Tapering immunosuppression in recipients of living donor kidney transplants

We have previously suggested that the in vitro donorspecific cytotoxic T-lymphocyte precursor (CTLp) assay can guide us to identify patients in which the immunosuppressive load can be tapered. In a clinical trial we had observed that a low (<10/10 6 PBMC) frequency of these CTLp was predictive for an uneventful rejection-free clinical course in patients that were converted from calcineurin inhibitors to mycophenolate mofetil or azathiopine. In the present prospective study in 81 stable kidney transplant recipients, already converted from calcineurin inhibitors, we measured CTLp frequencies and reduced the immunosuppressive load on a routine basis when CTLp were <10/10 6 PBMC. Donor-specific cytotoxicity could not be measured in 50/81 patients, while their reactivity against third-party lymphocytes was not impaired. These 50 patients were tapered in their immunosuppression. Only in one patient, who had stopped all his medication, was a rejection episode diagnosed. We conclude that in patients with a low donor-specific CTLp frequency it is safe to reduce the immunosuppression.