Peter Medawar
Peter Medawar was British although he was born in Brazil in `915. His early studies on skin grafting led to elucidation of the genetic basis of the rejection process. for example, he had distinguished between rejection of the different forms of grafts such as grafts between monozygotic and dizygotic twins. Medawar as aware of Burnet's concepts of tolerance and devised experiments to test them. He received the Nobel Prize in 1960 for his experiments that showed that mouse embryos inoculated with foreign tissues became tolerant to them. This was the first experimental demonstration of tolerance. He died in 1987