The 2025 Nobel Prize in Physiology or Medicine has been awarded to scientists Mary Brunkow, Fred Ramsdell, and Shimon Sakaguchi for their groundbreaking discoveries on peripheral immune tolerance—a finding that has reshaped modern immunology and paved the way for new treatments for cancer and autoimmune diseases.
Announcing the award, the Nobel Assembly at Sweden’s Karolinska Institute praised the trio’s work for “revealing the immune system’s own mechanisms of self-control,” describing it as a scientific milestone that “has laid the foundation for a new field of medical research.”
Understanding the Discovery
The immune system’s primary job is to defend the body from harmful pathogens. However, when this defense mechanism mistakenly targets the body’s own cells, it leads to autoimmune diseases such as type 1 diabetes, multiple sclerosis, and lupus.
In the mid-1990s, when scientists believed that immune tolerance was governed mainly by a process known as central tolerance, Japanese immunologist Shimon Sakaguchi made a discovery that changed this understanding forever. In 1995, he identified a new class of immune cells—later named regulatory T cells (Tregs)—that act as the immune system’s “security guards.” These cells prevent other immune cells from attacking the body’s own tissues, maintaining balance and preventing self-destruction.
The Role of the Foxp3 Gene
Years later, in 2011, American researchers Mary Brunkow and Fred Ramsdell made another crucial finding while studying a mouse strain unusually prone to autoimmune disorders. They discovered that these mice carried a mutation in a gene they named Foxp3. This gene turned out to be a key regulator of immune balance.
Further investigation revealed that mutations in the human version of the Foxp3 gene cause a rare but serious autoimmune condition known as IPEX syndrome (Immune dysregulation, Polyendocrinopathy, Enteropathy, X-linked).
By 2013, Sakaguchi had linked these discoveries, proving that the Foxp3 gene controls the development of the regulatory T cells he had discovered earlier. Together, their work established a new understanding of how the immune system distinguishes between self and non-self—protecting the body from within.
Transformative Impact on Medicine
This discovery has revolutionized immunology and inspired an entirely new field of medical research. It has provided scientists with the tools to design therapies that can fine-tune immune responses. From developing new cancer immunotherapies to creating treatments for autoimmune and inflammatory disorders, the influence of Treg and Foxp3 research continues to grow.
According to Nobel Committee chair Olle Kämpe, “Their discoveries have been decisive for our understanding of how the immune system functions and why we do not all develop serious autoimmune diseases.”
About the Laureates
Mary E. Brunkow, who earned her Ph.D. from Princeton University, currently serves as a Senior Program Manager at the Institute for Systems Biology in Seattle.
Fred Ramsdell is a Scientific Advisor at Sonoma Biotherapeutics, a U.S.-based company focusing on cell therapies for autoimmune diseases.
Shimon Sakaguchi is a Distinguished Professor at the Immunology Frontier Research Center, Osaka University, Japan.
The Prize and Its Legacy
Each laureate will receive a share of the 11 million Swedish crowns (approximately $1.2 million) prize money, along with a gold medal to be presented by Sweden’s King later this year.
The Nobel Prize, established by Swedish inventor Alfred Nobel, honors those who have made the “greatest benefit to humankind.” The 2025 award in medicine perfectly embodies that vision—recognizing a discovery that not only deepened our understanding of life’s inner defense system but also continues to save lives across the world.
