Severe necroinflammatory reaction caused by natural killer cell-mediated Fas/Fas ligand interaction and dendritic cells in human hepatocyte chimeric mouse

Hepatitis B virus-specific human stem cell memory T cells differentiate into cytotoxic T cells and eradicate HBV-infected hepatocytes in mice

Chronic infection with the hepatitis B virus (HBV) induces progressive hepatic impairment. Achieving complete eradication of the virus remains a formidable challenge. Cytotoxic T lymphocytes, specific to viral antigens, either exhibit a numerical deficiency or succumb to an exhausted state in individuals chronically afflicted with HBV. The comprehension of the genesis and dissemination of stem cell memory T cells (TSCMs) targeting HBV remains inadequately elucidated. We identified TSCMs in subjects with chronic HBV infection and scrutinized their efficacy in a murine model with human hepatocyte transplants, specifically the TK-NOG mice. TSCMs were discerned in all subjects under examination. Introduction of TSCMs into the HBV mouse model precipitated a severe necro-inflammatory response, resulting in the elimination of human hepatocytes. TSCMs may constitute a valuable tool in the pursuit of a remedial therapy for HBV infection.

A novel cDNA-uPA/SCID/Rag2-/- /Jak3-/- mouse model for hepatitis virus infection and reconstruction of human immune system

Although human hepatocyte-transplanted immunodeficient mice support infection with hepatitis viruses, these mice fail to develop viral hepatitis due to the lack of an adaptive immune system. In this study, we generated new immunodeficiency cDNA-urokinase-type plasminogen activator (uPA)/SCID/Rag2^-/- /Jak3^-/- mice and established a mouse model with both a humanized liver and immune system. Transplantation of human hepatocytes with human leukocyte antigen (HLA)-A24 resulted in establishment of a highly replaced liver in cDNA-uPA/SCID/Rag2^-/- /Jak3^-/- mice. These mice were successfully infected with hepatitis B virus (HBV) and hepatitis C virus (HCV) for a prolonged period and facilitate analysis of the effect of anti-HCV drugs. Administration of peripheral blood mononuclear cells (PBMCs) obtained from an HLA-A24 donor resulted in establishment of 22.6%-81.3% human CD45-positive mononuclear cell chimerism in liver-infiltrating cells without causing graft-versus-host disease in cDNA-uPA/SCID/Rag2^-/- /Jak3^-/- mice without human hepatocyte transplantation. When mice were transplanted with human hepatocytes and then administered HLA-A24-positive human PBMCs, an alloimmune response between transplanted human hepatocytes and PBMCs occurred, with production of transplanted hepatocyte-specific anti-HLA antibody. In conclusion, we succeeded in establishing a humanized liver/immune system characterized by an allo-reaction between transplanted human immune cells and human liver using a novel cDNA-uPA/SCID/Rag2^-/- /Jak3^-/- mouse. This mouse model can be used to generate a chronic hepatitis mouse model with a human immune system with application not only to hepatitis virus virology but also to investigation of the pathology of post-transplantation liver rejection.

Group 1 ILCs regulate T cell-mediated liver immunopathology by controlling local IL-2 availability

Group 1 innate lymphoid cells (ILCs), which comprise both natural killer (NK) cells and ILC1s, are important innate effectors that can also positively and negatively influence adaptive immune responses. The latter function is generally ascribed to the ability of NK cells to recognize and kill activated T cells. Here, we used multiphoton intravital microscopy in mouse models of hepatitis B to study the intrahepatic behavior of group 1 ILCs and their cross-talk with hepatitis B virus (HBV)-specific CD8⁺ T cells. We found that hepatocellular antigen recognition by effector CD8⁺ T cells triggered a prominent increase in the number of hepatic NK cells and ILC1s. Group 1 ILCs colocalized and engaged in prolonged interactions with effector CD8⁺ T cells undergoing hepatocellular antigen recognition; however, they did not induce T cell apoptosis. Rather, group 1 ILCs constrained CD8⁺ T cell proliferation by controlling local interleukin-2 (IL-2) availability. Accordingly, group 1 ILC depletion, or genetic removal of their IL-2 receptor a chain, considerably increased the number of intrahepatic HBV-specific effector CD8⁺ T cells and the attendant immunopathology. Together, these results reveal a role for group 1 ILCs in controlling T cell-mediated liver immunopathology by limiting local IL-2 concentration and have implications for the treatment of chronic HBV infection.

In Vivo Mouse Models for Hepatitis B Virus Infection and Their Application

Despite the availability of effective vaccination, hepatitis B virus (HBV) infection continues to be a major challenge worldwide. Research efforts are ongoing to find an effective cure for the estimated 250 million people chronically infected by HBV in recent years. The exceptionally limited host spectrum of HBV has limited the research progress. Thus, different HBV mouse models have been developed and used for studies on infection, immune responses, pathogenesis, and antiviral therapies. However, these mouse models have great limitations as no spread of HBV infection occurs in the mouse liver and no or only very mild hepatitis is present. Thus, the suitability of these mouse models for a given issue and the interpretation of the results need to be critically assessed. This review summarizes the currently available mouse models for HBV research, including hydrodynamic injection, viral vector-mediated transfection, recombinant covalently closed circular DNA (rc-cccDNA), transgenic, and liver humanized mouse models. We systematically discuss the characteristics of each model, with the main focus on hydrodynamic injection mouse model. The usefulness and limitations of each mouse model are discussed based on the published studies. This review summarizes the facts for considerations of the use and suitability of mouse model in future HBV studies.

Immunopathology of Chronic Hepatitis B Infection: Role of Innate and Adaptive Immune Response in Disease Progression

More than 250 million people are living with chronic hepatitis B despite the availability of highly effective vaccines and oral antivirals. Although innate and adaptive immune cells play crucial roles in controlling hepatitis B virus (HBV) infection, they are also accountable for inflammation and subsequently cause liver pathologies. During the initial phase of HBV infection, innate immunity is triggered leading to antiviral cytokines production, followed by activation and intrahepatic recruitment of the adaptive immune system resulting in successful virus elimination. In chronic HBV infection, significant alterations in both innate and adaptive immunity including expansion of regulatory cells, overexpression of co-inhibitory receptors, presence of abundant inflammatory mediators, and modifications in immune cell derived exosome release and function occurs, which overpower antiviral response leading to persistent viral infection and subsequent immune pathologies associated with disease progression towards fibrosis, cirrhosis, and hepatocellular carcinoma. In this review, we discuss the current knowledge of innate and adaptive immune cells transformations that are associated with immunopathogenesis and disease outcome in CHB patients.

Novel Immune Subsets and Related Cytokines: Emerging Players in the Progression of Liver Fibrosis

Liver fibrosis is a pathological process caused by persistent chronic injury of the liver. Kupffer cells, natural killer (NK) cells, NKT cells, and dendritic cells (DCs), which are in close contact with T and B cells, serve to bridge innate and adaptive immunity in the liver. Meanwhile, an imbalanced inflammatory response constitutes a challenge in liver disease. The dichotomous roles of novel immune cells, including T helper 17 (Th17), regulatory T cells (Tregs), mucosa-associated invariant T cells (MAIT), and innate lymphoid cells (ILCs) in liver fibrosis have gradually been revealed. These cells not only induce damage during liver fibrosis but also promote tissue repair. Hence, immune cells have unique, and often opposing, roles during the various stages of fibrosis. Due to this heterogeneity, the treatment, or reversal of fibrosis through the target of immune cells have attracted much attention. Moreover, activation of hepatic stellate cells (HSCs) constitutes the core of fibrosis. This activation is regulated by various immune mediators, including Th17, Th22, and Th9, MAIT, ILCs, and γδ T cells, as well as their related cytokines. Thus, liver fibrosis results from the complex interaction of these immune mediators, thereby complicating the ability to elucidate the mechanisms of action elicited by each cell type. Future developments in biotechnology will certainly aid in this feat to inform the design of novel therapeutic targets. Therefore, the aim of this review was to summarize the role of specific immune cells in liver fibrosis, as well as biomarkers and treatment methods related to these cells.

Abatacept treatment for patients with severe acute hepatitis caused by hepatitis B virus infection-Pilot study

Although glucocorticoids have been used for immunosuppression of patients with primary hepatitis B virus (HBV) infection-induced severe hepatitis, the treatment is associated with a high frequency of adverse events. We conducted a pilot study for evaluating the efficacy and safety of abatacept, a cytotoxic T lymphocyte antigen-4 immunoglobulin (CTLA4), for acute hepatitis B. Five patients with severe acute hepatitis B (prothrombin activity ≤ 60%) were treated for immunosuppression by abatacept. Four patients received abatacept concurrently with methylprednisolone, and another patient was treated with abatacept alone. Rapid decrease in serum alanine aminotransferase levels, increase in prothrombin activity and improvement of general condition were obtained in four out of five patients. The patient with the most severe hepatitis underwent liver transplantation due to exacerbation of hepatitis in spite of treatment with both abatacept and methylprednisolone. None of the patients developed significant adverse events associated with the use of abatacept. Hepatitis B surface antigen (HBsAg) became negative in all five patients. The effect of abatacept and methylprednisolone for severe hepatitis B was compared using a mouse model. Rapid reduction in mouse serum HBV DNA and human albumin levels and elevation of serum interferon-gamma and granzyme A levels were observed in HBV-infected human hepatocyte-transplanted immunodeficient mice that were administered human peripheral blood mononuclear cells. These hepatocyte injuries were inhibited to a greater extent by abatacept compared to methylprednisolone. Abatacept might be an effective therapy alternative to methylprednisolone to reduce acute massive liver damage for patients with severe acute hepatitis caused by HBV infection.

Microarray gene expression profiling provides insights into functions of TIPE2 in HBV-related apoptosis

Tumor necrosis factor-α-induced protein-8 like-2 (TNFAIP8L2, TIPE2), a member of TNFAIP8 family, functions as a regulator in inflammation. Our previous studies showed that TIPE2 can negatively regulate HBV-specific CD8⁺ T lymphocyte functions. But the effect of TIPE2 on the apoptosis of HBV-infected hepatocytes which is very important for eliminating viruses remains unclear. Using gene expression microarray analysis, we find that TIPE2 deficiency can regulate the expression of apoptotic genes in liver tissues from HBV hydrodynamic injection (HI) mouse model. TIPE2 protein was detected in TUNEL staining positive hepatocytes in HBV-infected C57 mice. Interestingly, the TIPE2 expressed hepatocytes were just the HBV infected cells. Furthermore, TIPE2 upregulates the mRNA levels of FasL, Bim and TNFRsF1b which promote cells death, when TIPE2 was transfected into HepG2 cells in vitro. As a result, TIPE2 overexpression cells showed a higher number of apoptotic cells and increased level of cleavage caspase3 compared to controls. Those results indicate that TIPE2 participates in HBV infection by regulating apoptosis of virus-infected hepatocytes.

STAT3 directly regulates NKp46 transcription in NK cells of HBeAg-negative CHB patients

NK cells play an important role in early control of HBV infection. The function of NK cells is inhibited in chronic hepatitis B virus (CHB) infection, although the underlying mechanism remains unknown. We found that the expression of STAT3 decreased in peripheral NK cells of CHB patients, and was associated with low levels of degranulation and IFN-γ secretion. In addition, STAT3 levels were positively correlated with cytolysis-associated molecules and antiviral cytokines, such as CD107a, granzyme B, perforin, and IFN-γ. HBsAg directly inhibited the expression and activation of STAT3 in NK cells, and knocking down STAT3 expression in NK cells inhibited proliferation, decreased cyclin d1 levels, and suppressed responsiveness to IL-21 stimulation. Furthermore, STAT3 directly bound to the promoter of NKp46, an important activating receptor of NK cells, to regulate its transcription and expression. Taken together, our findings indicate that STAT3 is an important positive regulator of NK cells, and provide a new mechanism of NK cell dysfunction in CHB.

Kctd9 Deficiency Impairs Natural Killer Cell Development and Effector Function

We previously showed that potassium channel tetramerization domain containing 9 (KCTD9) is aberrantly expressed in natural killer (NK) cells in patients with hepatitis B virus-associated acute-on-chronic liver failure and mice with experimental fulminant hepatitis. However, the mechanism underlying the regulation of NK cell function and fulminant hepatitis progression by KCTD9 is unknown. Here, we investigated the role of Kctd9 in regulation of early development, maturation, and function of NK cells using Kctd9-knockout mice. Compared to wild-type mice, Kctd9-deficient mice exhibited impaired NK cell lineage commitment, as evidenced by selective reduction in the refined NK progenitors, and incomplete NK cell maturation, as manifested by a higher proportion of CD11b^- NK cells and a lower percentage of CD11b⁺ NK cells with high proliferative potential. Moreover, Kctd9-depleted NK cells displayed insufficient IFN-γ production, degranulation, and granzyme B production in response to cytokine stimulation, and attenuated cytotoxicity to tumor cells in vitro. The defect in NK cells was further supported by ameliorated liver damage and improved survival in Kctd9-deficient mice following murine hepatitis virus strain-3 (MHV-3) infection, which otherwise leads to immune-mediated fulminant hepatitis, a phenotype homologous to that caused by NK cell depletion in wild-type mice. Further investigation to identify the underlying mechanism revealed that Kctd9 deficiency hindered the expression of transcription factors, including Ets1, Nfil3, Eomes, and Id2 in NK cells. Collectively, our data reveal that Kctd9 acts as a novel regulator for NK cell commitment, maturation, and effector function.

CTL-associated and NK cell-associated immune responses induce different HBV DNA reduction patterns in chronic hepatitis B patients

The activation of hepatitis B virus (HBV)-related hepatitis is associated with both natural killer (NK) cells and cytotoxic T lymphocytes (CTLs). We analyzed the association between the immune response and changes in the proportion of Pre-S deletion variants. We quantified Pre-S deleted HBV (HBV-del) and wild-type HBV (HBV-wt) DNA levels in sera obtained from HBV-infected mice and chronic hepatitis B patients. In chronic hepatitis B patients, the HBV-del proportion usually increased during or after ALT elevation but did not occur during all ALT elevations. To clarify this difference in the immunological responses, we performed in vivo analyses using HBV-infected human hepatocyte chimeric mice. Although HBV-del proportions did not change in mice with NK cell-associated hepatitis or in mice treated with entecavir, the proportions sharply increased in mice with CTL-associated hepatitis. Furthermore, the number of patients in which HBV-del proportions were greater than 5% was significantly higher in chronic hepatitis B patients than in asymptomatic carriers (P = 0.023). We identified associations between virological response in chronic hepatitis B patients and two different immune responses. The proportion of HBV-del variants could be a useful biomarker for distinguishing between chronic hepatitis and asymptomatic carriers.

NK cells in liver homeostasis and viral hepatitis

As an important member of the innate immune system, natural killer (NK) cells are well known for their rapid and efficient immune responses against infectious agents and tumors. NK cells are widely distributed throughout the body and are particularly enriched within the liver, where they display unique phenotypic and functional properties, playing important roles in various liver diseases. Herein, we present an overview of liver NK cell properties with regard to phenotype, function, and subset composition at steady state, and we also summarize the complex reciprocal interactions between liver NK cells and other cell types within the local environment of the liver. We also provide an overview of recent advances demonstrating the roles of NK cells in viral hepatitis, including a discussion of NK cell altered states and their beneficial versus harmful effects during hepatitis B virus and hepatitis C virus infection.

Combinational immune-cell therapy of natural killer cells and sorafenib for advanced hepatocellular carcinoma: a review

Background

High prevalence of hepatocellular carcinoma (HCC) and typically poor prognosis of this disease that lead to late stage diagnosis when potentially curative therapies are least effective; therefore, development of an effective and systematic treatment is an urgent requirement.

Main body

In this review, several current treatments for HCC patients and their advantages or disadvantages were summarized. Moreover, various recent preclinical and clinical studies about the performances of "two efficient agents, sorafenib or natural killer (NK) cells", against HCC cells were investigated. In addition, the focus this review was on the chemo-immunotherapy approach, correlation between sorafenib and NK cells and their effects on the performance of each other for better suppression of HCC.

Conclusion

It was concluded that combinational therapy with sorafenib and NK cells might improve the outcome of applied therapeutic approaches for HCC patients. Finally, it was also concluded that interaction between sorafenib and NK cells is dose and time dependent, therefore, a careful dose and time optimizing is necessary for development of a combinational immune-cell therapy.

Modulators of innate immunity as novel therapeutics for treatment of chronic hepatitis B

The first line defense mechanisms against viral infection are mediated by the innate immune system. Viral components are detected by infected cells and/or innate immune cells that express different sensory receptors. They in turn mediate induction of direct antiviral mechanisms and further modulation of innate and adaptive immune responses. For evading the innate system, most viruses have evolved efficient mechanisms to block sensing and/or antiviral functions of the innate response. Interestingly, hepatitis B virus (HBV) seems to act like a stealth virus that escapes cell intrinsic antiviral mechanisms through avoiding recognition by the innate system rather than blocking its effector functions. In line with this concept, agonistic activation of innate immunity has emerged as a promising novel anti-HBV therapy approach with several compounds having advanced to the clinical stage.

Interferon-stimulated gene of 20 kDa protein (ISG20) degrades RNA of hepatitis B virus to impede the replication of HBV in vitro and in vivo

Hepatitis B virus (HBV) barely induces host interferon (IFN)-stimulated genes (ISGs), which allows efficient HBV replication in the immortalized mouse hepatocytes as per human hepatocytes. Here we found that transfection of Isg20 plasmid robustly inhibits the HBV replication in HBV-infected hepatocytes irrespective of IRF3 or IFN promoter activation. Transfection of Isg20 is thus effective to eradicate HBV in the infected hepatocytes. Transfection of HBV genome or ε-stem of HBV pgRNA (active pgRNA moiety) failed to induce Isg20 in the hepatocytes, while control polyI:C (a viral dsRNA analogue mimic) activated MAVS pathway leading to production of type I IFN and then ISGsg20 via the IFN-α/β receptor (IFNAR). Consistently, addition of IFN-α induced Isg20 and partially suppressed HBV replication in hepatocytes. Chasing HBV RNA, DNA and proteins by blotting indicated that ISG20 expression decreased HBV RNA and replicative DNA in HBV-transfected cells, which resulted in low HBs antigen production and virus titer. The exonuclease domains of ISG20 mainly participated in HBV-RNA decay. In vivo hydrodynamic injection, ISG20 was crucial for suppressing HBV replication without degrading host RNA in the liver. Taken together, ISG20 acts as an innate anti-HBV effector that selectively degrades HBV RNA and blocks replication of infectious HBV particles. ISG20 would be a critical effector for ameliorating chronic HBV infection in the IFN therapy.

Animal models of HBV infection

The mechanisms determining hepatitis B virus (HBV) persistence and pathogenesis are not fully elucidated, but appear to be multi-factorial. Current medication to repress viral replication is available; however, the unique replication strategies employed by HBV enable the virus to persist within the infected hepatocytes. Consequently, cure is rarely achieved. Progresses in HBV research and preclinical testing of antiviral agents have been limited by the narrow species- and tissue-tropism of the virus, the paucity of infection models available and the restrictions imposed by the use of chimpanzees, the only animals fully susceptible to HBV infection. Mice are not HBV permissive but major efforts have focused on the development of mouse models of HBV replication and infection, such as the generation of humanized mice. By presenting the different animal models available, this review will highlight the most important and clinically relevant findings that have been retrieved from the respective systems.

Interplay between the Hepatitis B Virus and Innate Immunity: From an Understanding to the Development of Therapeutic Concepts

The hepatitis B virus (HBV) infects hepatocytes, which are the main cell type composing a human liver. However, the liver is enriched with immune cells, particularly innate cells (e.g., myeloid cells, natural killer and natural killer T-cells (NK/NKT), dendritic cells (DCs)), in resting condition. Hence, the study of the interaction between HBV and innate immune cells is instrumental to: (1) better understand the conditions of establishment and maintenance of HBV infections in this secondary lymphoid organ; (2) define the role of these innate immune cells in treatment failure and pathogenesis; and (3) design novel immune-therapeutic concepts based on the activation/restoration of innate cell functions and/or innate effectors. This review will summarize and discuss the current knowledge we have on this interplay between HBV and liver innate immunity.

Development of mouse models for analysis of human virus infections

Viruses usually exhibit strict species-specificity as a result of co-evolution with the host. Thus, in mouse models, a great barrier exists for analysis of infections with human-tropic viruses. Mouse models are unlikely to faithfully reproduce the human immune response to viruses or viral compounds and it is difficult to evaluate human therapeutic efficacy with antiviral reagents in mouse models. Humans and mice essentially have different immune systems, which makes it difficult to extrapolate mouse results to humans. In addition, apart from immunological reasons, viruses causing human diseases do not always infect mice because of species tropism. One way to determine tropism would be a virus receptor that is expressed on affected cells. The development of gene-disrupted mice and Tg mice, which express human receptor genes, enables us to analyze several viral infections in mice. Mice are, indeed, susceptible to human viruses when artificially infected in receptor-supplemented mice. Although the mouse cells less efficiently permit viral replication than do human cells, the models for analysis of human viruses have been established in vivo as well as in vitro, and explain viral pathogenesis in the mouse systems. In most systems, however, nucleic acid sensors and type I interferon suppress viral propagation to block the appearance of infectious manifestation. We herein review recent insight into in vivo antiviral responses induced in mouse infection models for typical human viruses.

Interferon alpha treatment stimulates interferon gamma expression in type I NKT cells and enhances their antiviral effect against hepatitis C virus

Interferon (IFN) inhibits hepatitis C virus (HCV) replication through up-regulation of intrahepatic IFN-stimulated gene expression but also through activation of host immune cells. In the present study, we analyzed the immune cell-mediated antiviral effects of IFN-α using HCV-infected mice. Urokinase-type plasminogen activator (uPA)-severe combined immunodeficiency (SCID) mice with transplanted human hepatocytes were infected with genotype 1b HCV and injected with human peripheral blood mononuclear cells (PBMCs). IFN-α treatment following human PBMC transplantation resulted in a significant reduction in serum HCV RNA titers and a higher human CD45-positive mononuclear cell chimerism compared to mice without human PBMC transplantation. In mice with human PBMCs treated with IFN-α, serum concentrations of IFN-γ increased, and natural killer T (NKT) cells, especially type I NKT cells, produced IFN-γ. Mice in which IFN-γ signaling was blocked using antibody or in which transplanted PBMCs were depleted for type I NKT cells showed similar levels of anti-HCV effect compared with mice treated only with IFN-α. These results show that IFN-α stimulates IFN-γ expression in type 1 NKT cells and enhances the inhibition of HCV replication. We propose that type 1 NKT cells might represent a new therapeutic target for chronic hepatitis C patients.

miR-223 Deficiency Protects against Fas-Induced Hepatocyte Apoptosis and Liver Injury through Targeting Insulin-Like Growth Factor 1 Receptor

The biological functions and molecular mechanisms of miR-223 action in liver cells and liver diseases remain unclear. We therefore determined the effect and mechanism of action of miR-233 in Fas-induced hepatocyte apoptosis and liver injury. Wild-type (WT) and miR-223 knockout (KO) mice were treated i.p. with 0.5 μg/g body weight anti-Fas antibody Jo2, and the animals were monitored for survival and the extent of liver injury. Although WT mice died 4 to 6 hours after Jo2 injection (n = 6), all of the miR-223 KO mice (n = 6) survived. In comparison to WT mice, the miR-223 KO mice showed resistance to Fas-induced liver injury, as indicated by less tissue damage under histopathological examination, fewer apoptotic hepatocytes under caspase-3 immunostaining, and less elevation of serum transaminases. miR-223 KO livers showed less caspase-3, caspase-8, and caspase-9 activation and less poly (ADP-ribose) polymerase cleavage compared with WT livers (P < 0.05). Furthermore, tail vein injection of miR-223 lentiviral vector to miR-223 KO mice restored Jo2-induced liver injury. Transfection of miR-223 KO hepatocytes with miR-223 mimic enhanced Jo2-induced activation of caspase-3, caspase-8, and caspase-9, whereas transfection of WT hepatocytes with the miR-223 inhibitor attenuated Jo2-induced apoptosis. These findings demonstrate that miR-223 deficiency protects against Fas-induced hepatocyte apoptosis and liver injury. Further in vitro and in vivo data indicate that miR-223 regulates Fas-induced hepatocyte apoptosis and liver injury by targeting the insulin-like growth factor 1 receptor.

Human liver chimeric mice as a new model of chronic hepatitis E virus infection and preclinical drug evaluation

BACKGROUND & AIMS

Hepatitis E virus (HEV) is a major cause of acute hepatitis as well as chronic infection in immunocompromised individuals; however, in vivo infection models are limited. The aim of this study was to establish a small animal model to improve our understanding of HEV replication mechanisms and permit the development of effective therapeutics.

METHODS

UPA/SCID/beige mice repopulated with primary human hepatocytes were used for infection experiments with HEV genotype (GT) 1 and 3. Virological parameters were determined at the serological and intrahepatic level by real time PCR, immunohistochemistry and RNA in situ hybridization.

RESULTS

Establishment of HEV infection was achieved after intravenous injection of stool-derived virions and following co-housing with HEV-infected animals but not via inoculation of serum-derived HEV. GT 1 infection resulted in a rapid rise of viremia and high stable titres in serum, liver, bile and faeces of infected mice for more than 25 weeks. In contrast, viremia in GT 3 infected mice developed more slowly and displayed lower titres in all analysed tissues as compared to GT 1. HEV-infected human hepatocytes could be visualized using HEV ORF2 and ORF3 specific antibodies and HEV RNA in situ hybridization probes. Finally, six-week administration of ribavirin led to a strong reduction of viral replication in the serum and liver of GT 1 infected mice.

CONCLUSION

We established an efficient model of HEV infection to test the efficacy of antiviral agents and to exploit mechanisms of HEV replication and interaction with human hepatocytes in vivo.

Experimental in vitro and in vivo models for the study of human hepatitis B virus infection

Chronic infection with the hepatitis B virus (HBV) affects an estimate of 240 million people worldwide despite the availability of a preventive vaccine. Medication to repress viral replication is available but a cure is rarely achieved. The narrow species and tissue tropism of the virus and the lack of reliable in vitro models and laboratory animals susceptible to HBV infection, have limited research progress in the past. As a result, several aspects of the HBV life cycle as well as the network of virus host interactions occurring during the infection are not yet understood. Only recently, the identification of the functional cellular receptor enabling HBV entry has opened new possibilities to establish innovative infection systems. Regarding the in vivo models of HBV infection, the classical reference was the chimpanzee. However, because of the strongly restricted use of great apes for HBV research, major efforts have focused on the development of mouse models of HBV replication and infection such as the generation of humanized mice. This review summarizes the animal and cell culture based models currently available for the study of HBV biology. We will discuss the benefits and caveats of each model and present a selection of the most important findings that have been retrieved from the respective systems.

The role of innate immunity in the immunopathology and treatment of HBV infection

In this review we give a brief update on sensors recently determined to be capable of detecting HBV, and examine how the virus represses the induction of pro-inflammatory cytokines like type I interferons. We overview cellular components of innate immunity that are present at high frequencies in the liver, and discuss their roles in HBV control and/or pathogenesis. We argue that many innate effectors have adaptive-like features or can exert specific effects on HBV through immunoregulation of T cells. Finally we consider current and possible future strategies to manipulate innate immunity as novel approaches towards a functional cure for HBV.

Natural Killer Cells and Liver Fibrosis

In the 40 years since the discovery of natural killer (NK) cells, it has been well established that these innate lymphocytes are important for early and effective immune responses against transformed cells and infections with different pathogens. In addition to these classical functions of NK cells, we now know that they are part of a larger family of innate lymphoid cells and that they can even mediate memory-like responses. Additionally, tissue-resident NK cells with distinct phenotypical and functional characteristics have been identified. Here, we focus on the phenotype of different NK cell subpopulations that can be found in the liver and summarize the current knowledge about the functional role of these cells with a special emphasis on liver fibrosis. NK cell cytotoxicity can contribute to liver damage in different forms of liver disease. However, NK cells can limit liver fibrosis by killing hepatic stellate cell-derived myofibroblasts, which play a key role in this pathogenic process. Therefore, liver NK cells need to be tightly regulated in order to balance these beneficial and pathological effects.

Deletion of Mir155 prevents Fas-induced liver injury through up-regulation of Mcl-1

Fas-induced apoptosis is involved in diverse liver diseases. Herein, we investigated the effect of Mir155 deletion on Fas-induced liver injury. Wild-type (WT) mice and Mir155 knockout (KO) mice were i.p. administered with the anti-Fas antibody (Jo2) to determine animal survival and the extent of liver injury. After Jo2 injection, the Mir155 KO mice exhibited prolonged survival versus the WT mice (P < 0.01). The Mir155 KO mice showed lower alanine aminotransferase and aspartate aminotransferase levels, less liver tissue damage, fewer apoptotic hepatocytes, and lower liver tissue caspase 3/7, 8, and 9 activities compared with the WT mice, indicating that Mir155 deletion prevents Fas-induced hepatocyte apoptosis and liver injury. Hepatocytes isolated from Mir155 KO mice also showed resistance to Fas-induced apoptosis, in vitro. Higher protein level of myeloid cell leukemia-1 (Mcl-1) was also observed in Mir155 KO hepatocytes compared to WT hepatocytes. A miR-155 binding site was identified in the 3'-untranslated region of Mcl-1 mRNA; Mcl1 was identified as a direct target of miR-155 in hepatocytes. Consistently, pretreatment with a siRNA specific for Mcl1 reversed Mir155 deletion-mediated protection against Jo2-induced liver tissue damage. Finally, restoration of Mir155 expression in Mir155 KO mice abolished the protection against Fas-induced hepatocyte apoptosis. Taken together, these findings demonstrate that deletion of Mir155 prevents Fas-induced hepatocyte apoptosis and liver injury through the up-regulation of Mcl1.

Tissue-Resident NK Cells Mediate Ischemic Kidney Injury and Are Not Depleted by Anti-Asialo-GM1 Antibody

NK cells are innate lymphoid cells important for immune surveillance, identifying and responding to stress, infection, and/or transformation. Whereas conventional NK (cNK) cells circulate systemically, many NK cells reside in tissues where they appear to be poised to locally regulate tissue function. In the present study, we tested the contribution of tissue-resident NK (trNK) cells to tissue homeostasis by studying ischemic injury in the mouse kidney. Parabiosis experiments demonstrate that the kidney contains a significant fraction of trNK cells under homeostatic conditions. Kidney trNK cells developed independent of NFIL3 and T-bet, and they expressed a distinct cell surface phenotype as compared with cNK cells. Among these, trNK cells had reduced asialo-GM1 (AsGM1) expression relative to cNK cells, a phenotype observed in trNK cells across multiple organs and mouse strains. Strikingly, anti-AsGM1 Ab treatment, commonly used as an NK cell-depleting regimen, resulted in a robust and selective depletion of cNKs, leaving trNKs largely intact. Using this differential depletion, we tested the relative contribution of cNK and trNK cells in ischemic kidney injury. Whereas anti-NK1.1 Ab effectively depleted both trNK and cNK cells and protected against ischemic/reperfusion injury, anti-AsGM1 Ab preferentially depleted cNK cells and failed to protect against injury. These data demonstrate unanticipated specificity of anti-AsGM1 Ab depletion on NK cell subsets and reveal a new approach to study the contributions of cNK and trNK cells in vivo. In total, these data demonstrate that trNK cells play a key role in modulating local responses to ischemic tissue injury in the kidney and potentially other organs.

Human Cytotoxic T Lymphocyte-Mediated Acute Liver Failure and Rescue by Immunoglobulin in Human Hepatocyte Transplant TK-NOG Mice

Hepatitis B virus (HBV)-specific cytotoxic T lymphocytes (CTLs) are critical in eliminating infection. We developed an animal model in which HBV-infected human hepatocytes are targeted by HBV-specific CTLs. After HBV inoculation in human hepatocyte-transplanted herpes simplex virus type-1 thymidine kinase-NOG mice, human peripheral blood mononuclear cells (PBMCs) were administered, and albumin, HBV DNA, alanine aminotransferase (ALT), and cytokine levels were analyzed. Histopathological and flow-cytometric analysis of infiltrating human immune cells were performed, and the efficacy of CTL-associated antigen-4 immunoglobulin (CTLA4Ig) against liver damage was evaluated. PBMC treatment resulted in massive hepatocyte damage with elevation of ALT, granzyme A, and gamma interferon and decrease in albumin and HBV DNA. The number of liver-infiltrating human lymphocytes and CD8-positive cells was significantly higher in HBV-infected mice. HBV-specific CTLs were detected by core and polymerase peptide-major histocompatibility complex-tetramer, and the population of regulatory T cells was significantly decreased in HBV-infected mice. Serum hepatitis B surface (HBs) antigen became negative, and HBs antibody appeared. CTLA4Ig treatment strongly inhibited infiltration of mononuclear cells. CTLA4Ig treatment will be used to treat patients who develop severe acute hepatitis B to prevent liver transplantation or lethality. This animal model is useful for virological and immunological analysis of HBV infection and to develop new therapies for severe acute hepatitis B.

IMPORTANCE

Without liver transplantation, some HBV-infected patients will die from severe liver damage due to acute overreaction of the immune system. No effective treatment exists, due in part to the lack of a suitable animal model. An animal model is necessary to investigate the mechanism of hepatitis and to develop therapeutic strategies to prevent acute liver failure in HBV infection. We developed an animal model in which HBV-infected human hepatocytes are targeted by human HBV-specific CTLs. In this model, HBV-infected human hepatocytes were transplanted into severely immunodeficient NOG mice in order to reconstruct elements of the human immune system. Using this model, we found that CTL-associated antigen-4 immunoglobulin was able to suppress damage to HBV-infected hepatocytes, suggesting an approach to treatment. This animal model is useful for virological and immunological analysis of HBV infection and to develop new therapies for severe acute hepatitis B.

Natural killer cells in hepatitis B virus infection

Natural killer cells are a unique type of lymphocytes with cytotoxic capacity, and play important roles against tumors and infections. Recently, natural killer cells have been increasingly valued in their effects in hepatitis B virus infection. Since hepatitis B virus is not cytopathic, the subsequent antiviral immune responses of the host are responsible for sustaining the liver injury, which may result in cirrhosis and even hepatocellular carcinoma. Many studies have confirmed that natural killer cells participate in anti-hepatitis B virus responses both in the early phase after infection and in the chronic phase via cytolysis, degranulation, and cytokine secretion. However, natural killer cells play dichotomic roles: they exert antiviral and immunoregulatory functions whilst contribute to the pathogenesis of liver injury. Here, we review the roles of natural killer cells in hepatitis B virus infection, introducing novel therapeutic strategies for controlling hepatitis B virus infection via the modulation of natural killer cells.

Effect of Puerarin on Expression of Fas/FasL mRNA in Pulmonary Injury induced by Ischemia-Reperfusion in Rabbits

The effect of puerarin (Pur) on expressions of Fas/FasL mRNAs in pulmonary ischemia and reperfusion injury (PIRI) in rabbit was investigated. The sole side lung ischemia and reperfusion model was used. Rabbits were randomly divided into three groups, a sham operated group (sham, n = 10), PIR group (IR, n =30) and PIR + Pur group (Pur, n =30). Changes of several parameters including apoptotic index (AI), wet to dry ratio of lung tissue weight (W/D) and index of quantitative assessment of histologic lung injury (IQA) were measured after 60, 180 and 300 minutes of reperfusion. Meanwhile, the location and expression of Fas/FasL mRNA were investigated. Lung tissue was prepared for light microscopic and electron microscopic observation after 60, 180 and 300 minutes of reperfusion. Compared with group IR, Fas/FasL mRNAs were slightly expressed in intima and extima of small pulmonary artery, alveoli, and bronchiole epithelia in group Pur. The values of AI, W/D and IQA were significantly lower than those in group IR after 60, 180, and 300 minutes of reperfusion in lung tissue ( P <0.01 or P <0.05). Meanwhile, the abnormal changes in lung tissue morphology were markedly less in group Pur. Puerarin notably protects lung from PIRI by inhibiting Fas/FasL mRNA expression and decreasing lung cell apoptosis in rabbits.

Role of natural kill cells in hepatitis B virus infection

Natural killer (NK) cells are a unique group of lymphocytes with cytotoxicity, playing an important role in anti-tumor and anti-infection activities. Recently, NK cells are increasingly recognized to play a role during hepatitis B virus (HBV) infection. Studies have confirmed NK cells participate in anti-HBV responses by secreting cytokines, mediating apoptosis and killing target cells, indicating a potential strategy for controlling HBV infection via regulation of NK cell functions. This review discusses the contribution of NK cells to HBV elimination, liver injury, and other parts of immune system and the formulation of new therapeutic strategies.

Mouse models of hepatitis B and delta virus infection

Liver disease associated to persistent infection with the hepatitis B virus (HBV) continues to be a major health problem of global impact. Therapeutic regimens currently available can efficiently suppress HBV replication; however, the unique replication strategies employed by HBV permit the virus to persist within the infected hepatocytes. As a consequence, relapse of viral activity is commonly observed after cessation of treatment with polymerase inhibitors. Among the HBV chronically infected patients, more than 15million patients are estimated to be co-infected with the hepatitis delta virus (HDV), a defective satellite virus that needs the HBV envelope for propagation. No specific drugs are currently available against HDV, while nucleos(t)ide analogs are not effective against HDV replication. Since chronic HBV/HDV co-infection leads to the most severe form of chronic viral hepatitis in men, a better understanding of the molecular mechanisms of HDV-mediated pathogenesis and the development of improved therapeutic approaches is urgently needed. The obvious limitations imposed by the use of great apes and the paucity of robust experimental models of HBV infection have hindered progresses in understanding the complex network of virus-host interactions that are established in the course of HBV and HDV infections. This review focuses on summarizing recent advances obtained with well-established and more innovative experimental mouse models, giving emphasis on the strength of infection systems based on the reconstitution of the murine liver with human hepatocytes, as tools for elucidating the whole life cycle of HBV and HDV, as well as for studies on interactions with the infected human hepatocytes and for preclinical drug evaluation.

NK cells in hepatitis B virus infection: a potent target for immunotherapy

Viruses, including hepatitis B virus (HBV), are the most prevalent and infectious agents that lead to liver disease in humans. Hepatocellular carcinoma (HCC) and cirrhosis of the liver are the most serious complications arising from prolonged forms of hepatitis B. Previous studies demonstrated that patients suffering from long-term HBV infections are unable to eradicate HBV from hepatocytes completely. The mechanisms responsible for progression of these forms of infection have not yet been clarified. However, it seems that there are differences in genetic and immunological parameters when comparing patients to subjects who successfully clear HBV infections, and these may represent the causes of long-term infection. Natural killer (NK) cells, the main innate immune cells that target viral infections, play important roles in the eradication of HBV from hepatocytes. NK cells carry several stimulatory and inhibitor receptors, and binding of receptors with their ligands results in activation and suppression of NK cells, respectively. The aim of this review is to address the recent information regarding NK cell phenotype, functions and modifications in hepatitis B. This review addresses the recent data regarding the roles of NK cells as novel targets for immunotherapies that target hepatitis B infection. It also discusses the potential to reduce the risk of HCC or cirrhosis of the liver by targeting NK cells.

Direct-acting antivirals for the treatment of chronic hepatitis C: open issues and future perspectives

Currently, two direct-acting antivirals (DAAs) show well-established efficacy against hepatitis C virus (HCV), namely, first-wave protease inhibitors telaprevir and boceprevir. Most clinical trials have examined DAAs in combination with standard of care (SOC) regimens. Future therapeutic drugs were divided into three categories. They are second-wave protease inhibitors, second-generation protease inhibitors, and polymerase inhibitors. Second-wave protease inhibitors are more improved form and can be administered once a day. Oral drug combinations can be favored because interferon (IFN) not only has to be given as intradermal injection, but also can cause several serious side effects. Combination of drugs with different mechanisms shows a good sustained virological response (SVR). But several mutations are associated with viral resistance to DAAs. Therefore, genotypic resistance data may provide insights into strategies aimed at maximizing SVR rates and minimizing resistance. Combined drug regimens are necessary to prevent the emergence of drug-resistant HCV. Many promising DAA candidates have been identified. Of these, a triple regimen containing sofosbuvir shows promise, and treatment with daclatasvir plus asunaprevir yields a high SVR rate (95%). Oral drug combinations will be standard of care in the near future.

Natural killer cells in liver disease

Natural killer (NK) cells are enriched in lymphocytes within the liver and have unique phenotypic features and functional properties, including tumor necrosis factor-related apoptosis-inducing ligand-dependent cytotoxicity and specific cytokine profiles. As a key component of innate immunity in the liver, NK cells perform critical roles in host defense against pathogens and tumors through their natural cytotoxicity and cytokine production, and they also act as regulatory cells by engaging in reciprocal interactions with other types of liver cells through cell-to-cell contact and the production of cytokines. Accumulating evidence from the last decade suggests that NK cells play an important role in controlling viral hepatitis, liver fibrosis, and liver tumorigenesis, but also contribute to the pathogenesis of liver injury and inflammation. The characterization of intrahepatic NK cell functions has not only helped us to better understand the pathogenesis of liver disease, but has also revealed new therapeutic targets for managing this disease.

NK cells: a double-edged sword in chronic hepatitis B virus infection

There is natural enrichment of NK cells in the human liver and this intrahepatic predominance underscores their potential importance in the control of infections with hepatotropic viruses such as hepatitis B virus (HBV). The contribution of innate components during chronic HBV infection has been a relatively under-investigated area. However, recent data have highlighted that NK cells are capable of exerting antiviral and immunoregulatory functions whilst also contributing to the pathogenesis of liver injury via death receptor pathways. We will present an overview of current knowledge regarding the complex biology of NK cells in the context of their antiviral versus pathogenic role in chronic hepatitis B as a clinically relevant avenue for further investigation.

Experimental models and therapeutic approaches for HBV

Liver disease associated to persistent infection with the hepatitis B virus (HBV) continues to be a major health problem of global impact. In spite of the existence of an effective vaccine, approximately 360 million people are chronically infected worldwide, who are at high risk of developing liver cirrhosis and hepatocellular carcinoma. Although current therapeutic regimens can efficiently suppress viral replication, the unique replication strategies employed by HBV permit the virus to persist within the infected hepatocytes. As a consequence, relapse of viral activity is commonly observed after cessation of treatment with polymerase inhibitors. The narrow host range of HBV has hindered progresses in understanding specific steps of HBV replication and the development of more effective therapeutic strategies aiming at achieving sustained viral control and, eventually, virus eradication. This review will focus on summarizing recent advances obtained with well-established and more innovative experimental models, giving emphasis on the strength of the different systems as tools for elucidating distinct aspects of HBV persistence and for the development of new therapeutic approaches.