Liver-Resident Bystander CD8+ T Cells Contribute to Liver Disease Pathogenesis in Chronic Hepatitis D Virus Infection

Investigating Human Liver Tissue-Resident Memory T Cells from the Perspectives of Gastroenterologists and Hepatologists

Liver tissue-resident memory T (TRM) cells play a pivotal role in hepatic immune responses. Their unique residence within liver sinusoids allow continuous antigen surveillance. In this review, we highlight the role of liver TRM cells in protective immunity and disease pathology. Comparisons between human and murine liver TRM cells reveal species-specific characteristics, suggesting the need for human-focused studies. One key finding is the involvement of liver TRM cells in viral hepatitis, where they can both control infection and contribute to liver damage. Liver TRM cells also exhibit dual roles in metabolic-associated steatotic liver disease, promoting inflammation and fibrosis while also contributing to fibrosis resolution. In autoimmune liver diseases, such as autoimmune hepatitis and primary sclerosing cholangitis, the presence of liver TRM cells correlates with disease severity. In this review, we underscore the importance of liver TRM cells in vaccine development, particularly vaccines against malaria. Future research should focus on the mechanisms governing TRM-cell formation, maintenance, and function, with the aim of supporting their protective roles while mitigating detrimental effects. Advancing our understanding of liver TRM cells will enhance our knowledge of liver immunology and inform novel therapeutic strategies for liver disease management.

Hepatitis D virus infection triggers CXCL9-11 upregulation in hepatocytes and liver infiltration of CXCR3+ CD4 T cells

Background & Aims

The role of hepatocytes in producing chemokines and triggering liver inflammation and damage in chronic hepatitis D (CHD) is not fully understood. Herein, we investigated the contribution of primary human hepatocytes (PHHs) infected with HDV in triggering inflammation by producing the chemokines CXCL9-11.

Methods

We performed quantitative PCR, RNA in situ hybridisation, activation-induced marker (AIM) assays, and FACS analysis to investigate the CXCR3/CXCL9-11 receptor/ligand axis of T cells in peripheral blood and livers from patients with chronic hepatitis B (n = 27 and 18, respectively) and CHD (n = 20 and 18, respectively). Chemokine expression was investigated in cultured HDV-infected PHHs and in livers of HBV- or HBV/HDV-infected humanised mice in the presence or absence of adoptively transferred human immune cells (n = 35 in total).

Results

In patient and chimeric mouse livers, higher expression levels of CXCL9-11 were found in an HBV/HDV-coinfected vs. HBV-mono-infected setting. Similarly, high levels of CXCL9-11 were observed in HDV-infected PHHs in vitro. Analysis by RNA in situ hybridisation on patient livers revealed that HDV-infected hepatocytes were a significant contributor to the chemokine expression. The corresponding chemokine receptor CXCR3 was found upregulated specifically on peripheral bulk CD4 T cells of patients with CHD. CXCR3 upregulation was unspecific and was not detected on HDAg- or HBsAg-specific CD4 T cells by activation-induced marker assay. Lastly, adoptive transfer of human T cells in humanised mice led to recruitment of non-HBV/HDV-specific CD4+ T cells only in the setting of HBV/HDV coinfection, but not in HBV-mono-infected mice.

Conclusions

HDV infection upregulated the intrahepatic expression of the CXCL9-11/CXCR3 receptor/ligand axis. Higher amounts of HBV/HDV-unspecific CD4 T cells expressing CXCR3 may contribute to the aggravated liver inflammation frequently observed in patients with CHD.

Impact and implications

Chronic hepatitis D (CHD) causes the most severe form of viral hepatitis, and treatment options are still limited; therefore, a more precise understanding of CHD immunopathology is needed. In this study, we demonstrated that HDV infection triggers CXCL9-11 expression in hepatocytes and liver infiltration of CXCR3-expressing CD4 T cells in preclinical models as well as patient biopsies. Because recruitment of Th1-polarised CD4 T cells to the liver has been also described for other severe liver diseases, such as autoimmune hepatitis, it may represent an important mechanism of aggravating liver diseases. The data of this study set hereby the basis for future studies analysing phenotype and function of intrahepatic T cells in CHD.

IL-15-induced CD38+HLA-DR+CD8+ T cells correlate with liver injury via NKG2D in chronic hepatitis B cirrhosis

Objectives

CD8+ T cells play a critical role in the immune dysfunction associated with liver cirrhosis. CD38+HLA-DR+CD8+ T cells, or bystander-activated CD8+ T cells, are involved in tissue injury but their specific contribution to liver cirrhosis remains unclear. This study sought to identify the mechanism for CD38+HLA-DR+CD8+ T cell-mediated pathogenesis during liver cirrhosis.

Methods

The immunophenotype, antigen specificity, cytokine secretion and cytotoxicity-related indicators of CD38+HLA-DR+CD8+ T cells were determined using flow cytometry. The functional properties of these cells were assessed using transcriptome analysis. CD38+HLA-DR+CD8+ T-cell killing was detected using cytotoxicity and antibody-blocking assays.

Results

The proportion of CD38+HLA-DR+CD8+ T cells was significantly elevated in liver cirrhosis patients and correlated with tissue damage. Transcriptome analysis revealed that these cells had innate-like functional characteristics. This CD8+ T-cell population primarily consisted of effector memory T cells and produced a high level of cytotoxicity-related cytokines, granzyme B and perforin. IL-15 promoted CD38+HLA-DR+CD8+ T-cell activation and proliferation, inducing significant TCR-independent cytotoxicity mediated through NKG2D.

Conclusions

CD38+HLA-DR+CD8+ T cells correlated with cirrhosis-related liver injury and contributed to liver damage by signalling through NKG2D in a TCR-independent manner.

PIEZO1 mechanically regulates the antitumour cytotoxicity of T lymphocytes

The killing function of cytotoxic T cells can be enhanced biochemically. Here we show that blocking the mechanical sensor PIEZO1 in T cells strengthens their traction forces and augments their cytotoxicity against tumour cells. By leveraging cytotoxic T cells collected from tumour models in mice and from patients with cancers, we show that PIEZO1 upregulates the transcriptional factor GRHL3, which in turn induces the expression of the E3 ubiquitin ligase RNF114. RNF114 binds to filamentous actin, causing its downregulation and rearrangement, which depresses traction forces in the T cells. In mice with tumours, the injection of cytotoxic T cells collected from the animals and treated with a PIEZO1 antagonist promoted their infiltration into the tumour and attenuated tumour growth. As an immunomechanical regulator, PIEZO1 could be targeted to enhance the outcomes of cancer immunotherapies.

Characterisation of HBV and co-infection with HDV and HIV through spatial transcriptomics

Background and aims

The intrahepatic processes associated with chronic hepatitis B (CHB), especially in the context of hepatitis delta virus (HDV) and HIV co-infection, require a better understanding. Spatial transcriptomics can provide new insights into the complex intrahepatic biological processes, guiding new personalised treatments. Our aim is to evaluate this method characterising the intrahepatic transcriptional landscape, cellular composition and biological pathways in liver biopsy samples from patients with hepatitis B virus (HBV) and HDV or HIV co-infection.

Method

The NanoString GeoMx digital spatial profiling platform was employed to assess expression of HBV surface antigen and CD45 in formalin-fixed paraffin-embedded (FFPE) biopsies from three treatment-naïve patients with chronic HBV and HDV or HIV co-infection. The GeoMx Human Whole Transcriptome Atlas assay quantified the expression of genes enriched in specific regions of interest (ROIs). Cell type proportions within ROIs were deconvoluted using a training matrix from the human liver cell atlas. A weighted gene correlation network analysis evaluated transcriptomic signatures across sampled regions.

Results

Spatially discrete transcriptomic signatures and distinct biological pathways were associated with HBV infection/disease status and immune responses. Shared features including 'cytotoxicity' and 'B cell receptor signalling' were consistent across patients, suggesting common elements alongside individual traits. HDV/HBV co-infection exhibited upregulated genes linked to apoptosis and immune cell recruitment, whereas HIV/HBV co-infection featured genes related to interferon response regulation. Varied cellular characteristics and immune cell populations, with an abundance of γδT cells in the HDV/HBV sample, were observed within analysed regions. Transcriptional differences in hepatocyte function suggest disrupted metabolic processes in HDV/HBV co-infection potentially impacting disease progression.

Conclusion

This proof-of-principle study shows the value of this platform in investigating the complex immune landscape, highlighting relevant host pathways to disease pathogenesis.

NK-like CD8 T cell: one potential evolutionary continuum between adaptive memory and innate immunity

CD8 T cells are crucial adaptive immune cells with cytotoxicity to fight against pathogens or abnormal self-cells via major histocompatibility complex class I-dependent priming pathways. The composition of the memory CD8 T-cell pool is influenced by various factors. Physiological aging, chronic viral infection, and autoimmune diseases promote the accumulation of CD8 T cells with highly differentiated memory phenotypes. Accumulating studies have shown that some of these memory CD8 T cells also exhibit innate-like cytotoxicity and upregulate the expression of receptors associated with natural killer (NK) cells. Further analysis shows that these NK-like CD8 T cells have transcriptional profiles of both NK and CD8 T cells, suggesting the transformation of CD8 T cells into NK cells. However, the specific induction mechanism underlying NK-like transformation and the implications of this process for CD8 T cells are still unclear. This review aimed to deduce the possible differentiation model of NK-like CD8 T cells, summarize the functions of major NK-cell receptors expressed on these cells, and provide a new perspective for exploring the role of these CD8 T cells in health and disease.

CXCR6+CD69+ CD8+ T cells in ascites are associated with disease severity in patients with cirrhosis

Background & Aims

Patients with advanced cirrhosis often develop hepatic decompensation, which is accompanied by systemic inflammation and may eventually lead to acute-on-chronic liver failure. One important cause of systemic hyperinflammation is a dysregulated overshooting immune response in ascites in the abdominal cavity. In this study, we analyzed the role of CD8+ T cells in the ascites immune compartment.

Methods

Peripheral blood and ascites fluid were collected from 50 patients with decompensated cirrhosis. Phenotype and functional responses of CD8+ T cells were analyzed, and obtained data were compared with each other as well as with healthy controls and patients with compensated cirrhosis.

Results

High-dimensional flow cytometry revealed that CD8+ T cells are abundant in the ascites of patients with cirrhosis and exhibit a chronically activated bystander phenotype with innate-like functions. Indeed, we identified distinct CXCR6+CD69+ clusters of late effector memory CD8+ T cells that were rarely found in blood and correlated with clinical parameters of disease severity. Moreover, this CD8+ T-cell population was hyperresponsive to innate cytokines and exhibited cytokine-mediated bystander activation. Interestingly, the Janus kinase (JAK) inhibitor tofacitinib was able to effectively block bystander-activated CXCR6+CD69+ CD8+ T cells and significantly suppress effector molecule production.

Conclusions

The results indicate that CXCR6+CD69+ CD8+ T cells in ascites are associated with disease severity and may contribute to inflammation in patients with decompensated cirrhosis, suggesting that targeted inhibition of this immune cell subset may be a viable therapeutic option.

Impact and Implications

Patients with advanced cirrhosis often develop hepatic decompensation, which is accompanied by systemic inflammation and eventually leads to acute-on-chronic liver failure. One important cause of systemic hyperinflammation is a dysregulated overshooting immune response in ascites in the abdominal cavity. In this study, we demonstrate that CXCR6+CD69+ CD8+ T cells are abundant in the ascites of patients with cirrhosis, exhibit a chronically activated bystander phenotype, and correlate with clinical parameters of disease severity. Moreover, we show that the Janus kinase (JAK) inhibitor tofacitinib can effectively block these bystander-activated CXCR6+CD69+ CD8+ T cells, suggesting that targeted inhibition of this immune cell subset may be a potential therapeutic strategy.

Clinical trial number

Prospective registry: INFEKTA (DRKS00010664).

JAML promotes the antitumor role of tumor-resident CD8+ T cells by facilitating their innate-like function in human lung cancer

Tissue-resident memory CD8+T cells (CD8+TRMs) are thought to play a crucial role in cancer immunosurveillance. However, the characteristics of CD8+TRMs in the tumor microenvironment (TME) of human non-small cell lung cancer (NSCLC) remain unclear. Here, we report that CD8+TRMs accumulate explicitly and exhibit a unique gene expression profile in the TME of NSCLC. Interestingly, these tumor-associated CD8+TRMs uniquely exhibit an innate-like phenotype. Importantly, we found that junction adhesion molecule-like (JAML) provides an alternative costimulatory signal to activate tumor-associated CD8+TRMs via combination with cancer cell-derived CXADR (CXADR Ig-like cell adhesion molecule). Furthermore, we demonstrated that activating JAML could promote the expression of TLR1/2 on CD8+TRMs, inhibit tumor progression and prolong the survival of tumor-bearing mice. Finally, we found that higher CD8+TRMs and JAML expression in the TME could predict favorable clinical outcomes in NSCLC patients. Our study reveals an intrinsic bias of CD8+TRMs for receiving the tumor-derived costimulatory signal in the TME, which sustains their innate-like function and antitumor role. These findings will shed more light on the biology of CD8+TRMs and aid in the development of potential targeted treatment strategies for NSCLC.

Protective role of RIPK1 scaffolding against HDV-induced hepatocyte cell death and the significance of cytokines in mice

Hepatitis delta virus (HDV) infection represents the most severe form of human viral hepatitis; however, the mechanisms underlying its pathology remain incompletely understood. We recently developed an HDV mouse model by injecting adeno-associated viral vectors (AAV) containing replication-competent HBV and HDV genomes. This model replicates many features of human infection, including liver injury. Notably, the extent of liver damage can be diminished with anti-TNF-α treatment. Here, we found that TNF-α is mainly produced by macrophages. Downstream of the TNF-α receptor (TNFR), the receptor-interacting serine/threonine-protein kinase 1 (RIPK1) serves as a cell fate regulator, playing roles in both cell survival and death pathways. In this study, we explored the function of RIPK1 and other host factors in HDV-induced cell death. We determined that the scaffolding function of RIPK1, and not its kinase activity, offers partial protection against HDV-induced apoptosis. A reduction in RIPK1 expression in hepatocytes through CRISPR-Cas9-mediated gene editing significantly intensifies HDV-induced damage. Contrary to our expectations, the protective effect of RIPK1 was not linked to TNF-α or macrophage activation, as their absence did not alter the extent of damage. Intriguingly, in the absence of RIPK1, macrophages confer a protective role. However, in animals unresponsive to type-I IFNs, RIPK1 downregulation did not exacerbate the damage, suggesting RIPK1's role in shielding hepatocytes from type-I IFN-induced cell death. Interestingly, while the damage extent is similar between IFNα/βR KO and wild type mice in terms of transaminase elevation, their cell death mechanisms differ. In conclusion, our findings reveal that HDV-induced type-I IFN production is central to inducing hepatocyte death, and RIPK1's scaffolding function offers protective benefits. Thus, type-I IFN together with TNF-α, contribute to HDV-induced liver damage. These insights may guide the development of novel therapeutic strategies to mitigate HDV-induced liver damage and halt disease progression.

Bystander activated CD8+ T cells mediate neuropathology during viral infection via antigen-independent cytotoxicity

Although many viral infections are linked to the development of neurological disorders, the mechanism governing virus-induced neuropathology remains poorly understood, particularly when the virus is not directly neuropathic. Using a mouse model of Zika virus (ZIKV) infection, we found that the severity of neurological disease did not correlate with brain ZIKV titers, but rather with infiltration of bystander activated NKG2D+CD8+ T cells. Antibody depletion of CD8 or blockade of NKG2D prevented ZIKV-associated paralysis, suggesting that CD8+ T cells induce neurological disease independent of TCR signaling. Furthermore, spleen and brain CD8+ T cells exhibited antigen-independent cytotoxicity that correlated with NKG2D expression. Finally, viral infection and inflammation in the brain was necessary but not sufficient to induce neurological damage. We demonstrate that CD8+ T cells mediate virus-induced neuropathology via antigen-independent, NKG2D-mediated cytotoxicity, which may serve as a therapeutic target for treatment of virus-induced neurological disease.

IL-15 in T-Cell Responses and Immunopathogenesis

IL-15 belongs to the common gamma chain cytokine family and has pleiotropic immunological functions. IL-15 is a homeostatic cytokine essential for the development and maintenance of NK cells and memory CD8+ T cells. In addition, IL-15 plays a critical role in the activation, effector functions, tissue residency, and senescence of CD8+ T cells. IL-15 also activates virtual memory T cells, mucosal-associated invariant T cells and γδ T cells. Recently, IL-15 has been highlighted as a major trigger of TCR-independent activation of T cells. This mechanism is involved in T cell-mediated immunopathogenesis in diverse diseases, including viral infections and chronic inflammatory diseases. Deeper understanding of IL-15-mediated T-cell responses and their underlying mechanisms could optimize therapeutic strategies to ameliorate host injury by T cell-mediated immunopathogenesis. This review highlights recent advancements in comprehending the role of IL-15 in relation to T cell responses and immunopathogenesis under various host conditions.

The Roles of Myeloid-Derived Suppressor Cells in Liver Disease

Liver disease-related mortality is a major cause of death worldwide. Hepatic innate and adaptive immune cells play diverse roles in liver homeostasis and disease. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells. MDSCs can be broadly divided into monocytic MDSCs and polymorphonuclear or granulocytic MDSCs, and they functionally interact with both liver parenchymal and nonparenchymal cells, such as hepatocytes and regulatory T cells, to impact liver disease progression. The infiltration and activation of MDSCs in liver disease can be regulated by inflammatory chemokines and cytokines, tumor-associated fibroblasts, epigenetic regulation factors, and gut microbiota during liver injury and cancer. Given the pivotal roles of MDSCs in advanced liver diseases, they can be targeted to treat primary and metastatic liver cancer, liver generation, alcoholic and nonalcoholic liver disease, and autoimmune hepatitis. Currently, several treatments such as the antioxidant and anti-inflammatory agent berberine are under preclinical and clinical investigation to evaluate their therapeutic efficacy on liver disease and their effect on MDSC infiltration and function. Phenotypic alteration of MDSCs in different liver diseases that are in a model-dependent manner and lack special markers for distinct MDSCs are challenges for targeting MDSCs to treat liver disease. Multi-omics study is an option to uncover the features of disease-specific MDSCs and potential gene or protein targets for liver disease treatment. In summary, MDSCs play important roles in the pathogenesis and progression of liver disease by regulating both intrahepatic innate and adaptive immune responses.

The role of natural killer T cells in liver transplantation

Natural killer T cells (NKTs) are innate-like lymphocytes that are abundant in the liver and participate in liver immunity. NKT cells express both NK cell and T cell markers, modulate innate and adaptive immune responses. Type I and Type II NKT cells are classified according to the TCR usage, while they recognize lipid antigen in a non-classical major histocompatibility (MHC) molecule CD1d-restricted manner. Once activated, NKT cells can quickly produce cytokines and chemokines to negatively or positively regulate the immune responses, depending on the different NKT subsets. In liver transplantation (LTx), the immune reactions in a series of processes determine the recipients' long-term survival, including ischemia-reperfusion injury, alloresponse, and post-transplant infection. This review provides insight into the research on NKT cells subpopulations in LTx immunity during different processes, and discusses the shortcomings of the current research on NKT cells. Additionally, the CD56-expressing T cells are recognized as a NK-like T cell population, they were also discussed during these processes.

Hepatitis D infection induces IFN-β-mediated NK cell activation and TRAIL-dependent cytotoxicity

Background and aims

The co-infection of hepatitis B (HBV) patients with the hepatitis D virus (HDV) causes the most severe form of viral hepatitis and thus drastically worsens the course of the disease. Therapy options for HBV/HDV patients are still limited. Here, we investigated the potential of natural killer (NK) cells that are crucial drivers of the innate immune response against viruses to target HDV-infected hepatocytes.

Methods

We established in vitro co-culture models using HDV-infected hepatoma cell lines and human peripheral blood NK cells. We determined NK cell activation by flow cytometry, transcriptome analysis, bead-based cytokine immunoassays, and NK cell-mediated effects on T cells by flow cytometry. We validated the mechanisms using CRISPR/Cas9-mediated gene deletions. Moreover, we assessed the frequencies and phenotype of NK cells in peripheral blood of HBV and HDV superinfected patients.

Results

Upon co-culture with HDV-infected hepatic cell lines, NK cells upregulated activation markers, interferon-stimulated genes (ISGs) including the death receptor ligand tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), produced interferon (IFN)-γ and eliminated HDV-infected cells via the TRAIL-TRAIL-R2 axis. We identified IFN-β released by HDV-infected cells as an important enhancer of NK cell activity. In line with our in vitro data, we observed activation of peripheral blood NK cells from HBV/HDV co-infected, but not HBV mono-infected patients.

Conclusion

Our data demonstrate NK cell activation in HDV infection and their potential to eliminate HDV-infected hepatoma cells via the TRAIL/TRAIL-R2 axis which implies a high relevance of NK cells for the design of novel anti-viral therapies.

Emerging anti-HDV drugs and HBV cure strategies with anti-HDV activity

Hepatitis delta virus (HDV) is a satellite RNA virus that requires the presence of hepatitis B virus (HBV) for its replication. HDV/HBV co-infection is often associated with a faster disease progression of chronic hepatitis in comparison to HBV mono-infection. Therefore, the development of novel antiviral therapies targeting HDV represents a high priority and an urgent medical need. In this review, we summarize the ongoing efforts to evaluate promising HDV-specific drugs, such as lonafarnib (LNF), pegylated interferon lambda (PEG-IFN-λ) and their use as a combination therapy. Furthermore, we review the most recent developments in the area of anti-HBV drugs with potential effects against HDV, including therapeutic agents targeting hepatitis B surface antigen (HBsAg) expression, secretion and function. Finally, we consider the important insights that have emerged from the development of these potential antiviral strategies, as well as the intriguing questions that remain to be elucidated in this rapidly changing field.

Immunology of hepatitis D virus infection: General concepts and present evidence

Infection with the hepatitis D virus induces the most severe form of chronic viral hepatitis, affecting over 12 million people worldwide. Chronic HDV infection leads to rapid development of liver cirrhosis and hepatocellular carcinoma in ~70% of patients within 15 years of infection. Recent evidence suggests that an interplay of different components of the immune system are contributing to viral control and may even be implicated in liver disease pathogenesis. This review will describe general concepts of antiviral immune response and elicit the present evidence concerning the interplay of the hepatitis D virus with the immune system.

Natural history of untreated HDV patients: Always a progressive disease?

A severe course has been described in early studies on chronic hepatitis D (CHD), with faster pace towards liver cirrhosis with subsequent high liver-related morbidity and mortality in the majority of patients. Earlier studies have included risk groups as people using intravenous drugs (PWID) or those with multiple co-morbidities. During the last decade, the epidemiological landscape of CHD has changed with domestic cases decreasing while increasing cases of CHD consisting of younger persons immigrating from endemic regions to low-endemic regions. Recently, further insights into the spectrum of the disease with an indolent disease course in a substantial proportion of persons with CHD have been gained. At diagnosis, ≥30%-50% had already established liver cirrhosis. Older age, liver cirrhosis, co-infection with HIV and lack of interferon (IFN) therapy are the main predictors of worse clinical outcome. The newly introduced and upcoming antivirals against CHD are highly anticipated, considering the historically low virological response rates to antiviral therapy. Further knowledge is needed to fully comprehend the natural course and the spectrum of this severe form of viral hepatitis. This is also to be able to evaluate the long-term effects of the new antivirals on disease progression.

Hepatitis Delta Virus Antigens Trigger Oxidative Stress, Activate Antioxidant Nrf2/ARE Pathway, and Induce Unfolded Protein Response

Hepatitis delta virus (HDV) is a viroid-like satellite that may co-infect individuals together with hepatitis B virus (HBV), as well as cause superinfection by infecting patients with chronic hepatitis B (CHB). Being a defective virus, HDV requires HBV structural proteins for virion production. Although the virus encodes just two forms of its single antigen, it enhances the progression of liver disease to cirrhosis in CHB patients and increases the incidence of hepatocellular carcinoma. HDV pathogenesis so far has been attributed to virus-induced humoral and cellular immune responses, while other factors have been neglected. Here, we evaluated the impact of the virus on the redox status of hepatocytes, as oxidative stress is believed to contribute to the pathogenesis of various viruses, including HBV and hepatitis C virus (HCV). We show that the overexpression of large HDV antigen (L-HDAg) or autonomous replication of the viral genome in cells leads to increased production of reactive oxygen species (ROS). It also leads to the upregulated expression of NADPH oxidases 1 and 4, cytochrome P450 2E1, and ER oxidoreductin 1α, which have previously been shown to mediate oxidative stress induced by HCV. Both HDV antigens also activated the Nrf2/ARE pathway, which controls the expression of a spectrum of antioxidant enzymes. Finally, HDV and its large antigen also induced endoplasmic reticulum (ER) stress and the concomitant unfolded protein response (UPR). In conclusion, HDV may enhance oxidative and ER stress induced by HBV, thus aggravating HBV-associated pathologies, including inflammation, liver fibrosis, and the development of cirrhosis and hepatocellular carcinoma.

Treating hepatitis D with bulevirtide - Real-world experience from 114 patients

Background & Aims

Bulevirtide is a first-in-class entry inhibitor of hepatitis B surface antigen. In July 2020, bulevirtide was conditionally approved for the treatment of hepatitis D, the most severe form of viral hepatitis, which frequently causes end-stage liver disease and hepatocellular carcinoma. Herein, we report the first data from a large multicenter real-world cohort of patients with hepatitis D treated with bulevirtide at a daily dose of 2 mg without additional interferon.

Methods

In a joint effort with 16 hepatological centers, we collected anonymized retrospective data from patients treated with bulevirtide for chronic hepatitis D.

Results

Our analysis is based on data from 114 patients, including 59 (52%) with cirrhosis, receiving a total of 4,289 weeks of bulevirtide treatment. A virologic response defined as an HDV RNA decline of at least 2 log or undetectable HDV RNA was observed in 87/114 (76%) cases with a mean time to virologic response of 23 weeks. In 11 cases, a virologic breakthrough (>1 log-increase in HDV RNA after virologic response) was observed. After 24 weeks of treatment, 19/33 patients (58%) had a virologic response, while three patients (9%) did not achieve a 1 log HDV RNA decline. No patient lost hepatitis B surface antigen. Alanine aminotransferase levels improved even in patients not achieving a virologic response, including five patients who had decompensated cirrhosis at the start of treatment. Treatment was well tolerated and there were no reports of drug-related serious adverse events.

Conclusions

In conclusion, we confirm the safety and efficacy of bulevirtide monotherapy in a large real-world cohort of patients with hepatitis D treated in Germany. Future studies need to explore the long-term benefits and optimal duration of bulevirtide treatment.

Impact and implications

Clinical trials proved the efficacy of bulevirtide for chronic hepatitis D and led to conditional approval by the European Medical Agency. Now it is of great interest to investigate the effects of bulevirtide treatment in a real-world setting. In this work, we included data from 114 patients with chronic hepatitis D who were treated with bulevirtide at 16 German centers. A virologic response was seen in 87/114 cases. After 24 weeks of treatment, only a small proportion of patients did not respond to treatment. At the same time, signs of liver inflammation improved. This observation was independent from changes in hepatitis D viral load. The treatment was generally well tolerated. In the future, it will be of interest to investigate the long-term effects of this new treatment.

Studying T Cell Responses to Hepatotropic Viruses in the Liver Microenvironment

T cells play an important role in the clearance of hepatotropic viruses but may also cause liver injury and contribute to disease progression in chronic hepatitis B and C virus infections which affect millions of people worldwide. The liver provides a unique microenvironment of immunological tolerance and hepatic immune regulation can modulate the functional properties of T cell subsets and influence the outcome of a virus infection. Extensive research over the last years has advanced our understanding of hepatic conventional CD4+ and CD8+ T cells and unconventional T cell subsets and their functions in the liver environment during acute and chronic viral infections. The recent development of new small animal models and technological advances should further increase our knowledge of hepatic immunological mechanisms. Here we provide an overview of the existing models to study hepatic T cells and review the current knowledge about the distinct roles of heterogeneous T cell populations during acute and chronic viral hepatitis.

Integrated bioinformatics analysis identifies shared immune changes between ischemic stroke and COVID 19

Although COVID-19 is primarily a respiratory disease, its neurological complications, such as ischemic stroke (IS), have aroused growing concerns and reports. However, the molecular mechanisms that underlie IS and COVID-19 are not well understood. Therefore, we implemented transcriptomic analysis from eight GEO datasets consist of 1191 samples to detect common pathways and molecular biomarkers in IS and COVID-19 that help understand the linkage between them. Differentially expressed genes (DEGs) were detected for IS and COVID-19 separately for finding shared mechanisms and we found that immune-related pathways were outlined with statistical significance. JAK2, which was identified as a hub gene, was supposed to be a potential therapeutic gene targets during the immunological process of COVID-19 and IS. Besides, we found a decrease in the proportion of CD8+ T and T helper 2 cells in the peripheral circulation of both COVID and IS patients, and NCR3 expression was significantly correlated with this change. In conclusion, we demonstrated that transcriptomic analyses reported in this study could make a deeper understanding of the common mechanism and might be promising for effective therapeutic for IS and COVID-19.

Liver-resident CD8+ T cells in viral hepatitis: not always good guys

More than twenty years ago, non-HBV-specific CD8+ T cells were found to contribute to liver immunopathology in chronic HBV infection, while HBV-specific CD8+ T cells were noted to contribute to viral control. The role of HBV-specific CD8+ T cells in viral control and the mechanisms of their failure in persistent infection have been intensively studied during the last two decades, but the exact nature of nonspecific bystander CD8+ T cells that contribute to immunopathology has remained elusive. In this issue of the JCI, Nkongolo et al. report on their application of two methodological advances, liver sampling by fine-needle aspiration (FNA) and single-cell RNA sequencing (scRNA-Seq), to define a liver-resident CD8+ T cell population that was not virus specific but associated with liver damage, thus representing hepatotoxic bystander CD8+ T cells.

A 3-Year Course Of Bulevirtide Monotherapy May Cure Hdv Infection In Cirrhotics

Bulevirtide has been recently conditionally approved by the European Medicines Agency for the treatment of Chronic Hepatitis Delta, but the ideal duration of therapy is unknown. Here we describe the first case of cure of Hepatitis Delta following 3 years of Bulevirtide monotherapy in a patient with compensated cirrhosis and esophageal varices. During the 72-week off-Bulevirtide follow-up, virological and biochemical responses were maintained. In the off-therapy liver biopsy, intrahepatic HDV RNA and Hepatitis D antigen were undetectable, <1% hepatocytes were Hepatitis B surface antigen positive while hepatitis B core antigen was negative. Grading and staging improved compared to pre-treatment biopsy.

Longitudinal liver sampling in patients with chronic hepatitis B starting antiviral therapy reveals hepatotoxic CD8+ T cells

Accumulation of activated immune cells results in nonspecific hepatocyte killing in chronic hepatitis B (CHB), leading to fibrosis and cirrhosis. This study aims to understand the underlying mechanisms in humans and to define whether these are driven by widespread activation or a subpopulation of immune cells. We enrolled CHB patients with active liver damage to receive antiviral therapy and performed longitudinal liver sampling using fine-needle aspiration to investigate mechanisms of CHB pathogenesis in the human liver. Single-cell sequencing of total liver cells revealed a distinct liver-resident, polyclonal CD8+ T cell population that was enriched at baseline and displayed a highly activated immune signature during liver damage. Cytokine combinations, identified by in silico prediction of ligand-receptor interaction, induced the activated phenotype in healthy liver CD8+ T cells, resulting in nonspecific Fas ligand-mediated killing of target cells. These results define a CD8+ T cell population in the human liver that can drive pathogenesis and a key pathway involved in their function in CHB patients.

Sequence diversity of hepatitis D virus in Mongolia

Introduction

The Hepatitis Delta Virus (HDV) is a defective, single-stranded RNA virusoid encoding for a single protein, the Hepatitis Delta Antigen (HDAg), which requires the hepatitis B virus (HBV) envelope protein (HBsAg) for its transmission. Currently, hepatitis D is the most aggressive form of viral hepatitis and treatment options are limited. Worldwide 12 million people are chronically infected with HDV being at high risk for progression to cirrhosis and development of liver cancer.

Objectives

Although it is well established that Mongolia is the country with the highest prevalence of HDV infections, the information on the molecular epidemiology and factors contributing to HDV sequence diversity are largely unclear. The aim of the study was to characterize the sequence diversity of HDV in rural areas from Mongolia and to determine the extent of HLA class I-associated selection pressure.

Patients and methods

From the HepMongolia cohort from rural areas in Mongolia, 451 HBsAg-positive individuals were selected and anti-HDV, HDV-RNA and the sequence of the large HDAg was determined. For all individuals the HLA class I locus was genotyped. Residues under selection pressure in the presence of individual HLA class I types were identified with the recently published analysis tool HAMdetector.

Results

Of 431 HBsAg positive patients, 281 were anti-HDV positive (65%), and HDV-RNA could be detected in 207 of 281 (74%) of patients. The complete large HDAg was successfully sequenced from 131 samples. Phylogenetic analysis revealed that all Mongolian HDV isolates belong to genotype 1, however, they separate into several different clusters without clear regional association. In turn, from phylogeny there is strong evidence for recent local transmission events. Importantly, we found multiple residues with strong support for HLA class I-associated selection pressure consistent with a functional CD8⁺ T cell response directed against HDV.

Conclusion

HDV isolates from Mongolia are highly diverse. The molecular epidemiology suggests circulation of multiple subtypes and provides evidence for ongoing recent transmissions.

The immune landscape in hepatitis delta virus infection-Still an open field!

Hepatitis delta virus (HDV) is known to cause the most aggressive and severe form of viral hepatitis, yet it remained under-diagnosed but does require early diagnosis for accurate disease staging. Antibody to HDV (anti-HDV) is the primary screening tool and should be assessed in patients with hepatitis B surface antigen (HBsAg) positivity, as HDV is a satellite RNA virus of hepatitis B. Additionally, the viral load (HDV RNA) should be assessed in those with positive anti-HDV, to differentiate between active infection and resolved hepatitis delta. Data regarding immune responses in HDV are limited but show dysfunctional adaptive and innate immunity. Many studies however fail to distinguish between active and resolved infection. Limited treatments are available for HDV, but promise has been shown with the newly approved Bulevirtide, a first-in-class HBV entry inhibitor. Thus immune response during therapy requires further investigation, along with additional targets for HDV cure.

NUDT1 promotes the accumulation and longevity of CD103+ TRM cells in primary biliary cholangitis

BACKGROUND & AIMS

Pyruvate dehydrogenase (PDC)-E2 specific CD8⁺ T cells play a leading role in biliary destruction in PBC. However, there are limited data on the characterization of these autoantigen-specific CD8⁺ T cells, particularly in the liver. Herein, we aimed to identify pathogenic intrahepatic CD8⁺ T-cell subpopulations and investigate their immunobiology in PBC.

METHODS

Phenotypic and functional analysis of intrahepatic T-cell subsets were performed by flow cytometry. CD103⁺ T_RM cell frequency was evaluated by histological staining. The transcriptome and metabolome were analyzed by RNA-seq and liquid chromatography-mass spectrometry, respectively. Cytotoxicity of T_RM cells against cholangiocytes was assayed in a 3D organoid co-culture system. Moreover, the longevity (long-term survival) of T_RM cells in vivo was studied by 2-octynoic acid-BSA (2OA-BSA) immunization, Nudt1 conditional knock-out and adoptive co-transfer in a murine model.

RESULTS

Intrahepatic CD103⁺ T_RM (CD69⁺CD103⁺CD8⁺) cells were significantly expanded, hyperactivated, and potentially specifically reactive to PDC-E2 in patients with PBC. CD103⁺ T_RM cell frequencies correlated with clinical and histological indices of PBC and predicted poor ursodeoxycholic acid response. NUDT1 blockade suppressed the cytotoxic effector functions of CD103⁺ T_RM cells upon PDC-E2 re-stimulation. NUDT1 overexpression in CD8⁺ T cells promoted tissue-residence programming in vitro; inhibition or knockdown of NUDT1 had the opposite effect. Pharmacological blockade or genetic deletion of NUDT1 eliminated CD103⁺ T_RM cells and alleviated cholangitis in mice immunized with 2OA-BSA. Significantly, NUDT1-dependent DNA damage resistance potentiates CD8⁺ T-cell tissue-residency via the PARP1-TGFβR axis in vitro. Consistently, PARP1 inhibition restored NUDT1-deficient CD103⁺ T_RM cell durable survival and TGFβ-Smad signaling.

CONCLUSIONS

CD103⁺ T_RM cells are the dominant population of PDC-E2-specific CD8⁺ T lymphocytes in the livers of patients with PBC. The role of NUDT1 in promoting pathogenic CD103⁺ T_RM cell accumulation and longevity represents a novel therapeutic target in PBC.

LAY SUMMARY

Primary biliary cholangitis (PBC) is a rare inflammatory condition of the bile ducts. It can be treated with ursodeoxycholic acid, but a large percentage of patients respond poorly to this treatment. Liver-infiltrating memory CD8⁺ T cells recognizing the PDC-E2 immunodominant epitope are critical in the pathogenesis of PBC. We identifed the key pathogenic CD8⁺ T cell subset, and worked out the mechanisms of its hyperactivation and longevity, which could be exploited therapeutically.

Identification of a distinct NK-like hepatic T-cell population activated by NKG2C in a TCR-independent manner

BACKGROUND & AIMS

The liver provides a unique niche of lymphocytes enriched with a large proportion of innate-like T cells. However, the heterogeneity and functional characteristics of the hepatic T-cell population remain to be fully elucidated.

METHODS

We obtained liver sinusoidal mononuclear cells from the liver perfusate of healthy donors and recipients with HBV-associated chronic liver disease (CLD) during liver transplantation. We performed a CITE-seq analysis of liver sinusoidal CD45⁺ cells in combination with T cell receptor (TCR)-seq and flow cytometry to examine the phenotypes and functions of liver sinusoidal CD8⁺ T cells.

RESULTS

We identified a distinct CD56^hiCD161^-CD8⁺ T-cell population characterized by natural killer (NK)-related gene expression and a uniquely restricted TCR repertoire. The frequency of these cells among the liver sinusoidal CD8⁺ T-cell population was significantly increased in patients with HBV-associated CLD. Although CD56^hiCD161^-CD8⁺ T cells exhibit weak responsiveness to TCR stimulation, CD56^hiCD161^-CD8⁺ T cells highly expressed various NK receptors, including CD94, killer immunoglobulin-like receptors, and NKG2C, and exerted NKG2C-mediated NK-like effector functions even in the absence of TCR stimulation. In addition, CD56^hiCD161^-CD8⁺ T cells highly respond to innate cytokines, such as IL-12/18 and IL-15, in the absence of TCR stimulation. We validated the results from liver sinusoidal CD8⁺ T cells using intrahepatic CD8⁺ T cells obtained from liver tissues.

CONCLUSIONS

In summary, the current study found a distinct CD56^hiCD161^-CD8⁺ T-cell population characterized by NK-like activation via TCR-independent NKG2C ligation. Further studies are required to elucidate the roles of liver sinusoidal CD56^hiCD161^-CD8⁺ T cells in immune responses to microbial pathogens or liver immunopathology.

LAY SUMMARY

The role of different immune cell populations in the liver is becoming an area of increasing interest. Herein, we identified a distinct T-cell population that had features similar to those of natural killer (NK) cells - a type of innate immune cell. This distinct population was expanded in the livers of patients with chronic liver disease and could thus have pathogenic relevance.

Tissue-resident memory T cells in chronic liver diseases: Phenotype, development and function

Tissue-resident memory (T_RM) T cells are a unique subset of memory T cells that are critical for the first line of defense against pathogens or antigens in peripheral non-lymphoid tissues such as liver, gut, and skin. Generally, T_RM cells are well adapted to the local environment in a tissue-specific manner and typically do not circulate but persist in tissues, distinguishing them from other memory T cell lineages. There is strong evidence that liver T_RM cells provide a robust adaptive immune response to potential threats. Indeed, the potent effector function of hepatic T_RM cells makes it essential for chronic liver diseases, including viral and parasite infection, autoimmune liver diseases (AILD), nonalcoholic fatty liver disease (NAFLD), hepatocellular carcinoma (HCC) and liver transplantation. Manipulation of hepatic T_RM cells might provide novel promising strategies for precision immunotherapy of chronic liver diseases. Here, we provide insights into the phenotype of hepatic T_RM cells through surface markers, transcriptional profiles and effector functions, discuss the development of hepatic T_RM cells in terms of cellular origin and factors affecting their development, analyze the role of hepatic T_RM cells in chronic liver diseases, as well as share our perspectives on the current status of hepatic T_RM cell research.

Immune Mechanisms Underlying Hepatitis B Surface Antigen Seroclearance in Chronic Hepatitis B Patients With Viral Coinfection

It is considered that chronic hepatitis B patients have obtained functional cure if they get hepatitis B surface antigen (HBsAg) seroclearance after treatment. Serum HBsAg is produced by cccDNA that is extremely difficult to clear and dslDNA that is integrated with host chromosome. High HBsAg serum level leads to failure of host immune system, which makes it unable to produce effective antiviral response required for HBsAg seroclerance. Therefore, it is very difficult to achieve functional cure, and fewer than 1% of chronic hepatitis B patients are cured with antiviral treatment annually. Some chronic hepatitis B patients are coinfected with other chronic viral infections, such as HIV, HCV and HDV, which makes more difficult to cure. However, it is found that the probability of obtaining HBsAg seroclearance in patients with coinfection is higher than that in patients with HBV monoinfection, especially in patients with HBV/HIV coinfection who have an up to 36% of HBsAg 5-year-seroclerance rate. The mechanism of this interesting phenomenon is related to the functional reconstruction of immune system after antiretroviral therapy (ART). The quantity increase and function recovery of HBV specific T cells and B cells, and the higher level of cytokines and chemokines such as IP-10, GM-CSF, promote HBsAg seroclearance. This review summarizes recent studies on the immune factors that have influence on HBsAg seroconversion in the chronic hepatitis B patients with viral coinfection, which might provide new insights for the development of therapeutic approaches to partially restore the specific immune response to HBV and other viruses.

Review article: emerging insights into the immunopathology, clinical and therapeutic aspects of hepatitis delta virus

BACKGROUND

Hepatitis delta virus (HDV), which causes the most severe form of viral hepatitis, is an obligated hepatitis B (HBV) satellite virus that can either infect naïve subjects simultaneously with HBV (co-infection), or chronically infect HBV carriers (super-infection). An estimated 12 million people are infected by HDV worldwide.

AIMS

To summarise the most relevant aspects of the molecular biology of HDV, and to discuss the latest understanding of the induced pathology, interactions with the immune system, as well as both approved and investigational treatment options.

METHODS

References for this review were identified through searches of PubMed with the terms "HDV" "viral hepatitis" "co-infection" and "super-infection," published between 1980 and October 2021 RESULTS: The limited access to the HDV-infected liver has hampered the investigation of the intrahepatic compartment and our understanding of the mechanisms of HDV pathogenesis. In the absence of standardised and sensitive diagnostic tools, HDV is often underdiagnosed and owing to its strong dependence on host cellular factors, the development of direct antiviral agents has been challenging. New therapeutic agents targeting different steps of the viral cycle have recently been investigated, among which bulevirtide (which was conditionally approved by EMA in July 2020) and lonafarnib; both drugs having received orphan drug designation from both the EMA and FDA.

CONCLUSIONS

The HBV cure programme potentially offers a unique opportunity to enhance HDV treatment strategies. In addition, a more comprehensive analysis of the intrahepatic compartment is mandated to better understand any liver-confined interaction of HDV with the host immune system.

Innate and Adaptive Immunopathogeneses in Viral Hepatitis; Crucial Determinants of Hepatocellular Carcinoma

Viral hepatitis B (HBV) and hepatitis C (HCV) infections remain the most common risk factors for the development of hepatocellular carcinoma (HCC), and their heterogeneous distribution influences the global prevalence of this common type of liver cancer. Typical hepatitis infection elicits various immune responses within the liver microenvironment, and viral persistence induces chronic liver inflammation and carcinogenesis. HBV is directly mutagenic but can also cause low-grade liver inflammation characterized by episodes of intermittent high-grade liver inflammation, liver fibrosis, and cirrhosis, which can progress to decompensated liver disease and HCC. Equally, the absence of key innate and adaptive immune responses in chronic HCV infection dampens viral eradication and induces an exhausted and immunosuppressive liver niche that favors HCC development and progression. The objectives of this review are to (i) discuss the epidemiological pattern of HBV and HCV infections, (ii) understand the host immune response to acute and chronic viral hepatitis, and (iii) explore the link between this diseased immune environment and the development and progression of HCC in preclinical models and HCC patients.

Adaptive Immune Responses, Immune Escape and Immune-Mediated Pathogenesis during HDV Infection

The hepatitis delta virus (HDV) is the smallest known human virus, yet it causes great harm to patients co-infected with hepatitis B virus (HBV). As a satellite virus of HBV, HDV requires the surface antigen of HBV (HBsAg) for sufficient viral packaging and spread. The special circumstance of co-infection, albeit only one partner depends on the other, raises many virological, immunological, and pathophysiological questions. In the last years, breakthroughs were made in understanding the adaptive immune response, in particular, virus-specific CD4+ and CD8+ T cells, in self-limited versus persistent HBV/HDV co-infection. Indeed, the mechanisms of CD8+ T cell failure in persistent HBV/HDV co-infection include viral escape and T cell exhaustion, and mimic those in other persistent human viral infections, such as hepatitis C virus (HCV), human immunodeficiency virus (HIV), and HBV mono-infection. However, compared to these larger viruses, the small HDV has perfectly adapted to evade recognition by CD8+ T cells restricted by common human leukocyte antigen (HLA) class I alleles. Furthermore, accelerated progression towards liver cirrhosis in persistent HBV/HDV co-infection was attributed to an increased immune-mediated pathology, either caused by innate pathways initiated by the interferon (IFN) system or triggered by misguided and dysfunctional T cells. These new insights into HDV-specific adaptive immunity will be discussed in this review and put into context with known well-described aspects in HBV, HCV, and HIV infections.