IN VIVO EFFECTS OF IMMUNOSUPPRESSIVE DRUGS ON DENDRITIC CELL KINETICS IN PERIPHERAL BLOOD OF PATIENTS UNDERGOING RENAL TRANSPLANTATION

Abstract

O213* Aims: The effects of immunosuppressive agents on T-cell function have been well characterized but virtually nothing is known about the in vivo effects of these drugs on human dendritic cells (DC). We therefore studied the DC number and composition in peripheral blood of renal allograft recipients before and after transplantation and in their donors before and after kidney donation. Methods: Using flowcytometry, we determined the number of myeloid (m) and plasmacytoid (p) DC in peripheral blood of 24 patients with end-stage renal disease (before, 7, 30 and 90 days after transplantation) and 23 living kidney donors (before, 3 and 90 days after donation). mDC were defined as T/B/NK-lymphocyte lineage-, CD34-, HLA-DR+, CD11c+ and CD123low and pDC as lineage-, CD34-, HLA-DR+, CD11c- and CD123high. Additionally, the maturation status of these DC subsets was determined based on the expression of CD83 and the chemokine receptor CCR7. All patients were treated with tacrolimus, mycophenolate mofetil and corticosteroids. Results: Transplantation resulted in a decrease of total DC numbers from 16.73±6.26 cells/uL at baseline to 6.30±5.12 cells/uL on day 7. The total DC count stabilized on day 30 at 5.73±4.04 cells/uL and increased to 11.05±5.46 cells/uL on day 90, which was still different from baseline (p<0.001, repeated measurements ANOVA). This pattern of initial decrease followed by a partial recovery, was observed in both DC subsets. However, the decrease in pDC was more pronounced, resulting in a relative increase of the mDC percentage from 73% at day 0 to 85% at week 1. The percentage mDC normalized at month 1 (74%) and was slighty skewed towards pDC at month 3 (69%)(p=0.025). After transplantation, expression levels of CD83 and CCR7 were comparable between time points and showed no evidence for DC activation. In kidney donors, DC counts also decreased significantly after surgery to 10.58±5.52 cells/uL on day 3. However, in contrast to renal transplant recipients, total DC numbers had completely recovered at month 3 (20.33±5.10 cells/uL) and no shift in the mDC to pDC ratio occurred. Again, surgery did not result in DC activation. The 7 patients treated for (presumed) acute rejection (AR)(6 with high-dose corticosteroids, 2 with rATG) had a lower total DC count at week 1 compared with non-rejectors (2.55±2.80 vs 7.94±5.09 cells/uL, p=0.016). This difference was caused by a significant difference in the mDC count: 2.15±2.41 vs 6.81±4.54 cells/uL (p=0.019) for patients treated and patients not treated for AR, respectively. pDC numbers at day 7 were comparable between patients who had received anti-AR therapy and those who did not: 0.40±0.47 vs 1.13±0.96 cells/uL. Conclusions: Surgical procedures in living kidney donors and their recipients result in a marked decrease of peripheral blood DC numbers. In donors this effect was transient, whereas in transplant recipients the DC recovery was far from complete. These findings, taken together with our observations in patients treated for AR, suggest an important additional effect of immunosuppression.