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Regulatory T cells (Tregs) are crucial in maintaining tolerance. Hence, Treg immunotherapy is an attractive therapeutic option in autoimmune diseases and organ transplantations. Currently, autoimmune diseases do not have a curative treatment and transplant recipients require life-long immunosuppression to prevent graft rejection. There has been significant progress in understanding polyclonal and antigen-specific Treg biology over the last decade. Clinical trials with good manufacturing practice (GMP) Treg cells have demonstrated safety and early efficacy of Treg therapy. GMP Treg cells can also be tracked following infusion. In order to improve efficacy of Tregs immunotherapy, it is necessary that Tregs migrate, survive and function at the specific target tissue. Application of antigen specific Tregs and maintaining cells' suppressive function and survival with low dose interleukin-2 (IL-2) will enhance the efficacy and longevity of infused GMP-grade Tregs. Notably, stability of Tregs in the local tissue can be manipulated by understanding the microenvironment. With the recent advances in GMP-grade Tregs isolation and antigen-specific chimeric antigen receptor (CAR)-Tregs development will allow functionally superior cells to migrate to the target organ. Thus, Tregs immunotherapy may be a promising option for patients with autoimmune diseases and organ transplantations in near future.

The tight relationship between the gut and liver on embryological, anatomical and physiological levels inspired the concept of a gut-liver axis as a central element in the pathogenesis of gut-liver axis diseases. This axis refers to the reciprocal regulation between these two organs causing an integrated system of immune homeostasis or tolerance breakdown guided by the microbiota, the diet, genetic background, and environmental factors. Continuous exposure of gut microbiome, various hormones, drugs and toxins, or metabolites from the diet through the portal vein adapt the liver to maintain its tolerogenic state. This is orchestrated by the combined effort of immune cells network: behaving as a sinusoidal and biliary firewall, along with a regulatory network of immune cells including, regulatory T cells and tolerogenic dendritic cells (DC). In addition, downregulation of costimulatory molecules on hepatic sinusoids, hepatocytes and biliary epithelial cells as well as regulating the bile acids chain also play a part in hepatic immune homeostasis. Recent evidence also demonstrated the link between changes in the gut microbiome and liver resident immune cells in the progression of cirrhosis and the tight correlation among primary sclerosing cholangitis (PSC) and also checkpoint induced liver and gut injury. In this review, we will summarize the most recent evidence of the bidirectional relationship among the gut and the liver and how it contributes to liver disease, focusing mainly on PSC and checkpoint induced hepatitis and colitis. We will also focus on completed therapeutic options and on potential targets for future treatment linking with immunology and describe the future direction of this research, taking advantage of modern technologies.

Thymic-derived naturally occurring regulatory T cells (tTreg) are crucial for maintaining peripheral immune homeostasis. They play a crucial role in preventing autoimmunity and maintaining organ transplant without requiring immunosuppression. Cellular metabolism has recently emerged as an important regulator of adaptive immune cell balance between Treg and effector T cells. While the metabolic requirements of conventional T cells are increasingly understood, the role of Treg cellular metabolism is less clear. The continuous exposure of metabolites and nutrients to the human liver the portal blood flow influences the lineage fitness, function, proliferation, migration, and survival of Treg cells. As cellular metabolism has an impact on its function, it is crucial to understand the metabolic pathways wiring in regulatory T cells. Currently, there are ongoing early phase clinical trials with polyclonal and antigen-specific good manufacturing practice (GMP) Treg therapy to treat autoimmune diseases and organ transplantation. Thus, enhancing immunometabolic pathways of Treg by translational approach with existing or new drugs would utilize Treg cells to their full potential for effective cellular therapy.

The induction of graft tolerance remains the holy grail of transplantation. This is important as chronic allograft dysfunction and the side effects of immunosuppression regimens place a major burden on the lives of transplant patients and their healthcare systems. This has mandated the need to understand the immunobiology of graft rejection and identify novel therapeutics. Regulatory T (Treg) cells play an important role in modulating pro‐inflammatory microenvironments and maintaining tissue homeostasis. However, there are fundamental unanswered questions regarding Treg cell immunobiology. These cells are a heterogeneous entity with functionally diverse roles. Moreover, the adoption of novel deeper immunophenotyping and genomic sequencing technologies has identified this phenotype and function to be more complex than expected. Hence, a comprehensive understanding of Treg cell heterogeneity is needed to safely and effectively exploit their therapeutic potential. From a clinical perspective, the recent decade has seen different clinical teams commence and complete first‐in‐man clinical trials utilising Treg cells as an adoptive cellular therapy. In this review, we discuss these trials from a translational perspective with an important focus on safety. Finally, we identify crucial knowledge gaps for future study. Treg cell therapy has the potential to revolutionise current post‐transplant immunosuppression protocols. Treg cells are presently undergoing early phase trials in solid organ transplantation. However, there are multiple questions regarding Treg cell immunobiology that need to be resolved.

Innate lymphoid cells (ILC) have been implicated in the initiation of inflammation and fibrosis in mice. However, ILC have not been characterized in inflamed human liver tissue. Human intrahepatic lymphocytes were isolated by mechanical digestion and phenotyped by flow cytometry. Conditioned medium from cultures of primary human biliary epithelial cells, stellate cells, fibroblasts and inflamed human liver tissue was used to model the effects of the inflammatory liver environment of ILC phenotype and function. All three ILC subsets were present in the human liver, with the ILC1 (CRTH2negCD117neg) subset constituting around 70% of intrahepatic ILCs. Both NCRpos (NKp44+) and NCRneg ILC3 (CRTH2negCD117pos) subsets were also detected. ILC2 (CRTH2pos) frequency correlated with disease severity measured by model of end stage liver disease (MELD) scoring leading us to study this subset in more detail. ILC2 displayed a tissue resident CD69+ CD161++ phenotype and expressed chemokine receptor CCR6 allowing them to respond to CCL20 secreted by cholangiocytes and stellate cells. ILC2 expressed integrins VLA-5 and VLA-6 and the IL-2 and IL-7 cytokine receptors CD25 and CD127 although IL-2 and IL-7 were barely detectable in inflamed liver tissue. Although biliary epithelial cells secrete IL-33, intrahepatic ILC2 had low expression of the ST2 receptor. Intrahepatic ILC2 secreted the immunoregulatory and repair cytokines IL-13 and amphiregulin. Intrahepatic ILC2 express receptors allowing them to be recruited to bile ducts in inflamed portal tracts. Their frequencies increased with worsening liver function. Their secretion of IL-13 and amphiregulin suggests they may be recruited to promote resolution and repair and thereby they may contribute to ongoing fibrogenesis in liver disease.

The increasing demand for liver transplantation and the decline in donor organs has highlighted the need for alternative novel therapies to prevent chronic active hepatitis, which eventually leads to liver cirrhosis and liver cancer. Liver histology of chronic hepatitis is composed of both effector and regulatory lymphocytes. The human liver contains different subsets of effector lymphocytes that are kept in check by a subpopulation of T cells known as Regulatory T cells (Treg). The balance of effector and regulatory lymphocytes generally determines the outcome of hepatic inflammation: resolution, fulminant hepatitis, or chronic active hepatitis. Thus, maintaining and adjusting this balance is crucial in immunological manipulation of liver diseases. One of the options to restore this balance is to enrich Treg in the liver disease patients. Advances in the knowledge of Treg biology and development of clinical grade isolation reagents, cell sorting equipment, and good manufacturing practice facilities have paved the way to apply Treg cells as a potential therapy to restore peripheral self-tolerance in autoimmune liver diseases (AILD), chronic rejection, and posttransplantation. Past and on-going studies have applied Treg in type-1 diabetes mellitus, systemic lupus erythematosus, graft versus host diseases, and solid organ transplantations. There have not been any new therapies for the AILD for more than three decades; thus, the clinical potential for the application of autologous Treg cell therapy to treat autoimmune liver disease is an attractive and novel option. However, it is fundamental to understand the deep immunology, genetic profiles, biology, homing behavior, and microenvironment of Treg before applying the cells to the patients.

The initial idea of a distinct group of T-cells responsible for suppressing immune responses was first postulated half a century ago. However, it is only in the last three decades that we have identified what we now term regulatory T-cells (Tregs), and subsequently elucidated and crystallized our understanding of them. Human Tregs have emerged as essential to immune tolerance and the prevention of autoimmune diseases and are typically contemporaneously characterized by their CD3 + CD4 + CD25 high CD127 low FOXP3 + phenotype. It is important to note that FOXP3 + Tregs exhibit substantial diversity in their origin, phenotypic characteristics, and function. Identifying reliable markers is crucial to the accurate identification, quantification, and assessment of Tregs in health and disease, as well as the enrichment and expansion of viable cells for adoptive cell therapy. In our comprehensive review, we address the contributions of various markers identified in the last two decades since the master transcriptional factor FOXP3 was identified in establishing and enriching purity, lineage stability, tissue homing and suppressive proficiency in CD4 + Tregs. Additionally, our review delves into recent breakthroughs in innovative Treg-based therapies, underscoring the significance of distinct markers in their therapeutic utilization. Understanding Treg subsets holds the key to effectively harnessing human Tregs for immunotherapeutic approaches.

Autoimmune hepatitis (AIH) is an immune‐mediated chronic liver disease that affects all ages, including women of childbearing age. Optimal management during pregnancy is poorly defined. We aimed to explore the clinical and biochemical course of AIH in the antenatal and postpartum periods, and assess factors associated with premature birth and postpartum flares. Pregnant women with AIH reviewed in the autoimmune liver disease clinic at the Queen Elizabeth Hospital Birmingham between 2009 and 2020 were identified retrospectively, and clinical, biochemical, and immunological data 1 year before conception to 1 year postpartum were collected. Analysis was performed to identify trends in blood markers over the antenatal period, with an interrupted time series approach used to assess postpartum trends. Data were available for n = 27 pregnancies (n = 20 women), with median gestation of 38 weeks (30% premature) and most having type 1 AIH (78%) and delivering via caesarean section (63%). Levels of alanine transaminase, aspartate transaminase, and immunoglobulin G all declined significantly during gestation, followed by significant step‐change increases after delivery. Postpartum flare developed in 58% of pregnancies. AIH type 2 was associated with a higher rate of premature births (67% vs. 19%, P = 0.044), and a trend toward a higher rate of postpartum flare (100% vs. 48%, P = 0.053). Although not significant, medication nonadherence was associated with almost double the risk of prematurity (40% vs. 24%, P = 0.415) and postpartum flare (80% vs. 44%, P = 0.109). Conclusion: Biochemical and immunological remission of AIH occurs during pregnancy, although subsequent postpartum flare is common. Type 2 AIH is associated with a higher risk of premature birth and postpartum flare, although further research is required to validate and explain this finding.

Background Autoimmune hepatitis (AIH) is an immune-mediated liver disease of unknown etiology. Increasing incidence of AIH in Asian patients has been reported. However, the phenotypic difference of Asian patients in Europe and Asia has still not been explored. Aim To evaluate the clinical presentation, biochemical and immunological profiles, treatment response and survival outcome of type 1 AIH from two tertiary liver transplant centres (United Kingdom and Singapore). Method Patients who fulfilled the simplified diagnostic scoring criteria of AIH were included in the study. Patients with overlap syndrome were excluded. Results Totals of 40 Asian patients and 159 Caucasian patients from the University Hospital of Birmingham National Health Service Foundation Trust, UK, were compared with 57 Asian patients from Singapore General Hospital, Singapore. Asian patients from Singapore present significantly much later (median 55 vs. 32 years, p  < 0.001), had higher MELD ( p  < 0.001) with lower albumin ( p  < 0.001) and higher bilirubin ( p  < 0.001) and lower ASMA positivity ( p  < 0.001) at diagnosis compared to UK Asian. Jaundice at presentation was much higher in Singapore Asian patients compared to UK Asian (53 vs. 30 %) but cirrhosis at diagnosis was more common in UK patients. Associated autoimmune conditions were less commonly seen in Singapore Asians. Comparing between UK cohorts, Asian patients present at younger age and have higher IgG level compared to Caucasian. Overall, 5-year transplant-free survival in all three cohorts was similar ( p  = 0.846). Conclusion We demonstrate that AIH patients from Singapore present at older age with jaundice and have a low positivity of SMA. Despite these differences, transplant-free survival is similar in the two groups.