ABSTRACT
It has now been more than 50 years since the first successful kidney transplant was performed between monozygotic twins [1]. At that time, the field of immunology was in its infancy and transplants between nonidentical twins ended in organ failure as a result of acute graft rejection. It was not until the introduction of azathioprine (a nucleotide analog less toxic than 6-mercaptopurine) in the early 1960s that chemical immunosuppression and prolonged kidney allograft survival became possible [2]. Azathioprine by itself was not potent enough to prevent acute graft rejection. However, the combination of azathioprine and corticosteroids was shown to provide effective chemical immunosuppression, with 1-year kidney allograft survival rates ranging from 40 to 50% [3]. This combination of chemical immunosuppression continued to be the cornerstone of transplant programs for the next 20 or so years until cyclosporine A (CsA) entered the transplantation arena in the late 1970s [4].
