Susumu Tonegawa

Susumu Tonegawa was born in Nagoya, Japan, on 5 September 1939, the second of three sons, with a younger sister. His father worked as an engineer for a textile company whose factories were scattered through rural southern Japan, so the children spent much of their childhood moving between small provincial towns. As adolescence approached, his parents sent Susumu and his elder brother to Tokyo for a stronger education. He lived with an uncle and attended Hibiya High School, where chemistry captured his interest. That early preference for chemistry, formed far from Japan's main scientific centers, set the direction of a career that would later span immunology and neuroscience.

After failing the Kyoto University entrance examination once, Tonegawa was admitted in 1959 to study chemistry. Campus politics around the Japan-United States security treaty often disrupted classes; he later said the experience helped turn him from chemical engineering toward academic science. In his senior year he read Francois Jacob and Jacques Monod on the operon theory and decided to pursue molecular biology. He briefly joined Itaru Watanabe's laboratory at Kyoto's Institute for Virus Research, but Watanabe urged him to train in the United States. With help from Watanabe and Takashi Yura, he entered the University of California, San Diego, earned a Ph.D. in 1968 under Masaki Hayashi on phage lambda transcription, and then trained with Renato Dulbecco at the Salk Institute on SV40 before visa limits forced a move to Europe.

In 1971, on Dulbecco's advice, Tonegawa joined the Basel Institute for Immunology. Knowing little of the field, he studied until he found the century-old question of antibody diversity. Using restriction enzymes and recombinant DNA, he showed that immunoglobulin gene segments rearrange in developing B cells. That somatic recombination, later called V(D)J recombination, together with somatic mutation, explained how a limited genome can produce vast antibody repertoires. His Basel group also identified a tissue-specific enhancer in the immunoglobulin heavy-chain locus. In 1981 he became a professor at MIT's Center for Cancer Research, where he extended rearrangement logic to T-cell receptors. In 1987 he alone received the Nobel Prize in Physiology or Medicine for the genetic principle of antibody diversity.

After the Nobel, Tonegawa deliberately changed fields again. At MIT he applied gene targeting to learning and memory, linking CaMKII and hippocampal NMDA receptors to synaptic plasticity and spatial memory. In 1994 he became founding director of MIT's Center for Learning and Memory, which became the Picower Institute for Learning and Memory; he directed it until the end of 2006 and remained Picower Professor. From 2009 to 2017 he also directed the RIKEN Brain Science Institute in Japan. In the 2010s his lab used optogenetics to identify and manipulate hippocampal memory engram cells, showing that activating labeled ensembles could evoke recall, alter valence, and affect models of depression and amnesia. The work helped define engrams as distributed cellular substrates of memory.

Tonegawa married Mayumi Yoshinari in September 1985. Mayumi, who had worked as an NHK director and interviewer, later wrote about science as a freelancer; MIT notes identify her as an alumna (class of 1992). He had earlier been married to Kyoko during his years in La Jolla and Basel. The couple had three children: Hidde Tonegawa (MIT class of 2009), Hanna Tonegawa, and Satto Tonegawa, who died in 2011 while an MIT freshman. The family long made their home in the Boston area. Tonegawa was an enthusiastic Boston Red Sox fan and threw a ceremonial first pitch at Fenway Park in May 2004. At his death he was also survived by two grandchildren.

Tonegawa described his scientific philosophy as curiosity-driven. In a 2022 Picower Institute interview he said that when he chose problems he asked whether they were interesting, not whether they were too risky or whether entering an unfamiliar field would hurt his career. Colleagues portrayed him as direct, unpretentious, and impatient with work that did not confront hypothesis-driven questions. He repeatedly left solved or crowded areas for harder frontiers, moving from phage genetics to immunology and then to memory engrams. That willingness to restart as a beginner, first in Basel and later in neuroscience, became part of how peers explained his two-field legacy.

V(D)J recombination is now a foundation of immunology textbooks and underpins understanding of vaccination, transplantation, and antibody-based therapies. Tonegawa's later engram studies helped make memory ensembles an experimental target rather than a metaphor, influencing research on psychiatric and neurodegenerative disease. He trained many scientists who became leaders in neuroscience. Picower director Myriam Heiman called his influence on science and on those who worked with him immeasurable. MIT established a Susumu Tonegawa Memorial Fund to support basic research at the Picower Institute. His ashes were to be buried in Kyoto after a private funeral.

Major honors included the Cloetta Prize (1978), Warren Triennial Prize (1980), Avery-Landsteiner Prize (1981), Asahi Prize (1982), Louisa Gross Horwitz Prize (1982), Gairdner Foundation International Award (1983), Person of Cultural Merit and Japan's Order of Culture (1983-1984), Bristol-Myers Award (1986), Robert Koch Prize (1986), Albert Lasker Award for Basic Medical Research (1987), and the Nobel Prize in Physiology or Medicine (1987). He became a foreign associate of the U.S. National Academy of Sciences (1986) and of the American Academy of Arts and Sciences (1984). Later recognitions included honorary degrees from Kyoto University, City University of Hong Kong, and others, election as an AAAS Fellow (2006), and UCSD's David M. Bonner Lifetime Achievement Award (2010). Gambia issued a stamp featuring him in 1995.

Tonegawa's story entered public culture through Nobel ceremonies, Japanese and international press, and later features on memory research. He appeared in long-form interviews for Nobelprize.org (2009), MIT Biology conversations, World Economic Forum talks on optogenetic memory reactivation, and Mendel Lectures. Popular and scientific outlets covered the 2012-2013 engram and false-memory papers widely. In Japan he was celebrated as the first Japanese Nobel laureate in physiology or medicine. MIT News, NHK, Nature Neuroscience, Neuron, and The New York Times published major obituaries after his death in July 2026.

Susumu Tonegawa died at his home in San Mateo, California, on 11 July 2026, at the age of 86. MIT announced his death on 15 July. A specific medical cause was not made public in major obituaries. He was survived by his wife Mayumi, children Hidde and Hanna, and two grandchildren; he was predeceased by his son Satto. After a private funeral, his ashes were to be buried in Kyoto, Japan. Memorial gifts were directed to the Susumu Tonegawa Memorial Fund at MIT's Picower Institute for Learning and Memory.