Induction of Foxp3 demethylation increases regulatory CD4+CD25+ T cells and prevents the occurrence of diabetes in mice

Immunomodulation for Tissue Repair and Regeneration

Various immune cells participate in repair and regeneration following tissue injury or damage, orchestrating tissue inflammation and regeneration processes. A deeper understanding of the immune system's involvement in tissue repair and regeneration is critical for the development of successful reparatory and regenerative strategies. Here we review recent technologies that facilitate cell-based and biomaterial-based modulation of the immune systems for tissue repair and regeneration. First, we summarize the roles of various types of immune cells in tissue repair. Second, we review the principle, examples, and limitations of regulatory T (Treg) cell-based therapy, a representative cell-based immunotherapy. Finally, we discuss biomaterial-based immunotherapy strategies that aim to modulate immune cells using various biomaterials for tissue repair and regeneration.

Augmenting chemotherapy with low-dose decitabine through an immune-independent mechanism

The DNA methyltransferase inhibitor decitabine has classically been used to reactivate silenced genes and as a pretreatment for anticancer therapies. In a variation of this idea, this study explores the concept of adding low-dose decitabine (DAC) following administration of chemotherapy to bolster therapeutic efficacy. We find that addition of DAC following treatment with the chemotherapy agent gemcitabine improves survival and slows tumor growth in a mouse model of high-grade sarcoma. Unlike prior studies in epithelial tumor models, DAC did not induce a robust antitumor T cell response in sarcoma. Furthermore, DAC synergizes with gemcitabine independently of the immune system. Mechanistic analyses demonstrate that the combination therapy induces biphasic cell cycle arrest and apoptosis. Therapeutic efficacy was sequence dependent, with gemcitabine priming cells for treatment with DAC through inhibition of ribonucleotide reductase. This study identifies an apparently unique application of DAC to augment the cytotoxic effects of conventional chemotherapy in an immune-independent manner. The concepts explored in this study represent a promising paradigm for cancer treatment by augmenting chemotherapy through addition of DAC to increase tolerability and improve patient response. These findings have widespread implications for the treatment of sarcomas and other aggressive malignancies.

Nature vs. nurture: FOXP3, genetics, and tissue environment shape Treg function

The importance of regulatory T cells (Tregs) in preventing autoimmunity has been well established; however, the precise alterations in Treg function in autoimmune individuals and how underlying genetic associations impact the development and function of Tregs is still not well understood. Polygenetic susceptibly is a key driving factor in the development of autoimmunity, and many of the pathways implicated in genetic association studies point to a potential alteration or defect in regulatory T cell function. In this review transcriptomic control of Treg development and function is highlighted with a focus on how these pathways are altered during autoimmunity. In combination, observations from autoimmune mouse models and human patients now provide insights into epigenetic control of Treg function and stability. How tissue microenvironment influences Treg function, lineage stability, and functional plasticity is also explored. In conclusion, the current efficacy and future direction of Treg-based therapies for Type 1 Diabetes and other autoimmune diseases is discussed. In total, this review examines Treg function with focuses on genetic, epigenetic, and environmental mechanisms and how Treg functions are altered within the context of autoimmunity.

Oxidative stress-mediated beta cell death and dysfunction as a target for diabetes management

The biggest drawback of a current diabetes therapy is the treatment of the consequences not the cause of the disease. Regardless of the diabetes type, preservation and recovery of functional pancreatic beta cells stands as the biggest challenge in the treatment of diabetes. Free radicals and oxidative stress are among the major mediators of autoimmune destruction of beta cells in type 1 diabetes (T1D) or beta cell malfunction and death provoked by glucotoxicity and insulin resistance in type 2 diabetes (T2D). Additionally, oxidative stress reduces functionality of beta cells in T2D by stimulating their de-/trans-differentiation through the loss of transcription factors critical for beta cell development, maturity and regeneration. This review summarizes up to date clarified redox-related mechanisms involved in regulating beta cell identity and death, underlining similarities and differences between T1D and T2D. The protective effects of natural antioxidants on the oxidative stress-induced beta cell failure were also discussed. Considering that oxidative stress affects epigenetic regulatory mechanisms involved in the regulation of pancreatic beta cell survival and insulin secretion, this review highlighted huge potential of epigenetic therapy. Special attention was paid on application of the state-of-the-art CRISPR/Cas9 technology, based on targeted epigenome editing with the purpose of changing the differentiation state of different cell types, making them insulin-producing with ability to attenuate diabetes. Clarification of the above-mentioned mechanisms could provide better insight into diabetes etiology and pathogenesis, which would allow development of novel, potentially more efficient therapeutic strategies for the prevention or reversion of beta cell loss.

Low-dose decitabine modulates T-cell homeostasis and restores immune tolerance in immune thrombocytopenia

Our previous clinical study showed that low-dose decitabine exhibited sustained responses in nearly half of patients with refractory immune thrombocytopenia (ITP). The long-term efficacy of decitabine in ITP is not likely due to its simple role in increasing platelet production. Whether decitabine has the potential to restore immune tolerance in ITP is unknown. In this study, we analyzed the effect of decitabine on T-cell subpopulations in ITP in vitro and in vivo. We found that low-dose decitabine promoted the generation and differentiation of regulatory T (Treg) cells and augmented their immunosuppressive function. Splenocytes from CD61 knockout mice immunized with CD61+ platelets were transferred into severe combined immunodeficient mouse recipients to induce a murine model of ITP. Low-dose decitabine alleviated thrombocytopenia and restored the balance between Treg and helper T (Th) cells in active ITP mice. Treg deletion and depletion offset the effect of decitabine in restoring CD4+ T-cell subpopulations in ITP mice. For patients who received low-dose decitabine, the quantity and function of Treg cells were substantially improved, whereas Th1 and Th17 cells were suppressed compared with the pretreatment levels. Next-generation RNA-sequencing and cytokine analysis showed that low-dose decitabine rebalanced T-cell homeostasis, decreased proinflammatory cytokines, and downregulated phosphorylated STAT3 in patients with ITP. STAT3 inhibition analysis suggested that low-dose decitabine might restore Treg cells by inhibiting STAT3 activation. In conclusion, our data indicate that the immunomodulatory effect of decitabine provides one possible mechanistic explanation for the sustained response achieved by low-dose decitabine in ITP.

5-Aza-2-deoxycytidine alleviates the progression of primary biliary cholangitis by suppressing the FoxP3 methylation and promoting the Treg/Th17 balance

Primary biliary cholangitis (PBC) is a common autoimmune liver disease manifested by the infiltration of CD4+ T cells, and the subsequent targeted injury of biliary epithelial cells (BECs). As important components of CD4 subsets, the Treg/Th17 axis maintains an immunological balance between self-tolerance and inflammation in the liver microenvironment. However, the role and regulatory mechanism of the Treg/Th17 axis in PBC remain unclear. In this study, we examined the Treg/Th17 axis in PBC patients and found that the Treg/Th17 axis was imbalanced in PBC at both the transcriptional and cellular levels, with Treg being a weak candidate, which correlates with the PBC progression. This imbalanced Treg/Th17 axis was likely to be affected by the FoxP3 hypermethylation, which was related to the increase of DNA methyltransferase. Furthermore, the effect of 5-Aza-2-deoxycytidine (DAC)-mediated FoxP3 demethylation on PBC mice was investigated. We verified that DAC significantly suppressed the FoxP3 methylation and rebuilt the Treg/Th17 balance, resulting in the alleviation of liver lesions and inflammation. Taken together, our data indicate that DAC plays a positive role in alleviating the progression of PBC through the inhibition of DNA methylation of FoxP3 to rebuild the balanced Treg/Th17 axis. DAC could be considered as a potential candidate for the development of new anti-inflammation strategies in the treatment of PBC.

Epigenetic DNA Methylation of EBI3 Modulates Human Interleukin-35 Formation via NFkB Signaling: A Promising Therapeutic Option in Ulcerative Colitis

Ulcerative colitis (UC), a severe chronic disease with unclear etiology that is associated with increased risk for colorectal cancer, is accompanied by dysregulation of cytokines. Epstein–Barr virus-induced gene 3 (EBI3) encodes a subunit in the unique heterodimeric IL-12 cytokine family of either pro- or anti-inflammatory function. After having recently demonstrated that upregulation of EBI3 by histone acetylation alleviates disease symptoms in a dextran sulfate sodium (DSS)-treated mouse model of chronic colitis, we now aimed to examine a possible further epigenetic regulation of EBI3 by DNA methylation under inflammatory conditions. Treatment with the DNA methyltransferase inhibitor (DNMTi) decitabine (DAC) and TNFα led to synergistic upregulation of EBI3 in human colon epithelial cells (HCEC). Use of different signaling pathway inhibitors indicated NFκB signaling was necessary and proportional to the synergistic EBI3 induction. MALDI-TOF/MS and HPLC-ESI-MS/MS analysis of DAC/TNFα-treated HCEC identified IL-12p35 as the most probable binding partner to form a functional protein. EBI3/IL-12p35 heterodimers (IL-35) induce their own gene upregulation, something that was indeed observed in HCEC cultured with media from previously DAC/TNFα-treated HCEC. These results suggest that under inflammatory and demethylating conditions the upregulation of EBI3 results in the formation of anti-inflammatory IL-35, which might be considered as a therapeutic target in colitis.

Implication of epigenetic factors in the pathogenesis of type 1 diabetes

Type 1 diabetes (T1D) is an autoimmune disease that resulted from the severe destruction of the insulin-producing β cells in the pancreases of individuals with a genetic predisposition. Genome-wide studies have identified HLA and other risk genes associated with T1D susceptibility in humans. However, evidence obtained from the incomplete concordance of diabetes incidence among monozygotic twins suggests that environmental factors also play critical roles in T1D pathogenesis. Epigenetics is a rapidly growing field that serves as a bridge to link T1D risk genes and environmental exposures, thereby modulating the expression of critical genes relevant to T1D development beyond the changes of DNA sequences. Indeed, there is compelling evidence that epigenetic changes induced by environmental insults are implicated in T1D pathogenesis. Herein, we sought to summarize the recent progress in terms of epigenetic mechanisms in T1D initiation and progression, and discuss their potential as biomarkers and therapeutic targets in the T1D setting.

Immune responses to azacytidine in animal models of inflammatory disorders: a systematic review

Inflammatory disorders like diabetes, systemic lupus erythematodes, inflammatory lung diseases, rheumatoid arthritis and multiple sclerosis, but also rejection of transplanted organs and GvHD, form a major burden of disease. Current classes of immune suppressive drugs to treat these disorders are never curative and side effects are common. Therefore there is a need for new drugs with improved and more targeted modes of action. Potential candidates are the DNA methyl transferase inhibitor 5-azacytidine (Aza) and its derivative 5-aza 2′deoxycitidine (DAC). Aza and DAC have been tested in several pre-clinical in vivo studies. In order to obtain an overview of disorders for which Aza and/or DAC can be a potential treatment, and to find out where information is lacking, we systematically reviewed pre-clinical animal studies assessing Aza or DAC as a potential therapy for distinct inflammatory disorders. Also, study quality and risk of bias was systematically assessed. In the 35 identified studies, we show that both Aza and DAC do not only seem to be able to alleviate a number of inflammatory disorders, but also prevent solid organ rejection and GvHD in in vivo pre-clinical animal models. Aza/DAC are known to upregulate FOXP3, a master transcription factor for Treg, in vitro. Seventeen studies described the effect on Treg, of which 16 studies showed an increase in Treg. Increasing Treg therefore seems to be a common mechanism in preventing inflammatory disorders by Aza/DAC. We also found, however, that many essential methodological details were poorly reported leading to an unclear risk of bias. Therefore, reported effects might be an overestimation of the true effect.

Autoimmune thyroid disease and type 1 diabetes mellitus: same pathogenesis; new perspective?

Autoimmune thyroid disease (AITD) and type 1 diabetes mellitus (T1DM) are two common autoimmune diseases that can occur concomitantly. In general, patients with diabetes have a high risk of AITD. It has been proposed that a complex genetic basis together with multiple nongenetic factors make a variable contribution to the pathogenesis of T1DM and AITD. In this paper, we summarize current knowledge in the field regarding potential pathogenic factors of T1DM and AITD, including human leukocyte antigen, autoimmune regulator, lymphoid protein tyrosine phosphatase, forkhead box protein P3, cytotoxic T lymphocyte-associated antigen, infection, vitamin D deficiency, and chemokine (C-X-C motif) ligand. These findings offer an insight into future immunotherapy for autoimmune diseases.

Prostaglandin E2 Reverses the Effects of DNA Methyltransferase Inhibitor and TGFB1 on the Conversion of Naive T Cells to iTregs

Naturally occurring regulatory T cells (nTregs) are produced under thymic (tTregs) or peripherally induced (pTregs) conditions in vivo. On the other hand, Tregs generated from naive T cells in vitro under some circumstances, such as treatment with transforming growth factor-β (TGFB), are called induced Tregs (iTregs). Tregs are especially characterized by FOXP3 expression, which is mainly controlled by DNA methylation. nTregs play important roles in the suppression of immune response and self-tolerance. The prostaglandin E2 (PGE2) pathway was reported to contribute to regulatory functions of tumor-infiltrating nTregs. In this study, we examined whether PGE2 contributes to the formation of iTregs treated with TGFB1 and 5-aza-2'-deoxycytidine (5-aza-dC), which is a DNA methyltransferase inhibitor. We found that the protein and gene expression levels of FOXP3 and IL-10 were increased in 5-aza-dC and TGFB1-treated T cells in vitro. However, the addition of PGE2 to these cells reversed these increments significantly. In CFSE-based cell suppression assays, we demonstrated that PGE2 decreased the suppressive functions of 5-aza-dC and TGFB1-treated T cells.

The Role of Epigenetics in Type 1 Diabetes

Type 1 diabetes (T1D) is an autoimmune disease caused by the interaction between genetic alterations and environmental factors. More than 60 susceptible genes or loci of T1D have been identified. Among them, HLA regions are reported to contribute about 50% of genetic susceptibility in Caucasians. There are many environmental factors involved in the pathogenesis of T1D. Environmental factors may change the expression of genes through epigenetic mechanisms, thus inducing individuals with susceptible genes to develop T1D; however, the underlying mechanisms remain poorly understood. The major epigenetic modifications include DNA methylation, histone modification, and non-coding RNA. There has been extensive research on the role of epigenetic mechanisms including aberrant DNA methylation, histone modification, and microRNA in the pathogenesis of T1D. DNA methylation and microRNA have been proposed as biomarkers to predict islet β cell death, which needs further confirmation before any clinical application can be developed. Small molecule inhibitors of histone deacetylases, histone methylation, and DNA methylation are potentially important for preventing T1D or in the reprogramming of insulin-producing cells. This chapter mainly focuses on T1D-related DNA methylation, histone modification, and non-coding RNA, as well as their possible translational potential in the early diagnosis and treatment of T1D.

Effects of Treatment with the Hypomethylating Agent 5-aza-2'-deoxycytidine in Murine Type II Collagen-Induced Arthritis

The emerging role of epigenetics in the pathogenesis of autoimmune diseases has recently attracted much interest on the possible use of epigenetic modulators for the prevention and treatment of these diseases. In particular, we and others have shown that drugs that inhibit DNA methylation, such as azacitidine (AZA) and decitabine (DAC), already used for the treatment of acute myeloid leukemia, exert powerful beneficial effects in rodent models of type 1 diabetes, multiple sclerosis, and Guillain Barrè syndrome. Along this line of research, we have presently studied the effects of DAC in a murine model of rheumatoid arthritis induced by type II collagen and have demonstrated that DAC administration was associated with a significant amelioration of the clinical condition, along with in vivo and ex vivo modification of the immunological profile of the so-treated mice, that exhibited a diminished production of Th1 and Th17 pro-inflammatory cytokines and reduction of anti-type II collagen autoantibodies.

The DNA Methylation Inhibitor Zebularine Controls CD4+ T Cell Mediated Intraocular Inflammation

CD4⁺ T cell mediated uveitis is conventionally treated with systemic immunosuppressive agents, including corticosteroids and biologics targeting key inflammatory cytokines. However, their long-term utility is limited due to various side effects. Here, we investigated whether DNA methylation inhibitor zebularine can target CD4⁺ T cells and control intraocular inflammation. Our results showed that zebularine restrained the expression of inflammatory cytokines IFN-γ and IL-17 in both human and murine CD4⁺ T cells in vitro. Importantly, it also significantly alleviated intraocular inflammation and retinal tissue damage in the murine experimental autoimmune uveitis (EAU) model in vivo, suggesting that the DNA methylation inhibitor zebularine is a candidate new therapeutic agent for uveitis.

Environmental Factors Associated With Type 1 Diabetes

Type 1 diabetes (T1D) is a chronic autoimmune disorder that leads to progressive pancreatic ß-cell destruction and culminates in absolute insulin deficiency and stable hyperglycaemia. It is very likely that environmental factors play a role in triggering islet autoimmunity. Knowing whether they have true relevance in favoring T1D development is essential for the effective prevention of the disease. Moreover, prevention could be obtained directly interfering with the development of autoimmunity through autoantigen-based immunotherapy. In this narrative review, the present possibilities for the prevention of T1D are discussed. Presently, interventions to prevent T1D are generally made in subjects in whom autoimmunity is already activated and autoantibodies against pancreatic cell components have been detected. Practically, the goal is to slow down the immune process by preserving the normal structure of the pancreatic islets for as long as possible. Unfortunately, presently methods able to avoid the risk of autoimmune activation are not available. Elimination of environmental factors associated with T1D development, reverse of epigenetic modifications that favor initiation of autoimmunity in subjects exposed to environmental factors and use of autoantigen-based immunotherapy are possible approaches, although for all these measures definitive conclusions cannot be drawn. However, the road is traced and it is possible that in a not so distant future an effective prevention of the disease to all the subjects at risk can be offered.

The Role of Histone Methyltransferases and Long Non-coding RNAs in the Regulation of T Cell Fate Decisions

T cell lineage decisions are critical for the development of proper immune responses to pathogens as well as important for the resolution of inflammatory responses. This differentiation process relies on a combination of intrinsic and extrinsic factors converging upon epigenetic regulation of transcriptional networks relevant to specific T cell lineages. As these biochemical modifications represent therapeutic opportunities in cancer biology and autoimmunity, implications of writers and readers of epigenetic marks to immune cell differentiation and function are highly relevant. Given the ready adoption of histone methyltransferase inhibitors in the clinic, we focus this review on the role of three histone modifying complexes: PRC-1, PRC-2, and G9A in modulating T cell fate decisions. Furthermore, we explore the role of long non-coding RNAs in regulating these processes, and discuss recent advances and challenges of implementing epigenetic therapies into clinical practice.

Decitabine induces regulatory T cells, inhibits the production of IFN-gamma and IL-17 and exerts preventive and therapeutic efficacy in rodent experimental autoimmune neuritis

Guillain-Barré syndrome (GBS) is an immune-mediated acute disorder of the peripheral nervous system. Despite treatment, there is an associated mortality and severe disability in 9 to 17% of the cases. Decitabine (DAC) is a hypomethylating drug used in myelodisplastic syndrome, that has been shown to exert immunomodulatory effects. We have evaluated the effects of DAC in two rodent models of GBS, the Experimental Allergic Neuritis (EAN). Both prophylactic and therapeutic treatment with DAC ameliorated the clinical course of EAN, increasing the numbers of thymic regulatory T cells and reducing the production of proinflammmatory cytokines. Our data suggest the possible use of decitabine for the treatment of GBS.

DNA Methyltransferase Inhibition Promotes Th1 Polarization in Human CD4+CD25high FOXP3+ Regulatory T Cells but Does Not Affect Their Suppressive Capacity

Regulatory T cells (Treg) can show plasticity whereby FOXP3 expression, the master transcription factor for Treg suppressor function, is lost and proinflammatory cytokines are produced. Optimal FOXP3 expression strongly depends on hypomethylation of the FOXP3 gene. 5-Azacytidine (Aza) and its derivative 5-aza-2'-deoxycytidine (DAC) are DNA methyltransferase inhibitors (DNMTi) that are therapeutically used in hematological malignancies, which might be an attractive strategy to promote Treg stability. Previous in vitro research primarily focused on Treg induction by DAC from naïve conventional CD4⁺ T cells (Tconv). Here, we examined the in vitro effect of DAC on the stability and function of FACS-sorted human naturally occurring CD4⁺CD25^high FOXP3⁺ Treg. We found that in vitro activation of Treg in the presence of DAC led to a significant inhibition of Treg proliferation, but not of Tconv. Although Treg activation in the presence of DAC led to increased IFNγ expression and induction of a Thelper-1 phenotype, the Treg maintained their suppressive capacity. DAC also induced a trend towards increased IL-10 expression. In vivo studies in patients with hematological malignancies that were treated with 5-azacytidine (Vidaza) supported the in vitro findings. In conclusion, despite its potential to increase IFNγ expression, DAC does preserve the suppressor phenotype of naturally occurring Treg.

Epigenetic regulation in B-cell maturation and its dysregulation in autoimmunity

B cells have a critical role in the initiation and acceleration of autoimmune diseases, especially those mediated by autoantibodies. In the peripheral lymphoid system, mature B cells are activated by self or/and foreign antigens and signals from helper T cells for differentiating into either memory B cells or antibody-producing plasma cells. Accumulating evidence has shown that epigenetic regulations modulate somatic hypermutation and class switch DNA recombination during B-cell activation and differentiation. Any abnormalities in these complex regulatory processes may contribute to aberrant antibody production, resulting in autoimmune pathogenesis such as systemic lupus erythematosus. Newly generated knowledge from advanced modern technologies such as next-generation sequencing, single-cell sequencing and DNA methylation sequencing has enabled us to better understand B-cell biology and its role in autoimmune development. Thus this review aims to summarize current research progress in epigenetic modifications contributing to B-cell activation and differentiation, especially under autoimmune conditions such as lupus, rheumatoid arthritis and type 1 diabetes.

Epigenetics and type 1 diabetes: mechanisms and translational applications

Type 1 diabetes (T1D) is an irreversible degenerative disease with severe complications such as heart disease, nephropathy, neuropathy, and retinopathy. Although exogenous insulin administration is a life-saving therapy, it does not cure the disease. This review addresses the epigenetic mechanisms responsible for the development of T1D and discusses epigenetic-based strategies for prevention and treatment of the disease. We describe novel epigenetic biomarkers for the identification of susceptible individuals and the establishment of innovative therapies with epidrugs and cell therapy to regenerate the lost β-cells. Despite the wealth of promising data regarding the potential benefits of epigenetic tools to reduce the burden of T1D, clinical trials are still very few, and this issue needs to be resolved in the near future.

Decitabine inhibits T cell proliferation via a novel TET2-dependent mechanism and exerts potent protective effect in mouse auto- and allo-immunity models

Multiple sclerosis (MS) is an autoimmune disease characterized by the dysregulated immune response including innate and adaptive immune responses. Increasing evidence has proven the importance of epigenetic modification in the progression of MS. Recent studies revealed that low-dose decitabine (Dec, 5-Aza-2′-deoxycytidine), which incorporates into replicating DNA and inhibits DNA methylation, could prevent experimental autoimmune encephalomyelitis (EAE) development by increasing the number of regulatory T cells (Tregs). Here, we showed that higher-dose decitabine relative to previous studies could also distinctly protect mice from EAE and allogeneic cardiac transplantation. Mechanistic studies revealed decitabine suppressed innate responses in EAE mice through inhibiting the activation of microglia and monocyte-derived macrophages that contributed to reduce the severity of EAE. Furthermore, differentiation of naïve CD4⁺ T cells into Th1 and Th17 cells was significantly suppressed by decitabine in vivo and in vitro. Though in vitro studies showed decitabine could induce Treg differentiation, there was no obvious change in the percentage of Tregs in Dec-treated EAE mice. Most importantly, we found that T cell proliferation was potently inhibited in vivo and in vitro by higher-dose decitabine through increased gene expression of the DNA dioxygenase TET2 which facilitated the expression of several cell cycle inhibitors. Collectively, our study provides novel mechanistic insights of using the epigenetic modifying agents in the management of both allo- and auto-immune responses.

The Microbiota and Epigenetic Regulation of T Helper 17/Regulatory T Cells: In Search of a Balanced Immune System

Immune cells not only affect tissue homeostasis at the site of inflammation but also exert systemic effects contributing to multiple chronic conditions. Recent evidence clearly supports an altered T helper 17/regulatory T cell (Th17/Treg) balance leading to the development and progression of inflammatory diseases that not only affect the gastrointestinal tract but also have whole-body manifestations, including insulin resistance. Epigenetic mechanisms are amenable to both environmental and circulating factors and contribute to determining the T cell landscape. The recently identified participation of the gut microbiota in the remodeling of the epigenome of immune cells has triggered a paradigm shift in our understanding of the etiology of various inflammatory diseases and opened new paths toward therapeutic strategies. In this review, we provide an overview of the contribution of the Th17/Treg balance in the development and progression of inflammatory bowel diseases and metabolic diseases. We discuss the involvement of epigenetic mechanisms in the regulation of T cell function in the particular context of dysbiosis. Finally, we examine the potential for nutritional interventions affecting the gut microbiota to reshape the T cell epigenome and address the inflammatory component of various diseases.

Azacytidine Treatment Inhibits the Progression of Herpes Stromal Keratitis by Enhancing Regulatory T Cell Function

Ocular infection with herpes simplex virus 1 (HSV-1) sets off an inflammatory reaction in the cornea which leads to both virus clearance and chronic lesions that are orchestrated by CD4 T cells. Approaches that enhance the function of regulatory T cells (Treg) and dampen effector T cells can be effective to limit stromal keratitis (SK) lesion severity. In this report, we explore the novel approach of inhibiting DNA methyltransferase activity using 5-azacytidine (Aza; a cytosine analog) to limit HSV-1-induced ocular lesions. We show that therapy begun after infection when virus was no longer actively replicating resulted in a pronounced reduction in lesion severity, with markedly diminished numbers of T cells and nonlymphoid inflammatory cells, along with reduced cytokine mediators. The remaining inflammatory reactions had a change in the ratio of CD4 Foxp3⁺ Treg to effector Th1 CD4 T cells in ocular lesions and lymphoid tissues, with Treg becoming predominant over the effectors. In addition, compared to those from control mice, Treg from Aza-treated mice showed more suppressor activity in vitro and expressed higher levels of activation molecules. Additionally, cells induced in vitro in the presence of Aza showed epigenetic differences in the Treg-specific demethylated region (TSDR) of Foxp3 and were more stable when exposed to inflammatory cytokines. Our results show that therapy with Aza is an effective means of controlling a virus-induced inflammatory reaction and may act mainly by the effects on Treg.IMPORTANCE HSV-1 infection has been shown to initiate an inflammatory reaction in the cornea that leads to tissue damage and loss of vision. The inflammatory reaction is orchestrated by gamma interferon (IFN-γ)-secreting Th1 cells, and regulatory T cells play a protective role. Hence, novel therapeutics that can rebalance the ratio of regulatory T cells to effectors are a relevant issue. This study opens up a new avenue in treating HSV-induced SK lesions by increasing the stability and function of regulatory T cells using the DNA methyltransferase inhibitor 5-azacytidine (Aza). Aza increased the function of regulatory T cells, leading to enhanced suppressive activity and diminished lesions. Hence, therapy with Aza, which acts mainly by its effects on Treg, can be an effective means to control virus-induced inflammatory lesions.

Indirubin Increases CD4+CD25+Foxp3+ Regulatory T Cells to Prevent Immune Thrombocytopenia in Mice

Indirubin, a traditional Chinese medicine, is used to treat autoimmune diseases in clinics. However, the effects of indirubin on the immunosuppressive CD4+CD25+Foxp3+ regulatory T cells (Treg) have not been addressed. Thus, we aimed to investigate the effects of indirubin on CD4+CD25+Treg cells in immune thrombocytopenia (ITP) CBA mice, which were established by immunization with Wistar rat platelets. 50 mg/kg indirubin treatment daily for 4 weeks significantly decreased anti-platelet antibody production and prevented the decrease of platelets caused by immunization in ITP mice. Consistently, indirubin significantly enhanced the percentage and cell number of CD4+CD25+Foxp3+Treg cells in the peripheral blood, spleen and lymph nodes. We also observed a significant increase of the frequency and cell number of CD4+CD25+Foxp3+Treg cells in the thymus upon indirubin treatment. Furthermore, CD4+CD25+Treg cells from indirubin-treated mice showed similar immunosuppression on T effector cells as compared to those from control mice. Altogether, indirubin ameliorates ITP by enhancing CD4+CD25+Foxp3+Treg cell level with preserving immunosuppressive function.

Epigenetic enzymes are the therapeutic targets for CD4(+)CD25(+/high)Foxp3(+) regulatory T cells

CD4(+)CD25(+/high)Foxp3(+) regulatory T (Treg) cells are a subset of CD4(+) T cells that play an essential role in maintaining peripheral immune tolerance. Several transcriptional cofactors have been recently identified, which form complexes with transcription factor Foxp3 of Treg cells and contribute in the suppressive function of Treg cells. However, Foxp3 is still defined as a "master" (multiple pathway) regulator gene that controls the development and stability of Treg cells. Because of its importance, the regulatory mechanisms underlying Foxp3 expression have been a focus of intensive investigation. Recent progress suggests that the epigenetic mechanisms responsible for regulating the Foxp3 gene expression are key components of suppressive activity of Treg cells. This review not only discusses the basic concepts of biology and epigenetic modifications of Treg cells, but also analyzes the translational clinical aspect of epigenetic modifications of Treg cells, focusing on several ongoing clinical trials and the Food and Drugs administration (FDA) approved epigenetic-based drugs. The new progress in identifying epigenetic enzymes functional in Treg cells is a new target for the development of novel therapeutic approaches for autoimmune and inflammatory diseases, graft-vs-host disease and cancers.

Treg functional stability and its responsiveness to the microenvironment

Regulatory T cells (Tregs) prevent autoimmunity and tissue damage resulting from excessive or unnecessary immune activation through their suppressive function. While their importance for proper immune control is undeniable, the stability of the Treg lineage has recently become a controversial topic. Many reports have shown dramatic loss of the signature Treg transcription factor Forkhead box protein 3 (Foxp3) and Treg function under various inflammatory conditions. Other recent studies demonstrate that most Tregs are extremely resilient in their expression of Foxp3 and the retention of suppressive function. While this debate is unlikely to be settled in the immediate future, improved understanding of the considerable heterogeneity within the Foxp3(+) Treg population and how Treg subsets respond to ranging environmental cues may be keys to reconciliation. In this review, we discuss the diverse mechanisms responsible for the observed stability or instability of Foxp3(+) Treg identity and function. These include transcriptional and epigenetic programs, transcript targeting, and posttranslational modifications that appear responsive to numerous elements of the microenvironment. These mechanisms for Treg functional modulation add to the discussion of Treg stability.

Low-dose 5-aza-2'-deoxycytidine pretreatment inhibits experimental autoimmune encephalomyelitis by induction of regulatory T cells

Forkhead box P3 (Foxp3) is the major transcription factor controlling the development and function of regulatory T (Treg) cells. Previous studies have indicated epigenetic regulation of Foxp3 expression. Here, we investigated whether the deoxyribonucleic acid (DNA) methyltransferase inhibitor 5-aza-2'-deoxycytidine (5-Aza) applied peripherally could modulate central nervous system (CNS) inflammation, by using a mouse experimental autoimmune encephalomyelitis (EAE) model. We found that disease activity was inhibited in a myelin oligodendrocyte glycoprotein (MOG) peptide-induced EAE mouse briefly pretreated with low-dose (0.15 mg/kg) 5-Aza, ameliorating significant CNS inflammatory responses, as indicated by greatly decreased proinflammatory cytokines. On the contrary, control EAE mice expressed high levels of IFN-γ and interleukin (IL)-17. In addition, 5-Aza treatment in vitro increased GFP expression in CD4(+)GFP(-) T cells isolated from GFP knock-in Foxp3 transgenic mice. Importantly, 5-Aza treatment increased Treg cell numbers, in EAE mice, at both disease onset and peak. However, Treg inhibition assays showed 5-Aza treatment did not enhance per-cell Treg inhibitory function, but did maintain a lower activation threshold for effector cells in EAE mice. In conclusion, 5-Aza treatment prevented EAE development and suppressed CNS inflammation, by increasing the number of Treg cells and inhibiting effector cells in the periphery.

Epigenetic modification of the FoxP3 TSDR in HAM/TSP decreases the functional suppression of Tregs

HTLV-1 is a human retrovirus that is associated with the neuroinflammatory disorder HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP). In these patients, HTLV-1 is primarily found in the CD4(+)CD25(+) T cell subset (Regulatory T cells:Tregs), which is responsible for peripheral immune tolerance and is known to be dysfunctional in HAM/TSP. Recent evidence suggests that FoxP3 expression and function is determined epigenetically through DNA demethylation in the Treg-specific demethylated region (TSDR). We analyzed the methylation of the TSDR in PBMCs, CD4(+) T cells, and CD4(+)CD25(+) T cells from normal healthy donors (NDs) and HAM/TSP patients. We demonstrated that there is decreased demethylation in analyzed PBMCs and CD4(+)CD25(+) T cells from HAM/TSP patients as compared to NDs. Furthermore, decreased TSDR demethylation was associated with decreased functional suppression by Tregs. Additionally, increased HTLV-1 Tax expression in HAM/TSP PBMC culture correlated with a concomitant decline in FoxP3 TSDR demethylation. Overall, we suggest that HTLV-1 infection decreases Treg functional suppressive capacity in HAM/TSP through modification of FoxP3 TSDR demethylation and that dysregulated Treg function may contribute to HAM/TSP disease pathogenesis.

Epigenetic changes in inflammatory and autoimmune diseases

In higher eukaryotic organisms epigenetic modifications are crucial for proper chromatin folding and thereby proper regulation of gene expression. In the last years the involvement of aberrant epigenetic modifications in inflammatory and autoimmune diseases has been recognized and attracted significant interest. However, the epigenetic mechanisms underlying the different disease phenotypes are still poorly understood. As autoimmune and inflammatory diseases are at least partly T cell mediated, we will provide in this chapter an introduction to the epigenetics of T cell differentiation followed by a summary of the current knowledge on aberrant epigenetic modifications that dysfunctional T cells display in various diseases such as type 1 diabetes, rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis, inflammatory bowel disease, and asthma.

The ubiquitin ligase Stub1 negatively modulates regulatory T cell suppressive activity by promoting degradation of the transcription factor Foxp3

Regulatory T (Treg) cells suppress inflammatory immune responses and autoimmunity caused by self-reactive T cells. The key Treg cell transcription factor Foxp3 is downregulated during inflammation to allow for the acquisition of effector T cell-like functions. Here, we demonstrate that stress signals elicited by proinflammatory cytokines and lipopolysaccharides lead to the degradation of Foxp3 through the action of the E3 ubiquitin ligase Stub1. Stub1 interacted with Foxp3 to promote its K48-linked polyubiquitination in an Hsp70-dependent manner. Knockdown of endogenous Stub1 or Hsp70 prevented Foxp3 degradation. Furthermore, the overexpression of Stub1 in Treg cells abrogated their ability to suppress inflammatory immune responses in vitro and in vivo and conferred a T-helper-1-cell-like phenotype. Our results demonstrate the critical role of the stress-activated Stub1-Hsp70 complex in promoting Treg cell inactivation, thus providing a potential therapeutic target for the intervention against autoimmune disease, infection, and cancer.

FOXP3 demethylation as a means of identifying quantitative defects in regulatory T cells in acute coronary syndrome

OBJECTIVE

The contribution of regulatory T cells (Tregs) to the pathogenesis of acute coronary syndrome (ACS) remains poorly understood. One core obstacle is the lack of Treg-specific markers. A highly conserved CpG enriched element in forkhead box P3 intron 1 (FOXP3 i l) is unmethylated only in Tregs, and measuring the unmethylation of FOXP3 i l can be used to identify the role of Tregs in clinical diseases. This study investigated whether analyzing the demethylation status of FOXP3 i 1 is a more reliable means than using Treg-specific surface markers in ACS.

METHODS AND RESULTS

We evaluated circulating Tregs percentages on different levels including cell frequencies (CD4(+)CD25(hi)FOXP3(+)Tregs and CD4(+)CD25(hi)CD45(+)naïve Tregs) or FOXP3 mRNA, FOXP3 i 1 demethylation status and related cytokine secretion in 89 patients with ACS and 35 controls. FOXP3 i 1 demethylation assay showed that the amount of Tregs in ACS patients was significantly reduced than that in controls (p = 0.0005). However, flow cytometry analysis did not identify any reduction of CD4(+)CD25(hi)FOXP3(+)Tregs in ACS patients. Notably, younger patients had higher percentage of CD4(+)CD25(hi)FOXP3(+)Tregs but decreased percentage of CD4(+)CD25(hi)CD45(+)naïve Tregs than either controls or older patients. Furthermore, a DNA hypomethylation agent increased the amount of CD4(+)CD25(hi)FOXP3(+)Tregs and Tregs related cytokine IL-10 and suppressed the production of pro-inflammatory cytokine interferon-γ by inducing FOXP3 i 1 demethylation in vitro.

CONCLUSIONS

A quantitative defect of Tregs, suggestive of decreased peripheral tolerance, could be a potential hallmark of ACS disease. Targeting FOXP3 i l demethylation might elevate the inhibitory activity of Tregs in ACS.

Cell penetrating recombinant Foxp3 protein enhances Treg function and ameliorates arthritis

Foxp3 is the master transcription factor for T regulatory (Treg) cell differentiation and function. This study aimed to test the therapeutic potential of cell penetrating recombinant Foxp3 protein in arthritis. Recombinant Foxp3 protein was fused to a cell penetrating polyarginine (Foxp3-11R) tag to facilitate intracellular transduction. In vitro Foxp3-11R treated CD4(+) T cells showed a 50% increase in suppressive function compared with control protein treated cells. Severity of arthritis in Foxp3-11R treated mice was significantly reduced compared with those treated with a control protein. CD4(+) T cells of lymph nodes and spleen from Foxp3-11R treated mice showed increased levels of Foxp3 expression compared with those of a control protein treated. These results demonstrated that Foxp3-11R can enhance T cell suppressive function and ameliorate experimental arthritis and suggest that cell penetrating recombinant Foxp3 is a potentially useful agent in therapy of arthritis.

DNA methylation impairs TLR9 induced Foxp3 expression by attenuating IRF-7 binding activity in fulminant type 1 diabetes

Fulminant type 1 diabetes (FT1D) is an extremely aggressive disease characterized by the abrupt onset of insulin-deficient hyperglycemia. However, the precise mechanisms underlying disease etiology almost remain unclear. As mice deficient in regulatory T cells (Tregs) are prone to the development of an FT1D-like phenotype, we thus investigated whether FT1D patients manifest Treg deficiency and explored the related mechanisms. We first noted a significant reduction for Foxp3 and CTLA4 expression levels in PBMCs of FT1D patients. IRF-7 was found to selectively bind to the Foxp3 promoter, and by which it promotes Foxp3 transcription. Therefore, ectopic IRF-7 expression significantly promoted Foxp3 and CTLA4 expression in PBMCs, while knockdown of IRF-7 manifested opposite effect. Importantly, stimulation of PBMCs with CpG ODN, a ligand for TLR9, significantly induced Foxp3 expression, demonstrating that TLR9 signaling positively regulates Treg development. However, knockdown of IRF-7 expression almost completely diminished the enhancing effect of TLR9 signaling on Foxp3 expression, suggesting that IRF-7 is a downstream molecule of TLR9 signaling and is essential for TLR9 induced Treg generation. Of interestingly note, the Foxp3 promoter in FT1D patients was hypermethylated, indicating that DNA methylation could be a causative factor responsible for the reduced Foxp3 expression in FT1D patients. Indeed, our mechanistic studies revealed that DNA methylation blocked IRF-7 binding to the Foxp3 promoter. Together, our data support the notion that environmental insults in genetic predisposed subjects trigger Foxp3 promoter hypermethylation, which then prevents IRF-7 binding to the Foxp3 promoter and impairs Treg development/functionality contributing to the pathogenesis of FT1D.

Targeting regulatory T cells in the treatment of type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM) is a T cell-mediated autoimmune disease resulting in islet β cell destruction, hypoinsulinemia, and severely altered glucose homeostasis. T1DM has classically been attributed to the pathogenic actions of auto-reactive effector T cells(Teffs) on the β cell. Recent literature now suggests that a failure of a second T cell subtype, known as regulatory T cells (Tregs), plays a critical role in the development of T1DM. During immune homeostasis, Tregs counterbalance the actions of autoreactive Teff cells, thereby participating in peripheral tolerance. An imbalance in the activity between Teff and Tregs may be crucial in the breakdown of peripheral tolerance, leading to the development of T1DM. In this review, we summarize our current understanding of Treg function in health and in T1DM, and examine the effect of experimental therapies for T1DM on Treg cell number and function in both mice and humans.

The DNA methylation inhibitor 5-azacytidine increases regulatory T cells and alleviates airway inflammation in ovalbumin-sensitized mice

BACKGROUND

Asthma is characterized as a chronic inflammatory disorder of the airways associated with an enhanced TH2 response to inhaled allergens. CD4+ T regulatory (Treg) cells are controlled by the master transcription factor FoxP3 and strictly maintain peripheral immunotolerance. Epigenetic regulation of FoxP3 by DNA methyltransferase inhibitors, such as 5-azacytidine (Aza), can generate a steady supply of functional Treg cells. Therefore, we propose that Aza can augment Treg cells in vivo to prevent the pathogenesis of asthma.

METHODS

BALB/c mice were sensitized with chicken ovalbumin (OVA) and treated with different doses of Aza. Airway hyperresponsiveness to methacholine, eosinophilia in bronchoalveolar lavage fluid, circulating titers of OVA-specific IgG1 and IgE, and stimulating levels of TH2 cytokines from splenocytes were then determined. Cellular populations were examined by flow cytometry. PC61 antibody, which depletes CD25+ cells, was used to verify the role of CD25+ cells in Aza-induced tolerance.

RESULTS

Administration of Aza to OVA-sensitized mice diminished airway hyperreactivity, pulmonary eosinophilia, levels of OVA-specific IgG1 and IgE in serum, and secretion of TH2 cytokines from OVA-stimulated splenocytes in a dose-dependent manner. Percentages of CD25+ and FoxP3+ cells in the CD4+ cell population were notably increased in Aza-treated mice compared to sensitized control mice. Furthermore, the major symptoms of asthma were exacerbated by depleting CD25+ cells in Aza-treated mice.

CONCLUSIONS

Aza may have applications as a novel clinical strategy to increase the production of Treg cells in order to modulate the airway inflammation associated with asthma.

T cell signaling targets for enhancing regulatory or effector function

To respond to infection, resting or naïve T cells must undergo activation, clonal expansion, and differentiation into specialized functional subsets of effector T cells. However, to prevent excessive or self-destructive immune responses, regulatory T cells (T(regs)) are instrumental in suppressing the activation and function of effector cells, including effector T cells. The transcription factor Forkhead box P3 (Foxp3) regulates the expression of genes involved in the development and function of T(regs). Foxp3 interacts with other transcription factors and with epigenetic elements such as histone deacetylases (HDACs) and histone acetyltransferases. T(reg) suppressive function can be increased by exposure to HDAC inhibitors. The individual contributions of different HDAC family members to T(reg) function and their respective mechanisms of action, however, remain unclear. A study showed that HDAC6, HDAC9, and Sirtuin-1 had distinct effects on Foxp3 expression and function, suggesting that selectively targeting HDACs individually or in combination may enhance T(reg) stability and suppressive function. Another study showed that the receptor programmed death 1 (PD-1), a well-known inhibitor of T cell activation, halted cell cycle progression in effector T cells by inhibiting the transcription of the gene encoding the substrate-recognition component (Skp2) of the ubiquitin ligase SCF(Skp2). Together, these findings reveal new signaling targets for enhancing T(reg) or effector T cell function that may be helpful in designing future therapies, either to increase T(reg) suppressive function in transplantation and autoimmune diseases or to block PD-1 function, thus increasing the magnitude of antiviral or antitumor immune responses of effector T cells.

Immunosuppressive drugs on inducing Ag-specific CD4(+)CD25(+)Foxp3(+) Treg cells during immune response in vivo

A variety of immunosuppressive drugs are currently used in patients with allo-grafts or autoimmune diseases. Though the effects of rapamycin (RPM) and other immunosuppressant on the CD4(+)CD25(+)Foxp3(+) T regulatory cells (Tregs) were studied, their impact on Ag-specific Tregs during immune response was not well defined. In our studies, we adoptively transferred TCR-transgenic CD4(+)KJ1-26(+) T cells, CD4(+)KJ1-26(+)CD25(-) naïve T cells or CD4(+)KJ1-26(+)CD25(+) Tregs into syngeneic BALB/c mice. 24h later, we treated the recipients with OVA immunization and immunosuppressant including rapamycin (RPM), fingolimod (FTY720), cyclosporin A (CsA), mycophenolate mofetil (MMF), leflunomide (LEF), cyclophosphamide (Cy) or none, respectively. The levels and function of CD4(+)KJ1-26(+)CD25(+)Foxp3(+) Tregs in draining lymph nodes (dLNs) and spleens were determined at different time points. Significantly higher percentage and cell number of Ag-specific CD4(+)KJ1-26(+)CD25(+)Foxp3(+) Tregs were observed in OVA immunized mice treated with RPM or FTY720 compared with mice that received OVA immunization alone. Furthermore, RPM augmented the population of functional iTregs in dLNs and spleens whereas inhibited nTregs during immune response. In contrast to RPM and FTY720, MMF, LEF, CsA, and Cy markedly decreased the levels of Ag-specific CD4(+)KJ1-26(+)CD25(+)Foxp3(+) Tregs during immune response. Thus, different immunosuppressive drugs have distinct effects on the Ag-specific CD4(+)CD25(+)Foxp3(+) Tregs during immune response. The stronger inhibiting effects of MMF, LEF, CsA and Cy on CD4(+)CD25(+)Foxp3(+) Tregs than on T effectors may block the host immune tolerance potentiality.

Total glucosides of paeony induces regulatory CD4(+)CD25(+) T cells by increasing Foxp3 demethylation in lupus CD4(+) T cells

Total glucosides of paeony (TGP), an active compound extracted from Paeony root, has been used in therapy for autoimmune diseases. However the molecular mechanism of TGP in the prevention of autoimmune response remains unclear. In this study, we found that TGP treatment significantly increased the percentage and number of Treg cells in lupus CD4(+) T cells. Further investigation revealed that treatment with TGP increased the expression of Foxp3 in lupus CD4(+) T cells by down-regulating Foxp3 promoter methylation levels. However, we couldn't observe similar results in healthy control CD4(+) T cells treated by TGP. Moreover, our results also showed that IFN-γ and IL-2 expression was enhanced in TGP-treated lupus CD4(+) T cells. These findings indicate that TGP inhibits autoimmunity in SLE patients possibly by inducing Treg cell differentiation, which may in turn be due to its ability to regulate the methylation status of the Foxp3 promoter and activate IFN-γ and IL-2 signaling.

DNA methylation of TH1/TH2 cytokine genes affects sensitization and progress of experimental asthma

BACKGROUND

Epigenetic changes in DNA methylation have recently been demonstrated to be involved in effector T-cell polarization, resulting in differential secretion of T(H)1 and T(H)2 cytokines. However, the contribution to the development of a chronic inflammatory phenotype remains still unclear.

OBJECTIVE

We sought to investigate changes in DNA methylation in marker genes of T-cell subsets during allergen sensitization/challenge and their influence on the development of an allergic airway inflammatory response.

METHODS

The relationship between changes in DNA methylation and phenotype development were examined in a well-established model of experimental asthma. DNA methylation was investigated at genomic loci associated with T(H)1 (IFNG promoter) or T(H)2 (conserved noncoding sequence 1 [CNS1]) cytokine production by using bisulfite pyrosequencing.

RESULTS

Analysis of CD4(+) T cells revealed a significant increase in DNA methylation at the IFNG promoter after allergen sensitization/challenge, which correlated with decreased IFN-γ cytokine expression, whereas only minor changes were observed at the CNS1 locus. Furthermore, the increase in DNA methylation at the IFNG promoter could be reversed with a DNA methyltransferase (DNMT) inhibitor in vitro and in vivo with beneficial effects on sensitization status and allergic phenotype. The specific importance of the DNA methylation status in CD4(+) T cells could be confirmed by using adoptive transfer experiments.

CONCLUSION

We here report the novel finding that epigenetic regulation in T cells contributes to the development of experimental asthma and can be targeted pharmacologically.

IL-21 is an antitolerogenic cytokine of the late-phase alloimmune response

OBJECTIVE

Interleukin-21 (IL-21) is a proinflammatory cytokine that has been shown to affect Treg/Teff balance. However, the mechanism by which IL-21 orchestrates alloimmune response and interplays with Tregs is still unclear.

RESEARCH DESIGN AND METHODS

The interplay between IL-21/IL-21R signaling, FoxP3 expression, and Treg survival and function was evaluated in vitro in immunologically relevant assays and in vivo in allogenic and autoimmune models of islet transplantation.

RESULTS

IL-21R expression decreases on T cells and B cells in vitro and increases in the graft in vivo, while IL-21 levels increase in vitro and in vivo during anti-CD3/anti-CD28 stimulation/allostimulation in the late phase of the alloimmune response. In vitro, IL-21/IL-21R signaling (by using rmIL-21 or genetically modified CD4(+) T cells [IL-21 pOrf plasmid-treated or hIL-21-Tg mice]) enhances the T-cell response during anti-CD3/anti-CD28 stimulation/allostimulation, prevents Treg generation, inhibits Treg function, induces Treg apoptosis, and reduces FoxP3 and FoxP3-dependent gene transcripts without affecting FoxP3 methylation status. In vivo targeting of IL-21/IL-21R expands intragraft and peripheral Tregs, promotes Treg neogenesis, and regulates the antidonor immune response, whereas IL-21/IL-21R signaling in Doxa-inducible ROSA-rtTA-IL-21-Tg mice expands Teffs and FoxP3(-) cells. Treatment with a combination of mIL-21R.Fc and CTLA4-Ig (an inhibitor of the early alloimmune response) leads to robust graft tolerance in a purely alloimmune setting and prolonged islet graft survival in NOD mice.

CONCLUSIONS

IL-21 interferes with different checkpoints of the FoxP3 Treg chain in the late phase of alloimmune response and, thus, acts as an antitolerogenic cytokine. Blockade of the IL-21/IL-21R pathway could be a precondition for tolerogenic protocols in transplantation.

Abnormal DNA methylation in CD4+ T cells from people with latent autoimmune diabetes in adults

Aberrant DNA methylation in T cells has been linked to pathogenesis of autoimmune diseases. To investigate genomic and gene-specific DNA methylation levels in CD4(+) T cells from patients with latent autoimmune diabetes in adults (LADA), and to investigate changes in the expression of genes that regulate methylation as well as the autoimmune-related gene FOXP3 in these patients. Global CD4(+) T cell DNA methylation was measured in 15 LADA patients and 11 healthy controls using a methylation quantification kit. mRNA levels of DNA methytransferases (DNMTs), methyl-DNA binding domain proteins (MBDs) and FOXP3 were measured by real time PCR. Methylation of a FOXP3 regulatory element region was determined by bisulphite genomic sequencing. Genomic DNA methylation in CD4(+) T cells from LADA patients was significantly increased compared to controls. DNMT3b mRNA levels were higher in CD4(+) T cells from LADA patients than in controls. DNMT3b expression positively correlated with global DNA methylation in LADA CD4(+) T cells. FOXP3 expression was decreased, and the FOXP3 promoter region was hypermethylated in CD4(+) T cells from LADA patients compared with controls. DNA methylation levels are altered in CD4(+) T cells from LADA patients, which may contribute to disease onset and progression by affecting the expression of autoimmune-related genes.

The nuclear orphan receptor Nr4a2 induces Foxp3 and regulates differentiation of CD4+ T cells

Regulatory T cells (Tregs) have a central role in maintaining immune homoeostasis through various mechanisms. Although the Forkhead transcription factor Foxp3 defines the Treg cell lineage and functions, the molecular mechanisms of Foxp3 induction and maintenance remain elusive. Here we show that Foxp3 is one of the direct targets of Nr4a2. Nr4a2 binds to regulatory regions of Foxp3, where it mediates permissive histone modifications. Ectopic expression of Nr4a2 imparts Treg-like suppressive activity to naïve CD4⁺ T cells by inducing Foxp3 and by repressing cytokine production, including interferon-γ and interleukin-2. Deletion of Nr4a2 in T cells attenuates induction of Tregs and causes aberrant induction of Th1, leading to the exacerbation of colitis. Nr4a2-deficeint Tregs are prone to lose Foxp3 expression and have attenuated suppressive ability both in vitro and in vivo. Thus, Nr4a2 has the ability to maintain T-cell homoeostasis by regulating induction, maintenance and suppressor functions of Tregs, and by repression of aberrant Th1 induction.

Regulatory T cells are characterized by the expression of Foxp3, however, how the expression of this protein is controlled is unclear. Here, the authors show that the nuclear orphan receptor, Nr4a2, is a transcriptional activator of Foxp3, and suggest that it is required for the function of regulatory T cells.

Plasticity of human Th17 cells and iTregs is orchestrated by different subsets of myeloid cells

CD4+ T helper cell differentiation is essential for mounting robust immune responses without compromising unresponsiveness toward self-tissue. Here, we show that different subsets of myeloid cells isolated from human peripheral blood modulate TGF-β-dependent CD4+ T-cell developmental programs ex vivo. Human CD14+HLA-DR(-/low) myeloid-derived suppressor cells (MDSCs) induce Foxp3+ regulatory T cells, whereas CD14+HLA-DR+ monocytes promote generation of IL-17-secreting RORc+ Th17 cells when cocultured with naive CD4+ T cells. More importantly, not only do these 2 subsets modulate the de novo induction of Tregs and Th17 cells from CD4+ T cells, but MDSCs also catalyze the transdifferentiation of Foxp3+ regulatory T cells from monocyte-induced Th17 cells. The mechanism of such Th17 plasticity is dependent on MDSC-derived TGF-β and retinoic acid. Our results identify a previously unknown feature of the different subsets of CD14+ myeloid cells namely their pivotal role in immune response regulation and plasticity of CD4+ T helper cells. We propose that different subsets of myeloid cells in humans can orchestrate the differentiation of naive CD4+ T cells into effector/regulatory T-cell subsets. The balance between these 2 subsets can impact the outcome of immune reaction from inflammation to tolerance.

The dual role of the X-linked FoxP3 gene in human cancers

The FoxP3 (forkhead box P3) gene is an X-linked gene that is submitted to inactivation. It is an essential transcription factor in CD4(+)CD25(+)FoxP3 regulatory T cells, which are therapeutic targets in disseminated cutaneous melanoma. Moreover, FoxP3 is an important tumor suppressor gene in carcinomas and has putative cancer suppressor gene function in cutaneous melanoma as well. Therefore understanding the structure and function of the FoxP3 gene is crucial to gaining insight into the biology of melanoma to better develop immunotherapeutics and future therapeutic strategies.