Shimon Sakaguchi is currently a Distinguished Professor at Osaka University, Japan. He is an immunologist recognized particularly for his discovery of regulatory T cells, an indispensable constituent of the immune system for the maintenance of immune self-tolerance and homeostasis. Sakaguchi obtained an M.D. in 1976 and a Ph.D. in 1982 from Kyoto University, Japan, and performed postdoctoral studies at Johns Hopkins University and Stanford University as a Lucille P. Markey Scholar. He has been a Professor at Kyoto University and Osaka University for many years. He was awarded the Medal with Purple Ribbon from the Emperor in 2009, elected to Foreign Member of National Academy of Sciences USA in 2012, designated as Person of Cultural Merit by the Japanese Government in 2017, and has been awarded with many international prizes including Cancer Research Institute’s William B. Coley Award, Keio Medical Science Prize, Canada Gairdner International Award and the Crafoord Prize.