Everolimus-treated renal transplant recipients have a more robust CMV-specific CD8+ T-cell response compared with cyclosporine- or mycophenolate-treated patients.

Background. In renal transplant recipients, mammalian target of rapamycin (mTOR) inhibitors have been reported to protect against cytomegalovirus (CMV) disease. Here, we questioned whether mTOR inhibitors specifically influence human CMV-induced T-cell responses. Methods. We studied renal transplant recipients treated with prednisolone, cyclosporine A (CsA), and mycophenolate sodium (MPS) for the first 6 months after transplantation followed by double therapy consisting of prednisolone/everolimus, which is an mTOR inhibitor (P/EVL; n=10), prednisolone/CsA (P/CsA; n=7), or prednisolone/MPS (P/MPS; n=9). All patients were CMV-IgG positive before transplantation. CMV reactivation was detectable in the first 6 months after transplantation and not thereafter. None of the patients included in this study suffered from CMV disease. Both CD27(-)CD8(+) and CD27(-)CD28(-)CD4(+) effector-type T-cell counts, known to be associated with CMV infection, were measured before transplantation and at 6 and 24 months after transplantation. Additionally, we determined both number and function of CMV-specific CD8(+) T cells at these time points. Results. The number of total CD8(+) T cells, CD27(-)CD8(+) T cells, and CD28(-)CD4(+) T cells increased significantly after switch to therapy with P/EVL but not after switch to P/CsA or P/MPS. Specifically, CMV-specific CD8(+) T-cell counts significantly increased after switch to therapy with P/EVL. Furthermore, the mTOR inhibitor sirolimus strongly inhibited alloresponses in vitro, whereas it did not affect CMV-specific responses. Conclusion. We observed a significant increase in (CMV-specific) effector-type CD8(+) and CD4(+) T-cell counts in everolimus-treated patients. These findings may at least in part explain the reported low incidence of CMV-related pathology in everolimus-treated patients.