GARP: a key receptor controlling FOXP3 in human regulatory T cells

Nasal anti-CD3 monoclonal antibody ameliorates traumatic brain injury, enhances microglial phagocytosis and reduces neuroinflammation via IL-10-dependent Treg-microglia crosstalk

Neuroinflammation plays a crucial role in traumatic brain injury (TBI), contributing to both damage and recovery, yet no effective therapy exists to mitigate central nervous system (CNS) injury and promote recovery after TBI. In the present study, we found that nasal administration of an anti-CD3 monoclonal antibody ameliorated CNS damage and behavioral deficits in a mouse model of contusional TBI. Nasal anti-CD3 induced a population of interleukin (IL)-10-producing regulatory T cells (Treg cells) that migrated to the brain and closely contacted microglia. Treg cells directly reduced chronic microglia inflammation and regulated their phagocytic function in an IL-10-dependent manner. Blocking the IL-10 receptor globally or specifically on microglia in vivo abrogated the beneficial effects of nasal anti-CD3. However, the adoptive transfer of IL-10-producing Treg cells to TBI-injured mice restored these beneficial effects by enhancing microglial phagocytic capacity and reducing microglia-induced neuroinflammation. These findings suggest that nasal anti-CD3 represents a promising new therapeutic approach for treating TBI and potentially other forms of acute brain injury.

Discovery and preclinical evaluation of BPB-101: a novel triple functional bispecific antibody targeting GARP-TGF-β complex/SLC, free TGF-β and PD-L1

Background

In the tumor microenvironment (TME), the transforming growth factor-β (TGF-β) and programmed cell death receptor 1 (PD-1)/programmed death ligand 1 (PD-L1) signaling axes are complementary, nonredundant immunosuppressive signaling pathways. Studies have revealed that active TGF-β is mainly released from the glycoprotein A repetitions predominant (GARP)-TGF-β complex on the surface of activated regulatory T cells (Tregs), B cells, natural killer (NK) cells, and tumor cells. The currently available antibodies or fusion proteins that target TGF-β are limited in their abilities to simultaneously block TGF-β release and neutralize active TGF-β in the TME, thus limiting their antitumor effects.

Methods

We designed and constructed a bispecific, trifunctional antibody, namely, BPB-101, that specifically targets the GARP-TGF-β complex and/or small latent complex (SLC), active TGF-β, and PD-L1. The binding ability of BPB-101 to the different antigens was determined by ELISA, FACS, and biolayer interferometry (BLI). The blocking ability of BPB-101 to the TGF-β and PD-1/PD-L1 signaling axes was determined by reporter gene assay (RGA). The antitumor effect and biosafety of BPB-101 were determined in a transgenic mouse tumor model and cynomolgus monkeys, respectively. Stability assessments, including stability in serum, after exposure to light, after repeated freeze-thaw cycles, and after high-temperature stress tests had been completed to evaluate the stability of BPB-101.

Results

BPB-101 bound efficiently to different antigenic proteins: the GARP-TGF-β complex and/or SLC, active TGF-β, and PD-L1. Data showed that BPB-101 not only effectively inhibited the release of TGF-β from human Tregs, but also blocked both the TGF-β and PD-1/PD-L1 signaling pathways. In an MC38-hPD-L1 tumor-bearing C57BL/6-hGARP mouse model, BPB-101 at a dose of 5 mg/kg significantly inhibited tumor growth, with a complete elimination rate of 50%. Stability assessments confirmed the robustness of BPB-101. Furthermore, BPB-101 showed a favorable safety profile in nonhuman primate (NHP) toxicity studies.

Conclusion

BPB-101 is a potentially promising therapeutic candidate that may address unmet clinical needs in cancer immunotherapy, thus, BPB-101 warrants further clinical investigation.

Phenotypic profiling of human induced regulatory T cells at early differentiation: insights into distinct immunosuppressive potential

Regulatory T cells (Tregs) play a key role in suppressing systemic effector immune responses, thereby preventing autoimmune diseases but also potentially contributing to tumor progression. Thus, there is great interest in clinically manipulating Tregs, but the precise mechanisms governing in vitro-induced Treg (iTreg) differentiation are not yet fully understood. Here, we used multiparametric mass cytometry to phenotypically profile human iTregs during the early stages of in vitro differentiation at single-cell level. A panel of 25 metal-conjugated antibodies specific to markers associated with human Tregs was used to characterize these immunomodulatory cells. We found that iTregs highly express the transcription factor FOXP3, as well as characteristic Treg-associated surface markers (e.g. CD25, PD1, CD137, CCR4, CCR7, CXCR3, and CD103). Expression of co-inhibitory factors (e.g. TIM3, LAG3, and TIGIT) increased slightly at late stages of iTreg differentiation. Further, CD103 was upregulated on a subpopulation of iTregs with greater suppressive capacity than their CD103- counterparts. Using mass-spectrometry-based proteomics, we showed that sorted CD103+ iTregs express factors associated with immunosuppression. Overall, our study highlights that during early stages of differentiation, iTregs resemble memory-like Treg features with immunosuppressive activity, and provides opportunities for further investigation into the molecular mechanisms underlying Treg function.

Treg Cell Therapeutic Strategies for Breast Cancer: Holistic to Local Aspects

Regulatory T cells (Tregs) play a key role in maintaining immune homeostasis and preventing autoimmunity through their immunosuppressive function. There have been numerous reports confirming that high levels of Tregs in the tumor microenvironment (TME) are associated with a poor prognosis, highlighting their role in promoting an immunosuppressive environment. In breast cancer (BC), Tregs interact with cancer cells, ultimately leading to the suppression of immune surveillance and promoting tumor progression. This review discusses the dual role of Tregs in breast cancer, and explores the controversies and therapeutic potential associated with targeting these cells. Researchers are investigating various strategies to deplete or inhibit Tregs, such as immune checkpoint inhibitors, cytokine antagonists, and metabolic inhibition. However, the heterogeneity of Tregs and the variable precision of treatments pose significant challenges. Understanding the functional diversity of Tregs and the latest advances in targeted therapies is critical for the development of effective therapies. This review highlights the latest approaches to Tregs for BC treatment that both attenuate Treg-mediated immunosuppression in tumors and maintain immune tolerance, and advocates precise combination therapy strategies to optimize breast cancer outcomes.

Many Faces of Regulatory T Cells: Heterogeneity or Plasticity?

Regulatory T cells (Tregs) are essential for maintaining the immune balance in normal and pathological conditions. In autoimmune diseases and transplantation, they restrain the loss of self-tolerance and promote engraftment, whereas in cancer, an increase in Treg numbers is mostly associated with tumor growth and poor prognosis. Numerous markers and their combinations have been used to identify Treg subsets, demonstrating the phenotypic diversity of Tregs. The complexity of Treg identification can be hampered by the unstable expression of some markers, the decrease in the expression of a specific marker over time or the emergence of a new marker. It remains unclear whether such phenotypic shifts are due to new conditions or whether the observed changes are due to initially different populations. In the first case, cellular plasticity is observed, whereas in the second, cellular heterogeneity is observed. The difference between these terms in relation to Tregs is rather blurred. Considering the promising perspectives of Tregs in regenerative cell-based therapy, the existing confusing data on Treg phenotypes require further investigation and analysis. In our review, we introduce criteria that allow us to distinguish between the heterogeneity and plasticity of Tregs normally and pathologically, taking a closer look at their diversity and drawing the line between two terms.

Compromised melanocyte survival due to decreased suppression of CD4+ & CD8+ resident memory T cells by impaired TRM-regulatory T cells in generalized vitiligo patients

Regulatory T cells (Tregs) are involved in the suppression of activated T cells in generalized vitiligo (GV). The study was aimed to investigate resident memory (TRM)-Tregs and antigen-specific Tregs' numbers and functional defects in 25 GV patients and 20 controls. CD4+ & CD8+ TRM cell proliferation was assessed by BrDU assay; production of IL-10, TGF-β, IFN-γ, perforin and granzyme B were assessed by ELISA and enumeration of TRM cells was done by flowcytometry. GV patients showed significantly increased frequency and absolute count of CD4+ & CD8+ TRM cells in lesional (L), perilesional (PL) and non-lesional (NL) skin compared to controls (p = 0.0003, p = 0.0029 & p = 0.0115, respectively & p = 0.0003, p = 0.003 & p = 0.086, respectively). Whereas, TRM-Treg (p < 0.0001 & p = 0.0015) and antigen-specific Tregs (p = 0.0014 & p = 0.003) exhibited significantly decreased frequency and absolute counts in L & PL skin. GV patients showed reduced suppression of CD8+ & CD4+ TRM cells (with increased IFN-γ, perforin & granzyme B) and decreased TRM-Tregs and antigen-specific Tregs (with decreased IL-10 & TGF-β production) and reduced proliferation of SK-Mel-28 cells in co-culture systems. Immunohistochemistry revealed increased expression of TRM stimulating cytokines: IL-15 & IL-17A and reduced expression of TGF-β & IL-10 in L, PL, NL skins compared to controls. These results for the first time suggest that decreased and impaired TRM-Tregs and antigen-specific Tregs are unable to suppress CD4+ & CD8+ TRMs' cytotoxic function and their proliferation due to decrease production of immunosuppressive cytokines (IL-10 & TGF-β) and increased production of TRM based IFN-γ, perforin and granzyme B production, thus compromising the melanocyte survival in GV.

Single‑nucleotide polymorphism rs6592645 confers asthma risk through regulating LRRC32 expression

Asthma is a complex disease, often with evident genetic predisposition; for example, the single-nucleotide polymorphism (SNP) rs7130588 was significantly associated with asthma by genome-wide association study (GWAS). Analysis of 1000 Genomes Project data suggests that there is another SNP, rs6592645, in complete linkage disequilibrium with rs7130588 and should present the same signal in GWAS. However, the causal SNP and the mechanism for the association between rs7130588 and asthma remain to be elucidated. In the presents study, results from dual-luciferase assays indicated that the A/G alleles of rs7130588 failed to present significantly different reporter gene expression. By contrast, A allele of rs6592645 presented a significant increase in relative luciferase activity than G allele, thus suggesting that rs6592645 may be a causal SNP. Using chromosome conformation capture, the enhancer region containing rs6592645 was observed to interact with promoter region of leucine-rich repeat-containing 32 (LRRC32). Gene expression quantification suggested that LRRC32 expression is significantly increased in lung tissue of patients with asthma and is dependent on the genotype of this locus, thus verifying that LRRC32 may be involved in asthma onset and that rs6592645 can regulate LRRC32 expression. Through chromatin immunoprecipitation, transcription factor 3 (TCF3) was identified to bind to rs6592645 surrounding region and the interaction between TCF3 and rs6592645 surrounding region was investigated. Results from the present study may improve our understanding of the mechanism by which the genetic variation in this locus might influence asthma susceptibility.

Analysis of LAP+ and GARP+ Treg subsets in peripheral blood of patients with neuromyelitis optica spectrum disorders

INTRODUCTION

Neuromyelitis optica spectrum disorder (NMOSD) is a group of antibody-mediated inflammatory demyelinating central nervous system diseases. T lymphocytes participate in NMOSD pathogenesis, with regulatory T cells (Treg) being the core in maintaining immune homeostasis. Studies have revealed that different Treg subsets play different roles in autoimmune diseases. The distribution of LAP+ or GARP+ Treg subsets in NMOSD may help us deeply understand their immune mechanism.

METHODS

This study reviewed 22 NMOSD patients and 20 normal controls. Flow cytometric analysis was utilized to detect subsets of Treg cells expressing Foxp3, Helios, LAP, or GARP in peripheral blood. ELISA was used to detect plasma TGF-β1 and IL-10. In addition, changes in the proportion of Treg cell subsets before and after glucocorticoid treatment in 10 patients were analyzed.

RESULTS

Compared with healthy controls, LAP and GARP expressions were significantly downregulated in the peripheral blood of NMOSD patients. TGF-β1 expression in NMOSD patients was lower and was positively correlated with the ratio of CD4+GARP+ Treg cells. After treatment with glucocorticoid, LAP and GARP expressions in the peripheral blood of NMOSD patients were upregulated.

CONCLUSIONS

The proportion of Treg cells expressing LAP and GARP is downregulated, implying that Treg cells with the best inhibitory function are insufficient to maintain autoimmune homeostasis in NMOSD patients. Upregulation of Treg cells expressing LAP and GARP in NMOSD patients may be one of the mechanisms of glucocorticoid treatment.

Complexity and diversity of FOXP3 isoforms: Novel insights into the regulation of the immune response in metastatic breast cancer

FOXP3 is a key transcription factor in the regulation of immune responses, and recent studies have uncovered the complexity and diversity of FOXP3 isoforms in various cancers, including metastatic breast cancers (mBCs). It has dual role in the tumor microenvironment of mBCs. This review aims to provide novel insights into the complexity and diversity of FOXP3 isoforms in the regulation of the immune response in breast cancer. We discuss the molecular mechanisms underlying the function of FOXP3 isoforms, including their interaction with other proteins, regulation of gene expression, and impact on the immune system. We also highlight the importance of understanding the role of FOXP3 isoforms in breast cancer and the potential for using them as therapeutic targets. This review highlights the crucial role of FOXP3 isoforms in the regulation of the immune response in breast cancer and underscores the need for further research to fully comprehend their complex and diverse functions.

Tumor-infiltrating regulatory T cells as targets of cancer immunotherapy

Regulatory T cells (Tregs) are abundant in tumor tissues, raising a question of whether immunosuppressive tumor-infiltrating Tregs (TI-Tregs) can be selectively depleted or functionally attenuated to evoke effective anti-tumor immune responses by conventional T cells (Tconvs), without perturbing Treg-dependent immune homeostasis in healthy organs and causing autoimmunity. Here, we review current cancer immunotherapy strategies, including immune checkpoint blockade (ICB) antibodies against CTLA-4 and PD-1 and discuss their effects on TI-Tregs. We also discuss approaches that exploit differentially regulated molecules on the cell surface (e.g., CTLA-4) and intracellularly (e.g., T cell receptor signaling molecules) between TI-Tregs and Tconvs as well as their dependence on cytokines (e.g., IL-2) and metabolites (e.g., lactate). We envisage that targeting TI-Tregs could be effective as a monotherapy and/or when combined with ICB antibodies.

CD4+ and CD8+ regulatory T cell characterization in the rat using a unique transgenic Foxp3-EGFP model

BACKGROUND

Regulatory T cells (Treg) in diverse species include CD4⁺ and CD8⁺ T cells. In all species, CD8⁺ Treg have been only partially characterized and there is no rat model in which CD4⁺ and CD8⁺ FOXP3⁺ Treg are genetically tagged.

RESULTS

We generated a Foxp3-EGFP rat transgenic line in which FOXP3 gene was expressed and controlled EGFP. CD4⁺ and CD8⁺ T cells were the only cells that expressed EGFP, in similar proportion as observed with anti-FOXP3 antibodies and co-labeled in the same cells. CD4⁺EGFP⁺ Treg were 5-10 times more frequent than CD8⁺EGFP⁺ Treg. The suppressive activity of CD4⁺ and CD8⁺ Treg was largely confined to EGFP⁺ cells. RNAseq analyses showed similarities but also differences among CD4⁺ and CD8⁺ EGFP⁺ cells and provided the first description of the natural FOXP3⁺CD8⁺ Treg transcriptome. In vitro culture of CD4⁺ and CD8⁺ EGFP^- cells with TGFbeta and IL-2 generated induced EGFP⁺ Treg. CD4⁺ and CD8⁺ EGFP⁺ Treg were expanded upon in vivo administration of a low dose of IL-2.

CONCLUSIONS

This new and unique rat line constitutes a useful model to identify and isolate viable CD4⁺ and CD8⁺ FOXP3⁺ Treg. Additionally, it allows to identify molecules expressed in CD8⁺ Treg that may allow to better define their phenotype and function not only in rats but also in other species.

GARP Regulates the Immune Capacity of a Human Autologous Platelet Concentrate

Autologous platelet concentrates, like liquid platelet rich fibrin (iPRF), optimize wound healing; however, the underlying immunological mechanisms are poorly understood. Platelets, the main cellular component of iPRF, highly express the protein, Glycoprotein A repetitions predominant (GARP), on their surfaces. GARP plays a crucial role in maintaining peripheral tolerance, but its influence on the immune capacity of iPRF remains unclear. This study analyzed the interaction of iPRF with immune cells implicated in the wound healing process (human monocyte derived macrophages and CD4⁺ T cells) and evaluated the distinct influence of GARP on these mechanisms in vitro. GARP was determined to be expressed on the surface of platelets and to exist as a soluble factor in iPRF. Platelets derived from iPRF and iPRF itself induced a regulatory phenotype in CD4⁺ T cells, shown by increased expression of Foxp3 and GARP as well as decreased production of IL-2 and IFN-γ. Application of an anti-GARP antibody reversed these effects. Additionally, iPRF polarized macrophages to a "M0/M2-like" phenotype in a GARP independent manner. Altogether, this study demonstrated for the first time that the immune capacity of iPRF is mediated in part by GARP and its ability to induce regulatory CD4⁺ T cells.

New insight into GARP striking role in cancer progression: application for cancer therapy

T regulatory cells play a crucial role in antitumor immunity suppression. Glycoprotein-A repetitions predominant (GARP), transmembrane cell surface marker, is mostly expressed on Tregs and mediates intracellular organization of transforming growth factor-beta (TGF-β). The physiological role of GARP is immune system homeostasis, while it may cause tumor development by upregulating TGF-β secretion. Despite the vast application of anti- programmed cell death protein-1 (PD-1)/programmed death-ligand 1 (PD-L1) and anti-cytotoxic T-lymphocyte Antigen-4 (CTLA-4) antibodies in immunotherapy, anti-GARP antibodies have the advantage of better response in patients who has resistance to anti-PD-1/PD-L1. Furthermore, simultaneous administration of anti-GARP antibody and anti-PD-1/PD-L1 antibody is much more effective than anti-PD-1/PD-L1 alone. It is worth mentioning that the GARP-mTGF-β complex is more potent than secretory TGF-β to induce T helper 17 cells differentiation in HIV + patients. On the other hand, TGF-β is an effective cytokine in cancer development, and some microRNAs could control its secretion by regulating GARP. In the present review, some information is provided about the undeniable role of GARP in cancer progression and its probable importance as a novel prognostic biomarker. Anti-GARP antibodies are also suggested for cancer immunotherapy.

Single-cell RNA sequencing analysis of T helper cell differentiation and heterogeneity

Single-cell transcriptomics has emerged as a powerful tool to investigate cells' biological landscape and focus on the expression profile of individual cells. Major advantage of this approach is an analysis of highly complex and heterogeneous cell populations, such as a specific subpopulation of T helper cells that are known to differentiate into distinct subpopulations. The need for distinguishing the specific expression profile is even more important considering the T cell plasticity. However, importantly, the universal pipelines for single-cell analysis are usually not sufficient for every cell type. Here, the aims are to analyze the diversity of T cell phenotypes employing classical in vitro cytokine-mediated differentiation of human T cells isolated from human peripheral blood by single-cell transcriptomic approach with support of labelled antibodies and a comprehensive bioinformatics analysis using combination of Seurat, Nebulosa, GGplot and others. The results showed high expression similarities between Th1 and Th17 phenotype and very distinct Th2 expression profile. In a case of Th2 highly specific marker genes SPINT2, TRIB3 and CST7 were expressed. Overall, our results demonstrate how donor difference, Th plasticity and cell cycle influence the expression profiles of distinct T cell populations. The results could help to better understand the importance of each step of the analysis when working with T cell single-cell data and observe the results in a more practical way by using our analyzed datasets.

Changes in circulating TCF1- and GARP-associated regulatory T cell subsets reflect the clinical status of patients with chronic HBV infection

This study aimed to clarify the expression changes and clinical significance of regulatory T (Treg) cells and follicular regulatory T (TFR) cell subsets divided by glycoprotein A repetitions predominant protein (GARP) and T cell factor 1(TCF1) in peripheral blood of patients with chronic HBV infection. The peripheral blood of 26 chronic hepatitis B (CHB) patients, 27 inactive HBsAg carriers and 32 healthy controls were collected and GARP + percentages in Treg and TFR cells were analyzed by flow cytometry. In addition, Treg and TFR cell subsets sorted by CD62L and TCF1 were analyzed and compared. Correlation analyses were performed between Treg and TFR cell subpopulations and clinical parameters as well as cytokine concentrations, including IL-21, IL-10 and TGF-β1 in plasma. Circulating Treg and TFR levels were elevated in CHB patients. Moreover, GARP and TCF1 were up-regulated in circulating Treg and TFR cells of CHB patients. TCF1 + CD62L- Treg cells were increased while TCF1-CD62L + Treg cells were decreased in CHB patients. TCF1 + CD62L- and TCF1-CD62L- TFR cells were increased while TCF1 + CD62L + TFR cells were decreased in CHB patients. TCF1 + CD62L- Treg cells were positively correlated with HBV DNA, ALT and plasma IL-10, while TCF1 + CD62L + TFR cells were negatively correlated with HBV DNA, HBeAg, HBsAg, ALT, AST, T-BIL and positively correlated with plasma IL-21. Treg and TFR subsets sorted by TCF1, CD62L and GARP were changed in CHB patients. Changes in Treg and TFR functional subsets are associated with antiviral immunity in CHB patients.

GARP as a Therapeutic Target for the Modulation of Regulatory T Cells in Cancer and Autoimmunity

Regulatory T cells (Treg) play a critical role in immune homeostasis by suppressing several aspects of the immune response. Herein, Glycoprotein A repetitions predominant (GARP), the docking receptor for latent transforming growth factor (LTGF-β), which promotes its activation, plays a crucial role in maintaining Treg mediated immune tolerance. After activation, Treg uniquely express GARP on their surfaces. Due to its location and function, GARP may represent an important target for immunotherapeutic approaches, including the inhibition of Treg suppression in cancer or the enhancement of suppression in autoimmunity. In the present review, we will clarify the cellular and molecular regulation of GARP expression not only in human Treg but also in other cells present in the tumor microenvironment. We will also examine the overall roles of GARP in the regulation of the immune system. Furthermore, we will explore potential applications of GARP as a predictive and therapeutic biomarker as well as the targeting of GARP itself in immunotherapeutic approaches.

Rho-GTPase dependent leukocyte interaction generates pro-inflammatory thymic Tregs and causes arthritis

Conditional mutation of protein geranylgeranyltransferase type I (GGTase-I) in macrophages (GLC) activates Rho-GTPases and causes arthritis in mice. Knocking out Rag1 in GLC mice alleviates arthritis which indicates that lymphocytes are required for arthritis development in those mice. To study GLC dependent changes in the adaptive immunity, we isolated CD4⁺ T cells from GLC mice (CD4⁺GLCs). Spleen and joint draining lymph nodes (dLN) CD4⁺GLCs exhibited high expression of Cdc42 and Rac1, which repressed the caudal HOXA proteins and activated the mechanosensory complex to facilitate migration. These CDC42/RAC1 rich CD4⁺GLCs presented a complete signature of GARP⁺NRP1⁺IKZF2⁺FOXP3⁺ regulatory T cells (Tregs) of thymic origin. Activation of the β-catenin/Lef1 axis promoted a pro-inflammatory Th1 phenotype of Tregs, which was strongly associated with arthritis severity. Knockout of Cdc42 in macrophages of GLC mice affected CD4⁺ cell biology and triggered development of non-thymic Tregs. Knockout of Rac1 and RhoA had no such effects on CD4⁺ cells although it alleviated arthritis in GLC mice. Disrupting macrophage and T cell interaction with CTLA4 fusion protein reduced the Th1-driven inflammation and enrichment of thymic Tregs into dLNs. Antigen challenge reinforced the CD4⁺GLC phenotype in non-arthritic heterozygote GLC mice and increased accumulation of Rho-GTPase expressing thymic Tregs in dLNs. Our study demonstrates an unexpected role of macrophages in stimulating the development of pro-inflammatory thymic Tregs and reveal activation of Rho-GTPases behind their arthritogenic phenotype.

PARK7/DJ-1 promotes pyruvate dehydrogenase activity and maintains Treg homeostasis during ageing

Pyruvate dehydrogenase (PDH) is the gatekeeper enzyme of the tricarboxylic acid (TCA) cycle. Here we show that the deglycase DJ-1 (encoded by PARK7, a key familial Parkinson's disease gene) is a pacemaker regulating PDH activity in CD4⁺ regulatory T cells (T_reg cells). DJ-1 binds to PDHE1-β (PDHB), inhibiting phosphorylation of PDHE1-α (PDHA), thus promoting PDH activity and oxidative phosphorylation (OXPHOS). Park7 (Dj-1) deletion impairs T_reg survival starting in young mice and reduces T_reg homeostatic proliferation and cellularity only in aged mice. This leads to increased severity in aged mice during the remission of experimental autoimmune encephalomyelitis (EAE). Dj-1 deletion also compromises differentiation of inducible T_reg cells especially in aged mice, and the impairment occurs via regulation of PDHB. These findings provide unforeseen insight into the complicated regulatory machinery of the PDH complex. As T_reg homeostasis is dysregulated in many complex diseases, the DJ-1-PDHB axis represents a potential target to maintain or re-establish T_reg homeostasis.

Different subpopulations of regulatory T cells in human autoimmune disease, transplantation, and tumor immunity

CD4⁺CD25⁺ regulatory T cells (Tregs), a subpopulation of naturally CD4⁺ T cells that characteristically express transcription factor Forkhead box P3 (FOXP3), play a pivotal role in the maintenance of immune homeostasis and the prevention of autoimmunity. With the development of biological technology, the understanding of plasticity and stability of Tregs has been further developed. Recent studies have suggested that human Tregs are functionally and phenotypically diverse. The functions and mechanisms of different phenotypes of Tregs in different disease settings, such as tumor microenvironment, autoimmune diseases, and transplantation, have gradually become hot spots of immunology research that arouse extensive attention. Among the complex functions, CD4⁺CD25⁺FOXP3⁺ Tregs possess a potent immunosuppressive capacity and can produce various cytokines, such as IL‐2, IL‐10, and TGF‐β, to regulate immune homeostasis. They can alleviate the progression of diseases by resisting inflammatory immune responses, whereas promoting the poor prognosis of diseases by helping cells evade immune surveillance or suppressing effector T cells activity. Therefore, methods for targeting Tregs to regulate their functions in the immune microenvironment, such as depleting them to strengthen tumor immunity or expanding them to treat immunological diseases, need to be developed. Here, we discuss that different subpopulations of Tregs are essential for the development of immunotherapeutic strategies involving Tregs in human diseases.

Photobiomodulation-Activated Latent Transforming Growth Factor-β1: A Critical Clinical Therapeutic Pathway and an Endogenous Optogenetic Tool for Discovery

Objective: The central role of the TGF-β pathway in embryonic development, immune responses, tissue healing, and malignancies is well established. Prior attempts with small molecules, peptides, and regulatory RNAs have failed mainly due to off-target effects in clinical studies. This review outlines the evidence for selectively activating the endogenous, latent transforming growth factor (TGF)-β1 with photobiomodulation (PBM) treatments. Background: Light treatments play a central role in current-directed energy therapeutics in medicine. Therapeutic use of low-dose light treatments has been noted since the 1960s. However, the breadth of treatments and inconsistencies with clinical outcomes have led to much skepticism. This can be primarily attributed to a lack of understanding of the fundamental light-tissue interactions and optimization of clinical treatment protocols. Methods: Recent advances in molecular mechanisms and improved biophotonic device technologies have led to a resurgence of interest in this field. Results: Over the past two decades, our work has focused on outlining a direct molecular mechanism involving PBM-generated redox-mediated activation of endogenous latent TGF-β1. Conclusions: Despite its critical roles in these processes, the complexity and cross talk in this potent growth factor signaling network have prevented the development of directed targeted therapeutics. PBM treatments offer a novel therapeutic and discovery tool in this aspect, especially with the growing evidence for its roles in cancer immunotherapy and stem cell biology.

CRISPR/Cas9-mediated demethylation of FOXP3-TSDR toward Treg-characteristic programming of Jurkat T cells

Demethylation of FOXP3-TSDR (Treg specific demethylated region) is a hallmark of stable differentiation and suppressive function of regulatory T (Treg) cells. Previous protocols aiming at human naïve T cell differentiation failed to implement a Treg cell specific epigenetic signature. Ten-eleven translocation (TET) enzymes catalyze DNA demethylation. Plasmids towardexpression of a fusion protein encompassing nonfunctional Cas9, the catalytic domain of TET1, blue fluorescent protein, and encoding single guide RNAs (sgRNAs) targeting specific segments of the FOXP3-TSDR were engineered and transfected into Jurkat T cells. FOXP3-TSDR methylation was analyzed by deep-amplicon bisulfite sequencing while cellular Foxp3, Tbet, Gata3, and Rorgt mRNA levels were determined by real-time PCR. Overexpression of dCas9TET1 significantly decreased Jurkat cell FOXP3-TSDR methylation and increased Foxp3 mRNA expression while expressions of master transcription factor mRNAs of other major T cell lineages remained largely unaffected. dCas9-TET1 construct transfection mediated Treg programming of patients' primary T cells might be feasible.

A Novel TGF-β Risk Score Predicts the Clinical Outcomes and Tumour Microenvironment Phenotypes in Bladder Cancer

BACKGROUND

The TGF-β pathway plays critical roles in numerous malignancies. Nevertheless, its potential role in prognosis prediction and regulating tumour microenvironment (TME) characteristics require further elucidation in bladder cancer (BLCA).

METHODS

TGF-β-related genes were comprehensively summarized from several databases. The TCGA-BLCA cohort (training cohort) was downloaded from the Cancer Genome Atlas, and the independent validation cohorts were gathered from Xiangya Hospital (Xinagya cohort) and Gene Expression Omnibus. Initially, we identified differentially expressed TGF-β genes (DEGs) between cancer and normal tissues. Subsequently, univariate Cox analysis was applied to identify prognostic DEGs, which were further used to develop the TGF-β risk score by performing LASSO and multivariate Cox analyses. Then, we studied the role of the TGF-β risk score in predicting prognosis and the TME phenotypes. In addition, the role of the TGF-β risk score in guiding precision treatments for BLCA has also been assessed.

RESULTS

We successfully constructed a TGF-β risk score with an independent prognostic prediction value. A high TGF-β risk score indicated an inflamed TME, which was supported by the positive relationships between the risk score, enrichment scores of anticancer immunity steps, and the infiltration levels of tumour-infiltrating immune cells. In addition, the risk score positively correlated with the expression of several immune checkpoints and the T cell inflamed score. Consistently, the risk score was positively related to the enrichment scores of most immunotherapy-positive pathways. In addition, the sensitivities of six common chemotherapeutic drugs were positively associated with the risk score. Furthermore, higher risk score indicated higher sensitivity to radiotherapy and EGFR-targeted therapy. On the contrary, patients with low-risk scores were more sensitive to targeted therapies, including the blockade of FGFR3 and WNT-β-catenin networks.

CONCLUSIONS

We first constructed and validated a TGF-β signature that could predict the prognosis and TME phenotypes for BLCA. More importantly, the TGF-β risk score could aid in individual precision treatment for BLCA.

GARP: A Key Target to Evaluate Tumor Immunosuppressive Microenvironment

Simple Summary

Tumors are not only composed of cancer cells but also of various infiltrating cells constituting the tumor microenvironment (TME); all these cells produce growth factors which contribute to tumor progression and invasiveness. Among them, transforming growth factor-β1 (TGF-β1) has been shown to be a potent immunosuppressive cytokine favoring cell proliferation and invasion and to be associated with resistance to anticancer treatments. Glycoprotein-A repetition predominant (GARP) plays a critical role in the activation of TGF-β1 and has been shown to be expressed at the membrane of cancer cells and also of regulatory T cells and platelets in the TME. An increased GARP expression has been shown in a variety of cancers. The objective of this review is to highlight GARP’s expression and function in cancer and to evaluate its potential as a predictive and therapeutic follow-up biomarker that could be assessed, in real time, by molecular imaging.

Abstract

Glycoprotein-A repetitions predominant (GARP) is the docking receptor for latent transforming growth factor (LTGF-β) and promotes its activation. In cancer, increased GARP expression has been found in many types of cancer. GARP is expressed by regulatory T cells and platelets in the tumor microenvironment (TME) and can be also expressed by tumor cells themselves. Thus, GARP can be widely present in tumors in which it plays a major role in the production of active TGF-β, contributing to immune evasion and cancer progression via the GARP-TGF-β pathway. The objective of this review is to highlight GARP expression and function in cancer and to evaluate the potential of membrane GARP as a predictive and therapeutic follow-up biomarker that could be assessed, in real time, by molecular imaging. Moreover, as GARP can be secreted, a focus will also be made on soluble GARP as a circulating biomarker.

Memory and naïve gamma delta regulatory T-cell gene expression in the first 24-weeks of peanut oral immunotherapy

BACKGROUND

Peanut oral immunotherapy (POIT) has provided desensitization to peanut allergic individuals. Limited immunological evaluation exists during the first 24-weeks of POIT.

OBJECTIVE

Regulatory T-cells (Tregs) are antigen induced immunosuppressive T-cells important in establishing tolerance. Delineation of early immunologic changes contributing to the development of peanut desensitization would help clarify the mechanism of action in POIT. We performed single-cell RNA sequencing (scRNAseq) on Tregs in pediatric subjects undergoing POIT during the first 24-weeks of therapy to evaluate early immunological changes induced by POIT.

METHODS

PBMC samples from peanut allergic subjects between 5 and 12 years of age enrolled in a Phase 1/2a POIT study were collected and analyzed at 0, 6, and 24-weeks after POIT initiation and samples were compared to healthy non-peanut allergic controls. Tregs were enriched from PBMCs and scRNAseq analysis performed. Cell Ranger 3.1.0 (10× Genomics) was utilized to identify cell clusters and differentially expressed genes, and results were analyzed with Seurat suite version 3.0.0.

RESULTS

Gene analysis revealed 10 major clusters corresponding to different cell types observed to change during POIT when compared to the healthy, non-peanut-allergic state. scRNAseq analysis of Tregs revealed strong CD3G expression correlating with gdTregs. scRNAseq analysis of gdTregs revealed dynamic changes occurring within the first 6-weeks of treatment and cell frequencies of naïve and memory gdTregs at 24-weeks of treatment reducing to levels similar to healthy controls. Analysis of transcriptomic cell identity analysis using SingleR showed gene expression in gdTregs similar to healthy control after 24-weeks of POIT treatment. scRNAseq analysis revealed alterations in gene expression for memory and naïve gdTregs during this timeframe. Specifically, expression of OX40R (TNFRSF4), GITR (TNFRSF18), TGFB1, CTLA4, ISG20, CD69 were upregulated in memory gdTregs compared to naive gdTregs by 24-weeks of POIT, while IL7R and SELL were downregulated in memory gdTregs compared to naïve gdTregs.

CONCLUSIONS

There are specific expression profiles of peripheral naïve and mature gdTreg cells in peanut allergic patients undergoing POIT in the first 24-weeks of treatment implicating pathways involved in maintenance of immune homeostasis. gdTreg cells may contribute to the tolerogenic effect of POIT within the first 24-weeks of POIT treatment. These findings suggest that gdTregs cells may be an early marker of desensitization in subjects undergoing POIT.

Targeting immunosuppression by TGF-β1 for cancer immunotherapy

The TGF-β1 cytokine is a key mediator of many biological processes. Complex regulatory mechanisms are in place that allow one single molecule to exert so many distinct indispensable activities. The complexity of TGF-β1 biology is further illustrated by the opposing dual roles it plays during cancer progression. Risks of toxicities combined with lack of convincing therapeutical efficacy explain at least in part why therapies targeting TGF-β1 have lagged behind in past decades. However, recent successes of immunostimulatory antibodies for the immunotherapy of cancer and findings that TGF-β1 activity associates with resistance to immunotherapeutic drugs have revived the field. In this review, we discuss the biology of TGF-β1 with a special focus on its roles in regulating immune responses in the context of cancer. We describe the various therapeutic approaches available to inhibit TGF-β signalling, and more recent findings that allow selective targeting of specific sources of TGF-β activity, which may prove relevant to increase the efficacy and reduce the toxicity of cancer immunotherapy.

GARP and GARP-Treated tDC Prevented the Formation of Atherosclerotic Plaques in ApoE-/- Mice

Purpose

This study aims to clarify the specific mechanism by which GARP affects the atherosclerotic plaques in ApoE^−/- mice and the effect of GARP-tDC on atherosclerosis.

Methods

The mice were randomly divided into three groups: the control group, the GARP-overexpressed group and the GARP-inhibited group. After 12 weeks, all the mice were euthanized, and the specimens were collected. In vitro, experiments were conducted to observe the effect of GARP on DC phenotype and the changes of the proportion of CD4⁺CD25⁺Foxp3⁺ Treg cells when GARP-tDCs were co-cultured with CD4⁺ T cells. Furthermore, adoptive transmission of GARP-tDCs was used to observe the effect on atherosclerotic plaque in mice.

Results

The GARP-overexpressed group enhanced the biological activity of Foxp3⁺ CD4⁺CD25⁺ Tregs and resulted in increased expression of LAP in T cells. In addition, the GARP-overexpressed group significantly suppressed the function of Th1 and Th17, and decreased the secretion of INF-γ and IL-17A. Thus, GARP had a protective effect on atherosclerosis. In vitro, we found that GARP-tDC had a tolerance-inducing phenotype, and GARP-tDC also had the ability to induce tolerance when co-cultured with CD4⁺ T cells. More importantly, adoptive transmission of GARP-tDCs reduced the size of atherosclerotic plaques.

Conclusion

GARP and the GARP-tDC play protective roles in atherosclerosis. The protective effect of GARP on atherosclerosis is achieved by increasing CD4⁺CD25⁺Foxp3⁺ Treg cells and inhibiting the production of IFN-γ and IL-17A.

Molecular Insights Into Regulatory T-Cell Adaptation to Self, Environment, and Host Tissues: Plasticity or Loss of Function in Autoimmune Disease

There has been much interest in the ability of regulatory T cells (Treg) to switch function in vivo, either as a result of genetic risk of disease or in response to environmental and metabolic cues. The relationship between levels of FOXP3 and functional fitness plays a significant part in this plasticity. There is an emerging role for Treg in tissue repair that may be less dependent on FOXP3, and the molecular mechanisms underpinning this are not fully understood. As a result of detailed, high-resolution functional genomics, the gene regulatory networks and key functional mediators of Treg phenotype downstream of FOXP3 have been mapped, enabling a mechanistic insight into Treg function. This transcription factor-driven programming of T-cell function to generate Treg requires the switching on and off of key genes that form part of the Treg gene regulatory network and raises the possibility that this is reversible. It is plausible that subtle shifts in expression levels of specific genes, including transcription factors and non-coding RNAs, change the regulation of the Treg gene network. The subtle skewing of gene expression initiates changes in function, with the potential to promote chronic disease and/or to license appropriate inflammatory responses. In the case of autoimmunity, there is an underlying genetic risk, and the interplay of genetic and environmental cues is complex and impacts gene regulation networks frequently involving promoters and enhancers, the regulatory elements that control gene expression levels and responsiveness. These promoter–enhancer interactions can operate over long distances and are highly cell type specific. In autoimmunity, the genetic risk can result in changes in these enhancer/promoter interactions, and this mainly impacts genes which are expressed in T cells and hence impacts Treg/conventional T-cell (Tconv) function. Genetic risk may cause the subtle alterations to the responsiveness of gene regulatory networks which are controlled by or control FOXP3 and its target genes, and the application of assays of the 3D organization of chromatin, enabling the connection of non-coding regulatory regions to the genes they control, is revealing the direct impact of environmental/metabolic/genetic risk on T-cell function and is providing mechanistic insight into susceptibility to inflammatory and autoimmune conditions.

Helios enhances the preferential differentiation of human fetal CD4+ naïve T cells into regulatory T cells

T cell receptor (TCR) stimulation and cytokine cues drive the differentiation of CD4⁺ naïve T cells into effector T cell populations with distinct proinflammatory or regulatory functions. Unlike adult naïve T cells, human fetal naïve CD4⁺ T cells preferentially differentiate into FOXP3⁺ regulatory T (T_reg) cells upon TCR activation independent of exogenous cytokine signaling. This cell-intrinsic predisposition for T_reg differentiation is implicated in the generation of tolerance in utero; however, the underlying mechanisms remain largely unknown. Here, we identify epigenetic and transcriptional programs shared between fetal naïve T and committed T_reg cells that are inactive in adult naïve T cells and show that fetal-derived induced T_reg (iT_reg) cells retain this transcriptional program. We show that a subset of T_reg-specific enhancers is accessible in fetal naïve T cells, including two active superenhancers at Helios Helios is expressed in fetal naïve T cells but not in adult naïve T cells, and fetal iT_reg cells maintain Helios expression. CRISPR-Cas9 ablation of Helios in fetal naïve T cells impaired their differentiation into iT_reg cells upon TCR stimulation, reduced expression of immunosuppressive genes in fetal iT_reg cells such as IL10, and increased expression of proinflammatory genes including IFNG Consequently, Helios knockout fetal iT_reg cells had reduced IL-10 and increased IFN-γ cytokine production. Together, our results reveal important roles for Helios in enhancing preferential fetal T_reg differentiation and fine-tuning eventual T_reg function. The T_reg-biased programs identified within fetal naïve T cells could potentially be used to engineer enhanced iT_reg populations for adoptive cellular therapies.

Harnessing proteases for T regulatory cell immunotherapy

The immune system is tightly regulated by a subset of T cells defined as regulatory T cells (Tregs). Tregs maintain immune homeostasis by restraining unwarranted immune cell activation and effector function. Here, we discuss an important but underappreciated role of proteases in controlling Treg function. Proteases regulate a number of vital processes that determine T cell immune responses and some of them such as furin, ADAM (through regulating LAG receptor), MALT, and asparaginyl endopeptidase are implicated in Treg immunobiology. Targeted protease inhibition, using either small molecule inhibitors or gene deficient mice has demonstrated their specificity in modulating Treg function in experimental murine models. These data further highlight the ability of proteases to specifically regulate Tregs but no other T effector lineages. Taken together, it is apparent that incorporating proteases as targets within Treg cell engineering protocols may enable generation of robust Treg cellular therapeutics. These engineered Tregs may possess enhanced regulatory function along with resistance to lineage deviation in inflammatory disease such as colitis and graft versus host disease. Within this review, we summarize research on the role of proteases in regulating Treg function and discuss the translational potential of harnessing Treg function by targeting protease driven regulatory pathways.

GARP is a key molecule for mesenchymal stromal cell responses to TGF-β and fundamental to control mitochondrial ROS levels

Multipotent mesenchymal stromal cells (MSCs) have emerged as a promising cell therapy in regenerative medicine and for autoimmune/inflammatory diseases. However, a main hurdle for MSCs-based therapies is the loss of their proliferative potential in vitro. Here we report that glycoprotein A repetitions predominant (GARP) is required for the proliferation and survival of adipose-derived MSCs (ASCs) via its regulation of transforming growth factor-β (TGF-β) activation. Silencing of GARP in human ASCs increased their activation of TGF-β which augmented the levels of mitochondrial reactive oxygen species (mtROS), resulting in DNA damage, a block in proliferation and apoptosis. Inhibition of TGF-β signaling reduced the levels of mtROS and DNA damage and restored the ability of GARP-/low ASCs to proliferate. In contrast, overexpression of GARP in ASCs increased their proliferative capacity and rendered them more resistant to etoposide-induced DNA damage and apoptosis, in a TGF-β-dependent manner. In summary, our data show that the presence or absence of GARP on ASCs gives rise to distinct TGF-β responses with diametrically opposing effects on ASC proliferation and survival.

Human Regulatory T Cells From Umbilical Cord Blood Display Increased Repertoire Diversity and Lineage Stability Relative to Adult Peripheral Blood

The human T lymphocyte compartment is highly dynamic over the course of a lifetime. Of the many changes, perhaps most notable is the transition from a predominantly naïve T cell state at birth to the acquisition of antigen-experienced memory and effector subsets following environmental exposures. These phenotypic changes, including the induction of T cell exhaustion and senescence, have the potential to negatively impact efficacy of adoptive T cell therapies (ACT). When considering ACT with CD4+CD25+CD127-/lo regulatory T cells (Tregs) for the induction of immune tolerance, we previously reported ex vivo expanded umbilical cord blood (CB) Tregs remained more naïve, suppressed responder T cells equivalently, and exhibited a more diverse T cell receptor (TCR) repertoire compared to expanded adult peripheral blood (APB) Tregs. Herein, we hypothesized that upon further characterization, we would observe increased lineage heterogeneity and phenotypic diversity in APB Tregs that might negatively impact lineage stability, engraftment capacity, and the potential for Tregs to home to sites of tissue inflammation following ACT. We compared the phenotypic profiles of human Tregs isolated from CB versus the more traditional source, APB. We conducted analysis of fresh and ex vivo expanded Treg subsets at both the single cell (scRNA-seq and flow cytometry) and bulk (microarray and cytokine profiling) levels. Single cell transcriptional profiles of pre-expansion APB Tregs highlighted a cluster of cells that showed increased expression of genes associated with effector and pro-inflammatory phenotypes (CCL5, GZMK, CXCR3, LYAR, and NKG7) with low expression of Treg markers (FOXP3 and IKZF2). CB Tregs were more diverse in TCR repertoire and homogenous in phenotype, and contained fewer effector-like cells in contrast with APB Tregs. Interestingly, expression of canonical Treg markers, such as FOXP3, TIGIT, and IKZF2, were increased in CB CD4+CD127+ conventional T cells (Tconv) compared to APB Tconv, post-expansion, implying perinatal T cells may adopt a default regulatory program. Collectively, these data identify surface markers (namely CXCR3) that could be depleted to improve purity and stability of APB Tregs, and support the use of expanded CB Tregs as a potentially optimal ACT modality for the treatment of autoimmune and inflammatory diseases.

Peptidase inhibitor 16 identifies a human regulatory T-cell subset with reduced FOXP3 expression over the first year of recent onset type 1 diabetes

CD4⁺ T-cell subsets play a major role in the host response to infection, and a healthy immune system requires a fine balance between reactivity and tolerance. This balance is in part maintained by regulatory T cells (Treg), which promote tolerance, and loss of immune tolerance contributes to autoimmunity. As the T cells which drive immunity are diverse, identifying and understanding how these subsets function requires specific biomarkers. From a human CD4 Tconv/Treg cell genome wide analysis we identified peptidase inhibitor 16 (PI16) as a CD4 subset biomarker and we now show detailed analysis of its distribution, phenotype and links to Treg function in type 1 diabetes. To determine the clinical relevance of Pi16 Treg, we analysed PI16⁺ Treg cells from type 1 diabetes patient samples. We observed that FOXP3 expression levels declined with disease progression, suggesting loss of functional fitness in these Treg cells in Type 1 diabetes, and in particular the rate of loss of FOXP3 expression was greatest in the PI16+ve Treg. We propose that PI16 has utility as a biomarker of functional human Treg subsets and may be useful for tracking loss of immune function in vivo. The ability to stratify at risk patients so that tailored interventions can be applied would open the door to personalised medicine for Type 1 diabetes.

Increased Expression of GARP in Papillary Thyroid Carcinoma

Regulatory T cells (Tregs) are immunosuppressive immune cells that play an important role in tumor development. Suppression of Treg function is considered to be an effective strategy for cancer therapy. Glycoprotein A repetitions predominant (GARP) has been found on the surface of activated Tregs. GARP has been recently observed in only a few solid tumors including breast, colon, lung cancers, and melanoma. However, its function in cancers remains unknown. Here, we investigated the expression of GARP in human papillary thyroid carcinoma (PTC) and its prognostic significance. In this study, immunohistochemistry was performed to examine the expression of GARP and Foxp3 in 19 human PTC tissues (including 10 cases with and 9 cases without lymph node metastasis) and 20 benign thyroid diseases (including 10 cases with nodular goiter and 10 cases with adenoma). Compared with benign thyroid diseases, we found a significant increase in the expression of GARP in PTC. Increased GARP expression in PTC was positively correlated with increased expression of Foxp3, which is very important for development of Tregs. But, there is no significant association of elevated expression of GARP with lymph node metastasis in PTC. Our results indicate that GARP is implicated in the development of PTC and might be a potential novel target for anticancer therapy. In addition, our findings further support the existence of a positive-feedback loop between GARP and Foxp3.

Heterogeneity in FoxP3- and GARP/LAP-Expressing T Regulatory Cells in an HLA Class II Transgenic Murine Model of Necrotizing Soft Tissue Infections by Group A Streptococcus

Invasive group A streptococcus (GAS) infections include necrotizing soft tissue infections (NSTI) and streptococcal toxic shock syndrome (STSS). We have previously shown that host HLA class II allelic variations determine the risk for necrotizing fasciitis (NF), a dominant subgroup of NSTI, and STSS by modulating responses to GAS superantigens (SAgs). SAgs are pivotal mediators of uncontrolled T-cell activation, triggering a proinflammatory cytokine storm in the host. FoxP3-expressing CD4⁺ CD25⁺ T regulatory cells (Tregs) comprise phenotypically and functionally heterogeneous subsets with a profound ability to suppress inflammatory responses. Specifically, activated Tregs, which express glycoprotein A repetitions predominant (GARP) and display latent transforming growth factor β1 (TGF-β1) complexes (latency-associated peptide [LAP]), exhibit strong immunosuppressive functions. The significance of Tregs that may participate in suppressing inflammatory responses during NSTI is unknown. Here, we phenotypically characterized FoxP3/GARP/LAP-expressing Tregs in GAS-infected or SAg (SmeZ)-stimulated splenocytes from transgenic (tg) mice expressing human HLA-II DRB1*15 (DR15 allele associated with nonsevere NF/STSS-protective responses) or DRB1*0402/DQB1*0302 (DR4/DQ8 alleles associated with neutral risk for combined NF/STSS). We demonstrated both in vivo and in vitro that the neutral-risk allele upregulates expression of CD4⁺ CD25⁺ activated effector T cells, with a significantly lower frequency of Foxp3⁺/GARP⁺ LAP^- but higher frequency of Foxp3^- LAP⁺ Tregs than seen with the protective allele. Additional in vitro studies revealed that the presentation of SmeZ by the neutral-risk allele significantly increases proliferation and expression of effector cytokines gamma interferon (IFN-γ) and interleukin-2 (IL-2) and upregulates CD4⁺ CD25⁺ T cell receptors (TCRs) carrying specific Vβ 11 chain (TCRVβ11⁺) T cells and Th1 transcription factor Tbx21 mRNA levels. Our data suggest that neutral-risk alleles may drive Th1 differentiation while attenuating the induction of Tregs associated with suppressive function.

An immunoregulatory and tissue-residency program modulated by c-MAF in human TH17 cells

Different types of effector and memory T lymphocytes are induced and maintained in protective or pathological immune responses. Here we characterized two human CD4⁺ T_H17 helper cell subsets that, in the recently activated state, could be distinguished on the basis of their expression of the anti-inflammatory cytokine IL-10. IL-10⁺ T_H17 cells upregulated a variety of genes encoding immunoregulatory molecules, as well as genes whose expression is characteristic of tissue-resident T cells. In contrast, IL-10^- T_H17 cells maintained a pro-inflammatory gene-expression profile and upregulated the expression of homing receptors that guide recirculation from tissues to blood. Expression of the transcription factor c-MAF was selectively upregulated in IL-10⁺ T_H17 cells, and it was bound to a large set of enhancer-like regions and modulated the immunoregulatory and tissue-residency program. Our results identify c-MAF as a relevant factor that drives two highly divergent post-activation fates of human T_H17 cells and provide a framework with which to investigate the role of these cells in physiology and immunopathology.

Intracellular and extracellular TGF-β signaling in cancer: some recent topics

Transforming growth factor (TGF)-β regulates a wide variety of cellular responses, including cell growth arrest, apoptosis, cell differentiation, motility, invasion, extracellular matrix production, tissue fibrosis, angiogenesis, and immune function. Although tumor-suppressive roles of TGF-β have been extensively studied and well-characterized in many cancers, especially at early stages, accumulating evidence has revealed the critical roles of TGF-β as a pro-tumorigenic factor in various types of cancer. This review will focus on recent findings regarding epithelial-mesenchymal transition (EMT) induced by TGF-β, in relation to crosstalk with some other signaling pathways, and the roles of TGF-β in lung and pancreatic cancers, in which TGF-β has been shown to be involved in cancer progression. Recent findings also strongly suggested that targeting TGF-β signaling using specific inhibitors may be useful for the treatment of some cancers. TGF-β plays a pivotal role in the differentiation and function of regulatory T cells (Tregs). TGF-β is produced as latent high molecular weight complexes, and the latent TGF-β complex expressed on the surface of Tregs contains glycoprotein A repetitions predominant (GARP, also known as leucine-rich repeat containing 32 or LRRC32). Inhibition of the TGF-β activities through regulation of the latent TGF-β complex activation will be discussed.

Role of GARP in the activation of latent TGF-β1

TGF-β1, 2 and 3 cytokines are involved in many cellular processes including cell proliferation, differentiation, migration and survival. Whereas TGF-β2 and 3 play important roles in embryonic development, TGF-β1 is mostly implicated in controlling immune responses after birth. The production of TGF-β1 is a tightly regulated process, occurring mostly at a post-translational level. Virtually all cells produce the latent, inactive form of TGF-β1. In latent TGF-β1, the mature TGF-β1 dimer is non-covalently associated to the Latency Associated Peptide, or LAP, which prevents binding to the TGF-β1 receptor. Activation of the cytokine implies release of mature TGF-β1 from LAP. Only a few cell types activate latent TGF-β1, via mechanisms that are cell type specific. Proteins such as integrins, proteases and thrombospondin-1 activate TGF-β1 in epithelial cells, fibroblasts and dendritic cells. More recently, the protein GARP was shown to be involved in TGF-β1 activation by regulatory T cells (Treg), a subset of CD4⁺ T lymphocytes specialized in suppression of immune responses. GARP is a transmembrane protein that binds latent-TGF-β1 and tethers it on the Treg surface. The role of GARP was studied mostly in Tregs, and this was recently reviewed in L. Sun, H. Jin and H. Li, Oncotarget, 2016, 7, 42826-42836. However, GARP is also expressed in non-immune cells. This review focuses on the roles of GARP in latent TGF-β1 activation by immune and non-immune cells.

Unravelling the molecular basis for regulatory T-cell plasticity and loss of function in disease

Regulatory T cells (Treg) are critical for preventing autoimmunity and curtailing responses of conventional effector T cells (Tconv). The reprogramming of T‐cell fate and function to generate Treg requires switching on and off of key gene regulatory networks, which may be initiated by a subtle shift in expression levels of specific genes. This can be achieved by intermediary regulatory processes that include microRNA and long noncoding RNA‐based regulation of gene expression. There are well‐documented microRNA profiles in Treg and Tconv, and these can operate to either reinforce or reduce expression of a specific set of target genes, including FOXP3 itself. This type of feedforward/feedback regulatory loop is normally stable in the steady state, but can alter in response to local cues or genetic risk. This may go some way to explaining T‐cell plasticity. In addition, in chronic inflammation or autoimmunity, altered Treg/Tconv function may be influenced by changes in enhancer–promoter interactions, which are highly cell type‐specific. These interactions are impacted by genetic risk based on genome‐wide association studies and may cause subtle alterations to the gene regulatory networks controlled by or controlling FOXP3 and its target genes. Recent insights into the 3D organisation of chromatin and the mapping of noncoding regulatory regions to the genes they control are shedding new light on the direct impact of genetic risk on T‐cell function and susceptibility to inflammatory and autoimmune conditions.

Immunoregulatory functions and the therapeutic implications of GARP-TGF-β in inflammation and cancer

GARP (glycoprotein-A repetitions predominant) is a type I transmembrane cell surface docking receptor for latent transforming growth factor-β (TGF-β) that is abundantly expressed on regulatory T lymphocytes and platelets. GARP regulates the availability of membrane-bound latent TGF-β and modulates its activation. For this reason, GARP expression on immune and non-immune cells is involved in maintaining peripheral tolerance. It plays an important role in preventing inflammatory diseases such as allergy and graft versus host disease (GvHD). GARP is also frequently hijacked by cancer cells to promote oncogenesis. This review summarizes the most important features of GARP biology described to date including gene regulation, protein expression and mechanism in activating latent TGF-β, and the function of GARP in regulatory T cell biology and peripheral tolerance, as well as GARP’s increasingly recognized roles in platelet-mediated cancer immune evasion. The promise for GARP-targeted strategy as a novel immunotherapy of cancer is also highlighted.

Identification of key genes implicated in the suppressive function of human FOXP3+CD25+CD4+ regulatory T cells through the analysis of time‑series data

Human forkhead box P3 (FOXP3)⁺ cluster of differentiation (CD)25⁺CD4⁺ regulatory T cells (Tregs) are a type of T cell that express CD4, CD25 and FOXP3, which are critical for maintaining immune homeostasis. The present study aimed to determine the mechanisms underlying Treg function. The GSE11292 dataset was downloaded from the Gene Expression Omnibus, which included data from Treg cells at 19 time points (0–360 min) with an equal interval of 20 min, and corresponding repeated samples. However, data for Treg cells at time point 120 min were missing. Using the Mfuzz package, the key genes were identified by clustering analysis. Subsequently, regulatory networks and protein-protein interaction (PPI) networks were constructed and merged into integrated networks using Cytoscape software. Using Database for Annotation, Visualization and Integrated Discover software, enrichment analyses were performed for the genes involved in the PPI networks. Cluster 1 (including 292 genes), cluster 2 (including 111 genes), cluster 3 (including 194 genes) and cluster 4 (including 103 genes) were obtained from the clustering analysis. GAPDH (degree, 40) in cluster 1, Janus kinase 2 (JAK2) (degree, 10) and signal transducer and activator of transcription 5A (STAT5A) (degree, 9) in cluster 3, and tumor necrosis factor (TNF) (degree, 26) and interleukin 2 (IL2) (degree, 22) in cluster 4 had higher degrees in the PPI networks. In addition, it was indicated that several genes may have a role in Treg function by targeting other genes [e.g. microRNA (miR)-146b-3p→TNF, miR-146b-5p→TNF, miR-142-5p→TNF and tripartite motif containing 28 (TRIM28)→GAPDH]. Enrichment analyses indicated that IL2 and TNF were enriched in the immune response and T cell receptor signaling pathway. In conclusion, GAPDH targeted by TRIM28, TNF targeted by miR-146b-3p, miR-146b-5p and miR-142-5p, in addition to JAK2, IL2, and STAT5A may serve important roles in Treg function.

A novel and effective method to generate human porcine-specific regulatory T cells with high expression of IL-10, TGF-β1 and IL-35

Organ transplantation remains the most effective treatment for patients with late stage organ failure. Transgenic pigs provide an alternative organ donor source to the limited availability of human organs. However, cellular rejection still remains to be the obstacle for xenotransplantation. Superior to other methods, antigen-specific regulatory T cells (Treg) alleviate cellular rejection with fewer side effects. Here we demonstrate the use of a fast method to provide tolerogenic dendritic cells (tolDC) that can be used to generate effective porcine-specific Treg cells (PSTreg). TolDC were produced within three days from human monocytes in medium supplemented with anti-inflammatory cytokines. Treg were generated from naïve CD4⁺ T cells and induced to become PSTreg by cocultivation with porcine-antigen-loaded tolDC. Results showed that PSTreg exhibited the expected phenotype, CD4⁺CD25⁺CD127^low/− Foxp3⁺, and a more activated phenotype. The specificity of PSTreg was demonstrated by suppression of effector T cell (Teff) activation markers of different stages and inhibition of Teff cell proliferation. TolDC and PSTreg exhibited high expression of IL-10 and TGF-β1 at both protein and RNA levels, and PSTreg also highly expressed IL-35 at RNA levels. Upon restimulation, PSTreg retained the activated phenotype and specificity. Taken together, the newly developed procedure allows efficient generation of highly suppressive PSTreg.

Suppression by human FOXP3 + regulatory T cells requires FOXP3-TIP60 interactions

Targeting the FOXP3-TIP60 interaction may modulate T reg activity in IPEX and other autoimmune and inflammatory diseases.

CD4+ CD25+ GARP+ regulatory T cells display a compromised suppressive function in patients with dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is a lethal inflammatory heart disease and closely connected with dysfunction of the immune system. Glycoprotein A repetitions predominant (GARP) expressed on activated CD4⁺ T cells with suppressive activity has been established. This study aimed to investigate the frequency and function of circulating CD4⁺  CD25⁺  GARP⁺ regulatory T (Treg) cells in DCM. Forty-five DCM patients and 46 controls were enrolled in this study. There was a significant increase in peripheral T helper type 1 (Th1) and Th17 number and their related cytokines [interferon-γ (IFN-γ), interleukin (IL-17)], and an obvious decrease in Treg number, transforming growth factor-β₁ (TGF-β₁ ) levels and the expression of forkhead box P3 (FOXP3) and GARP in patients with DCM compared with controls. In addition, the suppressive function of CD4⁺  CD25⁺  GARP⁺ Treg cells was impaired in DCM patients upon T-cell receptor stimulation detected using CFSE dye. Lower level of TGF-β₁ and higher levels of IFN-γ and IL-17 detected using ELISA were found in supernatants of the cultured CD4⁺  CD25⁺  GARP⁺ Treg cells in DCM patients compared with controls. Together, our results indicate that CD4⁺  CD25⁺  GARP⁺ Treg cells are defective in DCM patients and GARP seems to be a better molecular definition of the regulatory phenotype. Therefore, it might be an attractive stategy to pay more attention to GARP in DCM patients.

Chinese 1 strain of Toxoplasma gondii excreted-secreted antigens negatively modulate Foxp3 via inhibition of the TGFßRII/Smad2/Smad3/Smad4 pathway

Toxoplasma gondii is an opportunistic intracellular parasite and is considered an important aetiological factor in the process of abortion, especially as occurs in early gestation. Chinese 1 strain of T. gondii is a dominant genotype prevalent in China. Although it is known that early foetal resorption triggered by RH strain of T. gondii is attributable to immune mechanisms rather than its direct effect in uterus, the underlying mechanism of the abortion caused by Chinese 1 strain remains unclear. This study was designed to investigate the effect of excreted–secreted antigens (ESA) of Chinese 1 strain of T. gondii on the expression of forkhead box transcription factor (Foxp3) as it pertains to early pregnancy and abortion. ESA caused a marked inhibition in the expression of Foxp3 both in vivo and in vitro. In addition, ESA negatively modulated Smad2 and Smad3 at the posttranslational level. Smad2 siRNA cooperated with ESA to further suppress the level of Foxp3. This inhibitory effect on Foxp3 expression was partially abrogated by overexpression of Smad2, Smad3 and Smad4. Additionally, ESA attenuated the expression of TGFßRII, whereas TGFßRII agonist could profoundly reversed the decreased Foxp3 triggered by ESA. Collectively, the findings suggested that ESA restricted Foxp3 expression by inhibiting TGFßRII/Smad2/Smad3/Smad4 signalling, ultimately resulting in abortion.

Expression of GARP Is Increased in Tumor-Infiltrating Regulatory T Cells and Is Correlated to Clinicopathology of Lung Cancer Patients

Regulatory T cells (Tregs) are immunosuppressive T cells that play an important role in immune homeostasis. Multiple markers have been associated with the characterization, as well as function of Tregs. Recently, glycoprotein A repetitions predominant (GARP), a transmembrane protein containing leucine-rich repeats, has been found to be highly expressed on the surface of activated Tregs. GARP maintains Tregs' regulatory function and homeostasis through the activation and secretion of transforming growth factor β. In this study, we investigated the expression of GARP in Tregs from the peripheral blood (PB) and tumor tissues of lung cancer patients. The association between the proportion and expression level of GARP on Tregs and the clinicopathological factors of lung cancer patients was also analyzed. Results showed that in the tumor tissues of patients with lung cancer, GARP expression was increased in Tregs and was associated with lymph node metastasis, distant metastasis, and clinical stage. Furthermore, the infiltrating Tregs from early stage patients exhibited higher GARP expression than that from advanced cancer patients, which indicated that GARP might be an early prognostic biomarker. In vitro coculture studies demonstrated that human lung cancer cell lines might induce the expression of GARP in Tregs by certain mechanisms. Overall, this research demonstrated the potential value of GARP in Tregs definition and cancer immunotherapy.

Transient antibody targeting of CD45RC induces transplant tolerance and potent antigen-specific regulatory T cells

Rat and human CD4⁺ and CD8⁺ Tregs expressing low levels of CD45RC have strong immunoregulatory properties. We describe here that human CD45 isoforms are nonredundant and identify distinct subsets of cells. We show that CD45RC is not expressed by CD4⁺ and CD8⁺ Foxp3⁺ Tregs, while CD45RA/RB/RO are. Transient administration of a monoclonal antibody (mAb) targeting CD45RC in a rat cardiac allotransplantation model induced transplant tolerance associated with inhibition of allogeneic humoral responses but maintained primary and memory responses against cognate antigens. Anti-CD45RC mAb induced rapid death of CD45RC^high T cells through intrinsic cell signaling but preserved and potentiated CD4⁺ and CD8⁺ CD45RC^low/- Tregs, which are able to adoptively transfer donor-specific tolerance to grafted recipients. Anti-CD45RC treatment results in distinct transcriptional signature of CD4⁺ and CD8⁺ CD45RC^low/- Tregs. Finally, we demonstrate that anti-human CD45RC treatment inhibited graft-versus-host disease (GVHD) in immune-humanized NSG mice. Thus, short-term anti-CD45RC is a potent therapeutic candidate to induce transplantation tolerance in human.

T regulatory cell mediated immunotherapy for solid organ transplantation: A clinical perspective

T regulatory cells (Tregs) play a vital role in suppressing heightened immune responses, and thereby promote a state of immunological tolerance. Tregs modulate both innate and adaptive immunity, which make them a potential candidate for cell-based immunotherapy to suppress uncontrolled activation of graft specific inflammatory cells and their toxic mediators. These grafts specific inflammatory cells (T effector cells) and other inflammatory mediators (Immunoglobulins, active complement mediators) are mainly responsible for graft vascular deterioration followed by acute/chronic rejection. Treg mediated immunotherapy is under investigation to induce allospecific tolerance in various ongoing clinical trials in organ transplant recipients. Treg immunotherapy is showing promising results but the key issues regarding Treg immunotherapy are not yet fully resolved including their mechanism of action, and specific Treg cell phenotype responsible for a state of tolerance. This review highlights the involvement of various subsets of Tregs during immune suppression, novelty of Tregs functions, effects on angiogenesis, emerging technologies for effective Treg expansion, plasticity and safety associated with clinical applications. Altogether this information will assist in designing single/combined Treg mediated therapies for successful clinical trials in solid organ transplantations.

Garp as a therapeutic target for modulation of T regulatory cell function

INTRODUCTION

Foxp3⁺ T regulatory cells (Tregs) play critical roles in immune homeostasis primarily by suppressing many aspects of the immune response. Tregs uniquely express GARP on their cell surface and GARP functions as a delivery system for latent TGF-β. As Treg-derived TGF-β may mediate the suppressive functions of Tregs, GARP may represent a target to inhibit Treg suppression in cancer or augment suppression in autoimmunity. Areas covered: This article will focus on 1) the role of Treg-derived TGF-β in the suppressive activity of Treg, 2) the cellular and molecular regulation of expression of GARP on mouse and human Tregs, 3) the role of integrins in the activation of latent-TGF-β/GARP complex, 4) an overview of our present understanding of the function of the latent-TGF-β/GARP complex. Expert opinion: Two approaches are outlined for targeting the L-TGF-β1/GARP complex for therapeutic purposes. Tregs play a major role in suppressive effector T cell responses to tumors and TGF-β1 may be a major contributor to this process. One approach is to specifically block the production of active TGF-β1 from Tregs as an adjunct to tumor immunotherapy. The second approach in autoimmunity is to selectively enhance the production of TGF-β by Tregs at sites of chronic inflammation.