Tolerogenic Function Of Dendritic Cells Research Articles

Blocking senescence and tolerogenic function of dendritic cells induced by γδ Treg cells enhances tumor-specific immunity for cancer immunotherapy

BackgroundRegulatory T (Treg) cells are a key component in maintaining the suppressive tumor microenvironment and immune suppression in different types of cancers. A precise understanding of the molecular mechanisms used...

Optimal conditions for adenoviral transduction of immature dendritic cells without affecting the tolerogenic activity of DC-based immunotherapy

Dendritic cells (DCs) play a pivotal role in maintaining immune tolerance. Using recombinant adenovirus (rAd) to deliver vectors to immature dendritic cells (imDCs) is an important method for studying the tolerogenic function of DCs. We found that using RPMI medium and a higher MOI during transduction increased the expression of CD80, CD86, and MHC-II on the surface of imDCs. Our data reveal a significant increase in the secretion of the pro-inflammatory cytokine IL-6 in the group showing the most pronounced phenotypic changes. In the mouse heart transplant model, imDCs with unstable phenotype and function due to adenoviral transduction resulted in an increased proportion of Th1 and Th17 cells in recipients. However, these effects can be managed, and our proposed optimized transduction strategy significantly minimizes these adverse effects. Our study holds significant implications for the development and optimization of immunotherapy utilizing tolerogenic dendritic cells.

Age-mediated gut microbiota dysbiosis promotes the loss of dendritic cells tolerance.

The old age-related loss of immune tolerance inflicts a person with a wide range of autoimmune and inflammatory diseases. Dendritic cells (DCs) are the sentinels of the immune system that maintain immune tolerance through cytokines and regulatory T-cells generation. Aging disturbs the microbial composition of the gut, causing immune system dysregulation. However, the vis-à-vis role of gut dysbiosis on DCs tolerance remains highly elusive. Consequently, we studied the influence of aging on gut dysbiosis and its impact on the loss of DC tolerance. We show that DCs generated from either the aged (DCOld ) or gut-dysbiotic young (DCDysbiotic ) but not young (DCYoung ) mice exhibited loss of tolerance, as evidenced by their failure to optimally induce the generation of Tregs and control the overactivation of CD4+ T cells. The mechanism deciphered for the loss of DCOld and DCDysbiotic tolerance was chiefly through the overactivation of NF-κB, impaired frequency of Tregs, upregulation in the level of pro-inflammatory molecules (IL-6, IL-1β, TNF-α, IL-12, IFN-γ), and decline in the anti-inflammatory moieties (IL-10, TGF-β, IL-4, IDO, arginase, NO, IRF-4, IRF-8, PDL1, BTLA4, ALDH2). Importantly, a significant decline in the frequency of the Lactobacillus genus was noticed in the gut. Replenishing the gut of old mice with the Lactobacillus plantarum reinvigorated the tolerogenic function of DCs through the rewiring of inflammatory and metabolic pathways. Thus, for the first time, we demonstrate the impact of age-related gut dysbiosis on the loss of DC tolerance. This finding may open avenues for therapeutic intervention for treating age-associated disorders with the Lactobacillus plantarum.

Tolerogenic Dendritic Cells Shape a Transmissible Gut Microbiota That Protects From Metabolic Diseases.

Excess chronic contact between microbial motifs and intestinal immune cells is known to trigger a low-grade inflammation involved in many pathologies such as obesity and diabetes. The important skewing of intestinal adaptive immunity in the context of diet-induced obesity (DIO) is well described, but how dendritic cells (DCs) participate in these changes is still poorly documented. To address this question, we challenged transgenic mice with enhanced DC life span and immunogenicity (DChBcl-2 mice) with a high-fat diet. Those mice display resistance to DIO and metabolic alterations. The DIO-resistant phenotype is associated with healthier parameters of intestinal barrier function and lower intestinal inflammation. DChBcl-2 DIO-resistant mice demonstrate a particular increase in tolerogenic DC numbers and function, which is associated with strong intestinal IgA, T helper 17, and regulatory T-cell immune responses. Microbiota composition and function analyses reveal that the DChBcl-2 mice microbiota is characterized by lower immunogenicity and an enhanced butyrate production. Cohousing experiments and fecal microbial transplantations are sufficient to transfer the DIO resistance status to wild-type mice, demonstrating that maintenance of DCs’ tolerogenic ability sustains a microbiota able to drive DIO resistance. The tolerogenic function of DCs is revealed as a new potent target in metabolic disease management.

Abstract TP259: Tryptophan Metabolism Affects the Intestinal Immune Response After Stroke

Introduction: The gut microbiota influences the severity of brain injury through regulation of intestinal immune homeostasis. However, molecular cues involved in microbiota-immune interaction after stroke are unknown. Metabolites have a pivotal role in connecting commensals to the immune response. Specifically, bacteria-derived metabolites of tryptophan catabolism activate the transcription factor aryl hydrocarbon receptor (AhR) which regulates T cell polarization directly or via tolerogenic function of dendritic cells (DCs). Hypothesis: Since adaptive immune cells are involved in stroke, we hypothesize that modulation of tryptophan metabolism–orchestrated by bacteria–modifies T cell differentiation and influences stroke outcome. Methods: Stroke is induced by the occlusion of the middle cerebral artery (MCAO) in C57BL6 mice. Blood and the distal small intestine are sampled for the detection of tryptophan metabolites and quantified by metagenomics or mRNA expression. Immune cells are isolated from the intestine and analyzed by flow cytometry. Stroke outcome is measured by infarct volumetry and behaviour tests. Results: Tryptophan catabolism was augmented in mice subjected to stroke-induced dysbiosis–shown by a) an increase of the most proximal metabolite kynurenine and a concomitant decrease of tryptophan and b) an upregulation of mRNA expression of the rate-limiting enzyme involved in tryptophan’s breakdown. This was paralleled by an increase of AhR mRNA in the ileum after MCAO. To test the implication of AhR on the tolerogenic function of DCs, we used AhR-DCs knock-out mice. We found that CD103+CD11b+ DCs lacking AhR were downregulated after stroke compared to wild-type (WT) mice. Interestingly, polarization state of T cells was modified in DCs lacking AhR (regulatory versus Th17 cell ratio). This could influence the central nervous system immune response and induce protection after stroke, as suggested by a reduction of infarct volume observed 3 days after stroke in AhR-DCs knock-out mice compared to WT mice. Conclusion: These findings suggest that stroke-induced dysbiosis leads to an increase of tryptophan catabolism, and that AhR depletion in DCs influences immune cell polarization and stroke outcome.

Type 1 diabetes genetic susceptibility and dendritic cell function: potential targets for treatment.

Type 1 diabetes is an autoimmune disease that results from the defective induction or maintenance of T cell tolerance against islet β cell self-antigens. Under steady-state conditions, dendritic cells with tolerogenic properties are critical for peripheral immune tolerance. Tolerogenic dendritic cells can induce T cell anergy and deletion and, in some contexts, induce or expand regulatory T cells. Dendritic cells contribute to both immunomodulatory effects and triggering of pathogenesis in type 1 diabetes. This immune equilibrium is affected by both genetic and environmental factors that contribute to the development of type 1 diabetes. Genome-wide association studies and disease association studies have identified >50 polymorphic loci that lend susceptibility or resistance to insulin-dependent diabetes mellitus. In parallel, diabetes susceptibility regions known as insulin-dependent diabetes loci have been identified in the nonobese diabetic mouse, a model for human type 1 diabetes, providing a better understanding of potential immunomodulatory factors in type 1 diabetes risk. Most genetic candidates have annotated immune cell functions, but the focus has been on changes to T and B cells. However, it is likely that some of the genomic susceptibility in type 1 diabetes directly interrupts the tolerogenic potential of dendritic cells in the pathogenic context of ongoing autoimmunity. Here, we will review how gene polymorphisms associated with autoimmune diabetes may influence dendritic cell development and maturation processes that could lead to alterations in the tolerogenic function of dendritic cells. These insights into potential tolerogenic and pathogenic roles for dendritic cells have practical implications for the clinical manipulation of dendritic cells toward tolerance to prevent and treat type 1 diabetes.

High mitochondrial respiration and glycolytic capacity represent a metabolic phenotype of human tolerogenic dendritic cells.

Human dendritic cells (DCs) regulate the balance between immunity and tolerance through selective activation by environmental and pathogen-derived triggers. To characterize the rapid changes that occur during this process, we analyzed the underlying metabolic activity across a spectrum of functional DC activation states, from immunogenic to tolerogenic. We found that in contrast to the pronounced proinflammatory program of mature DCs, tolerogenic DCs displayed a markedly augmented catabolic pathway, related to oxidative phosphorylation, fatty acid metabolism, and glycolysis. Functionally, tolerogenic DCs demonstrated the highest mitochondrial oxidative activity, production of reactive oxygen species, superoxide, and increased spare respiratory capacity. Furthermore, assembled, electron transport chain complexes were significantly more abundant in tolerogenic DCs. At the level of glycolysis, tolerogenic and mature DCs showed similar glycolytic rates, but glycolytic capacity and reserve were more pronounced in tolerogenic DCs. The enhanced glycolytic reserve and respiratory capacity observed in these DCs were reflected in a higher metabolic plasticity to maintain intracellular ATP content. Interestingly, tolerogenic and mature DCs manifested substantially different expression of proteins involved in the fatty acid oxidation (FAO) pathway, and FAO activity was significantly higher in tolerogenic DCs. Inhibition of FAO prevented the function of tolerogenic DCs and partially restored T cell stimulatory capacity, demonstrating their dependence on this pathway. Overall, tolerogenic DCs show metabolic signatures of increased oxidative phosphorylation programing, a shift in redox state, and high plasticity for metabolic adaptation. These observations point to a mechanism for rapid genome-wide reprograming by modulation of underlying cellular metabolism during DC differentiation.

Cryo-ablation improves anti-tumor immunity through recovering tumor educated dendritic cells in tumor-draining lymph nodes.

BackgroundIn addition to minimally invasive destruction of tumors, cryo-ablation of tumors to some extent modulated anti-tumor immunity. Cryo-ablated tumors in glioma mice models induced anti-tumor cellular immunologic response which increases the percentage of CD3+ and CD4+T cells in blood as well as natural killer cells. As a crucial role in triggering anti-tumor immunity, dendritic cells (DCs) were educated by tumors to adopt a tolerance phenotype which helps the tumor escape from immune monitoring. This study aims to study whether cryo-ablation could influence the tolerogenic DCs, and influence anti-tumor immunity in tumor-draining lymph nodes (TDLNs).MethodsUsing the GL261 subcutaneous glioma mouse model, we created a tumor bearing group, cryo-ablation group, and surgery group. We analyzed alteration in phenotype and function of tolerogenic DCs, and evaluated the factors of anti-tumor immunity inhibition.ResultsDCs in TDLNs in GL261 subcutaneous glioma mouse model expressed tolerogenic phenotype. In contrast to surgery, cryo-ablation improved the quantity and quality of these tolerogenic DCs. Moreover, the DCs decreased the expression of intracellular interleukin-10 (IL-10) and extra-cellular IL-10. In vitro, DCs from the cryo-ablation group recovered their specific function and induced potent anti-tumor immunity through triggering T cells. In vivo, cryo-ablation showed weak anti-tumor immunity, only inhibiting the growth of rechallenged tumors. But many IL-10-low DCs, rather than IL-10-high DCs, infiltrated the tumors. More importantly, Tregs inhibited the performance of these DCs; and depletion of Tregs greatly improved anti-tumor immunity in vivo.ConclusionCryo-ablation could recover function of tumor induced tolerogenic DCs in vitro; and depletion of Tregs could improve this anti-tumor effect in vivo. The Tregs/CD4+T and Tregs/CD25+T cells in TDLNs inhibit DCs’ activity and function.

Disruption of the TSLP-TSLPR-LAP signaling between epithelial and dendritic cells through hyperlipidemia contributes to regulatory T-Cell defects in atherosclerotic mice

Regulatory T-Cells (Tregs) play a protective role against the development of atherosclerosis. Moreover, thymic stromal lymphopoietin (TSLP)/thymic stromal lymphopoietin receptor (TSLPR) signaling in myeloid dendritic cells (DCs) promote Treg differentiation. Here, we examined the potential role of TSLP/TSLPR on Treg homeostasis in atherosclerosis. The frequencies of both latency-associated peptide (LAP)+ and Foxp3+ Tregs were reduced in the thymus and spleen of ApoE−/− mice compared with C57BL/6 mice, and this effect was associated with decreased thymic output. The tolerogenic function of DCs obtained from ApoE−/− mice was compromised compared with those from C57BL/6 mice. The expression of TSLP and TSLPR was also inhibited in ApoE−/− mice. In addition, we found that ox-LDL attenuated TSLP expression in cultured thymic epithelial cells (TECs) through the activation of retinoid X receptor alpha (RXRA) and IL-1β and decreased LAP and PD-L1 expression in oxLDL-activated DCs while both were up-regulated in TSLP-activated DCs. We also observed that the TSLP-DCs mediated differentiation of Tregs was abrogated through LAP neutralization. Furthermore, TSLP injection rescued Treg defects in ApoE−/− mice. These findings suggest that Treg defects in ApoE−/− mice might partially be attributed to the disruption of TSLP-TSLPR-LAP signaling in epithelial cells (ECs) and DCs.

A preliminary study on the biological characteristics and function of tolerogenic dendritic cells induced by tacrolimus

To explore the biological characteristics and the immuno-suppression function of tolerogenic dendritic cells (tDC) induced by tacrolimus. Human monocytes derived from peripheral blood were cultured in the cGMP-compliant CellGro DC medium supplemented with GM-CSF and IL-4 to obtain dendritic cells (DCs), and 0.1 μmol/L immunosuppressive drug tacrolimus was added to the culture medium at the third and fifth day to obtain tDCs. The molecular markers of them and the livability were assayed by flow cytometry. Then the tolerance functionality of tDCs induced by many agents and these tDCs modulated allogeneic CD4 T cells was determined via CFSE proliferation assay. And the research also analyzed the biological characters and immunosuppression function of tDCs induced by tacrolimus after storing. tDCs induced by tacrolimus exhibit a typical tolerogenic phenotype, whose level of costimulatory molecules CD80, CD83, CD86 and HLA-DR is (2.95 ± 1.32)%, (2.33 ± 1.60)%, (90.02 ± 7.42)% and (91.80 ± 6.18)%, respectively. It's survival rate was (85.2 ± 4.72)%. And immunosuppressive drugs didn't influence the differentiation of tDCs from monocytes. tDCs induced by immunosuppressive drugs dexamethasone, cyclosporin A and tacrolimus had lower immunogenic than control DCs as CD4+ T proliferation rate of tDCs induced by tacrolimus is 0.42% and could not primed allogeneic CD4+ T cells proliferation. Functional analyses showed that tDCs induced by tacrolimus can more effectively suppressed mature DC-induced T cell proliferation than other tDCs, whose inhibition rate can reach (67.01 ± 19.73)%. Importantly, tDCs induced by tacrolimus had phenotypical and functional stability after storing. tDCs induced by tacrolimus with tolerance functionality are a promising cellular therapeutic for immunomodulation.

Research in practice: The impact of interferon-α therapy on immune tolerance

Interferon-α (IFN-α) is the only drug approved for adjuvant therapy of malignant melanoma and is also used in the treatment of hematological and solid tumors. Along with its proven clinical efficacy, IFN-α produces several side effects, particularly with regard to autoimmune disorders. Curious about symptoms of autoimmunity during IFN-α therapy, we asked whether IFN-α directly impacts on immune tolerance. We found that IFN-α does alter the function of tolerogenic dendritic cells (DC) as well as of induced and naturally occurring T-regulatory cells (nTregs). IFN-α blocks the tolerogenic phenotype of DC by inducing maturation and thus preventing the induction of inducible Tregs by DC. It also has direct effects on nTregs. IFN-α reduces cAMP in Tregs via ERK/phosphodiesterase-mediated pathways. Since cAMP is essentially involved in suppression by nTregs, the IFN-α-dependent reduction of cAMP levels abolishes the suppressive capacity of nTregs. Therefore, Tregs are incapable of suppressing the activity of effector T cells and natural killer cells, resulting in tumor rejection. Thus, IFN-α overcomes immunological tolerance processes, leading to an improved immunostimulation and efficient tumor rejection, but also increases the risk of autoimmunity.

Mast Cells Condition Dendritic Cells to Mediate Allograft Tolerance

Peripheral tolerance orchestrated by regulatory Tcells, dendritic cells (DCs), and mast cells (MCs) has been studied in several models including skin allograft tolerance. We now define a role for MCs in controlling DC behavior ("conditioning") to facilitate tolerance. Under tolerant conditions, we show that MCs mediated a marked increase in tumor necrosis factor (TNFα)-dependent accumulation of graft-derived DCs in the dLN compared to nontolerant conditions. This increase of DCs in the dLN is due to the local production of granulocyte macrophage colony-stimulating factor (GM-CSF) by MCs that induces a survival advantage of graft-derived DCs. DCs that migrated to the dLN from the tolerant allograft were tolerogenic; i.e., they dominantly suppress Tcell responses and control regional immunity. This study underscores the importance of MCs in conditioning DCs to mediate peripheral tolerance and shows a functional impact of peripherally produced TNFα and GM-CSF on the migration and function of tolerogenic DCs.

Tolerogenic function of Blimp-1 in dendritic cells

Blimp-1 has been identified as a key regulator of plasma cell differentiation in B cells and effector/memory function in T cells. We demonstrate that Blimp-1 in dendritic cells (DCs) is required to maintain immune tolerance in female but not male mice. Female mice lacking Blimp-1 expression in DCs (DCBlimp-1(ko)) or haploid for Blimp-1 expression exhibit normal DC development but an altered DC function and develop lupus-like autoantibodies. Although DCs have been implicated in the pathogenesis of lupus, a defect in DC function has not previously been shown to initiate the disease process. Blimp-1(ko) DCs display increased production of IL-6 and preferentially induce differentiation of follicular T helper cells (T(FH) cells) in vitro. In vivo, the expansion of T(FH) cells is associated with an enhanced germinal center (GC) response and the development of autoreactivity. These studies demonstrate a critical role for Blimp-1 in the tolerogenic function of DCs and show that a diminished expression of Blimp-1 in DCs can result in aberrant activation of the adaptive immune system with the development of a lupus-like serology in a gender-specific manner. This study is of particular interest because a polymorphism of Blimp-1 associates with SLE.

Dendritic Cells

Dendritic cells (DCs) control the initiation and differentiation of T cells. In the steady state, DCs mediate tolerance. To achieve immunization, the tolerogenic function of DCs must be switched off by inducing their maturation with appropriate "adjuvants." Dendritic cells form a system composed of distinct subsets that differ in their expression of endocytic and signaling receptors. These subsets have different capacities to differentiate and polarize T cells and to cross-present antigen to expand CD8+ T cells. Optimization of vaccines is possible by exploiting the unique biological properties of DCs.

Regulation of Expression and Function of IDO in Human Dendritic Cells

In the human immune system, IDO expression and activity (IDO competence), are preferentially found in the antigenpresenting cell population, of which dendritic cells (DCs) represent an essential part. As will be comprehensively reviewed, IDO competence in human DCs, in general, is induced by molecules such as interferon-γ, which otherwise initiate immunity. IDO activity therefore, can be interpreted as a negative feedback pathway that limits uncontrolled immune responses. Because of its potent immunosuppressive effects (down-regulation of T cell responses or the expansion of T cell regulatory activity), IDO competence in human DCs is tightly regulated, at the transcriptional, translational and post-translational levels. I will critically discuss the experimental prerequisites and limits of attributing IDO competence to a mechanism of immunosuppression and examine, whether IDO competence itself can be viewed as mediating immunosuppression, or as representing one component among other immunosuppressive factors, involved in tolerogenic function of DCs. Finally, the newly emerging concepts of manipulating IDO competence as a therapy for either augmenting immune responses, such as in cancer, or down-regulating immune responses, such as in transplantation, will be summarized.

Thymic Stromal Lymphopoietin and Thymic Stromal Lymphopoietin–Conditioned Dendritic Cells Induce Regulatory T-Cell Differentiation and Protection of NOD Mice Against Diabetes

OBJECTIVE—Autoimmune diabetes in the nonobese diabetic (NOD) mouse model results from a breakdown of T-cell tolerance caused by impaired tolerogenic dendritic cell development and regulatory T-cell (Treg) differentiation. Re-establishment of the Treg pool has been shown to confer T-cell tolerance and protection against diabetes. Here, we have investigated whether murine thymic stromal lymphopoietin (TSLP) re-established tolerogenic function of dendritic cells and induced differentiation and/or expansion of Tregs in NOD mice and protection against diabetes.RESEARCH DESIGN AND METHODS—We examined the phenotype of TSLP-conditioned bone marrow dendritic cells (TSLP-DCs) of NOD mice and their functions to induce noninflammatory Th2 response and differentiation of Tregs. The functional relevance of TSLP and TSLP-DCs to development of diabetes was also tested.RESULTS—Our results showed that bone marrow dendritic cells of NOD mice cultured in the presence of TSLP acquired signatures of tolerogenic dendritic cells, such as an absence of production of pro-inflammatory cytokines and a decreased expression of dendritic cell costimulatory molecules (CD80, CD86, and major histocompatibility complex class II) compared with LPS-treated dendritic cells. Furthermore, TSLP-DCs promoted noninflammatory Th2 response and induced the conversion of naïve T-cells into functional CD4+CD25+Foxp3+ Tregs. We further showed that subcutaneous injections of TSLP for 6 days or a single intravenous injection of TSLP-DCs protected NOD mice against diabetes.CONCLUSIONS—Our study demonstrates that TSLP re-established a tolerogenic immune response in NOD mice and protects from diabetes, suggesting that TSLP may have a therapeutic potential for the treatment of type 1 diabetes.

Mucosal immunization application to allergic disease: Sublingual immunotherapy

Sublingual immunotherapy (SLIT) is an effective and safe treatment for respiratory allergy, and its mechanism of action currently is investigated with increasing attention. Studies of pharmacokinetics showed that allergen extracts administered via the sublingual route are not directly absorbed by the oral mucosa but are long retained at mucosal level, where the allergen molecules are captured by dendritic cells and, following their migration in the draining lymph nodes, presented to T cells. This seems to be the pivotal factor underlying the mechanisms of action of SLIT, at least for the long-term effects, and for the short-term efficacy, observed with ultrarush or coseasonal treatment, a down-regulation of mast cells resulting in hyporeactivity at the peak of the pollen season may be suggested. Regarding the clinically established long-lasting effects, the core mechanism is likely to consist of T regulatory (Treg) cell activation. In particular, Treg cells differentiate from naive T cells after application of soluble antigens to the mucosae, a crucial factor being the tolerogenic function of dendritic cells, and exert a suppressive effect on both Th1 and Th2 responses. Moreover, at least for the type 1 cells (Treg1), a production of IL-10 with consequent down-modulation of the immune response has been reported. Another characteristic of sublingual immunization is the absence of effectors cells, viz., mast cells, basophils, and eosinophils, in the oral mucosa of allergic subjects, which account for the excellent tolerability of SLIT.

Role of dendritic cells in the generation of regulatory T cells

The induction of antigen-specific T-cell tolerance in the thymus and its maintenance in the periphery is crucial for the prevention of autoimmunity. It was recently proposed that cells of the dendritic family not only control immunity but also maintain tolerance to self-antigens, two complementary functions that would ensure the integrity of the organism in an environment full of pathogens. The tolerogenic function of dendritic cells has been shown to be dependent on certain maturation stages and subsets of different ontogenies, and can be influenced by immunomodulatory agents. Here we discuss the current knowledge of these tolerogenic dendritic cells and how might the understanding of the function and characterization of tolerance-inducing dendritic cells be relevant to therapeutic applications.