Hepatitis B virus sequence changes evolving in liver transplant recipients with fulminant hepatitis

Hepatitis B Surface Antigen Isoforms: Their Clinical Implications, Utilisation in Diagnosis, Prevention and New Antiviral Strategies

The hepatitis B surface antigen (HBsAg) is a multifunctional glycoprotein composed of large (LHB), middle (MHB), and small (SHB) subunits. HBsAg isoforms have numerous biological functions during HBV infection-from initial and specific viral attachment to the hepatocytes to initiating chronic infection with their immunomodulatory properties. The genetic variability of HBsAg isoforms may play a role in several HBV-related liver phases and clinical manifestations, from occult hepatitis and viral reactivation upon immunosuppression to fulminant hepatitis and hepatocellular carcinoma (HCC). Their immunogenic properties make them a major target for developing HBV vaccines, and in recent years they have been recognised as valuable targets for new therapeutic approaches. Initial research has already shown promising results in utilising HBsAg isoforms instead of quantitative HBsAg for correctly evaluating chronic infection phases and predicting functional cures. The ratio between surface components was shown to indicate specific outcomes of HBV and HDV infections. Thus, besides traditional HBsAg detection and quantitation, HBsAg isoform quantitation can become a useful non-invasive biomarker for assessing chronically infected patients. This review summarises the current knowledge of HBsAg isoforms, their potential usefulness and aspects deserving further research.

Hepatitis B virus pre-S region: Clinical implications and applications

Hepatitis B virus (HBV) infection is a major threat to global public health, which can result in many acute and chronic liver diseases. HBV, a member of the family Hepadnaviridae, is a small enveloped DNA virus containing a circular genome of 3.2 kb. Located upstream of the S-open-reading frame of the HBV genome is the pre-S region, which is vital to the viral life cycle. The pre-S region has high variability and many mutations in the pre-S region are associated with several liver diseases, such as fulminant hepatitis (FH), liver cirrhosis (LC), and hepatocellular carcinoma (HCC). In addition, the pre-S region has been applied in the development of several pre-S-based materials and systems to prevent or treat HBV infection. In conclusion, the pre-S region plays an essential role in the occurrence, diagnosis, and treatment of HBV-related liver diseases, which may provide a novel perspective for the study of HBV infection and relevant diseases.

Applications of next-generation sequencing analysis for the detection of hepatocellular carcinoma-associated hepatitis B virus mutations

BACKGROUND

Next-generation sequencing (NGS) is a powerful and high-throughput method for the detection of viral mutations. This article provides a brief overview about optimization of NGS analysis for hepatocellular carcinoma (HCC)-associated hepatitis B virus (HBV) mutations, and hepatocarcinogenesis of relevant mutations.

MAIN BODY

For the application of NGS analysis in the genome of HBV, four noteworthy steps were discovered in testing. First, a sample-specific reference sequence was the most effective mapping reference for NGS. Second, elongating the end of reference sequence improved mapping performance at the end of the genome. Third, resetting the origin of mapping reference sequence could probed deletion mutations and variants at a certain location with common mutations. Fourth, using a platform-specific cut-off value to distinguish authentic minority variants from technical artifacts was found to be highly effective. One hundred and sixty-seven HBV single nucleotide variants (SNVs) were found to be studied previously through a systematic literature review, and 12 SNVs were determined to be associated with HCC by meta-analysis. From comprehensive research using a HBV genome-wide NGS analysis, 60 NGS-defined HCC-associated SNVs with their pathogenic frequencies were identified, with 19 reported previously. All the 12 HCC-associated SNVs proved by meta-analysis were confirmed by NGS analysis, except for C1766T and T1768A which were mainly expressed in genotypes A and D, but including the subgroup analysis of A1762T. In the 41 novel NGS-defined HCC-associated SNVs, 31.7% (13/41) had cut-off values of SNV frequency lower than 20%. This showed that NGS could be used to detect HCC-associated SNVs with low SNV frequency. Most SNV II (the minor strains in the majority of non-HCC patients) had either low (< 20%) or high (> 80%) SNV frequencies in HCC patients, a characteristic U-shaped distribution pattern. The cut-off values of SNV frequency for HCC-associated SNVs represent their pathogenic frequencies. The pathogenic frequencies of HCC-associated SNV II also showed a U-shaped distribution. Hepatocarcinogenesis induced by HBV mutated proteins through cellular pathways was reviewed.

CONCLUSION

NGS analysis is useful to discover novel HCC-associated HBV SNVs, especially those with low SNV frequency. The hepatocarcinogenetic mechanisms of novel HCC-associated HBV SNVs defined by NGS analysis deserve further investigation.

Single-virion sequencing of lamivudine-treated HBV populations reveal population evolution dynamics and demographic history

BACKGROUND

Viral populations are complex, dynamic, and fast evolving. The evolution of groups of closely related viruses in a competitive environment is termed quasispecies. To fully understand the role that quasispecies play in viral evolution, characterizing the trajectories of viral genotypes in an evolving population is the key. In particular, long-range haplotype information for thousands of individual viruses is critical; yet generating this information is non-trivial. Popular deep sequencing methods generate relatively short reads that do not preserve linkage information, while third generation sequencing methods have higher error rates that make detection of low frequency mutations a bioinformatics challenge. Here we applied BAsE-Seq, an Illumina-based single-virion sequencing technology, to eight samples from four chronic hepatitis B (CHB) patients - once before antiviral treatment and once after viral rebound due to resistance.

RESULTS

With single-virion sequencing, we obtained 248-8796 single-virion sequences per sample, which allowed us to find evidence for both hard and soft selective sweeps. We were able to reconstruct population demographic history that was independently verified by clinically collected data. We further verified four of the samples independently through PacBio SMRT and Illumina Pooled deep sequencing.

CONCLUSIONS

Overall, we showed that single-virion sequencing yields insight into viral evolution and population dynamics in an efficient and high throughput manner. We believe that single-virion sequencing is widely applicable to the study of viral evolution in the context of drug resistance and host adaptation, allows differentiation between soft or hard selective sweeps, and may be useful in the reconstruction of intra-host viral population demographic history.

Detecting exact breakpoints of deletions with diversity in hepatitis B viral genomic DNA from next-generation sequencing data

Many studies have suggested that deletions of Hepatitis B Viral (HBV) are associated with the development of progressive liver diseases, even ultimately resulting in hepatocellular carcinoma (HCC). Among the methods for detecting deletions from next-generation sequencing (NGS) data, few methods considered the characteristics of virus, such as high evolution rates and high divergence among the different HBV genomes. Sequencing high divergence HBV genome sequences using the NGS technology outputs millions of reads. Thus, detecting exact breakpoints of deletions from these big and complex data incurs very high computational cost. We proposed a novel analytical method named VirDelect (Virus Deletion Detect), which uses split read alignment base to detect exact breakpoint and diversity variable to consider high divergence in single-end reads data, such that the computational cost can be reduced without losing accuracy. We use four simulated reads datasets and two real pair-end reads datasets of HBV genome sequence to verify VirDelect accuracy by score functions. The experimental results show that VirDelect outperforms the state-of-the-art method Pindel in terms of accuracy score for all simulated datasets and VirDelect had only two base errors even in real datasets. VirDelect is also shown to deliver high accuracy in analyzing the single-end read data as well as pair-end data. VirDelect can serve as an effective and efficient bioinformatics tool for physiologists with high accuracy and efficient performance and applicable to further analysis with characteristics similar to HBV on genome length and high divergence. The software program of VirDelect can be downloaded at https://sourceforge.net/projects/virdelect/.

Hepatitis B virus PreS/S gene variants: pathobiology and clinical implications

The emergence and takeover of hepatitis B virus (HBV) variants carrying mutation(s) in the preS/S genomic region is a fairly frequent event that may occur spontaneously or may be the consequence of immunoprophylaxis or antiviral treatments. Selection of preS/S mutants may have relevant pathobiological and clinical implications. Both experimental data and studies in humans show that several specific mutations in the preS/S gene may induce an imbalance in the synthesis of the surface proteins and their consequent retention within the endoplasmic reticulum (ER) of the hepatocytes. The accumulation of mutated surface proteins may cause ER stress with the consequent induction of oxidative DNA damage and genomic instability. Viral mutants with antigenically modified surface antigen may be potentially infectious to immune-prophylaxed patients and may account for cases of occult HBV infection. In addition, preS/S variants were reported to be associated with cases of fulminant hepatitis as well as of fibrosing cholestatic hepatitis, and they are associated with cirrhosis and hepatocellular carcinoma development.

Hepatitis B Virus (HBV) Infection in Liver Disease Patients in Mumbai, India with Special Reference to Hepatitis B Surface Antigen (HBsAg) Mutant Detection

OBJECTIVES

To determine the prevalence of Hepatitis B Surface antigen (HBsAg) in patients attending the Hepatology Out Patient Department (OPD) of a tertiary care hospital and to compare the routinely used HBsAg detection kit with the mutant detection kit to find out the presence of mutants in a given setting.

MATERIALS AND METHODS

A cross-sectional study was carried out in adult patients with liver disease attending the Hepatology OPD, of a tertiary care hospital in Mumbai, India. Age, gender and clinical history of the patient were recorded. Blood specimen was tested for HBsAg (Microscreen(TM) ELISA, Span diagnostics, India) and HBsAg mutants (Hepanostika HBsAg Ultra(TM) ELISA, Biomerieux, France). The samples with discordant results between these two ELISAs were confirmed by Hepatitis B Virus (HBV) Deoxyribonucleic Acid (DNA) Polymerase Chain Reaction (PCR) (Cobas Taqman(TM), Roche Molecular Systems, USA).

RESULTS

Seven hundred and eighteen patients were enrolled in the study. The mean age of patients in the study group was 41 years (range 17 to 69 years). Four hundred and ninety seven (69.22%) were males and remaining were females. The prevalence of HBsAg was found to be 17.4%. The positivity amongst the male population was 18.1% which was higher than the female population (15.8%). Of the 718 samples tested, 120 were positive for HBsAg by Microscreen(TM) ELISA and 132 were positive by Hepanostika HBsAg ultra(TM). Of the 12 discordant samples, HBV DNA was detected in five samples indicating 0.7% prevalence of mutants.

CONCLUSION

Hepatitis B is prevalent in liver disease patients. The mutant detecting assay is recommended in set-ups where missing HBsAg in patients would have tremendous impact on the outcome such as in blood donors, organ or tissue donors and antenatal screening of mothers. It is also helpful in chronic liver disease patients where the routine HBsAg detection test is negative and the other causes of chronic liver disease have been ruled out. However, it is not recommended for use in routine diagnostic set-ups where high false positivity would lead to over-diagnosis of the condition.

Molecular biology of the hepatitis B virus for clinicians

Hepatitis B virus (HBV) infection is one of the major global health problems, especially in economically under-developed or developing countries. HBV infection can lead to a number of clinical outcomes including chronic infection, cirrhosis and liver cancer. It ranks among the top 10 causes of death, being responsible for around 1 million deaths every year. Despite the availability of a highly efficient vaccine and potent antiviral agents, HBV infection still remains a significant clinical problem, particularly in those high endemicity areas where vaccination of large populations has not been possible due to economic reasons. Although HBV is among the smallest viruses in terms of virion and genome size, it has numerous unique features that make it completely distinct from other DNA viruses. It has a partially double stranded DNA with highly complex genome organization, life cycle and natural history. Remarkably distinct from other DNA viruses, it uses an RNA intermediate called pregenomic RNA (pgRNA) and reverse transcriptase for its genome replication. Genome replication is accomplished by a complex mechanism of primer shifting facilitated by direct repeat sequences encoded in the genome. Further, the genome has evolved in such a manner that every single nucleotide of the genome is used for either coding viral proteins or used as regulatory regions or both. Moreover, it utilizes internal in-frame translation initiation codons, as well as different reading frames from the same RNA to generate different proteins with diverse functions. HBV also shows considerable genetic variability which has been related with clinical outcomes, replication potential, therapeutic response etc. This review aims at reviewing fundamental events of the viral life cycle including viral replication, transcription and translation, from the molecular standpoint, as well as, highlights the clinical relevance of genetic variability of HBV.

Biological features of hepatitis B virus isolates from patients based on full-length genomic analysis

The mechanisms for HBV persistence and the pathogenesis of chronic HB have been shown mainly due to defects in host immune responses. However, HBV isolates with different biological features may also contribute to different clinical outcomes and epidemiological implications in viral hepatitis B (HB). This review presents interesting biological features of HBV isolates based on the structural and functional analysis of full-length HBV isolates from various patients. Among isolates from children after failure of HB vaccination, 129L mutant at the 'a' determinant was found with normal binding efficiency to anti-HBs, but with reduced immunogenicity, which could initiate persistent HBV infections. Isolates from fulminant hepatitis (FH) B patients were not all highly replicative, but differences in capacities of anti-HBs induction could be involved in the pathogenesis of FH. The high replicative competency of isolates from hepatocellular carcinoma (HCC) patients could result in enhanced immune-mediated cytopathic effects against HBV viral proteins, and increased transactivating activity by the X protein. The mechanism of a double-spliced variant in enhancing replication of the wild-type virus is presented. The importance of integrating structural and functional analysis to reveal biological features of HBV isolates in viral pathogenesis is discussed.

An overview of molecular epidemiology of hepatitis B virus (HBV) in India

Hepatitis B virus (HBV) is one of the major global public health problems. In India, HBsAg prevalence among general population ranges from 2% to 8%, placing India in intermediate HBV endemicity zone and the number of HBV carriers is estimated to be 50 million, forming the second largest global pool of chronic HBV infections. India is a vast country, comprised of multiracial communities with wide variations in ethnicity and cultural patterns, which is attributable to its geographical location, gene influx due to invasion and/or anthropological migrations in the past. Moreover, recent increase in trade, trafficking and use of illicit drugs has also considerably influenced the epidemiology of HBV, specifically in the eastern and north eastern parts of India. However, data on the molecular epidemiology of HBV in India is scanty. HBV genotypes A and D have been well documented from different parts of mainland India. Interestingly, in addition to genotypes A and D, genotype C having high nucleotide similarity with south East Asian subgenotype Cs/C1 strain, have been detected exclusively from eastern Indian HBV carriers, suggesting a recent introduction. Thus, compared to other parts of India, the molecular epidemiology of HBV is naturally distinct in eastern India. Very recently, taking the advantage of circulation of three distinct HBV genotypes within the population of eastern India, different aspects of HBV molecular epidemiology was studied that revealed very interesting results. In this study, the clinical significance of HBV genotypes, core promoter and precore mutations, possible routes of introduction of HBV genotype C in eastern India, the clinical implications of x gene variability, prevalence of the AFB₁ induced p53 gene codon 249 mutation, the transmission potentiality of HBV among asymptomatic/inactive or occult HBV carriers and the genetic variability of HBV persisting in the PBL was investigated. In this manuscript, the information available on the molecular epidemiology of HBV in India has been reviewed and the results of studies among the eastern Indian population have been summarised.

The amino Acid residues at positions 120 to 123 are crucial for the antigenicity of hepatitis B surface antigen

The major hydrophilic region (MHR) of hepatitis B surface antigen (HBsAg) harbors conformational B-cell epitopes and is the major target of neutralizing antibodies to HBsAg (anti-HBs). Mutant HBsAg (mtHBsAg) with amino acid substitutions such as G145R is known to affect the binding of specific anti-HB antibodies and their detection by conventional diagnostic assays. In the present study, we focused on the role of the amino acid positions 120 to 123, which are around MHR 2 according to the spectrum of recently identified, naturally occurring mtHBsAg. Strikingly, the amino acid substitution K122I abolished the reactivity of HBsAg in all immunoassays tested so far. Also, mtHBsAg G145R could be clearly detected with four different enzyme-linked immunosorbent assays that were based on monoclonal anti-HB antibodies (MAbs) with high affinity. Positive immunofluorescence staining of mtHBsAg K122I was achieved only by polyclonal anti-HBs, while all MAbs tested failed. mtHBsAg T123N showed a low reactivity in immunoassays and appeared to be secretion defective. The amino acid substitution P120T reduced the binding of anti-HBs but did not completely prevent the detection of mtHBsAg by anti-HB MAbs. The testing of naturally occurring mtHBsAg confirmed that the presence of amino acid substitutions within the region of 120 to 123 is strongly associated with impaired detection in immunoassays. In conclusion, MHR 2 is essential for HBsAg antigenicity, a fact that has not been recognized before.

Determination of hepatitis B virus genotype by flow-through reverse dot blot

BACKGROUND

The clinical outcome and response to therapy of hepatitis B virus infection differ depending upon viral genotype. Most methods of determining the viral genotype are relatively time-consuming and costly. Moreover, the results of some methods are influenced by single nucleotide mutations.

OBJECTIVES

To develop a novel HBV genotyping process insensitive to single nucleotide mutations using an improved reverse dot blot method employing the principle of "flow-through hybridization".

STUDY DESIGN

The flow through reverse dot blot (FT-RDB) method was developed using DNA from different HBV genotypes. HBV sequences from Genebank were used to design primers and probes. Specificity and sensitivity of the method were evaluated with clinical samples in which the HBV viral load was quantified by real-time PCR. Results were compared to those of multiplex PCR and sequencing. Another 59 clinical samples were used to test the clinical applicability of the method.

RESULTS

We showed that FT-RDB could be made insensitive to single nucleotide mismatch by adjusting the hybridization temperature. All HBV-negative samples showed no signals in the assay. The detection sensitivity of the method was found to be between 10(3) and 10(4) DNA copies/ml. The results of FT-RDB were 84% concordant with those of multiplex PCR, and 96% concordant with sequencing results in 101 cases. The genotype all 59 clinical samples was accurately identified.

CONCLUSIONS

We demonstrated that the FT-RDB method was rapid, reliable, accurate and inexpensive. It appears to be useful for routine clinical HBV genotyping even in non-specialized hospital laboratories.

Molecular biology of hepatitis B virus: effect of nucleotide substitutions on the clinical features of chronic hepatitis B

Hepatitis B virus (HBV) is a major cause of liver disease worldwide. It is covered with envelope (surface antigen) proteins with the nucleocapsid (core antigen) inside. In the nucleocapsid, there is an incomplete double-stranded DNA and a DNA polymerase. Four genes, S, C, X, and P, are encoded, and these partially overlap. Mutations have been reported in each gene and in their promoter regions, and these mutations can change the efficiency of HBV replication and the clinical course of patients. In this article, we review the relationship between the molecular biology of HBV and its clinical outcome.

Diagnostic impact of the genetic variability of the hepatitis B virus surface antigen gene

The genetic variability of hepatitis B virus (HBV) represents a challenge for the sensitivity of immunologic and molecular based assays. Genotyping studies show that the genetic diversity of HBV is very high even in industrialized countries. The analytical sensitivity of HBsAg and anti-HBs assays may be dependent on HBV genotype or subtype and could possibly lead to false negative results in samples with low-level HBsAg. It is possible that the recognition of genotypes E and F may be impaired. Immunoassays based on polyclonal capture antibody show the highest sensitivity for the recognition of recombinant mutants or serum samples harboring mutant forms of HBsAg. However, they do not guarantee full sensitivity, especially for the detection of the G145R mutation and amino acid insertions or substitutions in positions 120-123. Detection of HBsAg needs to be improved by the introduction of new HBsAg assays able to recognize so far described S gene mutants and with a lower detection threshold than current immunoassays in order to detect smallest amounts of HBsAg in low level carriers. There is also a need for more complete epidemiological data on the prevalence of HBsAg mutants especially for G145R and assays for the (differential) screening of mutants need to be developed and evaluated.

Identification of novel defective HCV clones in liver transplant recipients with recurrent HCV infection

Patients with recurrent hepatitis C after liver transplantation usually have a high viral load and are generally resistant to interferon (IFN)-alpha2b plus ribavirin (RBV) therapy. However, it remains unclear whether pretreatment viral titre determines the effectiveness of combination therapy, especially in patients with a high viral load. The aim of this study was to identify the viral factors associated with a sustained virological response (SVR) to antiviral therapy in patients with recurrent hepatitis C after living-donor liver transplantation. Twenty-three patients with recurrent hepatitis C received combination therapy of IFN-alpha2b plus RBV. SVR was achieved in 7 of the 23 patients (30.4%). Predictive factors for SVR included a 2 log10 decline in Hepatitis C virus (HCV) RNA at 2 weeks after the start of therapy and disappearance of HCV RNA at 4 or 24 weeks after the start of therapy. As the pretreatment high viral load showed no association with SVR, we asked whether other viral factor was associated with the response to the combination therapy in transplant recipients. We found the several novel defective HCV clones in 4 of 12 recipients' sera. All defective HCV clones had deletions in the envelope region. Interestingly, no patients with defective clones showed a prompt decrease in HCV RNA after the start of IFN-alpha2b plus RBV therapy. Thus, early decline in serum HCV RNA after treatment was closely associated with SVR. The circulating defective HCV clones are present and might be associated with the response to the combination therapy in patients with recurrent hepatitis after liver transplantation.

Prevalence of naturally occurring surface antigen variants of hepatitis B virus in Korean patients infected chronically

Although Korea is one of the endemic areas of hepatitis B virus (HBV) infection, the prevalence of naturally occurring variants in the major hydrophilic region (MHR) of the surface (S) gene of HBV has not been determined. In the present study, the prevalence of these variants was examined in terms of the clinical state, and HBeAg serostatus in a large series of Korean patients with chronic HBV infection by direct sequencing analysis of part of the S gene containing the MHR of HBV isolated from 101 chronic HBV patients (51 HBeAg-positive and 50 HBeAg-negative): 37 were asymptomatic carriers, 21 had chronic hepatitis, 20 had liver cirrhosis, and 23 had hepatocellular carcinoma (HCC). Forty-seven MHR variants (46.5%) of the 101 patients were detected, involving a total of 59 amino acid substitutions at 12 positions inside and 14 position outside the 'a' determinant, and 33 'a' determinant variants (32.7%). A total of 17 novel variants and 14 novel mutation patterns were detected. The prevalence of MHR variants in HBeAg-negative patients tended to be higher than in HBeAg-positive patients (54.0% vs.39.2%) and the prevalence of MHR variants in HCC and liver cirrhosis tended to be higher than in asymptomatic carriers (65.2% vs. 40.5% and 50.0% vs. 40.5%, respectively). In conclusion, three important findings were found in the present study. First, an unexpectedly high prevalence of naturally occurring MHR variants was found in Korean chronic patients. Second, several novel variants associated with mutations outside the 'a' determinant were detected. Finally, a higher prevalence of MHR variants was associated with HBeAg-negative serostatus and severe liver disease, particularly HCC.

Recent developments in the diagnosis and monitoring of HBV infection and role of the genetic variability of the S gene

Recent developments in the laboratory diagnosis of hepatitis B virus infection include the optimization of key serologic markers, including hepatitis B virus surface antigen and antihepatitis B virus core antibody, as well as the development of automated nucleic acid amplification assays. There is still a lack of standardization for nucleic acid amplification assays that are used for the monitoring of antiviral therapy and follow-up of chronic infection and the clinical significance of hepatitis B virus DNA levels need to be clarified. Although highly sensitive automated nucleic acid amplification assays for blood donor screening are available, their implementation is still subject to discussion and certain countries rejected hepatitis B virus DNA testing for blood donation due to poor cost effectiveness. Genetic variability of hepatitis B virus constitutes a major challenge for diagnosis of hepatitis B virus infection, particularly with regard to hepatitis B virus surface antigen detection, antihepatitis B virus surface antigen quantification and nucleic acid amplification assays. The performances of hepatitis B virus surface antigen enzyme immunoassays in regard to genotype and surface antigen variability need to be further improved. Polyclonal antibody-based hepatitis B virus surface antigen enzyme immunoassays, although they cannot guarantee 100% sensitivity, demonstrate superior S gene mutant recognition to assays using monoclonal capture and tracer antibodies. Isolated antihepatitis B virus core reactivity is an unusual but frequent result, which requires a test algorithm for resolution and hepatitis B virus DNA detection with sensitive nucleic acid amplification assays in order to exclude occult hepatitis B virus infection.

Genetic variability of the S gene of hepatitis B virus: clinical and diagnostic impact

The genetic variability of hepatitis B virus (HBV) represents a challenge for the sensitivity of immunologic and molecular based assays. Based on sequence divergence in the entire genome of >8%, HBV genomes have been classified into eight groups designated A to H. The genotypes of HBV have distinct geographical distributions. Although preliminary clinical studies seem to indicate that there is an association between HBV genotype and natural history of infection and response to antiviral therapy, further evaluations on larger collectives of patients are necessary to give a clearer picture of the subject. The analytical sensitivity of HBsAg and anti-HBs assays may be dependent on HBV genotype or subtype. The influence of genotypic variability on the sensitivity of nucleic acid amplification tests (NAT) has so far been poorly investigated. Preliminary results show that new real-time NAT detect genotypes A to G with an equal sensitivity. Different mechanisms intervening at the translational or post-translational level, including conformational changes, hydrophobic changes, insertion of basic residues and reduced synthesis or secretion of HBsAg may account solely or in conjunction for escape mutations to the immune response and to detection in HBsAg immunassays. The clinical significance of S-gene mutants, needs in analogy to that of HBV genotypes, to be further investigated. HBV mutants are stable over time and can be transmitted horizontally or vertically. The sensitivity of HBsAg assays for mutant detection is continuously improved. Immunoassays based on polyclonal capture antibody show the highest sensitivity for the recognition of recombinant mutants or serum samples harboring mutant forms of HBsAg. However, they do not guarantee full sensitivity. Detection of HBsAg needs to be improved by the introduction of new HBsAg assays able to recognize so far described S-gene mutants and with a lower detection threshold than current immunoassays in order to detect smallest amounts of HBsAg in low level carriers. There is also a need for more complete epidemiological data on the prevalence of HBsAg mutants and strategies for the (differential) screening of mutants need to be developed and evaluated.

Mutant hepatitis B virus surface antigens (HBsAg) are immunogenic but may have a changed specificity

Mutant hepatitis B virus with substitutions within the coding region for HBV surface antigen (HBsAg) has been found naturally in chronic carriers. It is therefore important to clarify whether the identified substitutions within the HBsAg have impact on the antigenicity and immunogenicity of HBsAg. A total of nine mutated HBV s-genes with single representative mutations were generated by site-directed mutagenesis and subcloned into an expression vector. The binding of polyclonal and monoclonal antibodies to these mutant HBsAg (mtHBsAg) was tested by immunofluorescence (IF) staining of cells transfected with the expression vectors. The amino acid (aa) substitutions like G145R, F134S, and C147W affected the binding of anti-HBs antibodies to corresponding mtHBsAg to different extents. The impact of aa substitutions G145R and F134S on the immunogenicity was accessed by genetic immunization of mice with vectors expressing middle HBsAg with the corresponding mutations. The immunized mice developed antibodies to recombinant HBsAg containing the HBV preS region and HBsAg-specific cytotoxic T-cell. However, the development of antibody response to wild-type small HBsAg was significantly impaired by the aa substitutions in HBsAg. Based on this fact, we further investigated whether the mtHBsAg with the aa substitution G145R is able to induce mutant-specific antibody responses. Strikingly, serum samples from mice immunized with mtHBsAg with G145R recognized plasma-derived mtHBsAg. Two mouse MAbs specific to mtHBsAg were generated. One MAb recognized mtHBsAg with G145R but not wild type and other mtHBsAg. We conclude that HBsAg with aa substitutions are immunogenic but may have a changed fine specificity.

Complete hepatitis B virus genome analysis in HBsAg positive mothers and their infants with fulminant hepatitis B

Background

After perinatal transmission of hepatitis B virus, infants of anti-HBe positive HBsAg carrier mothers may develop fulminant hepatitis B. Previously it has been suggested, that fulminant hepatitis B in adults was associated with specific mutations in the HBV-genome. The aim of this study was to investigate, whether specific viral variants are associated with fulminant hepatitis B in young infants.

Methods

The complete HBV-genomes of five mothers and their infants with fulminant hepatitis were isolated from the sera, amplified and directly sequenced.

Results

Between 6 and 43 base pair exchanges between the HBV genomes of the infants and their mothers were identified. The mutations spread over the entire virus genome. Nucleotide exchanges in the basic core promotor and precore region were identified in all cases. A heterogeneous virus population was detected in four mothers.

Conclusions

Many new mutations were proved to emerge during fulminant hepatitis B in infants, who had been perinatally infected. HBeAg negative variants were the predominant population in all children, whereas these mutants could only be detected as subpopulations in four mothers. The data suggest that the selection of a specific HBeAg negative viral strain may be associated with the development of fulminant hepatitis B in children.

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.

Characterization of hepatitis B virus surface antigen and polymerase mutations in liver transplant recipients pre- and post-transplant

We evaluated serum samples from 18 chronic hepatitis B virus (HBV) patients who underwent liver transplantation for the presence of HBV polymerase and S gene mutations and HBV genotype using a new commercially available sequencing assay. All three patients with hepatitis B immune globulin (HBIG) treatment failure followed by nucleoside analogue treatment failure were infected with HBV genotype C; a pre-existing HBV S antigen (HBsAg) mutation (sD144A) was identified in one patient pretransplant, while sG145R mutations emerged in the other two patients post-transplant. These HBsAg mutations persisted for the duration of the study (5-6 years), despite the absence of HBIG administration for a 4-5-year period. Significant viral polymerase mutations (rtL180M and rtM204I/V) also emerged in all of these patients following treatment with lamivudine and/or famciclovir. Four of six patients with HBIG breakthrough without nucleoside analogue treatment failure yielded potentially significant HBsAg mutations post transplant. These data do not support previous reports highlighting the disappearance of HBsAg mutants in liver transplant recipients after discontinuation of HBIG. Determination of HBV genotype, as well as identification of HBV polymerase and S gene mutations in liver transplant candidates may be warranted to optimize HBV management strategies post transplant.

A prospective study characterizing full-length hepatitis B virus genomes during acute exacerbation

BACKGROUND & AIMS

Hepatitis B virus (HBV) evolves rapidly in patients with chronic hepatitis B, and HBV variation may trigger acute exacerbation. To study this relationship, we investigated full-length viral sequences before, during, and after exacerbation.

METHODS

We prospectively studied 14 patients with exacerbation of hepatitis B, either spontaneously (n = 4) or after receiving various medical interventions (n = 10), and measured their serum alanine aminotransferase (ALT) and HBV DNA levels monthly. Full-length HBV genomes at baseline, at the peak of serum viral load, at ALT peak, and after ALT peak were obtained by polymerase chain reaction, sequenced, and compared. Replication activities of serial HBV variants were assayed by in vitro transfection.

RESULTS

Serum viral load was increased in all exacerbations. Viral peak preceded ALT peak in 13 (93%) of the 14 patients. At virologic peak, 12 patients (86%) harbored viral genome identical to the corresponding baseline genome. At and after ALT peak, 9 (64%) and 7 (50%) of the viral genomes remained identical to baseline, respectively. Mean nucleotide change per genome was 0.2 at virologic peak but increased to 4.4 and 8.1 at and after ALT peak, respectively. The replication potential of the viral variant that emerged during or after exacerbation was equivalent to that at baseline.

CONCLUSIONS

Most exacerbations were preceded by an upsurge of serum HBV identical to the preexisting HBV strain. After exacerbation, about half of the patients were repopulated by a different viral variant, which was likely a result of immune selection.

Core promoter mutations (A(1762)T and G(1764)A) and viral genotype in chronic hepatitis B and hepatocellular carcinoma in Guangxi, China

Hepatitis B viruses (HBV) with core promoter mutations (A(1762)T, G(1764)A) were found in a previous study to be highly prevalent in patients from Guangxi, China with hepatocellular carcinoma (HCC). The aim of this study was to determine whether the mutations are prevalent in areas of Guangxi with high and lower incidences of HCC and whether they are associated with other severe sequelae of chronic hepatitis B, including the development of cirrhosis. In addition, the genotypes of the various HBV sequences were determined. Core promoter mutations were significantly more common in HCC patients than asymptomatic carriers from both regions of Guangxi and also were common in patients with cirrhosis and chronic hepatitis. The data also support the hypothesis that genotype C HBV causes more severe liver disease than does genotype B.

Influence of a putative intermolecular interaction between core and the pre-S1 domain of the large envelope protein on hepatitis B virus secretion

Virion release of hepatitis B virus (HBV) from hepatocytes is a tightly regulated event. It is a dogma that only the mature HBV genome is preferentially allowed to export from the intracellular compartment (J. Summers and W. S. Mason, Cell 29:403-415, 1982). Recently, an "immature secretion" phenotype of a highly frequent naturally occurring HBV variant containing a leucine residue at amino acid 97 of the core protein was identified. Unlike wild-type HBV, this variant secretes almost equal amounts of mature and immature genomes. This phenomenon is not caused by any instability of core particles or by any deficiency in viral reverse transcription (T. T. Yuan, P. C. Tai, and C. Shih, J. Virol. 73:10122-10128, 1999). In this study, our kinetic analysis of virion secretion of the mutant F97L (phenylalanine to leucine) indicates that the secretion of its immature genome does not occur earlier than that of its mature genome. In addition, the secretion kinetics of the mature genomes are comparable between the wild-type HBV and the mutant F97L. Therefore, the immature secretion phenomenon of mutant F97L is not caused by premature secretion or more efficient secretion. Previously, we hypothesized that the immature secretion phenotype is probably caused by the aberrant interaction between its mutant core and wild-type envelope proteins. Here, we further demonstrated that a pre-S1 envelope mutation at position 119, changing an alanine (A) to a phenylalanine (F), can offset the immature secretion phenotype of the mutant I97L (isoleucine to leucine) and successfully restore the wild-type-like selective export of the mature genome of the double mutant pre-S1-A119F/core-I97L.

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.

Vaccine- and hepatitis B immune globulin-induced escape mutations of hepatitis B virus surface antigen

Hepatitis B virus surface antigen (HBsAg) vaccination has been shown to be effective in preventing hepatitis B virus (HBV) infection. The protection is based on the induction of anti-HBs antibodies against a major cluster of antigenic epitopes of HBsAg, defined as the 'a' determinant region of small HBsAg. Prophylaxis of recurrent HBV infection in patients who have undergone liver transplantation for hepatitis B-related end-stage liver disease is achieved by the administration of hepatitis B immune globulins (HBIg) derived from HBsAg-vaccinated subjects. The anti-HBs-mediated immune pressure on HBV, however, seems to go along with the emergence and/or selection of immune escape HBV mutants that enable viral persistence in spite of adequate antibody titers. These HBsAg escape mutants harbor single or double point mutations that may significantly alter the immunological characteristics of HBsAg. Most escape mutations that influence HBsAg recognition by anti-HBs antibodies are located in the second 'a' determinant loop. Notably, HBsAg with an arginine replacement for glycine at amino acid 145 is considered the quintessential immune escape mutant because it has been isolated consistently in clinical samples of HBIg-treated individuals and vaccinated infants of chronically infected mothers. Direct binding studies with monoclonal antibodies demonstrated a more dramatic impact of this mutation on anti-HBs antibody recognition, compared with other point mutations in this antigenic domain. The clinical and epidemiological significance of these emerging HBsAg mutants will be a matter of research for years to come, especially as data available so far document that these mutants are viable and infectious strains. Strategies for vaccination programs and posttransplantation prophylaxis of recurrent hepatitis need to be developed that may prevent immune escape mutant HBV from spreading and to prevent these strains from becoming dominant during the next decennia.

A frequent, naturally occurring mutation (P130T) of human hepatitis B virus core antigen is compensatory for immature secretion phenotype of another frequent variant (I97L)

A frequent mutation at codon 97 of human hepatitis B virus core antigen has been shown to cause an "immature secretion" phenotype, featuring nonselective and excessive secretions of virions containing immature viral genome. Our current study demonstrates that this abnormality can be efficiently offset by another frequent core mutation, P130T.

Hepatitis B virus core promoter mutations in children with multiple anti-HBe/HBeAg reactivations result in enhanced promoter activity

Sera of two children were examined to determine whether specific hepatitis B virus (HBV) mutants may contribute to anti-hepatitis B e/hepatitis B e antigen (anti-HBe/HBeAg) reactivations during the course of chronic hepatitis B. The full-length HBV genome isolated from sera of patient 1 and the basic core promoter (BCP) from patient 2 were amplified and sequenced before and after several reactivations. The functional significance of the mutant BCP from patient 1 was studied using the luciferase assay. In both patients, rare mutations were found in the BCP at nucleotides 1764(G-->T)/1766(C-->G) and 1766(C-->T)/1768(T-->A) in case 1 and 2, respectively. In the BCP from patient 1, a putative new binding site for the transcription factor hepatocyte nuclear factor 3 (HNF3) was generated. The functional analyses of the mutant showed a 2.8-fold increase of core promoter activity, whereas the BCP variant of patient 2 was also identified to result in enhanced promoter activity. The alignment of full-length genomes from child 1 to the reference sequence showed 61 nucleotide substitutions. Furthermore, the time of reactivations from child 1 was always accompanied by selection of a precore mutation at nucleotide position 1899. In liver tissue of patient 1 before development of hepatocellular carcinoma only free viral sequences were found, whereas a single site integration of HBV was detected in hepatocytes after activation of carcinogenesis. Specific mutations in the HBV BCP of the two patients that are rarely present in chronic carriers were identified to increase the core promoter activity possibly by altering transcription factor binding, suggesting that these variants may be involved in the pathogenesis of frequent HBV reactivations.

Characterization of the reactivity pattern of murine monoclonal antibodies against wild-type hepatitis B surface antigen to G145R and other naturally occurring "a" loop escape mutations

The hepatitis B surface antigen (HBsAg) "a" domain harbors major B-cell epitopes. Viruses with mutations in this region emerge after vaccination or during hepatitis B immune globulin (HBIg) prophylaxis. A strain with G145R replacement has been almost invariably isolated as a major escape mutant. We investigated mutant antigen-antibody interactions with direct binding assays. G145R and 16 other naturally occurring recombinant HBsAg mutants were expressed in mammalian Cos-1 cells. The reactivity of a panel of 28 murine anti-hepatitis B surface antigen (anti-HBs) monoclonal antibodies to mutant antigens was measured with enzyme immunoassay and expressed as percentage compared with the wild-type (wt) HBsAg signal for each antibody. All point-mutated proteins displayed diffuse intracellular immunofluorescent labeling corresponding to a secretory pathway. Monoclonal antibodies (mAbs) were classified according to different binding patterns. The effect of mutations on antibody binding differs depending on the amino acid involved and on the location within the "a" loop. As expected, most antibodies had absent or negligible binding (<40%), notably with residue 145 replacements. However, we identified antibodies that reacted with conformational epitopes but nevertheless had adequate reactivity (>40%) with all mutant antigens, including G145R. The effect of G145R was more pronounced than that of G145A. A subgroup of antibodies had substantially increased recognition (>120%) of antigens with mutations in the first loop. We demonstrated that antibodies can be selected or combined that react with all mutants investigated, including G145R. These data offer perspectives for improving anti-HBs-based protection against hepatitis B.

Natural and iatrogenic variation in hepatitis B virus

The existence of HBV as quasispecies is thought to be favoured by the infidelity of HBV RT, which would account for the emergence of the many natural mutants with point substitutions. RT infidelity may also underlie the hypermutation phenomenon. Indeed, the oft-reported point mutation in the preC gene that leads to failure of HBeAg synthesis may be driven by a hypermutation-related mechanism. The presence of mutants with deletions and insertions involving single nucleotides and oligonucleotides at specific positions in the genome, and of mutants with deletions of even longer stretches particularly in the C gene, suggests that other mutagenic mechanisms operate. Candidates include slippage during mispairing between template and progeny DNA strand, the action of cellular topoisomerase I, and gene splicing using alternative donor and acceptor sites. Natural substitutions, deletions or insertions involving the Cp/ENII locus in the X gene can significantly alter the extent of viral replicative activity. Similar mutations occurring at other locations of Cp/ENII, and at B-cell epitope sites of the S gene are associated with failure to detect serological markers of HBV infection. HBV variation can also arise from recombination between coinfecting strains. S gene mutations that become evident following HBIG administration and HBV vaccination are all point substitutions, as are mutations in functional RT domains of the P gene after treatment with viral RT-inhibitory drugs. Widespread and long-term use of prophylactic and therapeutic agents may potentially generate serologically occult HBV variants that might become difficult to eradicate.

Three cases of severe subfulminant hepatitis in heart-transplanted patients after nosocomial transmission of a mutant hepatitis B virus

Fulminant and severe viral hepatitis are frequently associated with mutant hepatitis B virus (HBV) strains. In this study, the genetic background of a viral strain causing severe subfulminant outcome in heart-transplanted patients was studied and compared with viral hepatitis B strains that were not linked to severe liver disease in the same setting. A total of 46 patients infected nosocomially with HBV genotype A were studied. Five different viral strains were detected, infecting 3, 9, 5, 24, and 5 patients, respectively. Only one viral strain was found to be associated with the subfulminant outcome and 3 patient deaths as a consequence of severe liver disease. The remaining 43 patients with posttransplantation HBV infection did not show this fatal outcome. Instead, symptoms of hepatitis were generally mild or clinically undiagnosed. Comparison of this virus genome with the four other strains showed an accumulation of mutations in the basic core promoter, a region that influences viral replication, but also in hepatitis B X protein (HBX) (7 mutant motifs), core (10 mutant motifs), the preS1 region (5 mutant motifs), and the HBpolymerase open reading frame (17 motifs). Some of these variations, such as those in the core region, were located on the tip of the protruding spike of the viral capsid (codons 60 to 90), also known in part as an important HLA class II-restricted epitope region. These mutations might therefore influence the immune-mediated response. The viral strain causing subfulminant hepatitis was, in addition, the only strain with a preCore stop codon mutation and, thus, hepatitis B e antigen (HBeAg) expression was never observed. The combination of these specific viral factors is thought to be responsible for the fatal outcome in these immune-suppressed heart-transplant recipients.

Severe clinical course of de novo hepatitis B infection after liver transplantation

The aim of this study is to determine the origin, clinical outcome, allograft histological characteristics, and virological outcome of de novo hepatitis B virus (HBV) infection after orthotopic liver transplantation (OLT). We studied 136 hepatitis B surface antigen (HBsAg)-negative liver transplant recipients. HBV DNA was detected by dot-blot hybridization and polymerase chain reaction (PCR). The S gene was sequenced. Hepatitis C virus (HCV) RNA was assessed by PCR. The long-term clinical and histological outcome was determined. Six of 136 HBsAg-negative patients (4.4%) became HBsAg positive after transplantation. The source of HBV infection was reactivation of latent HBV infection in 2 patients and was not identified in 4 patients. Two donors had isolated core antibody. Two of these 6 patients developed acute liver failure related to hepatitis B. The 4 other patients had severe chronic hepatitis related to hepatitis B. All patients had high-level HBV replication. No significant mutations in the S gene were found. These data suggest that de novo hepatitis B infection is not a mild disease and might represent a significant cause of graft dysfunction. This is the first report of fulminant hepatitis caused by de novo hepatitis B infection after OLT.