Author: Andrei Bilog

Every year, the Nobel Prize in Physiology or Medicine honors discoveries that truly change how we understand life and health. It’s one of the most prestigious awards in science, meant to celebrate breakthroughs that “benefit humankind.”

In 2025, the Nobel Prize was awarded to Mary E. Brunkow, Fred Ramsdell, and Shimon Sakaguchi for uncovering how our immune system prevents itself from attacking our own body. Their work explains a crucial idea called immune tolerance—specifically, how the body keeps its defense system from going rogue.

Our immune system is like an army trained to attack invaders such as viruses or bacteria. But sometimes, parts of this army make a mistake and attack healthy cells instead, leading to diseases like type 1 diabetes, rheumatoid arthritis, or lupus.

The three scientists discovered how the body prevents that from happening. They found special cells—called regulatory T cells, or Tregs—that act like peacekeepers. Their job is to calm down other immune cells that might overreact and cause damage.

Here’s what each scientist contributed:

In the 1990s, Dr. Sakaguchi noticed something strange. When certain immune cells were removed from mice, the animals developed severe autoimmune diseases. This meant that those missing cells were actually keeping the immune system under control.

He discovered that these “brake cells” were a special type of white blood cell called regulatory T cells (Tregs). Instead of fighting infections, Tregs keep other immune cells from attacking the body’s own tissues.

This idea was revolutionary because scientists used to think that self-protection only came from eliminating harmful cells early on. Sakaguchi proved that the immune system also has an active self-control mechanism.

A few years later, Brunkow and Ramsdell made the next key discovery—a gene called FOXP3. When this gene is missing or defective, Tregs cannot develop properly.

They saw this in mice that had a genetic mutation: without FOXP3, the animals’ immune systems went out of control, attacking their own organs. They also found that in humans, mutations in the same gene cause a rare but deadly autoimmune disease called IPEX syndrome, seen mostly in newborn boys.

This proved that FOXP3 is the “master switch” that programs regulatory T cells to become peacekeepers. Without it, the immune system loses balance.

This discovery changed how doctors and scientists think about the immune system. Instead of seeing it as just a defense force, we now understand it as a complex network that balances attack and tolerance.

That balance is critical. Too little activity, and we can’t fight infections. Too much activity, and we develop autoimmune diseases.

Because of this research, scientists are now developing new treatments that use Tregs to:

It’s even possible that one day, we could use engineered Tregs as a living medicine—boosting them when we need more control, or dialing them down when we need a stronger immune response.

What Brunkow, Ramsdell, and Sakaguchi discovered is not just about one cell type—it’s about balance. Their work shows that health isn’t just about fighting disease; it’s about knowing when to stop fighting.

That lesson applies far beyond biology. Just like the immune system, we need regulation and balance to function at our best.