Shimon Sakaguchi, co-recipient of the 2025 Nobel Prize in Physiology or Medicine, speaks at a news conference at the University of Osaka in Suita, Osaka Prefecture, on Oct. 6. (The Asahi Shimbun)

Photo/Illutration Shimon Sakaguchi, co-recipient of the 2025 Nobel Prize in Physiology or Medicine, speaks at a news conference at the University of Osaka in Suita, Osaka Prefecture, on Oct. 6. (Reo Komeda)

SUITA, Osaka Prefecture—Immunologist Shimon Sakaguchi, a co-winner of this year’s Nobel Prize in Physiology or Medicine, said he hopes research in his field will soon produce therapeutic applications to autoimmune diseases.

At a news conference here on Oct. 6 following the announcement by Sweden’s Karolinska Institute, Sakaguchi said two aspects of immune responses are crucial: how to enhance them and how to suppress excessive ones.

He said his research has focused on the latter.

“It is linked to how we can prevent the development of conditions such as rheumatoid arthritis and type 1 diabetes,” he said. “I hope that research in this field will continue to advance and progress toward practical clinical applications.”

Sakaguchi, 74, a specially appointed professor at the University of Osaka’s Immunology Frontier Research Center, was named a co-recipient of the Nobel Prize for the discovery of mechanisms by which the immune system is regulated.

“It is a delightful surprise,” he told the news conference at the university. “I had thought that if this research could become a little more useful to people, there might be some kind of reward. I am surprised and deeply honored.”

He expressed “deep appreciation” for researchers and students who have worked with him over the years.

Sakaguchi discovered a type of immune cells, known as “regulatory T cells,” which act as a brake to prevent runaway immune responses.

His research also showed that when the function of these cells is weakened, immune cells may attack the body’s own healthy tissues, leading to autoimmune diseases.

In the human body’s immune system, various types of cells work in concert to eliminate foreign substances, such as bacteria and viruses, that cause illness.

However, the immune system can sometimes react strongly to targets that are not pathogens.

This can trigger autoimmune diseases, including rheumatoid arthritis and type 1 diabetes, where the body attacks its own tissues, as well as allergies, in which the immune system overreacts to normally harmless substances like pollen.

In the 1980s, Sakaguchi conducted experiments using mice that were unable to produce T cells, which serve as the command center of the immune system, and noticed a type of T cell that halted the immune function.

He also confirmed that transplanting T cells from which the “brake” function had been removed into these mice caused them to develop autoimmune diseases.

In 1995, he published a paper proving the existence of these cells. He named them “regulatory T cells” and went on to elucidate their functions in detail.

Sakaguchi previously received prestigious awards for his work, including the Asahi Prize in 2011, the Canada Gairdner International Award in 2015, the Crafoord Prize in 2017 and the Robert Koch Award in 2020.

Regulatory T cells are involved in a wide range of diseases. Enhancing their function could potentially suppress autoimmune diseases, allergies and rejection after organ transplantation, raising hopes for therapeutic applications.

On the other hand, it has become clear that regulatory T cells can also inhibit immune cells that attack cancer cells, effectively acting as a “shield” that protects tumors.

Consequently, research is under way in Japan and abroad to weaken regulatory T cells as a means of treating cancer.

Sharing the Nobel Prize in Physiology or Medicine with Sakaguchi are Mary Brunkow of the Institute for Systems Biology in the United States and Fred Ramsdell of Sonoma Biotherapeutics, also in the United States. The two made key discoveries that supported the existence of regulatory T cells.

Sakaguchi is the 29th individual Nobel laureate from Japan, including those who obtained U.S. citizenship, and the sixth in the category of Physiology or Medicine.

The award ceremony will be held in Stockholm on Dec. 10. The prize money of 11 million Swedish kronor (170 million yen) will be shared among the three recipients.

 

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