Calcineurin inhibitors affect circulating regulatory T cells in stable renal transplant recipients

Introduction. Immunosuppression, although crucial for short-term management, has been described in renal transplantation to be a major hurdle for long-term graft survival. Efforts have been directed at achieving a true state of allotolerance, thereby reducing the load of immunosuppression. Recently, increased frequencies of CD4(+)CD25(high) high regulatory T cells (Tregs) have been described as an additional mechanism to induce alloimmune tolerance. Materials and methods. We assessed 64 renal transplant recipients with stable renal function for at least I year, divided into two groups: one composed of patients receiving rapamycin but not calcineurin inhibitors (CNIs), and another, of those receiving CNIs but not rapamycin. Results. We demonstrated that T cells with a regulatory phenotype were decreased in peripheral blood of renal transplant recipients under CNI therapy compared to those who were CNI-free. The Tregs in our patients showed a modest association with renal function as measured by the delta serum creatinine, which was not significant. Conclusions. CNIs, but not rapamycin, reduce the frequencies of circulating Tregs in renal transplant recipients. The use of rapamycin might be further exploited in strategies reducing immunosuppression in renal transplantation. Furthermore, quantification of blood Tregs may be a suitable tool to identify those recipients who are candidates for reducing immunosuppression.