Enhanced replication contributes to enrichment of hepatitis B virus with a deletion in the core gene

An antiviral drug-resistant mutant of hepatitis B virus with high replication capacity in association with a large in-frame deletion in the preS1 region of viral surface gene

We amplified a full-length hepatitis B virus (HBV) genome from the serum of a chronic hepatitis B patient who experienced virological breakthrough with high HBV DNA titer following adefovir (ADV) therapy. The PCR product was cloned and sequencing of the six clones revealed an isolate of C2 subgenotype. Mutation(s) in the polymerase gene responsible for ADV resistance included rtA181T (all clones) and rtN236T (four clones). The rtA181T mutation caused the W172* nonsense mutation in the overlapping S gene. In addition, all the clones harbored another nonsense mutation in the S gene (C69*) and a 207nt in-frame deletion in the preS1 region. These clones were converted to a 1.1mer construct for transient transfection of Huh7 cells. All the clones were deficient in hepatitis B surface antigen production. Three clones had similar levels of DNA replication. Comparison with a wild-type clone of the same genotype revealed a higher intracellular level of replicative DNA for clone c4, which was reduced by putting back the deleted 207nt, but not by co-transfection with an expression construct for the three surface proteins to rescue virion production. The HBcAg expression of the c4 and c4+207nt clones was mainly in the nucleus. Co-transfection with the L/M/S proteins expression construct did not alter the distribution of core. Clone c4 showed a significantly decreased susceptibility to ADV, a mild reduction in susceptibility to lamivudine and tenofovir, but remained sensitive to entecavir. In conclusion, this is an unusual ADV-resistant HBV isolate harboring two nonsense mutations in the S gene and a large in-frame deletion in the preS1 region, but still retains a high replication phenotype, which can provide a platform for recombinant vector construction.

Suppression of hepatitis B virus antigen production and replication by wild-type HBV dependently replicating HBV shRNA vectors in vitro and in vivo

Chronic infection with hepatitis B virus (HBV), a small DNA virus that replicates by reverse transcription of a pregenomic (pg) RNA precursor, greatly increases the risk for terminal liver disease. RNA interference (RNAi) based therapy approaches have shown potential to overcome the limited efficacy of current treatments. However, synthetic siRNAs as well as small hairpin (sh) RNAs expressed from non-integrating vectors require repeated applications; integrating vectors suffer from safety concerns. We pursue a new concept by which HBV itself is engineered into a conditionally replicating, wild-type HBV dependent anti-HBV shRNA vector. Beyond sharing HBV's hepatocyte tropism, such a vector would be self-renewing, but only as long as wild-type HBV is present. Here, we realized several important aspects of this concept. We identified two distinct regions in the 3.2 kb HBV genome which tolerate replacement by shRNA expression cassettes without compromising reverse transcription when complemented in vitro by HBV helper constructs or by wild-type HBV; a representative HBV shRNA vector was infectious in cell culture. The vector-encoded shRNAs were active, including on HBV as target. A dual anti-HBV shRNA vector delivered into HBV transgenic mice, which are not susceptible to HBV infection, by a chimeric adenovirus-HBV shuttle reduced serum hepatitis B surface antigen (HBsAg) up to ∼4-fold, and virus particles up to ∼20-fold. Importantly, a fraction of the circulating particles contained vector-derived DNA, indicating successful complementation in vivo. These data encourage further investigations to prove antiviral efficacy and the predicted self-limiting vector spread in a small animal HBV infection model.

HBV polymerase overexpression due to large core gene deletion enhances hepatoma cell growth by binding inhibition of microRNA-100

Different types of hepatitis B virus (HBV) core gene deletion mutants were identified in chronic hepatitis B patients. However, their clinical roles in different stages of natural chronic HBV infection remained unclear. To address this issue, HBV core genes were sequenced in three gender- and age-matched patient groups diagnosed as chronic hepatitis, cirrhosis and hepatocellular carcinoma (HCC), respectively. Functional analysis of the identified mutants was performed. A novel type of large-fragment core gene deletion (LFCD) was identified exclusively in HCC patients and significantly associated with unfavorable postoperative survival. The presence of LFCDs resulted in generation of precore-polymerase fusion protein or brought the polymerase reading frame under direct control of HBV precore/core promoter, leading to its over-expression. Enhanced cell proliferation and increased tumorigenicity in nude mice were found in hepatoma cells expressing LFCDs. Because of the epsilon-binding ability of HBV polymerase, we hypothesized that the over-expressed polymerase carrying aberrant amino-terminal sequence could bind to cellular microRNAs. Screening of a panel of microRNAs revealed physical association of a precore-polymerase fusion protein with microRNA-100. A binding inhibition effect on microRNA-100 by the precore-polymerase fusion protein with up-regulation of its target, polo-like kinase 1 (PLK1), was discovered. The binding inhibition and growth promoting effects could be reversed by overexpressing microRNA-100. Together, HCC patients carrying hepatitis B large-fragment core gene deletion mutants had an unfavorable postoperative prognosis. The growth promoting effect was partly due to polymerase overexpression, leading to binding inhibition of microRNA-100 and up-regulation of PLK1.

Substance abuse, HIV-1 and hepatitis

During the course of human immunodeficiency virus type 1 (HIV-1) disease, the virus has been shown to effectively escape the immune response with the subsequent establishment of latent viral reservoirs in specific cell populations within the peripheral blood (PB) and associated lymphoid tissues, bone marrow (BM), brain, and potentially other end organs. HIV-1, along with hepatitis B and C viruses (HBV and HCV), are known to share similar routes of transmission, including intravenous drug use, blood transfusions, sexual intercourse, and perinatal exposure. Substance abuse, including the use of opioids and cocaine, is a significant risk factor for exposure to HIV-1 and the development of acquired immune deficiency syndrome, as well as HBV and HCV exposure, infection, and disease. Thus, coinfection with HIV-1 and HBV or HCV is common and may be impacted by chronic substance abuse during the course of disease. HIV- 1 impacts the natural course of HBV and HCV infection by accelerating the progression of HBV/HCV-associated liver disease toward end-stage cirrhosis and quantitative depletion of the CD4+ T-cell compartment. HBV or HCV coinfection with HIV-1 is also associated with increased mortality when compared to either infection alone. This review focuses on the impact of substance abuse and coinfection with HBV and HCV in the PB, BM, and brain on the HIV-1 pathogenic process as it relates to viral pathogenesis, disease progression, and the associated immune response during the course of this complex interplay. The impact of HIV-1 and substance abuse on hepatitis virus-induced disease is also a focal point.

Effects of hepatitis B virus mutations on its replication and liver disease severity

Hepatitis B virus (HBV), nowadays, is one of the major human pathogens worldwide. Approximately, 400 million people worldwide have chronic HBV infection. Only 5% of persons infected during adulthood develop chronic infection. The reverse is true for those infected at birth or in early childhood, i.e. more than 90% of these persons progress to chronic infection. Currently, eight different genotypes o f HBV have been identified, differing in nucleotide sequence by greater than 8%. In addition, numerous subgenotypes have a l s o been recognized based on the nucleotide sequence variability of 4- 8%. It has invariably been found that these genotypes and mutations play a pivotal role in the liver disease aggravation and virus replication. The precore mutations (G1896A) and the double mutation (T1762/A1764) in the basal core promoter are important mutations that alter expression of the hepatitis B e antigen (HBeAg). The HBeAg is important for establishing viral persistence. The precore G1896A mutation abrogates the expression of HBeAg. Numerous other mutations alter the disease severity and progression. It is predictive that the infected patient has high risk of hepatocellular carcinoma if the genotype C is incriminated or if HBV possesses basal core promoter double mutation. Association of the remaining genotypes have been noted but with less degree than genotype C. Phenotypic assays of the different HBV protein markers with different molecular techniques illustrate the replication efficiency of the virus in cell lines. This review will discuss various mutations into their association with liver disease severity and progression as well as virus replication.

In vitro replication phenotype of a novel (-1G) hepatitis B virus variant associated with HIV co-infection

The -1G mutant HBV is more prevalent in individuals co-infected with HIV/HBV than in individuals infected with HBV alone and in some cases is the dominant virus in circulation. This mutant is created by the deletion of a dGMP (-1G) from the guanine rich homopolymer sequence located at nts 2,085-2,090 (numbering from EcoRI site as position 1) in the HBV core gene. This deletion causes a frameshift generating a premature stop codon at (64) Asn in the HBV core gene (codon 93 in the precore gene), that truncates the precore protein, precursor of the secreted hepatitis B "e" antigen (HBeAg), and the core protein which forms the viral nucleocapsid. However, the replication phenotype of the -1G mutant HBV is unknown. An in vitro cell culture model in which hepatoma cells were transiently transfected with infectious cDNAs was used to show that the -1G mutant HBV is incapable of autonomous replication and, as expected, replication was restored to wild-type (wt) levels by supplying HBV core protein in trans. Although the -1G mutation had no deleterious effect on intracellular HBV-DNA levels, high levels of -1G mutant HBV relative to wt HBV reduced virus secretion and HBeAg secretion relative to empty vector controls. Importantly, the -1G mutant HBV also caused intracellular retention of truncated precore protein in the endoplasmic reticulum (ER) and Golgi apparatus. Together, these effects may be contributing to the increased pathology observed in the setting of HIV/HBV co-infection.

HBV mutations in untreated HIV-HBV co-infection using genomic length sequencing

HIV infection has a significant impact on the natural progression of hepatitis B virus (HBV) related liver disease. In HIV-HBV co-infected patients, little is known about mutations in the HBV genome, which can influence severity of liver disease. The aim of this study was to characterize and to determine the frequency of known clinically significant mutations in the HBV genomes from HIV-HBV co-infected patients and from HBV mono-infected patients. To accomplish this, genomic length HBV sequencing was performed in highly-active anti-retroviral therapy (HAART)-naïve HIV-HBV co-infected patients (n=74) and in anti-HBV therapy-naïve HBV mono-infected patients (n=55). The frequency of HBV mutations differed between the co-infected and mono-infected patients when comparing patients with the same genotype. BCP mutations A1762T and G1764A were significantly more frequent in HBV genotype C mono-infection and the -1G frameshift was significantly more frequent in co-infection and was only observed in HBV genotype A co-infection. PreS2 deletions were observed more frequently in the setting of co-infection. Further work is needed to determine if these mutational patterns influence the differences in liver disease progression in HIV-HBV co-infected and HBV mono-infected patients.

Hepatitis B virus as a gene delivery vector activating foreign antigenic T cell response that abrogates viral expression in mouse models

Chronic hepatitis B virus (HBV) infection is characterized by functionally impaired T cell responses. To ensure active immunotherapy, the immune response must be switched from exhausted T cells to functional effectors that can attain the liver and cure the viral infection. We thus designed a recombinant HBV (rHBV) containing a modified viral core gene that specifically delivers a foreign antigenic polyepitope to the liver. This recombinant virus could only be self-maintained in hepatocytes already infected by HBV through capsid complementation. A strong foreign epitope-specific T cell response was first primed in the periphery by way of DNA immunization in human leukocyte antigen (HLA)-A2/DR1 transgenic mice. After the hydrodynamic (hyd.) injection of rHBV, expression of the foreign antigenic polyepitope in hepatocytes attracted/reactivated a vigorous T cell response in situ. Most liver-infiltrating CD8(+) T cells proved to be functional effectors. Following DNA priming and hyd. injection, the rHBV-based expression of hepatitis B surface antigen (HBsAg) in mouse liver was almost completely inhibited without causing major liver injury. Studies in HBsAg/HLA-A2/DR1 transgenic mice further validated our approach.

CONCLUSION

For the first time, HBV was used as a gene delivery vector, which strongly triggered functional T cell response and subsequently controlled the viral expression in the liver of surrogate mouse models for HBV infection. It might represent an innovative and promising strategy of active immunotherapy during HBV persistent infection. This concept could even be more generally extended to other chronic viral diseases.

Dynamic changes of HBV quasispecies and deletion patterns in a chronic hepatitis B patient

Hepatitis B virus (HBV) infection is a dynamic process during which molecular variants are selected continuously to adapt to changes. In addition to drug resistant mutations, sequential antiviral therapy may also lead to the selection of deleted mutants. To investigate this process, the following samples were collected from a patient who failed lamivudine therapy and then was switched to adefovir dipivoxil. HBV DNA was sequenced at two separate regions; a 1 kb region of reverse transcriptase (RT) and a 1.5 kb region encompassing the C gene and part of the preS gene. Sequence analysis of the RT region showed that the prevailing lamivudine resistant mutations were reduced after switching to adefovir dipivoxil, and ultimately the mutations were undetectable. Quasispecies distribution and deletion patterns in the C and preS regions were also different between the two antiviral therapies. In lamivudine-treated samples, wild-type strains (57.7%) were dominant and deletions in the preS region were observed. However, in the subsequent therapy involving adefovir dipivoxil, a virus population harboring 81 and 96 bp deletions (86%) in the C gene prevailed. Both major deletions encompassed T- and B-cell epitopes. Meanwhile, the frequencies of the preS deletions decreased significantly, except for the 129 bp deletion. Notably, the presence of 81, 96, and 129 bp deletions was always accompanied with some nucleotide substitutions. In conclusion, the prevalence of deletions at the C gene epitopes accompanied with the gradual disappearance of lamivudine resistance mutations may contribute to the survival of HBV under sequential antiviral therapy.

A case of HIV co-infected with hepatitis B virus precore/core deletion mutant treated by entecavir

We report a case of a HIV and hepatitis B virus (HBV)-co-infected patient to whom entecavir (ETV) was administered initially before the notification regarding the potential mutagenesis effect on HIV against the nucleoside analog. Since initial evaluations indicated the advanced stage of chronic hepatitis B and preserved numbers of peripheral CD4+ lymphocytes without the manifestation of immunodeficiency, priority was given to the management of HBV. We started HBV therapy with ETV at a dose of 0.5 mg daily without using any HIV drugs. The viral loads of both HBV and HIV-1 decreased gradually during the 5 months following the initial administration of ETV. HBV was well controlled by the gradual replacement of ETV with highly-active antiretroviral therapy against HIV with a regimen including atazanavir, emtricitabine, and tenofovir. HBV was genotyped as A2 with the quasispecies pool consisting of the -1G precore/core deletion mutant strain.

Molecular characterization of occult hepatitis B virus in genotype E-infected subjects

Occult hepatitis B virus (HBV) infection (OBI), defined as the presence of HBV DNA without detectable HBV surface antigen (HBsAg), is frequent in west Africa, where genotype E is prevalent. The prevalence of OBI in 804 blood donors and 1368 pregnant women was 1.7 and 1.5%, respectively. Nine of 32 OBI carriers were evaluated with HBV serology, viral load and complete HBV genome sequence of two to five clones. All samples except one were anti-HBV core antigen-positive and three contained antibodies against HBsAg (anti-HBs). All strains were of genotype E and formed quasispecies with 0.20-1.28% intra-sample sequence variation. Few uncommon mutations (absent in 23 genotype E reference sequences) were found across the entire genome. Two mutations in the core region encoded truncated or abnormal capsid protein, potentially affecting viral production, but were probably rescued by non-mutated variants, as found in one clone. No evidence of escape mutants was found in anti-HBs-carrying samples, as the 'a' region was consistently wild type. OBI carriers constitute approximately 10% of all HBV DNA-viraemic adult Ghanaians. OBI carriers appear as a disparate group, with a very low viral load in common, but multiple origins reflecting decades of natural evolution in an area essentially devoid of human intervention.

Identification of a novel hepatitis B virus precore/core deletion mutant in HIV/hepatitis B virus co-infected individuals

OBJECTIVES

Although HAART has resulted in improved health outcomes for most HIV-infected individuals, liver failure has emerged as a major cause of morbidity and mortality in people co-infected with hepatitis B virus (HBV). In HBV mono-infected individuals, core deletion mutants are associated with more aggressive liver disease. As HIV accelerates HBV liver disease progression, we hypothesized that HIV-HBV co-infected individuals have increased frequency of core mutations including deletions. To test this hypothesis, we have analysed genome-length sequences of HBV DNA from patients both prior to and during antiviral therapy.

SETTING

Prospective HIV/HBV co-infected cohort study.

METHODS

Genomic length HBV DNA was amplified by PCR from the serum samples of ten HIV/HBV co-infected individuals and five HBV mono-infected individuals prior to the commencement of lamivudine therapy and again after nine to 74 months of treatment. The complete genomes were sequenced and in order to further analyse some mutations, their frequency was determined in additional HIV/HBV co-infected and HBV mono-infected individuals.

RESULTS

A novel -1G mutation was identified in the HBV precore and overlapping core genes that truncated the deduced precore/core proteins. The mutant genome was the dominant species in some HIV/HBV co-infected individuals and was more prevalent in HIV/HBV co-infected individuals than HBV mono-infected individuals. The mutation was also associated with high HBV DNA concentrations in HIV/HBV co-infected individuals. Additional mutations were identified in the core/precore and polymerase genes and regulatory regions.

CONCLUSION

Mutations in the HBV core and precore genes may be contributing to disease pathogenesis in HIV/HBV co-infected individuals.

Proteasomal degradation of core protein variants from chronic hepatitis B patients

The accumulation of complex hepatitis B virus (HBV) variants with internal in-frame deletions in the C gene in immunosuppressed renal transplant recipients is associated with a severe course of the infection leading to end-stage liver disease (ESLD). A set of six HBV C genes with internal in-frame deletions corresponding to the pattern of HBV population in immunosuppressed patients has been expressed in two different eukaryotic cell lines. Synthesis and proteasomal degradation of HBV core (HBc) protein variants were compared with those of the wild-type HBc. In all cases, the steady-state level of internally deleted HBc proteins, predominantly with longer deletions, were considerably lower and turnover was significantly higher in comparison with those of the wild-type HBc, since all deletion variants were degraded rapidly via the proteasome pathway. Involvement and consequences of the proteasomal degradation machinery in the HBc protein turnover during HBV infection with complex HBV variants in the immunosuppressed patients are discussed.

Functional analysis of complex hepatitis B virus variants associated with development of liver cirrhosis

BACKGROUND & AIMS

Development of cirrhosis in renal transplant recipients with chronic hepatitis B is associated with the accumulation of complex hepatitis B virus (HBV) variants carrying deletions in the C gene and/or preS region and deletions/insertions in the core promoter. Here, we characterized for the first time the phenotype of these complex HBV variants.

METHODS

Representative full-length genomes of the HBV variants that were isolated and cloned from serum and liver of an immunosuppressed renal transplant recipient before and during end-stage liver disease were transfected into the human hepatoma cell line HuH7 and functionally analyzed.

RESULTS

The variant genomes showed considerably reduced levels of precore and surface messenger RNA (mRNA) and of the major spliced pregenomic RNA, an increased level of pregenomic RNA, and a partial or complete defect in hepatitis B e antigen, core, and surface protein expression/secretion. Very low amounts of variant core protein with internal deletion were detectable. Reduced hepatitis B surface antigen secretion of some variants correlated with aberrant localization of surface proteins in endoplasmic reticulum. Despite the defects in viral protein expression, enhanced replication and enrichment in competition to wild-type HBV were observed. Enhanced reverse transcription and possibly increased levels of pregenomic RNA seem to be responsible for this effect.

CONCLUSIONS

Development of cirrhosis is associated with accumulation of complex variants, which exhibit a drastically altered phenotype combining enhanced replication with defects in protein expression. This phenotype appears to be based on the major mutations in the core promoter and C gene but is considerably influenced by additional mutations throughout the genome.

Novel type of hepatitis B virus mutation: replacement mutation involving a hepatocyte nuclear factor 1 binding site tandem repeat in chronic hepatitis B virus genotype E

The genetic diversity of hepatitis B virus (HBV) strains has evolved through mutations such as point mutations, deletions or insertions, and recombination. We identified and characterized a novel type of mutation which is a complex of external insertion, deletion, and internal duplication in sequences from one of six patients with chronic hepatitis B virus genotype E (HBV/E). We provisionally named this mutation a "replacement mutation"; the core promoter upstream regulatory sequence/basic core promoter was replaced with a part of the S1 promoter covering the hepatocyte nuclear factor 1 (HNF1) binding site, followed by a tandem repeat of the HNF1 site. A longitudinal analysis of the HBV population over 6 years showed the clonal change from wild-type HBV/E to replacement-mutant type, resulting in a lower hepatitis B (HB) e antigen titer, a high HBV DNA level in serum, and progression of liver fibrosis. In an in vitro study using a replication model, the replacement-mutant HBV showed higher replication levels than the wild-type HBV/E replicon, probably mediated by altered transcription factor binding. Additionally, this HNF1 site replacement mutation was associated with excessive HB nucleocapsid protein expression in hepatocytes, in both in vivo and in vitro studies. This novel mutation may be specific to HBV genotype E, and its prevalence requires further investigation.

Alternative peptide-fusion proteins generated by out-of-frame mutations, just upstream ORFs or elongations in mutants of human hepatitis B viruses

By various means including out-of-frame mutations, just upstream ORFs and elongations, additional peptide fusions could be generated by mutants of Human Hepatitis B Virus (HBV). Numerous frameshift mutations inducing long alternative open reading frames have been evidenced in all HBV genes. Interestingly, these mutants are frequently detected in severe liver diseases, but seldom in asymptomatic carriers. The high level of conservation of some of these sequences in spite of the fact that they could be generated by different types of mutations, as their presence in mutants found on various continents, suggest that these mutations could play a role. These mutants could combine two advantages, that related to the loss of a part of a wild-type protein and that related to the putative advantage conferred by the additional sequences. In addition, in numerous Asian genomes (more than 300 to date) pre-X or pre-pre-S regions were found just upstream to, respectively, the X and the pre-S1 genes. These two regions are translated with their respective genes in frame and recent studies have evidenced the transactivating role of the corresponding proteins. With some exceptions, these regions are genotype- and serotype-specific (C/adr). In addition, these mutants have been found principally in patients with severe hepatitis diseases, for example, hepatocarcinoma in more than one third of the cases. As additional sequences generated by HBV variants may be relevant for viral life cycle, persistence and pathogenesis, further investigations are necessary to give a clearer picture of the subject.

Molecular and serological evaluation of surface antigen negative hepatitis B virus infection in blood donors from Venezuela

Surface antigen negative hepatitis B virus (HBV) infection was evaluated in Venezuela, by molecular characterization of blood samples positive for antibodies to core antigen (anti-HBc) and negative for surface antigen (HBsAg) in blood donors (residual infections). HBV DNA was found in 11/258 samples (4.3%), and was significantly associated with high levels of anti-HBc antibodies (>25 UI/ml, P < 0.05), while no correlation was found between the presence of HBV DNA and the levels of anti-HBs. Synonymous and non-synonymous mutations were found in the HBV surface region (but not vaccine escape mutants) and in the precore/core region (precore mutants in 2/7 samples and 33-45 bp deletions near the N-terminal core region in 4/19 samples). While HBV genotype F prevails among HBsAg positive samples from blood donors in Venezuela, residual infection isolates were mainly genotypes A and D. Phylogenetic analysis of viral surface and core region revealed discrepancies in genotype designation in 6/9 samples, suggesting the presence of mixed infection or recombination. In conclusion, HBV residual infection in Venezuela does not seem to be frequently observed in HBV genotype F. This type of infection is frequently associated with variants exhibiting mutations in the surface gene that might be affecting the correct recognition by commercial tests, with precore mutants and with core internal deletions. These variants do not seem to cause severe liver disease, and on the contrary, were found circulating at low viremia.

Structural and functional analysis of full-length hepatitis B virus genomes in patients: implications in pathogenesis

The structural analysis, replicative efficiency and immunogenicity of hepatitis B virus (HBV) full-length genomes isolated from different patients or asymptomatic carriers are presented in the present review. Data indicate the importance of viral genome-based studies in elucidating the pathogenesis of HBV infections. Comparison of structural and functional characteristics of viral genomes isolated from various geographical regions might contribute to explaining the differences in HBV clinical manifestation and prognosis in different geographical regions.

Exploring the biological basis of hepatitis B e antigen in hepatitis B virus infection

The function of the hepatitis B e antigen (HBeAg) is largely unknown because it is not required for viral assembly, replication, or infection. In this report we chronicle clinical and experimental studies in an attempt to understand the role of HBeAg in natural infection. These studies largely have focused on clinical-pathologic features of HBeAg-negative variants in acute and chronic HBV infection, mutational analysis in animal models of hepadnavirus infection, and the use of transgenic murine models. The clinical and experimental data suggest that serum HBeAg may serve an immunoregulatory role in natural infection. To the contrary, cytosolic HBeAg serves as a target for the inflammatory immune response. These dual roles of the HBeAg and its ability to activate or tolerize T cells show the complexity of the interactions between the HBeAg and the host during HBV infection.

Mosaic particles formed by wild-type hepatitis B virus core protein and its deletion variants consist of both homo- and heterodimers

Co-expression in Escherichia coli of wild-type (wt) hepatitis B virus core protein (HBc) and its naturally occurring variants with deletions at amino acid positions 77-93 or 86-93 leads to formation of mosaic particles, which consist of three dimer subunit compositions. These compositions are wt/variant HBc heterodimers and two types of homodimers, formed by wt HBc or the variant HBc themselves. Mosaic particles were found also when both HBc deletion variants 77-93 and 86-93 were co-expressed in E. coli. These findings are discussed in terms of their significance for hepatitis B virus pathogenesis and prospective use of mosaic particles in vaccine development.

In vivo transmission and dynamics of deleted genomes after experimental infection of woodchuck hepatitis B virus in adult animals

The presence of Deleted Genomes has been shown in a number of viral models including Hepadnaviridae. The analysis of woodchuck hepatitis B virus (WHV) population after experimental infection of woodchuck 197 (W197) with WHV7-PI inoculum revealed the presence of two Deleted Genomes: DG600 lacking a 1330 bp region (Core/Polymerase/PreS1) and DG900 showing a deletion of 869 nts (Pol/PreS/S). These mutants were also present in WHV7-PI. The successive WHV experimental infections in adult animals were performed using W197-w7 inoculum containing DG600 and DG900. Infections were divided into three groups presenting different patterns of viral replication, different presence of markers, occurrence of variants and persistence of infection. The first group displayed 2-3 weeks viremic phase and WHV-DNA titres of 10-30 ng/ml; the second a longer viremic phase (8-9 weeks) and higher WHV-DNA titres (up to 78 ng/ml). In contrast, the third group exhibited lifetime presence of WHV-DNA and WHVeAg in serum and viral replication in liver. The Deleted Genomes were transmitted in the newly infected animals with the same genomic organization. DG600 was persistently found only in chronically infected woodchuck, whereas a different pattern of presence was described for DG900. The characterization of these classes of deleted mutants in woodchuck-WHV model raises new questions on the link between DGs and persistent infections.

Complex HBV populations with mutations in core promoter, C gene, and pre-S region are associated with development of cirrhosis in long-term renal transplant recipients

Long-term immunosuppressed renal transplant recipients with chronic hepatitis B virus (HBV) infection often develop liver cirrhosis (LC) and end-stage liver disease (ESLD). This study investigated accumulation and persistence of specific HBV mutants in relation to the clinical course in these patients (n = 38; mean follow-up, 3.5 years). HBV was analyzed longitudinally via length polymorphism of polymerase chain reaction (PCR) fragments (median, 6.5 serum samples per patient) as well as by cloning and partial sequencing of 346 full-length HBV genomes. Fourteen patients (group 1) developed LC or died from ESLD, whereas 24 patients (group 2) showed no evidence of LC during follow-up. Development of LC and ESLD was associated with persistence of HBV mutant populations characterized by deletions/insertions in core promoter plus deletions in the C gene and/or deletions in the pre-S region (86% of group 1 vs. 17% of group 2; P <.0001). HBV without these mutations or with core promoter mutations alone were predominantly found in group 2 (14% of group 1 vs. 75% of group 2). In patients infected with core promoter mutants, the additional appearance and persistence of deletions in the C gene and/or the pre-S region were accompanied or followed by development of LC and ESLD. The mutations were distributed on individual genomes in various combinations, leading to a high complexity of the virus population. In conclusion, these data suggest that accumulation and persistence of specific HBV populations characterized by mutations in 3 subgenomic regions play a role in pathogenesis of LC and ESLD in long-term renal transplant recipients.

Out-of-frame versus in-frame core internal deletion variants of human and woodchuck hepatitis B viruses

Human hepatitis B virus (HBV) variants containing in-frame core internal deletion (CID) have been demonstrated to contain all the functional features of defective interfering (DI) particles (Yuan, T. T.-T., M.-H. Lin, D. S. Chen, and C. Shih, 1998, J. Virol. 72, 578-584). Here, we report that out-of-frame HBV CID variants exhibit defective interfering property similar to in-frame CID variants characterized previously. This result raises the possibility that it may be the deleted pregenomic RNA product, rather than the deleted core protein product, that is responsible for interference. Furthermore, a genomic deletion elsewhere does not cause interference since preS2 deletion variants exhibit no influence on wild-type HBV replication. Consistent with the natural occurrence of HBV CID variants, we recently identified CID variants of woodchuck hepatitis virus (WHV) in natural infection. However, unlike HBV CID variants, functional characterization of WHV CID variants using a human hepatoma cell line has not revealed any interference in tissue culture. In summary, defective interference is a general phenomenon for both in-frame and out-of-frame HBV CID variants.

Structural and functional heterogeneity of naturally occurring hepatitis B virus variants

Most organisms have developed sophisticated machineries to preserve their genomic integrity. On the contrary hepatitis B virus (HBV), like a lot of other viruses can undergo rapid and drastic sequence changes, especially if the virus has to cope with natural or therapy induced antiviral mechanisms in the host. Here, we try to summarize possible implications for the molecular pathogenesis of HBV based on the extensive research on the genetic variants of HBV.

Replication of naturally occurring woodchuck hepatitis virus deletion mutants in primary hepatocyte cultures and after transmission to naive woodchucks

Woodchuck hepatitis virus (WHV) mutants with core internal deletions (CID) occur naturally in chronically WHV-infected woodchucks, as do hepatitis B virus mutants in humans. We studied the replication of WHV deletion mutants in primary woodchuck hepatocyte cultures and in vivo after transmission to naive woodchucks. By screening 14 wild-caught, chronically WHV-infected woodchucks, two woodchucks, WH69 and WH70, were found to harbor WHV CID mutants. Consistent with previous results, WHV CID mutants from both animals had deletions of variable lengths (90 to 135 bp) within the middle of the WHV core gene. In woodchuck WH69, WHV CID mutants represented a predominant fraction of the viral population in sera, normal liver tissues, and to a lesser extent, in liver tumor tissues. In primary hepatocytes of WH69, the replication of wild-type WHV and CID mutants was maintained at least for 7 days. Although WHV CID mutants were predominant in fractions of cellular WHV replicative intermediates, mutant covalently closed circular DNAs (cccDNAs) appeared to be a small part of cccDNA-enriched fractions. Analysis of cccDNA-enriched fractions from liver tissues of other woodchucks confirmed that mutant cccDNA represents only a small fraction of the total cccDNA pool. Four naive woodchucks were inoculated with sera from woodchuck WH69 or WH70 containing WHV CID mutants. All four woodchucks developed viremia after 3 to 4 weeks postinoculation (p.i.). They developed anti-WHV core antigen (WHcAg) antibody, lymphoproliferative response to WHcAg, and anti-WHV surface antigen. Only wild-type WHV, but no CID mutant, was found in sera from these woodchucks. The WHV CID mutant was also not identified in liver tissue from one woodchuck sacrificed in week 7 p.i. Three remaining woodchucks cleared WHV. Thus, the presence of WHV CID mutants in the inocula did not significantly change the course of acute self-limiting WHV infection. Our results indicate that the replication of WHV CID mutants might require some specific selective conditions. Further investigations on WHV CID mutants will allow us to have more insight into hepadnavirus replication.