Susumu Tonegawa

Tonegawa was born in Nagoya, Japan, and attended Hibiya High School in Tokyo. While a student at Kyoto University, Tonegawa became fascinated with operon theory after reading papers by François Jacob and Jacques Monod, whom he credits in part with inspiring his interest in molecular biology. Tonegawa graduated from Kyoto University in 1963 and, due to limited options for molecular biology study in Japan at the time, moved to the University of California, San Diego, to do his doctorate study under Dr. Masaki Hayashi. He received his Ph.D. in 1968.

Tonegawa conducted post-doctoral work at the Salk Institute in San Diego in the laboratory of Renato Dulbecco. With encouragement from Dr. Dulbecco, Tonegawa moved to the Basel Institute for Immunology in Basel, Switzerland, in 1971, where he transitioned from molecular biology into immunology studies and carried out his landmark immunology studies.

In 1981, Tonegawa became a professor at the Massachusetts Institute of Technology. In 1994, he was appointed the first Director of the MIT Center for Learning and Memory, which developed under his guidance into The Picower Institute for Learning and Memory. Tonegawa resigned his directorship in 2006 and served as a Picower Professor of Neuroscience and Biology and a Howard Hughes Medical Institute Investigator.

He also served as Director of the RIKEN Brain Science Institute from 2009 to 2017.

Tonegawa's Nobel Prize work elucidated the genetic mechanism of the adaptive immune system, which had been the central question of immunology for over 100 years. Prior to Tonegawa's discovery, one early idea to explain the adaptive immune system suggested that each gene produces one protein; however, there are under 19,000 genes in the human body which nonetheless can produce millions of antibodies. In experiments beginning in 1976, Tonegawa showed that genetic material rearranges itself to form millions of antibodies. Comparing the DNA of B cells (a type of white blood cell) in embryonic and adult mice, he observed that genes in the mature B cells of the adult mice are moved around, recombined, and deleted to form the diversity of the variable region of antibodies. This process is known as V(D)J recombination.

In 1983, Tonegawa also discovered a transcriptional enhancer element associated with antibody gene complex, the first cellular enhancer element.

Shortly following his Nobel Prize, Tonegawa again changed fields from immunology to neuroscience, where he focused his research in the ensuing years.

Tonegawa's lab pioneered introductory transgenic and gene-knockout technologies in mammalian systems. He was involved in early work demonstrating the importance of CaMKII- (1992) and the NMDA receptor-dependent synaptic plasticity (1996) in memory formation.

His lab discovered that dendritic neuronal spines in the temporal cortex are a likely target for treatment of Fragile X Syndrome. With one dosage of the inhibitor drug FRAX586, Tonegawa showed a marked reduction of FXS symptoms in the mouse model.

Tonegawa was an early adopter of optogenetics and biotechnology in neuroscience research, leading to his groundbreaking work identifying and manipulating memory engram cells. In 2012, his lab demonstrated that the activation of a specific sub-population of mouse hippocampal neurons, labelled during a fear conditioning paradigm, is sufficient to evoke a behavioral response correlated with a precise memory trace. This demonstrated for the first time that memory information is stored in specific cellular ensembles in the hippocampus, now frequently called memory engram cells.

More recently, his lab continues to employ optogenetic technology and virus injection techniques to expand their findings on the engram cell ensemble. …

Tonegawa resided in the Boston area with his wife, Mayumi Yoshinari Tonegawa, who worked as an NHK (Japan Broadcasting Corporation) director/interviewer and is now a freelance science writer. The Tonegawas have three children, Hidde Tonegawa, Hanna Tonegawa, and Satto Tonegawa (deceased).

He was a fan of the Boston Red Sox, and threw out an opening pitch during their 2004 World Series championship season.

Tonegawa died at his home in San Mateo, California, on July 11, 2026, at the age of 86.