These observations could be interpreted as evidence that Foxp3+ Treg cells are dispensable for the autoimmune cell protection in the NOD model, but the interpretation of data in the constitutive absence of Treg cells is usually hampered by potentially confounding effects of immune adaptations and severe systemic autoimmunity, including premature death and alterations in thymic T cell development (12). the CD4+ TCR repertoire to a single diabetogenic specificity. Here we revisited the effect of acute Foxp3+ Treg cell ablation on cell autoimmunity in NOD mice in the context of a polyclonal TCR repertoire. For this, we took advantage of the well-established DTR/GFP transgene of DEREG mice, which allows for specific ablation of Foxp3+ Treg cells without promoting catastrophic autoimmune diseases. We show that this transient loss Mouse monoclonal to VAV1 of Foxp3+ Treg cells in prediabetic NOD.DEREG mice is sufficient to precipitate severe insulitis and persistent hyperglycemia within 5 days after DT administration. Importantly, DT-treated NOD.DEREG mice preserved many clinical features of spontaneous diabetes progression in the NOD model, including a prominent role of diabetogenic CD8+ T cells in terminal cell destruction. Despite the severity of destructive cell autoimmunity, anti-CD3 mAb therapy of DT-treated mice interfered with the progression to overt diabetes, indicating that the novel NOD.DEREG model can be exploited for preclinical studies on T1D under experimental conditions of synchronized, advanced cell autoimmunity. Overall, our studies highlight the continuous requirement of Foxp3+ Treg cell activity for the control of genetically pre-installed autoimmune diabetes. gene mutations (4, 5), demonstrating that a severe Treg cell defect is sufficient to promote destructive cell autoimmunity independently of other genetic and environmental factors. However, loss-of-function studies in non-autoimmune and diabetes-prone mice have not been able to demonstrate an unequivocal link between Foxp3+ Treg cell deficiency and catastrophic cell autoimmunity. In mice on a non-autoimmune genetic background, constitutive genetic deficiency (6, 7) or acute DR 2313 Foxp3+ Treg cell ablation based on Foxp3-driven expression of a human diphtheria toxin receptor (DTR) (8C10) recapitulates many clinical features of the human IPEX syndrome, but the manifestation of cell autoimmunity has not been reported. Moreover, Foxp3-deficient mice around the diabetes-prone NOD background (NOD.Foxp3mice is usually artificially restricted to a single highly diabetogenic specificity by transgenic expression of the BDC2.5 TCR (11). These observations could be interpreted as evidence that Foxp3+ Treg cells are dispensable for the autoimmune cell protection in the NOD model, but the interpretation of data in the constitutive absence of Treg cells is usually hampered by potentially confounding effects of immune adaptations and severe systemic autoimmunity, including premature DR 2313 death and alterations in thymic T cell development (12). The administration of mAbs directed against CD25 as surrogate Treg cell marker largely preserves systemic immune homeostasis and has been employed to examine the role of Foxp3+ Treg cells in the control of cell autoimmunity. However, CD25 is not uniquely expressed on Foxp3+ Treg cells, and anti-CD25 mAb treatment has been proposed to act on Treg cells by functional inactivation, rather than physical depletion (13C15), while sparing Foxp3+ Treg cells with a CD25C phenotype. These limitations in specificity and efficiency of CD25-targeted interference with Foxp3+ Treg cell activity may account for the largely contradictory range of data in the NOD model, including precipitation of overt diabetes (16C19), accelerated diabetes progression in young but not adult mice (20), as well as maintenance of cell tolerance (21C23), or even delayed onset of diabetes (22). Foxp3-driven DTR expression has been successfully employed for the specific and temporally controlled ablation of Foxp3+ Treg cells (8C10, 24), while the outcome can considerably differ between impartial Foxp3DTR mouse lines, depending on the transgenic strategy of Foxp3-driven DTR/GFP expression. In knock-in mice expressing a DTR/GFP fusion protein from an IRES down-stream of the endogenous gene (Foxp3IRES-DTR/GFP) on a non-autoimmune genetic background, DT-mediated Treg cell-ablation in young and adult Foxp3IRES-DTR/GFP mice resulted in an autoimmune disease comparable to that observed DR 2313 in Foxp3-deficient mice (8). In the DEREG (depletion of regulatory T cell) model, in which DTR/GFP is usually expressed from a transgenic Foxp3 bacterial artificial chromosome (Foxp3BAC-DTR/GFP), administration of DT into newborns resulted in gene, allowing for the accumulation of DT-resistant Foxp3+GFPC Treg cells (25C28). These unique features prompted us to hypothesize that this DEREG model is particularly suited to study the role of Foxp3+ Treg cells in organ-specific autoimmunity in mice on a genetically susceptible genetic background, while keeping collateral autoimmune damage to a minimum. In previous studies employing a NOD model, in which the spontaneous diabetes development was constrained by transgenic BDC2.5 TCR expression on all CD4+ T cells (29), acute Foxp3+ Treg cell ablation was shown to unleash a highly aggressive form of autoimmune diabetes (30), which fully abrogated the sex bias usually observed.