Functional crosstalk between dendritic cells and Foxp3+ regulatory T cells in the maintenance of immune tolerance

Peripheral immune tolerance requires a controlled balance between the maintenance of self-tolerance and the capacity to engage protective immune responses against pathogens. Dendritic cells (DCs) serve as sentinels of the immune system by sensing environmental and inflammatory signals, and play an essential role in the maintenance of immune tolerance. To achieve this, DC play a key role in dictating the outcome of immune responses by influencing the balance between inflammatory or Foxp3+ regulatory T (Treg) cell responses. At the heart of this immunological balance is a finely regulated DC and Treg cell crosstalk whereby Treg cells modulate DC phenotype and function, and DC drive the differentiation of Foxp3+ Treg cells in order to control immune responses. This review will focus on recent advances, which highlight the importance of this bidirectional DC and Treg cell crosstalk during the induction of tolerance and organ-specific autoimmunity. More specifically, we will discuss how Treg cells modulate DC function for the suppression of inflammatory responses and how DC subsets employ diverse mechanisms to drive differentiation of Treg cells. Finally, we will discuss the therapeutic potential of tolerogenic DCs for the induction of tolerance in autoimmune diseases

IL-2 as a therapeutic target for the restoration of Foxp3+ regulatory T cell function in organ-specific autoimmunity: implications in pathophysiology and translation to human disease

Peripheral immune tolerance requires a finely controlled balance between tolerance to self-antigens and protective immunity against enteric and invading pathogens. Self-reactive T cells sometimes escape thymic clonal deletion, and can subsequently provoke autoimmune diseases such as type 1 diabetes (T1D) unless they are controlled by a network of tolerance mechanisms in the periphery, including CD4+ regulatory T cells (Treg) cells. CD4+ Treg cells are characterized by the constitutive expression of the IL-2Rα chain (CD25) and preferentially express the forkhead winged helix transcriptional regulator Foxp3. These cells have been shown to possess immunosuppressive properties towards various immune cell subsets and their defects are thought to contribute to many autoimmune disorders. Strong evidence shows that IL-2 is one of the important stimulatory signals for the development, function and fitness of Treg cells. The non-obese diabetic (NOD) mouse model, a prototypic model of spontaneous autoimmunity, mimics many features of human T1 D. Using this model, the contribution of the IL-2-IL-2R pathway to the development of T1 D and other autoimmune disorders has been extensively studied. In the past years, strong genetic and molecular evidence has indicated an essential role for the IL-2/IL-2R pathway in autoimmune disorders. Thus, the major role of IL-2 is to maintain immune tolerance by promoting Treg cell development, functional fitness and stability. Here we first summarize the genetic and experimental evidence demonstrating a role for IL-2 in autoimmunity, mainly through the study of the NOD mouse model, and analyze the cellular and molecular mechanisms of its action on Treg cells. We then move on to describe how this data can be translated to applications for human autoimmune diseases by using IL-2 as a therapeutic agent to restore Treg cell fitness, numbers and functions

TAF6δ orchestrates an apoptotic transcriptome profile and interacts functionally with p53

<p>Abstract</p> <p>Background</p> <p>TFIID is a multiprotein complex that plays a pivotal role in the regulation of RNA polymerase II (Pol II) transcription owing to its core promoter recognition and co-activator functions. TAF6 is a core TFIID subunit whose splice variants include the major TAF6α isoform that is ubiquitously expressed, and the inducible TAF6δ. In contrast to TAF6α, TAF6δ is a pro-apoptotic isoform with a 10 amino acid deletion in its histone fold domain that abolishes its interaction with TAF9. TAF6δ expression can dictate life versus death decisions of human cells.</p> <p>Results</p> <p>Here we define the impact of endogenous TAF6δ expression on the global transcriptome landscape. TAF6δ was found to orchestrate a transcription profile that included statistically significant enrichment of genes of apoptotic function. Interestingly, gene expression patterns controlled by TAF6δ share similarities with, but are not equivalent to, those reported to change following TAF9 and/or TAF9b depletion. Finally, because TAF6δ regulates certain p53 target genes, we tested and demonstrated a physical and functional interaction between TAF6δ and p53.</p> <p>Conclusion</p> <p>Together our data define a TAF6δ-driven apoptotic gene expression program and show crosstalk between the p53 and TAF6δ pathways.</p

Mesenchymal Stromal Cells Improve Salivary Function and Reduce Lymphocytic Infiltrates in Mice with Sjögren's-Like Disease

Non-obese diabetic (NOD) mice develop Sjögren's-like disease (SS-like) with loss of saliva flow and increased lymphocytic infiltrates in salivary glands (SGs). There are recent reports using multipotent mesenchymal stromal cells (MSCs) as a therapeutic strategy for autoimmune diseases due to their anti-inflammatory and immunomodulatory capabilities. This paper proposed a combined immuno- and cell-based therapy consisting of: A) an injection of complete Freund's adjuvant (CFA) to eradicate autoreactive T lymphocytes, and B) transplantations of MSCs to reselect lymphocytes. The objective of this was to test the effectiveness of CD45(-)/TER119(-) cells (MSCs) in re-establishing salivary function and in reducing the number of lymphocytic infiltrates (foci) in SGs. The second objective was to study if the mechanisms underlying a decrease in inflammation (focus score) was due to CFA, MSCs, or CFA+MSCs combined.Donor MSCs were isolated from bones of male transgenic eGFP mice. Eight week-old female NOD mice received one of the following treatments: insulin, CFA, MSC, or CFA+MSC (combined therapy). Mice were followed for 14 weeks post-therapy. CD45(-)/TER119(-) cells demonstrated characteristics of MSCs as they were positive for Sca-1, CD106, CD105, CD73, CD29, CD44, negative for CD45, TER119, CD11b, had high number of CFU-F, and differentiated into osteocytes, chondrocytes and adipocytes. Both MSC and MSC+CFA groups prevented loss of saliva flow and reduced lymphocytic infiltrations in SGs. Moreover, the influx of T and B cells decreased in all foci in MSC and MSC+CFA groups, while the frequency of Foxp3(+) (T(reg)) cell was increased. MSC-therapy alone reduced inflammation (TNF-α, TGF-β), but the combination of MSC+CFA reduced inflammation and increased the regenerative potential of SGs (FGF-2, EGF).The combined use of MSC+CFA was effective in both preventing saliva secretion loss and reducing lymphocytic influx in salivary glands

ICOS dependent homeostasis and functions of Foxp3+ regulatory T cells in the pancreatic islets of non-obese diabetic mice

Type 1 Diabetes (T1D) development in non-obese diabetic (NOD) mice is accompanied by an age-associated waning of CD4+Foxp3+ regulatory T (Treg) cell function. Previous results from our laboratory have shown that T1D progression is associated with a temporal loss in the capacity of CD4+Foxp3+ Treg cells to expand and survive in the β-islets. This in turn perturbs the Treg and effector T (Teff) cell balance and results in anti-islet immune responses. It has also been shown that ICOS blockade in neonatal NOD.BDC2.5 transgenic mice, whose T cells recognize a β-islet-specific auto-antigen, disrupts the Teff/Treg cell balance, and exacerbates T1D. This suggests that ICOS may be important in controlling Treg cell function. We hypothesized that ICOS expression by Foxp3+ Treg cells and ICOS-mediated signals, are critical for the stabilization of Treg cell function in the pre-diabetic islets of NOD mice. First, we show that ICOS is preferentially expressed by intra-islet Treg cells, which cycle vigorously in situ and express the IL-2 receptor α chain (CD25) at higher levels than ICOS- Treg cells. We also found that ICOS+ Treg cells preferentially up-regulate CXCR3 homing receptor in response to inflammation in the pancreatic environment in which CXCR3’s ligands, CXCL9, 10 and 11 are expressed by islet-residing Foxp3+ Treg cells, innate cells and by insulin producing β-islets. By examining the functional relevance of ICOS+ Treg cells we found that ICOS+ Treg cells, compared to ICOS- Treg cells, are endowed with a greater suppressive capacity in vitro and in vivo, and produce the immunomodulatory cytokine IL-10. Furthermore, the importance of ICOS signaling is demonstrated by Ab-mediated blockade or genetic deficiency in ICOS, which selectively abrogates Treg-mediated T1D protection, and exacerbates disease in BDC2.5 mice. Our results also show that ICOS+ Treg cells, in contrast to ICOS- Treg cells, are more responsive to IL-2, a cytokine essential for the survival, fitness and functional stability of Treg cells. Additionally, in vivo ICOS expression on Treg cells can be restored by il2 allelic variants or IL-2 therapy demonstrating an essential role for IL-2 in sustaining ICOS+ Treg cells. Finally, we found that expression of the KLRG1 marker tracks a homeostatically impaired and fatigued ICOS+ Treg cell population. These ICOS+KLRG1+ Treg cells display increased susceptibility to cell death, loss of Foxp3 expression and poor suppressive potential that further contributes to T1D progression in our model. Altogether, we demonstrate that ICOS is critical for the homeostasis and functional stability of Treg cells and maintenance of T1D protection. Elucidation of the mechanisms involved in maintaining self-tolerance will build on our current understanding of autoimmune disorders, and provide possible therapeutic tools to combat diseases like T1D.Le développement du diabète de type 1 (T1D) dans les souris diabétiques non-obèses (NOD) s’accompagne d’un déclin fonctionnel des cellules T CD4+Foxp3+ régulatrices (Treg). Nous avons précédemment démontré que la progression du T1D est associée à la perte progressive par les cellules Treg de la capacité de proliférer et de survivre dans les îlots de Langerhans du pancréas, ce qui perturbe l’équilibre entre Treg et cellules T effectrices (Teff), et déclenche la réponse immunitaire contre les cellules bêta du pancréas. Il a également été démontré que le blocage de ICOS chez les souriceaux nouveau-nés de la lignée transgénique NOD.BDC2.5, dont les cellules T reconnaissent spécifiquement un antigène du soi exprimé par les cellules bêta, engendre un débalancement des cellules Teff vis-à-vis des Treg, et aggrave le T1D, ce qui suggère un rôle important de ICOS dans la régulation des cellules Treg. Nous proposons ici que l’expression de ICOS par les cellules Treg Foxp3+, et les signaux induits par ICOS, sont indispensables à une fonction stable des cellules Treg au sein des îlots des souris NOD pré-diabétiques.Nous montrons que les cellules Treg situées dans les îlots expriment préférentiellement ICOS, prolifèrent vigoureusement et expriment de plus hauts niveaux de la chaine alpha du récepteur de l’IL2 (CD25) que les cellules Treg ICOS-. De plus, nous avons trouvé que les cellules Treg ICOS+ sont plus susceptibles d’exprimer le récepteur d’adressage CXCR3 dans le contexte inflammatoire du pancréas, où les chimiokines CXCL9, 10 et 11 sont exprimées par les cellules Treg Foxp3+, les cellules immunitaires innées et les cellules bêta productrices d’insuline. Un examen approfondi de la pertinence fonctionnelle des cellules Treg ICOS+ nous a également permis d’établir que ces cellules présentent une meilleure capacité de suppression in vitro et in vivo, et produisent l’interleukine immuno-régulatrice IL-10. De plus, l’importance des signaux transmis par ICOS est démontrée par la perte d’ICOS, par blocage par anticorps ou par déficience génétique, qui conduit à l’abrogation de la protection contre le T1D par les cellules Treg, et accélère la maladie chez les souris BDC2.5. Nos résultats démontrent également que les cellules Treg qui expriment ICOS sont plus sensibles à l’IL-2, une cytokine essentielle à la survie, la santé et la stabilité fonctionnelle des cellules Treg. De plus, l’expression d’ICOS par les cellules Treg peut être restaurée par des variants alléliques du gène de l’il2 ou par l’injection directe d’IL-2, ce qui démontre le rôle indispensable de l’IL-2 dans le support des cellules Treg ICOS+. Enfin, nous observons que l’expression du récepteur KLRG1 permet l’identification d’une population de cellules Treg ICOS+ compromises et épuisées, qui présentent une susceptibilité accrue à la mort cellulaire, la perte de l’expression de Foxp3, et une fonction suppressive diminuée qui contribue à la progression du T1D dans notre model.En conclusion, nous démontrons que ICOS est indispensable à l’homéostasie et la stabilité fonctionnelle des cellules Treg dans les îlots de Langerhans pré-diabétiques, et au maintien de la protection contre le T1D. Elucider les mécanismes impliqués dans le maintien de la tolérance au soi permettra d’améliorer notre compréhension des désordres auto-immuns, et pourra apporter des outils thérapeutiques dans le combat contre des maladies telles que le T1D

KLRG1 expression identifies short-lived Foxp3+ Treg effector cells with functional plasticity in islets of NOD mice

A progressive waning in Foxp3+ regulatory T (Treg) cell function provokes autoimmunity in the non-obese diabetic (NOD) mouse model of type 1 diabetes (T1D), a cellular defect rescued by prophylactic IL-2 therapy. We showed that most islet-infiltrating Treg cells express inducible T-cell co-stimulator (ICOS) in pre-diabetic NOD mice, and that ICOS+ Treg cells display enhanced fitness and suppressive function in situ. Moreover, T1D progression is associated with decreased expansion and suppressive activity of ICOS+Foxp3+ Treg cells, in islets, an observation consistent with the exacerbated T1D seen in NOD.BDC2.5 mice in which the ICOS pathway is abrogated. Here, we show that a large proportion of islet-resident Treg cells express the KLRG1 marker of terminally differentiation, in contrast to islet-infiltrating ICOS− Treg or Teff cells. We hypothesized that KLRG1 expression designates a subpopulation of ICOS+ Treg cells in islets that progressively loses function, and contributes to the immune dysregulation observed at T1D onset. Indeed, KLRG1-expressing ICOS+ Treg cells are prone to apoptosis, and have an impaired proliferative capacity and suppressive function in vitro and in vivo. T1D protective low-dose IL-2 treatment in vivo could not rescue the loss of KLRG1-expressing Treg cells in situ. While the global pool of Foxp3+ Treg cells displays some degree of functional plasticity in vivo, the KLRG1+ ICOS+ Treg cell subset is particularly susceptible to lose Foxp3 expression and reprogram into Th1- or Th17-like effector T (Teff) cells in the pancreas microenvironment. Overall, KLRG1 expression delineates a subpopulation of dysfunctional Treg cells during T1D progression in autoantigen-specific TCR transgenic NOD mice

TAF6delta orchestrates an apoptotic transcriptome profile and interacts functionally with p53.

BACKGROUND: TFIID is a multiprotein complex that plays a pivotal role in the regulation of RNA polymerase II (Pol II) transcription owing to its core promoter recognition and co-activator functions. TAF6 is a core TFIID subunit whose splice variants include the major TAF6alpha isoform that is ubiquitously expressed, and the inducible TAF6delta. In contrast to TAF6alpha, TAF6delta is a pro-apoptotic isoform with a 10 amino acid deletion in its histone fold domain that abolishes its interaction with TAF9. TAF6delta expression can dictate life versus death decisions of human cells. RESULTS: Here we define the impact of endogenous TAF6delta expression on the global transcriptome landscape. TAF6delta was found to orchestrate a transcription profile that included statistically significant enrichment of genes of apoptotic function. Interestingly, gene expression patterns controlled by TAF6delta share similarities with, but are not equivalent to, those reported to change following TAF9 and/or TAF9b depletion. Finally, because TAF6delta regulates certain p53 target genes, we tested and demonstrated a physical and functional interaction between TAF6delta and p53. CONCLUSION: Together our data define a TAF6delta-driven apoptotic gene expression program and show crosstalk between the p53 and TAF6delta pathways