Clinical operational tolerance after kidney transplantation: a short literature review.

The clinical era of solid organ transplantation started with a renal transplantation (RT) performed between identical twins in Boston in 1954. The patient did not receive any immunosuppression, thus representing the very first case of operational tolerance (Tol). However, more than half a century later, we must admit the inadequacy of our knowledge regarding such a fundamental aspect of transplant immunology, as demonstrated by the fact that Tol has never been achieved in an intention-to-treat protocol. Herein we aim to shortly review the worldwide experience on clinical operational Tol after RT. Thus far, reports on successful cases of Tol after RT have been anecdotal: the largest series included no more than 10 individuals. We will understand that Tol can develop even in the presence of either HLA mismatches or blood group incompatibility at baseline, in the presence of anti-HLA antibodies during follow-up, as well as in patients having experienced acute rejection. Despite the lack of robust evidence, the fact that Tol is often accidentally discovered by transplant physicians during follow-up in noncompliant patients justifies the hypothesis that the real number of Tol cases might be much higher than currently reported.