How can the body’s defense system, powerful enough to destroy viruses and bacteria, suddenly, and without warning, turn against the very body it’s meant to protect? For the tens of millions suffering from autoimmune diseases, this betrayal can be deadly. The 2025 Nobel Prize in Physiology or Medicine finally uncovered the immune system’s balance between life and self-destruction that keeps us alive.
On October 6th, the science community celebrated a breakthrough that reminds the world of science’s power to transform lives. The 2025 Nobel Prize in Physiology or Medicine was awarded to Mary Brunkow, Fred Ramsdell, and Shimon Sakaguchi, for their research on the immune system’s ability to protect the human body without attacking itself. This answered one of biology’s biggest mysteries: how the human body avoids self-destruction.
For decades, scientists have understood the human body’s immune system detects and destroys infectious agents like viruses and bacteria. However, this response by our body can sometimes misfire, attacking the body’s own healthy cells and causing autoimmune diseases. Examples of this include type 1 diabetes, lupus, and multiple sclerosis. However, what’s long stood unclear was how the immune system is usually able to prevent this “misfire” from happening.
In the 1990s, Shimon Sakaguchi identified a rare type of white blood cell that acted as a restraint on the immune system. He called these cells regulatory T cells (or Tregs). Sakaguchi concluded that these cells prevent overactive immune responses, but the exact mechanism remains unclear as well as what actually triggers them and suppresses them.
In 2001, American scientists Mary Brunkow and Fred Ramsdell found the missing piece. While studying an immune disorder in mice, they traced the cause to a single gene: the FOXP3 gene. They discovered that the FOXP3 gene serves as a switch or command center to regulate the immune system. The gene essentially triggers developing T cells to turn into regulatory T cells (what Sakaguchi had found about a decade earlier) which gives them the molecular tools to keep other immune cells in check.
Brunkow and Ramsdell discovered that when FOXP3 is defective, the regulatory T cells fail to develop. Without them, the immune system lacks the signals to stop, leading to attacks on the body’s organs, ultimately causing autoimmune diseases. This link between FOXP3 and regulatory T cells explains the genetic causes of immune tolerance, and the body’s ability to distinguish when to stop attacking and when to start attacking things in your body.
This discovery transformed immunology. By showing that immune tolerance depends on a specific gene and cell type, Brunkow, Ramsdell, and Sakaguchi gave scientists a roadmap for treating diseases once thought untouchable.
Now, researchers are exploring ways to strengthen regulatory T cells in patients with autoimmune disorders to restore the body’s control of its immune system. Others are experimenting with ways to temporarily weaken T Cells for cancer therapy, so the immune system can attack tumors more aggressively. Their work has already led to early-stage clinical trials aimed at treating type 1 diabetes, inflammatory bowel disease, and transplant rejection.
When the Nobel Prize was announced Ramsdell was off the grid, and didn’t hear the news until days later when he turned on his phone to see congratulations messages from his friends and family. Ramsdell told reporters that the discovery wasn’t about awards or recognition, but an ode to all of the scientists that came before. Ramsdell told reporters that this discovery came from a combination of research done in multiple research fields across decades, showing that science is a collective effort built on curiosity and persistence.
