Japan's Sakaguchi, 2 Americans share Nobel Prize in medicine

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, 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, leading him to discover the molecule unique to regulatory T cells in 1995.

In 2001, U.S. scientists Mary E. Brunkow and Fred Ramsdell discovered a specific mutation in a gene that causes autoimmune diseases, with Sakaguchi later proving that the gene governs the production of the cells he identified in 1995.

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 winning of the peace prize by Nihon Hidankyo, Japan's leading group of atomic bomb survivors. There are now a total of 30 Japanese Nobel laureates.

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.