Helper-dependent adenoviral vector-mediated delivery of woodchuck-specific genes for alpha interferon (IFN-alpha) and IFN-gamma: IFN-alpha but not IFN-gamma reduces woodchuck hepatitis virus replication in chronic infection in vivo

Treatments for HBV: A Glimpse into the Future

The hepatitis B virus is responsible for most of the chronic liver disease and liver cancer worldwide. As actual therapeutic strategies have had little success in eradicating the virus from hepatocytes, and as lifelong treatment is often required, new drugs targeting the various phases of the hepatitis B virus (HBV) lifecycle are currently under investigation. In this review, we provide an overview of potential future treatments for HBV.

Gene Therapy for Chronic HBV-Can We Eliminate cccDNA?

Chronic infection with the hepatitis B virus (HBV) is a global health concern and accounts for approximately 1 million deaths annually. Amongst other limitations of current anti-HBV treatment, failure to eliminate the viral covalently closed circular DNA (cccDNA) and emergence of resistance remain the most worrisome. Viral rebound from latent episomal cccDNA reservoirs occurs following cessation of therapy, patient non-compliance, or the development of escape mutants. Simultaneous viral co-infections, such as by HIV-1, further complicate therapeutic interventions. These challenges have prompted development of novel targeted hepatitis B therapies. Given the ease with which highly specific and potent nucleic acid therapeutics can be rationally designed, gene therapy has generated interest for antiviral application. Gene therapy strategies developed for HBV include gene silencing by harnessing RNA interference, transcriptional inhibition through epigenetic modification of target DNA, genome editing by designer nucleases, and immune modulation with cytokines. DNA-binding domains and effectors based on the zinc finger (ZF), transcription activator-like effector (TALE), and clustered regularly interspaced short palindromic repeat (CRISPR) systems are remarkably well suited to targeting episomal cccDNA. This review discusses recent developments and challenges facing the field of anti-HBV gene therapy, its potential curative significance and the progress towards clinical application.

Measurement of Antiviral Effect and Innate Immune Response During Treatment of Primary Woodchuck Hepatocytes

An estimated 350 million people are chronically infected with hepatitis B virus (HBV), and over one million people die each year due to HBV-associated liver diseases, such as cirrhosis and liver cancer. Current therapeutics for chronic HBV infection are limited to nucleos(t)ide analogs and interferon. These anti-HBV drugs in general reduce viral load and improve the long-term outcome of infection but very rarely lead to a cure. Thus, new therapies for chronic HBV infection need to be developed by utilizing liver cell lines and primary cultures and small laboratory animals capable of replicating HBV or surrogate hepadnaviruses for antiviral testing. Natural infection with woodchuck hepatitis virus (WHV), a hepadnavirus closely related to HBV, occurs in woodchucks. Chronic WHV infection has been established over decades as a suitable model for evaluating direct-acting antivirals as well as vaccines, vaccine adjuvants, and immunotherapeutics because animals are fully immunocompetent. Before HBV-specific compounds are applied to woodchucks, they are usually tested in primary woodchuck hepatocytes (PWHs) replicating WHV at high levels for confirming drug specificity against viral or host targets. Here we describe a protocol for the isolation of PWHs from liver of WHV-infected woodchucks, maintenance in culture, and use in assays for determining antiviral efficacy, safety, and associated host innate immune response of new experimental drugs. Exemplary assays were performed with the nucleoside analog, lamivudine, and the immunomodulator, interferon-alpha.

Antiviral Efficacy and Host Innate Immunity Associated with SB 9200 Treatment in the Woodchuck Model of Chronic Hepatitis B

SB 9200, an oral prodrug of the dinucleotide SB 9000, is being developed for the treatment of chronic hepatitis B virus (HBV) infection and represents a novel class of antivirals. SB 9200 is thought to activate the viral sensor proteins, retinoic acid-inducible gene 1 (RIG-I) and nucleotide-binding oligomerization domain-containing protein 2 (NOD2) resulting in interferon (IFN) mediated antiviral immune responses in virus-infected cells. Additionally, the binding of SB 9200 to these sensor proteins could also sterically block the ability of the viral polymerase to access pre-genomic RNA for nucleic acid synthesis. The immune stimulating and direct antiviral properties of SB 9200 were evaluated in woodchucks chronically infected with woodchuck hepatitis virus (WHV) by daily, oral dosing at 15 and 30 mg/kg for 12 weeks. Prolonged treatment resulted in 2.2 and 3.7 log10 reductions in serum WHV DNA and in 0.5 and 1.6 log10 declines in serum WHV surface antigen from pretreatment level with the lower or higher dose of SB 9200, respectively. SB 9200 treatment also resulted in lower hepatic levels of WHV nucleic acids and antigen and reduced liver inflammation. Following treatment cessation, recrudescence of viral replication was observed but with dose-dependent delays in viral relapse. The antiviral effects were associated with dose-dependent and long-lasting induction of IFN-α, IFN-β and IFN-stimulated genes in blood and liver, which correlated with the prolonged activation of the RIG-I/NOD2 pathway and hepatic presence of elevated RIG-I protein levels. These results suggest that in addition to a direct antiviral activity, SB 9200 induces antiviral immunity during chronic hepadnaviral infection via activation of the viral sensor pathway.

Adaptive immunity in HBV infection

During hepatitis B virus (HBV) infection, the presence of HBV-specific antibody producing B cells and functional HBV-specific T cells (with helper or cytotoxic effects) ultimately determines HBV infection outcome. In this review, in addition to summarizing the present state of knowledge of HBV-adaptive immunity, we will highlight controversies and uncertainties concerning the HBV-specific B and T lymphocyte response, and propose future directions for research aimed at the generation of more efficient immunotherapeutic strategies.

Intrahepatic Transcriptional Signature Associated with Response to Interferon-α Treatment in the Woodchuck Model of Chronic Hepatitis B

Recombinant interferon-alpha (IFN-α) is an approved therapy for chronic hepatitis B (CHB), but the molecular basis of treatment response remains to be determined. The woodchuck model of chronic hepatitis B virus (HBV) infection displays many characteristics of human disease and has been extensively used to evaluate antiviral therapeutics. In this study, woodchucks with chronic woodchuck hepatitis virus (WHV) infection were treated with recombinant woodchuck IFN-α (wIFN-α) or placebo (n = 12/group) for 15 weeks. Treatment with wIFN-α strongly reduced viral markers in the serum and liver in a subset of animals, with viral rebound typically being observed following cessation of treatment. To define the intrahepatic cellular and molecular characteristics of the antiviral response to wIFN-α, we characterized the transcriptional profiles of liver biopsies taken from animals (n = 8-12/group) at various times during the study. Unexpectedly, this revealed that the antiviral response to treatment did not correlate with intrahepatic induction of the majority of IFN-stimulated genes (ISGs) by wIFN-α. Instead, treatment response was associated with the induction of an NK/T cell signature in the liver, as well as an intrahepatic IFN-γ transcriptional response and elevation of liver injury biomarkers. Collectively, these data suggest that NK/T cell cytolytic and non-cytolytic mechanisms mediate the antiviral response to wIFN-α treatment. In summary, by studying recombinant IFN-α in a fully immunocompetent animal model of CHB, we determined that the immunomodulatory effects, but not the direct antiviral activity, of this pleiotropic cytokine are most closely correlated with treatment response. This has important implications for the rational design of new therapeutics for the treatment of CHB.

Inhibition of hepatitis B virus replication by helper dependent adenoviral vectors expressing artificial anti-HBV pri-miRs from a liver-specific promoter

Research on applying RNA interference (RNAi) to counter HBV replication has led to identification of potential therapeutic sequences. However, before clinical application liver-specific expression and efficient delivery of these sequences remain an important objective. We recently reported short-term inhibition of HBV replication in vivo by using helper dependent adenoviral vectors (HD Ads) expressing anti-HBV sequences from a constitutively active cytomegalovirus (CMV) promoter. To develop the use of liver-specific transcription regulatory elements we investigated the utility of the murine transthyretin (MTTR) promoter for expression of anti-HBV primary microRNAs (pri-miRs). HD Ads containing MTTR promoter effected superior expression of anti-HBV pri-miRs in mice compared to HD Ads containing the CMV promoter. MTTR-containing HD Ads resulted in HBV replication knockdown of up to 94% in mice. HD Ads expressing trimeric anti-HBV pri-miRs silenced HBV replication for 5 weeks. We previously showed that the product of the codelivered lacZ gene induces an immune response, and the duration of HBV silencing in vivo is likely to be attenuated by this effect. Nevertheless, expression of anti-HBV pri-miRs from MTTR promoter is well suited to countering HBV replication and development of HD Ads through attenuation of their immunostimulatory effects should advance their clinical utility.

The anti-HBV effect mediated by a novel recombinant eukaryotic expression vector for IFN-α

BACKGROUND

Chronic hepatitis B is a primary cause of liver-related death. Interferon alpha (IFN-α) is able to inhibit the replication of hepadnavirus, and the sustained and stable expression of IFN-α at appropriate level may be beneficial to HBV clearance. With the development of molecular cloning technology, gene therapy plays a more and more important role in clinical practice. In light of the findings, an attempt to investigate the anti-HBV effects mediated by a eukaryotic expression plasmid (pSecTagB-IFN-α) in vitro was carried out.

METHODS

HBV positive cell line HepG2.2.15 and its parental cell HepG2 were transfected with pSecTagB-IFN-α or empty plasmid by using Lipofectamine™ 2000 reagent. The expression levels of IFN-α were determined by reverse transcriptase polymerase chain reaction (RT-PCR) and ELISA methods. The effects of pSecTagB-IFN-α on HBV mRNA, DNA and antigens were analyzed by real-time fluorescence quantitative PCR (qRT-PCR) and ELISA assays. RT-PCR, qRT-PCR and western blot were employed to investigate the influence of pSecTagB-IFN-α on IFN-α-induced signal pathway. Furthermore, through qRT-PCR and ELISA assays, the suppressive effects of endogenously expressed IFN-α and the combination with lamivudine on HBV were also examined.

RESULTS

pSecTagB-IFN-α could express efficiently in hepatoma cells, and then inhibited HBV replication, characterized by the decrease of HBV S gene (HBs) and HBV C gene (HBc) mRNA, the reduction of HBV DNA load, and the low contents of hepatitis B surface antigen (HBsAg) and hepatitis B e antigen (HBeAg). Mechanism research showed that the activation of Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signal pathway, the up-regulation of IFN-α-induced antiviral effectors and double-stranded (ds) RNA sensing receptors by delivering pSecTagB-IFN-α, could be responsible for these phenomena. Furthermore, pSecTagB-IFN-α vector revealed effectively anti-HBV effect than exogenously added IFN-α. Moreover, lamivudine combined with endogenously expressed IFN-α exhibited stronger anti-HBV effect than with exogenous IFN-α.

CONCLUSION

Our results showed that endogenously expressed IFN-α can effectively and persistently inhibit HBV replication in HBV infected cells. These observations opened a promising way to design new antiviral genetic engineering drugs based on IFN-α.

Molecular characterization of woodchuck CD4 (wCD4) and production of a depletion monoclonal antibody against wCD4

CD4 T cells play an important role in the immune response against hepatitis B virus (HBV) infection. Woodchucks represent an excellent animal model to study HBV infection. In this study, we characterized the cDNA sequence of woodchuck CD4 (wCD4). The deduced wCD4 protein has four extracellular immunoglobulin-like domains comparable to the other mammalian CD4 molecules. The important extracellular cysteine residues and the intracellular tyrosine protein kinase-binding site of wCD4 are also conserved. The deduced wCD4 protein shows 53-63% identity with the counterparts of other mammalians. Phylogenetic analysis indicates that wCD4 is closely related with the counterparts of primates. Two polyclonal antibodies (pAbs) and four monoclonal Abs (mAbs) against wCD4 were produced. Two pAbs and one mAbs (G2) were found to effectively suppress ConA induced proliferation in vitro. Anti-wCD4 mAb G2 depleted 60% of CD4 cells from healthy woodchucks, while the remaining CD4 cells responded well to ConA stimulation. This work provides a basis for studying CD4 T cell mediated immune responses against HBV infection in the woodchuck model.

Safety profile, efficacy, and biodistribution of a bicistronic high-capacity adenovirus vector encoding a combined immunostimulation and cytotoxic gene therapy as a prelude to a phase I clinical trial for glioblastoma

Adenoviral vectors (Ads) are promising gene delivery vehicles due to their high transduction efficiency; however, their clinical usefulness has been hampered by their immunogenicity and the presence of anti-Ad immunity in humans. We reported the efficacy of a gene therapy approach for glioma consisting of intratumoral injection of Ads encoding conditionally cytotoxic herpes simplex type 1 thymidine kinase (Ad-TK) and the immunostimulatory cytokine fms-like tyrosine kinase ligand 3 (Ad-Flt3L). Herein, we report the biodistribution, efficacy, and neurological and systemic effects of a bicistronic high-capacity Ad, i.e., HC-Ad-TK/TetOn-Flt3L. HC-Ads elicit sustained transgene expression, even in the presence of anti-Ad immunity, and can encode large therapeutic cassettes, including regulatory elements to enable turning gene expression "on" or "off" according to clinical need. The inclusion of two therapeutic transgenes within a single vector enables a reduction of the total vector load without adversely impacting efficacy. Because clinically the vectors will be delivered into the surgical cavity, normal regions of the brain parenchyma are likely to be transduced. Thus, we assessed any potential toxicities elicited by escalating doses of HC-Ad-TK/TetOn-Flt3L (1×10(8), 1×10(9), or 1×10(10) viral particles [vp]) delivered into the rat brain parenchyma. We assessed neuropathology, biodistribution, transgene expression, systemic toxicity, and behavioral impact at acute and chronic time points. The results indicate that doses up to 1×10(9) vp of HC-Ad-TK/TetOn-Flt3L can be safely delivered into the normal rat brain and underpin further developments for its implementation in a phase I clinical trial for glioma.

Therapeutic vaccination in chronic hepatitis B: preclinical studies in the woodchuck

Recommended treatment of chronic hepatitis B with interferon-α and/or nucleos(t)ide analogues does not lead to a satisfactory result. Induction of HBV-specific T cells by therapeutic vaccination or immunotherapies may be an innovative strategy to overcome virus persistence. Vaccination with commercially available HBV vaccines in patients did not result in effective control of HBV infection, suggesting that new formulations of therapeutic vaccines are needed. The woodchuck (Marmota monax) is a useful preclinical model for developing the new therapeutic approaches in chronic hepadnaviral infections. Several innovative approaches combining antiviral treatments with nucleos(t)ide analogues, DNA vaccines, and protein vaccines were tested in the woodchuck model. In this paper we summarize the available data concerning therapeutic immunization and gene therapy using recombinant viral vectors approaches in woodchucks, which show encouraging results. In addition, we present potential innovations in immunomodulatory strategies to be evaluated in this animal model.

Lipopolysaccharide-induced innate immune responses in primary hepatocytes downregulates woodchuck hepatitis virus replication via interferon-independent pathways

Our previous studies have shown that Toll-like receptor (TLR) ligands, Poly I:C and lipopolysaccharide (LPS), are able to activate non-parenchymal liver cells and trigger the production of interferon (IFN) to inhibit hepatitis B virus replication in vivo and in vitro. However, little is known about TLR-mediated cellular responses in primary hepatocytes. By the model of woodchuck hepatitis virus (WHV) infected primary woodchuck hepatocytes (PWHs), Poly I:C and LPS stimulation resulted in upregulation of cellular antiviral genes and relevant TLRs mRNA expression respectively. LPS stimulation led to a pronounced reduction of WHV replicative intermediates without a significant IFN induction. Poly I:C transfection resulted in the production of IFN and a highly increased expression of antiviral genes in PWHs and slight inhibitory effect on WHV replication. LPS could activate nuclear factor kappa B, MAPK and PI-3k/Akt pathways in PWHs. Further, inhibitors of MAPK-ERK and PI-3k/Akt pathways, but not that of IFN signalling pathway, were able to block the antiviral effect of LPS. These results indicate that IFN- independent pathways which activated by LPS are able to downregulate hepadnaviral replication in hepatocytes.

Antiviral gene therapy

This chapter describes the major gene therapeutic approaches for viral infections. The vast majority of published approaches target severe chronic viral infections such as hepatitis B or C and HIV infection. Two basic gene therapy strategies are introduced here. The first involves the expression of a protein or an RNA that inhibits viral replication by targeting crucial steps of the viral life cycle or by interfering with a cellular factor required for virus replication. The major limitation of this approach is that primary levels of gene modification have generally not been sufficient to reduce the availability of target cells permissive for virus replication to a level that significantly decreases overall viral load. Thus, investigators have banked on the expectation that gene-protected cells have a sufficient selective advantage to accumulate and gain prevalence over time, a prediction that so far could not be confirmed in clinical trials. In vivo levels of gene modification can be improved, however, by introducing an additional selectable marker. In addition, a secreted antiviral gene product that exerts a bystander effect could significantly reduce overall virus replication despite relatively low levels of gene modification. In addition to these direct antiviral approaches, several strategies have been developed that employ or aim to enhance host immune responses. The innate immune response has been enhanced, for example, by the in vivo expression of interferons. Alternatively, T cells can be grafted with recombinant receptors to boost adaptive virus-specific immunity. These approaches are especially promising for chronic virus infection, where natural immune responses are evidently not sufficient to effectively control virus replication.

APOBEC and iNOS are not the main intracellular effectors of IFN-gamma-mediated inactivation of Hepatitis B virus replication

BACKGROUND/AIM

Interferon-gamma (IFN-gamma) produced by activated T-cells is the principle mediator of non-cytolytic Hepatitis B virus (HBV) inactivation; however the intracellular pathways responsible are poorly defined. We investigated the role of IFN-gamma-inducible nitric oxide synthase (iNOS) and APOBEC3 (A3) enzyme family in the inhibition of HBV replication by IFN-gamma.

METHODS

Hepatoma-cell lines transfected with HBV DNA were treated with IFN-gamma. Viral replication, iNOS and A3 mRNAs were quantitated by TaqManPCR and the direct nitric oxide (NO) effect on HBV replication was investigated using an NO-donor. A3G antiviral activity was verified by co-transfection with its inhibitor, human immunodeficiency virus (HIV)-associated virion infectivity factor (Vif).

RESULTS

IFN-gamma caused a dose-dependent reduction (>50%) of HBV DNA in the absence of cytotoxicity. Although iNOS mRNA increased 45-fold in IFN-gamma treated cells, NO2- was not detectable in supernatants and the use of an NO-donor did not inhibit HBV replication. A3 enzyme mRNAs varied between cells and were >10-fold higher in lymphocytes than in liver tissue. IFN-gamma up-regulated A3G mRNA by three-fold, associated with significant HBV DNA decrease. However, A3G degradation by Vif did not abolish the antiviral effect of IFN-gamma against HBV.

CONCLUSIONS

IFN-gamma inhibits HBV replication and up-regulates both iNOS and A3G. However, other pathways appear to have a greater role in IFN-gamma-induced HBV inactivation in the liver.

Molecular characterization of woodchuck type I interferons and their expression by woodchuck peripheral blood lymphocytes

Interferon (IFN)-alpha and -beta are important antiviral mediators. IFN-alpha is widely used for the treatment of chronic hepatitis B. In our previous studies, a subtype of woodchuck IFN-alpha (wIFN-alpha) was characterized and has been shown to be active in suppressing the replication of woodchuck hepatitis virus (WHV) in vitro and vivo. Here, we refined the analysis of the IFN-alpha/beta system of the woodchuck and studied the expression of wIFN-alpha/beta in peripheral blood lymphocytes (PBLs) from naïve and WHV-infected woodchucks. A number of wIFN-alpha genes were sequenced and could be classified into 10 subtypes and 3 pseudotypes. The biological activity of different subtypes of wIFN-alpha was demonstrated by their ability to protect woodchuck cells against encephalomyocarditis virus infection and to induce MxA expression in woodchuck cells. Additionally, a partial sequence of wIFN-beta was characterized. A subtyping method for wIFN-alpha based on restriction length polymorphism analysis was developed. Further, the expression of wIFN by woodchuck PBLs after stimulation with polyI/C was investigated. The maximal production of wIFN by woodchuck PBLs occurred within the first 48 h after addition poly I/C. The wIFN-alpha subtypes 1, 4, and 5 were found to be produced by poly I/C-stimulated woodchuck PBLs, indicating a selective expression of wIFN-alpha subtypes. PBLs from chronically WHV-infected woodchucks showed a reduced ability to produce wIFN when stimulated with poly I/C. The results suggest that woodchucks with chronic WHV infection have impaired immunological responses to poly I/C.

The interferon-alpha gene family of Marmota himalayana, a Chinese marmot species with susceptibility to woodchuck hepatitis virus infection

The interferon-alpha (IFN-alpha) gene family is an important part of the immune system. Recombinant interferon-alpha is widely used to treat viral hepatitis and malignant diseases. Marmota himalayana has been found to be susceptible to woodchuck hepatitis virus, a virus genetically related to hepatitis B virus (HBV), and is suitable as an animal model for studies on HBV infection. Here, the IFN-alpha gene family of M. himalayana (cwIFN-alpha) was characterized. Sequence data indicate that the cwIFN-alpha family consists of at least 8 functional sequences and 6 pseudogenes with high homology within the family and to IFN-alpha of Marmota monax, a related species and well-established animal model. The recombinant cwIFN-alpha subtypes were expressed and tested to be active in viral protection assay and to induce expression of MxA in a species-specific manner. This work provides essential information for future work on testing new therapeutic approaches of HBV infection based on IFN-alpha in M. himalayana.

Immunomodulation as an option for the treatment of chronic hepatitis B virus infection: preclinical studies in the woodchuck model

New therapeutic approaches for chronic hepatitis B virus infection based on immunomodulation are now under investigation. The woodchuck model for hepatitis B virus infection has emerged as a useful animal model for the evaluation of such approaches, after developing necessary assays and reagents for immunologic studies in this model. Conventional and novel vaccines such as DNA vaccines were tested in woodchucks for their ability to induce protective immune responses against challenge infection with the woodchuck hepatitis virus (WHV). Furthermore, immunotherapeutic approaches for the control of chronic hepadnaviral infection were evaluated in woodchucks. Immunizations with WHV proteins and DNA vaccines led to the development of antibodies to the WHV surface antigen and to a significant decrease of viral load in chronically WHV-infected woodchucks. Viral vector-mediated gene transfer was explored for the delivery of antiviral cytokines IFN-alpha in woodchucks and resulted in the decrease of viral replication. It is now generally accepted that a combination of antiviral treatment and immunization will be necessary to achieve successful immunomodulation with a long-term control of chronic hepatitis B virus infection.

The woodchuck as an animal model for pathogenesis and therapy of chronic hepatitis B virus infection

This review describes the woodchuck and the woodchuck hepatitis virus (WHV) as an animal model for pathogenesis and therapy of chronic hepatitis B virus (HBV) infection and disease in humans. The establishment of woodchuck breeding colonies, and use of laboratory-reared woodchucks infected with defined WHV inocula, have enhanced our understanding of the virology and immunology of HBV infection and disease pathogenesis, including major sequelae like chronic hepatitis and hepatocellular carcinoma. The role of persistent WHV infection and of viral load on the natural history of infection and disease progression has been firmly established along the way. More recently, the model has shed new light on the role of host immune responses in these natural processes, and on how the immune system of the chronic carrier can be manipulated therapeutically to reduce or delay serious disease sequelae through induction of the recovery phenotype. The woodchuck is an outbred species and is not well defined immunologically due to a limitation of available host markers. However, the recent development of several key host response assays for woodchucks provides experimental opportunities for further mechanistic studies of outcome predictors in neonatal- and adult-acquired infections. Understanding the virological and immunological mechanisms responsible for resolution of self-limited infection, and for the onset and maintenance of chronic infection, will greatly facilitate the development of successful strategies for the therapeutic eradication of established chronic HBV infection. Likewise, the results of drug efficacy and toxicity studies in the chronic carrier woodchucks are predictive for responses of patients chronically infected with HBV. Therefore, chronic WHV carrier woodchucks provide a well-characterized mammalian model for preclinical evaluation of the safety and efficacy of drug candidates, experimental therapeutic vaccines, and immunomodulators for the treatment and prevention of HBV disease sequelae.

Gene therapy for viral hepatitis

Hepatitis B and C infections are two of the most prevalent viral diseases in the world. Existing therapies against chronic viral hepatitis are far from satisfactory due to low response rates, undesirable side effects and selection of resistant viral strains. Therefore, new therapeutic approaches are urgently needed. This review, after briefly summarising the in vitro and in vivo systems for the study of both diseases and the genetic vehicles commonly used for liver gene transfer, examines the existing status of gene therapy-based antiviral strategies that have been employed to prevent, eliminate or reduce viral infection. In particular, the authors focus on the results obtained in clinical trials and experimental clinically relevant animal models.

Hepatitis C virus genotype 1b chimeric replicon containing genotype 3 NS5A domain

Infections with hepatitis C virus (HCV) genotype 3 exhibit differences in clinical phenotype including an increase in response to interferon therapy and development of steatosis. To initiate studies on genotype 3, we created a chimeric genotype 1b replicon containing a genotype 3a NS5A domain. The chimera was capable of efficient colony formation after the selection of a novel dominant adaptive mutation. Thus, domains from highly different strains can interact to form a functional replicase. A new genotype 1a replicon was constructed as well. Genotype specific influence on interferon sensitivity was examined using genotype 1a, 1b and chimeric 1b-3a replicons. The genotype 3a NS5A domain did not increase the sensitivity of the chimeric replicon to IFNalpha. The results suggest that NS5A is not sufficient to convey the increased IFNalpha response by genotype 3 or the replicon model is not capable of mimicking the events involved in increased sustained viral response.

IFNgamma expression inhibits LHBs storage disease and ground glass hepatocyte appearance, but exacerbates inflammation and apoptosis in HBV surface protein-accumulating transgenic livers

BACKGROUND/AIMS

Interferon gamma (IFNgamma) controls hepatitis B virus replication. As systemic application may cause severe adverse effects, approaches of liver-directed IFNgamma gene therapy may represent an attractive alternative for treatment of chronic viral hepatitis B and thus needs testing in vivo in suitable animal models.

METHODS

We therefore crossbred Alb-1HBV transgenic mice overexpressing the large HBV surface protein (LHBs) in their livers and developing LHBs storage disease and ground glass hepatocyte appearance with SAP-IFNgamma transgenic animals previously shown to exhibit constitutive hepatic IFNgamma expression, and analyzed the resulting double-transgenic offspring.

RESULTS

We found that IFNgamma coexpression significantly reduced hepatic LHBs expression and thereby inhibited hepatocellular LHBs storage disease and ground glass hepatocyte appearance. The beneficial antiviral IFNgamma effects as observed in Alb1-HBV SAP-IFNgamma double-transgenic livers were associated with significantly elevated serum ALT concentrations, massive mononuclear cell infiltrates, appearance of Councilman bodies, and increased alpha-PARP (poly(ADP-ribose) polymerase cleavage).

CONCLUSIONS

Exacerbation of hepatic necroinflammation and increased hepatocellular apoptosis rate in IFNgamma-expressing Alb1-HBV transgenic livers suggest that special precautions be taken for testing approaches of liver-specific IFNgamma expression in patients with chronic hepatitis B.

[New therapies for hepatitis C]

Hepatitis C virus is an important public health threat, not only because of the high prevalence of this infection in western and third world countries, but also because of the high rate of resistance to the available antiviral therapy that consists on the use of pegylated interferon plus ribavirin. Currently, new forms of therapy are being developed based on a more precise knowledge of the structure and function of the viral proteins and of the strategies used by the virus to escape the immune and interferon systems. The new therapeutic approaches aim at different objectives: a) the inhibition of viral replication by blocking the viral protease and/or replicase; b) the use of other types of interferon with more potent antiviral effect, c) the induction of a specific anti-viral immune response by means of immunomodulatory compounds or therapeutic vaccination, d) the blockade of "de novo" infection of other cells with neutralizing antibodies, e) the induction of a antiviral state in the liver by transferring to this organ the gene of interferon and/or immunostimulating cytokines.

IFN-alpha gene therapy for woodchuck hepatitis with adeno-associated virus: differences in duration of gene expression and antiviral activity using intraportal or intramuscular routes

Gene delivery of IFN-alpha to the liver may represent an interesting strategy to maximize its antiviral efficacy and reduce side effects. We used a recombinant adeno-associated virus (AAV) encoding woodchuck IFN-alpha (AAV-IFN) to treat animals with chronic woodchuck hepatitis virus infection. The vector was given by intraportal or intramuscular route. Long-term transgene expression was detected after intraportal administration of an AAV encoding luciferase. In contrast, in the majority of the animals that received AAV-IFN through the portal vein, the expression of IFN-alpha was transient (30-40 days) and was associated with a significant but transient decrease in viral load. One animal, in which hepatic production of IFN-alpha persisted at high levels, died because of bone marrow toxicity. The disappearance of IFN-alpha expression correlated with the disappearance of AAV genomes from the liver. Intramuscular administration of AAV-IFN resulted in prolonged but fluctuating expression of the cytokine with no significant antiviral effect. In summary, this report shows that long-term expression of IFN-alpha in muscle is feasible but higher interferon levels might be needed to control viral replication. On the other hand, IFN-alpha gene delivery to the liver using an AAV vector induces a significant but transient antiviral effect in the woodchuck model.

Gutless adenovirus: last-generation adenovirus for gene therapy

Last-generation adenovirus vectors, also called helper-dependent or gutless adenovirus, are very attractive for gene therapy because the associated in vivo immune response is highly reduced compared to first- and second-generation adenovirus vectors, while maintaining high transduction efficiency and tropism. Nowadays, gutless adenovirus is administered in different organs, such as the liver, muscle or the central nervous system achieving high-level and long-term transgene expression in rodents and primates. However, as devoid of all viral coding regions, gutless vectors require viral proteins supplied in trans by a helper virus. To remove contamination by a helper virus from the final preparation, different systems based on the excision of the helper-packaging signal have been generated. Among them, Cre-loxP system is mostly used, although contamination levels still are 0.1-1% too high to be used in clinical trials. Recently developed strategies to avoid/reduce helper contamination were reviewed.

Lamivudine plus interleukin-12 combination therapy in chronic hepatitis B: antiviral and immunological activity

Interleukin-12 (IL-12) is an immunomodulatory cytokine that promotes cellular immunity. Pre-clinical data suggest that IL-12 inhibits hepatitis B virus (HBV) replication by stimulating interferon-gamma (IFN-gamma) production. We investigated whether a combination treatment with lamivudine plus recombinant human interleukin-12 (rhIL-12) will result in a greater and prolonged suppression of HBV replication in comparison with lamivudine monotherapy. Fifteen patients with HBeAg-positive chronic hepatitis B were randomized to receive either lamivudine alone for 24 weeks (group 1); combination of lamivudine for 16 weeks and rhIL-12 (200 ng/kg twice weekly), starting 4 weeks after initiation of lamivudine, for 20 weeks (group 2), or the same schedule as for group 2, with lamivudine and a higher dose of rhIL-12 (500 ng/kg, group 3). Serum HBV DNA levels, T-cell proliferation, frequency of virus-specific T-cells, and IFN-gamma production were evaluated serially during and 24 weeks posttreatment. Lamivudine plus rhIL-12/500 showed greater antiviral activity than lamivudine monotherapy. However, after stopping lamivudine in groups 2 and 3, serum HBV DNA increased significantly despite continuing rhIL-12 administration. Lamivudine plus rhIL-12 treatment was associated with a greater increase in virus-specific T-cell reactivity, IFN-gamma production, and an inverse correlation between the frequency of IFN-gamma-producing CD4+ T-cells and viremia. The T-cell proliferative response to HBcAg did not differ between the three groups. In conclusion, the addition of IL-12 to lamivudine enhances T-cell reactivity to HBV and IFN-gamma production. However, IL-12 does not abolish HBV replication in HBeAg-positive patients and does not maintain inhibition of HBV replication after lamivudine withdrawal.

Fluctuation of the cytokine expression in the liver during the chronic woodchuck hepatitis virus (WHV) infection is not related to viral load

The woodchuck together with the woodchuck hepatitis virus (WHV) is an excellent model to study the pathogenesis of hepadnaviral infections. Chronic WHV infection causes severe liver disease and hepatocellular carcinoma in woodchucks. The mechanism of viral clearance is not fully understood, interferons seem to play a major role in down-regulating viral replication prior to elimination of infected hepatocytes. We investigated on the pattern of cytokine and T-cell-marker expression in livers of woodchucks chronically infected with WHV. RNase-protection-assay (RPA) was used to determine mRNA of woodchuck specific genes (TNF-alpha, IFN-gamma, IL-15, CD3, CD4, CD8). Serial liver biopsies were performed daily or weekly in eight chronic WHV-carrier woodchucks. Cytokine/T-cell-marker expression differed significantly between the time points up to +/-50% within each woodchuck. The different expression patterns of cytokines or T-cell-markers did not correlate to the (weak) fluctuations in the viremia but may explain the observed fluctuations in the WHV/HBV-load in chronically infected individuals. Furthermore, we observed associations between cytokine and T-cell-marker expression. The marginal fluctuations in viremia during the chronic infection may indicate, that, once the chronic hepadnaviral infection is established, cytokines/interferons expressed endogenously (i.e. not vector-borne or injected) play only a minor role.

Regulated and liver-specific tamarin alpha interferon gene delivery by a helper-dependent adenoviral vector

Gene therapy approaches based on liver-restricted and regulated alpha interferon (IFN-alpha) expression, recently shown to be effective in different murine hepatitis models, appear promising alternatives to inhibit hepatitis C virus (HCV) replication in patients and minimize side effects. Tamarins (Saguinus species) infected by GB virus B (GBV-B) are considered a valid surrogate model for hepatitis C to study the biology of HCV infection and the development of new antiviral drugs. To test the efficacy of local delivery and expression of IFN-alpha in this model, we have developed HD-TET-tIFN, a helper-dependent adenovirus vector expressing tamarin IFN-alpha (tIFN) under the control of the tetracycline-inducible transactivator rtTA2s-S2. Expression of tIFN was successfully induced both in vitro and in vivo in rodents by doxycycline administration with consequent activation of IFN-responsive genes. More importantly, tIFN efficiently inhibited GBV-B replicon in a Huh-7 hepatoma cell line at low HD-TET-tIFN doses. A certain degree of transcriptional control of tIFN was achieved in tamarins injected with HD-TET-tIFN, but under the conditions used in this study, infection and replication of GBV-B were only delayed and not totally abrogated upon virus challenge. Hepatic delivery and regulated expression of IFN-alpha appear to be a possible approach for the cure of hepatitis, but this approach requires more studies to increase its efficacy. To our knowledge, this is the first report showing a regulated gene expression in a nonhuman primate hepatitis model.

Combination of nucleoside analogues in the treatment of chronic hepatitis B virus infection: lesson from experimental models

Owing to the persistence of hepatitis B virus (HBV) and the selection of drug-resistant mutants, a new concept of antiviral therapy for chronic hepatitis B relies on the combination of nucleoside analogues. In experimental models of HBV infection, several key points concerning these combinations were addressed. (i) Is it possible to achieve a synergic antiviral effect with polymerase inhibitors? (ii) Is it possible to impact on intracellular viral covalently closed circular DNA? (iii) What is the impact of the cross-resistance patterns of the different nucleoside analogues? (iv) What is the effect of viral load suppression on the restoration of specific antiviral cellular responses? The clinical impact of these key issues is discussed in the perspective of new clinical trials.