Regulatory ability and Foxp3 expression of CD4⁺CD25⁺ T cells generated in vitro by IFN-λ–treated DCs. (A) CD4⁺CD25⁺ T cells generated in vitro by IFN-λ–treated DCs were purified from MLR culture reaction and assayed for their suppressive activity on CD4⁺ T-cell proliferation in MLR cultures. CD4⁺ responding T cells were stimulated with LPS-treated DCs at a 1:10 DC/T ratio. Cellular [³H]-thymidine incorporation found for this control MLR is indicated by the dotted line. Various numbers of CD4⁺CD25⁺ T cells were directly added either to the MLR culture reaction (□) or to permeable filters to avoid cell–cell contact interactions (▨). Data are the mean ± SD of 2 independent experiments performed in 6 replicates with cells from different blood donors. (B) Quantification of Foxp3 mRNA expression by real-time PCR in CD4⁺ T cells purified from MLR cultures mixing the indicated DCs and CD4⁺ T cells. For comparison, Foxp3 levels were quantified in freshly purified CD25⁺ or CD25^–CD4⁺ T cells derived from a same donor. Results are expressed relative to GAPDH level. The experiment was performed twice on 2 blood donors with similar results.