In 1987, Susumu Tonegawa became the first Japanese recipient of the Nobel Prize for Physiology or Medicine for his study of the immune system and his subsequent discovery of the causes of antibody diversity--the ability of an antibody to resist infection from millions of different viruses and bacteria. Tonegawa provided direct evidence that a gene's ability to encode antibody proteins is produced from separate, chain-like segments of DNA (deoxyribonucleic acid) molecules which mutate to code for different antibodies. Since 1981, Tonegawa has worked at the Massachusetts Institute of Technology (MIT), and was honored as Howard Hughes Medical Institute Investigator in 1988.

Tonegawa was born in Nagoya, Japan, on September 5, 1939, the second of four children born to Tsutomu Tonegawa and the former Miyoko Masuko. Tonegawa's father was an engineer whose work required him to move frequently from town to town across the country. As a result, Tonegawa and his older brother were...