Homeostasis and anergy of CD4(+)CD25(+) suppressor T cells in vivo

CD137-expressing regulatory T cells in cancer and autoimmune diseases

Regulatory T cells (Tregs) are essential for maintaining immune homeostasis, with critical roles in preventing aberrant immune responses that occur in autoimmune diseases and chronic inflammation. Conversely, the abundance of Tregs in cancer is associated with impaired anti-tumor immunity, and tumor immune evasion. Recent work demonstrates that CD137, a well-known costimulatory molecule for T cells, is highly expressed on Tregs in pathological conditions, while its expression is minimal or negligible on peripheral Tregs. The expression of CD137 marks Tregs with potent immunosuppressive phenotype that foster cancer progression and are protective against certain autoimmune diseases. Hence CD137 has emerged as a marker for Tregs. However, several important questions still remain regarding the expression and function of CD137 in Tregs. Here, we provide an overview of our current knowledge of Treg mechanisms of action, with a focus on the role of CD137 in modulating Treg activity. We also explore the implications of CD137+ Tregs in both cancer and autoimmune diseases, emphasizing the significance of targeting these cells for therapeutic intervention in these conditions.

Activated/Cycling Treg Deficiency and Mitochondrial Alterations in Immunological Non-Responders to Antiretroviral Therapy

BACKGROUND

Regulatory T-cells (Tregs) play a crucial role in maintaining immune homeostasis, but their dynamics are altered in a subset of people living with Human Immunodeficiency Virus (HIV) known as immunological non-responders (INRs). INRs fail to reconstitute CD4+ T-cell counts despite viral suppression. This study aimed to examine Treg dysregulation in INRs, comparing them to immunological responders (IRs) and healthy controls (HCs).

METHODS

The study included 40 INRs, 42 IRs, and 23 HCs. Peripheral blood mononuclear cells were isolated and analyzed by flow cytometry. Conventional CD4+ T-cells (Tconvs) were identified as CD25-/loFOXP3- cells, while Tregs were identified as CD25+CD127loFOXP3+ CD4+ T-cells. Cells were further divided into naive, central memory, effector memory, and effector memory cells re-expressing CD45RA (TEMRA) subsets. Activated/cycling cells were identified as CD71+ and quiescent cells were CD71-. Mitochondrial mass and transmembrane potential were measured using MitoTracker Green and MitoTracker Orange dyes, respectively. Statistical comparisons were made using the Kruskal-Wallis test with Dunn's post-hoc analysis and Mann-Whitney U-test.

RESULTS

INRs exhibited the highest frequencies of activated/cycling CD4+ T-cells. The proportion of activated/cycling cells was higher in Tregs compared to Tconvs in all groups. Cycling rates of Tregs and Tconvs were correlated, suggesting Tregs help control Tconv proliferation. Despite high overall Treg frequencies in INRs, they showed a Treg deficiency in activated/cycling CD4+ T-cells, specifically in naive and central memory subsets, causing an imbalance in the Tconv/Treg ratio. This deficiency was hidden by increased Treg frequencies in quiescent effector memory CD4+ T-cells. Activated/cycling naive and memory Tregs from INRs had normal forkhead box P3 (FOXP3) and CD25 expression, but activated/cycling memory Tregs showed decreased ability to regulate mitochondrial transmembrane potential, indicating impaired mitochondrial fitness. These mitochondrial abnormalities were similar to those observed in memory conventional T-cells.

CONCLUSIONS

The complex Treg dysregulation in immunological non-responders involves quantitative and functional alterations, including a Treg deficiency within activated/cycling naive and central memory CD4+ T-cells, impaired mitochondrial fitness of activated/cycling memory Tregs, and functional disorders of the parent conventional T-lymphocytes. These findings underscore the need for a nuanced understanding of Treg dynamics in suboptimal CD4+ T-cell reconstitution during HIV-infection.

Hyperactivating EZH2 to augment H3K27me3 levels in regulatory T cells enhances immune suppression by driving early effector differentiation

The immunosuppressive function of regulatory T (Treg) cells is essential for maintaining immune homeostasis. Enhancer of zeste homolog 2 (EZH2), a histone H3 lysine 27 (H3K27) methyltransferase, plays a key role in maintaining Treg cell function upon CD28 co-stimulation, and Ezh2 deletion in Treg cells causes autoimmunity. Here, we assess whether increasing H3K27me3 levels, by using an Ezh2Y641F gain-of-function mutation, will improve Treg cell function. We find that Treg cells expressing Ezh2Y641F display an effector Treg phenotype, are poised for improved homing to organ tissues, and can accelerate remission from autoimmunity. The H3K27me3 landscape and transcriptome of naive Ezh2Y641F Treg cells exhibit a redistribution of H3K27me3 modifications that recapitulates the gene expression profile of activated Ezh2WT Treg cells after CD28 co-stimulation. Altogether, increased H3K27me3 levels promote the differentiation of effector Treg cells that can better suppress autoimmunity.

Increased EZH2 function in regulatory T cells promotes their capacity to suppress autoimmunity by driving effector differentiation prior to activation

The immunosuppressive function of regulatory T (Treg) cells is essential for maintaining immune homeostasis. Enhancer of zeste homolog 2 (EZH2), a histone H3 lysine 27 (H3K27) methyltransferase, plays a key role in maintaining Treg cell function upon CD28 co-stimulation, and Ezh2 deletion in Treg cells causes autoimmunity. Here we assessed whether increased EZH2 activity in Treg cells would improve Treg cell function. Using an Ezh2 gain-of-function mutation, Ezh2 Y641F , we found that Treg cells expressing Ezh2 Y641F displayed an increased effector Treg phenotype and were poised for improved homing to organ tissues. Expression of Ezh2 Y641F in Treg cells led to more rapid remission from autoimmunity. H3K27me3 profiling and transcriptomic analysis revealed a redistribution of H3K27me3, which prompted a gene expression profile in naïve Ezh2 Y641F Treg cells that recapitulated aspects of CD28-activated Ezh2 WT Treg cells. Altogether, increased EZH2 activity promotes the differentiation of effector Treg cells that can better suppress autoimmunity.

Highlights

EZH2 function promotes effector differentiation of Treg cells.EZH2 function promotes Treg cell migration to organ tissues.EZH2 function in Treg cells improves remission from autoimmunity.EZH2 function poises naïve Treg cells to adopt a CD28-activated phenotype.

Beyond FOXP3: a 20-year journey unravelling human regulatory T-cell heterogeneity

The initial idea of a distinct group of T-cells responsible for suppressing immune responses was first postulated half a century ago. However, it is only in the last three decades that we have identified what we now term regulatory T-cells (Tregs), and subsequently elucidated and crystallized our understanding of them. Human Tregs have emerged as essential to immune tolerance and the prevention of autoimmune diseases and are typically contemporaneously characterized by their CD3+CD4+CD25high CD127lowFOXP3+ phenotype. It is important to note that FOXP3+ Tregs exhibit substantial diversity in their origin, phenotypic characteristics, and function. Identifying reliable markers is crucial to the accurate identification, quantification, and assessment of Tregs in health and disease, as well as the enrichment and expansion of viable cells for adoptive cell therapy. In our comprehensive review, we address the contributions of various markers identified in the last two decades since the master transcriptional factor FOXP3 was identified in establishing and enriching purity, lineage stability, tissue homing and suppressive proficiency in CD4+ Tregs. Additionally, our review delves into recent breakthroughs in innovative Treg-based therapies, underscoring the significance of distinct markers in their therapeutic utilization. Understanding Treg subsets holds the key to effectively harnessing human Tregs for immunotherapeutic approaches.

Classification of regulatory T cells and their role in myocardial ischemia-reperfusion injury

Myocardial ischemia-reperfusion injury (MIRI) is closely related to the final infarct size in acute myocardial infarction (AMI). Therefore, reducing MIRI can effectively improve the prognosis of AMI patients. At the same time, the healing process after AMI is closely related to the local inflammatory microenvironment. Regulatory T cells (Tregs) can regulate various physiological and pathological immune inflammatory responses and play an important role in regulating the immune inflammatory response after AMI. However, different subtypes of Tregs have different effects on MIRI, and the same subtype of Tregs may also have different effects at different stages of MIRI. This article systematically reviews the classification and function of Tregs, as well as the role of various subtypes of Tregs in MIRI. A comprehensive understanding of the role of each subtype of Tregs can help design effective methods to control immune reactions, reduce MIRI, and provide new potential therapeutic options for AMI.

OX40 shapes an inflamed tumor immune microenvironment and predicts response to immunochemotherapy in diffuse large B-cell lymphoma

OX40 enhances the T-cell activation via costimulatory signaling. However, its molecular characteristics and value in predicting response to immunochemotherapy in DLBCL remain largely unexplored. Here, we performed an integrative analysis of sequencing and multiplex immunofluorescence staining, and discovered abnormally higher expression of OX40 in DLBCL patients. Elevated OX40 could activate T cells leading to a higher immune score for tumor immune microenvironment (TiME). OX40 upregulation simultaneously happened with immune-related genes including PD-1, CTLA4 and TIGIT et,al. Patients with high OX40 expression exhibited a lower Ann Arbor stage and IPI score and more easily achieved a complete response/partial response. The analysis of infiltrated T-cell subset revealed that patients with a greater number of CD4+/OX40+ or CD8+/OX40+ T cells had a longer OS. Our findings indicated that OX40 shapes an inflamed tumor immune microenvironment and predicts response to immunochemotherapy, providing insights for the application of OX40 agonist in DLBCL patients.

GZMKhigh CD8+ T effector memory cells are associated with CD15high neutrophil abundance in non-metastatic colorectal tumors and predict poor clinical outcome

CD8⁺ T cells are a major prognostic determinant in solid tumors, including colorectal cancer (CRC). However, understanding how the interplay between different immune cells impacts on clinical outcome is still in its infancy. Here, we describe that the interaction of tumor infiltrating neutrophils expressing high levels of CD15 with CD8⁺ T effector memory cells (T_EM) correlates with tumor progression. Mechanistically, stromal cell-derived factor-1 (CXCL12/SDF-1) promotes the retention of neutrophils within tumors, increasing the crosstalk with CD8⁺ T cells. As a consequence of the contact-mediated interaction with neutrophils, CD8⁺ T cells are skewed to produce high levels of GZMK, which in turn decreases E-cadherin on the intestinal epithelium and favors tumor progression. Overall, our results highlight the emergence of GZMK^high CD8⁺ T_EM in non-metastatic CRC tumors as a hallmark driven by the interaction with neutrophils, which could implement current patient stratification and be targeted by novel therapeutics.

The long and winding road: From mouse linkage studies to a novel human therapeutic pathway in type 1 diabetes

Autoimmunity involves a loss of immune tolerance to self-proteins due to a combination of genetic susceptibility and environmental provocation, which generates autoreactive T and B cells. Genetic susceptibility affects lymphocyte autoreactivity at the level of central tolerance (e.g., defective, or incomplete MHC-mediated negative selection of self-reactive T cells) and peripheral tolerance (e.g., failure of mechanisms to control circulating self-reactive T cells). T regulatory cell (Treg) mediated suppression is essential for controlling peripheral autoreactive T cells. Understanding the genetic control of Treg development and function and Treg interaction with T effector and other immune cells is thus a key goal of autoimmunity research. Herein, we will review immunogenetic control of tolerance in one of the classic models of autoimmunity, the non-obese diabetic (NOD) mouse model of autoimmune Type 1 diabetes (T1D). We review the long (and still evolving) elucidation of how one susceptibility gene, Cd137, (identified originally via linkage studies) affects both the immune response and its regulation in a highly complex fashion. The CD137 (present in both membrane and soluble forms) and the CD137 ligand (CD137L) both signal into a variety of immune cells (bi-directional signaling). The overall outcome of these multitudinous effects (either tolerance or autoimmunity) depends upon the balance between the regulatory signals (predominantly mediated by soluble CD137 via the CD137L pathway) and the effector signals (mediated by both membrane-bound CD137 and CD137L). This immune balance/homeostasis can be decisively affected by genetic (susceptibility vs. resistant alleles) and environmental factors (stimulation of soluble CD137 production). The discovery of the homeostatic immune effect of soluble CD137 on the CD137-CD137L system makes it a promising candidate for immunotherapy to restore tolerance in autoimmune diseases.

R4 RGS proteins as fine tuners of immature and mature hematopoietic cell trafficking

G-protein-coupled receptors (GPCRs) are the largest and most diverse group of membrane receptors. They are involved in almost every physiologic process and consequently have a pivotal role in an extensive number of pathologies, including genetic, neurologic, and immune system disorders. Indeed, the vast array of GPCRs mechanisms have led to the development of a tremendous number of drug therapies and already account for about a third of marketed drugs. These receptors mediate their downstream signals primarily via G proteins. The regulators of G-protein signaling (RGS) proteins are now in the spotlight as the critical modulatory factors of active GTP-bound Gα subunits of heterotrimeric G proteins to fine-tune the biologic responses driven by the GPCRs. Also, they possess noncanonical functions by multiple mechanisms, such as protein-protein interactions. Essential roles and impacts of these RGS proteins have been revealed in physiology, including hematopoiesis and immunity, and pathologies, including asthma, cancers, and neurologic disorders. This review focuses on the largest subfamily of R4 RGS proteins and provides a brief overview of their structures and G-proteins selectivity. With particular interest, we explore and highlight, their expression in the hematopoietic system and the regulation in the engraftment of hematopoietic stem/progenitor cells (HSPCs). Distinct expression patterns of R4 RGS proteins in the hematopoietic system and their pivotal roles in stem cell trafficking pave the way for realizing new strategies for enhancing the clinical performance of hematopoietic stem cell transplantation. Finally, we discuss the exciting future trends in drug development by targeting RGS activity and expression with small molecules inhibitors and miRNA approaches.

CD103 integrin identifies a high IL-10-producing FoxP3+ regulatory T-cell population suppressing allergic airway inflammation

BACKGROUND

Although FoxP3⁺ regulatory T (Treg) cells constitute a highly heterogeneous population, with different regulatory potential depending on the disease context, distinct subsets or phenotypes remain poorly defined. This hampers the development of immunotherapy for allergic and autoimmune disorders. The present study aimed at characterizing distinct FoxP3⁺ Treg subpopulations involved in the suppression of Th2-mediated allergic inflammation in the lung.

METHODS

We used an established mouse model of allergic airway disease based on ovalbumin sensitization and challenge to analyze FoxP3⁺ Tregs during the induction and resolution of inflammation, and identify markers that distinguish their most suppressive phenotypes. We also developed a new knock-in mouse model (Foxp3^cre Cd103^dtr ) enabling the specific ablation of CD103⁺ FoxP3⁺ Tregs for functional studies.

RESULTS

We found that during resolution of allergic airway inflammation in mice >50% of FoxP3⁺ Treg cells expressed the integrin CD103 which marks FoxP3⁺ Treg cells of high IL-10 production, increased expression of immunoregulatory molecules such as KLRG1, ICOS and CD127, and enhanced suppressive capacity for Th2-mediated inflammatory responses. CD103⁺ FoxP3⁺ Tregs were essential for keeping allergic inflammation under control as their specific depletion in Foxp3^cre Cd103^dtr mice lead to severe alveocapillary damage, eosinophilic pneumonia, and markedly reduced lifespan of the animals. Conversely, adoptive transfer of CD103⁺ FoxP3⁺ Tregs effectively treated disease, attenuating Th2 responses and allergic inflammation in an IL-10-dependent manner.

CONCLUSIONS

Our study identifies a novel regulatory T-cell population, defined by CD103 expression, programmed to prevent exuberant type 2 inflammation and keep homeostasis in the respiratory tract under control. This has important therapeutic implications.

Immune Checkpoints OX40 and OX40L in Small-Cell Lung Cancer: Predict Prognosis and Modulate Immune Microenvironment

Background

OX40 and OX40 ligand (OX40L), as essential immune checkpoint (IC) modulators, are highly correlated with cancer immunity regulation as well as tumor microenvironment (TME). Immunotherapy showed outstanding advantages in small-cell lung cancer (SCLC) therapy. However, functions and clinical significance of OX40 and OX40L in SCLC were not clear yet.

Materials and Methods

SCLC samples of 143 patients were collected for immunohistochemistry (IHC) or whole-exome sequencing (WES). We comprehensively explored the expression and mutation of OX40/OX40L in SCLC, and systematically linked OX40/OX40L with TME.

Results

The expression of OX40/OX40L on tumor cells and tumor-infiltrating lymphocytes (TILs) was found in the IHC cohort and verified in other cohorts with SCLC tissues and cell lines. The results showed co-expression patterns among OX40/OX40L, other ICs, and T-cell markers. The WES data suggested that OX40/OX40L mutation is rare in SCLC (<5%). Patients with positive OX40 protein expression on TILs showed substantially higher recurrence-free survival than those with negative expression (p=0.009). The external dataset also indicated that high OX40/OX40L expression was correlated with better prognosis [overall survival: OX40, p<0.001; OX40L, p=0.019]. Importantly, activation of immunity and high infiltration of CD4(+) and CD8(+) T cells were observed in the high OX40/OX40L expression group.

Conclusions

Collectively, this work highlighted the significance of OX40 and OX40L in prognosis and TME cell infiltration characterization of SCLC. Evaluating the OX40/OX40L-expression levels of individual patients with SCLC might contribute to guiding more precise therapy.

Targeting Leukocyte Trafficking in Inflammatory Bowel Disease

In the last two decades, understanding of inflammatory bowel disease (IBD) immunopathogenesis has expanded considerably. Histopathological examination of the intestinal mucosa in IBD demonstrates the presence of a chronic inflammatory cell infiltrate. Research has focused on identifying mechanisms of immune cell trafficking to the gastrointestinal tract that may represent effective gut-selective targets for IBD therapy whilst avoiding systemic immunosuppression that may be associated with off-target adverse effects such as infection and malignancy. Integrins are cell surface receptors that can bind to cellular adhesion molecules to mediate both leukocyte homing and retention. In 2014, Vedolizumab (Entyvio^®) was the first anti-integrin (anti-α4ß7 monoclonal antibody) treatment to be approved for use in IBD. Several other anti-integrin therapies are currently in advanced stages of development, including novel orally administered small-molecule drugs. Drugs targeting alternative trafficking mechanisms such as mucosal addressin cellular adhesion molecule-1 and sphingosine-1-phosphate receptors are also being evaluated. Here, we summarise key established and emerging therapies targeting leukocyte trafficking that may play an important role in realising the goal of stratified precision medicine in IBD care.

In Vivo Expansion of Antigen-Specific Regulatory T Cells through Staggered Fc.IL-2 Mutein Dosing and Antigen-Specific Immunotherapy

In mice, Ag administration in the absence of adjuvant typically elicits tolerogenic immune responses through the deletion or inactivation of conventional CD4 T cells and the formation or expansion of regulatory CD4 T cells (Treg). Although these "Ag-specific immunotherapy" (ASI) approaches are currently under clinical development to treat autoinflammatory conditions, efficacy and safety may be variable and unpredictable because of the diverse activation states of immune cells in subjects with autoimmune and allergic diseases. To reliably induce Ag-specific tolerance in patients, novel methods to control T cell responses during ASI are needed, and strategies that permanently increase Treg frequencies among Ag-specific CD4 T cells may provide long-lasting immunosuppression between treatments. In this study, we present an approach to durably increase the frequency of Ag-specific Treg in mice by administering ASI when Treg numbers are transiently increased with individual doses of a half-life-extended Treg-selective IL-2 mutein. Repeated weekly cycles of IL-2 mutein doses (day 0) followed by ASI (day 3) resulted in a 3- to 5-fold enrichment in Treg among Ag-responsive CD4 T cells. Expanded Ag-specific Treg persisted for more than 3 wk following treatment cessation, as well as through an inflammatory T cell response to an Ag-expressing virus. Combining Treg enrichment with ASI has the potential to durably treat autoimmune disease or allergy by increasing the Treg/conventional CD4 T cell ratio among autoantigen- or allergen-specific T cells.

Expansion of tumor-associated Treg cells upon disruption of a CTLA-4-dependent feedback loop

Foxp3+ T regulatory (Treg) cells promote immunological tumor tolerance, but how their immune-suppressive function is regulated in the tumor microenvironment (TME) remains unknown. Here, we used intravital microscopy to characterize the cellular interactions that provide tumor-infiltrating Treg cells with critical activation signals. We found that the polyclonal Treg cell repertoire is pre-enriched to recognize antigens presented by tumor-associated conventional dendritic cells (cDCs). Unstable cDC contacts sufficed to sustain Treg cell function, whereas T helper cells were activated during stable interactions. Contact instability resulted from CTLA-4-dependent downregulation of co-stimulatory B7-family proteins on cDCs, mediated by Treg cells themselves. CTLA-4-blockade triggered CD28-dependent Treg cell hyper-proliferation in the TME, and concomitant Treg cell inactivation was required to achieve tumor rejection. Therefore, Treg cells self-regulate through a CTLA-4- and CD28-dependent feedback loop that adjusts their population size to the amount of local co-stimulation. Its disruption through CTLA-4-blockade may off-set therapeutic benefits in cancer patients.

The OX40/OX40L Axis Regulates T Follicular Helper Cell Differentiation: Implications for Autoimmune Diseases

T Follicular helper (Tfh) cells, a unique subset of CD4+ T cells, play an essential role in B cell development and the formation of germinal centers (GCs). Tfh differentiation depends on various factors including cytokines, transcription factors and multiple costimulatory molecules. Given that OX40 signaling is critical for costimulating T cell activation and function, its roles in regulating Tfh cells have attracted widespread attention. Recent data have shown that OX40/OX40L signaling can not only promote Tfh cell differentiation and maintain cell survival, but also enhance the helper function of Tfh for B cells. Moreover, upregulated OX40 signaling is related to abnormal Tfh activity that causes autoimmune diseases. This review describes the roles of OX40/OX40L in Tfh biology, including the mechanisms by which OX40 signaling regulates Tfh cell differentiation and functions, and their close relationship with autoimmune diseases.

A most versatile kinase: The catalytic subunit of PKA in T-cell biology

The cAMP-dependent protein kinase, more commonly referred to as protein kinase A (PKA), is one of the most-studied enzymes in biology. PKA is ubiquitously expressed in mammalian cells, can be activated in response to a plethora of biological stimuli, and phosphorylates more than 250 known substrates. Indeed, PKA is of central importance to a wide range of organismal processes, including energy homeostasis, memory formation and immunity. It serves as the primary effector of the second-messenger molecule 3',5'-cyclic adenosine monophosphate (cAMP), which is believed to have mostly inhibitory effects on the adaptive immune response. In particular, elevated levels of intracellular cAMP inhibit the activation of conventional T cells by limiting signal transduction through the T-cell receptor and altering gene expression, primarily in a PKA-dependent manner. Regulatory T cells have been shown to increase the cAMP levels in adjacent T cells by direct and indirect means, but the role of cAMP within regulatory T cells themselves remains incompletely understood. Paradoxically, cAMP has been implicated in promoting T-cell activation as well, adding another functional dimension beyond its established immunosuppressive effects. Furthermore, PKA can phosphorylate the NF-κB subunit p65, a transcription factor that is essential for T-cell activation, independently of cAMP. This phosphorylation of p65 drastically enhances NF-κB-dependent transcription and thus is likely to facilitate immune activation. How these immunosuppressive and immune-activating properties of PKA balance in vivo remains to be elucidated. This review provides a brief overview of PKA regulation, its ability to affect NF-κB activation, and its diverse functions in T-cell biology.

CD4+CD25-FoxP3+ T cells: a distinct subset or a heterogeneous population?

In addition to generating effective immunity against infectious agents, the immune system helps to fight against different noninfectious human diseases while maintaining the balance between self and non-self discrimination. The breakdown of tolerance in autoimmune diseases or sustainable tolerance in an abnormal microenvironment such as chronic inflammation may initiate the process of malignancy. Immune system regulation is controlled by a complex, dynamic network of cells and mediators. Understanding the cellular and molecular basis of immune regulation provides better insight into the mechanisms governing the immune pathology of diseases. Among several cellular subsets and mediators with regulatory roles, a subpopulation of CD4⁺ T cells was recently reported to be positive for FoxP3 and negative for CD25, with a suggested range of functional activities in both cancer and autoimmune diseases. This CD4 subset was first reported in 2006 and thought to have a role in the pathogenesis of cancer. However, the spectrum of roles played by this T cell subset is broad, and no consensus has been reached regarding its immunological functions. In this review, we focused on the possible origin of CD4⁺CD25^‒FoxP3⁺ T cells and their function in cancer and autoimmune diseases.

The CD137 Ligand Is Important for Type 1 Diabetes Development but Dispensable for the Homeostasis of Disease-Suppressive CD137+ FOXP3+ Regulatory CD4 T Cells

CD137 modulates type 1 diabetes (T1D) progression in NOD mice. We previously showed that CD137 expression in CD4 T cells inhibits T1D, but its expression in CD8 T cells promotes disease development by intrinsically enhancing the accumulation of β-cell-autoreactive CD8 T cells. CD137 is expressed on a subset of FOXP3+ regulatory CD4 T cells (Tregs), and CD137+ Tregs are the main source of soluble CD137. Soluble CD137 suppresses T cells in vitro by binding to the CD137 ligand (CD137L) upregulated on activated T cells. To further study how the opposing functions of CD137 are regulated, we successfully targeted Tnfsf9 (encoding CD137L) in NOD mice using the CRISPR/Cas9 system (designated NOD.Tnfsf9 -/-). Relative to wild-type NOD mice, T1D development in the NOD.Tnfsf9 -/- strain was significantly delayed, and mice developed less insulitis and had reduced frequencies of β-cell-autoreactive CD8 T cells. Bone marrow chimera experiments showed that CD137L-deficient hematopoietic cells were able to confer T1D resistance. Adoptive T cell transfer experiments showed that CD137L deficiency on myeloid APCs was associated with T1D suppression. Conversely, lack of CD137L on T cells enhanced their diabetogenic activity. Furthermore, neither CD137 nor CD137L was required for the development and homeostasis of FOXP3+ Tregs. However, CD137 was critical for the in vivo T1D-suppressive activity of FOXP3+ Tregs, suggesting that the interaction between CD137 and CD137L regulates their function. Collectively, our results provide new insights into the complex roles of CD137-CD137L interaction in T1D.

Traitor or warrior-Treg cells sneaking into the lesions of psoriatic arthritis

Regulatory T (Treg) cells have been recognized to maintain immune tolerance, which contributes to prevention of autoimmune diseases. However, recent evidence has demonstrated different characteristics of these cells between those that are in circulation compared to those in various local tissues. In addition, the ability of Treg cells to have plasticity in certain disease settings and in inflammatory lesions has been increasingly recognized. Herein we summarize updated knowledge of Treg biology and discuss the current understanding of tissue-resident Treg cells in psoriatic arthritis (PsA), attempting to provide new insights into precise role of Treg cells in the immune response and as a possible therapeutic intervention in patients with PsA.

Analysis of regulatory T cells and CTLA-4 expression in pregnant women according to seropositivity to Toxoplasma gondii

Pregnancy is considered a period in which immunomodulation occurs, although it is important for the maintenance of the foetus, could contribute to infections as Toxoplasma gondii. Immune response cells such as regulatory T cells participate in this immunomodulation, and surface molecules such as CTLA-4 develop an immunosuppressive role, could contribute to the establishment of the parasite. This study aimed to evaluate the presence of regulatory T cells and the expression of CTLA-4 in parturient and non-pregnant seropositive and seronegative for anti-T. gondii antibodies. Sixty-two participants were evaluated, 14 parturient with negative serology, 23 parturient with positive serology, 16 non-pregnant women seronegative and 9 non-pregnant women seropositive. Immunophenotyping was performed for characterize TCD4+Foxp3+ cells, T CD4+CD25-Foxp3+, TCD4+CD25highFoxp3+, TCD4+CTLA-4+, TCD4+CD25-CTLA-4+ and TCD4+CD25highCTLA-4+. We observed a lower level of CD4+CD25highFoxp3+ cells from seropositive parturient compared with seropositive non-pregnant cells. Significative levels of CD4+CD25-Foxp3+ cells from seronegative pregnant were observed compared with seropositive pregnant cells. Furthermore, the higher level of CD4+CD25-CTLA-4+ cells populations was detected in seropositive pregnant cells compared with seropositive non-pregnant. Although a significant increase in CTLA-4 cells was observed in pregnant women positive for anti-T. gondii antibodies, this increase did not cause a risk of reactivation of the infection.

Therapeutic strategies for the costimulatory molecule OX40 in T-cell-mediated immunity

The T cell co-stimulatory molecule OX40 and its cognate ligand OX40L have attracted broad research interest as a therapeutic target in T cell-mediated diseases. Accumulating preclinical evidence highlights the therapeutic efficacy of both agonist and blockade of the OX40-OX40L interaction. Despite this progress, many questions about the immuno-modulator roles of OX40 on T cell function remain unanswered. In this review we summarize the impact of the OX40-OX40L interaction on T cell subsets, including Th1, Th2, Th9, Th17, Th22, Treg, Tfh, and CD8+ T cells, to gain a comprehensive understanding of anti-OX40 mAb-based therapies. The potential therapeutic application of the OX40-OX40L interaction in autoimmunity diseases and cancer immunotherapy are further discussed; OX40-OX40L blockade may ameliorate autoantigen-specific T cell responses and reduce immune activity in autoimmunity diseases. We also explore the rationale of targeting OX40-OX40L interactions in cancer immunotherapy. Ligation of OX40 with targeted agonist anti-OX40 mAbs conveys activating signals to T cells. When combined with other therapeutic treatments, such as anti-PD-1 or anti-CTLA-4 blockade, cytokines, chemotherapy, or radiotherapy, the anti-tumor activity of agonist anti-OX40 treatment will be further enhanced. These data collectively suggest great potential for OX40-mediated therapies.

Next-generation regulatory T cell therapy

Regulatory T cells (Treg cells) are a small subset of immune cells that are dedicated to curbing excessive immune activation and maintaining immune homeostasis. Accordingly, deficiencies in Treg cell development or function result in uncontrolled immune responses and tissue destruction and can lead to inflammatory disorders such as graft-versus-host disease, transplant rejection and autoimmune diseases. As Treg cells deploy more than a dozen molecular mechanisms to suppress immune responses, they have potential as multifaceted adaptable smart therapeutics for treating inflammatory disorders. Indeed, early-phase clinical trials of Treg cell therapy have shown feasibility, tolerability and potential efficacy in these disease settings. In the meantime, progress in the development of chimeric antigen receptors and in genome editing (including the application of CRISPR-Cas9) over the past two decades has facilitated the genetic optimization of primary T cell therapy for cancer. These technologies are now being used to enhance the specificity and functionality of Treg cells. In this Review, we describe the key advances and prospects in designing and implementing Treg cell-based therapy in autoimmunity and transplantation.

Phenotypic analysis of monocytes and CD4+ T cells in hepatitis E patients with or without pregnancy

High mortality in pregnant women is a characteristic of hepatitis E virus (HEV) infection. Role of monocytes/T cells in HEV infection during pregnancy is still unclear. We compared CD14⁺monocytes and CD4⁺T cells by flow-cytometry in hepatitis-E patients including 13 pregnant (Antenatal care, ANC), 25 non-ANC patients and respective controls (12 and 20). Non-ANC-patients showed significantly higher frequency of monocytes with increased expression of CD80, CD86 and HLA-DR than control individuals (p < 0.001). Healthy pregnancy was associated with increased frequency of monocytes with higher CD80 expression and lower levels of HLA-DR (p < 0.05) compared to non-ANC controls. ANC-patients exhibited elevated levels of monocytes (p < 0.01) with higher expression of CD80 (p < 0.001) and reduced levels of HLA-DR and CD86 (p < 0.05) when compared with non-ANC patients. TLR2 and TLR4 surface expression on monocytes was higher in non-ANC-patients (p < 0.00) and lower in the ANC-patients (p < 0.01). Healthy-ANCs exhibited lower TLR4 expression on monocytes (p < 0.05). HEV infection did not change the frequency of CD4⁺ and CD4⁺CD28⁺T cells in patients' group (p > 0.05). Compared to respective controls, CD137⁺ and CD152⁺CD4⁺T cells were higher (p < 0.05) in both patients' categories. Higher levels of CD152⁺CD4⁺T cells (p < 0.001) was noted in healthy pregnant women. Among patients' groups, the CD4⁺T cells and their subpopulation were not different (p > 0.05). We found higher and reduced levels of circulating inflammatory cytokines (IL12, TNFα, IL6 and IL8; miliplex-assay) in non-ANC and ANC-patients respectively. In conclusion, on contrary to the classical activation of CD14⁺monocytes in the non-ANC-patients, impaired response was evident in the ANC-patients while the CD4⁺T cell populations were similar in the patient groups.

Control of T Cell Responses, Tolerance and Autoimmunity by Regulatory T Cells: Current Concepts

Regulatory T cells have emerged as an important mechanism of regulating tolerance and T cell responses. CD4+ regulatory T cells can be divided into two main groups, natural regulatory T cells, which express high levels of CD25 on their cell surface and phenotypically diverse adaptive (antigen induced) regulatory T cells. Natural regulatory T cells are made in the thymus, and require strong costimulatory signals for induction and maintenance, express a transcription factor called Foxp3, and function by a largely unknown mechanism. Adaptive (antigen induced) regulatory T cells are made by sub-optimal antigenic signals in the periphery, in the presence of immunosuppressive cytokines, often in special circumstances, such as chronic viral infections or after mucosal administration of antigen, and rely on cytokines such as IL-10 and TGF-β for suppression. Regulatory T cells offer a great potential for the treatment of autoimmune diseases and during transplantation.

Tissue resident and follicular Treg cell differentiation is regulated by CRAC channels

T regulatory (Treg) cells maintain immunological tolerance and organ homeostasis. Activated Treg cells differentiate into effector Treg subsets that acquire tissue-specific functions. Ca²⁺ influx via Ca²⁺ release-activated Ca²⁺ (CRAC) channels formed by STIM and ORAI proteins is required for the thymic development of Treg cells, but its function in mature Treg cells remains unclear. Here we show that deletion of Stim1 and Stim2 genes in mature Treg cells abolishes Ca²⁺ signaling and prevents their differentiation into follicular Treg and tissue-resident Treg cells. Transcriptional profiling of STIM1/STIM2-deficient Treg cells reveals that Ca²⁺ signaling regulates transcription factors and signaling pathways that control the identity and effector differentiation of Treg cells. In the absence of STIM1/STIM2 in Treg cells, mice develop a broad spectrum of autoantibodies and fatal multiorgan inflammation. Our findings establish a critical role of CRAC channels in controlling lineage identity and effector functions of Treg cells.

Regulatory T (Treg) cells are important for maintaining immune homeostasis. Here the authors show that STIM1 and STIM2, which activate the Ca²⁺ channel ORAI1, are essential for the differentiation of peripheral Treg cells into tissue-resident and follicular Treg cells and their ability to limit autoimmunity in mice.

High concentrations of atorvastatin reduce in-vitro function of conventional T and regulatory T cells

Regulatory T cells (T_regs ) modulate the magnitude of immune responses and possess therapeutic potential in an array of immune diseases. Statins reduce the activation and proliferation of conventional T cells (T_cons ), and they seem to up-regulate the frequency and function of T_regs . However, there is a lack of simultaneous evaluation of the in-vitro effect of statins on the functional profile of T_regs versus T_cons . Herein, magnetically purified T_cons and T_regs were stimulated with CD3/CD28/interleukin (IL)-2 in the presence of atorvastatin (ATV) at 1 or 10 µM. The suppressive function of T_regs , the expression of markers associated with T_reg function, activation levels, cytokine production and calcium flux in both subpopulations were assessed by flow cytometry. ATV had no cytotoxic effect on T cells at the concentrations used. Interestingly, 10 µM ATV hampered the suppressive capacity of T_regs . Moreover, this higher concentration reduced the expression of forkhead box protein 3 (FoxP3), cytotoxic T lymphocyte antigen (CTLA-4) and programmed death 1 (PD-1). In T_cons , ATV at 10 µM decreased PD-1 and CD45RO expression. The expression of CD25, CD69, CD95, CD38, CD62L, CCR7 and perforin was not affected in both subpopulations or at any ATV concentrations. Remarkably, 10 µM ATV increased the percentage of tumour necrosis factor (TNF)-α-producing T_regs . Although there was a reduction of calcium flux in T_cons and T_regs , it was only significant in 10 µM ATV-treated T_cons . These results suggested that 10 µM ATV affects the cellular functions of both populations; however, this concentration particularly affected several aspects of T_reg biology: its suppressive function, cytokine production and expression of T_reg -specific markers.

Cutting Edge: Dynamic Expression of Id3 Defines the Stepwise Differentiation of Tissue-Resident Regulatory T Cells

Foxp3+ regulatory T (TR) cells are phenotypically and functionally diverse and broadly distributed in lymphoid and nonlymphoid tissues. However, the pathways guiding the differentiation of tissue-resident TR cell populations have not been well defined. By regulating E-protein function, Id3 controls the differentiation of CD8+ effector T cells and is essential for TR cell maintenance and function. We show that dynamic expression of Id3 helps define three distinct mouse TR cell populations: Id3+CD62LhiCD44lo central TR cells, Id3+CD62LloCD44hi effector TR (eTR) cells, and Id3- eTR cells. Adoptive transfer experiments and transcriptome analyses support a stepwise model of differentiation from Id3+ central TR to Id3+ eTR to Id3- eTR cells. Furthermore, Id3- eTR cells have high expression of functional inhibitory markers and a transcriptional signature of tissue-resident TR cells. Accordingly, Id3- eTR cells are highly enriched in nonlymphoid organs but virtually absent from blood and lymph. Thus, we propose that tissue-resident TR cells develop in a multistep process associated with Id3 downregulation.

GM-CSF therapy inhibits chronic graft-versus-host disease via expansion of regulatory T cells

Regulatory T cells (Tregs) attenuate excessive immune responses, making their expansion beneficial in immune-mediated diseases, including allogeneic bone marrow transplantation associated with graft-versus-host disease (GVHD). In addition to interleukin-2, Tregs require T-cell receptor and costimulatory signals from antigen-presenting cells, such as DCs, for their optimal proliferation. Granulocyte-macrophage colony-stimulating factor (GM-CSF) increases DC number and may promote DC-dependent Treg proliferation. Here, we demonstrate that GM-CSF treatment increases CD4⁺ CD8^- DCs, which are associated with Treg expansion. In a mouse model of chronic GVHD (cGVHD), GM-CSF therapy expanded Tregs, protected against the development of skin GVHD, and regulated both Th1 and Th17 responses in the peripheral lymph nodes, resulting in an attenuation of skin cGVHD. Notably, the expanded Tregs were instrumental to GM-CSF-mediated cGVHD inhibition, which was dependent upon an increased ratio of Tregs to conventional T cells rather than augmentation of suppressive function. These data suggest that GM-CSF induces Treg proliferation by expanding CD4⁺ CD8^- DCs, which in turn regulate alloimmune responses in a cGVHD mouse model. Thus, GM-CSF could be used as a therapeutic DC modulator to induce Treg expansion and to inhibit excessive alloimmune responses in immune-related diseases.

Antibodies to Costimulatory Receptor 4-1BB Enhance Anti-tumor Immunity via T Regulatory Cell Depletion and Promotion of CD8 T Cell Effector Function

The costimulatory receptor 4-1BB is expressed on activated immune cells, including activated T cells. Antibodies targeting 4-1BB enhance the proliferation and survival of antigen-stimulated T cells in vitro and promote CD8 T cell-dependent anti-tumor immunity in pre-clinical cancer models. We found that T regulatory (Treg) cells infiltrating human or murine tumors expressed high amounts of 4-1BB. Intra-tumoral Treg cells were preferentially depleted by anti-4-1BB mAbs in vivo. Anti-4-1BB mAbs also promoted effector T cell agonism to promote tumor rejection. These distinct mechanisms were competitive and dependent on antibody isotype and FcγR availability. Administration of anti-4-1BB IgG2a, which preferentially depletes Treg cells, followed by either agonistic anti-4-1BB IgG1 or anti-PD-1 mAb augmented anti-tumor responses in multiple solid tumor models. An antibody engineered to optimize both FcγR-dependent Treg cell depleting capacity and FcγR-independent agonism delivered enhanced anti-tumor therapy. These insights into the effector mechanisms of anti-4-1BB mAbs lay the groundwork for translation into the clinic.

TNFR2 ligation in human T regulatory cells enhances IL2-induced cell proliferation through the non-canonical NF-κB pathway

Human T regulatory cells (T regs) express high levels of TNF receptor 2 (TNFR2). Ligation of TNFR2 with TNF, which can recognise both TNFR1 and TNFR2, or with a TNFR2-selective binding molecule, DARPin 18 (D18) activates canonical NF-κB signalling, assessed by IκBα degradation, and the magnitude of the response correlates with the level of TNFR2 expression. RNA-seq analysis of TNF- or D18-treated human T regs revealed that TNFR2 ligation induces transcription of NFKB2 and RELB, encoding proteins that form the non-canonical NF-κB transcription factor. In combination with IL2, D18 treatment is specific for T regs in (1) stabilising NF-κB-inducing kinase protein, the activator of non-canonical NF-κB signalling, (2) inducing translocation of RelB from cytosol to nucleus, (3) increasing cell cycle entry, and (4) increasing cell numbers. However, the regulatory function of the expanded T regs is unaltered. Inhibition of RelB nuclear translocation blocks the proliferative response. We conclude that ligation of TNFR2 by D18 enhances IL2-induced T regs proliferation and expansion in cell number through the non-canonical NF-κB pathway.

Allergen immunotherapy modulates sensitivity of Treg cells to apoptosis in a rat model of allergic asthma

AIM

To study the apoptosis of Foxp3⁺ Treg cells following Alstonia scholaris pollen sensitization-challenge and following allergen immunotherapy.

MATERIALS & METHODS

Wistar rats were sensitized-challenged with Alstonia scholaris pollen and were further given intranasal immunotherapy. For the analysis of the apoptotic proteins on Treg cells by flow cytometry, multiple gating procedures were followed.

RESULTS

Allergen sensitization-challenge increases Annexin-V, Fas, FasL, caspases-8, 9, 3 cytochrome-C, APAF-1, Bax, perforin-1 and granzyme-B on Treg cells which is decreased following intranasal immunotherapy. On the other hand, Bcl-2 expression is decreased in allergy and increased by immunotherapy.

CONCLUSION

Apoptosis of Treg cells is increased following allergen sensitization-challenge via extrinsic, intrinsic and perforin/granzyme pathways and allergen immunotherapy decreased the sensitivity to apoptosis of Treg cells.

Regulatory T cell subsets are differentially dependent on CD28 for their proliferation

It is thought that CD28 plays a crucial role in the maintenance of regulatory T cell (Treg) pool size through promoting the development and proliferation of these cells. However, recently we found that the dependency on CD28 co-stimulation for their development is different between Treg subsets, thymus-derived Tregs (tTregs, CD28-dependent) and peripherally-derived Tregs (pTregs, CD28-independent), suggesting that CD28 may also have differential influences on the homeostasis of each Treg subset. Here, we demonstrated that both Treg subsets were reduced in secondary lymphoid organs of CD28 deficient mice, and that this reduction was due to impaired proliferation in both Treg subsets by the intrinsic CD28 defect. However, we found that the massive proliferation of both Treg subsets under lymphopenic condition was regulated by CD28, whereas the proliferative activity of tTregs but not pTregs in the steady state was dependent on CD28. Also, experiments using mutant CD28 knock-in mice revealed that proliferation of pTregs under lymphopenic condition required only the Lck-NFκB pathway of CD28, whereas tTregs required an additional unknown pathway. These findings indicate that the dependency on CD28 for proliferation in each Treg subset differs depending on the environment.

Tumor Tolerance-Promoting Function of Regulatory T Cells Is Optimized by CD28, but Strictly Dependent on Calcineurin

Regulatory T cells (Treg) restrain immune responses against malignant tumors, but their global depletion in cancer patients will likely be limited by systemic autoimmune toxicity. Instead, approaches to "tune" their activities may allow for preferential targeting of tumor-reactive Treg. Although Ag recognition regulates Treg function, the roles of individual TCR-dependent signaling pathways in enabling Treg to promote tumor tolerance are not well characterized. In this study, we examined in mouse tumor models the role of calcineurin, a key mediator of TCR signaling, and the role of the costimulatory receptor CD28 in the differentiation of resting central Treg into effector Treg endowed with tumor tropism. We find that calcineurin, although largely dispensable for suppressive activity in vitro, is essential for upregulation of ICOS and CTLA-4 in Treg, as well as for expression of chemokine receptors driving their accumulation in tumors. In contrast, CD28 is not critical, but optimizes the formation of tumor-homing Treg and their fitness in tumor tissue. Accordingly, although deletion of either CnB or CD28 strongly impairs Treg-mediated tumor tolerance, lack of CnB has an even more pronounced impact than lack of CD28. Hence, our studies reveal distinct roles for what has classically been defined as signal 1 and signal 2 of conventional T cell activation in the context of Treg-mediated tumor tolerance.

Profiling calcium signals of in vitro polarized human effector CD4+ T cells

Differentiation of naïve CD4⁺ T cells into effector subtypes with distinct cytokine profiles and physiological roles is a tightly regulated process, the imbalance of which can lead to an inadequate immune response or autoimmune disease. The crucial role of Ca²⁺ signals, mainly mediated by the store operated Ca²⁺ entry (SOCE) in shaping the immune response is well described. However, it is unclear if human effector CD4⁺ T cell subsets show differential Ca²⁺ signatures in response to different stimulation methods. Herein, we provide optimized in vitro culture conditions for polarization of human CD4⁺ effector T cells and characterize their SOCE following both pharmacological store depletion and direct T-cell receptor (TCR) activation. Moreover, we measured whole cell Ca²⁺ release activated Ca²⁺ currents (I_CRAC) and investigated whether the observed differences correlate to the expression of CRAC genes. Our results show that Ca²⁺ profiles of helper CD4⁺ Th1, Th2 and Th17 are distinct and in part shaped by the intensity of stimulation. Regulatory T cells (Treg) are unique being the subtype with the most prominent SOCE response. Analysis of in vivo differentiated Treg unraveled the role of differential expression of ORAI2 in fine-tuning signals in Treg vs. conventional CD4⁺ T cells.

Single-cell gene expression reveals a landscape of regulatory T cell phenotypes shaped by the TCR

CD4⁺ T regulatory (T_reg) cells are central to immune homeostasis, their phenotypic heterogeneity reflecting the diverse environments and target cells they regulate. To understand this heterogeneity, we combined single-cell RNAseq, activation reporter and TCR analysis to profile thousands of T_regs or T_convs from mouse lymphoid organs or human blood. T_reg and T_conv pools showed areas of overlap, as resting “furtive” T_regs with overall similarity to T_conv, or as a convergence of activated states. All T_regs express a small core of FoxP3-dependent transcripts, onto which additional programs are added less uniformly. Among suppressive functions, Il2ra and Ctla4 were quasi-constant, inhibitory cytokines being more sparsely distributed. TCR signal intensity didn’t affect resting/activated T_reg proportions, but molded activated T_reg programs. The main lines of T_reg heterogeneity in mice were strikingly conserved in human blood. These results reveal unexpected TCR-shaped states of activation, providing a framework to synthesize previous observations about T_reg heterogeneity.

Regulatory T Cells: Differentiation and Function

The immune system of vertebrate animals has evolved to mount an effective defense against a diverse set of pathogens while minimizing transient or lasting impairment in tissue function that could result from the inflammation caused by immune responses to infectious agents. In addition, misguided immune responses to "self" and dietary antigens, as well as to commensal microorganisms, can lead to a variety of inflammatory disorders, including autoimmunity, metabolic syndrome, allergies, and cancer. Regulatory T cells expressing the X chromosome-linked transcription factor Foxp3 suppress inflammatory responses in diverse biological settings and serve as a vital mechanism of negative regulation of immune-mediated inflammation. Cancer Immunol Res; 4(9); 721-5. ©2016 AACR.

Induced Regulatory T Cells Superimpose Their Suppressive Capacity with Effector T Cells in Lymph Nodes via Antigen-Specific S1p1-Dependent Egress Blockage

Regulatory T cells (Tregs) restrict overexuberant lymphocyte activation. While close proximity between Tregs and their suppression targets is important for optimal inhibition, and literature indicates that draining lymph nodes (LNs) may serve as a prime location for the suppression, signaling details orchestrating this event are not fully characterized. Using a protocol to enable peripheral generation of inducible antigen-specific Tregs (asTregs) to control allergen-induced asthma, we have identified an antigen-specific mechanism that locks asTregs within hilar LNs which in turn suppresses airway inflammation. The suppressive asTregs, upon antigen stimulation in the LN, downregulate sphingosine-1-phosphate receptor 1 egress receptor expression. These asTregs in turn mediate the downregulation of the same receptor on incoming effector T cells. Therefore, asTregs and effector T cells are locked in these draining LNs for prolonged interactions. Disruption of individual steps of this retention sequence abolishes the inflammation controlled by asTregs. Collectively, this study identifies a new requirement of spatial congregation with their suppression targets essential for asTreg functions and suggests therapeutic programs via Treg traffic control.

Protein kinase C theta is dispensable for suppression mediated by CD25+CD4+ regulatory T cells

The activation of conventional T cells upon T cell receptor stimulation critically depends on protein kinase C theta (PKCθ). However, its role in regulatory T (Treg) cell function has yet to be fully elucidated. Using siRNA or the potent and PKC family-selective pharmacological inhibitor AEB071, we could show that murine Treg-mediated suppression in vitro is independent of PKCθ function. Likewise, Treg cells of PKCθ-deficient mice were fully functional, showing a similar suppressive activity as wild-type CD25⁺CD4⁺ T cells in an in vitro suppression assay. Furthermore, in vitro-differentiated wild-type and PKCθ-deficient iTreg cells showed comparable Foxp3 expression as well as suppressive activity. However, we observed a reduced percentage of Foxp3⁺CD25⁺ CD4⁺ T cells in the lymphatic organs of PKCθ-deficient mice. Taken together, our results suggest that while PKCθ is involved in Treg cell differentiation in vivo, it is dispensable for Treg-mediated suppression.

The Guanine-Nucleotide Exchange Factor Caldag Gefi Fine-Tunes Functional Properties of Regulatory T Cells

Using quantitative phosphopeptide sequencing of unstimulated versus stimulated primary murine Foxp3⁺ regulatory and Foxp3^– conventional T cells (Tregs and Tconv, respectively), we detected a novel and differentially regulated tyrosine phosphorylation site within the C1 domain of the guanine-nucleotide exchange factor CalDAG GEFI. We hypothesized that the Treg-specific and activation-dependent reduced phosphorylation at Y523 allows binding of CalDAG GEFI to diacylglycerol, thereby impacting the formation of a Treg-specific immunological synapse. However, diacylglycerol binding assays of phosphomutant C1 domains of CalDAG GEFI could not confirm this hypothesis. Moreover, CalDAG GEFI^–/– mice displayed normal Treg numbers in thymus and secondary lymphoid organs, and CalDAG GEFI^–/– Tregs showed unaltered in vitro suppressive capacity when compared to CalDAG GEFI^+/+ Tregs. Interestingly, when tested in vivo, CalDAG GEFI^–/– Tregs displayed a slightly reduced suppressive ability in the transfer colitis model when compared to CalDAG GEFI^+/+ Tregs. Additionally, CRISPR-Cas9-generated CalDAG GEFI^–/– Jurkat T cell clones showed reduced adhesion to ICAM-1 and fibronectin when compared to CalDAG GEFI-competent Jurkat T cells. Therefore, we speculate that deficiency in CalDAG GEFI impairs adherence of Tregs to antigen-presenting cells, thereby impeding formation of a fully functional immunological synapse, which finally results in a reduced suppressive potential.

CD101 inhibits the expansion of colitogenic T cells

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

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

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

Protein SUMOylation Is Required for Regulatory T Cell Expansion and Function

Foxp3-expressing regulatory T (Treg) cells are essential for immune tolerance; however, the molecular mechanisms underlying Treg cell expansion and function are still not well understood. SUMOylation is a protein post-translational modification characterized by covalent attachment of SUMO moieties to lysines. UBC9 is the only E2 conjugating enzyme involved in this process, and loss of UBC9 completely abolishes the SUMOylation pathway. Here, we report that selective deletion of Ubc9 within the Treg lineage results in fatal early-onset autoimmunity similar to Foxp3 mutant mice. Ubc9-deficient Treg cells exhibit severe defects in TCR-driven homeostatic proliferation, accompanied by impaired activation and compromised suppressor function. Importantly, TCR ligation enhanced SUMOylation of IRF4, a critical regulator of Treg cell function downstream of TCR signals, which regulates its stability in Treg cells. Our data thus have demonstrated an essential role of SUMOylation in the expansion and function of Treg cells.

Monoclonal regulatory T cells provide insights into T cell suppression

Regulatory T cells (Tregs) have a crucial role in maintaining lymphocyte homeostasis. However an understanding of how Tregs function at a cellular and molecular level has not yet been fully elucidated. Here, we make use of a T cell receptor (TCR) transgenic, Rag^−/− mouse expressing a Forkhead-Box-Protein P3 (Foxp3) transgene. This mouse provides a source of monoclonal CD4⁺ Foxp3⁺ T cells with a defined specificity. Here we show that monoclonal B3K506 Tregs are functional in vitro and in vivo and clearly require cognate antigen to be suppressive. We further show that the strength of Treg stimulation determines the strength of Treg mediated suppression. Finally we analysed various suppressive mechanisms used by monoclonal Tregs and found that Treg-Tconv proximity is a parameter, which correlates with enhanced suppression.

Lymph node trafficking of regulatory T cells is prerequisite for immune suppression

Regulatory T cells have a crucial role in health and disease because of their immune regulation function. However, the anatomic sites where regulatory T cells exert optimal immune regulation are open to debate. In our current study with the use of a shear-stress flow assay, we found that regulatory T cells exhibited significantly decreased adhesion to either activated endothelial monolayer or intercellular adhesion molecule 1 or E-selectin-coated surfaces compared with activated effector T cells. The less transmigration capacity of the regulatory T cells prompted our speculation of preferential lymph node localization for the regulatory T cells that endowed these cells with immune regulation function in the most efficient manner. To test this hypothesis, the role of lymph node localization in regulatory T cell-mediated immune suppression was evaluated with a footpad inflammation model. We found that adoptively transferred regulatory T cells inhibited the development of footpad inflammation. In addition, although blockage of CCR7 or CD62L had no effect on the immune suppressive function of the regulatory T cells per se, pretreatment of the regulatory T cells with either CCR7 or CD62L blocking antibodies prevented their recruitment into draining lymph nodes and concomitantly abrogated the immune suppressive effects of adoptively transferred regulatory T cells during footpad inflammation. Our data demonstrate the crucial role of lymph node localization in regulatory T cell-mediated immune suppression and suggest a probable hierarchy in the anatomic sites for optimal immune regulation. Elucidating the relationships between the transmigration characteristics of the regulatory T cells and their immune regulation function will provide insightful information for regulatory T cell-based cell therapy.

Alloantigen presentation and graft-versus-host disease: fuel for the fire

Allogeneic stem cell transplantation (SCT) is a unique procedure, primarily in patients with hematopoietic malignancies, involving chemoradiotherapy followed by the introduction of donor hematopoietic and immune cells into an inflamed and lymphopenic environment. Interruption of the process by which recipient alloantigen is presented to donor T cells to generate graft-versus-host disease (GVHD) represents an attractive therapeutic strategy to prevent morbidity and mortality after SCT and has been increasingly studied in the last 15 years. However, the immune activation resulting in GVHD has no physiological equivalent in nature; alloantigen is ubiquitous, persists indefinitely, and can be presented by multiple cell types at numerous sites, often on incompatible major histocompatibility complex, and occurs in the context of intense inflammation early after SCT. The recognition that alloantigen presentation is also critical to the development of immunological tolerance via both deletional and regulatory mechanisms further adds to this complexity. Finally, GVHD itself appears capable of inhibiting the presentation of microbiological antigens by donor dendritic cells late after SCT that is mandatory for the establishment of effective pathogen-specific immunity. Here, we review our current understanding of alloantigen, its presentation by various antigen-presenting cells, subsequent recognition by donor T cells, and the potential of therapeutic strategies interrupting this disease-initiating process to modify transplant outcome.