The impact of induction therapy on the homeostasis and function of regulatory T cells in kidney transplant patients.

To evaluate the influence of induction therapy on Tregs we investigated their origin, kinetics and function in kidney transplant patients after treatment with T-cell depleting rabbit antithymocyte globulin (rATG) or IL-2 receptor antagonist basiliximab. Flow cytometry was used to study thymopoiesis by CD31+ naïve Tregs, homeostatic proliferation by Ki-67+ Tregs and Treg origin by the expression of Helios (nTreg-marker). FACSsorted Tregs were analysed for the demethylation status of the Treg-specific demethylated region (TSDR) of the FoxP3 gene, and Treg-suppressive function. Differential effects of rATG and basiliximab induction therapies were measured on the repopulation kinetics of Tregs. While decreased absolute numbers of Tregs were found in both study arms, increased percentages of Tregs were found in rATG treated patients and decreased percentages in basiliximab treated patients. In both groups, Treg repopulation was the result of homeostatic proliferation and not of thymopoiesis. At 1 month after rATG and 6 months after basiliximab therapy, high percentages of Ki-67+ Treg were measured, which in the rATG group, was accompanied by low percentages of Ki-67+Helios+ Treg, and by cells with a demethylated TSDR in the FoxP3 gene. After both rATG and basiliximab therapy, repopulated Tregs inhibited proliferation of allo-antigen activated T effector cells (Teff). In kidney transplant patients, repopulation of Treg after rATG and basiliximab therapy is the result of homeostatic proliferation and not of thymopoiesis. These repopulated Treg were functional after both induction strategies; however only after rATG therapy, were increased proportions of Helios(-) methylated FoxP3 Treg found.