Sir Peter Brian Medawar shared the 1960 Nobel Prize in physiology or medicine with Australian, Sir Frank MacFarlane Burnet for discovering that tissue transplantation failed because of immune system rejection and not because of genetic differences, as previously believed. During five years of experiments, Medawar learned that "immunological tolerance" could be produced by grafting cells from one animal into the fetus of another, permitting successful tissue grafts between the two subjects. As the first clear evidence that tissue rejection could be overcome, this discovery opened the door to transplant surgery and the development of complex immunosuppressant drugs which help prevent rejection of transplanted organs.

Medawar, called "a great scientist, a man of great courage, and a great writer," was born in Rio de Janeiro, Brazil. His father, who was born in Lebanon, became a naturalized British subject while living in London, England as a paying guest in the home...