BACKGROUND:Dendritic cells(DCs) can initiate the expansion of regulatory T cells(Tregs),which play an indispensable role in inducing transplantation tolerance.Some studies have investigated the effect of the immunosuppressant rapamycin(Rapa) on Tregs in vitro.However,the in vivo effect of Rapa combined with immature DCs(iDCs) on Tregs is unknown.This study was undertaken to determine whether allogenic iDCs combined with a short course of Rapa have the ability to selectively expand the CD4 + CD25 + Foxp3 + Tregs in a rat model.METHODS:Brown Norway rats were injected intravenously with 2×10 6 Lewis iDCs followed by 1 mg/kg per day Rapa intraperitoneally for 7 consecutive days.On day 8,the levels of CD4 + CD25 + Foxp3 + Treg cells in peripheral blood and spleen cells were analyzed by flow cytometry.IL-2,IL-4,TGF-β1,and IFN-γ levels in serum were assessed by ELISA.The experimental animals were divided into four groups:control,Rapa-treated,iDC-treated,and combination-treated.RESULTS:CD4 + CD25 + Foxp3 + Tregs comprised 7%-8% of CD4 + T cells in control rats.Rapa combined with iDCs enhanced this percentage in the peripheral blood and spleen.However,the levels of Tregs did not significantly change after treatment with Rapa or iDCs alone.The levels of CD4 + CD25 Foxp3 + T cells and CD4 + CD25 + Foxp3 T cells in CD4 + T cells did not significantly change in the combined group.The TGF-β1 level in serum from the combined group increased significantly compared with the other groups.CONCLUSIONS:A significantly higher percentage of CD4 + CD25 + Foxp3 + Tregs was found in rats treated with allogenic iDCs and a short course of Rapa,along with an increase in the TGF-β1 level in serum.This improved protocol may be a promising therapeutic strategy to increase Tregs,which are beneficial to the induction of peritransplant tolerance. BACKGROUND: Dendritic cells (DCs) can play an indispensable role in inducing transplantation tolerance. Studies have investigated the effect of the immunosuppressant rapamycin (Rapa) on Tregs in vitro. However, the in vivo effect of Rapa combined with immature DCs (iDCs) on Tregs is unknown. This study was undertaken to determine whether allogenic iDCs combined with a short course of Rapa have the ability to seeably expand the CD4 + CD25 + Foxp3 + Tregs in a rat model.METHODS: Brown Norway rats were injected intravenously with 2 × 10 6 Lewis iDCs followed by 1 mg / kg per day Rapa intraperitoneally for 7 consecutive days. On day 8, the levels of CD4 + CD25 + Foxp3 + Treg cells in peripheral blood and spleen cells were analyzed by flow cytometry. IL-2, IL-4, TGF-β1, and IFN-γ levels in serum were assessed by ELISA. The experimental animals were divided into four groups: control, Rapa-treated, iDC- treated, and combination-treated .RESULTS: CD4 + CD25 + Foxp3 + Tregs 7% -8% of CD4 + T cells in control rats. Rapa combined with iDCs enhanced this percentage in the peripheral blood and spleen. Despite the levels of Tregs did not significantly change after treatment with Rapa or iDCs alone.The levels of CD4 + CD25 Foxp3 + T cells and CD4 + CD25 + Foxp3 T cells in CD4 + T cells did not change significantly in the combined group. The TGF-β1 level in serum from the combined group increased significantly compared with the other groups. CONCLUSIONS: A significantly higher percentage of CD4 + CD25 + Foxp3 + Tregs was found in rats treated with allogenic iDCs and a short course of Rapa, along with an increase in the TGF-β1 level in serum. This improved protocol may be a promising therapeutic strategy to increase Tregs, which are beneficial to the induction of peritransplant tolerance.