Tasuku Honjo is a distinguished Japanese physician-scientist, immunologist and Nobel laureate best known for discovering Programmed cell death protein 1 (PD-1) with his colleagues at Kyoto University and for concluding that the protein was a negative regulator of immune responses. This discovery by Honjo encouraged the development of anti-PD-1 and anti-PD-L1 antibodies as anti-cancer immunotherapeutic agents, thus paving way for development of therapies that have proved quite effective in the fight against cancer. He jointly received the 2014 Tang Prize in Biopharmaceutical Science and the 2018 Nobel Prize in Physiology or Medicine along with American immunologist James P. Allison for discovering a cancer therapy by inhibition of negative immune regulation. He was successful in cDNA cloning of the cytokines interleukin 4 (IL4, IL-4) and interleukin 5 (IL5) and discovered activation-induced cytidine deaminase (AID), besides demonstrating significance of this 24 kDa enzyme in somatic hypermutation and class switch recombination. He has served in several academic positions in Japan, including the Tokyo University, Osaka University and Kyoto University and has been a professor at the latter since 1984. He became a member of the Japan Academy and the German Academy of Natural Scientists Leopoldina and was made a foreign associate of the National Academy of Sciences of the US.