Reminiscences of Sir Peter Medawar: in hope of antigen-specific transplantation tolerance.

Peter Medawar's career in medical research (he always described himself as a medical research scientist) began as a student of zoology in Oxford. He obtained a first class degree in 1936, aged 21, and undertook postgraduate studies with Florey. His work was anchored in a broad field; he was adept at addressing novel questions in the context of prior ideas and knowledge. His earlier interest in growth, driven as much by mathematics as biology, gave way to transplantation at the beginning of World War II, treatment of burns patients being the driver. He interpreted the results of grafting autologous and allogeneic human skin, observed clinically and microscopically, as immunological; he identified accelerated donor-specific reactions to subsequent grafts as 'second set', and described cell (lymphocyte) mediated infiltration of allo- but not auto-grafts following initial vascularization, both in the patient context and in experimental animals. He became intrigued by the consequences of hematopoietic chimerism, from which his landmark discoveries on the induction of transplantation tolerance derive. These results, his interpretation and dissemination of them, gave hope to transplant surgeons that donor-specific transplant tolerance would be achievable. Many immunosuppressive drugs later, we are now reapproaching this hope, from various angles.