Japanese scientist Shimon Sakaguchi gives a press conference in Suita, Osaka Prefecture, on Oct. 6, 2025, after winning the Nobel Prize in Physiology or Medicine along with two Americans. (Kyodo)
STOCKHOLM (Kyodo) — Japanese scientist Shimon Sakaguchi and two Americans were awarded the Nobel Prize in Physiology or Medicine on Monday for their “groundbreaking” discoveries on how the immune system is kept in check, the Nobel Assembly at the Karolinska Institute said.
“The laureates’ discoveries launched the field of peripheral tolerance, spurring the development of medical treatments for cancer and autoimmune diseases,” the assembly said in a press release.
Sakaguchi’s co-winners are U.S. scientists Mary E. Brunkow and Fred Ramsdell.
Sakaguchi, a 74-year-old distinguished professor at Osaka University, discovered that regulatory T cells, or Tregs, prevent other T cells from attacking the body’s own healthy cells that are sometimes mistaken for foreign substances.
“I feel truly honored,” Sakaguchi told reporters in front of his laboratory at the university after the announcement was made.
Sakaguchi theorized that there should be cells that prevent excessive reactions in the immune system, noting that mice suffer an autoimmune disease once the thymus, a lymphoid organ closely associated with the immune system, is removed.
Although many disagreed with his hypothesis, Sakaguchi persevered with his research, which ultimately led to the discovery of a molecule unique to regulatory T cells in 1995.
In 2001, Brunkow and Ramsdell discovered a specific gene mutation that causes autoimmune diseases, and Sakaguchi later proved that the gene regulates the production of the cells he had identified in 1995.
At a press conference at Osaka University, Sakaguchi expressed hope that his research in the field will “advance further and be applied to clinical situations.”
Sakaguchi also said that with advances in medical treatment, he believes “there will be useful treatments and preventive methods for diseases that were once considered difficult to treat.”
The prize of 11 million kronor ($1.2 million) will be shared equally among the three recipients.
It marks the second consecutive year a Japanese individual or group has been awarded a Nobel prize, following last year’s awarding of the Nobel Peace Prize to Nihon Hidankyo, Japan’s leading group of atomic bomb survivors. There are now a total of 30 Japanese Nobel laureates.
Prime Minister Shigeru Ishiba called Sakaguchi to congratulate him, praising the scientist’s work as “a great piece of research” that Japan “can boast to the world.”
Born in Shiga Prefecture, Sakaguchi earned his medical degree from Kyoto University in 1976. He left its graduate program the following year to join the Aichi Cancer Center for more in-depth research, before returning to Kyoto University to earn a Ph.D. in 1983.
In 2015, he received the Gairdner International Award, often seen as a forerunner to the Nobel Prize, for his contributions to medical science.
AloJapan.com