Egr-2 transcription factor is required for Blimp-1-mediated IL-10 production in IL-27-stimulated CD4+ T cells

Identification of a transcription factor network regulating anti-TNF mediated IL10 expression in human CD4+ T cells

CD4+ T cells are key players in immune-mediated inflammatory diseases (IMIDs) through the production of inflammatory mediators including tumour necrosis factor (TNF). Anti-TNF therapy has revolutionized the treatment of several IMIDs and we previously demonstrated that in vitro treatment of human CD4+ T cells with anti-TNF promotes anti-inflammatory IL-10 expression in multiple subpopulations of CD4+ T cells. Here we investigated the transcriptional mechanisms underlying the IL-10 induction by TNF-blockade in CD4+ T cells, isolated from PBMCs of healthy volunteers, stimulated in vitro for 3 days with anti-CD3/CD28 mAb in the absence or presence of anti-TNF. After culture, CD45RA+ cells were depleted before performing gene expression profiling and chromatin accessibility analysis. Gene expression analysis of CD45RA-CD4+ T cells showed a distinct anti-TNF specific gene signature of 183 genes (q-value < 0.05). Pathway enrichment analysis of differentially expressed genes revealed multiple pathways related to cytokine signalling and regulation of cytokine production; in particular, IL10 was the most upregulated gene by anti-TNF, while the proinflammatory cytokines and chemokines IFNG, IL9, IL22, and CXCL10 were significantly downregulated (q-value < 0.05). Transcription factor motif analysis at the differentially open chromatin regions, after anti-TNF treatment, revealed 58 transcription factor motifs enriched at the IL10 locus. We identified seven transcription factor candidates for the anti-TNF mediated regulation of IL-10, which were either differentially expressed or whose locus was differentially accessible upon anti-TNF treatment. Correlation analysis between the expression of these transcription factors and IL10 suggests a role for MAF, PRDM1, and/or EOMES in regulating IL10 expression in CD4+ T cells upon anti-TNF treatment.

Cenicriviroc, a CCR2/CCR5 antagonist, promotes the generation of type 1 regulatory T cells

Cenicriviroc, a dual CCR2/CCR5 antagonist, initially developed as an anti-HIV drug, has shown promising results in nonalcoholic steatohepatitis phase 2 clinical trials. It inhibits the infiltration and activation of CCR2+/CCR5+ monocytes and macrophages to the site of liver injury, preventing liver fibrosis. However, the role of Cenicriviroc in the modulation of helper T cell differentiation and functions remains to be explored. In inflamed colons of Crohn's disease patients, CCR2+ and CCR5+ CD4+ T cells are enriched. Considering the role of CCR2+ and CCR5+ T cells in IBD pathogenesis, we investigated the potential role of Cenicriviroc in colitis. Our in vitro studies revealed that Cenicriviroc inhibits Th1-, Th2-, and Th17-cell differentiation while promoting the generation of type 1 regulatory T cells (Tr1), known for preventing inflammation through induction of IL-10. This study is the first to report that Cenicriviroc promotes Tr1 cell generation by up-regulating the signature of Tr1 cell transcription factors such as c-Maf, Prdm1, Irf-1, Batf, and EGR-2. Cenicriviroc displayed a protective effect in experimental colitis models by preventing body weight loss and intestinal inflammation and preserving epithelial barrier integrity. We show that Cenicriviroc induced IL-10 and inhibited the generation of pro-inflammatory cytokines IFN-γ, IL-17, IL-6, and IL-1β during colitis. Based on our data, we propose Cenicriviroc as a potential therapeutic in controlling tissue inflammation by inhibiting the generation and functions of effector T cells and promoting the induction of anti-inflammatory Tr1 cells.

An updated advancement of bifunctional IL-27 in inflammatory autoimmune diseases

Interleukin-27 (IL-27) is a member of the IL-12 family. The gene encoding IL-27 is located at chromosome 16p11. IL-27 is considered as a heterodimeric cytokine, which consists of Epstein-Barr virus (EBV)-induced gene 3 (Ebi3) and IL-27p28. Based on the function of IL-27, it binds to receptor IL-27rα or gp130 and then regulates downstream cascade. To date, findings show that the expression of IL-27 is abnormal in different inflammatory autoimmune diseases (including systemic lupus erythematosus, rheumatoid arthritis, Sjogren syndrome, Behcet's disease, inflammatory bowel disease, multiple sclerosis, systemic sclerosis, type 1 diabetes, Vogt-Koyanagi-Harada, and ankylosing spondylitis). Moreover, in vivo and in vitro studies demonstrated that IL-27 is significantly in3volved in the development of these diseases by regulating innate and adaptive immune responses, playing either an anti-inflammatory or a pro-inflammatory role. In this review, we comprehensively summarized information about IL-27 and autoimmunity based on available evidence. It is hoped that targeting IL-27 will hold great promise in the treatment of inflammatory autoimmune disorders in the future.

Epigenetic signature and key transcriptional regulators of human antigen-specific type 1 regulatory T cells

Human adaptive immunity is orchestrated by effector and regulatory T (Treg) cells. Natural Tregs arise in the thymus where they are shaped to recognize self-antigens, while type 1 Tregs or Tr1 cells are induced from conventional peripheral CD4 + T cells in response to peripheral antigens, such as alloantigens and allergens. Tr1 cells have been developed as a potential therapy for inducing antigen-specific tolerance, because they can be rapidly differentiated in vitro in response to a target antigen. However, the epigenetic landscape and the identity of transcription factors (TFs) that regulate differentiation, phenotype, and functions of human antigen-specific Tr1 cells is largely unknown, hindering Tr1 research and broader clinical development. Here, we reveal the unique epigenetic signature of antigen-specific Tr1 cells, and TFs that regulate their differentiation, phenotype and function. We showed that in vitro induced antigen-specific Tr1 cells are distinct both clonally and transcriptionally from natural Tregs and other conventional CD4 + T cells on a single-cell level. An integrative analysis of Tr1 cell epigenome and transcriptome identified a TF signature unique to antigen-specific Tr1 cells, and predicted that IRF4, BATF, and MAF act as their transcriptional regulators. Using functional genomics, we showed that each of these TFs play a non-redundant role in regulating Tr1 cell differentiation, suppressive function, and expression of co-inhibitory and cytotoxic proteins. By using the Tr1-specific TF signature as a molecular fingerprint, we tracked Tr1 cells in peripheral blood of recipients of allogeneic hematopoietic stem cell transplantation treated with adoptive Tr1 cell therapy. Furthermore, the same signature identified Tr1 cells in resident CD4 + T cells in solid tumors. Altogether, these results reveal the epigenetic signature and the key transcriptional regulators of human Tr1 cells. These data will guide mechanistic studies of human Tr1 cell biology and the development and optimization of adoptive Tr1 cell therapies.

Intestinal factors promoting the development of RORγt+ cells and oral tolerance

The gastrointestinal tract has to harmonize the two seemingly opposite functions of fulfilling nutritional needs and avoiding the entry of pathogens, toxins and agents that can cause physical damage. This balance requires a constant adjustment of absorptive and defending functions by sensing environmental changes or noxious substances and initiating adaptive or protective mechanisms against them through a complex network of receptors integrated with the central nervous system that communicate with cells of the innate and adaptive immune system. Effective homeostatic processes at barrier sites take the responsibility for oral tolerance, which protects from adverse reactions to food that cause allergic diseases. During a very specific time interval in early life, the establishment of a stable microbiota in the large intestine is sufficient to prevent pathological events in adulthood towards a much larger bacterial community and provide tolerance towards diverse food antigens encountered later in life. The beneficial effects of the microbiome are mainly exerted by innate and adaptive cells that express the transcription factor RORγt, in whose generation, mediated by different bacterial metabolites, retinoic acid signalling plays a predominant role. In addition, recent investigations indicate that food antigens also contribute, analogously to microbial-derived signals, to educating innate immune cells and instructing the development and function of RORγt+ cells in the small intestine, complementing and expanding the tolerogenic effect of the microbiome in the colon. This review addresses the mechanisms through which microbiota-produced metabolites and dietary antigens maintain intestinal homeostasis, highlighting the complementarity and redundancy between their functions.

Lineage origin and transcriptional control of autoantigen-specific T-regulatory type 1 cells

T Regulatory type-1 (TR1) cells represent an immunosuppressive T cell subset, discovered over 25 years ago, that produces high levels of interleukin-10 (IL-10) but, unlike its FoxP3+ T regulatory (Treg) cell counterpart, does not express FoxP3 or CD25. Experimental evidence generated over the last few years has exposed a promising role for TR1 cells as targets of therapeutic intervention in immune-mediated diseases. The discovery of cell surface markers capable of distinguishing these cells from related T cell types and the application of next generation sequencing techniques to defining their transcriptional make-up have enabled a more accurate description of this T cell population. However, the developmental biology of TR1 cells has long remained elusive, in particular the identity of the cell type(s) giving rise to bona fide TR1 cells in vivo. Here, we review the fundamental phenotypic, transcriptional and functional properties of this T cell subset, and summarize recent lines of evidence shedding light into its ontogeny.

Combinations of anti-GITR antibody and CD28 superagonist induce permanent allograft acceptance by generating type 1 regulatory T cells

Type 1 regulatory T (Tr1) cells represent a subset of IL-10-producing CD4⁺Foxp3^- T cells and play key roles in promoting transplant tolerance. However, no effective pharmacological approaches have been able to induce Tr1 cells in vivo. We herein report the combined use of a CD28 superagonist (D665) and anti-glucocorticoid-induced tumor necrosis factor receptor-related protein monoclonal antibody (G3c) to induce Tr1 cells in vivo. Large amounts of IL-10/interferon-γ-co-producing CD4⁺Foxp3^- Tr1 cells were generated by D665-G3c sequential treatment in mice. Mechanistic studies suggested that D665-G3c induced Tr1 cells via transcription factors Prdm1 and Maf. G3c contributed to Tr1 cell generation via the activation of mitogen-activated protein kinase-signal transducer and activator of transcription 3 signaling. Tr1 cells suppressed dendritic cell maturation and T cell responses and mediated permanent allograft acceptance in fully major histocompatibility complex-mismatched mice in an IL-10-dependent manner. In vivo Tr1 cell induction is a promising strategy for achieving transplant tolerance.

Roles of type 1 regulatory T (Tr1) cells in allergen-specific immunotherapy

Allergen-specific immunotherapy (AIT) is the only causative treatment for allergic diseases by modification of the immune response to allergens. A key feature of AIT is to induce immunotolerance to allergens by generating antigen-specific regulatory T (Treg) cells in allergic patients. Type 1 regulatory T (Tr1) cells and forkhead box protein 3 (Foxp3)-expressing Treg cells are well known among Treg cell subsets. Foxp3 was identified as a master transcription factor of Treg cells, and its expression is necessary for their suppressive activity. In contrast to Foxp3⁺ Treg cells, the master transcription factor of Tr1 cells has not been elucidated. Nevertheless, Tr1 cells are generally considered as a distinct subset of Treg cells induced in the periphery during antigen exposure in tolerogenic conditions and can produce large amounts of anti-inflammatory cytokines such as interleukin-10 and transforming growth factor-β, followed by down-regulation of the function of effector immune cells independently of Foxp3 expression. Since the discovery of Tr1 cells more than 20 years ago, research on Tr1 cells has expanded our understanding of the mechanism of AIT. Although the direct precursors and true identity of these cells continues to be disputed, we and others have demonstrated that Tr1 cells are induced in the periphery by AIT, and the induced cells are re-activated by antigens, followed by suppression of allergic symptoms. In this review, we discuss the immune mechanisms for the induction of Tr1 cells by AIT and the immune-suppressive roles of Tr1 cells in AIT.

A Notch/STAT3-driven Blimp-1/c-Maf-dependent molecular switch induces IL-10 expression in human CD4+ T cells and is defective in Crohn´s disease patients

Immunosuppressive Interleukin (IL)-10 production by pro-inflammatory CD4⁺ T cells is a central self-regulatory function to limit aberrant inflammation. Still, the molecular mediators controlling IL-10 expression in human CD4⁺ T cells are largely undefined. Here, we identify a Notch/STAT3 signaling-module as a universal molecular switch to induce IL-10 expression across human naïve and major effector CD4⁺ T cell subsets. IL-10 induction was transient, jointly controlled by the transcription factors Blimp-1/c-Maf and accompanied by upregulation of several co-inhibitory receptors, including LAG-3, CD49b, PD-1, TIM-3 and TIGIT. Consistent with a protective role of IL-10 in inflammatory bowel diseases (IBD), effector CD4⁺ T cells from Crohn's disease patients were defective in Notch/STAT3-induced IL-10 production and skewed towards an inflammatory Th1/17 cell phenotype. Collectively, our data identify a Notch/STAT3-Blimp-1/c-Maf axis as a common anti-inflammatory pathway in human CD4⁺ T cells, which is defective in IBD and thus may represent an attractive therapeutic target.

Guidelines for the use of flow cytometry and cell sorting in immunological studies (third edition)

The third edition of Flow Cytometry Guidelines provides the key aspects to consider when performing flow cytometry experiments and includes comprehensive sections describing phenotypes and functional assays of all major human and murine immune cell subsets. Notably, the Guidelines contain helpful tables highlighting phenotypes and key differences between human and murine cells. Another useful feature of this edition is the flow cytometry analysis of clinical samples with examples of flow cytometry applications in the context of autoimmune diseases, cancers as well as acute and chronic infectious diseases. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid. All sections are written and peer-reviewed by leading flow cytometry experts and immunologists, making this edition an essential and state-of-the-art handbook for basic and clinical researchers.

Alloantigen-specific type 1 regulatory T cells suppress through CTLA-4 and PD-1 pathways and persist long-term in patients

[Figure: see text].

Re-Programming Autoreactive T Cells Into T-Regulatory Type 1 Cells for the Treatment of Autoimmunity

Systemic delivery of peptide-major histocompatibility complex (pMHC) class II-based nanomedicines can re-program cognate autoantigen-experienced CD4+ T cells into disease-suppressing T-regulatory type 1 (TR1)-like cells. In turn, these TR1-like cells trigger the formation of complex regulatory cell networks that can effectively suppress organ-specific autoimmunity without impairing normal immunity. In this review, we summarize our current understanding of the transcriptional, phenotypic and functional make up of TR1-like cells as described in the literature. The true identity and direct precursors of these cells remain unclear, in particular whether TR1-like cells comprise a single terminally-differentiated lymphocyte population with distinct transcriptional and epigenetic features, or a collection of phenotypically different subsets sharing key regulatory properties. We propose that detailed transcriptional and epigenetic characterization of homogeneous pools of TR1-like cells will unravel this conundrum.

BHLHE40 Regulates IL-10 and IFN-γ Production in T Cells but Does Not Interfere With Human Type 1 Regulatory T Cell Differentiation

Type 1 regulatory T (Tr1) cells are subset of peripherally induced antigen-specific regulatory T cells. IL-10 signaling has been shown to be indispensable for polarization and function of Tr1 cells. However, the transcriptional machinery underlying human Tr1 cell differentiation and function is not yet elucidated. To this end, we performed RNA sequencing on ex vivo human CD49b⁺LAG3⁺ Tr1 cells. We identified the transcription factor, BHLHE40, to be highly expressed in Tr1 cells. Even though Tr1 cells characteristically produce high levels of IL-10, we found that BHLHE40 represses IL-10 and increases IFN-γ secretion in naïve CD4⁺ T cells. Through CRISPR/Cas9-mediated knockout, we determined that IL10 significantly increased in the sgBHLHE40-edited cells and BHLHE40 is dispensable for naïve CD4⁺ T cells to differentiate into Tr1 cells in vitro. Interestingly, BHLHE40 overexpression induces the surface expression of CD49b and LAG3, co-expressed surface molecules attributed to Tr1 cells, but promotes IFN-γ production. Our findings uncover a novel mechanism whereby BHLHE40 acts as a regulator of IL-10 and IFN-γ in human CD4⁺ T cells.

Deficiency in the frequency and function of Tr1 cells in IgAV and the possible role of IL-27

Objective

Type 1 regulatory T (Tr1) cells are involved in the pathogenesis of numerous immune-mediated diseases. However, little is known about whether and how Tr1 cells affect the development of IgA vasculitis (IgAV). We aimed to investigate this question in IgAV patients.

Methods

. Tr1 cells in peripheral blood and kidney tissue of IgAV patients were analysed by multi-parametric flow cytometry and immunofluorescence techniques. An in vitro assay of suppression of T cell proliferation and cytokine release was performed to evaluate the function of Tr1 cells. Real-time PCR and cell stimulation in vitro were used to explore the roles of IL-27 and early growth response gene 2 (EGR2).

Results

The frequency of Tr1 cells was decreased in peripheral blood but increased in kidney tissue from IgAV patients. A defective suppressive function of Tr1 cells in IgAV was observed. The frequency of Tr1 cells and the cytokines secreted by them were up-regulated in the presence of recombinant IL-27 in vitro. Moreover, IL-27 also increased the expression of EGR2. Furthermore, lower frequency of Tr1 cells during remission had a higher recurrence rate.

Conclusion

Tr1 cells are involved in the pathogenesis of IgAV. The low IL-27 in IgAV is responsible for impaired frequency and function of Tr1 cells, and EGR2 may be the specific transcription factor involved in the progression. Tr1 may be a risk factor for IgAV recurrence.

Conversion of Anergic T Cells Into Foxp3- IL-10+ Regulatory T Cells by a Second Antigen Stimulus In Vivo

T cell anergy is a common mechanism of T cell tolerance. However, although anergic T cells are retained for longer time periods in their hosts, they remain functionally passive. Here, we describe the induction of anergic CD4⁺ T cells in vivo by intravenous application of high doses of antigen and their subsequent conversion into suppressive Foxp3^- IL-10⁺ Tr1 cells but not Foxp3⁺ Tregs. We describe the kinetics of up-regulation of several memory-, anergy- and suppression-related markers such as CD44, CD73, FR4, CD25, CD28, PD-1, Egr-2, Foxp3 and CTLA-4 in this process. The conversion into suppressive Tr1 cells correlates with the transient intracellular CTLA-4 expression and required the restimulation of anergic cells in a short-term time window. Restimulation after longer time periods, when CTLA-4 is down-regulated again retains the anergic state but does not lead to the induction of suppressor function. Our data require further functional investigations but at this stage may suggest a role for anergic T cells as a circulating pool of passive cells that may be re-activated into Tr1 cells upon short-term restimulation with high and systemic doses of antigen. It is tentative to speculate that such a scenario may represent cases of allergen responses in non-allergic individuals.

The Yin and Yang of Type 1 Regulatory T Cells: From Discovery to Clinical Application

Regulatory T cells are essential players of peripheral tolerance and suppression of inflammatory immune responses. Type 1 regulatory T (Tr1) cells are FoxP3^- regulatory T cells induced in the periphery under tolerogenic conditions. Tr1 cells are identified as LAG3⁺CD49b⁺ mature CD4⁺ T cells that promote peripheral tolerance through secretion of IL-10 and TGF-β in addition to exerting perforin- and granzyme B-mediated cytotoxicity against myeloid cells. After the initial challenges of isolation were overcome by surface marker identification, ex vivo expansion of antigen-specific Tr1 cells in the presence of tolerogenic dendritic cells (DCs) and IL-10 paved the way for their use in clinical trials. With one Tr1-enriched cell therapy product already in a Phase I clinical trial in the context of allogeneic hematopoietic stem cell transplantation (allo-HSCT), Tr1 cell therapy demonstrates promising results so far in terms of efficacy and safety. In the current review, we identify developments in phenotypic and molecular characterization of Tr1 cells and discuss the potential of engineered Tr1-like cells for clinical applications of Tr1 cell therapies. More than 3 decades after their initial discovery, Tr1 cell therapy is now being used to prevent graft versus host disease (GvHD) in allo-HSCT and will be an alternative to immunosuppression to promote graft tolerance in solid organ transplantation in the near future.

Harnessing Mechanisms of Immune Tolerance to Improve Outcomes in Solid Organ Transplantation: A Review

Survival after solid organ transplantation (SOT) is limited by chronic rejection as well as the need for lifelong immunosuppression and its associated toxicities. Several preclinical and clinical studies have tested methods designed to induce transplantation tolerance without lifelong immune suppression. The limited success of these strategies has led to the development of clinical protocols that combine SOT with other approaches, such as allogeneic hematopoietic stem cell transplantation (HSCT). HSCT prior to SOT facilitates engraftment of donor cells that can drive immune tolerance. Recent innovations in graft manipulation strategies and post-HSCT immune therapy provide further advances in promoting tolerance and improving clinical outcomes. In this review, we discuss conventional and unconventional immunological mechanisms underlying the development of immune tolerance in SOT recipients and how they can inform clinical advances. Specifically, we review the most recent mechanistic studies elucidating which immune regulatory cells dampen cytotoxic immune reactivity while fostering a tolerogenic environment. We further discuss how this understanding of regulatory cells can shape graft engineering and other therapeutic strategies to improve long-term outcomes for patients receiving HSCT and SOT.

SARS-CoV-2 B.1.1.7 and B.1.351 variants of concern induce lethal disease in K18-hACE2 transgenic mice despite convalescent plasma therapy

SARS-CoV-2 variants of concern (VoCs) are impacting responses to the COVID-19 pandemic. Here we present a comparison of the SARS-CoV-2 USA-WA1/2020 (WA-1) strain with B.1.1.7 and B.1.351 VoCs and identify significant differences in viral propagation in vitro and pathogenicity in vivo using K18-hACE2 transgenic mice. Passive immunization with plasma from an early pandemic SARS-CoV-2 patient resulted in significant differences in the outcome of VoC-infected mice. WA-1-infected mice were protected by plasma, B.1.1.7-infected mice were partially protected, and B.1.351-infected mice were not protected. Serological correlates of disease were different between VoC-infected mice, with B.1.351 triggering significantly altered cytokine profiles than other strains. In this study, we defined infectivity and immune responses triggered by VoCs and observed that early 2020 SARS-CoV-2 human immune plasma was insufficient to protect against challenge with B.1.1.7 and B.1.351 in the mouse model.

Tr1 Cells as a Key Regulator for Maintaining Immune Homeostasis in Transplantation

The immune system is composed of effectors and regulators. Type 1 regulatory T (Tr1) cells are classified as a distinct subset of T cells, and they secret high levels of IL-10 but lack the expression of the forkhead box P3 (Foxp3). Tr1 cells act as key regulators in the immune network, and play a central role in maintaining immune homeostasis. The regulatory capacity of Tr1 cells depends on many mechanisms, including secretion of suppressive cytokines, cell-cell contacts, cytotoxicity and metabolic regulation. A breakdown of Tr1-cell-mediated tolerance is closely linked with the pathogenesis of various diseases. Based on this observation, Tr1-cell therapy has emerged as a successful treatment option for a number of human diseases. In this review, we describe an overview of Tr1 cell identification, functions and related molecular mechanisms. We also discuss the current protocols to induce/expand Tr1 cells in vitro for clinical application, and summarize the recent progress of Tr1 cells in transplantation.

A Comparison of Cell Activation, Exhaustion, and Expression of HIV Coreceptors and Restriction Factors in HIV-1- and HIV-2-Infected Nonprogressors

Human immunodeficiency viruses induce rare attenuated diseases due either to HIV-1 in the exceptional long-term nonprogressors (LTNPs) or to HIV-2 in West Africa. To better understand characteristics of these two disease types we performed a multiplex comparative analysis of cell activation, exhaustion, and expression of coreceptors and restriction factors in CD4 T cells susceptible to harbor those viruses. We analyzed by flow cytometry the expression of HLA-DR, PD1, CCR5, CXCR6, SAMHD1, Blimp-1, and TRIM5α on CD4 T cell subsets from 10 HIV-1⁺ LTNPs and 14 HIV-2⁺ (12 nonprogressors and 2 progressors) of the ANRS CO-15 and CO-5 cohorts, respectively, and 12 HIV^- healthy donors (HD). The V3 loop of the HIV-1 envelope from 6 HIV-1+ LTNPs was sequenced to determine the CXCR6-binding capacity. Proportions of HLA-DR⁺ and PD1+ cells were higher in memory CD4 T subsets from HIV-1 LTNPs compared with HIV-2 and HD. Similar findings were observed for CCR5+ cells although limited to central-memory CD4 T cell (TCM) and follicular helper T cell subsets, whereas all major subsets from HIV-1 LTNPs contained less CXCR6+ cells compared with HIV-2. All six V3 loop sequences from HIV-1 LTNPs contained a proline at position 326. Proportions of SAMHD1+ cells were higher in all resting CD4 T subsets from HIV-1 LTNPs compared with the other groups, whereas Blimp-1+ and Trim5α+ cells did not differ. The CD4 T cell subsets from HIV-1 LTNPs differ from those of HIV-2-infected subjects by higher levels of activation, exhaustion, and SAMHD1 expression that can reflect the distinct patterns of host/virus relationships.

LAG3's Enigmatic Mechanism of Action

LAG3 is an important immune checkpoint with relevance in cancer, infectious disease and autoimmunity. However, despite LAG3's role in immune exhaustion and the great potential of LAG3 inhibition as treatment, much remains unknown about its biology, particularly its mechanism of action. This review describes the knowns, unknowns and controversies surrounding LAG3. This includes examination of how LAG3 is regulated transcriptionally and post-translationally by endocytosis and proteolytic cleavage. We also discuss the interactions of LAG3 with its ligands and the purpose thereof. Finally, we review LAG3's mechanism of action, including the roles of LAG3 intracellular motifs and the lack of a role for CD4 competition. Overall, understanding the biology of LAG3 can provide greater insight on LAG3 function, which may broaden the appreciation for LAG3's role in disease and potentially aid in the development of targeted therapies.

Regulatory T Cells: Concept, Classification, Phenotype, and Biological Characteristics

Regulatory T cells (Treg) play an indispensable role in maintaining the body's immune nonresponse to self-antigens and suppressing the body's unwarranted and potentially harmful immune responses. Their absence, reduction, dysfunction, transformation, and instability can lead to numerous autoimmune diseases. There are several distinct subtypes of the Treg cells, although they share certain biological characteristics and have unique phenotypes with different regulatory functions, as well as mechanistic abilities. In this book chapter, we introduce the latest advances in Treg cell subtypes pertaining to classification, phenotype, biological characteristics, and mechanisms. We also highlight the relationship between Treg cells and various diseases, including autoimmune, infectious, as well as tumors and organ transplants.

Early growth response genes 2 and 3 induced by AP-1 and NF-κB modulate TGF-β1 transcription in NK1.1- CD4+ NKG2D+ T cells

NK1.1^- CD4⁺ NKG2D⁺ T cells are a subpopulation of regulatory T cells that downregulate the functions of CD4⁺ T, CD8⁺ T, natural killer (NK) cells, and macrophages through TGF-β1 production. Early growth response genes 2 (Egr2) and 3 (Egr3) maintain immune homeostasis by modulating T lymphocyte development, inhibiting effector T cell function, and promoting the induction of regulatory T cells. Whether Egr2 and Egr3 directly regulate TGF-β1 transcription in NK1.1^- CD4⁺ NKG2D⁺ T cells remains elusive. The expression levels of Egr2 and Egr3 were higher in NK1.1^- CD4⁺ NKG2D⁺ T cells than in NK1.1^- CD4⁺ NKG2D^- T cells. Egr2 and Egr3 expression were remarkably increased after stimulating NK1.1^- CD4⁺ NKG2D⁺ T cells with sRAE or α-CD3/sRAE. The ectopic expression of Egr2 or Egr3 resulted in the enhancement of TGF-β1 expression, while knockdown of Egr2 or Egr3 led to the decreased expression of TGF-β1 in NK1.1^- CD4⁺ NKG2D⁺ T cells. Egr2 and Egr3 directly bound with the TGF-β1 promoter as demonstrated by the electrophoretic mobility shift assay and dual-luciferase gene reporter assay. Furthermore, the Egr2 and Egr3 expression of NK1.1^- CD4⁺ NKG2D⁺ T cells could be induced by the AP-1 and NF-κB transcriptional factors, but had no involvement with the activation of NF-AT and STAT3. In conclusion, Egr2 and Egr3 induced by AP-1 and NF-κB directly initiate TGF-β1 transcription in NK1.1^- CD4⁺ NKG2D⁺ T cells. This study indicates that manipulating Egr2 and Egr3 expression would potentiate or alleviate the regulatory function of NK1.1^- CD4⁺ NKG2D⁺ T cells and this strategy could be used in the therapy for patients with autoimmune diseases or tumor.

Key role of macrophages in tolerance induction via T regulatory type 1 (Tr1) cells

T regulatory type 1 (Tr1) cells are a class of regulatory T cells (T_regs ) participating in peripheral tolerance, hence the rationale behind their testing in clinical trials in different disease settings. One of their applications is tolerance induction to allogeneic islets for long-term diabetes-free survival. Currently the cellular and molecular mechanisms that promote Tr1-cell induction in vivo remain poorly understood. We employed a mouse model of transplant tolerance where treatment with granulocyte colony-stimulating factor (G-CSF)/rapamycin induces permanent engraftment of allogeneic pancreatic islets in C57BL/6 mice via Tr1 cells. The innate composition of graft and spleen cells in tolerant mice was analyzed by flow cytometry. Graft phagocytic cells were co-cultured with CD4⁺ T cells in vitro to test their ability to induce Tr1-cell induction. Graft phagocytic cells were depleted in vivo at different time-points during G-CSF/rapamycin treatment, to identify their role in Tr1-cell induction and consequently in graft survival. In the spleen, the site of Tr1-cell induction, no differences in the frequencies of macrophages or dendritic cells (DC) were observed. In the graft, the site of antigen uptake, a high proportion of macrophages and not DC was detected in tolerant but not in rejecting mice. Graft-infiltrating macrophages of G-CSF/rapamycin-treated mice had an M2 phenotype, characterized by higher CD206 expression and interleukin (IL)-10 production, whereas splenic macrophages only had an increased CD206 expression. Graft-infiltrating cells from G-CSF/rapamycin-treated mice-induced Tr1-cell expansion in vitro. Furthermore, Tr1-cell induction was perturbed upon in-vivo depletion of phagocytic cells, early and not late during treatment, leading to graft loss suggesting that macrophages play a key role in tolerance induction mediated by Tr1 cells. Taken together, in this mouse model of Tr1-cell induced tolerance to allogeneic islets, M2 macrophages infiltrating the graft upon G-CSF/rapamycin treatment are key for Tr1-cell induction. This work provides mechanistic insight into pharmacologically induced Tr1-cell expansion in vivo in this stringent model of allogeneic transplantation.

Interplay between Cytokine Circuitry and Transcriptional Regulation Shaping Helper T Cell Pathogenicity and Plasticity in Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a chronic disorder manifested as Crohn’s disease (CD) and ulcerative colitis (UC) characterized by intestinal inflammation and involves a dysregulated immune response against commensal microbiota through the activation of CD4 T helper cells. T helper cell differentiation to effector or regulatory phenotypes is controlled by cytokine networks and transcriptional regulators. Distinct polarized T helper cells are able to alter their phenotypes to adapt to diverse and fluctuating physiological environments. T helper cells exhibit intrinsic instability and flexibility to express cytokines of other lineages or transdifferentiate from one T helper cell type to another in response to various perturbations from physiological cytokine milieu as a means of promoting local immunity in response to injury or ensure tissue homeostasis. Furthermore, functional plasticity and diversity of T helper cells are associated with pathogenicity and are critical for immune homeostasis and prevention of autoimmunity. In this review, we provide deeper insights into the combinatorial extrinsic and intrinsic signals that control plasticity and transdifferentiation of T helper cells and also highlight the potential of exploiting the genetic reprogramming plasticity of T helper cells in the treatment of IBD.

IL-27 and autoimmune rheumatologic diseases: The good, the bad, and the ugly

The footprint of cytokines is evident in almost every biological process, such as development, as well as the pathogenesis of the different diseases, immune responses to pathogens, etc. These small proteins are categorized into different functional classes; for instance, they can play a pro-inflammatory or anti-inflammatory role in different situations, or they can confer a polarization to the immune system. Interleukin (IL)-27 is a member of the IL-12 family. Antigen-presenting cells are the primary source of IL-27 production, which exerts its effects by bindings to the IL-27 receptor expressed on the surface of target cells. Interaction of IL-27 and IL-27 receptor leads to activation of the JAK-STAT and p38 MAPK signaling pathways. Most studies focused on the inflammatory effects of this cytokine, but gradually anti-inflammatory effects were also revealed for this cytokine, which changed the traditional perception of the function of this cytokine. The functionality of IL-27 in the pathogenesis of rheumatic diseases has been attributed to a double-blade sword. Hence, novel therapeutic approaches have been devised targeting IL-12 family that has been accompanied with promising results. In this review, we focused on the inflammatory and anti-inflammatory properties of IL-27 in different autoimmune rheumatologic diseases and its plausible therapeutic potentials.

Regulatory T and B cells in peripheral blood of subcutaneous immunotherapy-treated Japanese cedar pollinosis patients

AIM

The aim of this study was to clarify whether there are more regulatory T (Treg) and regulatory B (Breg) cells, and higher levels of IL-10-related transcription factors in subcutaneous immunotherapy (SCIT)-treated pollinosis patients than in non-SCIT-treated patients.

METHODS

Japanese cedar pollinosis patients undergoing SCIT had received treatment for at least 2.8 years. Peripheral blood mononuclear cells were used for flow cytometer analyses and mRNA measurement.

RESULTS

The numbers of type 1 regulatory T (Tr1)-like cells and Breg cells, and expression of E4BP4 mRNA by peripheral blood mononuclear cells in SCIT-treated patients were higher than those in non-SCIT-treated patients.

CONCLUSION

Tr1-like cells, Breg cells and E4BP4 may be involved in the effectiveness of SCIT.

Molecular switches for regulating the differentiation of inflammatory and IL-10-producing anti-inflammatory T-helper cells

CD4 T-helper (Th) cells secret a variety of inflammatory cytokines and play critical roles in host defense against invading foreign pathogens. On the other hand, uncontrolled inflammatory responses mediated by Th cells may result in tissue damage and inflammatory disorders including autoimmune and allergic diseases. Thus, the induction of anti-inflammatory cytokine expression becomes an important "brake" to repress and/or terminate aberrant and/or unnecessary immune responses. Interleukin-10 (IL-10) is one of the most important anti-inflammatory cytokines to limit inflammatory Th cells and immunopathology and to maintain tissue homeostasis. Many studies have indicated that Th cells can be a major source of IL-10 under specific conditions both in mouse and human and that extracellular signals and cell intrinsic molecular switches are required to turn on and off Il10 expression in different Th cells. In this review, we will highlight the recent findings that have enhanced our understanding on the mechanisms of IL-10 induction in distinct Th-cell subsets, including Th1, Th2, and Th17 cells, as well as the importance of these IL-10-producing anti-inflammatory Th cells in immunity and inflammation.

Lactobacillus pentosus Modulates Immune Response by Inducing IL-10 Producing Tr1 Cells

Several gut commensals have been shown to modulate host immune response. Recently, many food derived microbes have also been reported to affect the immune system. However, a mechanism to identify immunostimulatory and immunoregulatory microbes is needed. Here, we successfully established an in vitro screening system and identified an immunoregulatory bacterium, Lactobacillus pentosus KF340 (LP340), present in various fermented foods. LP340 induced a regulatory phenotype in mice Ag presenting cells which, in turn, induced IL-10 and IFN-γ producing Type 1 regulatory T cells (Tr1 cells) from naïve CD4+ T cells. Naïve CD4+ T cells co-cultured with LP340 treated dendritic cells highly expressed cytokine receptor IL-27R and were CD49b and lymphocyte-activation gene 3 double positive. Oral administration of LP340 in mice with atopic dermatitis reduced cellular infiltration in affected ear lobes and serum IgE levels, thus, ameliorating the disease symptoms. This suggests a systemic immunoregulatory effect of LP340. These findings demonstrate that LP340, a bacterium derived from food, prevents systemic inflammation through the induction of IL-10 producing Tr1 cells.

IL-10 producing regulatory and helper T-cells in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a highly heterogeneous autoimmune disease characterised by the production of pathogenic autoantibodies against nuclear self-antigens. The anti-inflammatory and tolerogenic cytokine Interleukin-10 appears to play a paradoxical pathogenic role in SLE and is therefore currently therapeutically targeted in clinical trials. It is generally assumed that the pathogenic effect of IL-10 in SLE is due to its growth and differentiation factor activity on autoreactive B-cells, but effects on other cells might also play a role. To date, a unique cellular source of pathogenic IL-10 in SLE has not been identified. In this review, we focus on the contribution of different CD4⁺T-cell subsets to IL-10 and autoantibody production in SLE. In particular, we discuss that IL-10 produced by different subsets of adaptive regulatory T-cells, follicular helper T-cells and extra-follicular B-helper T-cells is likely to have different effects on autoreactive B-cell responses. A better understanding of the role of IL-10 in B-cell responses and lupus would allow to identify the most promising therapies for individual SLE patients in the future.

Title: IL-10-producing T cells and their dual functions

Interleukin (IL)-10 is considered a prototypical anti-inflammatory cytokine, which significantly contributes to the maintenance and reestablishment of immune homeostasis. However, this classical view fails to fully describe the pleiotropic roles of IL-10. Indeed, IL-10 can also promote immune responses, e.g. by supporting B-cell and CD8⁺ T-cell activation. The reasons for these seemingly opposing functions are unclear to a large extent. Recent and previous studies suggest that the cellular source and the microenvironment impact the function of IL-10. However, studies addressing the mechanisms which determine whether IL-10 promotes inflammation or controls it have just begun. This review first summarizes the recent findings on the heterogeneity of IL-10 producing T cells and their impact on the target cells. Finally, we will propose two possible explanations for the dual functions of IL-10.

Functions and regulation of T cell-derived interleukin-10

Interleukin (IL)-10 is an essential anti-inflammatory cytokine and functions as a negative regulator of immune responses to microbial antigens. IL-10 is particularly important in maintaining the intestinal microbe-immune homeostasis. Loss of IL-10 promotes the development of inflammatory bowel disease (IBD) as a consequence of an excessive immune response to the gut microbiota. IL-10 also functions more generally to prevent excessive inflammation during the course of infection. Although IL-10 can be produced by virtually all cells of the innate and adaptive immune system, T cells constitute a non-redundant source for IL-10 in many cases. The various roles of T cell-derived IL-10 will be discussed in this review. Given that IL-10 is at the center of maintaining the delicate balance between effective immunity and tissue protection, it is not surprising that IL-10 expression is highly dynamic and tightly regulated. We summarize the environmental signals and molecular pathways that regulate IL-10 expression. While numerous studies have provided us with a deep understanding of IL-10 biology, the majority of findings have been made in murine models, prompting us to highlight gaps in our knowledge about T cell-derived IL-10 in the human system.

Gal-1 regulates dendritic cells-induced Treg/Th17 balance though NF-κB/RelB-IL-27 pathway

Background

This study aimed to investigate the mechanism of galectin (Gal)-1 of regulating Treg/Th17 in pathogenesis of acute rejection after liver transplantation in rat.

Methods

Mononuclear cells were induced to immature dendritic cells (imDCs), which were transfected with or without NF-κB/RelB. Western Blot was performed to detect the expression of NF-κB/RelB. the expression of CD11c, CD45RB, CD80 and MHC II were detected by flow cytometry. Enzyme-linked immunosorbent assay (ELISA) was employed to detect cytokines IL-27 and TGF-β. Lewis and dark agouti (DA) rats were generally anaesthetized by isoflurane inhalation to establish liver transplant models.

Results

We demonstrate that Gal-1 disturbs maturation of imDCs by downregulating NF-κB/RelB expression, and Gal-1 negatively controls CD4⁺ proliferation though IL-27 pathway.

Conclusions

In aggregate, Gal-1 promotes Treg differentiation in CD4⁺ T cells though NF-κB/RelB-IL-27 pathway. These findings suggest a new therapeutic target to mediate Treg population.

Epigenetic and transcriptional mechanisms for the regulation of IL-10

IL-10 is a critical immunoregulatory cytokine expressed in virtually all immune cell types. Maintaining a delicate balance between effective immune response and tolerance requires meticulous and dynamic control of IL-10 expression both epigenetically and transcriptionally. In this Review, we describe the epigenetic mechanisms controlling IL-10 expression, including chromatin remodeling, 3D chromatin loops, histone modification and DNA methylation. We discuss the role of transcription factors in directing chromatin modifications, with a special highlight on the emerging concept of pioneer transcription factors in setting up the chromatin landscape in T helper cells for IL-10 induction. Besides summarizing the recent progress on transcriptional regulation in specialized IL-10 producers such as type 1 regulatory T cells, regulatory B cells and regulatory innate lymphoid cells, we also discuss common transcriptional mechanisms for IL-10 regulation that are shared with other IL-10 producing cells.

Interleukin-10 mediated immune regulation after stem cell transplantation: Mechanisms and implications for therapeutic intervention

Interleukin-10 (IL-10) is a multi-faceted anti-inflammatory cytokine which plays an essential role in immune tolerance. Indeed, deficiency of IL-10 or its receptor results in aberrant immune responses that lead to immunopathology. Graft-versus-host disease (GVHD) is the limiting complication of allogeneic stem cell transplantation (SCT) and results from an imbalance in pathological versus regulatory immune networks. A number of immune cells exert their immunomodulatory role through secretion of IL-10 or induction of IL-10-secreting cells after SCT. Type-1 regulatory T cells (Tr1 cells) and FoxP3⁺ regulatory T cells (T_regs) are predominant sources of IL-10 after SCT and the critical role of this cytokine in preventing GVHD is now established. Recently, intriguing interactions among IL-10, immune cells, commensal microbes and host tissues in the gastrointestinal (GI) tract and other barrier surfaces have been uncovered. We now understand that IL-10 secretion is dynamically modulated by the availability of antigen, co-stimulatory signals, cytokines, commensal microbes and their metabolites in the microenvironment. In this review, we provide an overview of the control of IL-10 secretion and signaling after SCT and the therapeutic interventions, with a focus on Tr1 cells.

The Role of IL-10 in Malaria: A Double Edged Sword

IL-10 produced by CD4⁺ T cells suppresses inflammation by inhibiting T cell functions and the upstream activities of antigen presenting cells (APCs). IL-10 was first identified in Th2 cells, but has since been described in IFNγ-producing Tbet⁺ Th1, FoxP3⁺ CD4⁺ regulatory T (Treg) and IL-17-producing CD4⁺ T (Th17) cells, as well as many innate and innate-like immune cell populations. IL-10 production by Th1 cells has emerged as an important mechanism to dampen inflammation in the face of intractable infection, including in African children with malaria. However, although these type I regulatory T (Tr1) cells protect tissue from inflammation, they may also promote disease by suppressing Th1 cell-mediated immunity, thereby allowing infection to persist. IL-10 produced by other immune cells during malaria can also influence disease outcome, but the full impact of this IL-10 production is still unclear. Together, the actions of this potent anti-inflammatory cytokine along with other immunoregulatory mechanisms that emerge following Plasmodium infection represent a potential hurdle for the development of immunity against malaria, whether naturally acquired or vaccine-induced. Recent advances in understanding how IL-10 production is initiated and regulated have revealed new opportunities for manipulating IL-10 for therapeutic advantage. In this review, we will summarize our current knowledge about IL-10 production during malaria and discuss its impact on disease outcome. We will highlight recent advances in our understanding about how IL-10 production by specific immune cell subsets is regulated and consider how this knowledge may be used in drug delivery and vaccination strategies to help eliminate malaria.

Regulation of Interleukin-10 Expression

Interleukin (IL)-10 is an essential anti-inflammatory cytokine that plays important roles as a negative regulator of immune responses to microbial antigens. Loss of IL-10 results in the spontaneous development of inflammatory bowel disease as a consequence of an excessive immune response to the gut microbiota. IL-10 also functions to prevent excessive inflammation during the course of infection. IL-10 can be produced in response to pro-inflammatory signals by virtually all immune cells, including T cells, B cells, macrophages, and dendritic cells. Given its function in maintaining the delicate balance between effective immunity and tissue protection, it is evident that IL-10 expression is highly dynamic and needs to be tightly regulated. The transcriptional regulation of IL-10 production in myeloid cells and T cells is the topic of this review. Drivers of IL-10 expression as well as their downstream signaling pathways and transcription factors will be discussed. We will examine in more detail how various signals in CD4⁺ T cells converge on common transcriptional circuits, which fine-tune IL-10 expression in a context-dependent manner.

Roles, function and relevance of LAG3 in HIV infection

HIV causes several forms of immune dysfunction that need to be addressed in a functional cure for HIV. Immune exhaustion describes a dysfunctional phenotype caused by chronic cellular activation. Lymphocyte activation gene-3 (LAG3) is one of several negative coreceptors known as immune checkpoints that contribute to this exhaustion phenotype. Antibodies targeting immune checkpoints are now used clinically to restore immunity against cancer and hold promise in restoring immunity during HIV infection. Here, we summarize current knowledge surrounding LAG3 and discuss its relevance during HIV infection and the potential for LAG3-targeting antibodies in a functional HIV cure.

Molecular and functional heterogeneity of IL-10-producing CD4+ T cells

IL-10 is a prototypical anti-inflammatory cytokine, which is fundamental to the maintenance of immune homeostasis, especially in the intestine. There is an assumption that cells producing IL-10 have an immunoregulatory function. However, here we report that IL-10-producing CD4⁺ T cells are phenotypically and functionally heterogeneous. By combining single cell transcriptome and functional analyses, we identified a subpopulation of IL-10-producing Foxp3^neg CD4⁺ T cells that displays regulatory activity unlike other IL-10-producing CD4⁺ T cells, which are unexpectedly pro-inflammatory. The combinatorial expression of co-inhibitory receptors is sufficient to discriminate IL-10-producing CD4⁺ T cells with regulatory function from others and to identify them across different tissues and disease models in mice and humans. These regulatory IL-10-producing Foxp3^neg CD4⁺ T cells have a unique transcriptional program, which goes beyond the regulation of IL-10 expression. Finally, we found that patients with Inflammatory Bowel Disease demonstrate a deficiency in this specific regulatory T-cell subpopulation.

Tr1 cells are considered an immunosuppressive CD4 T cell population producing IL-10. Here the authors show that IL-10 is insufficient for Tr1 immunosuppression, define surface markers and transcriptional program of the immunosuppressive subset within Tr1, and reveal its deficiency in patients with IBD.

LAG-3 Inhibitory Receptor Expression Identifies Immunosuppressive Natural Regulatory Plasma Cells

B lymphocytes can suppress immunity through interleukin (IL)-10 production in infectious, autoimmune, and malignant diseases. Here, we have identified a natural plasma cell subset that distinctively expresses the inhibitory receptor LAG-3 and mediates this function in vivo. These plasma cells also express the inhibitory receptors CD200, PD-L1, and PD-L2. They develop from various B cell subsets in a B cell receptor (BCR)-dependent manner independently of microbiota in naive mice. After challenge they upregulate IL-10 expression via a Toll-like receptor-driven mechanism within hours and without proliferating. This function is associated with a unique transcriptome and epigenome, including the lowest amount of DNA methylation at the Il10 locus compared to other B cell subsets. Their augmented accumulation in naive mutant mice with increased BCR signaling correlates with the inhibition of memory T cell formation and vaccine efficacy after challenge. These natural regulatory plasma cells may be of broad relevance for disease intervention.

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LAG-3 expression identifies natural regulatory plasma cells

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LAG-3⁺CD138^hi plasma cells express IL-10 within hours of stimulation

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LAG-3⁺CD138^hi plasma cells have a unique epigenome poised to express IL-10

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LAG-3⁺CD138^hi plasma cells develop via an antigen-specific mechanism

Early Growth Response Gene 2-Expressing CD4+LAG3+ Regulatory T Cells: The Therapeutic Potential for Treating Autoimmune Diseases

Regulatory T cells (Tregs) are necessary for the maintenance of immune tolerance. Tregs are divided into two major populations: one is thymus derived and the other develops in the periphery. Among these Tregs, CD4⁺CD25⁺ Tregs, which mainly originate in the thymus, have been extensively studied. Transcription factor Foxp3 is well known as a master regulatory gene for the development and function of CD4⁺CD25⁺ Tregs. On the other hand, peripheral Tregs consist of distinct cell subsets including Foxp3-dependent extrathymically developed Tregs and interleukin (IL)-10-producing type I regulatory T (Tr1) cells. Lymphocyte activation gene 3 (LAG3) and CD49b are reliable cell surface markers for Tr1 cells. CD4⁺CD25⁻LAG3⁺ Tregs (LAG3⁺ Tregs) develop in the periphery and produce a large amount of IL-10. LAG3⁺ Tregs characteristically express the early growth response gene 2 (Egr2), a zinc-finger transcription factor, and exhibit its suppressive activity in a Foxp3-independent manner. Although Egr2 was known to be essential for hindbrain development and myelination of the peripheral nervous system, recent studies revealed that Egr2 plays vital roles in the induction of T cell anergy and also the suppressive activities of LAG3⁺ Tregs. Intriguingly, forced expression of Egr2 converts naive CD4⁺ T cells into IL-10-producing Tregs that highly express LAG3. Among the four Egr gene family members, Egr3 is thought to compensate for the function of Egr2. Recently, we reported that LAG3⁺ Tregs suppress humoral immune responses via transforming growth factor β3 production in an Egr2- and Egr3-dependent manner. In this review, we focus on the role of Egr2 in Tregs and also discuss its therapeutic potential for the treatment of autoimmune diseases.

Engineered T Regulatory Type 1 Cells for Clinical Application

T regulatory cells, a specialized subset of T cells, are key players in modulating antigen (Ag)-specific immune responses in vivo. Inducible T regulatory type 1 (Tr1) cells are characterized by the co-expression of CD49b and lymphocyte-activation gene 3 (LAG-3) and the ability to secrete IL-10, TGF-β, and granzyme (Gz) B, in the absence of IL-4 and IL-17. The chief mechanisms by which Tr1 cells control immune responses are secretion of IL-10 and TGF-β and killing of myeloid cells via GzB. Tr1 cells, first described in peripheral blood of patients who developed tolerance after HLA-mismatched fetal liver hematopoietic stem cell transplantation, have been proven to modulate inflammatory and effector T cell responses in several immune-mediated diseases. The possibility to generate and expand Tr1 cells in vitro in an Ag-specific manner has led to their clinical use as cell therapy in patients. Clinical grade protocols to generate or to enrich and expand Tr1 cell medicinal products have been established. Proof-of-concept clinical trials with Tr1 cell products have demonstrated the safety and the feasibility of this approach and indicated some clinical benefit. In the present review, we provide an overview on protocols established to induce/expand Tr1 cells in vitro for clinical application and on results obtained in Tr1 cell-based clinical trials. Moreover, we will discuss a recently developed protocol to efficient convert human CD4⁺ T cells into a homogeneous population of Tr1-like cells by lentiviral vector-mediated IL-10 gene transfer.

TH17 cell plasticity: The role of dendritic cells and molecular mechanisms

Upon interaction with dendritic cells (DCs), naïve CD4 T cells differentiate into distinct subsets and orchestrate the development of a physiological immune response. When uncontrolled by cellular and molecular mechanisms, CD4 T cells can also lead to immune mediated inflammatory diseases (IMIDs). Initially, these distinct CD4 T-cell subsets were defined according to the expression of a limited number of cytokines. Later it was revealed that CD4 T cells can acquire much more complex functional phenotypes than previously thought. Experimental data showed that the CD4 T-cell subset T_H17 can secrete IFN-γ and IL-4, which are signature molecules of other T-cell subsets. Furthermore, some T_H17 cells can also explore an anti-inflammatory fate and participate in the resolution of the immune response. A more flexible theory has therefore evolved with the scope to better represent the plastic biology of CD4 T cells. In this context, several aspects still remain unclear. The goal of this review is to discuss the role of extrinsic and intrinsic cellular and molecular mechanisms, which can drive the plasticity of T_H17 cells. In particular, we will outline the role of DCs and the function of transcriptional factors in shaping the fate of T_H17 cells towards either a pathogenic or a regulatory phenotype. Finally, we will discuss whether T_H17 cell plasticity could be a target for new therapies for IMIDs. We indeed envision that when the cellular and molecular mechanisms controlling T_H17 plasticity are known, new therapies, which aim to reset the immune system, will be developed. This will be achieved by either selectively depleting only the pathogenic T_H17 cells or, if possible, re converting these cells from pathogenic to regulatory. This will overcome the challenge posed by the immune suppressive side effects caused by the current therapies, which impair the function of CD4 cells or delete all of them, to the detriment of the patient.

Basic Aspects of T Helper Cell Differentiation

CD4+ T helper cells orchestrate the immune response and play a pivotal role during infection, chronic inflammatory, autoimmune diseases, and carcinogenesis. CD4+ T helper cells can be subdivided into different subsets, which are characterized by a specific network of transcriptional regulators and unique cytokine profiles: Th17 cells express RORγt that in turn promotes the transcription of Il17a, Il17f; Th1 cells, expresses T-bet and produces IFN-γ, IL-2, and TNF-α; Th2 cells express GATA-3 and secrete IL-4, IL-5, and IL-13. The two most studied regulatory T cell subtypes are Foxp3+ regulatory T cells, which can be generated either in the thymus (tTreg) or induced in peripheral lymphoid organs (pTregs) and type 1 regulatory T cells (Tr1), which are induced in the periphery. These T helper cell subsets can be differentiated from naïve T cells. In addition, recent findings indicate that some T helper cell subsets can emerge from other T helper cells, suggesting a certain degree of plastiticy. Here we report basic aspects of T helper cell differentiation and function while underlining some still open questions.

Host Methyltransferases and Demethylases: Potential New Epigenetic Targets for HIV Cure Strategies and Beyond

A successful HIV cure strategy may require reversing HIV latency to purge hidden viral reservoirs or enhancing HIV latency to permanently silence HIV transcription. Epigenetic modifying agents show promise as antilatency therapeutics in vitro and ex vivo, but also affect other steps in the viral life cycle. In this review, we summarize what we know about cellular DNA and protein methyltransferases (PMTs) as well as demethylases involved in HIV infection. We describe the biology and function of DNA methyltransferases, and their controversial role in HIV infection. We further explain the biology of PMTs and their effects on lysine and arginine methylation of histone and nonhistone proteins. We end with a focus on protein demethylases, their unique modes of action and their emerging influence on HIV infection. An outlook on the use of methylation-modifying agents in investigational HIV cure strategies is provided.

Functional heterogeneity of gut-resident regulatory T cells

Regulatory T cells (Treg cells) have a central role in the maintenance of intestinal homeostasis by restraining inappropriate immune responses in the healthy gut. Although distinct intestinal immune cell populations have been described to exhibit regulatory activity, several genetic and functional studies provided a strong evidence for a pivotal role of forkhead box P3 (Foxp3)⁺CD4⁺ Treg cells in prevention of dysregulated mucosal immune reactions and development of chronic immunological disorders such as celiac disease, food allergies and inflammatory bowel disease. Treg cells provide an important layer of intestinal defense by suppressing immune responses against innocuous food and commensal-derived antigens. Recent functional studies suggest that Treg cells are also involved in several other processes such as controlling microbial diversity in the gut, immunoglobulin A selection and supporting tissue repair in response to intestinal tissue damage. A better understanding of the functional heterogeneity as well as of the molecular signals, which regulate distinct intestinal Treg cell subsets, will encourage strategies aimed at transplanting the optimal Treg cell subset for cellular therapy in humans.

Differential regulation of Effector and Regulatory T cell function by Blimp1

The transcriptional regulator Blimp1 plays crucial roles in controlling terminal differentiation in several lineages. In T cells, Blimp1 is expressed in both effector (Teff) and regulatory (Treg) cells, and mice with T cell-specific deletion of Blimp1 (Blimp1CKO mice) spontaneously develop severe intestinal inflammation, indicating a crucial role for Blimp1 in T cell homeostasis regulation. Blimp1 has been shown to function as a direct activator of the Il10 gene and although its requirement for IL10 expression has been demonstrated in both Treg and Teff cells under inflammatory conditions, the intrinsic requirement of Blimp1 for homeostatic maintenance of these T cell subsets had not been investigated. Using mice with Foxp3⁺ Treg-cell specific deletion of Blimp1 and other approaches, here we show that Foxp3⁺ Treg cell-intrinsic expression of Blimp1 is required to control Treg and Teff cells homeostasis but, unexpectedly, it is dispensable to prevent development of severe spontaneous intestinal inflammation. In addition, we show that Blimp1 controls common and unique aspects of Treg and Teff cell function by differentially regulating gene expression in these T cell subsets. These findings document previously unappreciated aspects of Blimp1’s role in T cell biology and shed light on the intricate mechanisms regulating Treg and Teff cell function.

Neuroendocrine Modulation of IL-27 in Macrophages

Heterodimeric IL-27 (p28/EBV-induced gene 3) is an important member of the IL-6/IL-12 cytokine family. IL-27 is predominantly synthesized by mononuclear phagocytes and exerts immunoregulatory functional activities on lymphocytic and nonlymphocytic cells during infection, autoimmunity or neoplasms. There is a great body of evidence on the bidirectional interplay between the autonomic nervous system and immune responses during inflammatory disorders, but so far IL-27 has not been defined as a part of these multifaceted neuroendocrine networks. In this study, we describe the role of catecholamines (as mediators of the sympathetic nervous system) related to IL-27 production in primary mouse macrophages. Noradrenaline and adrenaline dose-dependently suppressed the release of IL-27p28 in LPS/TLR4-activated macrophages, which was independent of α₁ adrenoceptors. Instead, β₂ adrenoceptor activation was responsible for mediating gene silencing of IL-27p28 and EBV-induced gene 3. The β₂ adrenoceptor agonists formoterol and salbutamol mediated suppression of IL-27p28 production, when triggered by zymosan/TLR2, LPS/TLR4, or R848/TLR7/8 activation, but selectively spared the polyinosinic-polycytidylic acid/TLR3 pathway. Mechanistically, β₂ adrenergic signaling reinforced an autocrine feedback loop of macrophage-derived IL-10 and this synergized with inhibition of the JNK pathway for limiting IL-27p28. The JNK inhibitors SP600125 and AEG3482 strongly decreased intracellular IL-27p28 in F4/80⁺CD11b⁺ macrophages. In endotoxic shock of C57BL/6J mice, pharmacologic activation of β₂ adrenoceptors improved the severity of shock, including hypothermia and decreased circulating IL-27p28. Conversely, IL-27p28 was 2.7-fold increased by removal of the catecholamine-producing adrenal glands prior to endotoxic shock. These data suggest a novel role of the sympathetic neuroendocrine system for the modulation of IL-27-dependent acute inflammation.

New insights into Blimp-1 in T lymphocytes: a divergent regulator of cell destiny and effector function

B lymphocyte-induced maturation protein-1 (Blimp-1) serves as a master regulator of the development and function of antibody-producing B cells. Given that its function in T lymphocytes has been identified within the past decade, we review recent findings with emphasis on its role in coordinated control of gene expression during the development, differentiation, and function of T cells. Expression of Blimp-1 is mainly confined to activated T cells and is essential for the production of interleukin (IL)-10 by a subset of forkhead box (Fox)p3⁺ regulatory T cells with an effector phenotype. Blimp-1 is also required to induce cell elimination in the thymus and critically modulates peripheral T cell activation and proliferation. In addition, Blimp-1 promotes T helper (Th) 2 lineage commitment and limits Th1, Th17 and follicular helper T cell differentiation. Furthermore, Blimp-1 coordinates with other transcription factors to regulate expression of IL-2, IL-21 and IL-10 in effector T lymphocytes. In CD8⁺ T cells, Blimp-1 expression is distinct in heterogeneous populations at the stages of clonal expansion, differentiation, contraction and memory formation when they encounter antigens. Moreover, Blimp-1 plays a fundamental role in coordinating cytokine receptor signaling networks and transcriptional programs to regulate diverse aspects of the formation and function of effector and memory CD8⁺ T cells and their exhaustion. Blimp-1 also functions as a gatekeeper of T cell activation and suppression to prevent or dampen autoimmune disease, antiviral responses and antitumor immunity. In this review, we discuss the emerging roles of Blimp-1 in the complex regulation of gene networks that regulate the destiny and effector function of T cells and provide a Blimp-1-dominated transcriptional framework for T lymphocyte homeostasis.