Novel Foxo1-dependent transcriptional programs control T(reg) cell function

Immunometabolism of regulatory T cells

The bidirectional interaction between the immune system and whole-body metabolism has been well recognized for many years. Via effects on adipocytes and hepatocytes, immune cells can modulate whole-body metabolism (in metabolic syndromes such as type 2 diabetes and obesity) and, reciprocally, host nutrition and commensal-microbiota-derived metabolites modulate immunological homeostasis. Studies demonstrating the metabolic similarities of proliferating immune cells and cancer cells have helped give birth to the new field of immunometabolism, which focuses on how the cell-intrinsic metabolic properties of lymphocytes and macrophages can themselves dictate the fate and function of the cells and eventually shape an immune response. We focus on this aspect here, particularly as it relates to regulatory T cells.

Serum miR-146a, miR-155, and miR-210 as potential markers of Graves' disease

BACKGROUND

Previous studies have demonstrated that dysfunctional regulatory T cells (Tregs) may be associated with Graves' disease (GD). In this study, we evaluated four serum Treg-associated miRNAs (miR-210, miR-182, miR-155, and miR-146a) expressions and assessed the potential of serum miRNAs as biomarkers of GD.

METHODS

Foxp3 and serum miRNAs expressions both in GD patients and healthy controls were measured by RT-PCR.

RESULTS

Serum miR-210 in GD patients was significantly higher than that of healthy controls (2.64-fold, P<.001); in contrast, miR-155 and miR-146a were lower (P<.001 and P=.008). No significant difference was found in miR-182. ROC curve analysis indicated that miR-210, miR-155, and miR-146a with the area under ROC (AUC) of 0.803 (70.0% sensitivity and 83.1% specificity), 0.796 (76.3% sensitivity and 76.9% specificity), and 0.736 (68.8% sensitivity and 73.8% specificity), respectively, could differentiate GD patients from healthy controls. Combination of three miRNAs yielded an AUC of 0.976 (91.3% sensitivity and 93.8% specificity) with 92.41% diagnostic efficiency. In addition, serum miR-210 and miR-155 in GD were associated with the extent of goiter. Three miRNAs levels were different by gender. Besides, serum miR-210 was positively correlated with free thyroxine (FT4) and thyrotrophin receptor antibody (TRAb) level.

CONCLUSION

The serum levels of miR-210, miR-155, and miR-146a may be potential new markers for the diagnosis of GD and play important roles in GD pathogenesis.

Molecular Signatures of Human Regulatory T Cells in Colorectal Cancer and Polyps

Regulatory T cells (Tregs), a subset of CD4⁺ or CD8⁺ T cells, play a pivotal role in regulating immune homeostasis. An increase in Tregs was reported in many tumors to be associated with immune suppression and evasion in cancer patients. Despite the importance of Tregs, the molecular signatures that contributed to their pathophysiological relevance remain poorly understood and controversial. In this study, we explored the gene expression profiles in Tregs derived from patients with colorectal cancer [colorectal carcinoma (CRC), n = 15], colorectal polyps (P, n = 15), and in healthy volunteers (N, n = 15). Tregs were analyzed using CD4⁺CD25⁺CD127^lowFoxP3⁺ antibody markers. Gene expression profiling analysis leads to the identification of 61 and 66 immune-related genes in Tregs derived from CRC and P patients, respectively, but not in N-derived Treg samples. Of these, 30 genes were differentially expressed both in CRC- and P-derived Tregs when compared to N-derived Tregs. Most of the identified genes were involved in cytokine/chemokine mediators of inflammation, chemokine receptor, lymphocyte activation, and T cell receptor (TCR) signaling pathways. This study highlights some of the molecular signatures that may affect Tregs’ expansion and possible suppression of function in cancer development. Our findings may provide a better understanding of the immunomodulatory nature of Tregs and could, therefore, open up new avenues in immunotherapy.

Viral RNA-Unprimed Rig-I Restrains Stat3 Activation in the Modulation of Regulatory T Cell/Th17 Cell Balance

Innate immunity activation by viral RNA-primed retinoid acid inducible gene-I (Rig-I) in CD4⁺ T cells antagonizes TGFβ signaling to suppress the differentiation of regulatory T cells (Tregs). However, how viral RNA-unliganded Rig-I (apo-Rig-I) modulates Treg generation remains unclear. In this article, we show that, in the absence of viral infection, Treg differentiation of Rig-I^-/- CD4⁺ T cells was compromised, in the presence of increased generation of Th17 cells and overactivation of Stat3, a critical regulator tilting the Treg/Th17 cell balance. Mechanistically, apo-Rig-I physically associates with Stat3, thereby inhibiting Jak1's association with Stat3 while facilitating Shp2's association to inhibit p-Stat3 levels. Interestingly, inhibition of Stat3 ameliorates the Treg/Th17 imbalance and the colitis observed in Rig-I^-/- mice. Collectively, these results uncover an independent functional contribution of the apo-Rig-I/Stat3 interaction in the maintenance of Treg/Th17 cell balance.

PKB/Akt-dependent regulation of inflammation in cancer

Chronic inflammation is a major cause of human cancer. Clinical cancer therapies against inflammatory risk factors are strategically determined. To rationally guide a novel drug development, an improved mechanistic understanding on the pathological connection between inflammation and carcinogenesis is essential. PI3K-PKB signaling axis has been extensively studied and shown to be one of the key oncogenic drivers in most types of cancer. Pharmacological inhibition of the components along this signaling axis is of great interest for developing novel therapies. Interestingly, emerging studies have shown a close association between PKB activation and inflammatory activity in the vicinity of the tumor, and either blockade of PKB or attenuation of para-tumoral inflammation reveals a mutual-interactive pattern through pathway crosstalk. In this review, we intend to discuss recent advances of PKB-regulated chronic inflammation and its potential impacts on tumor development.

Forkhead-box transcription factor 1 affects the apoptosis of natural regulatory T cells by controlling Aven expression

Background

Regulatory T (Treg) cells play important roles in autoimmune diseases, cancer, and organ transplantation. Forkhead box protein o1 (Foxo1) and IL-7Rα(CD127) are closely related to the homeostasis of Treg cells. However, the mechanism underlying Treg proliferation and activation remains unclear. Here, we evaluated how the over-expression of Foxo1 affects Treg cell proliferation via intracellular signaling. nTreg cells were transfected separately with Foxo1 and Aven small-interfering RNA (siRNA) or over-expression plasmid. The expression of signaling pathway genes and CD127 was confirmed using RT-qPCR and western blot analysis. The expression of cell surface molecules and apoptosis was confirmed by Flow Cytometry 3-(4, 5-Dimethylthiazol-2-yl) 2,5- diphenyltetrazolium bromide for cell proliferation assays.

Results

Foxo1 strengthened the proliferative ability of Treg cells by activating IL-7/CD127 signaling. In addition, Foxo1 suppressed Treg cell apoptosis by regulating Aven expression.

Conclusions

The results in this study indicated that Foxo1 is a positive regulatory factor for the proliferation and activity of Treg cells. Foxo1 might be a potential target for the activation of nTreg cells in vivo and in vitro.

Ex vivo modulation of the Foxo1 phosphorylation state does not lead to dysfunction of T regulatory cells

Peripheral regulatory CD4+ T cells (Treg cells) prevent maladaptive inflammatory responses to innocuous foreign antigens. Treg cell dysfunction has been linked to many inflammatory diseases, including allergic airway inflammation. Glucocorticoids that are used to treat allergic airway inflammation and asthma are thought to work in part by promoting Treg cell differentiation; patients who are refractory to these drugs have defective induction of anti-inflammatory Treg cells. Previous observations suggest that Treg cells deficient in the transcription factor FoxO1 are pro-inflammatory, and that FoxO1 activity is regulated by its phosphorylation status and nuclear localization. Here, we asked whether altering the phosphorylation state of FoxO1 through modulation of a regulatory phosphatase might affect Treg cell function. In a mouse model of house dust mite-induced allergic airway inflammation, we observed robust recruitment of Treg cells to the lungs and lymph nodes of diseased mice, without an apparent increase in the Treg cytokine interleukin-10 in the airways. Intriguingly, expression of PP2A, a serine/threonine phosphatase linked to the regulation of FoxO1 phosphorylation, was decreased in the mediastinal lymph nodes of HDM-treated mice, mirroring the decreased PP2A expression seen in peripheral blood monocytes of glucocorticoid-resistant asthmatic patients. When we asked whether modulation of PP2A activity alters Treg cell function via treatment with the PP2A inhibitor okadaic acid, we observed increased phosphorylation of FoxO1 and decreased nuclear localization. However, dysregulation of FoxO1 did not impair Treg cell differentiation ex vivo or cause Treg cells to adopt a pro-inflammatory phenotype. Moreover, inhibition of PP2A activity did not affect the suppressive function of Treg cells ex vivo. Collectively, these data suggest that modulation of the phosphorylation state of FoxO1 via PP2A inhibition does not modify Treg cell function ex vivo. Our data also highlight the caveat in using ex vivo assays of Treg cell differentiation and function, in that while these assays are useful, they may not fully recapitulate Treg cell phenotypes that are observed in vivo.

PTEN at the interface of immune tolerance and tumor suppression

BACKGROUND

PTEN is well known to function as a tumor suppressor that antagonizes oncogenic signaling and maintains genomic stability. The PTEN gene is frequently deleted or mutated in human cancers and the wide cancer spectrum associated with PTEN deficiency has been recapitulated in a variety of mouse models of Pten deletion or mutation. Pten mutations are highly penetrant in causing various types of spontaneous tumors that often exhibit resistance to anticancer therapies including immunotherapy. Recent studies demonstrate that PTEN also regulates immune functionality.

OBJECTIVE

To understand the multifaceted functions of PTEN as both a tumor suppressor and an immune regulator.

METHODS

This review will summarize the emerging knowledge of PTEN function in cancer immunoediting. In addition, the mechanisms underlying functional integration of various PTEN pathways in regulating cancer evolution and tumor immunity will be highlighted.

RESULTS

Recent preclinical and clinical studies revealed the essential role of PTEN in maintaining immune homeostasis, which significantly expands the repertoire of PTEN functions. Mechanistically, aberrant PTEN signaling alters the interplay between the immune system and tumors, leading to immunosuppression and tumor escape.

CONCLUSION

Rational design of personalized anti-cancer treatment requires mechanistic understanding of diverse PTEN signaling pathways in modulation of the crosstalk between tumor and immune cells.

Treg-Centric View of Immunosuppressive Drugs in Transplantation: A Balancing Act

Regulatory CD4+ Foxp3+ T cells (Tregs) are critical in controlling immunity and tolerance. Thus, preserving Treg numbers and function in transplanted patients is essential for the successful minimization of maintenance immunosuppression. Multiple cellular signals control the development, differentiation, and function of Tregs. Many of these signals are shared with conventional Foxp3^- T cells (Tconv) and are targeted by immunosuppressive drugs, negatively affecting both Tregs and Tconv. Because intracellular signals vary in optimal intensity in different T cell subsets, improved specificity in immunosuppressive regimens must occur to benefit long-term transplant outcomes. In this regard, recent advances are gradually uncovering differences in the signals required in Tregs and Tconv biology, opening the door to new potential therapeutic approaches to either enhance or spare Tregs. In this review, we will explain the prominent cell signaling pathways critical for Treg maintenance and function, while reporting the effects of immunosuppressive drugs targeting these signaling pathways in clinical transplantation settings.

miR-16 controls myoblast proliferation and apoptosis through directly suppressing Bcl2 and FOXO1 activities

Myogenesis mainly involves several steps including myoblast proliferation, differentiation, apoptosis and fusion. Except for muscle specific regulators, few miRNAs were proved to coordinate this complex process. Here, we reported that miR-16 inhibited myoblast proliferation and promoted myoblast apoptosis by directly targeting Bcl2 and FOXO1. The expression level of miR-16 was significantly decreased in the hypertrophic pectoral muscle compared to the normal pectoral muscle in chicken. In vitro, elevating miR-16 significantly inhibited myoblast proliferation and promoted myoblast apoptosis, resulting in about 11.2% cells arrested in G1 phase and 12.3% apoptotic cells in the early stage. Bioinformatic and biochemical analyses revealed Bcl2 and FOXO1 as direct targets of miR-16. Consist to the effect of miR-16 on myogenesis, specific inhibition of Bcl2 or FOXO1 significantly suppressed myoblast proliferation and induced myoblast apoptosis, indicating that both Bcl2 and FOXO1 contributed to miR-16 regulatory function in myogenesis. Interestingly, FOXO1, as the core target, mediated multiple growth-related pathways induced by miR-16 such as PI3K-AKT-MAPK and PI3K-AKT-mTOR. Chromatin immunoprecipitation coupled with high-throughput sequencing (ChIP-seq) revealed that 234 annotated genes bound by FOXO1 in the early-differentiated myoblasts, which were significantly enriched in myogenic proliferation, death and hypotrophy. Altogether, we proposed that miR-16 acted as a coordinated mediator to suppress myogenesis in avian through the control of myoblast proliferation and apoptosis. These findings have provided a novel mechanism whereby miR-16 represses Bcl2 and FOXO1 expression to maintain myoblast growth and skeletal muscle mass.

The Potential of MicroRNAs as Novel Biomarkers for Transplant Rejection

The control of gene expression by microRNAs (miRNAs, miR) influences many cellular functions, including cellular differentiation, cell proliferation, cell development, and functional regulation of the immune system. Recently, miRNAs have been detected in serum, plasma, and urine and circulating miR profiles have been associated with a variety of diseases. Rejection is one of the major causes of allograft failure and preventing and treating acute rejection are the central task for clinicians working with transplant patients. Invasive biopsies used in monitoring rejection are burdensome and risky to transplant patients. Novel and easily accessible biomarkers of acute rejection could make it possible to detect rejection earlier and make more fine-tuned calibration of immunosuppressive or new target treatment possible. In this review, we discuss whether circulating miRNA can serve as an early noninvasive diagnostic biomarker and an expression fingerprint of allograft rejection and transplant failure. Understanding the regulatory interplay of relevant miRNAs and the rejecting allograft will result in a better understanding of the molecular pathophysiology of alloimmune injury.

Excessive expression of miR-27 impairs Treg-mediated immunological tolerance

MicroRNAs (miRs) are tightly regulated in the immune system, and aberrant expression of miRs often results in hematopoietic malignancies and autoimmune diseases. Previously, it was suggested that elevated levels of miR-27 in T cells isolated from patients with multiple sclerosis facilitate disease progression by inhibiting Th2 immunity and promoting pathogenic Th1 responses. Here we have demonstrated that, although mice with T cell-specific overexpression of miR-27 harbor dysregulated Th1 responses and develop autoimmune pathology, these disease phenotypes are not driven by miR-27 in effector T cells in a cell-autonomous manner. Rather, dysregulation of Th1 responses and autoimmunity resulted from a perturbed Treg compartment. Excessive miR-27 expression in murine T cells severely impaired Treg differentiation. Moreover, Tregs with exaggerated miR-27-mediated gene regulation exhibited diminished homeostasis and suppressor function in vivo. Mechanistically, we determined that miR-27 represses several known as well as previously uncharacterized targets that play critical roles in controlling multiple aspects of Treg biology. Collectively, our data show that miR-27 functions as a key regulator in Treg development and function and suggest that proper regulation of miR-27 is pivotal to safeguarding Treg-mediated immunological tolerance.

Regulatory T Cells: Molecular and Cellular Basis for Immunoregulation

CD4⁺ regulatory T cells (Tregs) are a highly immune-suppressive subset of CD4⁺ T cells, characterized by expression of the master regulatory transcription factor FOXP3. Tregs are proven to play central roles in the maintenance of self-tolerance in healthy individuals. Tregs are involved in maintaining immune homeostasis: they protect hosts from developing autoimmune diseases and allergy, whereas in malignancies, they promote tumor progression by suppressing anti-tumor immunity. Elucidating factors influencing Treg homeostasis and function have important implications for understanding disease pathogenesis and identifying therapeutic opportunities. Thus, the manipulating Tregs for up- or down-regulation of their suppressive function is a new therapeutic strategy for treating various diseases including autoimmune disorders and cancer. This review will focus on recent advances in how Tregs integrate extracellular and intracellular signals to control their survival and stability. Deeper mechanistic understanding of disease-specific Treg development, maintenance, and function could make disease-specific Treg-targeted therapy more effective, resulting in an increase of efficacy and decrease of side effects related to manipulating Tregs.

Neutrophils induce proangiogenic T cells with a regulatory phenotype in pregnancy

Although neutrophils are known to be fundamental in controlling innate immune responses, their role in regulating adaptive immunity is just starting to be appreciated. We report that human neutrophils exposed to pregnancy hormones progesterone and estriol promote the establishment of maternal tolerance through the induction of a population of CD4⁺ T cells displaying a GARP⁺CD127^loFOXP3⁺ phenotype following antigen activation. Neutrophil-induced T (niT) cells produce IL-10, IL-17, and VEGF and promote vessel growth in vitro. Neutrophil depletion during murine pregnancy leads to abnormal development of the fetal-maternal unit and reduced empbryo development, with placental architecture displaying poor trophoblast invasion and spiral artery development in the maternal decidua, accompanied by significantly attenuated niT cell numbers in draining lymph nodes. Using CD45 congenic cells, we show that induction of niT cells and their regulatory function occurs via transfer of apoptotic neutrophil-derived proteins, including forkhead box protein 1 (FOXO1), to T cells. Unlike in women with healthy pregnancies, neutrophils from blood and placental samples of preeclamptic women fail to induce niT cells as a direct consequence of their inability to transfer FOXO1 to T cells. Finally, neutrophil-selective FOXO1 knockdown leads to defective placentation and compromised embryo development, similar to that resulting from neutrophil depletion. These data define a nonredundant function of neutrophil-T cell interactions in the regulation of vascularization at the maternal-fetal interface.

PI3Kδ and primary immunodeficiencies

Primary immunodeficiencies are inherited disorders of the immune system, often caused by the mutation of genes required for lymphocyte development and activation. Recently, several studies have identified gain-of-function mutations in the phosphoinositide 3-kinase (PI3K) genes PIK3CD (which encodes p110δ) and PIK3R1 (which encodes p85α) that cause a combined immunodeficiency syndrome, referred to as activated PI3Kδ syndrome (APDS; also known as p110δ-activating mutation causing senescent T cells, lymphadenopathy and immunodeficiency (PASLI)). Paradoxically, both loss-of-function and gain-of-function mutations that affect these genes lead to immunosuppression, albeit via different mechanisms. Here, we review the roles of PI3Kδ in adaptive immunity, describe the clinical manifestations and mechanisms of disease in APDS and highlight new insights into PI3Kδ gleaned from these patients, as well as implications of these findings for clinical therapy.

Foxo3 Transcription Factor Drives Pathogenic T Helper 1 Differentiation by Inducing the Expression of Eomes

The transcription factor Foxo3 plays a crucial role in myeloid cell function but its role in lymphoid cells remains poorly defined. Here, we have shown that Foxo3 expression was increased after T cell receptor engagement and played a specific role in the polarization of CD4⁺ T cells toward pathogenic T helper 1 (Th1) cells producing interferon-γ (IFN-γ) and granulocyte monocyte colony stimulating factor (GM-CSF). Consequently, Foxo3-deficient mice exhibited reduced susceptibility to experimental autoimmune encephalomyelitis. At the molecular level, we identified Eomes as a direct target gene for Foxo3 in CD4⁺ T cells and we have shown that lentiviral-based overexpression of Eomes in Foxo3-deficient CD4⁺ T cells restored both IFN-γ and GM-CSF production. Thus, the Foxo3-Eomes pathway is central to achieve the complete specialized gene program required for pathogenic Th1 cell differentiation and development of neuroinflammation.

mTORC1 and mTORC2 Kinase Signaling and Glucose Metabolism Drive Follicular Helper T Cell Differentiation

Follicular helper T (Tfh) cells are crucial for germinal center (GC) formation and humoral adaptive immunity. Mechanisms underlying Tfh cell differentiation in peripheral and mucosal lymphoid organs are incompletely understood. We report here that mTOR kinase complexes 1 and 2 (mTORC1 and mTORC2) are essential for Tfh cell differentiation and GC reaction under steady state and after antigen immunization and viral infection. Loss of mTORC1 and mTORC2 in T cells exerted distinct effects on Tfh cell signature gene expression, whereas increased mTOR activity promoted Tfh responses. Deficiency of mTORC2 impaired CD4(+) T cell accumulation and immunoglobulin A production and aberrantly induced the transcription factor Foxo1. Mechanistically, the costimulatory molecule ICOS activated mTORC1 and mTORC2 to drive glycolysis and lipogenesis, and glucose transporter 1-mediated glucose metabolism promoted Tfh cell responses. Altogether, mTOR acts as a central node in Tfh cells by linking immune signals to anabolic metabolism and transcriptional activity.

CD101 inhibits the expansion of colitogenic T cells

CD101 exerts negative-costimulatory effects in vitro, but its function in vivo remains poorly defined. CD101 is abundantly expressed on lymphoid and myeloid cells in intestinal tissues, but absent from naïve splenic T cells. Here, we assessed the impact of CD101 on the course of inflammatory bowel disease (IBD). Using a T-cell transfer model of chronic colitis, we found that in recipients of naïve T cells from CD101(+/+) donors up to 30% of the recovered lymphocytes expressed CD101, correlating with an increased interleukin (IL)-2-mediated FoxP3 expression. Transfer of CD101(-/-) T cells caused more severe colitis and was associated with an expansion of IL-17-producing T cells and an enhanced expression of IL-2Rα/β independently of FoxP3. The co-transfer of naïve and regulatory T cells (Treg) protected most effectively from colitis, when both donor and recipient mice expressed CD101. Although the expression of CD101 on T cells was sufficient for Treg-function and the inhibition of T-cell proliferation, sustained IL-10 production required additional CD101 expression by myeloid cells. Finally, in patients with IBD a reduced CD101 expression on peripheral and intestinal monocytes and CD4(+) T cells correlated with enhanced IL-17 production and disease activity. Thus, CD101 deficiency is a novel marker for progressive colitis and potential target for therapeutic intervention.

Empowering Regulatory T Cells in Autoimmunity

Regulatory T cells (Tregs) are capable of dampening immune-mediated inflammation and avert the destructive effects of uncontrolled inflammation. Distinct molecules and pathways, including various transcription factors, phosphatases, and kinases, impact the ability of Tregs to function as negative regulators of the immune response, and are presumably amenable to therapeutic manipulation. Here, we discuss recently identified molecular networks and the therapeutic potential for treating autoimmune diseases.

T cell receptor signalling in the control of regulatory T cell differentiation and function

Regulatory T cells (TReg cells), a specialized T cell lineage, have a pivotal function in the control of self tolerance and inflammatory responses. Recent studies have revealed a discrete mode of T cell receptor (TCR) signalling that regulates TReg cell differentiation, maintenance and function and that affects gene expression, metabolism, cell adhesion and migration of these cells. Here, we discuss the emerging understanding of TCR-guided differentiation of TReg cells in the context of their function in health and disease.

Memory of Inflammation in Regulatory T Cells

Eukaryotic cells can "remember" transient encounters with a wide range of stimuli, inducing lasting states of altered responsiveness. Regulatory T (Treg) cells are a specialized lineage of suppressive CD4 T cells that act as critical negative regulators of inflammation in various biological contexts. Treg cells exposed to inflammatory conditions acquire strongly enhanced suppressive function. Using inducible genetic tracing, we analyzed the long-term stability of activation-induced transcriptional, epigenomic, and functional changes in Treg cells. We found that the inflammation-experienced Treg cell population reversed many activation-induced changes and lost its enhanced suppressive function over time. The "memory-less" potentiation of Treg suppressor function may help avoid a state of generalized immunosuppression that could otherwise result from repeated activation.

Characterization of the direct targets of FOXO transcription factors throughout evolution

FOXO transcription factors (FOXOs) are central regulators of lifespan across species, yet they also have cell‐specific functions, including adult stem cell homeostasis and immune function. Direct targets of FOXOs have been identified genome‐wide in several species and cell types. However, whether FOXO targets are specific to cell types and species or conserved across cell types and throughout evolution remains uncharacterized. Here, we perform a meta‐analysis of direct FOXO targets across tissues and organisms, using data from mammals as well as Caenorhabditis elegans and Drosophila. We show that FOXOs bind cell type‐specific targets, which have functions related to that particular cell. Interestingly, FOXOs also share targets across different tissues in mammals, and the function and even the identity of these shared mammalian targets are conserved in invertebrates. Evolutionarily conserved targets show enrichment for growth factor signaling, metabolism, stress resistance, and proteostasis, suggesting an ancestral, conserved role in the regulation of these processes. We also identify candidate cofactors at conserved FOXO targets that change in expression with age, including CREB and ETS family factors. This meta‐analysis provides insight into the evolution of the FOXO network and highlights downstream genes and cofactors that may be particularly important for FOXO's conserved function in adult homeostasis and longevity.

The E3 ligase Itch in immune regulation and beyond

Itch or itchy E3 ubiquitin ligase was initially discovered by genetic studies on the mouse coat color changes, and its deletion results in an itchy phenotype with constant skin scratching and multi-organ inflammation. It is a member of the homologous to E6-associated protein C-terminus (HECT)-type family of E3 ligases, with the protein-interacting WW-domains for the recruitment of substrate and the HECT domain for the transfer of ubiquitin to the substrate. Since its discovery, numerous studies have demonstrated that Itch is involved in the control of many aspects of immune responses including T-cell activation and tolerance and T-helper cell differentiation. Itch is also implicated in other biological contexts such as tumorigenesis, development, and stress responses. Many signaling pathways are regulated by Itch-promoted ubiquitylation of diverse target proteins. Itch is also involved in human diseases. Here, we discuss the major progress in understanding the biological significance of Itch-promoted protein ubiquitylation in the immune and other systems and in Itch-mediated regulation of signal transduction.

Immune dysregulation in patients with PTEN hamartoma tumor syndrome: Analysis of FOXP3 regulatory T cells

Background

Patients with heterozygous germline mutations in phosphatase and tensin homolog deleted on chromosome 10 (PTEN) experience autoimmunity and lymphoid hyperplasia.

Objectives

Because regulation of the phosphoinositide 3-kinase (PI3K) pathway is critical for maintaining regulatory T (Treg) cell functions, we investigate Treg cells in patients with heterozygous germline PTEN mutations (PTEN hamartoma tumor syndrome [PHTS]).

Methods

Patients with PHTS were assessed for immunologic conditions, lymphocyte subsets, forkhead box P3 (FOXP3)⁺ Treg cell levels, and phenotype. To determine the functional importance of phosphatases that control the PI3K pathway, we assessed Treg cell induction in vitro, mitochondrial depolarization, and recruitment of PTEN to the immunologic synapse.

Results

Autoimmunity and peripheral lymphoid hyperplasia were found in 43% of 79 patients with PHTS. Immune dysregulation in patients with PHTS included lymphopenia, CD4⁺ T-cell reduction, and changes in T- and B-cell subsets. Although total CD4⁺FOXP3⁺ Treg cell numbers are reduced, frequencies are maintained in the blood and intestine. Despite pathogenic PTEN mutations, the FOXP3⁺ T cells are phenotypically normal. We show that the phosphatase PH domain leucine-rich repeat protein phosphatase (PHLPP) downstream of PTEN is highly expressed in normal human Treg cells and provides complementary phosphatase activity. PHLPP is indispensable for the differentiation of induced Treg cells in vitro and Treg cell mitochondrial fitness. PTEN and PHLPP form a phosphatase network that is polarized at the immunologic synapse.

Conclusion

Heterozygous loss of function of PTEN in human subjects has a significant effect on T- and B-cell immunity. Assembly of the PTEN-PHLPP phosphatase network allows coordinated phosphatase activities at the site of T-cell receptor activation, which is important for limiting PI3K hyperactivation in Treg cells despite PTEN haploinsufficiency.

AKT isoforms modulate Th1-like Treg generation and function in human autoimmune disease

Foxp3(+) regulatory T cells (Tregs) exhibit plasticity, which dictates their function. Secretion of the inflammatory cytokine IFNγ, together with the acquisition of a T helper 1 (Th1)-like effector phenotype as observed in cancer, infection, and autoimmune diseases, is associated with loss of Treg suppressor function through an unknown mechanism. Here, we describe the signaling events driving the generation of human Th1-Tregs. Using a genome-wide gene expression approach and pathway analysis, we identify the PI3K/AKT/Foxo1/3 signaling cascade as the major pathway involved in IFNγ secretion by human Tregs. Furthermore, we describe the opposing roles of AKT isoforms in Th1-Treg generation ex vivo Finally, we employ multiple sclerosis as an in vivo model with increased but functionally defective Th1-Tregs. We show that the PI3K/AKT/Foxo1/3 pathway is activated in ex vivo-isolated Tregs from untreated relapsing-remitting MS patients and that blockade of the pathway inhibits IFNγ secretion and restores the immune suppressive function of Tregs. These data define a fundamental pathway regulating the function of human Tregs and suggest a novel treatment paradigm for autoimmune diseases.

The Nuclear Zinc Finger Protein Zfat Maintains FoxO1 Protein Levels in Peripheral T Cells by Regulating the Activities of Autophagy and the Akt Signaling Pathway

Forkhead box O1 (FoxO1) is a key molecule for the development and functions of peripheral T cells. However, the precise mechanisms regulating FoxO1 expression in peripheral T cells remain elusive. We previously reported that Zfat(f/f)-CD4Cre mice showed a marked decline in FoxO1 protein levels in peripheral T cells, partially through proteasomal degradation. Here we have identified the precise mechanisms, apart from proteasome-mediated degradation, of the decreased FoxO1 levels in Zfat-deficient T cells. First, we confirmed that tamoxifen-inducible deletion of Zfat in Zfat(f/f)-CreERT2 mice coincidently decreases FoxO1 protein levels in peripheral T cells, indicating that Zfat is essential for maintaining FoxO1 levels in these cells. Although the proteasome-specific inhibitors lactacystin and epoxomicin only moderately increase FoxO1 protein levels, the inhibitors of lysosomal proteolysis bafilomycin A1 and chloroquine restore the decreased FoxO1 levels in Zfat-deficient T cells to levels comparable with those in control cells. Furthermore, Zfat-deficient T cells show increased numbers of autophagosomes and decreased levels of p62 protein, together indicating that Zfat deficiency promotes lysosomal FoxO1 degradation through autophagy. In addition, Zfat deficiency increases the phosphorylation levels of Thr-308 and Ser-473 of Akt and the relative amounts of cytoplasmic to nuclear FoxO1 protein levels, indicating that Zfat deficiency causes Akt activation, leading to nuclear exclusion of FoxO1. Our findings have demonstrated a novel role of Zfat in maintaining FoxO1 protein levels in peripheral T cells by regulating the activities of autophagy and the Akt signaling pathway.

Milk: a postnatal imprinting system stabilizing FoxP3 expression and regulatory T cell differentiation

BACKGROUND

Breastfeeding has protective effects for the development of allergies and atopy. Recent evidence underlines that consumption of unboiled farm milk in early life is a key factor preventing the development of atopic diseases. Farm milk intake has been associated with increased demethylation of FOXP3 and increased numbers of regulatory T cells (Tregs). Thus, the questions arose which components of farm milk control the differentiation and function of Tregs, critical T cell subsets that promote tolerance induction and inhibit the development of allergy and autoimmunity.

FINDINGS

Based on translational research we identified at least six major signalling pathways that could explain milk's biological role controlling stable FoxP3 expression and Treg differentiation: (1) via maintaining appropriate magnitudes of Akt-mTORC1 signalling, (2) via transfer of milk fat-derived long-chain ω-3 fatty acids, (3) via transfer of milk-derived exosomal microRNAs that apparently decrease FOXP3 promoter methylation, (4) via transfer of exosomal transforming growth factor-β, which induces SMAD2/SMAD3-dependent FoxP3 expression, (5) via milk-derived Bifidobacterium and Lactobacillus species that induce interleukin-10 (IL-10)-mediated differentiation of Tregs, and (6) via milk-derived oligosaccharides that serve as selected nutrients for the growth of bifidobacteria in the intestine of the new born infant.

CONCLUSION

Accumulating evidence underlines that milk is a complex signalling and epigenetic imprinting network that promotes stable FoxP3 expression and long-lasting Treg differentiation, crucial postnatal events preventing atopic and autoimmune diseases.

PD-1 marks dysfunctional regulatory T cells in malignant gliomas

Immunotherapies targeting the immune checkpoint receptor programmed cell death protein 1 (PD-1) have shown remarkable efficacy in treating cancer. CD4⁺CD25^hiFoxP3⁺ Tregs are critical regulators of immune responses in autoimmunity and malignancies, but the functional status of human Tregs expressing PD-1 remains unclear. We examined functional and molecular features of PD-1^hi Tregs in healthy subjects and patients with glioblastoma multiforme (GBM), combining functional assays, RNA sequencing, and cytometry by time of flight (CyTOF). In both patients with GBM and healthy subjects, circulating PD-1^hi Tregs displayed reduced suppression of CD4⁺ effector T cells, production of IFN-γ, and molecular signatures of exhaustion. Transcriptional profiling of tumor-resident Tregs revealed that several genes coexpressed with PD-1 and associated with IFN-γ production and exhaustion as well as enrichment in exhaustion signatures compared with circulating PD-1^hi Tregs. CyTOF analysis of circulating and tumor-infiltrating Tregs from patients with GBM treated with PD-1-blocking antibodies revealed that treatment shifts the profile of circulating Tregs toward a more exhausted phenotype reminiscent of that of tumor-infiltrating Tregs, further increasing IFN-γ production. Thus, high PD-1 expression on human Tregs identifies dysfunctional, exhausted Tregs secreting IFN-γ that exist in healthy individuals and are enriched in tumor infiltrates, possibly losing function as they attempt to modulate the antitumoral immune responses.

FoxO1-mediated autophagy is required for NK cell development and innate immunity

Natural killer (NK) cells exert a crucial role in early immune responses as a major innate effector component. However, the underlying mechanisms of NK cell development remain largely elusive. Here we show that robust autophagy appears in the stage of immature NK cells (iNKs), which is required for NK cell development. Autophagy defects result in damaged mitochondria and accumulation of reactive oxygen species (ROS) that leads to apoptosis of NK cells. Autophagy protects NK cell viability during development through removal of damaged mitochondria and intracellular ROS. Phosphorylated Forkhead box O (FoxO)1 is located to the cytoplasm of iNKs and interacts with Atg7, leading to induction of autophagy. FoxO1 deficiency or an inactive FoxO1^AAA mutant abrogates autophagy initiation in iNKs and impairs NK cell development and viral clearance. Therefore we conclude that FoxO1-mediated autophagy is required for NK cell development and NK cell-induced innate immunity.

Natural killer cells are a major component of the innate immune response. Here, Wang et al. show that natural killer cell development requires robust activation of autophagy at the immature stage where it acts to remove damaged mitochondria and reduces levels of reactive oxygen species.

The CASTOR Proteins Are Arginine Sensors for the mTORC1 Pathway

Amino acids signal to the mTOR complex I (mTORC1) growth pathway through the Rag GTPases. Multiple distinct complexes regulate the Rags, including GATOR1, a GTPase activating protein (GAP), and GATOR2, a positive regulator of unknown molecular function. Arginine stimulation of cells activates mTORC1, but how it is sensed is not well understood. Recently, SLC38A9 was identified as a putative lysosomal arginine sensor required for arginine to activate mTORC1 but how arginine deprivation represses mTORC1 is unknown. Here, we show that CASTOR1, a previously uncharacterized protein, interacts with GATOR2 and is required for arginine deprivation to inhibit mTORC1. CASTOR1 homodimerizes and can also heterodimerize with the related protein, CASTOR2. Arginine disrupts the CASTOR1-GATOR2 complex by binding to CASTOR1 with a dissociation constant of ~30 μM, and its arginine-binding capacity is required for arginine to activate mTORC1 in cells. Collectively, these results establish CASTOR1 as an arginine sensor for the mTORC1 pathway.

Signaling in T cells - is anything the m(a)TOR with the picture(s)?

The excitement surrounding checkpoint inhibitors in the treatment of patients with cancer exemplifies a triumph of the long-term value of investing in basic science and fundamental questions of T-cell signaling. The pharmaceutical future actively embraces ways of making more patients’ cancers responsive to these inhibitors. Such a process will be aided by elucidation of signaling and regulation. With thousands of articles spread across almost 30 years, this commentary can touch only on portions of the canonical picture of T-cell signaling and provide a few parables from work on mammalian (or mechanistic) target of rapamycin (mTOR) pathways as they link to early and later phases of lymphocyte activation. The piece will turn a critical eye to some issues with models about these pathways in T cells. Many of the best insights lie in the future despite all that is uncovered already, but a contention is that further therapeutic successes will be fostered by dealing with disparities among findings and attention to the temporal, spatial, and stochastic aspects of T-cell responses. Finally, thoughts on some (though not all) items urgently needed for future progress will be mooted.

Harnessing the plasticity of CD4(+) T cells to treat immune-mediated disease

CD4(+) T cells differentiate and acquire distinct functions to combat specific pathogens but can also adapt their functions in response to changing circumstances. Although this phenotypic plasticity can be potentially deleterious, driving immune pathology, it also provides important benefits that have led to its evolutionary preservation. Here, we review CD4(+) T cell plasticity by examining the molecular mechanisms that regulate it - from the extracellular cues that initiate and drive cells towards varying phenotypes, to the cytosolic signalling cascades that decipher these cues and transmit them into the cell and to the nucleus, where these signals imprint specific gene expression programmes. By understanding how this functional flexibility is achieved, we may open doors to new therapeutic approaches that harness this property of T cells.

Potential role of circulating microRNAs as a biomarker for unexplained recurrent spontaneous abortion

OBJECTIVE

To compare circulating microRNA (miRNA) profiles between unexplained recurrent spontaneous abortion (URSA) and normal early pregnancies (NEP) and to evaluate the potential role of circulating miRNA as a biomarker for URSA.

DESIGN

Laboratory study using human plasma samples.

SETTING

Special hospital and research institutes.

PATIENT(S)

From September 2012 to April 2013, samples of plasma were obtained from 27 URSA patients and 28 NEP patients at 6-10 weeks of gestation at the Department of Reproductive Immunology in Family Planning Special Hospital of Guangdong Province.

INTERVENTION(S)

Differential miRNA profiling analysis of plasma collected from URSA and NEP patients was performed with the use of microarray.

MAIN OUTCOME MEASURE(S)

The circulating miRNA expression profile was assessed by means of microarray and real-time quantitative reverse-transcription polymerase chain reaction (qRT-PCR) analysis.

RESULT(S)

Twenty-five circulating miRNAs were expressed differentially in URSA compared with NEP. Of these, nine were overexpressed and 16 down-regulated. Six differentially expressed circulating miRNAs were selected to validate the microarray results, and qRT-PCR data confirmed the reliability of the microarray results. Further analysis showed that four circulating miRNAs (miR-320b, miR-146b-5p, miR-221-3p, miR-559) were up-regulated. In URSA, one circulating miRNA (miR-101-3p) was down-regulated in other larger scale samples according to qRT-PCR. Based on target gene analysis, we speculate that these circulating miRNAs regulate URSA by targeting immune, apoptosis, and angiogenic gene functions.

CONCLUSION(S)

Circulating microRNAs may be involved in URSA pathogenesis and provide a promising new diagnostic biomarker for URSA.

Graded Foxo1 activity in Treg cells differentiates tumour immunity from spontaneous autoimmunity

Regulatory T (Treg) cells expressing the transcription factor Foxp3 have a pivotal role in maintaining immunological self-tolerance; yet, excessive Treg cell activities suppress anti-tumour immune responses. Compared to the resting Treg (rTreg) cell phenotype in secondary lymphoid organs, Treg cells in non-lymphoid tissues exhibit an activated Treg (aTreg) cell phenotype. However, the function of aTreg cells and whether their generation can be manipulated are largely unexplored. Here we show that the transcription factor Foxo1, previously demonstrated to promote Treg cell suppression of lymphoproliferative diseases, has an unexpected function in inhibiting aTreg-cell-mediated immune tolerance in mice. We find that aTreg cells turned over at a slower rate than rTreg cells, but were not locally maintained in tissues. aTreg cell differentiation was associated with repression of Foxo1-dependent gene transcription, concomitant with reduced Foxo1 expression, cytoplasmic localization and enhanced phosphorylation at the Akt sites. Treg-cell-specific expression of an Akt-insensitive Foxo1 mutant prevented downregulation of lymphoid organ homing molecules, and impeded Treg cell homing to non-lymphoid organs, causing CD8(+) T-cell-mediated autoimmune diseases. Compared to Treg cells from healthy tissues, tumour-infiltrating Treg cells downregulated Foxo1 target genes more substantially. Expression of the Foxo1 mutant at a lower dose was sufficient to deplete tumour-associated Treg cells, activate effector CD8(+) T cells, and inhibit tumour growth without inflicting autoimmunity. Thus, Foxo1 inactivation is essential for the migration of aTreg cells that have a crucial function in suppressing CD8(+) T-cell responses; and the Foxo signalling pathway in Treg cells can be titrated to break tumour immune tolerance preferentially.

HDAC5 controls the functions of Foxp3(+) T-regulatory and CD8(+) T cells

Histone/protein deacetylases (HDACs) are frequently upregulated in human malignancies and have therefore become therapeutic targets in cancer therapy. However, inhibiting certain HDAC isoforms can have protolerogenic effects on the immune system, which could make it easier for tumor cells to evade the host immune system. Therefore, a better understanding of how each HDAC isoform affects immune biology is needed to develop targeted cancer therapy. Here, we studied the immune phenotype of HDAC5(-/-) mice on a C57BL/6 background. While HDAC5(-/-) mice replicate at expected Mendelian ratios and do not develop overt autoimmune disease, their T-regulatory (Treg) cells show reduced suppressive function in vitro and in vivo. Likewise, CD4(+) T-cells lacking HDAC5 convert poorly to Tregs under appropriately polarizing conditions. To test if this attenuated Treg formation and suppressive function translated into improved anticancer immunity, we inoculated HDAC5(-/-) mice and littermate controls with a lung adenocarcinoma cell line. Cumulatively, lack of HDAC5 did not lead to better anticancer immunity. We found that CD8(+) T cells missing HDAC5 had a reduced ability to produce the cytokine, IFN-γ, in vitro and in vivo, which may offset the benefit of weakened Treg function and formation. Taken together, targeting HDAC5 weakens suppressive function and de-novo induction of Tregs, but also reduces the ability of CD8(+) T cells to produce IFN-γ.

T(reg) stability: to be or not to be

Regulatory T cell (T(reg)) stability has been primarily determined by the maintained expression of the transcription factor Forkhead box P3 (Foxp3). However, T(regs) can exhibit instability while maintaining Foxp3 expression, requiring a re-examination of what defines T(reg) stability. Recent work suggests that the establishment and stability of T(regs) is mediated by a number of mechanisms besides Foxp3 expression, such as epigenetic modifications, Foxo1/3a localization, expression of Eos and signaling via Neuropilin-1. Additional studies may help to define approaches that can undermine T(reg) stability in cancer or enhance T(reg) stability in transplantation, autoimmune or inflammatory diseases and therefore have substantial therapeutic utility. In this review, we will discuss how T(reg) stability is defined and the mechanisms utilized to maintain stability.

Differential effect of DJ-1/PARK7 on development of natural and induced regulatory T cells

Regulatory T cells (Tregs) are essential for maintaining an effective immune tolerance and a homeostatic balance of various other immune cells. To manipulate the immune response during infections and autoimmune disorders, it is essential to know which genes or key molecules are involved in the development of Tregs. Transcription factor Foxp3 is required for the development of Tregs and governs most of the suppressive functions of these cells. Inhibited PI3K/AKT/mTOR signalling is critical for Foxp3 stability. Previous studies have suggested that DJ-1 or PARK7 protein is a positive regulator of the PI3K/AKT/mTOR pathway by negatively regulating the activity of PTEN. Thus, we hypothesised that a lack of DJ-1 could promote the development of Tregs. As a result, loss of DJ-1 decreased the total CD4(+) T cell numbers but increased the fraction of thymic and peripheral nTregs. In contrast, Foxp3 generation was not augmented following differentiation of DJ-1-deficient naïve CD4(+) T cells. DJ-1-deficient-iTregs were imperfect in replication, proliferation and more prone to cell death. Furthermore, DJ-1 deficient iTregs were less sensitive to pSmad2 and pStat5 signalling but had activated AKT/mTOR signalling. These observations reveal an unexpected differential role of DJ-1 in the development of nTregs and iTregs.

Expression pattern and transcriptional regulatory mechanism of noxa gene in grass carp (Ctenopharyngodon idella)

Noxa, a pro-apoptotic protein, plays an important role in cell apoptosis. The researches about noxa gene were concentrated in mammalians, whereas the role and transcriptional regulatory mechanism of noxa in fish were still unclear. In this study, the expression pattern and transcriptional regulatory mechanism of noxa gene in grass carp were analyzed. Noxa was constitutively expressed in all the examined tissues but the relative expression level differed. After exposure to grass carp reovirus (GCRV), mRNA expression level of noxa was down-regulated at the early phase whereas up-regulated at the late phase of infection. Luciferase assays showed that the promoter region -867 ∼ +107 of noxa had high activity and the region -678 ∼ -603 was important in the response to GCRV infection. By deleting the predicted transcription factor binding sites, transcription factors FOXO1 and CEBPβ were found important for noxa in response to GCRV infection. Moreover, the noxa promoter was biotin-labeled and incubated with nuclear extracts from GCRV infected cells. Mass spectrometry analysis showed that transcription factors FOXO1 and CEBPβ were also enriched in the combined proteins. Therefore, the results suggested that transcription factors FOXO1 and CEBPβ may play an important role in the regulation of noxa. Our study would provide new insight into the transcriptional regulatory mechanism of noxa in teleost fish.

Targeting Treg signaling for the treatment of autoimmune diseases

Regulatory T (Treg) cells are crucial players in the prevention of autoimmunity. Treg lineage commitment and functional stability are influenced by selected extracellular signals from the local environment, shaped by distinctive intracellular signaling network, and secured by their unique epigenetic profile. Recent advances in our understanding of the complex processes of Treg lineage differentiation, maintenance, and function has paved the way for developing strategies to manipulate these important cells for therapeutic benefit in many diseases. In this review, we will summarize recent advances in our understanding of Treg biology as well as Treg-targeted therapies in the context of autoimmune disease.

The Molecular Control of Regulatory T Cell Induction

Regulatory T cells (Tregs) are characterized by the expression of the master transcription factor forkhead box P3 (Foxp3). Although Foxp3 expression is widely used as a marker of the Treg lineage, recent data show that the Treg fate is determined by a multifactorial signaling pathway, involving cytokines, nuclear factors, and epigenetic modifications. Foxp3 expression and the Treg phenotype can be acquired by T cells in the periphery, illustrating that the Treg fate is not necessarily conferred during thymic development. The two main Treg populations in vivo, thymic Tregs and peripheral Tregs, differ in the pathways followed for their maturation. This chapter discusses the molecular control of Treg induction, in the thymus as well as the periphery.

Control of peripheral tolerance by regulatory T cell-intrinsic Notch signaling

Receptors of the Notch family direct the differentiation of helper T cell subsets, but their influence on regulatory T cell (T(reg) cell) responses is obscure. We found here that lineage-specific deletion of components of the Notch pathway enhanced T(reg) cell-mediated suppression of type 1 helper T cell (T(H)1 cell) responses and protected against their T(H)1 skewing and apoptosis. In contrast, expression in T(reg) cells of a gain-of-function transgene encoding the Notch1 intracellular domain resulted in lymphoproliferation, exacerbated T(H)1 responses and autoimmunity. Cell-intrinsic canonical Notch signaling impaired T(reg) cell fitness and promoted the acquisition by T(reg) cells of a T(H)1 cell-like phenotype, whereas non-canonical Notch signaling dependent on the adaptor Rictor activated the kinase AKT-transcription factor Foxo1 axis and impaired the epigenetic stability of Foxp3. Our findings establish a critical role for Notch signaling in controlling peripheral T(reg) cell function.

Lack of association between FOXO1 polymorphisms and bacteremia

Increasing evidence suggests that FOXO1, one critical gene related to the human immune system, probable is closely to the human infection. In the present study we aimed to investigate genetic association of FOXO1 with bacteremia in Han Chinese. 188 patients with bacteremia diagnosed with blood culture and 250 healthy blood donors without signs of infection were studied, two tagging SNPs of FOXO1 (rs9532571, rs3751436) were selected and genotyped using predesigned TaqMan allelic discrimination assays. The results showed that the allele frequency of rs9532571 and rs3751436 in FOXO1 was not associated with an increased risk of bacteremia (P=0.762, OR=1.05, 95% CI 0.77-1.43; P=0.059, OR=1.34, 95% CI 0.99-1.81 respectively), the genotype distribution of these two SNPs was also not significantly different between bacteremia patients and control groups (P=0.9; P=0.16). Haplotypes in this block were not significantly associated with bacteremia risk.

CONCLUSION

the association between FOXO1 genetic polymorphism and bacteremia has not been observed in the study, maybe a larger sample population and more SNPs in the FOXO1 need to reveal the role in bacteremia in the future.

IL-10 Potentiates Differentiation of Human Induced Regulatory T Cells via STAT3 and Foxo1

Foxp3(+) regulatory T cells (Tregs) play essential roles in maintaining the immune balance. Although the majority of Tregs are formed in the thymus, increasing evidence suggests that induced Tregs (iTregs) may be generated in the periphery from naive cells. However, unlike in the murine system, significant controversy exists regarding the suppressive capacity of these iTregs in humans, especially those generated in vitro in the presence of TGF-β. Although it is well known that IL-10 is an important mediator of Treg suppression, the action of IL-10 on Tregs themselves is less well characterized. In this article, we show that the presence of IL-10, in addition to TGF-β, leads to increased expansion of Foxp3(+) iTregs with enhanced CTLA-4 expression and suppressive capability, comparable to that of natural Tregs. This process is dependent on IL-10R-mediated STAT3 signaling, as supported by the lack of an IL-10 effect in patients with IL-10R deficiency and dominant-negative STAT3 mutation. Additionally, IL-10-induced inhibition of Akt phosphorylation and subsequent preservation of Foxo1 function are critical. These results highlight a previously unrecognized function of IL-10 in human iTreg generation, with potential therapeutic implications for the treatment of immune diseases, such as autoimmunity and allergy.

Regulatory T Cells in Kidney Transplantation: New Directions?

The contribution of regulatory T cells in the maintenance of kidney graft survival is of major interest. Although many experimental models suggest a role in the induction of graft tolerance, reproducing these findings in clinic is less clear. While modulation of the regulatory T cell response is a promising therapeutic concept in transplantation, a better understanding of function, phenotype and biology is needed to be able to optimally exploit these cells in order to induce graft tolerance. With this in mind, we review here the current understanding of the phenotypic-functional delineation of Tregs and how Tregs can contribute to graft survival. We highlight their potential role in long-term graft survival and kidney operational tolerance. We also discuss the mechanisms needed for the molecular development of regulatory T cells: A combination of FOXP3 molecular partners, epigenetic, metabolic, and posttranslational modifications are necessary to generate well-functioning regulatory T cells and maintain their core identify. We discuss how an improved understanding of these mechanisms will permit the identification of new potent therapeutic strategies to improve kidney graft survival.

Regulatory T cells turn pathogenic

Foxp3(+) regulatory T (Treg) cells are considered a sub-lineage of CD4(+) T cells that are protective against autoimmunity due to their essential roles in maintaining immune homeostasis and self-tolerance. However, Treg cells are unstable in vivo in terms of lineage specialization and suppressive function. These unstable Treg cells play roles in the pathogenesis of diseases, which cause safety concerns regarding human Treg cell therapy. In this review, we highlight recent findings that demonstrate the pathogenic conversion of Treg cells in different disease models.

E3 Ubiquitin Ligase VHL Regulates Hypoxia-Inducible Factor-1α to Maintain Regulatory T Cell Stability and Suppressive Capacity

Foxp3(+) regulatory T (Treg) cells play a critical role in immune homeostasis; however, the mechanisms to maintain their function remain unclear. Here, we report that the E3 ubiquitin ligase VHL is essential for Treg cell function. Mice with Foxp3-restricted VHL deletion displayed massive inflammation associated with excessive Treg cell interferon-γ (IFN-γ) production. VHL-deficient Treg cells failed to prevent colitis induction, but converted into Th1-like effector T cells. VHL intrinsically orchestrated such conversion under both steady and inflammatory conditions followed by Foxp3 downregulation, which was reversed by IFN-γ deficiency. Augmented hypoxia-inducible factor 1α (HIF-1α)-induced glycolytic reprogramming was required for IFN-γ production. Furthermore, HIF-1α bound directly to the Ifng promoter. HIF-1α knockdown or knockout could reverse the increased IFN-γ by VHL-deficient Treg cells and restore their suppressive function in vivo. These findings indicate that regulation of HIF-1α pathway by VHL is crucial to maintain the stability and suppressive function of Foxp3(+) T cells.

Suppression of Th2 and Tfh immune reactions by Nr4a receptors in mature T reg cells

Sekiya et al. demonstrate that deletion of the nuclear orphan receptor Nr4a in T reg cells results in a fatal systemic immunopathology due to abrogated suppressive capability in limiting Th2 and Tfh conversion.

Regulatory T (T reg) cells are central mediators of immune suppression. As such, T reg cells are characterized by a distinct pattern of gene expression, which includes up-regulation of immunosuppressive genes and silencing of inflammatory cytokine genes. Although an increasing number of transcription factors that regulate T reg cells have been identified, the mechanisms by which the T reg cell–specific transcriptional program is maintained and executed remain largely unknown. The Nr4a family of nuclear orphan receptors, which we recently identified as essential for the development of T reg cells, is highly expressed in mature T reg cells as well, suggesting that Nr4a factors play important roles even beyond T reg cell development. Here, we showed that deletion of Nr4a genes specifically in T reg cells caused fatal systemic immunopathology. Nr4a-deficient T reg cells exhibited global alteration of the expression of genes which specify the T reg cell lineage, including reduction of Foxp3 and Ikzf4. Furthermore, Nr4a deficiency abrogated T reg cell suppressive activities and accelerated conversion to cells with Th2 and follicular helper T (Tfh) effector-like characteristics, with heightened expression of Th2 and Tfh cytokine genes. These findings demonstrate that Nr4a factors play crucial roles in mature T reg cells by directly controlling a genetic program indispensable for T reg cell maintenance and function.