Background: A growing amount of data shows that CD4+CD25+ regulatory T
cells (Tregs) can induce transplantation tolerance by suppressing immune responses to allograft antigens. However, both the generation and the suppressive capacity of CD4+CD25+ Tregs can be substantially affected by different immunosuppressive drugs used in clinical transplantation. The goal of this study was to compare the effects of cyclosporine A and rapamycin on the induction and suppressive function of human CD4+CD25+Tregs in vitro.
Material/Methods: CD4+CD25+Tregs were induced in MLR in the presence of rapamycin (Treg-Rapa) or cyclosporine A (Treg-CsA). Tregs were identified by flow cytometry using anti-CD4, anti-CD25, anti-CTLA-4, anti-CD122, anti-GITR, anti-FOXP3 mAbs. Suppressive capacity of induced Tregs was evaluated by their capability to inhibit anti-CD3 Ab-triggered proliferation of PBMCs, as measured by flow cytometry. The concentration of TGF-a1 in culture supernatants was measured by ELISA.
Results: Although both rapamycin and cyclosporine A suppressed the induction of CD4+CD25+Tregs during MLRs, this effect was significantly more pronounced in cells cultured with cyclosporine. On the other hand, only rapamycin significantly decreased the percentage of CD4+CD25+Tregs which expressed GITR, a negative regulator of Treg's suppressive capacity. Importantly, Treg-Rapa, unlike Treg-CsA, displayed significant supressive activity and were capable of inhibiting the proliferation of CD4+ T cells. This activity was likely mediated by TGF-α[sub]1[/sub].
Conclusions: Rapamycin, unlike cyclosporine A, doesn't inhibit the generation of functional CD4+CD25+Tregs. This implies that rapamycin could contribute to the development of transplantation tolerance by promoting the induction of functional CD4+CD25+Tregs. Moreover, our results suggest beneficial effects of combining rapamycin with Tregs.

Keywords: Immunosuppression