Congratulations to Professor Shimon Sakaguchi and his wife, Mrs. Noriko Sakaguchi, on winning the Nobel Prize in Physiology or Medicine.
Professor Sakaguchi has long been an esteemed senior researcher, a mentor in immunology, and a comrade with whom I have shared both ideals and challenges from the ground up to start RegCell.
To see someone so close receive the Nobel Prize is truly overwhelming. Although Professor Sakaguchi’s name had appeared among the potential candidates for several years, hearing his name announced live during the Nobel Prize broadcast gave me goosebumps. For a few moments, I was speechless—then, I found myself exclaiming “What? Oh!” involuntarily.
Professor Sakaguchi and I share the same future therapeutic strategies, which led me to join RegCell as a co-founder when he established it in 2016. Our shared vision was to develop therapies using acquired immune cells. Professor Sakaguchi focused on regulatory T cells, while I worked on killer T cells, and we started the company to develop T-cell–based therapies.
Professor Sakaguchi’s Nobel Prize is therefore deeply meaningful for the company I established, Rebirthel, as well. Although Rebirthel was spun out from RegCell in 2019, because of the differences of target disease and development stages, we continue to share the same aspirations. We often talk about future collaboration plans.
Let me briefly talk about the significance of his discovery of regulatory T cells. The question “How is self-tolerance established?” has long been one of fundamental unsolved questions in immunology. During the 1980s, the theory that self-reactive cells were eliminated in the thymus through negative selection has been proved, and many believed the question had been solved. Despite such a situation, Professor Sakaguchi alone arrived at an entirely new insight. His discovery is that immune tolerance is induced by regulatory T cells at the peripheral level. This is not only a landmark discovery in life sciences but also one of profound medical discoveries, as the breakdown of this immune system causes autoimmune diseases.
Allow me to share a few words about my relationship with Professor Sakaguchi. He joined Institute for Frontier Life and Medical Sciences, Kyoto University (the predecessor of the current Institute for Life and Medical Sciences) in 1999. Although I belonged to a different laboratory and was not his direct staff member, he has been always generous with his time, and I had the privilege of learning the essence of immunology directly from him.
In 2004, I moved to RIKEN Yokohama to work as a team leader, yet we remained close. Although he transferred to Osaka University in 2010, he continued to maintain his laboratory at Kyoto University. After I returned to Kyoto University as a professor in 2012, we began to interact more frequently to have research discussions. As I mentioned earlier, we shared the same goals to develop new cell therapy, and eventually founded RegCell together.
After the establishment of RegCell, I often discussed closely on company managements with Mrs. Noriko Sakaguchi who was deeply involved as an executive. Professor Sakaguchi affectionately refers to his wife as his “comrade.” I consider myself—albeit modest, to have been one of his comrades during the founding of RegCell. Even today, the three of us often dine together, reaffirming our shared commitment to achieve.
The picture below was taken on October 10, 2025 , when Professor Sakaguchi visited his laboratory at Institute for Life and Medical Sciences, Kyoto University for the first time after the award announcement. The interview video was also taken on that day, and it will be available on the Institute’s official YouTube channel.
Once again, my heartfelt congratulations to Professor Sakaguchi.
CTO, Rebirthel Co., Ltd.
Director of Institute for Life and Medical Sciences, Kyoto University
Professor Hiroshi Kawamoto