Background: Recently, we described a significant decrease in donor-specific cytotoxic T-lymphocyte precursor frequency (CTLpf) after discontinuation of calcineurin inhibitors (CNI), while the proliferative capacity in mixed lymphocyte culture (MLC), and the number of interferon-γ (IFN-γ) producing cells (pc) in Elispot remained unchanged. Methods: We tested T-cell reactivity in CNI free patients with stable renal graft function, on mycophenolate mofetil (MMF) or azathioprine (AZA) plus prednisone, who were tapered to 50% of their MMF or AZA dose. Results: Furthermore, tapering of the MMF or AZA dose resulted in a decrease of donor-reactive CTLpf in all patients with detectable CTLpf. Detectable numbers decreased from a median of 32 to 8 CTLp/106 peripheral blood mononuclear cell (PBMC). No effect on third-party reactive CTLpf was found, while the T-cell reactivity to donor and third-party cells as tested in MLC and in IFN-γ Elispot was not affected either by tapering of immunosuppression. Third-party reactivity was significantly higher than donor-specific reactivity in all tests. A control group showed no changes in any of the in vitro assays. Conclusion: Both withdrawal of CNI and tapering of MMF or AZA dose decreases the donor-specific CTLpf. Our data suggest that reduction of immunosuppression results in a specific decrease of donor-directed cytotoxic capacity of immunocompetent cells, while their proliferation and cytokine production capacity remained unchanged. Immunosuppression hinders development of cytotoxic non-responsiveness.

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Keywords Immune monitoring, T cells, Tapering immunosuppression, Tolerance, article, azathioprine, calcineurin inhibitor, clinical article, controlled study, cytokine, cytokine production, cytotoxic T lymphocyte, cytotoxicity, drug dose reduction, enzyme linked immunospot assay, gamma interferon, human, human cell, immune response, immunoreactivity, immunosuppressive treatment, in vitro study, kidney graft rejection, lymphocyte proliferation, mixed lymphocyte culture, mycophenolic acid 2 morpholinoethyl ester, peripheral blood mononuclear cell, prednisone, priority journal, treatment withdrawal
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Journal Clinical Transplantation
van Besouw, N.M, van de Wetering, J, van der Mast, B.J, de Kuiper, R, Baan, C.C, & Weimar, W. (2008). After discontinuation of calcineurin inhibitors, tapering of mycophenolate mofetil further impairs donor-directed cytotoxicity. Clinical Transplantation, 22(2), 129–135. doi:10.1111/j.1399-0012.2007.00754.x