Regulation of regulatory T cells: epigenetics and plasticity

Unveiling Novel Drug Targets and Emerging Therapies for Rheumatoid Arthritis: A Comprehensive Review

Rheumatoid arthritis (RA) is a chronic debilitating autoimmune disease, that causes joint damage, deformities, and decreased functionality. In addition, RA can also impact organs like the skin, lungs, eyes, and blood vessels. This autoimmune condition arises when the immune system erroneously targets the joint synovial membrane, resulting in synovitis, pannus formation, and cartilage damage. RA treatment is often holistic, integrating medication, physical therapy, and lifestyle modifications. Its main objective is to achieve remission or low disease activity by utilizing a "treat-to-target" approach that optimizes drug usage and dose adjustments based on clinical response and disease activity markers. The primary RA treatment uses disease-modifying antirheumatic drugs (DMARDs) that help to interrupt the inflammatory process. When there is an inadequate response, a combination of biologicals and DMARDs is recommended. Biological therapies target inflammatory pathways and have shown promising results in managing RA symptoms. Close monitoring for adverse effects and disease progression is critical to ensure optimal treatment outcomes. A deeper understanding of the pathways and mechanisms will allow new treatment strategies that minimize adverse effects and maintain quality of life. This review discusses the potential targets that can be used for designing and implementing precision medicine in RA treatment, spotlighting the latest breakthroughs in biologics, JAK inhibitors, IL-6 receptor antagonists, TNF blockers, and disease-modifying noncoding RNAs.

Applications of CRISPR Epigenome Editors in Tumor Immunology and Autoimmunity

Over the past decade, CRISPR-Cas systems have become indispensable tools for genetic engineering and have been used in clinical trials for various diseases. Beyond genome editing, CRISPR-Cas systems can also be used for performing programmable epigenetic modifications. Recent efforts in enhancing CRISPR-based epigenome modifiers have yielded potent tools enabling targeted DNA methylation/demethylation capable of sustaining epigenetic memory through numerous cell divisions. Moreover, it has been understood that during chronic inflammatory states, including cancer, T cells encounter a state called T cell exhaustion that involves elevated inhibitory receptors (e.g., LAG-3, TIM3, PD-1, CD39) and reduced effector T cell-related protein levels (IFN-γ, granzyme B, and perforin). Importantly, epigenetic dysregulation has been identified as one of the key drivers of T cell exhaustion, and it remains one of the biggest obstacles in the field of immunotherapy and decreases the efficiency of chimeric antigen receptor T (CAR-T) cell therapy. Similarly, autoimmune diseases exhibit epigenetically dysfunctional regulatory T (Treg) cells. For instance, FOXP3 intronic regions, known as conserved noncoding sequences, display hypomethylation in healthy states but hypermethylation in pathological contexts. Therefore, the reversal of epigenetic dysregulation in cancer and autoimmune diseases using CRISPR-based epigenome modifiers has important therapeutic implications. In this review, we outline the progressive refinement of CRISPR-based epigenome modifiers and explore their potential therapeutic applications in tumor immunology and autoimmunity.

Protein arginine N-methyltransferase 4 (PRMT4) contributes to lymphopenia in experimental sepsis

BACKGROUND

One hallmark of sepsis is the reduced number of lymphocytes, termed lymphopenia, that occurs from decreased lymphocyte proliferation or increased cell death contributing to immune suppression. Histone modification enzymes regulate immunity by their epigenetic and non-epigenetic functions; however, the role of these enzymes in lymphopenia remains elusive.

METHODS

We used molecular biological approaches to investigate the high expression and function of a chromatin modulator protein arginine N-methyltransferase 4 (PRMT4)/coactivator-associated arginine methyltransferase 1 in human samples from septic patients and cellular and animal septic models.

RESULTS

We identified that PRMT4 is elevated systemically in septic patients and experimental sepsis. Gram-negative bacteria and their derived endotoxin lipopolysaccharide (LPS) increased PRMT4 in B and T lymphocytes and THP-1 monocytes. Single-cell RNA sequencing results indicate an increase of PRMT4 gene expression in activated T lymphocytes. Augmented PRMT4 is crucial for inducing lymphocyte apoptosis but not monocyte THP-1 cells. Ectopic expression of PRMT4 protein caused substantial lymphocyte death via caspase 3-mediated cell death signalling, and knockout of PRMT4 abolished LPS-mediated lymphocyte death. PRMT4 inhibition with a small molecule compound attenuated lymphocyte death in complementary models of sepsis.

CONCLUSIONS

These findings demonstrate a previously uncharacterised role of a key chromatin modulator in lymphocyte survival that may shed light on devising therapeutic modalities to lessen the severity of septic immunosuppression.

CD27-Expressing Xenoantigen-Expanded Human Regulatory T Cells Are Efficient in Suppressing Xenogeneic Immune Response

Clinically, xenotransplantation often leads to T-cell-mediated graft rejection. Immunosuppressive agents including polyclonal regulatory T cells (poly-Tregs) promote global immunosuppression, resulting in serious infections and malignancies in patients. Xenoantigen-expanded Tregs (xeno-Tregs) have become a promising immune therapy strategy to protect xenografts with fewer side effects. In this study, we aimed to identify an efficient and stable subset of xeno-Tregs. We enriched CD27⁺ xeno-Tregs using cell sorting and evaluated their suppressive functions and stability in vitro via mixed lymphocyte reaction (MLR), real-time polymerase chain reaction, inflammatory induction assay, and Western blotting. A STAT5 inhibitor was used to investigate the relationship between the function and stability of CD27⁺ xeno-Tregs and the JAK3-STAT5 signaling pathway. A humanized xenotransplanted mouse model was used to evaluate the function of CD27⁺ xeno-Tregs in vivo. Our results show that CD27⁺ xeno-Tregs express higher levels of Foxp3, cytotoxic T-lymphocyte antigen-4 (CTLA4), and Helios and lower levels of interleukin-17 (IL-17) than their CD27^- counterparts. In addition, CD27⁺ xeno-Tregs showed enhanced suppressive function in xeno-MLR at ratios of 1:4 and 1:16 of Tregs:responder cells. Under inflammatory conditions, a lower percentage of CD27⁺ xeno-Tregs secretes IL-17 and interferon-γ (IFN-γ). CD27⁺ xeno-Tregs demonstrated an upregulated JAK3-STAT5 pathway compared with that of CD27^- xeno-Tregs and showed decreased Foxp3, Helios, and CTLA4 expression after addition of STAT5 inhibitor. Mice that received porcine skin grafts showed a normal tissue phenotype and less leukocyte infiltration after reconstitution with CD27⁺ xeno-Tregs. Taken together, these data indicate that CD27⁺ xeno-Tregs may suppress immune responses in a xenoantigen-specific manner, which might be related to the activation of the JAK3-STAT5 signaling pathway.

Rheumatoid Arthritis: Pathogenic Roles of Diverse Immune Cells

Rheumatoid arthritis (RA) is a chronic, systemic autoimmune disease associated with synovial tissue proliferation, pannus formation, cartilage destruction, and systemic complications. Currently, advanced understandings of the pathologic mechanisms of autoreactive CD4+ T cells, B cells, macrophages, inflammatory cytokines, chemokines, and autoantibodies that cause RA have been achieved, despite the fact that much remains to be elucidated. This review provides an updated pathogenesis of RA which will unveil novel therapeutic targets.

Lineage Reprogramming of Effector Regulatory T Cells in Cancer

Regulatory T-cells (Tregs) are important for maintaining self-tolerance and tissue homeostasis. The functional plasticity of Tregs is a key feature of this lineage, as it allows them to adapt to different microenvironments, adopt transcriptional programs reflective of their environments and tailor their suppressive capacity in a context-dependent fashion. Tregs, particularly effector Tregs (eTregs), are abundant in many types of tumors. However, the functional and transcriptional plasticity of eTregs in tumors remain largely to be explored. Although depletion or inhibition of systemic Tregs can enhance anti-tumor responses, autoimmune sequelae have diminished the enthusiasm for such approaches. A more effective approach should specifically target intratumoral Tregs or subvert local Treg-mediated suppression. This mini-review will discuss the reported mechanisms by which the stability and suppressive function of tumoral Tregs are modulated, with the focus on eTregs and a subset of eTregs, follicular regulatory T (T_FR) cells, and how to harness this knowledge for the future development of new effective cancer immunotherapies that selectively target the tumor local response while sparing the systemic side effects.

Function and Role of Regulatory T Cells in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a systemic and heterogeneous autoimmune disease with symmetrical polyarthritis as its critical clinical manifestation. The basic cause of autoimmune diseases is the loss of tolerance to self or harmless antigens. The loss or functional deficiency of key immune cells, regulatory T (Treg) cells, has been confirmed in human autoimmune diseases. The pathogenesis of RA is complex, and the dysfunction of Tregs is one of the proposed mechanisms underlying the breakdown of self-tolerance leading to the progression of RA. Treg cells are a vital component of peripheral immune tolerance, and the transcription factor Foxp3 plays a major immunosuppressive role. Clinical treatment for RA mainly utilizes drugs to alleviate the progression of disease and relieve disease activity, and the ideal treatment strategy should be to re-induce self-tolerance before obvious tissue injury. Treg cells are one of the ideal options. This review will introduce the classification, mechanism of action, and characteristics of Treg cells in RA, which provides insights into clinical RA treatment.

Regulatory T Cell Plasticity and Stability and Autoimmune Diseases

CD4⁺CD25⁺ regulatory T cells (Tregs) are a class of CD4⁺ T cells with immunosuppressive functions that play a critical role in maintaining immune homeostasis. However, in certain disease settings, Tregs demonstrate plastic differentiation, and the stability of these Tregs, which is characterized by the stable expression or protective epigenetic modifications of the transcription factor Foxp3, becomes abnormal. Plastic Tregs have some features of helper T (Th) cells, such as the secretion of Th-related cytokines and the expression of specific transcription factors in Th cells, but also still retain the expression of Foxp3, a feature of Tregs. Although such Th-like Tregs can secrete pro-inflammatory cytokines, they still possess a strong ability to inhibit specific Th cell responses. Therefore, the plastic differentiation of Tregs not only increases the complexity of the immune circumstances under pathological conditions, especially autoimmune diseases, but also shows an association with changes in the stability of Tregs. The plastic differentiation and stability change of Tregs play vital roles in the progression of diseases. This review focuses on the phenotypic characteristics, functions, and formation conditions of several plastic Tregs and also summarizes the changes of Treg stability and their effects on inhibitory function. Additionally, the effects of Treg plasticity and stability on disease prognosis for several autoimmune diseases were also investigated in order to better understand the relationship between Tregs and autoimmune diseases.

Enabling allogeneic therapies: CIRM-funded strategies for immune tolerance and immune evasion

A major goal for the field of regenerative medicine is to enable the safe and durable engraftment of allogeneic tissues and organs. In contrast to autologous therapies, allogeneic therapies can be produced for many patients, thus reducing costs and increasing availability. However, the need to overcome strong immune system barriers to engraftment poses a significant biological challenge to widespread adoption of allogeneic therapies. While the use of powerful immunosuppressant drugs has enabled the engraftment of lifesaving organ transplants, these drugs have serious side effects and often the organ is eventually rejected by the recipient immune system. Two conceptually different strategies have emerged to enable durable engraftment of allogeneic therapies in the absence of immune suppression. One strategy is to induce immune tolerance of the transplant, either by creating “mixed chimerism” in the hematopoietic system, or by retraining the immune system using modified thymic epithelial cells. The second strategy is to evade the immune system altogether, either by engineering the donor tissue to be “invisible” to the immune system, or by sequestering the donor tissue in an immune impermeable barrier. We give examples of research funded by the California Institute for Regenerative Medicine (CIRM) in each of these areas, ranging from early discovery‐stage work through clinical trials. The advancements that are being made in this area hold promise that many more patients will be able to benefit from regenerative medicine therapies in the future.

Metabolic Control of Treg Cell Stability, Plasticity, and Tissue-Specific Heterogeneity

Regulatory T (Treg) cells are crucial for peripheral immune tolerance and prevention of autoimmunity and tissue damage. Treg cells are inherently defined by the expression of the transcription factor Foxp3, which enforces lineage development and immune suppressive function of these cells. Under various conditions as observed in autoimmunity, cancer and non-lymphoid tissues, a proportion of Treg cells respond to specific environmental signals and display altered stability, plasticity and tissue-specific heterogeneity, which further shape their context-dependent suppressive functions. Recent studies have revealed that metabolic programs play pivotal roles in controlling these processes in Treg cells, thereby considerably expanding our understanding of Treg cell biology. Here we summarize these recent advances that highlight how cell-extrinsic factors, such as nutrients, vitamins and metabolites, and cell-intrinsic metabolic programs, orchestrate Treg cell stability, plasticity, and tissue-specific heterogeneity. Understanding metabolic regulation of Treg cells should provide new insight into immune homeostasis and disease, with important therapeutic implications for autoimmunity, cancer, and other immune-mediated disorders.

Epigenetic Regulation via Altered Histone Acetylation Results in Suppression of Mast Cell Function and Mast Cell-Mediated Food Allergic Responses

Mast cells are highly versatile cells that perform a variety of functions depending on the immune trigger, context of activation, and cytokine stimulus. Antigen-mediated mast cell responses are regulated by transcriptional processes that result in the induction of numerous genes contributing to mast cell function. Recently, we also showed that exposure to dietary agents with known epigenetic actions such as curcumin can suppress mast cell-mediated food allergy, suggesting that mast cell responses in vivo may be epigenetically regulated. To further assess the effects of epigenetic modifications on mast cell function, we examined the behavior of bone marrow-derived mast cells (BMMCs) in response to trichostatin A (TSA) treatment, a well-studied histone deacetylase inhibitor. IgE-mediated BMMC activation resulted in enhanced expression and secretion of IL-4, IL-6, TNF-α, and IL-13. In contrast, pretreatment with TSA resulted in altered cytokine secretion. This was accompanied by decreased expression of FcεRI and mast cell degranulation. Interestingly, exposure to non-IgE stimuli such as IL-33, was also affected by TSA treatment. Furthermore, continuous TSA exposure contributed to mast cell apoptosis and a decrease in survival. Further examination revealed an increase in I-κBα and a decrease in phospho-relA levels in TSA-treated BMMCs, suggesting that TSA alters transcriptional processes, resulting in enhancement of I-κBα transcription and decreased NF-κB activation. Lastly, treatment of wild-type mice with TSA in a model of ovalbumin-induced food allergy resulted in a significant attenuation in the development of food allergy symptoms including decreases in allergic diarrhea and mast cell activation. These data therefore suggest that the epigenetic regulation of mast cell activation during immune responses may occur via altered histone acetylation, and that exposure to dietary substances may induce epigenetic modifications that modulate mast cell function.

Restoring self-tolerance in autoimmune diseases by enhancing regulatory T-cells

Self-tolerance, the state of unresponsiveness to self-tissues/antigens, is maintained through central and peripheral tolerance mechanisms, and a breach of these mechanisms leads to autoimmune diseases. Foxp3 + T-regulatory cells (Tregs) play an essential role in suppressing autoimmune response directed against self-antigens and thereby regulate self-tolerance. Natural Tregs are differentiated in the thymus on the basis of their higher TCR-affinity to self-antigens and migrate to the periphery where they maintain peripheral tolerance. In addition, extra-thymic differentiation of induced Tregs can occur in the periphery which can control abrupt immune responses under inflammatory conditions. A defect in Treg cell numbers and/or function is found to be associated with the development of autoimmune disease in several experimental models and human autoimmune diseases. Moreover, augmentation of Tregs has been shown to be beneficial in treating autoimmunity in preclinical models, and Treg based cellular therapy has shown initial promise in clinical trials. However, emerging studies have identified an unstable subpopulation of Tregs which expresses pro-inflammatory cytokines under both homeostatic and autoimmune conditions, as well as in ex vivo cultures. In addition, clinical translation of Treg cellular therapy is impeded by limitations such as lack of easier methods for selective expansion of Tregs and higher cost associated with GMP-facilities required for cell sorting, ex vivo expansion and infusion of ex vivo expanded Tregs. Here, we discuss the recent advances in molecular mechanisms regulating Treg differentiation, Foxp3 expression and lineage stability, the role of Tregs in the prevention of various autoimmune diseases, and critically review their clinical utility for treating human autoimmune diseases.

Critical role of OX40 signaling in the TCR-independent phase of human and murine thymic Treg generation

Regulatory T cells (Tregs) play a pivotal role in immune-tolerance, and loss of Treg function can lead to the development of autoimmunity. Natural Tregs generated in the thymus substantially contribute to the Treg pool in the periphery, where they suppress self-reactive effector T cells (Teff) responses. Recently, we showed that OX40L (TNFSF4) is able to drive selective proliferation of peripheral Tregs independent of canonical antigen presentation (CAP-independent) in the presence of low-dose IL-2. Therefore, we hypothesized that OX40 signaling might be integral to the TCR-independent phase of murine and human thymic Treg (tTreg) development. Development of tTregs is a two-step process: Strong T-cell receptor (TCR) signals in combination with co-signals from the TNFRSF members facilitate tTreg precursor selection, followed by a TCR-independent phase of tTreg development in which their maturation is driven by IL-2. Therefore, we investigated whether OX40 signaling could also play a critical role in the TCR-independent phase of tTreg development. OX40^-/- mice had significantly reduced numbers of CD25^-Foxp3^low tTreg precursors and CD25⁺Foxp3⁺ mature tTregs, while OX40L treatment of WT mice induced significant proliferation of these cell subsets. Relative to tTeff cells, OX40 was expressed at higher levels in both murine and human tTreg precursors and mature tTregs. In ex vivo cultures, OX40L increased tTreg maturation and induced CAP-independent proliferation of both murine and human tTregs, which was mediated through the activation of AKT-mTOR signaling. These novel findings show an evolutionarily conserved role for OX40 signaling in tTreg development and proliferation, and might enable the development of novel strategies to increase Tregs and suppress autoimmunity.

Oestrogen Receptor-α binds the FOXP3 promoter and modulates regulatory T-cell function in human cervical cancer

Oestrogen controls Foxp3 expression in regulatory T cells (Treg cells) via a mechanism thought to involve oestrogen receptor alpha (ERα), but the molecular basis and functional impact of ERα signalling in Treg cells remain unclear. We report that ERα ligand oestradiol (E2) is significantly increased in human cervical cancer (CxCa) tissues and tumour-infiltrating Treg cells (CD4+CD25hiCD127low), whereas blocking ERα with the antagonist ICI 182,780 abolishes FOXP3 expression and impairs the function of CxCa infiltrating Treg cells. Using a novel approach of co-immunoprecipitation with antibodies to E2 for capture, we identified binding of E2:ERα complexes to FOXP3 protein in CxCa-derived Treg cells. Chromatin immunoprecipitation analyses of male blood Treg cells revealed ERα occupancy at the FOXP3 promoter and conserved non-coding DNA elements 2 and 3. Accordingly, computational analyses of the enriched regions uncovered eight putative oestrogen response elements predicted to form a loop that can activate the FOXP3 promoter. Together, these data suggest that E2-mediated ERα signalling is critical for the sustenance of FOXP3 expression and Treg cell function in human CxCa via direct interaction of ERα with FOXP3 promoter. Overall, our work gives a molecular insight into ERα signalling and highlights a fundamental role of E2 in controlling human Treg cell physiology.

Basic science for the clinician: Mechanisms of sublingual and subcutaneous immunotherapy

OBJECTIVE

To discuss the general immunologic changes that occur during immunotherapy, focusing on the differences between subcutaneous immunotherapy (SCIT) and sublingual immunotherapy (SLIT).

DATA SOURCES

PubMed literature review.

STUDY SELECTIONS

Articles pertaining to SCIT and SLIT, with specific emphasis on those that included immune mechanistic studies.

RESULTS

Both SCIT and SLIT are characterized by the induction of regulatory B and T cells, decreased allergen-specific T-cell proliferation, a shift from a TH2 to TH1 cytokine milieu and from an IgE to an IgG4/IgA antibody response. These changes are accompanied by clinical improvement in symptoms.

CONCLUSION

Immunotherapy using allergen extracts administered via both subcutaneous and sublingual approaches have demonstrated efficacy in the treatment of allergic rhinoconjunctivitis and other allergic conditions. There are subtle differences between the approaches, and understanding these differences may help clinicians select a preferred route of therapy for particular patients or allergens, depending on the immune response that is being targeted.

Development and function of Foxp3(+) regulatory T cells

Regulatory T cells (Tregs) have been recognized as having a major role in maintaining peripheral tolerance and preventing and limiting autoimmune and chronic inflammatory diseases. Tregs derive from the thymus and also develop peripherally. In this review, we discuss recent progress in our understanding of the basic mechanisms involved in Treg development and function in protecting against autoimmunity in the periphery, including thymic selection, peripheral induction and the many mechanisms of Treg suppression. Specifically in kidney disease, Tregs have been shown to play a role in limiting injury and may potentially have a therapeutic role.

Integrated analysis of DNA methylation and RNA‑sequencing data in Down syndrome

Down syndrome (DS) is the most common birth defect in children. To investigate the mechanisms of DS, the present study analyzed the bisulfite‑sequencing (seq) data GSE42144, which was downloaded from the Gene Expression Omnibus. GSE42144 included DNA methylation data of three DS samples and three control samples, and RNA‑seq data of two DS samples and five control samples. The methylated sites in the bisulfite‑seq data were detected using Bismark and Bowtie2. The BiSeq tool was applied to determine differentially methylated regions and to identify adjacent genes. Using the Database for Annotation, Visualization and Integrated Discovery, the functions of the abnormal demethylated genes were predicted by functional enrichment analyses. Differentially expressed genes (DEGs) were then screened using a paired t‑test. Furthermore, the interactions of the proteins encoded by selected genes were determined using the Search Tool for the Retrieval of Interacting Genes, and a protein‑protein interaction (PPI) network was constructed using Cytoscape. A total of 74 CpG regions showed significant differential DNA methylation between the DS and normal samples. There were five abnormal demethylated DNA regions in chromosome 21. In the DS samples, a total of 43 adjacent genes were identified with demethylation in their promoter regions and one adjacent gene was identified with upregulated methylation in its promoter regions. In addition, 584 upregulated genes were identified, including 24 genes with transcriptional regulatory function. In particular, upregulated Runt‑related transcription factor 1 (RUNX1) was located on chromosome 21. Functional enrichment analysis indicated that inhibitor of DNA binding 4 (ID4) was involved in neuronal differentiation and transcriptional suppression. In the PPI network, genes may be involved in DS by interacting with others, including nuclear receptor subfamily 4 group A member 2 (NR4A2)‑early growth response (EGR)2 and NR4A2‑EGR3. Therefore, RUNX1, NR4A2, EGR2, EGR3 and ID4 may be key genes associated with the pathogenesis of DS.

Impact of Enriched Environment on Murine T Cell Differentiation and Gene Expression Profile

T cells are known to be plastic and to change their phenotype according to the cellular and biochemical milieu they are embedded in. In this study, we transposed this concept at a macroscopic level assessing whether changes in the environmental housing conditions of C57/BL6 mice would influence the phenotype and function of T cells. Our study shows that exposure to 2 weeks in an enriched environment (EE) does not impact the T cell repertoire in vivo and causes no changes in the early TCR-driven activation events of these cells. Surprisingly, however, T cells from enriched mice showed a unique T helper effector cell phenotype upon differentiation in vitro. This was featured by a significant reduction in their ability to produce IFN-γ and by an increased release of IL-10 and IL-17. Microarray analysis of these cells also revealed a unique gene fingerprint with key signaling pathways involved in autoimmunity being modulated. Together, our results provide first evidence for a specific effect of EE on T cell differentiation and its associated changes in gene expression profile. In addition, our study sheds new light on the possible mechanisms by which changes in environmental factors can significantly influence the immune response of the host and favor the resolution of the inflammatory response.

Concise Review: Cellular Therapies: The Potential to Regenerate and Restore Tolerance in Immune-Mediated Intestinal Diseases

Chronic inflammatory enteropathies, including celiac disease, Crohn's disease, and ulcerative colitis, are lifelong disabling conditions whose cure is still an unmet need, despite the great strides made in understanding their complex pathogenesis. The advent of cellular therapies, mainly based on the use of stem cells, represents a great step forward thanks to their multitarget strategy. Both hematopoietic stem cells (HSC) and mesenchymal stem/stromal cells (MSC) have been employed in the treatment of refractory cases with promising results. The lack of immunogenicity makes MSC more suitable for therapeutic purposes as their infusion may be performed across histocompatibility locus antigen barriers without risk of rejection. The best outcome has been obtained when treating fistulizing Crohn's disease with local injections of MSC. In addition, both HSC and MSC proved successful in promoting regeneration of intestinal mucosa, and favoring the expansion of a T-cell regulatory subset. By virtue of the ability to favor mucosal homeostasis, this last cell population has been exploited in clinical trials, with inconsistent results. Finally, the recent identification of the epithelial stem cell marker has opened up the possibility of tissue engineering, with an array of potential applications for intestinal diseases. However, the underlying mechanisms of action of these interconnected therapeutic strategies are still poorly understood. It is conceivable that over the next few years their role will become clearer as the biological interactions with injured tissues and the hierarchy by which they deliver their action are unraveled through a continuous moving from bench to bedside and vice versa. Stem Cells 2016;34:1474-1486.

The NF-κB transcription factor RelA is required for the tolerogenic function of Foxp3(+) regulatory T cells

The properties of CD4(+) regulatory T cell (Treg) subsets are dictated by distinct patterns of gene expression determined by FOXP3 and different combinations of various transcription factors. Here we show the NF-κB transcription factor RelA is constitutively active in naïve and effector Tregs. The conditional inactivation of Rela in murine FOXP3(+) cells induces a rapid onset, multi-focal autoimmune disease that depends on RelA being expressed in conventional T cells. In addition to promoting Treg lineage stability, RelA determines the size of the effector Treg population, a function influenced by the presence or absence of RelA in conventional T cells. These findings showing that RelA controls Treg stability and promotes the competitive fitness of effector Tregs highlight the importance of RelA activity in peripheral Treg induced tolerance.

Continuum model of T-cell avidity: Understanding autoreactive and regulatory T-cell responses in type 1 diabetes

Type 1 diabetes (T1D) is an autoimmune disease that results from the destruction of insulin-secreting pancreatic β cells, leading to abolition of insulin secretion and onset of diabetes. Cytotoxic CD4(+) and CD8(+) T cells, activated by antigen presenting cells (APCs), are both implicated in disease onset and progression. Regulatory T cells (Tregs), on the other hand, play a leading role in regulating immunological tolerance and resistant homoeostasis in T1D by suppressing effector T cells (Teffs). Recent data indicates that after activation, conventional Teffs transiently produce interleukin IL-2, a cytokine that acts as a growth factor for both Teffs and Tregs. Tregs suppress Teffs through IL-2 deprivation, competition and Teff conversion into inducible Tregs (iTregs). To investigate the interactions of these components during T1D progression, a mathematical model of T-cell dynamics is developed as a predictor of β-cell loss, with the underlying hypothesis that avidity of Teffs and Tregs, i.e., the binding affinity of T-cell receptors to peptide-major histocompatibility complexes on host cells, is continuum. The model is used to infer a set of criteria that determines susceptibility to T1D in high risk subjects. Our findings show that diabetes onset is guided by the absence of Treg-to-Teff dominance at specific high avidities, rather than over the whole range of avidity, and that the lack of overall dominance of Teffs-to-Tregs over time is the underlying cause of the "honeymoon period", the remission phase observed in some T1D patients. The model also suggests that competition between Teffs and Tregs is more effective than Teff-induction into iTregs in suppressing Teffs, and that a prolonged full width at half maximum of IL-2 release is a necessary condition for curbing disease onset. Finally, the model provides a rationale for observing rapid and slow progressors of T1D based on modest heterogeneity in the kinetic parameters.

Unstable Foxp3+ regulatory T cells and altered dendritic cells are associated with lipopolysaccharide-induced fetal loss in pregnant interleukin 10-deficient mice

Maternal interleukin (IL) 10 deficiency elevates susceptibility to fetal loss induced by the model Toll-like receptor agonist lipopolysaccharide, but the mechanisms are not well elucidated. Here, we show that Il10 null mutant (Il10(-/-)) mice exhibit altered local T cell responses in pregnancy, exhibiting pronounced hyperplasia in para-aortic lymph nodes draining the uterus with >6-fold increased CD4(+) and CD8(+) T cells compared with wild-type controls. Among these CD4(+) cells, Foxp3(+) T regulatory (Treg) cells were substantially enriched, with 11-fold higher numbers at Day 9.5 postcoitum. Lymph node hypertrophy in Il10(-/-) mice was associated with more activated phenotypes in dendritic cells and macrophages, with elevated expression of MHCII, scavenger receptor, and CD80. Affymetrix microarray revealed an altered transcriptional profile in Treg cells from pregnant Il10(-/-) mice, with elevated expression of Ctse (cathepsin E), Il1r1, Il12rb2, and Ifng. In vitro, Il10(-/-) Treg cells showed reduced steady-state Foxp3 expression, and polyclonal stimulation caused greater loss of Foxp3 and reduced capacity to suppress IL17 in CD4(+)Foxp3(-) T cells. We conclude that despite a substantially expanded Treg cell pool, the diminished stability of Treg cells, increased numbers of effector T cells, and altered phenotypes in dendritic cells and macrophages in pregnancy all potentially confer vulnerability to inflammation-induced fetal loss in Il10(-/-) mice. These findings suggest that IL10 has a pivotal role in facilitating robust immune protection of the fetus from inflammatory challenge and that IL10 deficiency could contribute to human gestational disorders in which altered T cell responses are implicated.

Pathological conditions re-shape physiological Tregs into pathological Tregs

CD4⁺FOXP3⁺ regulatory T cells (Tregs) are a subset of CD4 T cells that play an essential role in maintaining peripheral immune tolerance, controlling acute and chronic inflammation, allergy, autoimmune diseases, and anti-cancer immune responses. Over the past 20 years, significant progress has been made since Tregs were first characterized in 1995. Many concepts and principles regarding Tregs generation, phenotypic features, subsets (tTregs, pTregs, iTregs, and iTreg35), tissue specificity (central Tregs, effector Tregs, and tissue resident Tregs), homeostasis (highly dynamic and apoptotic), regulation of Tregs by receptors for PAMPs and DAMPs, Treg plasticity (re-differentiation to other CD4 T helper cell subsets, Th1, Th2, Tfh and Th17), and epigenetic regulation of Tregs phenotypes and functions have been innovated. In this concise review, we want to briefly analyze these eight new progresses in the study of Tregs. We have also proposed for the first time a novel concept that "physiological Tregs" have been re-shaped into "pathological Tregs" in various pathological environments. Continuing of the improvement in our understanding on this important cellular component about the immune tolerance and immune suppression, would lead to the future development of novel therapeutics approaches for acute and chronic inflammatory diseases, allergy, allogeneic transplantation-related immunity, sepsis, autoimmune diseases, and cancers.

Treg-specific demethylated region activity in isolated regulatory t lymphocytes is a surrogate for disease severity in hepatocellular carcinoma

In certain unique conditions like viral infections of the liver like hepatitis B (HBV) and hepatitis C (HCV), activation of Tregs may be associated with chronicity of the viral infections and subsequent predisposition to development of hepatocellular carcinoma (HCC) by the integrated viral genome. In parallel, potential persistence of Tregs activity may lead to immune evasion of cancerous cells and thus persistence of the carcinomatous conditions. In this study, we hypothesized that although the relative proportions of Tregs may remain unaltered in HCC, persistence of activity of Tregs may lead to immune evasion in advanced stages of HCC. To examine the issue of activation of Treg in liver cancer pathogenesis, we obtained liver biopsy and peripheral blood samples from patients with advanced grades of HCC, isolated Tregs, and examined the methylation status of "Treg-specific demethylated region" (TSDR), a key region whose methylation suppresses Treg activity and demethylation stimulates its genomic activity. This study provides evidence of demethylation of TSDR, increased gene expression examined by luciferase assays, and nuclear translocation of key transcription factors that function as gene enhancers in CD4+CD25+FoxP3 regulatory T cells in advanced grades of HCC.

Proceedings: Immune Tolerance and Stem Cell Transplantation: A CIRM Mini-Symposium and Workshop Report

The mission of the California Institute for Regenerative Medicine (CIRM) is to accelerate stem cell treatments to patients with unmet medical needs. Immune rejection is one hurdle that stem cell therapies must overcome to achieve a durable and effective therapeutic benefit. In July 2014, CIRM convened a group of clinical investigators developing stem cell therapeutics, immunologists, and transplantation biologists to consider strategies to address this challenge. Workshop participants discussed current approaches for countering immune rejection in the context of organ transplant and cellular therapy and defined the risks, challenges, and opportunities for adapting them to the development of stem cell-based therapeutics. This effort led to the development of a Roadmap to Tolerance for allogeneic stem cell therapy, with four fundamental steps: (a) the need to identify "tolerance-permissive" immune-suppressive regimens to enable the eventual transition from current, drug-based approaches to a newer generation of technologies for inducing tolerance; (b) testing new biologics and small molecules for inducing tolerance in stem cell-based preclinical and clinical studies; (c) stimulation of efforts to develop novel therapeutic approaches to induce central and peripheral tolerance, including manipulation of the thymus, transplantation of purified stem cells, and cell therapy with T-regulatory cells; and (d) development of robust and sensitive immune monitoring technologies for identifying biomarkers of tolerance and rejection after allogeneic stem cell treatments in the clinical setting.