MDSC convert Th17 T cells to regulatory T cells. (A) Experimental setup: Th17 cells were isolated after 21 days of in vitro culture in the presence of CD14⁺HLA-DR⁺ cells. Th17 cells were incubated with CD14⁺HLA-DR^−/low cells and analyzed at the indicated time points for the expression of IL-17 and Foxp3 by ICS. In control experiments, either Th17 cells were incubated with CD14⁺HLA-DR⁺ cells or IL-17⁻ CD4⁺ T cells were stimulated in the presence of CD14⁺HLA-DR^−/low cells. (B) Th17 T cells were incubated with CD14⁺HLA-DR^−/low cells for 12, 24, and 72 hours and then analyzed for the expression of Foxp3 and IL-17 by intracellular FACS staining. (C) Th17 T cells were incubated with CD14⁺HLA-DR^−/low cells. After 72 hours, CD14⁺HLA-DR^−/low cells were added to the cultures and the expression of Foxp3 and IL-17 was analyzed on gated CD4⁺ T cells at the indicated time points. (D) Cumulative results of FACS analysis shown in panels B and C: Th17 T cells were incubated with CD14⁺HLA-DR^−/low cells for the indicated time points and analyzed for the expression of Foxp3 and IL-17 by intracellular FACS staining. Data represent results from 4 independent experiments. Large-scale magnification is shown as supplemental Figure 2 (*P < .05). (E) IL-17⁻ CD4⁺ T cells were coincubated with CD14⁺HLA-DR^−/low cells and analyzed for the expression of Foxp3 and IL-17 after 24 and 72 hours (top row). Th17 T cells were incubated with CD14⁺HLA-DR⁺ cells and CD4⁺ T cells were analyzed for the expression of Foxp3 and IL-17 after 24 and 72 hours (middle row). Th17 cells were incubated in the absence of additional CD14⁺ cells (bottom row). Results shown are representative of at least 2 independent experiments. (F-G) Th17 cells were isolated as described and cultured with CD14⁺HLA-DR^−/low cells for 24 hours. Quantitative PCR was performed on different gates as shown in panel F. Relative mRNA expression levels for the indicated genes in cells isolated from 6 different gates (R1-R6) are shown. Shown are cumulative results of 2 independent experiments.