Production of Proinflammatory Cytokines by Monocytes in Liver-Transplanted Recipients with De Novo Autoimmune Hepatitis Is Enhanced and Induces TH1-like Regulatory T Cells

Immune evasion mechanisms in early-stage I high-grade serous ovarian carcinoma: insights into regulatory T cell dynamics

The mechanisms driving immune evasion in early-stage I high-grade serous ovarian carcinoma (HGSOC) remain poorly understood. To investigate this, we performed single-cell RNA-sequencing analysis. Our findings revealed a highly immunosuppressive HGSOC microenvironment, characterized by abundant infiltration of regulatory T cells (Tregs). Trajectory analysis uncovered differentiation pathways of naïve Tregs, which underwent either activation and proliferation or transcriptional instability. The predicted Treg-cell interaction network, including crosstalk within tumor cells, facilitates Treg mobility and maturation while reinforcing their immunosuppressive function and persistence in the tumor. Moreover, their interactions with immune cells likely inhibit CD8 T cells and antigen-presenting cells, supporting tumor immune escape. Additionally, more immunogenic tumor conditions, marked by IFNγ production, may contribute to Treg destabilization. Our findings underscore the pivotal role of Tregs in early immune evasion of HGSOC and provide insights into potential therapeutic strategies targeting their activity and differentiation fate.

Peripheral immune profiling highlights a dynamic role of low-density granulocytes in myasthenia gravis

BACKGROUND

Myasthenia gravis (MG) is an autoimmune neuromuscular disease marked by dysregulation of several immune cell populations. Here we explored peripheral immune landscape, particularly the role of low-density granulocytes (LDGs).

METHODS

Single-cell and bulk RNA sequencing analyzed peripheral immune cells from MG patients pre- (n = 4) and after treatment (n = 2), as well as healthy controls (n = 3). Flow cytometry was employed for validating LDG subsets, and various functional assays were conducted to assess their impact on T cell proliferation and differentiation, NET formation, and ROS production.

RESULTS

Single-cell analysis highlighted a shift towards inflammatory Th1/Th17/Tfh subsets, an intense interferon-mediated immune response, and an expansion of immature myeloid subsets in MG. Flow cytometry showed increased LDGs correlated with disease severity. Unlike myeloid-derived suppressor cells, MG LDGs do not restrict T cell proliferation but induce a pro-inflammatory Th1/Th17 response. They also display enhanced spontaneous neutrophil extracellular traps (NETs) formation and basal reactive oxygen species (ROS) production. LDGs decreased after intravenous immunoglobulin and increased after prolonged immunotherapy in minimal manifestation status (MM), with reduced pro-inflammatory activity. Bulk RNA sequencing revealed significant transcriptional differences in LDGs, especially in cell cycle and granule protein genes.

CONCLUSION

Peripheral immune profiling sheds light on the intricate role of LDGs in MG. These cells, as a distinct subtype of neutrophils with a proinflammatory phenotype, are notable increased in MG, exacerbating chronic inflammation. Furthermore, immunotherapy expanded LDGs but reduced their proinflammatory capacities. The complex interplay of LDGs in MG underscores their potential as biomarkers and therapeutic targets.

The possible anti-tumor effects of regulatory T cells plasticity / IL-35 in the tumor microenvironment of the major three cancer types

T lymphocytes are among the immunological cells that make up the tumor microenvironment (TME), and they are essential in the growth of tumors and anti-tumor reactions. Regulatory T cells (Treg cells) are a subset of CD4+ T cells in the immune system that suppress the immune system. They are distinguished by their expression of the master transcription factor forkhead box protein P3 (FOXP3). Furthermore, Treg cells are essential for maintaining immunological homeostasis, inhibiting inflammation, and maintaining self-tolerance. In a variety of malignancies within the TME, Treg cells demonstrate notable flexibility and functional diversity. Highly plastic Treg cells can change into Th-like Treg cells in specific circumstances, which allow them to secrete particular pro-inflammatory cytokines. Interleukin 35 (IL-35) is a part of the immunosuppressive cytokines that belong to the IL-12 family. Treg cells release IL-35, which was elevated in the peripheral blood and TME of numerous cancer patients, implying that IL-35 in the TME may be an intriguing target for cancer therapy. In cancer, IL-35 is a two-edged sword; it promotes tumorigenicity in cancer cells while shielding them from apoptosis. Nonetheless, other investigations have mentioned its conflicting effects on cancer prevention. Herein, we provide an updated understanding of the critical mechanisms behind the anticancer immunity mediated by Treg cells plasticity, the role of IL-35, and tactics to strengthen the immune response against malignancies, outlining major clinical trials that used Treg cells/IL-35 therapies in the three main cancer types (lung, breast, and colorectal cancers).

Serum and tissue biomarkers of plasma cell-rich rejection in liver transplant recipients

The distinction between autoimmune and alloimmune reactions in liver transplant recipients can be challenging. Plasma cell-rich rejection (PCRR), previously known as de novo autoimmune hepatitis or plasma cell hepatitis, is an atypical and underrecognized form of allograft rejection observed post-liver transplantation, often in conjunction with features of T cell-mediated and antibody-mediated rejection. If PCRR is not recognized and treated with prompt immunosuppressive augmentation, patients can develop advanced hepatic fibrosis, necroinflammation, and allograft failure. Given the significant morbidity and mortality associated with PCRR, there exists a need to develop noninvasive biomarkers which can be used in screening, diagnosis, and treatment monitoring of PCRR. This study is a literature review of candidate serum-based and tissue-based biomarkers in adult and pediatric liver transplant PCRR. We also discuss biomarkers from plasma cell-rich processes observed in other disease states and other organ transplant recipients that might be tested in liver transplant PCRR. We conclude with proposed future directions in which biomarker implementation into clinical practice could lead to advances in personalized management of PCRR.

Sphingosine-1-Phosphate Signalling Inhibition Suppresses Th1-Like Treg Generation by Reversing Mitochondrial Uncoupling

Inflammatory environments induce the generation of dysfunctional IFNγ+T-bet+FOXP3+ Th1-like Tregs, which show defective function and are found in autoimmune conditions including multiple sclerosis (MS). The pathways that control the generation of Th1-like Tregs are not well understood. Sphingosine-1-phosphate (S1P) signalling molecules are upregulated in Th1-like Tregs, and in vivo S1P inhibition with Fingolimod (FTY720) inhibits the expression of genes responsible for Treg plasticity in MS patients. However, the underlying mechanisms are unknown. Here we show that S1P signalling inhibition by FTY720 inhibits the generation of Th1-like Tregs and rescues their suppressive function. These effects are mediated by a decrease in mTORC1 signalling and reversal of the mitochondrial uncoupling that Tregs undergo during their reprogramming into Th1-like Tregs in vitro. Finally, these results are validated in in vivo-generated Th1-like Tregs, as Tregs from MS patients treated with FTY720 display decreased Th1-like Treg frequency, increased suppressive function and mitochondrial metabolism rebalance. These results highlight the involvement of mitochondrial uncoupling in Treg reprogramming and identify S1P signalling inhibition as a target to suppress the generation of dysfunctional Th1-like Tregs.

SHIP-1 regulates the differentiation and function of Tregs via inhibiting mTORC1 activity

Cell metabolism is crucial for orchestrating the differentiation and function of regulatory T cells (Tregs). However, the underlying mechanism that coordinates cell metabolism to regulate Treg activity is not completely understood. As a pivotal molecule in lipid metabolism, the role of SHIP-1 in Tregs remains unknown. In this study, we found SHIP-1 Treg KO mice (SHIP-1 specifically deleted in regulatory T cells) had severe autoimmunity with increased Tregs in the thymus and disrupted peripheral T cell homeostasis. Mechanistically, CD4Cre Ship-1flox/flox mice were found to have increased Treg precursors and SHIP-1 KO Tregs had reduced migration and stability, which caused decreased Tregs in the spleen. Additionally, the suppressive function of Tregs from SHIP-1 KO mice was diminished, along with their promotion of anti-tumor immunity. Interestingly, the PI3K-mTORC1, but not mTORC2, signaling axis was enhanced in SHIP-1 KO Tregs. In vivo treatment of SHIP-1 Treg KO mice with rapamycin rescued the abnormal Treg percentages and peripheral T cell homeostasis, as well as Treg suppressive function. Furthermore, the treatment of wild-type mice with SHIP-1 inhibitor enhanced anti-tumor activity. Our study highlights the SHIP-1-PI3K-mTORC1 axis that regulates Treg differentiation and function, and it is a potential target for cancer treatment.

The role of regulatory T cells in vitiligo and therapeutic advances: a mini-review

BACKGROUND

Regulatory T cells (Tregs) play vital roles in controlling immune reactions and maintaining immune tolerance in the body. The targeted destruction of epidermal melanocytes by activated CD8+T cells is a key event in the development of vitiligo. However, Tregs may exert immunosuppressive effects on CD8+T cells, which could be beneficial in treating vitiligo.

METHODS

A comprehensive search of PubMed and Web of Science was conducted to gather information on Tregs and vitiligo.

RESULTS

In vitiligo, there is a decrease in Treg numbers and impaired Treg functions, along with potential damage to Treg-related signaling pathways. Increasing Treg numbers and enhancing Treg function could lead to immunosuppressive effects on CD8+T cells. Recent research progress on Tregs in vitiligo has been summarized, highlighting various Treg-related therapies being investigated for clinical use. The current status of Treg-related therapeutic strategies and potential future directions for vitiligo treatment are also discussed.

CONCLUSIONS

A deeper understanding of Tregs will be crucial for advancing Treg-related drug discovery and treatment development in vitiligo.

Fragile Treg cells: Traitors in immune homeostasis?

Regulatory T (Treg) cells play a key role in maintaining immune tolerance and tissue homeostasis. However, in some disease microenvironments, Treg cells exhibit fragility, which manifests as preserved FoxP3 expression accompanied by inflammation and loss of immunosuppression. Fragile Treg cells are formatively, phenotypically and functionally diverse in various diseases, further complicating the role of Treg cells in the immunotherapeutic response and offering novel targets for disease treatment by modulating specific Treg subsets. In this review, we summarize findings on fragile Treg cells to provide a framework for characterizing the formation and role of fragile Treg cells in different diseases, and we discuss how this information may guide the development of more specific Treg-targeted immunotherapies.

B and T cells: (Still) the dominant orchestrators in autoimmune hepatitis

Autoimmune hepatitis (AIH) is a severe hepatopathy characterized by hypergammaglobulinemia, presence of serum autoantibodies and histological appearance of interface hepatitis. Liver damage in AIH is initiated by the presentation of a liver autoantigen to uncommitted Th0 lymphocytes, followed by a cascade of effector immune responses culminating with the production of inflammatory cytokines, activation of cytotoxic cells and subsequent hepatocyte injury. B cells actively participate in AIH liver damage by presenting autoantigens to uncommitted T lymphocytes. B cells also undergo maturation into plasma cells that are responsible for production of immunoglobulin G and autoantibodies, which mediate antibody dependent cell cytotoxicity. Perpetuation of effector immunity with consequent progression of liver damage is permitted by impairment in regulatory T cells (Tregs), a lymphocyte subset central to the maintenance of immune homeostasis. Treg impairment in AIH is multifactorial, deriving from numerical decrease, reduced suppressive function, poor response to IL-2 and less stable phenotype. In this review, we discuss the role of B and T lymphocytes in the pathogenesis of AIH. Immunotherapeutic strategies that could limit inflammation and halt disease progression while reconstituting tolerance to liver autoantigens are also reviewed and discussed.

Pathogenic role of different phenotypes of immune cells in airway allergic diseases: a study based on Mendelian randomization

Background

Airway allergic disease (AAD) is a class of autoimmune diseases with predominantly Th2-type inflammation, mainly including allergic rhinitis (AR), allergic asthma (AS), and chronic sinusitis (CRS). There are very complex regulatory mechanisms between immune cells and AAD; however, previous reports found that the functions of the same immune cells in AAD are not identical.

Objective

The aim of this study was to explore the causal relationship between different phenotypic immune cells and their association with AAD.

Method

Utilizing the publicly available Genome-Wide Association Studies (GWAS) database, this study conducted a bidirectional Mendelian randomization (MR) to assess the causal relationship between immune cells of 731 different immunophenotypes and AAD. The primary assessment methods included inverse variance weighting, weighted median, and MR Egger. Additionally, sensitivity analyses such as MR-PRESSO, leave-one-out, and scatter plots were employed to eliminate the interference of heterogeneity and pleiotropy, ensuring the stability of the causal inference.

Result

A total of 38 immune cells with different immunophenotypes were found to be positively and causally associated with AR, of which 26 were protective factors and 12 were risk factors. Positive associations were found between 33 immune cells and AS, of which 14 were protective factors and 19 were risk factors, as well as between 39 immune cells and CRS, of which 22 were protective factors and 17 were risk factors. Finally, the results of all relevant immune cells for the three diseases were taken and intersected, and it was found that CD3 on CD39+-activated Treg (IVWAR = 0.001, IVWCRS = 0.043, IVWAS = 0.027) may be the key immune cell that inhibits the development of AAD (ORAR = 0.940, ORAS = 0.967, ORCRS = 0.976).

Conclusion

This study reveals that different immune phenotypes of immune cells are closely related to AAD at the genetic level, which provides a theoretical basis for future clinical studies.

Harnessing innate immune pathways for therapeutic advancement in cancer

The innate immune pathway is receiving increasing attention in cancer therapy. This pathway is ubiquitous across various cell types, not only in innate immune cells but also in adaptive immune cells, tumor cells, and stromal cells. Agonists targeting the innate immune pathway have shown profound changes in the tumor microenvironment (TME) and improved tumor prognosis in preclinical studies. However, to date, the clinical success of drugs targeting the innate immune pathway remains limited. Interestingly, recent studies have shown that activation of the innate immune pathway can paradoxically promote tumor progression. The uncertainty surrounding the therapeutic effectiveness of targeted drugs for the innate immune pathway is a critical issue that needs immediate investigation. In this review, we observe that the role of the innate immune pathway demonstrates heterogeneity, linked to the tumor development stage, pathway status, and specific cell types. We propose that within the TME, the innate immune pathway exhibits multidimensional diversity. This diversity is fundamentally rooted in cellular heterogeneity and is manifested as a variety of signaling networks. The pro-tumor effect of innate immune pathway activation essentially reflects the suppression of classical pathways and the activation of potential pro-tumor alternative pathways. Refining our understanding of the tumor's innate immune pathway network and employing appropriate targeting strategies can enhance our ability to harness the anti-tumor potential of the innate immune pathway and ultimately bridge the gap from preclinical to clinical application.

Immunological Landscape of Retinal Ischemia-Reperfusion Injury: Insights into Resident and Peripheral Immune Cell Responses

Retinal ischemia-reperfusion injury (RIRI) is a complex condition characterized by immune cell-mediated inflammation and consequent neuronal damage. This review delves into the immune response mechanisms in RIRI, particularly emphasizing the roles played by resident and peripheral immune cells. It highlights the pivotal role of microglia, the primary resident immune cells, in exacerbating neuroinflammation and neuronal damage through their activation and subsequent release of pro-inflammatory mediators. Additionally, the review explores the contributions of other glial cell types, such as astrocytes and Müller cells, in modulating the immune response within the retinal environment. The dual role of the complement system in RIRI is also examined, revealing its complex functions in both safeguarding and impairing retinal health. Inflammasomes, triggered by various danger signals, are discussed as crucial contributors to the inflammatory pathways in RIRI, with an emphasis on the involvement of different NOD-like receptor family proteins. The review further analyzes the infiltration and impact of peripheral immune cells like neutrophils, macrophages, and T cells, which migrate to the retina following ischemic injury. Critical to this discussion is the interplay between resident and peripheral immune cells and its implications for RIRI pathophysiology. Finally, the review outlines future research directions, focusing on basic research and the potential for clinical translation to enhance understanding and treatment of RIRI.

Non-fatal outcomes of COVID-19 disease in pediatric organ transplantation associates with down-regulation of senescence pathways

This is a cross-sectional study examining kinetics and durability of immune response in children with solid organ transplants (SOTs) who had COVID-19 disease between November 2020 through June 2022, who were followed for 60-days at a single transplant center. Blood was collected between 1-14 (acute infection), and 15-60 days of a positive PCR (convalescence). SOT children with peripheral blood mononuclear cells (PBMC) cryopreserved before 2019 were non-infected controls (ctrls). PBMCs stimulated with 15-mer peptides from spike protein and anti-CD49d/anti-CD28. Testing done included mass cytometry, mi-RNA sequencing with confirmatory qPCR. 38 children formed the study cohort, 10 in the acute phase and 8 in the convalescence phase. 20 subjects were non-infected controls. Two subjects had severe disease. Subjects in the acute and convalescent phases were different subjects. The median age and tacrolimus level at blood draw was not significantly different. There was no death, and no subject was lost to follow-up. During acute infection CD57 expression was low in NKT, Th17 effector memory, memory Treg, CD4-CD8-, and γδT cells (p = 0.01, p = 0.04, p = 0.03, p = 0.03, p = 0.004 respectively). The frequencies of NK and Th2 effector memory cells increased (p = 0.01, p = 0.02) during acute infection. Non-switched memory B and CD8 central memory cell frequencies were decreased during acute infection (p = 0.02; p = 0.02), but the decrease in CD8 central memory cells did not persist. CD4-CD8- and CD14 monocyte frequencies increased during recovery (p = 0.03; p = 0.007). Our observations suggest down regulation of CD57 with absence of NK cell contraction protect against death from COVID-19 disease in children with SOTs.

Harnessing the innate immune system by revolutionizing macrophage-mediated cancer immunotherapy

Immunotherapy is a promising and safer alternative to conventional cancer therapies. It involves adaptive T-cell therapy, cancer vaccines, monoclonal antibodies, immune checkpoint blockade (ICB), and chimeric antigen receptor (CAR) based therapies. However, most of these modalities encounter restrictions in solid tumours owing to a dense, highly hypoxic and immune-suppressive microenvironment as well as the heterogeneity of tumour antigens. The elevated intra-tumoural pressure and mutational rates within fastgrowing solid tumours present challenges in efficient drug targeting and delivery. The tumour microenvironment is a dynamic niche infiltrated by a variety of immune cells, most of which are macrophages. Since they form a part of the innate immune system, targeting macrophages has become a plausible immunotherapeutic approach. In this review, we discuss several versatile approaches (both at pre-clinical and clinical stages) such as the direct killing of tumour-associated macrophages, reprogramming pro-tumour macrophages to anti-tumour phenotypes, inhibition of macrophage recruitment into the tumour microenvironment, novel CAR macrophages, and genetically engineered macrophages that have been devised thus far. These strategies comprise a strong and adaptable macrophage-toolkit in the ongoing fight against cancer and by understanding their significance, we may unlock the full potential of these immune cells in cancer therapy.

Treg plasticity and human diseases

INTRODUCTION

As a subset of CD4+ T cells, regulatory T cells (Tregs) with the characteristic expression of transcription factor FOXP3 play a key role in maintaining self-tolerance and regulating immune responses. However, in some inflammatory circumstances, Tregs can express cytokines of other T help (Th) cells by internal reprogramming, which is called Treg plasticity. These reprogrammed Tregs with impaired suppressive ability contribute to the progression of diseases by secreting pro-inflammatory cytokines. However, in the tumor microenvironment (TME), such changes in phenotype rarely occur in Tregs, on the contrary, Tregs usually display a stronger suppressive function and inhibit anti-tumor immunity. It is important to understand the mechanisms of Treg plasticity in inflammatory diseases and cancers.

OBJECTIVES

In this review, we summarize the characteristics of different Th-like Tregs and discuss the potential mechanisms of these changes in phenotype. Furthermore, we summarize the Treg plasticity in human diseases and discuss the effects of these changes in phenotype on disease progression, as well as the potential application of drugs or reagents that regulate Treg plasticity in human diseases.

CONCLUSIONS

Treg plasticity is associated with inflammatory diseases and cancers. Regulating Treg plasticity is a promising direction for the treatment of inflammatory diseases and cancers.

CD226 maintains regulatory T cell phenotype stability and metabolism by the mTOR/Myc pathway under inflammatory conditions

Regulatory T (Treg) cells exhibit immunosuppressive phenotypes and particular metabolic patterns with certain degrees of plasticity. Previous studies of the effects of the co-stimulatory molecule CD226 on Treg cells are controversial. Here, we show that CD226 primarily maintains the Treg cell stability and metabolism phenotype under inflammatory conditions. Conditional deletion of CD226 within Foxp3+ cells exacerbates symptoms in murine graft versus host disease models. Treg cell-specific deletion of CD226 increases the Treg cell percentage in immune organs but weakens their immunosuppressive function with a T helper 1-like phenotype conversion under inflammation. CD226-deficient Treg cells exhibit reduced oxidative phosphorylation and increased glycolysis rates, which are regulated by the adenosine 5'-monophosphate-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR)/myelocytomatosis oncogene (Myc) pathway, and inhibition of Myc signaling restores the impaired functions of CD226-deficient Treg cells in an inflammatory disease model of colitis. This study reveals an Myc-mediated CD226 regulation of Treg cell phenotypic stability and metabolism, providing potential therapeutic strategies for targeted interventions of Treg cell-specific CD226 in inflammatory diseases.

The role of inflammation in autoimmune disease: a therapeutic target

Autoimmune diseases (AIDs) are immune disorders whose incidence and prevalence are increasing year by year. AIDs are produced by the immune system's misidentification of self-antigens, seemingly caused by excessive immune function, but in fact they are the result of reduced accuracy due to the decline in immune system function, which cannot clearly identify foreign invaders and self-antigens, thus issuing false attacks, and eventually leading to disease. The occurrence of AIDs is often accompanied by the emergence of inflammation, and inflammatory mediators (inflammatory factors, inflammasomes) play an important role in the pathogenesis of AIDs, which mediate the immune process by affecting innate cells (such as macrophages) and adaptive cells (such as T and B cells), and ultimately promote the occurrence of autoimmune responses, so targeting inflammatory mediators/pathways is one of emerging the treatment strategies of AIDs. This review will briefly describe the role of inflammation in the pathogenesis of different AIDs, and give a rough introduction to inhibitors targeting inflammatory factors, hoping to have reference significance for subsequent treatment options for AIDs.

IFN-γ: An overlooked cytokine in dermatomyositis with anti-MDA5 antibodies

Dermatomyositis with anti-melanoma differentiation-associated gene 5 antibody (anti-MDA5 DM) is a rare autoimmune disease, often complicated by life-threatening, rapidly progressive interstitial lung disease. Additional manifestations of the disease include skin lesions, vascular abnormalities, joints and muscles pain. Despite its clinical significance, the pathogenesis of anti-MDA5 DM remains largely unknown. Currently, the disease is perceived as driven by type I interferon (IFN) whose expression is increased in most of the patients. Importantly, the regulation of IFN-γ is also altered in anti-MDA5 DM as evidenced by the presence of IFN-γ positive histiocytes in the lungs of patients, and the identification of autoantibodies that directly stimulate the production of IFN-γ by mononuclear cells. This review critically examines the pathogenesis of the disease, shedding light on recent findings that emphasize a potential role of IFN-γ. A novel conceptual framework is proposed, which integrates the molecular mechanisms altering IFN-γ regulation in anti-MDA5 DM with the known functional effects of IFN-γ on key tissues affected during the disease, such as the lungs, skin, and vessels. Understanding the precise role and relevance of IFN-γ in the pathogenesis of the disease will not only enhance the selection of available therapies for anti-MDA5 DM patients but also pave the way for the development of new therapeutic approaches targeting the altered molecular pathways.

A genetic method specifically delineates Th1-type Treg cells and their roles in tumor immunity

Regulatory T (Treg) cells expressing the transcription factor (TF) Foxp3 also express other TFs shared by T helper (Th) subsets under certain conditions. Here, to determine the roles of T-bet-expressing Treg cells, we generate a mouse strain, called VeDTR, in which T-bet/Foxp3 double-positive cells are engineered to be specifically labeled and depleted by a combination of Cre- and Flp-recombinase-dependent gene expression control. Characterization of T-bet⁺Foxp3⁺ cells using VeDTR mice reveals high resistance under oxidative stress, which is involved in accumulation of T-bet⁺Foxp3⁺ cells in tumor tissues. Moreover, short-term depletion of T-bet⁺Foxp3⁺ cells leads to anti-tumor immunity but not autoimmunity, whereas that of whole Treg cells does both. Although ablation of T-bet⁺Foxp3⁺ cells during Toxoplasma infection slightly enhances Th1 immune responses, it does not affect the course of the infection. Collectively, the intersectional genetic method reveals the specific roles of T-bet⁺Foxp3⁺ cells in suppressing tumor immunity.

T cells in health and disease

T cells are crucial for immune functions to maintain health and prevent disease. T cell development occurs in a stepwise process in the thymus and mainly generates CD4+ and CD8+ T cell subsets. Upon antigen stimulation, naïve T cells differentiate into CD4+ helper and CD8+ cytotoxic effector and memory cells, mediating direct killing, diverse immune regulatory function, and long-term protection. In response to acute and chronic infections and tumors, T cells adopt distinct differentiation trajectories and develop into a range of heterogeneous populations with various phenotype, differentiation potential, and functionality under precise and elaborate regulations of transcriptional and epigenetic programs. Abnormal T-cell immunity can initiate and promote the pathogenesis of autoimmune diseases. In this review, we summarize the current understanding of T cell development, CD4+ and CD8+ T cell classification, and differentiation in physiological settings. We further elaborate the heterogeneity, differentiation, functionality, and regulation network of CD4+ and CD8+ T cells in infectious disease, chronic infection and tumor, and autoimmune disease, highlighting the exhausted CD8+ T cell differentiation trajectory, CD4+ T cell helper function, T cell contributions to immunotherapy and autoimmune pathogenesis. We also discuss the development and function of γδ T cells in tissue surveillance, infection, and tumor immunity. Finally, we summarized current T-cell-based immunotherapies in both cancer and autoimmune diseases, with an emphasis on their clinical applications. A better understanding of T cell immunity provides insight into developing novel prophylactic and therapeutic strategies in human diseases.

T-cell infiltrate intensity is associated with delayed response to treatment in late acute cellular rejection in pediatric liver transplant recipients

BACKGROUND

Late acute cellular rejection (ACR) is associated with donor-specific antibodies (DSA) development, chronic rejection, and allograft loss. However, accurate predictors of late ACR treatment response are lacking. ACR is primarily T-cell mediated, yet B cells and plasma cells (PC) also infiltrate the portal areas during late ACR. To test the hypothesis that the inflammatory milieu is associated with delayed response (DR) to rejection therapy, we performed a single-center retrospective case-control study of pediatric late liver ACR using multiparameter immunofluorescence for CD4, CD8, CD68, CD20, and CD138 to identify immune cell subpopulations.

METHODS

Pediatric liver transplant recipients transplanted at <17 years of age and treated for biopsy-proven late ACR between January 2014 and 2019 were stratified into rapid response (RR) and DR based on alanine aminotransferase (ALT) normalization within 30 days of diagnosis. All patients received IV methylprednisolone as an initial rejection treatment. Immunofluorescence was performed on archived formalin-fixed paraffin embedded (FFPE) liver biopsy tissue.

RESULTS

Liver biopsies from 60 episodes of late ACR in 54 patients were included in the analysis, of which 33 were DR (55%). Anti-thymocyte globulin was only required in the DR group. The frequency of liver-infiltrating CD20+ and CD8+ lymphocytes and the prevalence of autoantibodies were higher in the DR group. In univariate logistic regression analysis, serum gamma-glutamyl transpeptidase (GGT) level at diagnosis, but not ALT, Banff score or presence of DSA, predicted DR.

CONCLUSIONS

Higher serum GGT level, presence of autoantibodies, and increased CD8+ T-cell infiltration portends DR in late ACR treatment in children.

HERV1-env Induces Unfolded Protein Response Activation in Autoimmune Liver Disease: A Potential Mechanism for Regulatory T Cell Dysfunction

Regulatory T cells (Tregs) are not terminally differentiated but can acquire effector properties. Here we report an increased expression of human endogenous retrovirus 1 (HERV1-env) proteins in Tregs of patients with de novo autoimmune hepatitis and autoimmune hepatitis, which induces endoplasmic reticulum (ER) stress. HERV1-env-triggered ER stress activates all three branches (IRE1, ATF6, and PERK) of the unfolded protein response (UPR). Our coimmunoprecipitation studies show an interaction between HERV1-env proteins and the ATF6 branch of the UPR. The activated form of ATF6α activates the expression of RORC and STAT3 by binding to promoter sequences and induces IL-17A production. Silencing of HERV1-env results in recovery of Treg suppressive function. These findings identify ER stress and UPR activation as key factors driving Treg plasticity (species: human).

Regulatory T-cell stability and functional plasticity in health and disease

FOXP3-expressing regulatory T cells (T_reg ) are indispensable for immune homeostasis and tolerance, and in addition tissue-resident T_reg have been found to perform noncanonical, tissue-specific functions. For optimal tolerogenic function during inflammatory disease, T_reg are equipped with mechanisms that assure lineage stability. T_reg lineage stability is closely linked to the installation and maintenance of a lineage-specific epigenetic landscape, specifically a T_reg -specific DNA demethylation pattern. At the same time, for local and directed immune regulation T_reg must possess a level of functional plasticity that requires them to partially acquire T helper cell (T_H ) transcriptional programs-then referred to as T_H -like T_reg . Unleashing T_H programs in T_reg , however, is not without risk and may threaten the epigenetic stability of T_reg with consequently pathogenic ex-T_reg contributing to (auto-) inflammatory conditions. Here, we review how the T_reg -stabilizing epigenetic landscape is installed and maintained, and further discuss the development, necessity and lineage instability risks of T_H 1-, T_H 2-, T_H 17-like T_reg and follicular T_reg .

Challenges and opportunities in achieving effective regulatory T cell therapy in autoimmune liver disease

Autoimmune liver diseases (AILD) include autoimmune hepatitis (AIH), primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC). These immune-mediated liver diseases involve a break down in peripheral self-tolerance with largely unknown aetiology. Regulatory T cells (Treg) are crucial in maintaining immunological tolerance. Hence, Treg immunotherapy is an attractive therapeutic option in AILD. Currently, AILD do not have a curative treatment option and patients take life-long immunosuppression or bile acids to control hepatic or biliary inflammation. Clinical investigations using good manufacturing practice (GMP) Treg in autoimmune liver disease have thus far demonstrated that Treg therapy is safe and that Treg migrate to inflamed liver tissue. For Treg immunotherapy to achieve efficacy in AILD, Treg must be retained within the liver and maintain their suppressive phenotype to dampen ongoing immune responses to hepatocytes and biliary epithelium. Therefore, therapeutic Treg subsets should be selected for tissue residency markers and maximal functionality. Optimisation of dosing regime and understanding longevity of Treg in vivo are critical to successful Treg therapy. It is also essential to consider combination therapy options to complement infused Treg, for instance low-dose interleukin-2 (IL-2) to support pre-existing and infused Treg survival and suppressive function. Understanding the hepatic microenvironment in both early- and late-stage AILD presents significant opportunity to better tailor Treg therapy in different patient groups. Modification of a hostile microenvironment to a more favourable one either prior to or during Treg therapy could enhance the efficacy and longevity of infused GMP-Treg. Applying recent technology to discovery of autoantigen responses in AILD, T cell receptor (TCR) sequencing and use of chimeric antigen receptor (CAR) technology represents the next frontier for disease-specific CAR-Treg therapies. Consideration of all these aspects in future trials and discovery research would position GMP Treg immunotherapy as a viable personalised-medicine treatment option for effective control of autoimmune liver diseases.

T-cell Immunometabolism: Therapeutic Implications in Organ Transplantation

Although solid-organ transplantation has evolved steadily with many breakthroughs in the past 110 y, many problems remain to be addressed, and advanced therapeutic strategies need to be considered. T-cell immunometabolism is a rapidly advancing field that has gathered much attention recently, providing ample mechanistic insight from which many novel therapeutic approaches have been developed. Applications from the field include antitumor and antimicrobial therapies, as well as for reversing graft-versus-host disease and autoimmune diseases. However, the immunometabolism of T cells remains underexplored in solid-organ transplantation. In this review, we will highlight key findings from hallmark studies centered around various metabolic modes preferred by different T-cell subtypes (categorized into naive, effector, regulatory, and memory T cells), including glycolysis, glutaminolysis, oxidative phosphorylation, fatty acid synthesis, and oxidation. This review will discuss the underlying cellular signaling components that affect these processes, including the transcription factors myelocytomatosis oncogene, hypoxia-inducible factor 1-alpha, estrogen-related receptor alpha, and sterol regulatory element-binding proteins, along with the mechanistic target of rapamycin and adenosine monophosphate-activated protein kinase signaling. We will also explore potential therapeutic strategies targeting these pathways, as applied to the potential for tolerance induction in solid-organ transplantation.

Dysfunctional Immune Regulation in Autoimmune Hepatitis: From Pathogenesis to Novel Therapies

Autoimmune hepatitis (AIH) is a chronic inflammatory disorder characterized by hypergammaglobulinemia, presence of serum autoantibodies and histological features of interface hepatitis. AIH therapeutic management still relies on the administration of corticosteroids, azathioprine and other immunosuppressants like calcineurin inhibitors and mycophenolate mofetil. Withdrawal of immunosuppression often results in disease relapse, and, in some cases, therapy is ineffective or associated with serious side effects. Understanding the mechanisms underlying AIH pathogenesis is therefore of paramount importance to develop more effective and well tolerated agents capable of restoring immunotolerance to liver autoantigens. Imbalance between effector and regulatory cells permits liver damage perpetuation and progression in AIH. Impaired expression and regulation of CD39, an ectoenzyme key to immunotolerance maintenance, have been reported in Tregs and effector Th17-cells derived from AIH patients. Interference with these altered immunoregulatory pathways may open new therapeutic avenues that, in addition to limiting aberrant inflammatory responses, would also reconstitute immune homeostasis. In this review, we highlight the most recent findings in AIH immunopathogenesis and discuss how these could inform and direct the development of novel therapeutic tools.

Regulatory T Cells in Autoimmunity and Cancer: A Duplicitous Lifestyle

Regulatory T (Treg) cells, possess a strategic role in the maintenance of immune homeostasis, and their function has been closely linked to development of diverse pathologies including autoimmunity and cancer. Comprehensive studies in various disease contexts revealed an increased plasticity as a characteristic of Treg cells. Although Treg cell plasticity comes in various flavors, the major categories enclose the loss of Foxp3 expression, which is the master regulator of Treg cell lineage, giving rise to “ex-Treg” cells and the “fragile” Treg cells in which FOXP3 expression is retained but accompanied by the engagement of an inflammatory program and attenuation of the suppressive activity. Treg cell plasticity possess a tremendous therapeutic potential either by inducing Treg cell de-stabilization to promote anti-tumor immunity, or re-enforcing Treg cell stability to attenuate chronic inflammation. Herein, we review the literature on the Treg cell plasticity with lessons learned in autoimmunity and cancer and discuss challenges and open questions with potential therapeutic implications.

Regulatory T Cells and Inflammatory Mediators in Autoimmune Disease

Regulatory T cells (Tregs) play a critical role in regulating tissue inflammation. Reduced Treg numbers and/or suppressive function contribute to autoimmune disease. Tregs can adopt the transcriptional programming of T helper (Th) type-1/2/17 cells to optimally suppress these subsets. Under specific conditions, these Th-like Tregs lose suppressive capacity and release proinflammatory cytokines to promote inflammation. This Treg plasticity depends on inflammatory mediators in the local environment. In this study, we review how cytokines impact Treg function and may contribute to autoimmune disease. A comprehensive understanding of Th-like Tregs may elucidate novel and more focused therapeutic approaches.

Regulatory T cells in autoimmune hepatitis: an updated overview

Regulatory T-cells (Tregs) are key players in the maintenance of immune homeostasis by preventing immune responses to self-antigens. Defects in Treg frequency and/or function result in overwhelming CD4 and CD8 T cell immune responses participating in the autoimmune attack. Perpetuation of autoimmune damage is also favored by Treg predisposition to acquire effector cell features upon exposure to a proinflammatory challenge. Treg impairment plays a permissive role in the initiation and perpetuation of autoimmune liver diseases, namely autoimmune hepatitis, primary biliary cholangitis and primary sclerosing cholangitis. In this Review, we outline studies reporting the role of Treg impairment in the pathogenesis of these conditions and discuss methods to restore Treg number and function either by generation/expansion in the test tube or through in vivo expansion upon administration of low dose IL-2. Challenges and caveats of these potential therapeutic strategies are also reviewed and discussed.

Regulatory T cell heterogeneity and therapy in autoimmune diseases

Regulatory T (Treg) cells are a group of CD4⁺ T cell with high expression of CD25 and cell linage specific transcription factor forkhead box P3 (Foxp3) and play a vital role in maintaining immune homeostasis. In the last two decades, researchers have shown that Treg cells involved in the occurrence, development and prognosis of many diseases, especially in autoimmune diseases. Treg targeted therapies, such as low-dose interleukin-2 (IL-2) treatment and Treg infusion therapy, which are aimed at restoring the number or function of Treg cells, have become a hot topic in clinical trials of these diseases. It is believed that Treg cells are heterogeneous. Different subsets of Treg cells have various functions and play different parts in immunomodulatory. Gaining insights into Treg heterogeneity will help us further understand the function of Treg cells and provide news ideas for the selective therapeutic manipulation of Treg cells. In this review, we mainly summarize the heterogeneity of Treg cells and their potential therapeutic value in autoimmune diseases.

Monocyte Transmodulation: The Next Novel Therapeutic Approach in Overcoming Ischemic Stroke?

The immune response following neuroinflammation is a vital element of ischemic stroke pathophysiology. After the onset of ischemic stroke, a specialized vasculature system that effectively protects central nervous system tissues from the invasion of blood cells and other macromolecules is broken down within minutes, thereby triggering the inflammation cascade, including the infiltration of peripheral blood leukocytes. In this series of processes, blood-derived monocytes have a significant effect on the outcome of ischemic stroke through neuroinflammatory responses. As neuroinflammation is a necessary and pivotal component of the reparative process after ischemic stroke, understanding the role of infiltrating monocytes in the modulation of inflammatory responses may offer a great opportunity to explore new therapies for ischemic stroke. In this review, we discuss and highlight the function and involvement of monocytes in the brain after ischemic injury, as well as their impact on tissue damage and repair.

Regulating the regulators: Is introduction of an antigen-specific approach in regulatory T cells the next step to treat autoimmunity?

In autoimmunity, the important and fragile balance between immunity and tolerance is disturbed, resulting in abnormal immune responses to the body's own tissues and cells. CD4⁺CD25^hiFoxP3⁺ regulatory T cells (Tregs) induce peripheral tolerance in vivo by means of direct cell-cell contact and release of soluble factors, or indirectly through antigen-presenting cells (APC), thereby controlling auto-reactive effector T cells. Based on these unique capacities of Tregs, preclinical studies delivered proof-of-principle for the clinical use of Tregs for the treatment of autoimmune diseases. To date, the first clinical trials using ex vivo expanded polyclonal Tregs have been completed. These pioneering studies demonstrate the feasibility of generating large numbers of polyclonal Tregs in a good manufacturing practices (GMP)-compliant manner, and that infusion of Tregs is well tolerated by patients with no evidence of general immunosuppression. Nonetheless, only modest clinical results were observed, arguing that a more antigen-specific approach might be needed to foster a durable patient-specific clinical cell therapy without the risk for general immunosuppression. In this review, we discuss current knowledge, applications and future goals of adoptive immune-modulatory Treg therapy for the treatment of autoimmune disease and transplant rejection. We describe the key advances and prospects of the potential use of T cell receptor (TCR)- and chimeric antigen receptor (CAR)-engineered Tregs in future clinical applications. These approaches could deliver the long-awaited breakthrough in stopping undesired autoimmune responses and transplant rejections.

Regulatory T Cell Plasticity and Stability and Autoimmune Diseases

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

Regulatory T cells in tumor microenvironment: new mechanisms, potential therapeutic strategies and future prospects

Regulatory T cells (Tregs) characterized by the expression of the master transcription factor forkhead box protein p3 (Foxp3) suppress anticancer immunity, thereby hindering protective immunosurveillance of tumours and hampering effective antitumour immune responses in tumour-bearing hosts, constitute a current research hotspot in the field. However, Tregs are also essential for the maintenance of the immune tolerance of the body and share many molecular signalling pathways with conventional T cells, including cytotoxic T cells, the primary mediators of tumour immunity. Hence, the inability to specifically target and neutralize Tregs in the tumour microenvironment without globally compromising self-tolerance poses a significant challenge. Here, we review recent advances in characterizing tumour-infiltrating Tregs with a focus on the functional roles of costimulatory and inhibitory receptors in Tregs, evaluate their potential as clinical targets, and systematically summarize their roles in potential treatment strategies. Also, we propose modalities to integrate our increasing knowledge on Tregs phenotype and function for the rational design of checkpoint inhibitor-based combination therapies. Finally, we propose possible treatment strategies that can be used to develop Treg-targeted therapies.

Modulation of regulatory T cell function and stability by co-inhibitory receptors

Regulatory T (T_reg) cells constitute a dynamic population that is essential for controlling immune responses in health and disease. Defects in T_reg cell function and decreases in T_reg cell numbers have been observed in patients with autoimmunity and the opposite effects on T_reg cells occur in cancer settings. Current research on new therapies for these diseases is focused on modulating T_reg cell function to increase or decrease suppressive activity in autoimmunity and cancer, respectively. In this regard, several co-inhibitory receptors that are preferentially expressed by T_reg cells under homeostatic conditions have recently been shown to control T_reg cell function and stability in different disease settings. These receptors could be amenable to therapeutic targeting aimed at modulating T_reg cell function and plasticity. This Review summarizes recent data regarding the role of co-inhibitory molecules in the control of T_reg cell function and stability, with a focus on their roles and potential therapeutic use in autoimmunity and cancer.

The Impact of Dietary Components on Regulatory T Cells and Disease

The rise in the prevalence of autoimmune diseases in developed societies has been associated with a change in lifestyle patterns. Among other factors, increased consumption of certain dietary components, such as table salt and fatty acids and excessive caloric intake has been associated with defective immunological tolerance. Dietary nutrients have shown to modulate the immune response by a direct effect on the function of immune cells or, indirectly, by acting on the microbiome of the gastrointestinal tract. FOXP3⁺ regulatory T cells (Tregs) suppress immune responses and are critical for maintaining peripheral tolerance and immune homeostasis, modulating chronic tissue inflammation and autoimmune disease. It is now well-recognized that Tregs show certain degree of plasticity and can gain effector functions to adapt their regulatory function to different physiological situations during an immune response. However, plasticity of Tregs might also result in conversion into effector T cells that may contribute to autoimmune pathogenesis. Yet, which environmental cues regulate Treg plasticity and function is currently poorly understood, but it is of significant importance for therapeutic purposes. Here we review the current understanding on the effect of certain dietary nutrients that characterize Western diets in Treg metabolism, stability, and function. Moreover, we will discuss the role of Tregs linking diet and autoimmunity and the potential of dietary-based interventions to modulate Treg function in disease.

Treg cells in health and autoimmune diseases: New insights from single cell analysis

Autoimmune diseases, such as Systemic Lupus Erythematosus (SLE) or Rheumatoid Arthritis (RA) are characterized by the breakdown of immunological tolerance. Defects of regulatory T cells have been described among the various mechanisms, that are important for the development of autoimmune diseases, due to their critical role as regulators of peripheral immune tolerance and homeostasis. Initially T suppressor cells have been described as one population of peripheral T cells. Based on new technological advances a new understanding of the heterogeneity of different Treg cell populations in the lymphoid and non-lymphoid tissue has evolved over the last years. While initially Foxp3 has been defined as the main master regulator of Treg cells, we have learned that Treg cells from various tissue can be identified by a specific transcriptomic and epigenetic signature. Epigenetic mechanisms allow Treg cell stability, but we have also learned that certain Treg subsets are plastic and can under specific circumstances even enhance autoimmunity and inflammatory processes. Quantitative and functional defects of Treg cells have been observed in a variety of autoimmune diseases. Due to our understanding of the nature of this cell population, Treg cells have been a target of new Treg based therapies, such as low-dose IL-2. In addition, ongoing clinical trials aim to test safety and efficacy of transferred, in vitro expanded Treg cells in patients with autoimmune diseases and transplant patients.

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

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

Tbet Expression in Regulatory T Cells Is Required to Initiate Th1-Mediated Colitis

In normal conditions gut homeostasis is maintained by the suppressive activity of regulatory T cells (Tregs), characterized by the expression of the transcription factor FoxP3. In human inflammatory bowel disease, which is believed to be the consequence of the loss of tolerance toward antigens normally contained in the gut lumen, Tregs have been found to be increased and functionally active, thus pointing against their possible role in the pathogenesis of this immune-mediated disease. Though, in inflammatory conditions, Tregs have been shown to upregulate the T helper (Th) type 1-related transcription factor Tbet and to express the pro-inflammatory cytokine IFNγ, thus suggesting that at a certain point of the inflammatory process, Tregs might contribute to inflammation rather than suppress it. Starting from the observation that Tregs isolated from the lamina propria of active but not inactive IBD patients or uninflamed controls express Tbet and IFNγ, we investigated the functional role of Th1-like Tregs in the dextran sulfate model of colitis. As observed in human IBD, Th1-like Tregs were upregulated in the inflamed lamina propria of treated mice and the expression of Tbet and IFNγ in Tregs preceded the accumulation of conventional Th1 cells. By using a Treg-specific Tbet conditional knockout, we demonstrated that Tbet expression in Tregs is required for the development of colitis. Indeed, Tbet knockout mice developed milder colitis and showed an impaired Th1 immune response. In these mice not only the Tbet deficient Tregs but also the Tbet proficient conventional T cells showed reduced IFNγ expression. However, Tbet deficiency did not affect the Tregs suppressive capacity in vitro and in vivo in the adoptive transfer model of colitis. In conclusion here we show that Tbet expression by Tregs sustains the early phase of the Th1-mediated inflammatory response in the gut.

Treg cells in autoimmunity: from identification to Treg-based therapies

Regulatory (Treg) cells are key regulators of inflammation and important for immune tolerance and homeostasis. A major progress has been made in the identification and classification of Treg cells. Due to technological advances, we have gained deep insights in the epigenetic regulation of Treg cells. The use of fate reporter mice allowed addressing the functional consequences of loss of Foxp3 expression. Depending on the environment Treg cells gain effector functions upon loss of Foxp3 expression. However, the traditional view that Treg cells become necessarily pathogenic by gaining effector functions was challenged by recent findings and supports the notion of Treg cell lineage plasticity. Treg cell stability is also a major issue for Treg cell therapies. Clinical trials are designed to use polyclonal Treg cells as therapeutic tools. Here, we summarize the role of Treg cells in selected autoimmune diseases and recent advances in the field of Treg targeted therapies.

TIGIT signaling restores suppressor function of Th1 Tregs

Th1 Tregs are characterized by the acquisition of proinflammatory cytokine secretion and reduced suppressor activity. Th1 Tregs are found at increased frequency in autoimmune diseases, including type 1 diabetes and multiple sclerosis (MS). We have previously reported that in vitro stimulation with IL-12 recapitulates the functional and molecular features of MS-associated Th1 Tregs, revealing a central role for hyperactivation of the Akt pathway in their induction. TIGIT is a newly identified coinhibitory receptor that marks Tregs that specifically control Th1 and Th17 responses. Here, we report that signaling through TIGIT counteracts the action of IL-12 in inducing the Th1 program. Specifically, TIGIT signaling represses production of IFN-γ and T-bet expression and restores suppressor function in Tregs treated with IL-12. FoxO1 functional inhibition abolishes the protective effect of TIGIT, indicating that TIGIT signaling promotes FoxO1 nuclear localization. Consistent with this observation, signaling through TIGIT leads to a rapid suppression of Akt function and FoxO1 phosphorylation. Finally, TIGIT stimulation reduces the production of IFN-γ and corrects the suppressor defect of Tregs from patients with MS. Our results indicate an important role for TIGIT in controlling the functional stability of Tregs through repression of Akt, suggesting that the TIGIT pathway could be targeted for immunomodulatory therapies in human autoimmune disorders.

Past, Present, and Future of Regulatory T Cell Therapy in Transplantation and Autoimmunity

Regulatory T cells (Tregs) are important for the induction and maintenance of peripheral tolerance therefore, they are key in preventing excessive immune responses and autoimmunity. In the last decades, several reports have been focussed on understanding the biology of Tregs and their mechanisms of action. Preclinical studies have demonstrated the ability of Tregs to delay/prevent graft rejection and to control autoimmune responses following adoptive transfer in vivo. Due to these promising results, Tregs have been extensively studied as a potential new tool for the prevention of graft rejection and/or the treatment of autoimmune diseases. Currently, solid organ transplantation remains the treatment of choice for end-stage organ failure. However, chronic rejection and the ensuing side effects of immunosuppressants represent the main limiting factors for organ acceptance and patient survival. Autoimmune disorders are chronic diseases caused by the breakdown of tolerance against self-antigens. This is triggered either by a numerical or functional Treg defect, or by the resistance of effector T cells to suppression. In this scenario, patients receiving high doses of immunosuppressant are left susceptible to life-threatening opportunistic infections and have increased risk of malignancies. In the last 10 years, a few phase I clinical trials aiming to investigate safety and feasibility of Treg-based therapy have been completed and published, whilst an increasing numbers of trials are still ongoing. The first results showed safety and feasibility of Treg therapy and phase II clinical trials are already enrolling. In this review, we describe our understanding of Tregs focussing primarily on their ontogenesis, mechanisms of action and methods used in the clinic for isolation and expansion. Furthermore, we will describe the ongoing studies and the results from the first clinical trials with Tregs in the setting of solid organ transplantation and autoimmune disorders. Finally, we will discuss strategies to further improve the success of Treg therapy.

Regulatory T Cells: From Discovery to Autoimmunity

Multiple sclerosis (MS) is a genetically mediated autoimmune disease of the central nervous system. Allelic variants lead to lower thresholds of T-cell activation resulting in activation of autoreactive T cells. Environmental factors, including, among others, diet, vitamin D, and smoking, in combination with genetic predispositions, play a substantial role in disease development and activation of autoreactive T cells. FoxP3⁺ regulatory T cells (Tregs) have emerged as central in the control of autoreactive T cells. A consistent finding in patients with MS is defects in Treg cell function with reduced suppression of effector T cells and production of proinflammatory cytokines. Emerging data suggests that functional Tregs become effector-like T cells with loss of function associated with T-bet expression and interferon γ (IFN-γ) secretion.

Clinical use of an immune monitoring panel in liver transplant recipients: A prospective, observational study

Immunosuppressive therapy greatly contributed to making liver transplantation the standard treatment for end-stage liver diseases. However, it remains difficult to predict and measure the efficacy of pharmacological immunosuppression. Therefore, we used a panel of standardized, commonly available, biomarkers with the aim to describe their changes in the first 3 weeks after the transplant procedure and assess if they may help therapeutic drug monitoring in better tailoring the dose of the immunosuppressive drugs. We prospectively studied 72 consecutive patients from the day of liver transplant (post-operative day #0) until the post-operative day #21. Leukocytes, neutrophils, lymphocytes (CD4+, CD8+), natural killer cells, monocytes, immunoglobulins and tacrolimus serum levels were measured on peripheral blood (at day 0, 3, 7, 14, 21 after surgery). Patients who developed infections showed significantly higher CD64+ monocytes on post operative day #7. IgG levels were lower on post operative day #3 among patients who later developed infections. We also found that a sharp decrease in IgA from post operative day #0 to 3 (-226 mg/dL in the ROC curve analysis) strongly correlates with the onset of infections among HCV- patients. No specific markers of rejection emerged from the tested panel of markers. Our results show that some early changes in peripheral blood white cells and immunoglobulins may predict the onset of infections and may be useful in modulating the immunosuppressive therapy. However, a panel of commonly available, standardized biomarkers do not support in improving therapeutic drug monitoring ability to individualize immunosuppressive drugs dosing.

Inflammasome Priming Mediated via Toll-Like Receptors 2 and 4, Induces Th1-Like Regulatory T Cells in De Novo Autoimmune Hepatitis

De novo autoimmune hepatitis (DAIH) is an important cause of late allograft dysfunction following liver transplantation, but its cause and underlying pathogenesis remains unclear. We sought to identify specific innate and adaptive immune mechanisms driving the pro-inflammatory cytokine secreting regulatory T cell (Treg) phenotype in DAIH and determine if modulation of these pathways could resolve the inflammatory milieu observed in the livers of patients with DAIH. Here, we demonstrate toll-like receptors (TLRs) 2- and 4-mediated inflammasome activation in CD14++ monocytes, a finding that is key to maintaining dysfunctional Tregs in patients with DAIH. Furthermore, silencing of TLR 2 and 4 in CD14++ monocytes prevented activation of the inflammasome and significantly decreased IFN-γ production by FOXP3+ Tregs. We also observed significantly increase in expression of tumor necrosis factor α-induced protein 3 (TNFAIP3), a negative regulator of the NLRP3 Inflammasome, in monocytes/macrophages of liver transplant subjects who have normal allograft function and do not have DAIH. TNFAIP3 expression was virtually absent in monocytes/macrophages of patients with DAIH. Our findings suggest that autoimmunity in DAIH is promoted by CD14++ monocytes predominantly through activation of inflammatory signaling pathways.

Regulatory T cells in autoimmune disease

In recent years, the understanding of regulatory T cell (T_reg cell) biology has expanded considerably. Key observations have challenged the traditional definition of T_reg cells and have provided insight into the underlying mechanisms responsible for the development of autoimmune diseases, with new therapeutic strategies that improve disease outcome. This Review summarizes the newer concepts of T_reg cell instability, T_reg cell plasticity and tissue-specific T_reg cells, and their relationship to autoimmunity. Those three main concepts have changed the understanding of T_reg cell biology: how they interact with other immune and non-immune cells; their functions in specific tissues; and the implications of this for the pathogenesis of autoimmune diseases.

Serum Levels of IL-33 and Correlation with IL-4, IL-17A, and Hypergammaglobulinemia in Patients with Autoimmune Hepatitis

This study investigated the role of IL-33 in the pathogenesis of autoimmune hepatitis (AIH). The levels of IL-33/sST2 and Th1/Th2/Th17-type cytokines were determined by enzyme-linked immunosorbent assay in serum samples obtained from 30 AIH patients and 20 healthy controls (HCs). In addition, a murine model of experimental AIH (EAIH) was established to investigate the role of IL-33 in disease progression. The serum levels of IL-33, sST2, Th17 cytokines (IL-17A), Th1 cytokines (IFN-γ, TNF-α), and Th2 cytokines (IL-4) were significantly elevated in AIH patients compared to HCs. Following immunosuppression therapy, serum levels of IL-33 and sST2 were significantly decreased. Additionally, the serum levels of IL-33 in AIH patients were correlated positively with markers of hypergammaglobulinemia (IgG, IgM, and IgA) and liver injury (γ-GT/ALP). Also, the serum levels of IL-33 in AIH patients were correlated positively with proinflammatory cytokine levels (IL-17A and IL-4). Interestingly, treatment of EAIH mice with a specific IL-33 neutralizing antibody significantly reversed the increasing trend in serum ALT/AST and inhibited the production of the type 2 (IL-4) and type 17 cytokines (IL-17) but not the type 1 cytokine (IFN-γ). Our findings highlight the possible role of the IL-33/sST2 axis in the progression of AIH, opening a new door for developing a novel therapeutic strategy for AIH.