 diabetes, multiple sclerosis, and rheumatoid arthritis, scientists are testing therapies that boost regulatory T cells to stop the immune system from attacking the body. Similar approaches could also help prevent organ transplant rejection. More than 200 clinical trials building on this research are currently underway. The three scientists will share a prize of 11M Swedish kronor, approximately $1.17M.