Decline of miR-124 in myeloid cells promotes regulatory T-cell development in hepatitis C virus infection.

Myeloid-derived suppressor cells (MDSCs) and microRNAs (miRNAs) contribute to attenuating immune responses during chronic viral infection; however, the precise mechanisms underlying their suppressive activities remain incompletely understood. We have recently shown marked expansion of MDSCs that promote regulatory T (Treg) cell development in patients with chronic hepatitis C virus (HCV) infection. Here we further investigated whether the HCV-induced expansion of MDSCs and Treg cells is regulated by an miRNA-mediated mechanism. The RNA array analysis revealed that six miRNAs were up-regulated and six miRNAs were down-regulated significantly in myeloid cells during HCV infection. Real-time RT-PCR confirmed the down-regulation of miR-124 in MDSCs from HCV patients. Bioinformatic analysis suggested that miR-124 may be involved in the regulation of signal transducer and activator of transcription 3 (STAT-3), which was overexpressed in MDSCs from HCV patients. Notably, silencing of STAT-3 significantly increased the miR-124 expression, whereas reconstituting miR-124 decreased the levels of STAT-3, as well as interleukin-10 and transforming growth factor-ß, which were overexpressed in MDCSs, and reduced the frequencies of Foxp3+ Treg cells that were developed during chronic HCV infection. These results suggest that reciprocal regulation of miR-124 and STAT-3 in MDSCs promotes Treg cell development, thus uncovering a novel mechanism for the expansion of MDSC and Treg cells during HCV infection.

Hepatitis C virus-induced myeloid-derived suppressor cells regulate T-cell differentiation and function via the signal transducer and activator of transcription 3 pathway.

T cells play a pivotal role in controlling viral infection; however, the precise mechanisms responsible for regulating T-cell differentiation and function during infections are incompletely understood. In this study, we demonstrated an expansion of myeloid-derived suppressor cells (MDSCs), in particular the monocytic MDSCs (M-MDSCs; CD14(+) CD33(+) CD11b(+) HLA-DR(-/low) ), in patients with chronic hepatitis C virus (HCV) infection. Notably, HCV-induced M-MDSCs express high levels of phosphorylated signal transducer and activator of transcription 3 (pSTAT3) and interleukin-10 (IL-10) compared with healthy subjects. Blocking STAT3 signalling reduced HCV-mediated M-MDSC expansion and decreased IL-10 expression. Importantly, we observed a significant increase in the numbers of CD4(+) CD25(+) Foxp3(+) regulatory T (Treg) cells following incubation of healthy peripheral blood mononuclear cells (PBMCs) with MDSCs derived from HCV-infected patients or treated with HCV core protein. In addition, depletion of MDSCs from PBMCs led to a significant reduction of Foxp3(+) Treg cells developed during chronic HCV infection. Moreover, depletion of MDSCs from PBMCs significantly increased interferon-γ production by CD4(+) T effector (Teff) cells derived from HCV patients. These results suggest that HCV-induced MDSCs promote Treg cell development and inhibit Teff cell function, suggesting a novel mechanism for T-cell regulation and a new strategy for immunotherapy against human viral diseases.

Expansion of myeloid-derived suppressor cells promotes differentiation of regulatory T cells in HIV-1+ individuals.

OBJECTIVE: Regulatory T cells (Tregs) contribute to HIV-1 disease progression by impairing antiviral immunity; however, the precise mechanisms responsible for the development of Tregs in the setting of HIV-1 infection are incompletely understood. DESIGN: In this study, we provide evidence that HIV-induced expansion of monocytic myeloid-derived suppressor cells (M-MDSCs) promote the differentiation of Foxp3 Tregs. METHODS: We measured MDSC induction and cytokine expression by flow cytometry and analyzed their functions by coculturing experiments. RESULTS: We observed a dramatic increase in M-MDSC frequencies in the peripheral blood of HIV-1 seropositive (HIV-1) individuals, even in those on antiretroviral therapy with undetectable viremia, when compared with healthy participants. We also observed increases in M-MDSCs after incubating healthy peripheral mononuclear cells (PBMCs) with HIV-1 proteins (gp120 or Tat) or Toll-like receptor 4 ligand lipopolysaccharides in vitro, an effect that could be abrogated in the presence of the phosphorylated signal transducer and activator of transcription 3 inhibitor, STA-21. Functional analyses indicated that M-MDSCs from HIV-1 individuals express higher levels of IL-10, tumor growth factor-ß, IL-4 receptor α, p47, programmed death-ligand 1, and phosphorylated signal transducer and activator of transcription 3 - all of which are known mediators of myelopoiesis and immunosuppression. Importantly, incubation of healthy CD4 T cells with MDSCs derived from HIV-1 individuals significantly increased differentiation of Foxp3 Tregs. In addition, depletion of MDSCs from PBMCs of HIV-1 individuals led to a significant reduction of Foxp3 Tregs and increase of IFNγ production by CD4 T effector cells. CONCLUSIONS: These results suggest that HIV-induced MDSCs promote Treg cell development and inhibit T cell function - a hallmark of many chronic infectious diseases.

Protection of CD4+ T cells from hepatitis C virus infection-associated senescence via ΔNp63-miR-181a-Sirt1 pathway.

T cell dysfunction has a crucial role in establishing and maintaining viral persistence. We have previously shown a decline in miR-181a, which regulates CD4+ T cell responses via DUSP6 overexpression, in individuals with hepatitis C virus (HCV) infection. Here, we describe accelerated T cell senescence in HCV-infected individuals compared with age- and sex-matched healthy subjects. Mechanistic studies revealed that up-regulation of transcription factor ΔNp63 led to the decline of miR-181a expression, resulting in an overexpression of the antiaging protein Sirt1, in CD4+ T cells from HCV-infected individuals. Either reconstituting miR-181a or silencing ΔNp63 or Sirt1 expression in CD4+ T cells led to accelerated T cell senescence, as evidenced by an increased senescence-associated ß-galactosidase (SA-ß-gal) expression, shortened telomere length, and decreased EdU incorporation; this suggests that HCV-induced T cell senescence is counterregulated by the ΔNp63-miR-181a-Sirt1 pathway. An increase of IL-2 production was observed in these senescent CD4+ T cells and was driven by a markedly reduced frequency of Foxp3+ regulatory T (Treg) cells and increased number of Foxp3- effector T (Teff) cells upon manipulating the ΔNp63-miR-181a-Sirt1 pathway. In conclusion, these findings provide novel mechanistic insights into how HCV uses cellular senescent pathways to regulate T cell functions, revealing new targets for rejuvenating impaired T cell responses during chronic viral infection.