Novel and frequent mutations of hepatitis B virus coincide with a major histocompatibility complex class I-restricted T-cell epitope of the surface antigen

Virion Secretion of Hepatitis B Virus Naturally Occurring Core Antigen Variants

In natural infection, hepatitis B virus (HBV) core protein (HBc) accumulates frequent mutations. The most frequent HBc variant in chronic hepatitis B patients is mutant 97L, changing from an isoleucine or phenylalanine to a leucine (L) at HBc amino acid 97. One dogma in the HBV research field is that wild type HBV secretes predominantly virions containing mature double-stranded DNA genomes. Immature genomes, containing single-stranded RNA or DNA, do not get efficiently secreted until reaching genome maturity. Interestingly, HBc variant 97L does not follow this dogma in virion secretion. Instead, it exhibits an immature secretion phenotype, which preferentially secretes virions containing immature genomes. Other aberrant behaviors in virion secretion were also observed in different naturally occurring HBc variants. A hydrophobic pocket around amino acid 97 was identified by bioinformatics, genetic analysis, and cryo-EM. We postulated that this hydrophobic pocket could mediate the transduction of the genome maturation signal for envelopment from the capsid interior to its surface. Virion morphogenesis must involve interactions between HBc, envelope proteins (HBsAg) and host factors, such as components of ESCRT (endosomal sorting complex required for transport). Immature secretion can be offset by compensatory mutations, occurring at other positions in HBc or HBsAg. Recently, we demonstrated in mice that the persistence of intrahepatic HBV DNA is related to virion secretion regulated by HBV genome maturity. HBV virion secretion could be an antiviral drug target.

Mutations and methods of analysis of mutations in Hepatitis B virus

Immunization programmes against hepatitis-B are being carried out since more than three decades but still HBV is a major public health problem. Hepatitis B virus (HBV) genome consists of circular and partial double stranded DNA. Due to partial double stranded DNA, it uses an RNA intermediate during replication. This replicative strategy of HBV and lack of polymerase proofreading activity give rise to error occurrences comparable to retroviruses. The low fidelity of polymerase, overlapping reading frames and high replication rate produces many non-identical variants at every cycle of replication. Therefore, HBV spreads with mutations and variations. The mutations have been reported both in non-structural as well as structural genes of HBV genome. Recent advances in molecular biology have made easier to analyse these mutations. Hepatitis B antiviral therapy and immunization are all influenced by genetic variability. The analysis and understanding of these mutations are important for therapy against hepatitis B and updating of diagnostic tools. The present review discusses about mutations occurring in whole HBV genome. The mutation occurring both in structural and non-structural genes and non-coding regions have been described in details. It is much more informative because most of literature available, covers only individual gene or DNA regions of HBV.

Phylogenetic Analysis of Hepatitis B Virus among Household Members with HBV Chronic Infection

BACKGROUND

Intrafamilial spread of Hepatitis B virus (HBV) infection in Iran has only been investigated with serological testing without using molecular studies as the most informative and definitive type of analysis.

METHODS

In the present study, intrafamilial transmission of HBV among family members of Iranian index HBsAg carriers was investigated using phylogenetic analysis of the S region of the viral genome. Nested polymerase chain reaction was used for detection of HBV DNA in serum samples from 22 index and 43 contact patients with chronic HBV infection. HBV DNA was detected in 37 samples (14 indexes, 23 contacts). The S gene region of the DNA isolates was subjected to direct sequencing and phylogenetic analysis by Bioedit, Mega and Phylip programs.

RESULTS

All isolates (from 26 patients) were clustered with genotype D, of which 24 strains were of subgenotype D1, subtype ayw2, while 2 additional strains were of subgenotype D2, subtype ayw3. Evidence of intrafamilial transmission of the virus was found in 8 families studied phylogenetically. Overall, 60 changes were detected in the amino acid sequences of the surface antigen protein in 23 patients. Four premature stop codons occurred in 3 isolates at residues 69 and 182. Seven out of 8 families displayed 25-100% common amino acid substitutions among their members.

CONCLUSION

Our data corroborated intrafamilial transmission of HBV, as evidenced by concordant HBV genotype among household members, viral sequence homology and close genetic relatedness of the strains on the phylogenetic tree, and horizontal transmission of S gene mutations among family members.

Genogeography and Immune Epitope Characteristics of Hepatitis B Virus Genotype C Reveals Two Distinct Types: Asian and Papua-Pacific

Distribution of hepatitis B virus (HBV) genotypes/subgenotypes is geographically and ethnologically specific. In the Indonesian archipelago, HBV genotype C (HBV/C) is prevalent with high genome variability, reflected by the presence of 13 of currently existing 16 subgenotypes. We investigated the association between HBV/C molecular characteristics with host ethnicity and geographical distribution by examining various subgenotypes of HBV/C isolates from the Asia and Pacific region, with further analysis on the immune epitope characteristics of the core and surface proteins. Phylogenetic tree was constructed based on complete HBV/C genome sequences from Asia and Pacific region, and genetic distance between isolates was also examined. HBV/C surface and core immune epitopes were analyzed and grouped by comparing the amino acid residue characteristics and geographical origins. Based on phylogenetic tree and geographical origins of isolates, two major groups of HBV/C isolates—East-Southeast Asia and Papua-Pacific—were identified. Analysis of core and surface immune epitopes supported these findings with several amino acid substitutions distinguishing the East-Southeast Asia isolates from the Papua-Pacific isolates. A west-to-east gradient of HBsAg subtype distribution was observed with adrq+ prominent in the East and Southeast Asia and adrq- in the Pacific, with several adrq-indeterminate subtypes observed in Papua and Papua New Guinea (PNG). This study indicates that HBV/C isolates can be classified into two types, the Asian and the Papua-Pacific, based on the virus genome diversity, immune epitope characteristics, and geographical distribution, with Papua and PNG as the molecular evolutionary admixture region in the switching from adrq+ to adrq-.

Hepatitis B virus infection in post-vaccination South Africa: occult HBV infection and circulating surface gene variants

BACKGROUND AND OBJECTIVE

The aim of this study was to investigate the prevalence of occult hepatitis B virus (HBV) infection and the HBV surface (S) gene variants circulating in the South African population after nearly two decades of universal hepatitis B vaccination.

STUDY DESIGN

From a previous serosurvey, 201 serum samples with serological evidence of exposure to HBV were identified and these were stratified into post- and pre-vaccine introduction populations. For all samples, HBV DNA was screened and quantified using a real-time PCR assay and results analysed together with HBV serological markers. Where HIV results were available, subset analysis was performed. The HBV S gene was PCR-amplified and sequences analysed for a total of 37 isolates.

RESULTS

The prevalence of occult HBV infection reduced from 70.4% in the pre-vaccine introduction era to 66.0% post-vaccine introduction. There was an association between HIV infection and an increase in prevalence of occult HBV infection within the post-vaccine introduction population, although this was not statistically significant. Furthermore, sequence analysis revealed the following HBV subgenotypes; A1 (n=34), A2 (n=2) and a rare D4 isolate. HBV S gene variants, including diagnostic escape mutants were isolated.

CONCLUSION

There was a decline in the prevalence of occult HBV infection in post-vaccination South Africa, although the disease burden remains significant in the HIV co-infected population. After nearly two decades of a universal hepatitis B vaccination programme, no positive selection of vaccine escape mutants were observed.

The emerging role of hepatitis B virus pre-S2 deletion mutant proteins in HBV tumorigenesis

Chronic hepatitis B virus (HBV) infection can cause hepatocellular carcinoma (HCC). Several hypotheses have been proposed to explain the mechanisms of HBV tumorigenesis, including inflammation and liver regeneration associated with cytotoxic immune injuries and transcriptional activators of mutant HBV gene products. The mutant viral oncoprotein-driven tumorigenesis is prevailed at the advanced stage or anti-HBe-positive phase of chronic HBV infection. Besides HBx, the pre-S2 (deletion) mutant protein represents a newly recognized oncoprotein that is accumulated in the endoplasmic reticulum (ER) and manifests as type II ground glass hepatocytes (GGH). The retention of pre-S2 mutant protein in ER can induce ER stress and initiate an ER stress-dependent VEGF/Akt/mTOR and NFκB/COX-2 signal pathway. Additionally, the pre-S2 mutant large surface protein can induce an ER stress-independent pathway to transactivate JAB-1/p27/RB/cyclin A,D pathway, leading to growth advantage of type II GGH. The pre-S2 mutant protein-induced ER stress can also cause DNA damage, centrosome overduplication, and genomic instability. In 5-10% of type II GGHs, there is co-expression of pre-S2 mutant protein and HBx antigen which exhibited enhanced oncogenic effects in transgenic mice. The mTOR signal cascade is consistently activated throughout the course of pre-S2 mutant transgenic livers and in human HCC tissues, leading to metabolic disorders and HCC tumorigenesis. Clinically, the presence of pre-S2 deletion mutants in sera frequently develop resistance to nucleoside analogues anti-virals and predict HCC development. The pre-S2 deletion mutants and type II GGHs therefore represent novel biomarkers of HBV-related HCCs. A versatile DNA array chip has been developed to detect pre-S2 mutants in serum. Overall, the presence of pre-S2 mutants in serum has implications for anti-viral treatment and can predict HCC development. Targeting at pre-S2 mutant protein-induced, ER stress-dependent, mTOR signal cascade and metabolic disorders may offer potential strategy for chemoprevention or therapy in high risk chronic HBV carriers.

Prevalence and molecular analysis of occult hepatitis B virus infection isolated in a sample of cryptogenic cirrhosis patients in iran

OBJECTIVES

The aims of this study are to investigate the prevalence of occult hepatitis B virus infection among patients with cryptogenic cirrhosis and to analyze the relationship between surface protein variability and occult hepatitis B virus infection, which may be related to the pathogenesis of occult hepatitis B virus infection in cryptogenic cirrhosis. Occult hepatitis B virus infection is a well-recognized clinical entity characterized by the detection of hepatitis B virus DNA in serum and/or liver in the absence of detectable hepatitis B virus surface antigen, with or without any serological markers of a past infection.

METHODS

Sera from patients with cryptogenic chronic liver disease were tested for hepatitis B virus DNA using both real-time and nested PCR. In the detected hepatitis B virus DNA samples, the surface gene was analyzed for mutations.

RESULTS

Hepatitis B virus DNA was detected in 38% of patients, all of whom had a viral load below 10,000 copies/mL. All hepatitis B virus belonged to genotype D. There were no significant associations between occult hepatitis B virus infection status and age, gender, ALT/AST levels, viral load or serologic markers of previous hepatitis B virus infection. There were 14 mutations found in 5 patients; 6 were in the major hydrophilic region, of which 4 were Y134F assigning for the "a" determinant region. All patients who acquired Y134F contained S207R (within HLA-A2-restricted CTL epitope) as a combination.

CONCLUSION

Hepatitis B virus surface antigen variants may arise as a result of natural selection to evade the immune surveillance of the infected host, and subsequently may go undetected by conventional hepatitis B virus surface antigen screening tests. Etiological diagnosis of cryptogenic cirrhosis is significantly underestimated with current serology testing methods alone.

Naturally occurring hepatitis B virus B-cell and T-cell epitope mutants in hepatitis B vaccinated children

To control hepatitis B virus (HBV) infection, a universal HBV vaccination program for infants was launched in Taiwan in 1984. The aim of this study was to investigate the role of B-cell and T-cell epitope variations of HBsAg and polymerase in HBV infection in vaccinated children. One hundred sixty-three sera from vaccinated children were enrolled randomly. HBV serum markers, including hepatitis B surface antigen (HBsAg) and antibodies to HBsAg (anti-HBs) and core antigen (anti-HBc), were detected by ELISA. Nucleotide sequences encoding the S and the pre-S regions of HBsAg were analyzed in all HBsAg positive sera. Five children were HBsAg positive. Sequence analysis of S, pre-S, and overlapped polymerase (P) genes showed that HBV isolates of HBsAg-positive vaccinees were variants; no G145R but G145A and other substitutions were found in the “a” determinant. Fifteen, six, and eight amino acid substitutions within B-cell and T-cell epitopes of S, pre-S, and P regions were detected, respectively. Several immune-epitope mutants, such as S45T/A, N131T, I194V, and S207N in S, were detected in all isolates. In conclusion, our results suggested that these naturally occurring immunoepitope mutants, which changed their immunogenicity leading to escape from immune response, might cause HBV infection.

Hepatitis B virus surface protein mutations clustered mainly in CTL immune epitopes in chronic carriers: results of an Iranian nationwide study

Mutations within the coding region of hepatitis B surface antigen (HBsAg) have been found naturally in chronic carriers. To characterize the mutations of HBsAg from Iranian chronic carriers who were vaccine and/or medication naive. The surface genes from 360 patients were amplified and directly sequenced. The distribution of amino acid substitutions was classified according to different immune epitopes of the surface protein. All isolates belonged to genotype D. 222 (61.6%) of 360 patients contained at least one amino acid substitution. 404 (74.5%) of 542 amino acid changes occurred in different immune epitopes of HBsAg, of which 112 (27.7%) in 32 residues of B-cell epitopes (62 in the 'a' determinant); 111 (27.4%) in 32 residues of T helper; and 197 (48.7%) in 32 residues inside cytotoxic T lymphocyte (CTL) epitopes. One Th (186-197) and two CTL (28-51 and 206-215) epitopes were found to be hotspot motifs for the occurrence of 213 (52.7%) substitutions. 20 stop codons were identified in different epitopes. There was a significant association between amino acid substitutions and anti-HBe seropositivity; however, the correlation between such changes with viral load and ALT levels was not significant. In chronic hepatitis B virus(HBV) carriers, positive selection in particular outside the 'a' determinant appeared to exert influence on the surface proteins. These changes could be immune escape mutations naturally occurring due to the host immune surveillance especially at the T-cell level.

HBsAg variants: diagnostic-escape and diagnostic dilemma

A wide variety of commercial assays is available for the detection of hepatitis B surface antigen (HBsAg). Clearly, the sensitivity of an assay to detect a variant is dependent on the anti-HBs usage. Thus, it is not surprising that there are examples of variants that cannot be detected by all assays. Data from Europe, Asia and Africa about HBsAg variants which are not recognized by either monoclonal or polyclonal antibodies specific for wild-type group 'a' determinant, but positive by DNA polymerase chain reaction (PCR) in chronic patients and from vaccinated children are increasing. This would impose a challenge for public health issues of hepatitis B virus. In this review we tried to summarize the discrepancies between results of HBsAg assays and to explain some rationales for these inconsistencies.

Hepatitis B virus S gene escape mutants

Hepatitis B virus (HBV) can be classified into nine immunological subtypes or eight genotypes. The most prevalent genotypes in Asia are genotypes B and C. HBV is transmitted parenteraly and can produce either asymptomatic or symptomatic disease. Although the consequences of acute hepatitis B can be severe, serious sequelae are associated with chronic infections. HBV seroprevalence ranges from intermediate (2%-7%) to high (≥8%) levels in Asia. Several strategies for the control and prevention of HBV infection have been found to be efficacious. They include vaccination and the administration of HBIG, interferon-a and nucleoside/nucleotide analogues. However, these procedures also apply selective pressures on HBV in infected individuals leading to the generation and accumulation of mutations in the S gene. Most of these mutations occur in the major hydrophilic region (MHR) of the S gene. These mutations create public health concerns as they can be responsible for reactivation of hepatitis B and occult hepatitis B infection. The inability to detect occult infections means that these individuals may become blood donors. This suggests that new strategies for donor evaluation and selection may need to be developed to protect the blood supply.

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.

Natural history of hepatitis B virus infection: pediatric perspective

Hepatitis B virus (HBV) infection is an important disease globally. Chronic HBV infection may result in serious complications. Its transmission may be either perinatal or horizontal. Perinatal transmission is particularly important after the implementation of a universal vaccination program. Through either route, chronic carrier status is usually established in early childhood. The course of the disease course is determined by the host-virus interaction. The host's immune system initially tolerates the virus, and then gradually attempts to clear it. The virus, on the other hand, tries to avoid host immune system attack by a strategy involving targeted epitope mutations. By generating mutants, the virus can survive attacks from the host's immune system, enabling the infection to persist. Different individuals have different responses to HBV infection; genetic polymorphisms in cytokines, hormones, and other immune modulators may affect the final outcome of chronic HBV infection. Due to the implementation of a universal infant HBV vaccination program, HBV infection is now under control. Unfortunately, there still are some cases of vaccination failure. Very high maternal viremia, in utero infection, or escape mutants are possible reasons for vaccination failure. Immunocompromised hosts also risk vaccination failure. Blood or organ donors with occult HBV infection are possible sources for immunocompromised hosts. These victims of vaccination failure may exhibit a different disease course due to chronic HBV infection from those who acquired the infection before the universal vaccination era. The achievement of our ultimate goal of HBV elimination depends on a globally effective universal vaccination program, as well as the application of some novel successful medications to control those who are already infected.

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.

Full-length hepatitis B virus sequences from naïve patients with fluctuation of viral load during ADV monotherapy

The reasons for adefovir dipivoxil (ADV) treatment failures appear diverse. Few studies have reported full-length hepatitis B virus (HBV) genome in patients with ADV treatment failures. The patients were from a phase III clinical trial that investigated the antiviral response to ADV in China. Seven patients had increase in HBV-DNA (>1 log(10) copies/ml above on-treatment nadir) at week 52. The serum HBV-DNA levels were above 10(4)copies/ml at week 92 in four of them. Sixteen full-length HBV genomes from the four patients at four time points were sequenced using cloning sequencing method. The frequency of substitutions at week 52 was higher than at weeks 28(16 wt) and 92(80). HBV-DNA reduction was correlated negatively with the frequency of substitutions at the three time points. No published ADV-resistant mutations were detected. The mutations, including substitutions in immunogenic epitopes and conserved sites of the polymerase gene, were frequent during ADV treatment. Amino acid deletions in X gene and basal core promoter/pre-core mutations appeared before or during ADV treatment. The substitutions in immunogenic epitopes (mainly of the surface gene) and conserved sites of the polymerase gene other than ADV-resistant mutations may have influenced antiviral efficacy in the study. More potent antiviral drugs may be important to rescue individual patients and for public health safety. It is needed to study how these substitutions influence HBV replication, disease progression, and antiviral treatment efficacy.

Pre-S2 deletion mutants of hepatitis B virus could have an important role in hepatocarcinogenesis in Asian children

Although many studies on the risk factors and their carcinogenesis in adult hepatocellular carcinoma (HCC) have been reported, they remain poorly understood in childhood HCC. A retrospective study of 42 HCC cases in Asian children was conducted. Hepatitis B virus (HBV)-DNA in HCC tissues was detected in 36 of 42 (86%) cases tested, while no hepatitis C virus (HCV)-RNA was detectable in any of HCCs. Twenty of 36 (56%) HCC cases were accompanied by cirrhosis. Surprisingly, very high prevalence of the HBV pre-S deletion mutant was recognized in 27 of 30 (90%) HCCs examined. They occurred most frequently in pre-S2 (20/27, 74%) followed by pre-S1 (5/27, 18.5%), and both pre-S1/S2 (2/27, 7.4%). Interestingly, the pre-S2 mutant consistently appeared with deletion at nt 4-57 in all of the 20 cases with the pre-S2 mutant (100%) and within this locus in the two cases with both pre-S-1/S2 mutants. Type II ground-glass hepatocytes in non-tumorous livers were seen in 15 of the 22 HCCs with the pre-S2 deletion mutant (68%). This hotspot mutation in the pre-S2 was further confirmed by complete genomic sequence of HBV in a Japanese boy who eventually developed HCC. Our result strongly suggests that HBV is a major contributor to the development of HCC in Asian children. The HBV pre-S2 deletion mutant at nt 4-57 which has a CD8 T-cell epitope could be responsible for the emergence and aggressive outcome of childhood HCC. Determination of this hotspot mutation in the pre-S2 region could be a useful index for predicting the clinical outcome of HCC development.

Molecular characterization and functional analysis of occult hepatitis B virus infection in Chinese patients infected with genotype C

Occult HBV infection is defined as the persistence of HBV DNA in individuals negative for HBV surface antigen (HBsAg), and many different mechanisms have been reported in different countries. However, in China, one of the endemic areas for HBV infection, no reports have been published on occult HBV infection. The present study investigated the virological features and the mechanism of occult HBV infection in China. Full-length HBV DNA from eight patients with occult HBV infection (S1-S8) and three HBsAg-positive cases (SWT1-SWT3) was cloned and sequenced. Additionally, four entire linear HBV genomes from occult cases were transfected transiently into HepG2 cells. The sequencing results showed two major mutations in patients with occult HBV infection as follows: deletions in the pre-S1 (S3, S4, and S7) and X (S1, S2, and S5) regions. Such deletions covered the S promoter and the basal core promoter (BCP), and function analysis of these variants also showed a decrease in DNA replication and antigen expression. Two patients with occult infection (S6 and S8) had no mutations capable of interfering with viral replication and gene expression in the major viral population. Thus, the deletions in the S promoter and the BCP regions that disable the regulatory elements may be the reason for the absence of HBsAg, and multiple mechanisms may be responsible for occult HBV infection.

Envelope protein variability among HBV-Infected asymptomatic carriers and immunized children with breakthrough infections

A detailed study of hepatitis B virus (HBV) surface variants and their role in breakthrough infections has been conducted in The Gambia, West Africa. Samples from 1856 vaccinated subjects were tested for hepatitis B surface antigen (HBsAg). Evidence of infection was found in 11% (22/192) of subjects with breakthrough infections and 18 (81.8%) were also positive for HBV DNA following PCR analysis. A cohort of 58 unvaccinated carriers which also included 11 patients with hepatocellular carcinoma was also investigated in order to establish the prevalence of surface variants in the unvaccinated population. Analysis of the S gene from HBV PCR-positive subjects (n = 64) revealed little variation in the S gene of these subjects. Twenty-four S protein sequences (37.5%) were identical and a further 22 sequences differed by only a single amino acid. The K141E variant found in previous work was not detected and little variation was observed in the immunodominant "a" determinant; a single change was found in one vaccinated patient (Q129H) and nine changes detected among six unvaccinated carriers. This study showed that breakthrough HBV infection in vaccinated Gambians is mainly caused by the wild type genoytype E strain and that immune escape mutants are uncommon. However, HBV mutants may play a role in establishing infection later in life when anti-HBs antibodies have begun to decline. Further investigation is required to determine the cause of these breakthrough infections and whether they contribute to the establishment of the carrier state.

Ground glass hepatocytes contain pre-S mutants and represent preneoplastic lesions in chronic hepatitis B virus infection

The discovery of "ground glass" hepatocytes (GGH) that contain hepatitis B virus (HBV) surface antigens by Hadziyannis and Popper in 1973 represents a historical landmark in the pathology of chronic HBV infection. Different types of GGH have been correlated to the expression patterns of surface/core antigens and the stages of virus replication. The original two types (designated types I & II) of GGH were found to contain specific pre-S mutants with deletions over either pre-S1 or pre-S2 regions, respectively. Type II GGH consistently harbor pre-S2 deletion mutants, which can escape from immune attack and grow preferentially to form clusters. Both types of pre-S mutants can induce endoplasmic reticulum (ER) stress and oxidative DNA damage. The pre-S2 mutants, albeit inducing a weaker level of ER stress signals, could additionally initiate ER stress-independent retinoblastoma/adenovirus E2 promoter binding factor/cyclin A signaling through their interaction with c-Jun activation domain binding protein 1 to degrade p27, illustrating the growth advantage of type II GGH. The combined effects of genomic instability and the proliferation of hepatocytes harboring pre-S mutants could potentially lead to hepatocarcinogenesis over the decades of chronic HBV infection. The presence of pre-S mutants in sera was reported to carry a high risk of developing hepatocellular carcinoma (HCC). Furthermore, transgenic mice harboring pre-S2 mutant plasmids have been shown to develop a dysplastic change of hepatocytes and HCC. Therefore, in addition to being a histological marker of chronic HBV infection, GGH, particularly type II GGH, may represent the preneoplastic lesions of HBV-related HCC.

Mutations of T-cell epitopes in the hepatitis B virus surface gene in children with chronic infection and hepatocellular carcinoma

BACKGROUND AND OBJECTIVES

Hepatitis B virus (HBV) infection induces an interaction of host immune responses against virus antigen-presenting hepatocytes. The emergence of mutants is a strategy through which the virus can escape host attacks and produce chronic infection. In this study, we aimed to investigate mutations of the human leukocyte antigen-A2-restricted T-cell epitope (TCE) in chronic HBV-infected children.

METHODS

In total, 441 chronic HBV-infected children were longitudinally followed-up every 6 months. They were divided into hepatitis B e antigen (HBeAg) (-) (N = 60) and HBeAg (+) (N = 381) groups according to this seromarker at their enrollment. The HBeAg (+) group was further divided into HBeAg (+/-) (N = 229) and HBeAg (+/+) (N = 152) groups, depending on the occurrence of spontaneous HBeAg seroconversion. Twenty-five children with HBV-related hepatocellular carcinoma (HCC) were also recruited. TCE mutations were examined using the latest serum samples, and serum samples at enrollment were used if TCE mutations were present in the latest serum samples in the seroconverters. HBV genotypes and liver enzymes were also analyzed.

RESULTS

The HBeAg (+/+) group had a lower TCE mutation rate (7.9%) than that of the HBeAg (+/-) (29.2%), HBeAg (-) (26.7%), and HCC (28.0%) groups. In the HBeAg (+/-) group, TCE mutations were present before HBeAg seroconversion in 11.9% of the subjects. Those with TCE mutations showed HBeAg seroconversion at an older age (16.1 +/- 5.3 yr vs 12.7 +/- 5.7 yr, P < 0.001) and with higher peak alanine aminotransferase (ALT) levels (median 175 U/L vs 119 U/L, P = 0.03) than those without TCE mutations.

CONCLUSIONS

TCE mutations tended to be positively associated with HBeAg seroconversion and higher ALT levels in chronic HBV-infected children.

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

OBJECTIVES

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

SETTING

Prospective HIV/HBV co-infected cohort study.

METHODS

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

RESULTS

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

CONCLUSION

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

Quasispecies and its impact on viral hepatitis

Quasispecies dynamics mediates adaptability of RNA viruses through a number of mechanisms reviewed in the present article, with emphasis on the medical implications for the hepatitis viruses. We discuss replicative and non-replicative molecular mechanisms of genome variation, modulating effects of mutant spectra, and several modes of viral evolution that can affect viral pathogenesis. Relevant evolutionary events include the generation of minority virus variants with altered functional properties, and alterations of mutant spectrum complexity that can affect disease progression or response to treatment. The widespread occurrence of resistance to antiviral drugs encourages new strategies to control hepatic viral disease such as combination therapies and lethal mutagenesis. In particular, ribavirin may be exerting in some cases its antiviral activity with participation of its mutagenic action. Despite many unanswered questions, here we document that quasispecies dynamics has provided an interpretation of the adaptability of the hepatitis viruses, with features conceptually similar to those observed with other RNA viruses, a reflection of the common underlying Darwinian principles.

Molecular and functional analysis of occult hepatitis B virus isolates from patients with hepatocellular carcinoma

Occult HBV infection is characterized by the persistence of HBV DNA in the liver of individuals negative for HBV surface antigen (HBsAg). Occult HBV may exist in the hepatocytes as a free genome, although the factors responsible for the very low viral replication and gene expression usually observed in this peculiar kind of infection are mostly unknown. Aims of this study were to investigate whether the viral genomic variability might account for the HBsAg negativity and the inhibition of the viral replication in occult HBV carriers, and to verify in vitro the replication capability of occult HBV strains. We studied liver viral isolates from 17 HBV patients, 13 with occult infection and 4 HBsAg-positive. Full-length HBV genomes from each case were amplified and directly sequenced. Additionally, full-length HBV DNA from eight occult-HBV and two HBsAg-positive cases were cloned and sequenced. Finally, three entire, linear HBV genomes from occult cases were transiently transfected in HuH7 cells. Direct sequencing showed the absence of mutations capable of interfering with viral replication and gene expression in the major viral population of each case. Cloning experiments showed highly divergent HBV strains both in HBsAg-positive and HBsAg-negative individual cases (range of divergence 1.4%-7.1%). All of the 3 transfected full-length HBV isolates showed normal patterns of replication in vitro.

CONCLUSION

Multiple viral variants accumulate in the liver of occult HBV-infected patients. Occult HBV strains are replication-competent in vitro, suggesting that host, rather than viral factors are responsible for cryptic HBV infection.

Dynamics of a hepatitis B virus e antigen minus population ascribed to genotype F during the course of a chronic infection despite the presence of anti-HBs antibodies

The in vivo evolution of genotype F HBV variants was recorded in a chronically infected patient throughout a 3-year observation period. Fluctuating levels of HBs Ag and anti-HBs antibodies were recorded, both of them cocirculating in peripheral blood samples at given times. Fifty S gene derived clones were sequenced and phylogenetically analyzed. As expected, some amino acid replacements within the S ORF were also observed within the P ORF while others were silent for the former. Such change was statistically significant for both S and P overlapping genes, which clearly indicates the appearance of a positive selection pressure. Supporting this notion, amino acid replacements were documented at both B and T cell epitopes in samples from 1997 and 1998. Several mutations were documented within and outside the "a" determinant in the major hydrophilic region. Such substitutions might have resulted from the attempt of HBV to evade both humoral and/or cellular immune response. To the best of our knowledge this unusual profile of HBV variants in presence of usually "neutralizing" anti-HBs antibodies was examined in vivo for the first time.

Unusual naturally occurring humoral and cellular mutated epitopes of hepatitis B virus in a chronically infected argentine patient with anti-HBs antibodies

Serum hepatitis B virus (HBV) DNA was extracted from a chronically infected patient with cocirculation of hepatitis B surface antigen (HBsAg) and anti-HBs antibodies. Direct PCR and clone-derived sequences of the S and overlapped P genes were obtained. DNA sequences and phylogenetic analysis ascribed this isolate to genotype A (serotype adw2). Five of six HBV DNA clones exhibited point mutations inside and outside the major hydrophilic region, while the sixth clone exhibited a genotype A "wild-type" amino acid sequence. Observed replacements included both humoral and/or cellular (major histocompatibility complex class I [MHC-I] and MHC-II) HBV mutated epitopes, such as S45A, P46H, L49H, C107R, T125A, M133K, I152F, P153T, T161S, G185E, A194T, G202R, and I213L. None of these mutants were individually present within a given clone. The I213L replacement was the only one observed in the five clones carrying nonsynonymous mutations in the S gene. Some of the amino acid substitutions are reportedly known to be responsible for the emergence of immune escape mutants. C107R replacement prevents disulfide bonding, thus disrupting the first loop of the HBsAg. Circulation of some of these mutants may represent a potential risk for the community, since neither current hepatitis B vaccines nor hyperimmune hepatitis B immune globulin are effectively prevent the liver disease thereto associated. Moreover, some of the recorded HBsAg variants may influence the accuracy of the results obtained with currently used diagnostic tests.

Mutations in surface and polymerase gene of chronic hepatitis B patients with coexisting HBsAg and anti-HBs

AIM

To investigate the clinical significance and presence of mutations in the surface (S) and overlapping polymerase gene of hepatitis B patients with coexisting HBsAg and anti-HBs.

METHODS

Twenty-three patients with chronic hepatitis B were studied. Of the 23 patients, 11 were both positive for hepatitis B virus (HBV) surface antigen (HBsAg) and antibody to HBV surface antigen (anti-HBs), 12 were negative for anti-HBs while positive for HBsAg. DNA was extracted from 200 muL serum of the patients. Nucleotide of the surface and overlapping polymerase gene from HBV-infected patients was amplified by PCR, and the PCR products were sequenced.

RESULTS

Forty-one mutations were found within the surface gene protein of HBV in 15 patients (10 with coexisting HBsAg and anti-HBs). Six (14.6%) out of 41 mutations were located at "alpha " determinant region in 5 patients (4 positive for HBsAg and anti-HBs). Eleven mutations (26.8%) occurred in the downstream or upstream of "alpha " determinant region. Lamivudine (LMV)-selected mutations were found in three patients who developed anti-HBs, which occurred in amino acid positions (196, 198, 199) of the surface protein and in YMDD motif (M204I/V) of the polymerase protein simultaneously. Presence of these mutations did not relate to changes in ALT and HBV DNA levels.

CONCLUSION

Besides mutations in the "alpha " deter-minant region, mutations at downstream or upstream of the "alpha " determinant region may contribute to the development of anti-HBs. These mutations do not block the replicating competency of HBV in the presence of high titer of anti-HBs.

A novel approach to characterise pathogen candidate genetic polymorphisms involved in clinical outcome

Understanding the key factors influencing the clinical outcome of an infection is crucial for early diagnosis and optimised treatment. Despite widespread recognition of the importance of the genetics composition of pathogens, most efforts so far have focused on characterising disease and susceptibility genes in humans. Here, we propose a new flexible and powerful methodological framework to detect candidate genetic polymorphisms influencing clinical outcome from pathogen genomes. The rationale is to use well-supported clades in a phylogeny as statistical predictors for clinical outcomes rather than the individual polymorphisms themselves. This greatly increases the statistical power to detect candidate polymorphisms when analysing a large number of variable sites. In a second step, the candidate polymorphisms are recovered by characterising the polymorphisms that most strongly support the clades predicting the clinical outcome. The modelling approach further allows including host factors and testing for possible interactions between factors. We illustrate the approach by an application on a dataset of hepatitis B polymerase genes. The statistical model retains age at infection as well as six candidate polymorphisms as predictors for clinical outcome (acute, chronic and fulminant). The method is straightforward to apply and computationally effective. While the approach is focused on detecting candidate polymorphisms from pathogen genomes, the method might be more broadly applied for characterising the link between genotype and phenotype while statistically controlling for environmental factors.

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.

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.

Genotyping of hepatitis B virus in Malaysia based on the nucleotide sequence of preS and S genes

Hepatitis B virus (HBV) has been classified into eight genotypes, designated A-H. These genotypes are known to have distinct geographic distributions. The clinical importance of genotype-related differences in the pathogenicity of HBV has been revealed recently. In Malaysia, the current distribution of HBV remains unclear. The aim of this study was to determine the genotypes and subtypes of HBV by using PCR, followed by DNA sequencing, as well as to analyse the mutations in the immunodominant region of preS and S proteins. The S gene sequence was determined from HBV DNA of four apparently healthy blood donors' sera and three sera from asymptomatic chronic hepatitis B carriers. Of this batch of sera, the preS gene sequence was obtained from HBV DNA from three out of the four blood donors and two out of the three chronic carriers. Due to insufficient sera, we had to resort to using sera from another blood donor to make up for the sixth DNA sequence of the preS gene. Based on the comparative analysis of the preS sequences with the reported sequences in the GenBank database, HBV DNA from two normal carriers was classified as genotype C. Genotype B was assigned to HBV from one blood donor and two hepatitis B chronic carriers, whereas HBV of one chronic carrier was of genotype D. Based on the S gene sequences, HBV from three blood donors was of genotype C, that of one blood donor and one chronic carrier was of genotype B, and the remaining, of genotype D. In the five cases where both preS and S gene sequences were determined, the genotypes assigned based on either the preS or S gene sequences were in concordance. The nature of the deduced amino acid (aa) sequences at positions 125, 127, 134, 143, 159, 161 and 168 of the S gene enabled the classification of these sequences into subtypes, namely, adrq+, adw2 and ayw2. The clustering of our DNA sequences into genotype groups corresponded to their respective subtype, that is, adw2 in genotype B, adrq in genotype C and ayw in genotype D. Analysis of the point mutations revealed that five of the sequences contained aa substitutions at immunodominant epitopes involved in B or/and T cell recognition. In conclusion, despite the low numbers of samples studied, due to budget constraints, these data are still worthwhile reporting, as it is important for the control of HBV infections. In addition, the genotype and mutational data obtained in this study may be useful for designing new treatment regimes for HBV patients.

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.

Different types of ground glass hepatocytes in chronic hepatitis B virus infection contain specific pre-S mutants that may induce endoplasmic reticulum stress

Ground glass hepatocyte (GGH) represents a histological hallmark of chronic hepatitis B virus infection and contains surface antigens in the endoplasmic reticulum (ER). Several types of GGHs are recognized at different hepatitis B virus replicative stages. The recent identification of pre-S mutants from GGHs encourages us to investigate whether different GGHs may harbor specific mutants and exhibit differential biological activities. In this study, we applied laser capture microdissection to isolate specific GGHs from a total of 50 samples on eight resected liver specimens. The surface genes in two major types of GGHs were analyzed. Type I GGHs expressed an inclusion-like pattern of hepatitis B surface antigens and harbored mutants with deletions over pre-S1 region, whereas type II GGHs, distributed in clusters and emerged at late replicative phase, contained mutants with deletions over pre-S2 region that defines a cytotoxic T lymphocyte (CTL) immune epitope, and may represent an immune escape mutant. Transfection of pre-S mutants in Huh7 revealed decreased syntheses of middle and small S proteins with accumulation of large surface antigen in ER, which in turn led to the activation of ER stress response with differential activities for different mutants. This study therefore demonstrates that different GGHs may contain specific mutants and exhibit differential biological activities.

Dominant mutations of hepatitis B virus variants in hepatoma accumulate in B-cell and T-cell epitopes of the HBx antigen

Hepatitis B virus (HBV) X gene, encoding a pleotropic transactivator of HBx protein, has been associated with the development of hepatocellular carcinoma (HCC). Molecular information on liver-derived HBV variants isolated from HCC among Taiwanese population was studied. Amplification of the HBV X genes of 20 HCC patients in high stringency with HBV specific primers was observed. The resulting amplified HBV X genes were purified and individually-cloned into pUC-T vector. Sequences of the eight liver-derived X gene were aligned and compared with the wild type, the ayw HBV serotype. Results indicate that the HBx protein of variants were found predominantly within the regions of amino acid positions 26-45 in N-terminus, and positions 87, 88, 116, 118, 119, 127 and 144. Sequences from six out of the eight variants were found to be identical. These accumulated sequence mutations among the eight HBx variants were found to coincide within the B-cell epitopes (positions 29-48), particularly in the HBx proline and serine rich (PSR) domain, and the T-cell epitopes regions (positions 116-127). These frequent mutations of HBV variants, rather than subtype-specific polymorphic sites, may be involved in immunoevasion.

Replication efficiency and sequence analysis of full-length hepatitis B virus isolates from hepatocellular carcinoma tissues

Prolonged replication of hepatitis B virus (HBV) in liver tissues of hepatitis B patients has been considered as an important risk factor for the development of malignancy. Few studies on full-length HBV sequencing in association with the replication efficiency of isolates from HCC tissues have been reported. To study the structural and functional genomics of HBV isolates from Chinese hepatocellular carcinoma (HCC) patients, full-length HBV genomes were amplified from 6 HBV-marker positive HCC tissues and used to transfect HepG2 cells. Five of 6 isolates showed high replicative efficiency. All isolates were of genotype C and "hot-spots" mutations were detected in the B cell and T helper (Th) cell epitopes of the envelope and the core region. In addition, the X region of 2 isolates contained a stop-codon mutation that was predicted to result in a truncated X protein. High replicative HBV immune escape mutants that persist in infected hepatocytes could be 1 of the important factors to initiate pathological processes for the development of HCC in Chinese patients.

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.

Comparing the immunogenicity of hepatitis B virus S gene variants by DNA immunization

DNA immunization was used to compare the immunogenicity of hepatitis B virus S gene variants. Four recombinant plasmid DNAs containing the full-length virus genome with different S gene inserts were used to immunize BALB/c and C57/BL/6 mice. These inserts were cloned from 129L (residue 129, glutamine to leucine), 129H (residue 129, glutamine to histidine) 145R (residue 145, glycine to arginine) variants and the wild-type virus. The titer of hepatitis B virus core antibodies (anti-HBc) in immunized mice was used as the control for the efficiency of DNA immunization. Serum hepatitis B surface antibody (anti-HBs) titer and cytokines induced in splenocytes stimulated with hepatitis B surface antigen (HBsAg) were monitored as specific immune responses induced by different plasmid DNAs. 129L DNA induced significantly lower anti-HBs antibodies (IgG, IgG1, and IgG2a) and less interferon-gamma, compared to those in mice immunized with the 129H variant and the wild-type HBV DNA (p < 0.05). Computer modeling showed that a change from glutamine to leucine at 129 residue led to higher hydrophobicity and could result in decreased immunogenicity. Results indicate that DNA immunization can be used to compare the humoral and cellular immunogenicity among different HBV S variants.

Molecular epidemiology of hepatitis B viral serotypes and genotypes in taiwan

Subtypes of hepatitis B virus (HBV) have specific geographic distributions and can serve as epidemiological markers. The relationship of HBV serotypes and genotypes in Taiwan and their correlation with the domiciles of origin in 122 patients with chronic HBV infection were investigated. The serotype of HBV was determined by comparing the surface gene encoding amino acids 22-148 of the major surface protein with published sequences. Genotyping of HBV was performed by polymerase chain reaction-restriction fragment length polymorphism. Serotype adw accounted for 70% (85/122) of all HBVs, with the remaining belonging to serotype adr. All adr HBVs were genotype C, regardless of the patient's domicile. Of the 85 adw HBVs, 69 (81%) were genotype B, 10 (12%) were genotype C, 5 (6%) were genotype F and only 1 (1%) was genotype A. In the 31 patients originating from mainland China, the prevalence of adr/genotype C was higher than in the 91 Taiwanese patients (15/31 vs. 22/91; p < 0.05). The distribution of the HBV serotypes and genotypes was not significantly different between 17 patients born in Taiwan (6 adw/genotype B, 2 adw/genotype C, 1 adw/genotype F and 8 adr/genotype C) and 14 patients born in mainland China (5 adw/genotype B, 2 adw/genotype C and 7 adr/genotype C). Our results indicate that in Taiwan, most HBVs of serotype adw are genotype B, and all HBVs of serotype adr are genotype C. Patients with origins in mainland China have a higher proportion of serotype adr/genotype C infection.

Hypermodification and immune escape of an internally deleted middle-envelope (M) protein of frequent and predominant hepatitis B virus variants

Naturally occurring deletions within the human hepatitis B virus (HBV) preS2 region have frequently been identified in patients with hepatocellular carcinoma (HCC), while chronic carriers without cirrhosis and HCC contain no detectable preS2 deletion variants. We have characterized two different preS2 internal deletion variants from two patients. In addition to several weak phenotypes, our study revealed three unexpected strong phenotypes: (1) a paradoxical "hypermodification" phenomenon was observed with significantly increased size heterogeneity and molecular weights of the secreted middle (M) envelope proteins containing a preS2 internal deletion. This phenomenon was observed in transient transfection with a human hepatoma Huh7 cell line as well as in stable transfection with a rodent hepatoma cell line 7777. (2) A significantly increased intracellular accumulation of all three envelope proteins (large, middle, and small) was detected by both Western blot analysis and immunofluorescence microscopy. (3) The middle envelope proteins with a preS2 internal deletion were not recognized in vitro by a putative neutralizing antiserum, suggesting that these variants can evade immune recognition in vivo. To our knowledge, this is the first identification and characterization of the M deletion variant protein in HBV natural 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.

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.

Genetic variations of hepatitis B virus

The emergence of hepatitis B virus genetic variants occurs under the influence of host immunity, immunization, the use of immune globulin or antiviral chemotherapy. Most of these are probably the result of the 'immune escape' phenomenon. Some variants, in particular those in the precore and core promoter regions, have been associated with disease severity and progression. Surface antigen variants have implications for the accuracy of laboratory diagnosis and may reduce the effectiveness of vaccination. Polymerase variants are selected as a result of the use of antiviral chemotherapeutic agents. It is important to monitor the occurrence of these variants.

Identification of a pre-S2 mutant in hepatocytes expressing a novel marginal pattern of surface antigen in advanced diseases of chronic hepatitis B virus infection

BACKGROUND AND AIMS

The expression of hepatitis B viral (HBV) antigens in liver tissue reflects the replicative status of chronic HBV infection. We have previously recognized a novel marginal pattern of hepatitis B surface antigen (HBsAg) in hepatocytes, which usually clusters in groups and emerges at the late non-replicative phase. This study was designed to investigate whether the marginal-type HBsAg represented the gene product of a specific HBV-surface mutant.

METHODS

Microdissection of cirrhotic nodules homogeneously expressing marginal HBsAg was performed on two of 12 resected livers from HBsAg-seropositive patients with hepatocellular carcinoma. The gene presumably encoding marginal HBsAg was polymerase chain reaction (PCR)-cloned, sequenced and analysed. In vitro transfection and expression of the cloned surface mutant plasmids were performed on the Huh7 cell line to illustrate intrahepatic HBsAg expression.

RESULTS

Immunohistochemical staining revealed that the marginal HBsAg was positive for pre-S1 and thus contained large surface proteins. The PCR cloning and sequencing of the genes presumably encoding marginal-type HBsAg in both cases revealed the same deletion at the 5' terminus (nt 2-55) of pre-S2. A point mutation on the small-surface (S) antigen was also found in one case. The pre-S2 deletion sequence and the mutation sites of the S gene coincide with human lymphocyte antigen-restricted T- and/or B-cell epitopes. In vitro transfection of the mutant plasmid revealed a blot-like retention or accumulation of HBsAg in the cytoplasm or at the periphery of hepatocytes, accompanied by a decreased secretion of HBsAg in the culture supernatant, mimicking intrahepatic expression.

CONCLUSION

A natural pre-S2 deletion mutant was identified in hepatocytes expressing a novel marginal pattern of HBsAg, which probably contains mutant, large, surface proteins. The biological significance of the pre-S2 deletion mutant should be interesting in view of the clustering proliferation of hepatocytes expressing marginal HBsAg.

Long-term mutation rates in the hepatitis B virus genome

Mutations in the hepatitis B virus (HBV) genome have so far been investigated in cross-sectional or short-term longitudinal studies. Information about long-term changes is lacking due to the difficulty of sampling over long observation periods. In this study, a retrospective approach was used that allowed the analysis of changes in the viral genome from transmission to late stages of infection without the requirement for sampling early during this period. The entire viral genome was sequenced from serum samples of three mothers and their 10 adult children, who presumably had been infected vertically. The emergence of mutations between birth and sampling (mean 26.5 years) was assessed by comparing the individual sequences with the sequence of the strain assumed to have been transmitted. The mean differences from this sequence were 0.02 and 0. 28% in seven asymptomatic and one symptomatic hepatitis B e antigen (HBeAg)-positive carriers, respectively, and 0.62 % in five HBeAg-negative carriers. Mutations occurred throughout the genome and 88% of the mutations caused amino acid substitutions spread over all genes. In HBeAg-negative carriers, the number of nucleotide and amino acid changes was independent of the severity of liver disease and, except the (1762)AGG(1764)-->TGA changes, no specific mutation was associated with liver disease. In conclusion, by using a novel method it was found that the entire HBV genome is extremely stable over long periods of time during the HBeAg-positive phase if the immune response (inflammation) is weak, whereas an average of 20 mutations emerged after development of hepatitis and/or loss of HBeAg without association with clinical outcome.

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.

Mutation "hot spot" in HLA class I-restricted T cell epitope on hepatitis B surface antigen in chronic carriers and hepatocellular carcinoma

Mutations in the human hepatitis B virus (HBV) genome contribute to its escape from host immune surveillance and result in persistent infection. We report the identification of frequent mutations encompassing residues 29 to 53 of the HBV surface antigen in chronic HBV carriers as well as in patients with hepatocellular carcinoma. The location of these mutations, not found in patients with acute hepatitis and vaccinated infants, coincides with a human leukocyte antigen class I-restricted cytotoxic T lymphocyte epitope. Significantly, mutations occur at a higher frequency (83%) compared with those identified on the immunogenic "a" determinant (25%) of the corresponding patients. Our findings therefore suggest the potential importance of this novel mutation "hot spot" in the establishment of chronic HBV infection.

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.