Dr. Honjo is well known for his discovery of activation-induced cytidine deaminase that is essential for class switch recombination and somatic hypermutation. He has established the basic conceptual framework of class switch recombination starting from discovery of DNA deletion (1978). Dr. Honjo identified a series of key molecules involved in immune regulation, including IL-4, IL-5, SDF-1, and IL-2R αchain. Also appreciated is his seminal contribution to developmental biology by identification of RBP-J as the Notch signaling target. In addition, he discovered PD-1 (program cell death 1), a negative coreceptor at the effector phase of immune response and demonstrated that PD-1 inhibition contributes to cancer treatments. Anti-PD-1 cancer immunotherapy has been approved in US, EU, and Japan. This treatment revolutionalized the cancer therapy and is considered to be equivalent to penicillin in infectious diseases.

For these contributions, Dr. Honjo has received many awards, including the Imperial Prize, Japan Academy Prize (1996), Robert Koch Prize (2012), Order of Culture from the Emperor of Japan (2013), Tang Prize (2014), William B. Coley Award (2014), Richard V. Smalley, MD Memorial Award (2015), Kyoto Prize (2016), and Keio Medical Science Prize (2016). He is an honorary member of American Association of Immunologists. Honored by the Japanese Government as a person of cultural merits (2000). Elected as a foreign associate of National Academy of Sciences, USA in 2001, as a member of Leopoldina, the German Academy of Natural Scientists in 2003, and also as a member of Japan Academy in 2005.