Susumu Tonegawa

Susumu Tonegawa (born 6 September 1939) is a Japanese scientist who won the Nobel Prize in Physiology or Medicine in 1987.
He discovered the genetic mechanism that produces antibody diversity. Although he won the Nobel Prize for his work in immunology, Tonegawa is a molecular biologist by training. In his later years, he has turned his attention to the molecular and cellular basis of memory.
Tonegawa is best known for elucidating the genetic mechanism in the adaptive immune system. If each antibody was coded by one gene, it would take millions of genes to protect against antigens.
Instead, as Tonegawa showed in a landmark series of experiments beginning in 1976, genetic material can rearrange itself to form the vast array of available antibodies. The main mechanism is called RNA splicing.
Antibodies have a 'variable region' in their structure. Tonegawa compared the DNA of B cells (a type of white blood cell) in embryonic and adult mice. He found that genes in the mature B cells of the adult mice are moved around, recombined, and deleted to make the many versions of the variable region of antibodies.
The critical work.
The critical work was started in Basle, Switzerland, and later at MIT. "Our work resolved the long held debate on the genetic origin of antibody diversity. It turned out that this diversity is generated by somatic recombination of the inherited gene segments and by somatic mutation".