Precore mutations and core clustering mutations in chronic hepatitis B virus infection

Amino Acid Polymorphism in Hepatitis B Virus Associated With Functional Cure

BACKGROUND & AIMS

To provide an adequate treatment strategy for chronic hepatitis B, it is essential to know which patients are expected to have a good prognosis and which patients do not require therapeutic intervention. Previously, we identified the substitution of isoleucine to leucine at amino acid 97 (I97L) in the hepatitis B core region as a key predictor among patients with stable hepatitis. In this study, we attempted to identify the point at which I97L affects the hepatitis B virus (HBV) life cycle and to elucidate the underlying mechanisms governing the stabilization of hepatitis.

METHODS

To confirm the clinical features of I97L, we used a cohort of hepatitis B e antigen-negative patients with chronic hepatitis B infected with HBV-I97 wild-type (wt) or HBV-I97L. The effects of I97L on viral characteristics were evaluated by in vitro HBV production and infection systems with the HBV reporter virus and cell culture-generated HBV.

RESULTS

The ratios of reduction in hepatitis B surface antigen and HBV DNA were higher in patients with HBV-I97L than in those with HBV-I97wt. HBV-I97L exhibited lower infectivity than HBV-I97wt in both infection systems with reporter HBV and cell culture-generated HBV. HBV-I97L virions exhibiting low infectivity primarily contained a single-stranded HBV genome. The lower efficiency of cccDNA synthesis was demonstrated after infection of HBV-I97L or transfection of the molecular clone of HBV-I97L.

CONCLUSIONS

The I97L substitution reduces the level of cccDNA through the generation of immature virions with single-stranded genomes. This I97L-associated low efficiency of cccDNA synthesis may be involved in the stabilization of hepatitis.

Deep sequencing identifies hepatitis B virus core protein signatures in chronic hepatitis B patients

BACKGROUND

We aimed to identify HBc amino acid differences between subgroups of chronic hepatitis B (CHB) patients.

METHODS

Deep sequencing of HBc was performed in samples of 89 CHB patients (42 HBeAg positive, 47 HBeAg negative). Amino acid types were compared using Sequence Harmony to identify subgroup specific sites between HBeAg-positive and -negative patients, and between patients with combined response and non-response to peginterferon/adefovir combination therapy.

RESULTS

We identified 54 positions in HBc where the frequency of appearing amino acids was significantly different between HBeAg-positive and -negative patients. In HBeAg negative patients, 22 positions in HBc were identified which differed between patients with treatment response and those with non-response. The fraction non-consensus sequence on selected positions was significantly higher in HBeAg-negative patients, and was negatively correlated with HBV DNA and HBsAg levels.

CONCLUSIONS

Sequence Harmony identified a number of amino acid changes associated with HBeAg-status and response to peginterferon/adefovir combination therapy.

Potential Susceptibility Mutations in C Gene for Hepatitis B-Related Hepatocellular Carcinoma Identified by a Two-Stage Study in Qidong, China

A two stage study was conducted to explore new potential mutations in the full genome of hepatitis B virus (HBV) on the progression of hepatocellular carcinoma (HCC) in Qidong, China. In stage 1, full genomes of HBV were compared between 30 HCC cases and 30 controls. In stage 2, an independent case-control study including 100 HCC cases and 100 controls was enrolled to verify the relationship between hot-spot mutations and HCC development. Furthermore, a longitudinal study was conducted on 11 HCC cases with serial serum samples available before HCC diagnosis. A total of 10 mutations (including pre-S2 start codon mutation and pre-S deletion in pre-S gene, G1613A, C1653T, A1762T, and G1764A mutations in X gene, A2159G, A2189Y, G2203W, and C2288R mutations in C gene) showed an increased risk of HCC. In the validation study, pre-S deletion, C1653T, A1762T/G1764A, A2159G, A2189Y, G2203W, and C2288R mutations were associated with increased HCC risk in univariate analysis. Multivariate analysis indicated that pre-S deletion, A1762T/G1764A, A2159G, and A2189Y mutations were independently related with HCC development. Moreover, a significant biological gradient of HCC risk by number of mutations in the C gene was observed. Longitudinal observation demonstrated a gradual combination of the above mutations accumulated during the progression of HCC.

Impact of Nucleotide Mutations at the HNF3- and HNF4-Binding Sites in Enhancer 1 on Viral Replication in Patients with Chronic Hepatitis B Virus Infection

Background/Aims

The hepatitis B virus (HBV) genome contains binding sites for hepatocyte nuclear factors (HNF) 3 and 4 in the core domain of enhancer 1 (Enh1), and mutations in this domain have a strong impact on virus replication. We aimed to identify frequent base-mutation sites in the core domain of Enh1 and to examine the impact of these mutations on viral replication.

Methods

We studied virological characteristics and genetic sequences in 387 patients with chronic hepatitis B. We evaluated functional differences associated with specific mutations within the core domain of Enh1.

Results

Mutations in the core domain were found with significant frequency in C1126 (122/387 [31.5%], the binding site for HNF3) and in C1134 (106/387 [27.4%], the binding site for HNF4). A single mutation at nt 1126 (C1126) was identified in 17/123 (13.8%), and 105/123 (85.4%) had double mutations (C1126/1134). The level of HBV DNA (log10 copies/mL) was lower in single mutants (C1126, 5.81±1.25) than in wild (6.80±1.65) and double mutants (C1126/1134, 6.81±1.54). Similarly, the relative luciferase activity of C1126 and C1126/C1134 was 0.18 and 1.12 times that of the wild-type virus, respectively.

Conclusions

Mutations in the HNF3 binding site inhibit viral replication, whereas mutations at the HNF4 binding site restore viral replication.

Combination and evolution of HBV mutant strains in the HBeAg-positive status predict clinical outcomes after HBeAg seroconversion

PURPOSE

We investigated whether the combined presence and evolution of hepatitis B virus (HBV) mutant strains in the hepatitis B e antigen (HBeAg)-positive status can predict clinical outcomes after HBeAg seroconversion.

METHODS

One hundred and eighty-six patients with spontaneous HBeAg seroconversion were enrolled into this longitudinal study. The sequences of pre-S, core promoter, and precore regions were determined at study entry and at the visit immediately before HBeAg seroconversion.

RESULTS

Age ≥40 years at HBeAg seroconversion, male sex, and higher HBV DNA levels at entry were independent predictors for HBeAg-negative chronic hepatitis B (CHB). Patients with combined mutations of pre-S deletions and T1762/A1764 had a significantly increased risk of cirrhosis and hepatocellular carcinoma (HCC) compared to patients with the wild type at both genomic regions. Combinations of pre-S deletions and T1762/A1764 were found on the same HBV genome by cloning analysis of full-length HBV genomes. Patients with a persistent presence of pre-S deletions and T1762/A1764 mutations, and new development of pre-S deletions in the HBeAg-positive status were significantly at an increased risk of HBeAg-negative CHB, cirrhosis, and HCC after HBeAg seroconversion than those with a persistent presence of the wild type at both genomic regions. After adjusting the other risk factors, the evolution of pre-S deletions was an independent predictor for cirrhosis [hazard ratio (HR): 1.52, 95 % confidence interval (CI) 1.02-2.25] and HCC (HR: 4.0, 95 % CI 1.6-10.1).

CONCLUSIONS

The combined presence and evolution of pre-S deletions and T1762/A1764 in the HBeAg-positive status was a useful factor significantly predictive of clinical outcomes in patients with spontaneous HBeAg seroconversion.

Analysis of precore/core covariances associated with viral kinetics and genotypes in hepatitis B e antigen-positive chronic hepatitis B patients

Hepatitis B virus (HBV) is one of the most common DNA viruses that can cause aggressive hepatitis, cirrhosis and hepatocellular carcinoma. Although many people are persistently infected with HBV, the kinetics in serum levels of viral loads and the host immune responses vary from person to person. HBV precore/core open reading frame (ORF) encoding proteins, hepatitis B e antigen (HBeAg) and core antigen (HBcAg), are two indicators of active viral replication. The aim of this study was to discover a variety of amino acid covariances in responses to viral kinetics, seroconversion and genotypes during the course of HBV infection. A one year follow-up study was conducted with a total number of 1,694 clones from 23 HBeAg-positive chronic hepatitis B patients. Serum alanine aminotransferase, HBV DNA and HBeAg levels were measured monthly as criteria for clustering patients into several different subgroups. Monthly derived multiple precore/core ORFs were directly sequenced and translated into amino acid sequences. For each subgroup, time-dependent covariances were identified from their time-varying sequences over the entire follow-up period. The fluctuating, wavering, HBeAg-nonseroconversion and genotype C subgroups showed greater degrees of covariances than the stationary, declining, HBeAg-seroconversion and genotype B. Referring to literature, mutation hotspots within our identified covariances were associated with the infection process. Remarkably, hotspots were predominant in genotype C. Moreover, covariances were also identified at early stage (spanning from baseline to a peak of serum HBV DNA) in order to determine the intersections with aforementioned time-dependent covariances. Preserved covariances, namely representative covariances, of each subgroup are visually presented using a tree-based structure. Our results suggested that identified covariances were strongly associated with viral kinetics, seroconversion and genotypes. Moreover, representative covariances may benefit clinicians to prescribe a suitable treatment for patients even if they have no obvious symptoms at the early stage of HBV infection.

Evolutionary pattern of full hepatitis B virus genome during sequential nucleos(t)ide analog therapy

The evolutionary and mutational pattern of full hepatitis B virus (HBV) quasispecies during sequential nucleos(t)ide analog (NUC) therapy remains unclear. In this study, full-length HBV clones were generated from serial serum samples of five chronic hepatitis B patients who received sequential NUC therapies (treated patients) and two untreated patients with acute flares. The evolutionary and mutational patterns of full HBV quasispecies were studied. In the three treated patients who received lamivudine as initial antiviral therapy, nucleotide polymorphism and nonsynonymous divergence all decreased at lamivudine breakthrough but increased after rescue therapies. Conversely, two other treated patients showed a distinct change in divergence during adefovir-telbivudine sequential therapies. Untreated subjects exhibited increased polymorphism and divergence in the preC/C region at ALT flare. Four of the treated patients presented amino acid changes in the "a" determinant during NUC therapy. All of the treated subjects showed amino acid changes within the known T-cell or B-cell epitopes in the surface or core antigen, most of which were accompanied by mutations in reverse transcriptase (RT) region. Co-variations in the core promoter, the preC region and in the known epitopes of the preS gene accompanied by RT mutations, were common. In untreated patients, most of these co-variations located in the preC/C gene. In conclusion, the distribution of genetic variability of HBV shows remarkably different patterns between the treated and untreated subjects and the quasispecies divergence of different regions of HBV may vary remarkably even within a single host.

Evolution of full-length HBV sequences in chronic hepatitis B patients with sequential lamivudine and adefovir dipivoxil resistance

BACKGROUND & AIMS

The aim of this study was to determine the evolution of full-length hepatitis B virus (HBV) sequences in chronic hepatitis B (CHB) patients with sequential lamivudine (LAM) and adefovir (ADV) resistance.

METHODS

The full-length genomes of HBV were sequenced from 11 CHB patients before LAM treatment and at the emergence of LAM- and ADV-resistant HBV.

RESULTS

Besides the known LAM-resistant polymerase gene mutations, 10 of 11 patients who had LAM-resistant HBV variants had additional amino acid changes in the reverse transcriptase (RT) domain, and ADV therapy reversed these additional changes to pre-LAM therapy status. Furthermore, new amino acid changes in the RT domain, distinct from the known ADV-resistant HBV variants, were selected at the emergence of ADV resistance in six of 11 patients. Seven patients had amino acid changes within the known T-cell or B-cell epitopes of HBV surface and core antigens at the emergence of LAM and/or ADV resistance. The frequency of pre-S deletions between nucleotide 3037-56 was higher at the emergence of ADV resistance compared with that at the emergence of LAM resistance (7/11 vs. 1/11; p=0.024). Combined LAM-ADV resistance was detected in one of 11 patients. This patient had resistant mutations to both drugs on the same viral genome by molecular cloning (5/24 polymerase gene clones).

CONCLUSIONS

In addition to the known LAM- and ADV-resistant mutations accompanying the emergence of LAM and ADV resistance, the changes of nucleotide or amino acid sequences occurred commonly in the HBV surface antigen or RT domain and were scattered along the full-length HBV genomes.

Analysis of the core gene of hepatitis B virus in Korean patients

BACKGROUND/AIMS

As the core gene of hepatitis B virus (HBV) is a major immunological target, its mutation may evoke or evade immune clearance. We investigated the frequency and location of HBV core gene substitutions according to hepatitis B e antigen (HBeAg) status and viral replication status, and evaluated the association of these substitutions with the different stages of chronic HBV infection in Korean patients.

METHODS

The study population included 45 HBeAg-positive/DNA-positive patients (group I), 49 HBeAg-negative/DNA-positive patients (II) and 50 HBeAg-negative/DNA-negative patients (III). The HBV core gene was analysed by polymerase chain reaction (PCR) and sequencing.

RESULTS

The frequency of core gene substitutions increased from group I to group III. Substitutions were commonly detected at codons 87, 97, 112 and 130. The frequency of substitutions at codons 87 and 112 was higher in groups II/III than in group I. The frequency of the codon I97F substitutions was the highest in group III. However, the codon 130 substitution was more frequently found in groups I/II than in group III.

CONCLUSION

Core gene substitutions were more frequently detected in HBeAg-negative and/or HBV DNA-negative patients. The substitutional hot spots were codons 87, 97, 112 and 130; substitutions at these codons might play a role in immune-modulation during the course of chronic HBV infection.

Characterization of sequence variations in immunodominant regions of the HBV-nucleocapsid protein as a prerequisite for the development of an epitope-based vaccine

BACKGROUND/AIMS

In hepatitis B virus infection, viral elimination is dependent on an efficient antiviral T cell response which is not detectable in chronic hepatitis B. Therefore, new therapeutic concepts focus on T cell activation, such as epitope-based T cell-targeted vaccines. However, with the development of peptide-based vaccines in mind, viral mutations frequently described in hepatitis B within known immunodominant helper epitopes may have an influence on peptide selection.

METHODS

Mutant peptides within immunodominant epitopes (aa 1-20, aa 91-105, and aa 143-157) at position 12, 14, 93, 97, 147, 151, 153, and 155 were tested with peripheral blood mononuclear and specific clone cells for their ability to induce proliferation, produce cytokines, induce T cell receptor down-regulation or antagonize wild-type activity of the hepatitis B core antigen-specific CD4+ T cell clones.

RESULTS

Five variants could not induce T cell proliferation or cytokine production when the variants were presented alone. Coincubation with wild-type epitopes leads to T cell activation showing that the variants do not act as T cell receptor antagonists for hepatitis B virus-specific CD4+ T cells. In contrast, five other variants and wild-type peptides stimulated CD4+ T cell proliferation and production of Th1 cytokines.

CONCLUSIONS

Our data demonstrate that frequently occurring mutations within immunodominant epitopes have rather a nonstimulatory than a strengthening effect and thus should not included in a vaccine.

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.

Phosphorylation of hepatitis B virus Cp at Ser87 facilitates core assembly

Protein-protein interactions can be regulated by protein modifications such as phosphorylation. Some of the phosphorylation sites (Ser155, Ser162 and Ser170) of HBV (hepatitis B virus) Cp have been discovered and these sites are implicated in the regulation of viral genome encapsidation, capsid localization and nucleocapsid maturation. In the present report, the dimeric form of HBV Cp was phosphorylated by PKA (protein kinase A), but not by protein kinase C in vitro, and the phosphorylation of dimeric Cp facilitated HBV core assembly. Matrix-assisted laser-desorption ionization-time-of-flight analysis revealed that the HBV Cp was phosphorylated at Ser87 by PKA. This was further confirmed using a mutant HBV Cp with S87G mutation. The S87G mutation inhibited the phosphorylation and, as a result, the in vitro HBV core assembly was not facilitated by PKA. In addition, when either pCMV/FLAG-Core(WT) or pCMV/FLAG-Core(S87G) was transfected into HepG2 cells, few mutant Cps (S87G) assembled into capsids compared with the wild-type (WT) Cps, although the same level of total Cps was expressed in both cases. In conclusion, PKA facilitates HBV core assembly through phosphorylation of the HBV Cp at Ser87.

The clinical virology of hepatitis B

Hepatitis B virus (HBV) is a major human health problem as approximately 8% of the world’s population are chronic carriers and there are over a million HBV-related deaths annually. Treatment of HBV is extremely difficult, as the unique viral replication strategy results in both a continual source of stable DNA molecules that are the template for viral replication and gene expression, and a pool of viral quasispecies from which different isolates may emerge as selection pressures alter. Although the use of antiviral therapies has improved outcomes significantly for many chronically infected individuals, the emergence of drug-resistant and immune/vaccine-escape viruses ensures there is a continuing need for the development of new and imaginative approaches to control and eventually eradicate HBV.

Characterization of naturally occurring and Lamivudine-induced surface gene mutants of hepatitis B virus in patients with chronic hepatitis B in India

BACKGROUND

Besides vaccine escape or immune escape hepatitis B virus (HBV) mutants, naturally occurring and drug-induced mutations have been reported in the surface gene (S-gene) of HBV.

AIM

To investigate the frequency and profile of naturally occurring S-gene mutants and the influence of long-term lamivudine therapy in patients with chronic hepatitis B (CHB).

MATERIALS AND METHODS

57 patients with histologically proven CHB, on lamivudine 100 mg/day for more than 24 months, were included. Viral DNA was extracted at baseline and from on-therapy serum samples. The region encoding the complete major hydrophilic region (MHR) and flanking regions (nucleotides 425-840) of major S-gene that overlapped with the viral polymerase was PCR amplified and sequenced. End-of-therapy response (ETR) was assessed.

RESULTS

Two (3.5%) patients had naturally occurring HBV mutants, sP127S and sS143L seen in the 'a' determinant of the S-gene. Following lamivudine therapy, 14 of 57 (24.5%) patients developed 16 types of S-gene mutations (sP120S, sA128V, sS143L, sW182St., sT189I, sV190A, sS193L, sI195M, sW196L, sW196St., sS207R, sI208T, sS210E, sF219S, sF220L and sC221G). Thirteen (81.2%) of these mutations emerged downstream to the MHR. Nine of 16 types of S-gene mutations observed with lamivudine therapy were also associated with the corresponding changes in the polymerase gene. Baseline viral DNA was significantly higher (2,093 vs. 336 pg/ml; p < 0.05) among patients developing S-gene mutants and the ETR in them was significantly lower [3 of 16 (18.8%) vs. 17 of 41 (41.5%); p < 0.05].

CONCLUSIONS

Naturally occurring S-gene mutations are uncommon and are restricted to the 'a' determinant region. Mutations develop in about a quarter of the patients on lamivudine therapy, mostly downstream to the MHR. They may contribute to non-response to the antiviral therapy.

Reduced secretion of virions and hepatitis B virus (HBV) surface antigen of a naturally occurring HBV variant correlates with the accumulation of the small S envelope protein in the endoplasmic reticulum and Golgi apparatus

We identified two novel naturally occurring mutations (W74L and L77R) in the small S envelope protein of hepatitis B virus (HBV). Mutation L77R alone resulted in >10-fold-reduced secretion of virions. In addition, the 2.8-fold reduction of the extracellular HBV surface antigen (HBsAg) of mutant L77R from transfected Huh7 cells appeared to be correlated with a 1.7-fold reduction of intracellular HBsAg, as measured by enzyme-linked immunosorbent assay (ELISA). Surprisingly, opposite to the ELISA results, Western blot analysis revealed a near-10-fold-increased level of the intracellular mutant small S envelope protein. The discrepancy between ELISA and Western blot data was due to significant accumulation of the mutant L77R HBsAg in the intracellular pellet fraction. In contrast to HBsAg, the secretion of HBeAg was normal in L77R-transfected cells. The wild-type HBsAg was usually more diffuse and evenly distributed in the cytoplasm, often outside the perinuclear endoplasmic reticulum (ER) and Golgi apparatus, as observed by immunofluorescence assay. In contrast, the L77R mutant HBsAg tends to be highly restricted within the ER and Golgi, often accumulated in the Golgi compartments distal from the nucleus. The almost exclusive retention in the ER-Golgi of L77R HBsAg was similar to what was observed when the large envelope protein was overexpressed. These multiple aberrant phenotypes of mutant L77R can be corrected by a second naturally occurring S envelope mutation, W74L. Despite the accumulation of L77R HBsAg in ER-Golgi of transfected Huh7 cells, we detected no increase in Grp78 mRNA and proteins, which are common markers for ER stress response.

Variability and conservation in hepatitis B virus core protein

Background

Hepatitis B core protein (HBVc) has been extensively studied from both a structural and immunological point of view, but the evolutionary forces driving sequence variation within core are incompletely understood.

Results

In this study, the observed variation in HBVc protein sequence has been examined in a collection of a large number of HBVc protein sequences from public sequence repositories. An alignment of several hundred sequences was carried out, and used to analyse the distribution of polymorphisms along the HBVc. Polymorphisms were found at 44 out of 185 amino acid positions analysed and were clustered predominantly in those parts of HBVc forming the outer surface and spike on intact capsid. The relationship between HBVc diversity and HBV genotype was examined. The position of variable amino acids along the sequence was examined in terms of the structural constraints of capsid and envelope assembly, and also in terms of immunological recognition by T and B cells.

Conclusion

Over three quarters of amino acids within the HBVc sequence are non-polymorphic, and variation is focused to a few amino acids. Phylogenetic analysis suggests that core protein specific forces constrain its diversity within the context of overall HBV genome evolution. As a consequence, core protein is not a reliable predictor of virus genotype. The structural requirements of capsid assembly are likely to play a major role in limiting diversity. The phylogenetic analysis further suggests that immunological selection does not play a major role in driving HBVc diversity.

Hepatitis B and C Virus Variants in Long-Term Immunosuppressed Renal Transplant Patients in Latvia

The incidence of genome variants of hepatitis B and hepatitis C viruses among 38 long-term (2-15 years) immunosuppressed patients after renal transplantation and 10 patients undergoing dialysis was investigated. Twelve patients had only HBV infection, 9 had only HCV infection and 14 were co-infected. Regions corresponding to the HBV X/EnII/BCP, preC/C, preS/S and to the HCV core were sequenced for molecular characterization of the HBV and HCV genomes. Fifty-seven percent of HBV DNA isolates belonged to genotype D and 42% to genotype A, whereas 77% of HCV RNA isolates belonged to genotype 1b and only 17% to genotype 3a. One sample (6%) was of genotype 2c. Detailed analysis of the above-mentioned HBV genome regions revealed the presence of nucleotide point mutations, which, in some cases, resulted in amino acid substitutions. The clinical significance of such mutations is discussed.

Hot-spot mutations in hepatitis B virus core gene: eliciting or evading immune clearance?

The biological implications of substitutions L60V and I97L in the core (c) gene of hepatitis B virus (HBV) were investigated in order to determine whether they could change the immunogenicity of HBcAg or influence the immune response in mice. Three strains of recombinant adenoviruses--AdHBV-WT, AdHBV-L60V and AdHBV-I97L--containing wild-type or mutant HBV genomes were constructed using the AdEasy system and used to infect BALB/c mice intranasally. Infected mice produced anti-HBc efficiently to comparable levels. IgG1 and IgG2a specific for HBcAg were present in mice sera, and the response was dominated by IgG2a. The lymphocyte proliferative response specific for HBcAg was assessed by [3H]-thymidine uptake. We found that AdHBV-WT induced a stronger T-cell proliferation response than AdHBV-L60V and AdHBV-I97L. In conclusion, the L60V and I97L substitutions had no influence on humoral immune responses, but could downregulate T-cell responses to HBcAg, suggesting that L60V and I97L were immune escape mutants.

Nucleolar localization of human hepatitis B virus capsid protein

Wild-type human hepatitis B virus (HBV) exhibits selective export of virions containing mature genomes. In contrast, changing an isoleucine to a leucine at amino acid 97 (I97L) of the HBV core antigen (HBcAg) causes it to release immature genomes. To elucidate the structure-function relationship of HBcAg at amino acid 97, we systematically replaced the isoleucine residue at this position with 18 other amino acids via mutagenesis. Twelve of the 18 mutants exhibited no significant phenotype, while five new mutants displayed strong phenotypes. The I97D mutant had a near lethal phenotype, the I97P mutant exhibited a significantly reduced level of virion secretion, and the I97G mutant lacked the full-length relaxed circular form of viral DNA. The tip of the spike of the capsid particle is known to contain a predominant B-cell epitope. However, the recognition of this exposed epitope by an anti-HBc antibody appeared to be affected by the I97E mutation or by histidine tagging at the C terminus of mutant HBcAg, which is presumably in the capsid interior. Surprisingly, the nuclear HBcAg of mutants I97E and I97W, produced from either a replicon or an expression vector, was found to be colocalized with nucleolin and B23 at a frequency of nearly 100% by confocal immunofluorescence microscopy. In contrast, this colocalization occurred with wild-type HBcAg only to a limited extent. We also noted that nucleolin-colocalizing cells were often binucleated or apoptotic, suggesting that the presence of HBcAg in the nucleolus may perturb cytokinesis. The mechanism of this phenomenon and its potential involvement in liver pathogenesis are discussed. To our knowledge, this is the first report of nucleolar HBcAg in culture.

HBV core sequence: definition of genotype-specific variability and correlation with geographical origin

There are eight genotypes and nine subtypes of HBV. Small differences in geographical origin are associated with sequence changes in the surface gene. Here, we compared core gene sequences from different genotypes and geographical regions. Specific combinations of 24 amino acid substitutions at nine residues allowed allocation of a sequence to a subtype. Six of these nine residues were located in different T cell epitopes depending on HBV geographical area and/or genotype. Thirty-seven nucleotide changes were associated uniquely with specific genotypes and subtypes. Unique amino acid and nucleotide variants were found in a majority of sequences from specific countries as well as within subtype ayw2 and adr. Specific nucleotide motifs were defined for Korean, Indian, Chinese, Italian and Pacific region isolates. Finally, we observed amino acid motifs that were common to either South-east Asian or Western populations, irrespective of subtype. We believe that HBV strains spread within constrained ethnic groups, result in selection pressures that define sequence variability within each subtype. It suggests that particular T cell epitopes are specific for geographical regions, and thus ethnic groups; this may affect the design of immunomodulatory therapies.

Origin of serum hepatitis B virus in acute exacerbation: comparison with HBV in the liver and from other exacerbation

Acute exacerbation (AE) of chronic hepatitis B is usually preceded by reemergence or increase of hepatitis B virus (HBV) in the serum. To investigate the origin of the reemergence or increase, we compared the identity of the serum viral genome to that in the liver and in previous AE by full-length sequencing. The full-length viral genome and extent of quasispecies were obtained from serum and liver biopsy specimens at the same time from 9 subjects with hepatitis B exacerbation (group I). Composition of viral quasispecies was compared by the genetic diversity and the average number of nucleotide substitutions within and between different viral sources. Another 2 patients with repeated AEs (group II) were also enrolled, and their serial serum alanine aminotransferase, HBV DNA levels and full-length sequences were determined. In all group I patients, serum viral genome was identical to that in the liver. The genetic diversity and the average number of nucleotide difference were also comparable between serum and liver tissue. In 2 group II patients, the viral variant that emerged after previous AE was not identical to that caused by the subsequent AE. Dominant viral strains for serial AEs in a single patient did not show a sequential evolution, but presented as a horizontal selection of a minor population from the original viral pool. In conclusion, the findings suggest that viral strain in serum reflects the intrahepatic strain of the AE. Random reactivation of the original HBV pool, rather than a sequential evolution of one strain, also contributes to the onset of repeated AE. Supplementary material for this article can be found on the HEPATOLOGY website (http://interscience.wiley.com/jpages/0270-9139/suppmat/index.html).

Hepatitis B virus X protein (HBx)-induced apoptosis in HuH-7 cells: influence of HBV genotype and basal core promoter mutations

BACKGROUND

Hepatitis B virus (HBV) infection is a serious, world-wide problem. HBV genotype and basal core promoter (BCP) mutations affect the clinical course of HBV-infected patients. BCP mutations also lead to mutations at HBV X protein (HBx) codons 130/131. The functional significance of naturally occurring variants of human HBx remains largely unknown. The purpose of the study was to investigate whether HBV genotypes or double mutations affect HBx-induced apoptosis.

METHODS

We constructed genotype A, B, C, and D HBx expression vectors and HBx expression vectors with double mutations at HBx codons 130K and 131V or positions 130M and 131I using site-directed mutagenesis. A transient expression system in HuH-7 cells was established and this model was utilized to address the effect of HBx on cell viability.

RESULTS

HBx-transfected cells showed a dose-dependent decrease in cell viability by MTS assay. A subset of cells expressing HBx underwent apoptosis according to terminal transferase enzyme-mediated end labeling of DNA and caspase-3 activity. This study demonstrated that HBx can induce cell death by apoptosis in a dose-dependent manner and that HBV genotypes and double mutations did not affect HBx-induced apoptosis.

CONCLUSIONS

HBV genotypes and mutation of two amino acids directly adjacent to the conserved Kunitz domain essential for transcription activating activity of HBx did not change the pro-apoptotic activity of HBx. Further study is needed to determine whether HBV genotypes and double mutations have any effect on the function of HBx.

Direct evidence that naturally occurring mutations within hepatitis B core epitope alter CD4+ T-cell reactivity

Exacerbations of chronic hepatitis B have been associated with accumulation of mutations in the HBV core gene, with amino acid (aa) substitutions clustering between aa 50 and 69. This region of the nucleocapsid protein is known as an immunodominant epitope for CD4+ T-lymphocytes, however the impact of these mutations on T-cell reactivity has not been investigated. For this purpose, we undertook fine mapping of the reactivity of peripheral blood lymphocytes, isolated from patients with acute (n = 8) or chronic hepatitis B (n = 10), against a panel of branched synthetic peptides. The peptide aa sequences corresponded to the wild type HBV (aa 50-69), or contained 1-3 aa changes derived on the basis of naturally occurring mutations. In four of eight patients with acute hepatitis B the wild type peptide 50-69, which corresponded to the core gene sequence of HBV present in these patients, induced a strong T-cell proliferative response. In the same cases, the T-cell response to the mutant peptides was altered at various degrees, depending on the number and the position of aa changes. The most pronounced inhibition of CD4+ T-cell response (between 44 and 92%) was caused by a peptide ligand with two aa substitutions at positions 64 and 67. These results demonstrate that mutations within immunodominant epitopes of the HBV nucleocapsid can affect the CD4+ T-lymphocyte reactivity, which may have a role for the accumulation of certain HBV strains after hepatitis flares during the course of chronic HBV infection.

Coexistence of two distinct secretion mutations (P5T and I97L) in hepatitis B virus core produces a wild-type pattern of secretion

Unlike a Tokyo isolate of hepatitis B virus variants, we found a Shanghai isolate that secretes few virions with an immature genome despite its core I97L mutation. Core mutations P5T and I97L were found to be mutually compensatory in offsetting their respective distinct effects on virion secretion.

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.

Replication advantage and host factor-independent phenotypes attributable to a common naturally occurring capsid mutation (I97L) in human hepatitis B virus

Mutations of human hepatitis B virus (HBV) occur frequently within the capsid (core) protein in natural infections. The most frequent mutation of the core protein in HBV from Southeast Asia occurs at amino acid 97, changing an isoleucine (I) to a leucine (L). In our systematic study of virus-host interactions, we have examined the replication efficiency of a site-directed mutant, I97L, and its parental wild-type HBV in several different hepatoma cell lines. Interestingly, we found that this capsid variant replicated in human Huh7 hepatoma cells approximately 4.8-fold better than its parental wild-type HBV. A similar phenomenon was observed in another hepatoma cell line, J3. In addition, the level of encapsidated RNA pregenome in mutant I97L was about 5.7-fold higher than that of the wild-type HBV in Huh7 cells. Unlike Huh7 cells, no significant difference in viral DNA replication between the same I97L mutant and its parental wild-type HBV was observed in HepG2, a human hepatoblastoma cell line. This finding of a profound replication advantage for mutant I97L in Huh7 and J3 cells but not in HepG2 cells may have important implications for the emergence of this mutant in chronic HBV carriers. We speculate here that the mutation confers a host factor-independent growth advantage for the survival of HBV variants in gradually dedifferentiating hepatocytes and thus helps prolong viral persistence.

Naturally occurring hepatitis B surface gene variants in chronic hepatitis B virus infection: correlation with viral serotypes and clinical stages of liver disease

Virus variants escaping from host immunity may be implicated in the pathogenesis of hepatitis B virus (HBV) infection. In this cross-sectional study, the association was evaluated of the frequency of amino acid variation within the immunogenic epitopes of surface gene with different disease stages of chronic HBV infection. The surface gene of HBV encompassing the a determinant (amino acids 124-148) and the putative HLA class I restricted cytotoxic T lymphocyte (CTL) epitope (amino acids 28- 51) were amplified and directly sequenced in 33 asymptomatic carriers (Group I), 31 patients with chronic hepatitis (Group II), 22 with cirrhosis (Group III), and 36 with hepatocellular carcinoma (Group IV). The amino acid sequences were compared subsequently with the consensus sequences of HBV serotype adw or adr. The frequency of amino acid variation per site per sequence (FEQ) was analyzed by generalized estimating equation with Poisson model after stratification by clinical and virological features. The FEQ was 1.21% overall, and was highest in Group IV patients and in patients above 50 years of age. In contrast, nine Group IV patients aged below 50 years who were infected with serotype adw had an inversely higher FEQ than those above 50; the age effect among hepatocellular carcinoma patients was significantly different from that among non-cancerous patients (P = 0.04). Variation of amino acid clustered within a determinant and CTL epitope for serotype adw but was distributed at random for serotype adr. Mutation hotspots differed between serotypes adw and adr. The FEQ of HBV surface protein is correlated positively with advancing age and severity of liver disease, and certain variants may contribute to the persistence of HBV infection.

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.

Nitric oxide in liver diseases: friend, foe, or just passerby?

Research on the free radical gas, nitric oxide (NO), during the past twenty years is one of the most rapid growing areas in biology. NO seems to play a part in almost every organ and tissue. However, there is considerable controversy and confusion in understanding its role. The liver is one organ that is clearly influenced by NO. Acute versus chronic exposure to NO has been associated with distinct patterns of liver disease. In this paper we review and discuss the involvement of NO in various liver diseases collated from observations by various researchers. Overall, the important factors in determining the beneficial versus harmful effects of NO are the amount, duration, and site of NO production. A low dose of NO serves to maximize blood perfusion, prevent platelet aggregation and thrombosis, and neutralize toxic oxygen radicals in the liver during acute sepsis and reperfusion events. NO also demonstrates antimicrobial and antiapoptosis properties during acute hepatitis infection and other inflammatory processes. However, in the setting of chronic liver inflammation, when a large sustained amount of NO is present, NO might become genotoxic and lead to the development of liver cancer. Additionally, during prolonged ischemia, high levels of NO may have cytotoxic effects leading to severe liver injury. In view of the various possible roles that NO plays, the pharmacologic modulation of NO synthesis is promising in the future treatment of liver diseases, especially with the emergence of selective NO synthase inhibitors and cell-specific NO donors.

Impact of HLA-compatibilities in patients undergoing liver transplantation for HBV-cirrhosis

Liver transplantation (OLT) for end-stage chronic hepatitis-B-virus (HBV) infection is frequently complicated by HBV recurrence. In the present study we investigated whether human leucocyte antigen (HLA)-matching influences the outcome after OLT. In a retrospective analysis we reviewed 84 recipients of liver transplants for end-stage HBV-cirrhosis and complete HLA-typing for outcome after OLT. Follow-up ranges from 1 to 110 months (median = 55.6 months). Immunosuppression consisted of Cyclosporin A (CsA)-based quadruple induction therapy or Tacrolimus-based induction protocols. Immunoprophylaxis with hepatitis B immunoglobulin was started at OLT and continued long-term. Actuarial 1- and 5-yr graft survival figures were 90.5 and 80.4%, respectively. Hepatitis-B recurrence was responsible for 15 of 20 (75%) graft failures. We observed a significantly improved graft survival in patients with more HLA-A, -B compatibilities (p = 0.02), whereas the degree of HLA-DR compatibilities did not influence the outcome. The occurrence of HBV-reinfection was significantly lower in HLA-A, -B matched grafts (p < 0.05). Additionally, graft survival was prolonged in patients with HBV-reinfection and 1 or 2 HLA-B compatibilities when compared with patients with HBV-reinfection and a complete HLA-B mismatch (p = 0.02). In conclusion, this retrospective analysis shows that more HLA-A, -B compatibilities seems to be associated with an improved graft survival in patients after OLT for end-stage HBV infection.

Molecular, immunological and clinical properties of mutated hepatitis B viruses

Hepatitis B virus (HBV) is at the origin of severe liver diseases like chronic active hepatitis, liver cirrhosis and hepatocellular carcinoma. There are some groups of patients with high risk of generation of HBV mutants: infected infants, immunosuppressed individuals (including hemodialysis patients), patients treated with interferon and lamivudine for chronic HBV infection. These groups are the target for molecular investigations reviewed in this paper. The emergence of lamivudine- or other antiviral-resistant variants, rises concern regarding long term use of these drugs. Infection or immunization with one HBV subtype confers immunity to all subtypes. However, reinfection or reactivation of latent HBV infection with HBV mutants have been reported in patients undergoing transplant and those infected with HIV. Mutations of the viral genome which are not replicative incompetent can be selected in further course of infection or under prolonged antiviral treatment and might maintain the liver disease. Four open reading frames (ORF) which are called S-gene, C-gene, X-gene and P-gene were identified within the HBV genome. Mutations may affect each of the ORFs. Mutated S-genes were described to be responsible for HBV-infections in successfully vaccinated persons, mutated C-genes were found to provoke severe chronic liver diseases, mutated X-genes could cause serious medical problems in blood donors by escaping the conventional test systems and mutated P-genes were considered to be the reason for chemotherapeutic drug resistance. This paper reviews molecular, immunological and clinical aspects of the HBV mutants.

Prevalence of HBV core promoter/precore/core mutations in Gambian chronic carriers

One hundred forty-two precore/core sequences were obtained from Gambian chronic hepatitis B virus (HBV) carriers and the predominant variants defined. The two point mutations, from A to T and G to A at nt positions 1762 and 1764 in the basic core promoter region, were found in only 7/99 (7%) of the samples where this region was sequenced. These mutations were found in both HBeAg-positive and -negative patients. The precore stop-codon mutation at nt position 1896 was found in 14/51 (27%) of HBeAg-negative samples, which is a lower prevalence rate in comparison with other parts of the world with high carrier rates. In HBeAg-positive patients the core amino acid sequences were conserved, but after seroconversion to anti-HBe significantly more changes were apparent. Several of the amino acid substitutions found have been described previously been in wild-type viruses of other genotypes.

Naturally occurring woodchuck hepatitis virus (WHV) deletion mutants in chronically WHV-infected woodchucks

Deletion mutants of hepatitis B virus (HBV) are often found in chronically HBV-infected patients. It has not been possible to study the significance of such deletion mutants on liver diseases in a suitable animal model. In this study, we characterized naturally occurring deletion mutants of woodchuck hepatitis virus (WHV) in 11 chronically WHV-infected woodchucks. Deletions within the WHV preS region (nt 2992-338) had a length of 72 or 84 bp and were located in the amino terminal part of preS1. Internal deletions within the core gene (CID) had variable lengths (103 to 312 bp) and were identified within the center of this gene (nt 2021-2587). Four of seven CIDs were in-frame deletions, whereas the remaining three CIDs were out-of-frame deletions and led to the interruption of the reading frame. Sequence analysis of cloned PCR products of CIDs showed that heterogeneous WHV deletion mutants coexisted in single woodchucks. In addition, WHV genomes with double deletions in the preS1 and the core region could be found. We were unable to detect the expression of truncated core proteins in transfection experiments. The CID mutations led to a marked increase of the expression of the luciferase gene which was fused to the start codon of WHV polymerase, probably due to the shortening of the untranslated region or the removal of AUGs preceding the polymerase start codon. The characterization of naturally occurring WHV deletion mutants will allow us to study their biological and pathogenic properties in the woodchuck model in the future.

Low-level secretion of human hepatitis B virus virions caused by two independent, naturally occurring mutations (P5T and L60V) in the capsid protein

The functional significance of naturally occurring variants of human hepatitis B virus (HBV) remains largely unknown. Previously, we reported an immature secretion phenotype caused by a highly frequent mutation at amino acid 97 of the HBV core (capsid) protein (HBcAg). This phenotype is characterized by a nonselective and excessive secretion of virions containing an immature genome of single-stranded viral DNA. To extend our study of virion secretion to other naturally occurring variants, we have characterized mutations at HBcAg codons 5, 38, and 60 via site-directed mutagenesis. Although the phenotype of the mutation at codon 38 is nearly identical to that for the wild-type virus, our study reveals that a single mutation at codon 5 or 60 exhibits a new extracellular phenotype with significantly reduced virion secretion yet maintains normal intracellular viral DNA replication. A complementation study indicates that the mutant core protein alone is sufficient for the "low-secretion" phenotype. Furthermore, the low-secretion phenotype of the codon 5 mutant appears to be induced by the loss of a parental proline residue, rather than by the gain of a new amino acid. Our study underscores the core protein as another crucial determinant in virion secretion, in addition to the known envelope proteins. Our present results suggest that a very precise structure of both alpha-helical and nonhelical loop regions of the entire HBcAg molecule is important for virion secretion. The low-secretion variants may contribute to the phenomenon of gradually decreasing viremia in chronic carriers during the late phase of persistent infection.

How can the cellular immune response control hepatitis B virus replication?

In this review we focus on aspects of the virus-specific cellular immune response, although we should point out that all the components of the innate and adaptive immune response are likely to play a role in successful control of hepatitis B virus (HBV) infection. We concentrate particularly on the relevance of the polyclonality and multispecificity of the HBV-specific cytotoxic T cell response to its antiviral activity. In this context, we discuss the possible role of viral escape mutations and highlight evidence from other models of the benefit of multispecificity in antiviral responses. We stress the contribution of CD4 help for effective CD8 responses and raise the possibility that HBV may produce factors inhibiting the antiviral response.

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.

Subtype-independent immature secretion and subtype-dependent replication deficiency of a highly frequent, naturally occurring mutation of human hepatitis B virus core antigen

The most frequent mutation of the human hepatitis B virus (HBV) core antigen occurs at amino acid 97. Recently, a phenylalanine (F)-to-leucine (L) mutation at this position (mutant F97L) in HBV surface antigen subtype ayw has been shown to result in an immature secretion phenotype, which is characterized by the nonselective export of an excessive amount of virions containing minus-strand, single-stranded HBV DNA. While subtype ayw mutant F97L has been found in Europe, the major reservoir of HBV resides in Asia and Africa. We report here that the immature secretion phenotype indeed can be found in an HBV strain (subtype adr) prevalent in Asia, changing from an isoleucine (I) to a leucine (mutant I97L). Despite its immature secretion phenotype, the adr variant I97L replicates as well as its parental adr wild-type I97I, supporting the conclusion that the extracellular phenotype of immature secretion is not a consequence of the intracellular HBV DNA replication defect. Further studies demonstrated that it is the acquisition of a leucine, rather than the loss of a wild-type amino acid at codon 97, that is important for immature secretion. We conclude that immature secretion is a subtype-independent phenotype and deficiency in intracellular DNA synthesis is a subtype-dependent phenotype. The former is caused by the trans-acting effect of a mutant core protein, while the latter by a cis-acting effect of a mutated nucleotide on the ayw genome. These immature secretion variants provide an important tool for studying the regulation of HBV virion assembly and secretion.

The mechanism of an immature secretion phenotype of a highly frequent naturally occurring missense mutation at codon 97 of human hepatitis B virus core antigen

A very frequent missense mutation at codon 97 of human hepatitis B virus (HBV) core antigen (HBcAg) has been found in chronic carriers worldwide. Functional characterization of this mutant revealed one intracellular and two extracellular phenotypes in contrast to wild-type HBV: (i) a 6- to 12-fold decrease in the level of the full-length relaxed circular DNA, a 4- to 5-fold decrease in the plus-strand DNA, and an approximately 1.8-fold decrease in the minus-strand and overall DNA levels in the intracellular viral core particles; (ii) a 5.7-fold increase in the immature secretion of Dane particles, containing minus-strand, single-stranded virion DNA; and (iii) a significant reduction of nonenveloped core particles in the medium. The steady-state levels of mutant and wild-type core proteins expressed from the same vector appeared to be similar. Using a complementation assay and gradient centrifugation analysis, we demonstrated that this mutant core protein alone is necessary and sufficient for immature secretion. The decreased level of intracellular HBV DNA is caused by both the cis defect of the mutant genome and the trans defect of the mutant core protein. We have dissected further the relationship between the intracellular and extracellular phenotypes of mutant F97L. The pleiotropic effects of the HBcAg codon 97 mutation were observed consistently in several different experimental settings. The mechanism and biological significance of these findings are discussed.

Fluctuations of hepatitis C virus load are not related to amino acid substitutions in hypervariable region 1 and interferon sensitivity determining region

Hepatitis C virus (HCV) load is one of the most important predictive factors of response to interferon treatment. However, little is known about the mode and determinants of viremia. The mode of viremia was investigated in 78 patients with chronic HCV genotype 1b infection during 1-2 years follow up. Virus load, determined by a branched chain DNA amplification assay, was stable in 73 of 78 (93.6%) patients, whereas 5 (6.4%) showed marked fluctuation (from undetectable level to more than 10 Meq/ml) in viral titer. To study the mechanisms mediating fluctuations in viral titer, amino acid sequences of two regions were examined; hypervariable region (HVR) 1 and the interferon sensitivity determining region (ISDR). Multiple amino acid substitutions were observed in HVR 1 but no relationship was evident between substitutions and virus titers. In contrast, no amino acid substitutions were observed in the ISDR in any patients with stable virus titer during a follow-up period of 12-24 months (7-24 samples) or in one patient who was observed for 15 years. Interestingly, multiple amino acid substitutions in the ISDR appeared in only two of the five patients with marked titer fluctuation, when the virus decreased markedly. Alanine aminotransferase levels in these five patients correlated with viral load. The data suggest that amino acid substitutions in HVR1 and ISDR are not essential for changes in viral titer. Possible mechanisms of fluctuations of viral titer and amino acid substitutions in the ISDR accompanying marked reductions in viral load are discussed.

A novel primer-extension assay for the detection of a G to A mutation in the distal precore region of hepatitis B virus DNA

The roles of genetic heterogeneity of the hepatitis B virus (HBV) precore gene in the pathogenesis of HBV infection are unclear. Various methods have been used to detect nucleotide (nt) 1896 precore mutants. We established a new primer-extension assay to facilitate the detection of these mutants. This assay is based upon the fact that there is no adenine in the distal precore region of wild-type HBV. Polymerase chain reaction (PCR)-amplified template DNA was denatured and annealed to the [gamma-32P]-labelled primer. During primer extension in the presence of DNA polymerase and dCTP, dGTP, dTTP and ddATP, the reaction terminates if there is a nucleotide A. When mixtures of different ratios of wild-type and nt 1896 precore mutants were analysed in the primer-extension assay, correlation between the percentage known amounts and the percentage measured amounts of nt 1896 precore mutants was excellent (r2=0. 9669). When the primer-extension assay and direct sequencing were compared in hepatitis B e antigen (HBeAg)-positive and -negative chronic active hepatitis B patients, the primer-extension assay detected a greater number of nt 1896 precore mutants than direct sequencing and thus most HBV infections were found to be mixed infections. In conclusion, the primer-extension assay is a reliable and sensitive method for the detection of nt 1896 precore mutants.

In situ detection of mutated hepatitis B virus in microdissected, formalin-fixed liver tissues from patients with chronic hepatitis B

BACKGROUND/AIMS

Hepatitis B virus (HBV) quasispecies have been detected in patients with chronic hepatitis B. In order to elucidate the relationship between HBV mutation and liver cell necrosis in situ, we analyzed sublobule-sized specimens microdissected from formalin-fixed paraffin-embedded liver biopsy tissues taken from patients with chronic hepatitis B.

METHODS

The subjects were 20 patients with chronic hepatitis B. We extracted HBV-DNA from two sublobular regions of HBV-infected liver biopsy tissue, those with the most severe and the mildest hepatitis activity, demonstrated microscopically. The DNA coding sequence of the precore-core region of HBV was determined by amplifying the DNA by the polymerase chain reaction, followed by direct sequencing.

RESULTS

In all seven patients with minimal to mild hepatitis activity, but only 4 of 13 with moderate to severe activity, the amino acid sequence of the precore-core region of HBV obtained from the region with the most severe hepatitis activity showed over 99% homology with the corresponding sequence of HBV obtained from region with the mildest hepatitis activity (p<0.05).

CONCLUSION

The differences between intrahepatic HBVs observed in patients with highly active hepatitis suggest that exacerbation of hepatitis in vivo is related to the appearance of variants in the precore-core region of HBV.

Core variability does not affect response to interferon alpha in HBeAg negative chronic hepatitis B

BACKGROUND/AIMS

The pre-core stop codon variant (A 1896) of hepatitis B virus (HBV) has been associated with chronic active liver disease with acute exacerbations and a high relapse rate after an initial response to alpha-interferon (IFN-alpha) therapy. Poor sustained response has been correlated with a high prevalence of mutations in the core region, potentially enabling escape from the immune system. The aim of this study was to analyse the predictive factors of response to IFN-alpha in such patients.

METHODS

We studied the baseline clinical, biochemical, histological, serological and virological parameters in 30 hepatitis B s antigen positive (HBsAg-positive)/hepatitis B e antigen negative (HBeAg-negative) Greek patients with chronic liver disease. The patients were selected from a cohort who received IFN-alpha for 24 weeks. These were divided into three groups of ten sequential patients: those with no response to IFN-alpha treatment, those who relapsed after an initial response, and those with a sustained response. Serum HBV DNA was measured by a liquid hybridisation method, and the anti-HBc IgM was quantitated by the IMx analyser. The amino-acid sequence of core protein residues 40-89, a region where a clustering of mutations has been detected previously in severe hepatitis, was compared with a sequence from an HBeAg positive patient with chronic liver disease.

RESULTS

Multiple logistic regression analysis showed that the initial response to IFN-alpha could be predicted by pre-treatment absence of HBcAg staining in the liver and high ALT values, but no parameter could predict sustained response. The pre-treatment extent and pattern of aminoacid substitutions in the core region sequenced was similar in all groups studied and was not associated with IFN-alpha response.

CONCLUSIONS

In HBsAg-positive/HBeAg-negative patients with chronic liver disease, response to IFN-alpha therapy was not correlated with genomic variability of the core region. Other parameters such as pre-treatment HBcAg positivity in the liver and alanine aminotransferase values indicative of disease activity before treatment were associated with initial IFN-alpha response.

Precore stop codon mutant in chronic hepatitis B virus infection in children: its relation to hepatitis B e seroconversion and maternal hepatitis B surface antigen

BACKGROUND/AIMS

The aims of this study were to investigate the significance of the precore stop codon mutant in the natural course of hepatitis B virus infection in children, and the influence of maternal transmission.

METHODS

Sequential sera from 80 hepatitis B virus carrier children both before and after e seroconversion during long-term follow-up were studied using the polymerase chain reaction-amplification created restriction site method. Direct sequencing of the precore region was performed in 89 sera from 32 of the 80 children.

RESULTS

The precore stop codon mutant coexisting with wild strain was found in 10% of children initially, and later in 25% of children before e seroconversion. After e seroconversion, wild type was still present in 75% and mutant in 39% of children at the end of follow-up. The mutant alone was present in 15% of anti-HBe positive children without concomitant aminotransferase elevation. Children with earlier emergence of this mutant tended to have higher peak aminotransferase levels. This mutant emerged less frequently in children of hepatitis B virus carrier mothers (37.5%) than in those of non-carrier mothers (65%) (p<0.05).

CONCLUSIONS

These observations suggest that this mutant is selected by host immune pressure, but is not an initiator in the loss of immune tolerance during childhood chronic hepatitis B virus infection.

Variability of the Hepatitis B Surface Protein in HBV-Infected Liver Transplant Recipients

Variations in the major surface proteins (HBsAg) of hepatitis B virus (HBV) have been implicated in the high rate of reinfection in HBV-infected recipients of orthotopic liver transplantations (OLT). Sera from 6 OLT patients positive for HBsAg and from 3 recipients negative for it prior to transplantation were analyzed over several years, and 39 HBsAg sequences were compared. Despite anti-HBs immunoprophylaxis resulting in the disappearance of HBsAg, HBV DNA was detectable by a sensitive nested PCR in almost all sera. In 1 patient, a significant temporary shift in HBV subtypes was observed, indicating a mixed infection or the presence of multiple HBV populations in this patient; this was also true for other patients. Amino acid substitutions compared to wild-type HBV subtypes in 7 patients and variations within patients in 5 patients were detectable over time; the 'escape mutation' at amino acid position 145 was detected in 2 patients. Our data suggest that the high rate of reinfection in OLT recipients seems not to be associated with specific sequence variations in the major HBs gene, but shows a remarkable inter- and intraindividual variability. Obviously, no correlation between heterogeneity in this gene and clinical outcome was present. Copyright 1997 S. Karger AG, Basel

Precore codon 28 stop mutation in hepatitis B virus from patients with hepatocellular carcinoma

OBJECTIVES

Hepatitis B virus (HBV) with a stop mutation at precore codon 28 (TGG-->TAG, tryptophan-->stop) was investigated to clarify if such a mutant virus might play a role in hepatocarcinogenesis.

METHODS

A total of 73 patients with HBV-related hepatocellular carcinoma were included in this study. Polymerase chain reaction (PCR) was performed in DNA samples extracted from 73 sera to amplify a HBV-DNA segment involving the precore and proximal core regions, and sequences of PCR products were analyzed to see the presence of the mutations at precore codon 28 by a direct sequencing method.

RESULTS

HBV-DNA was detectable in 64 (88%) patients by PCR. The stop mutation at precore codon 28 was identified in 50 of 58 PCR products (86%), in which direct sequencing was performed. Among patients with this mutant HBV, 21/50 (42%) patients were co-infected with wild-type HBV. The mutant virus was found in 23/28 (82%) patients with hepatitis B e antigen (HBeAg) and 27/30 (90%) patients without HBeAg. The mutant HBV alone was found in 10/28 (36%) patients with HBeAg and 19/30 (63%) without HBeAg. Among those patients on whom laparoscopy was performed, 22/24 (92%) with the precore codon 28 stop mutant alone had cirrhosis, compared to 12/19 (63%) co-infected by both the mutant and the wild-type (p < 0.05). The association of this mutant virus with both the presence and absence of HBeAg, and its association with cirrhosis when there is no co-infection with wild-type HBV, suggests an evolving pattern of liver pathology.

CONCLUSION

The high prevalence of a stop mutation at precore codon 28 in these patients with hepatocellular carcinoma suggests that HBV with this mutation may contribute to the development of hepatocellular carcinoma.

Emergence and selection of HBV variants in an anti-HBe positive patient persistently infected with quasi-species

BACKGROUND/AIMS

Infection with the hepatitis B e antigen (HBeAg) negative variant of hepatitis B virus (HBV) causes chronic liver disease characterised by occasional acute exacerbations. This virus exhibits a high prevalence of mutations in the core region. Our aim was to study the changes in the pre-core/core region of the virus in relation to exacerbations of the disease.

METHODS/RESULTS

We performed direct sequencing on DNA amplified from 7 sequential sera taken over a 5-year period from a hepatitis B surface antigen (HBsAg) and anti-HBe positive Greek patient infected with the HBeAg negative variant. The patient had chronic hepatitis with several acute exacerbation episodes and underwent interferon therapy twice. We found significant variability in the core region at different time points. To determine whether these variants were present in the initial serum sample and subsequently selected under immune pressure or whether they arose de novo during the course of the disease, we cloned the pre-core/core region from 4 sera before and after episodes of acute exacerbation. Fifteen clones from each time point were sequenced. Fourteen nucleotide mutations in the pre-core/core region were recorded, 7 (50%) of which led to amino-acid substitutions. All the amino-acid changes occurred at recognised B- and CD4+ epitopes. The cloning results indicate the presence of quasi-species in all the samples investigated. Some of the variants present as a minor population in the first sample appear to have been selected and become dominant in subsequent sera. However, the emergence of novel variants, not present at a detectable level in earlier samples, during the course of the disease, was also established. The quasi-species nature of HBV only became apparent after the cloning experiments and was not obvious from the direct sequencing results.

CONCLUSIONS

New dominant variants occurring during the course of the disease arose either by the selection of pre-existing mutants that were not detected by direct sequencing or by mutation of existing strains. All changes were located within B- and CD4+ epitopes. The continuous production and selection of variants may enable virus to evade elimination by the immune system, resulting in persistent infection.