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It is emerging that CD4+Foxp3+ regulatory T (Treg) cells can produce the proinflammatory cytokine IFN-&ggr; when stimulated in a Thl cytokine environment. In this study, we report that Foxp3+ Treg cells readily produced IFN-&ggr; in vivo in a highly inflammatory model of graft-versus-host disease (GVHD) and during a Thl-dominated immune response to intracellular bacteria. Moreover, stimulation in vitro via TCR in the presence of IL-12 alone was sufficient to induce IFN-&ggr; production by Treg cells in a dose-dependent manner. Transfer of donor Treg cells can prevent lethal GVHD; therefore, we used this model as a robust readout for in vivo Treg function. Interestingly, >50% of allogeneic donor, but not residual recipient Foxp3+ Treg cells produced IFN-&ggr; after transplantation, suggesting that this cytokine production was alloantigen specific. These IFN-&ggr; producers were stable Foxp3+ Treg cells because methylation analysis of the Foxp3 gene locus of transferred and reisolated Treg cells during GVHD showed a fully demethylated Treg-specific-demethylated region. Next, we addressed whether IFN-&ggr; production was supporting or rather impairing the immunosuppressive function of Treg cells during GVHD. Blocking of IFN-&ggr; with specific mAb completely abolished the beneficial effect of donor Treg cells. We could further show that only wild-type Treg cells, but not Treg cells from IFN-&ggr;-deficient donor mice, prevented GVHD. This indicated that Treg cell-intrinsic IFN-&ggr; production was required for their protective function. In conclusion, our data show that IFN-&ggr; produced by Foxp3+ Treg cells has essential immune-regulatory functions that are required for prevention of expérimentai GVHD. [ABSTRACT FROM AUTHOR]

CMV reactivation is a major complication after allogeneic stem cell transplantation (SCT). Immune reconstitution of CMV-specific CTLs (CMV-CTLs) is essential for virus control. During CMV-CTL monitoring using mutated HLA/CMV tetramers selectively detecting high-avidity T cells, we observed coappearance of CMV-CTLs with low (CMV tetlow CTLs) and high tetramer binding (CMV tethigh CTLs) in 53/115 CMV IgG+ patients stem cell transplanted from CMV IgG+ donors. However, the relevance of these coappearing differentially tetramer binding ("dual") CMV-CTLs was unclear. In this study, we investigated the kinetics, properties, and clinical impact of coappearing CMV tetlow and tethigh CTLs after allogeneic SCT. Patients with dual CMV-CTLs had more CMV tethigh than tetlow CTLs. Chimerism analysis of isolated CMV tetlow and tethigh CTLs revealed their exclusive donor origin. CMV tetlow and tethigh CTLs had an identical effector memory CD45RA-CCR7- and CD45RA+CCR7- T cell distribution, equal differentiation, senescence, and exhaustion marker expression and were negative for regulatory CD8+ T cell markers. Isolated CMV tetlow and tethigh CTLs were equally sensitive to CMV peptides in IFN-γ release and cytotoxicity assays. However, CMV tethigh CTLs proliferated more in response to low CMV peptide concentrations than tetlow CTLs. TCR repertoire analysis revealed that CMV tetlow and tethigh CTLs use different TCRs. Finally, dual CMV-CTLs were not associated with CMV antigenemia. In conclusion, these data show for the first time, to our knowledge, that both CMV tetlow and tethigh CTLs are functional effector T cells differing by proliferation, numbers in peripheral blood, and probably by their precursors without increasing the CMV reactivation risk after allogeneic SCT. [ABSTRACT FROM AUTHOR]

Because miR-181a has been described to alter T cell activation, we hypothesized that manipulation of miR-181a expression in donor T cells may alter acute graft-versus-host disease (aGvHD) after allogeneic bone marrow transplantation (BMT). We therefore analyzed the impact of enhanced and reduced miR-181a expression in donor T cells on aGvHD induction by lentiviral gene transfer into primary T cells and using miR-181a/b-1-/- T cells, respectively. BMT-recipient mice receiving donor T cells with enhanced miR-181a expression showed no signs of aGvHD and survived for the time of follow-up, whereas T cells lacking miR-181a/b-1 accelerated aGvHD. In line with these data, analysis of donor T cells in blood, secondary lymphoid organs, and target organs of aGvHD after BMT showed significantly reduced numbers of miR-181a-transduced T cells, as compared with controls. In addition, expansion of activated T cells with enhanced miR-181a expression was reduced in vitro and in vivo. We further show that anti-apoptotic BCL-2 protein expression is reduced in murine and human T cells upon overexpression of miR-181a, suggesting that regulation of BCL-2-expression by miR-181a may contribute to altered alloreactivity of T cells in aGvHD. These data indicate that proteins regulated by miR-181a may be therapeutic targets for aGvHD prevention. [ABSTRACT FROM AUTHOR]