Background. In a prospective study, calcineurin inhibitors (CNI) were withdrawn in patients two years after kidney transplantation. We questioned whether stopping CNI had an effect on the donor-specific reactivity, as CNI might hinder immune responses leading to graft acceptance. Methods. We measured the donor-specific cytotoxic T lymphocyte (CTL) precursor frequency (CTLpf) in 54 patients before and after withdrawal of CNI. In addition, the T-cell reactivity of PBMC to donor and third-party antigens was tested in MLR, and in IFNγ-Elispot. Reactivity to tetanus toxoid (TET) was studied as well. Results. Donor-specific CTLpf significantly decreased after CNI withdrawal (P=0.0001).In contrast, no difference was observed in third-party reactive CTLpf, donor and third-party reactive MLR and IFNγ-Elispot. Proliferative responses and the number of IFNγ-producing cells to TET also decreased after CNI withdrawal. The decrease in CTLpf correlated with the time between the two blood samples (before and after stopping CNI, P=0.05). This decrease was caused by stopping CNI, because there was no correlation between CTLpf and the duration of the CNI treatment after transplantation. Moreover, the percentage of regulatory T cells in the peripheral blood increased after CNI withdrawal. Conclusions. We report here that after withdrawal of CNI the donor-specific CTLpf decreases. We hypothesize that CNI suppress regulatory mechanisms that have the potential to down-regulate donor-specific CTL responses and reactivity to TET. Copyright

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Department of Immunology