Nobel Prize for Medicine Awarded to Immune System Researchers

Oct. 7, 2025

Why in news?

The 2025 Nobel Prize in Physiology or Medicine, the first of this year’s awards, has been jointly given to Mary E. Brunkow and Fred Ramsdell of the USA, and Shimon Sakaguchi of Japan, for their groundbreaking discoveries on the human immune system.

Their work represents two interconnected phases — Sakaguchi’s earlier research laid the foundation, while Brunkow and Ramsdell’s later findings complemented and completed it, together advancing understanding of immune regulation and tolerance.

The Medicine Prize traditionally opens the Nobel season, followed by those for Physics, Chemistry, Literature, Peace, and Economics.

What’s in Today’s Article?

The Discovery: Key Cells That Prevent the Body from Attacking Itself
The Immune System and the Discovery of Regulatory T Cells
Shimon Sakaguchi’s Discovery of Regulatory T Cells
Brunkow and Ramsdell Linked the FOXP3 Gene to Immune Regulation
How the Nobel-Winning Discoveries Are Transforming Medicine

The Discovery: Key Cells That Prevent the Body from Attacking Itself

The 2025 Nobel Prize in Medicine laureates — Mary Brunkow, Fred Ramsdell, and Shimon Sakaguchi — were honoured for discovering the mechanism of peripheral immune tolerance.
Their research revealed regulatory T cells, the body’s “immune security guards,” which prevent immune cells from attacking healthy tissues.
This breakthrough has been crucial to understanding autoimmune diseases and developing targeted therapies for immune-related disorders and cancers.
- For years, scientists were puzzled by how the immune system fights infections without harming the body’s own cells.
- By the 1980s, they understood central tolerance, where self-reactive T cells are eliminated. But this couldn’t explain all immune regulation.
- In 1995, Shimon Sakaguchi provided groundbreaking evidence for a special class of T cells, later called regulatory T cells, which act as “police” preventing other T cells from attacking healthy tissues.

The Immune System and the Discovery of Regulatory T Cells

The immune system protects the body from thousands of microbes daily, distinguishing between harmful invaders and the body’s own healthy cells.
When this identification fails, it leads to autoimmune diseases or organ transplant rejection.
T cells are central to this defence: helper T cells detect threats, while killer T cells destroy them.
Traditionally, scientists believed the thymus gland ensured immune tolerance by filtering out self-attacking T cells — a process called central tolerance.
However, the 2025 Nobel laureates — Mary Brunkow, Fred Ramsdell, and Shimon Sakaguchi — discovered an additional layer of control.
This control involved regulatory T cells, which act as immune system “security guards”, preventing other T cells from attacking the body’s own tissues.
This breakthrough transformed the understanding of immune regulation and opened new paths for treating autoimmune and transplant-related disorders.

Shimon Sakaguchi’s Discovery of Regulatory T Cells

In the mid-1990s, Shimon Sakaguchi challenged prevailing scientific views by proposing that certain specialised T cells act as “security guards” of the immune system, preventing excessive immune reactions.
Through experiments on mice without a thymus, into which mature T cells were later injected, he identified a unique class of cells — now known as regulatory T cells — that suppress other T cells attacking the body’s own tissues.
Although initially overlooked due to skepticism from earlier unconvincing studies, Sakaguchi’s insight later became a cornerstone of modern immunology, redefining how the body maintains self-tolerance.

Brunkow and Ramsdell Linked the FOXP3 Gene to Immune Regulation

Working independently from Sakaguchi, Mary Brunkow and Fred Ramsdell studied sick male mice and traced their condition to a mutation linked to a rare human autoimmune disorder called IPEX.
Both the mouse disease and IPEX were caused by defects in the FOXP3 gene.
Subsequent research confirmed that the FOXP3 gene is crucial for the development of regulatory T cells — the same immune “security guards” that Sakaguchi had discovered earlier.
Together, their complementary findings explained how the immune system maintains self-tolerance and laid the scientific foundation for the 2025 Nobel Prize in Medicine.

How the Nobel-Winning Discoveries Are Transforming Medicine?

The discoveries of regulatory T cells and the FOXP3 gene have revolutionised immune-regulation research, opening new therapeutic pathways for several major diseases.
In cancer, scientists are exploring ways to block regulatory T cells that shield tumours from immune attacks, helping the body’s defences target cancer cells more effectively.
In contrast, for autoimmune diseases, treatments aim to enhance regulatory T cell activity to suppress harmful immune responses that damage healthy tissues.
These insights are also improving organ transplant success, helping prevent rejection by fine-tuning the immune system’s response.
Overall, the discoveries have laid the groundwork for precision immunotherapy and targeted treatment innovations.