Mapping of immunodominant B-cell epitopes and the human serum albumin-binding site in natural hepatitis B virus surface antigen of defined genosubtype

Identification of Two Critical Neutralizing Epitopes in the Receptor Binding Domain of Hepatitis B Virus preS1

Hepatitis B virus (HBV) infection is a major public health problem. Human hepatocytes are infected with HBV via binding between the preS1 region in the large envelope protein of HBV and sodium taurocholate cotransporting polypeptide. Although several monoclonal antibodies (MAbs) that recognize the receptor binding domain in preS1 and neutralize HBV infection have been isolated, details of neutralizing epitopes are not understood. In this study, we generated 13 MAbs targeting the preS1 receptor binding domain from preS1-specific memory B cells derived from DNA immunized mice. The MAbs were classified into three groups according to the epitope regions, designated epitopes I-III. A virus neutralization assay revealed that MAbs recognizing epitopes I and III neutralized HBV infection, suggesting that these domains are critical epitopes for viral neutralization. In addition, a neutralization assay against multiple genotypes of HBV revealed that epitope I is a semi-pangenotypic neutralizing epitope, whereas epitope III is a genotype-specific epitope. We also showed that neutralizing MAbs against preS1 could neutralize HBV bearing vaccine-induced escape mutation. These findings provide insight into novel immunoprophylaxis for the prevention and treatment of HBV infection.IMPORTANCE The HBV preS1 2-47 aa region (preS1/2-47) is essential for virus binding with sodium taurocholate cotransporting polypeptide. Several MAbs targeting preS1/2-47 have been reported to neutralize HBV infection; however, which region in preS1/2-47 contains the critical neutralizing epitope for HBV infection is unclear. Here, we generated several MAbs targeting preS1/2-47 and found that MAbs recognizing the N- or C-terminus of preS1/2-47 remarkably neutralized HBV infection. We further confirmed the neutralizing activity of anti-preS1 MAbs against HBV with vaccine escape mutation. These data clarified the relationship between the antibody epitope and the virus neutralizing activity and also suggested the potential ability of a vaccine antigen containing the preS1 region to overcome the weakness of current HB vaccines comprising the small S protein.

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

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

CTL-associated and NK cell-associated immune responses induce different HBV DNA reduction patterns in chronic hepatitis B patients

The activation of hepatitis B virus (HBV)-related hepatitis is associated with both natural killer (NK) cells and cytotoxic T lymphocytes (CTLs). We analyzed the association between the immune response and changes in the proportion of Pre-S deletion variants. We quantified Pre-S deleted HBV (HBV-del) and wild-type HBV (HBV-wt) DNA levels in sera obtained from HBV-infected mice and chronic hepatitis B patients. In chronic hepatitis B patients, the HBV-del proportion usually increased during or after ALT elevation but did not occur during all ALT elevations. To clarify this difference in the immunological responses, we performed in vivo analyses using HBV-infected human hepatocyte chimeric mice. Although HBV-del proportions did not change in mice with NK cell-associated hepatitis or in mice treated with entecavir, the proportions sharply increased in mice with CTL-associated hepatitis. Furthermore, the number of patients in which HBV-del proportions were greater than 5% was significantly higher in chronic hepatitis B patients than in asymptomatic carriers (P = 0.023). We identified associations between virological response in chronic hepatitis B patients and two different immune responses. The proportion of HBV-del variants could be a useful biomarker for distinguishing between chronic hepatitis and asymptomatic carriers.

Quantification of large and middle proteins of hepatitis B virus surface antigen (HBsAg) as a novel tool for the identification of inactive HBV carriers

OBJECTIVE

Among individuals with chronic hepatitis B, those with hepatitis B e-antigen (HBeAg)-negative chronic hepatitis (CHB) can be difficult to distinguish from those with HBeAg-negative chronic HBV infection, also referred to as inactive HBV carriers (ICs), but both require different medical management. The level of HBV surface antigen (HBsAg) has been proposed as a marker to discriminate between chronic infection and hepatitis stages. HBsAg consists of large, middle and small HBs. The aim of this study was to determine whether the composition of HBsAg improved the identification of ICs among HBsAg-positive subjects with different phases of HBV infections.

DESIGN

HBV large surface proteins (LHBs) and HBV middle surface proteins (MHBs) were quantified in serum samples from 183 clinically well-characterised untreated patients with acute (n=14) HBV infection, ICs (n=44), CHBs (n=46), chronic HBeAg-positive phase (n=68) and hepatitis delta coinfection (n=11) using an ELISA, with well-defined monoclonal antibodies against the preS1 domain (LHBs) and the preS2-domain (MHBs). A Western blot analysis was used to verify the quantitation of the components of HBsAg. Total HBsAg was quantified using a modified commercially available assay (HBsAg V.6.0, Enzygnost, Siemens, Erlangen).

RESULTS

The composition of HBsAg showed specific patterns across different phases of hepatitis B. Individuals in the IC phase had significantly lower proportions of LHBs and MHBs than patients in acute or chronic phases irrespective of their HBV e-antigen status (p<0.0001) or HBsAg level. Both LHBs and MHBs ratios better predicted the IC phase than total HBsAg levels.

CONCLUSION

Quantification of MHBs, particularly LHBs represents a novel tool for the identification of the IC stage.

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

BACKGROUND

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

MAIN BODY

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

CONCLUSION

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

Pre-S deletions of hepatitis B virus predict recurrence of hepatocellular carcinoma after curative resection

The relationship between hepatitis B virus (HBV) and the prognosis of hepatocellular carcinoma (HCC) after surgery remains uncertain. A retrospective cohort study was performed to evaluate the impact of pre-S deletions, T1762/A1764, and A1896 mutations on prognosis of HCC after curative resection. A total of 113 patients with positive serum HBV DNA (>200 IU/mL) who had underwent curative resection of pathologically proven HCC were recruited to determine the risk factors affecting the prognosis.The median follow-up time was 36.5 months and recurrence was detected in 67 patients (59.3%). The cumulative recurrence rates and overall survival rates at 1-, 3-, and 5-year after curative resection were 18.0%, 49.7%, 70.3%, and 93.7%, 61.0%, 42.5%, respectively. Patients with pre-S deletions showed significantly higher recurrence rates compared with those with wild type infection (HR: 1.822, P = .018), but not related with a significantly poor survival (HR: 1.388, P = .235). Subgroup analysis indicated that the patients with type III deletion had significant higher tumor recurrence rates than other deletion types (HR: 2.211, 95% confidence intervals [CI]: 1.008-4.846, P = .048). Multivariate analysis revealed that pre-S deletion, tumor size >3 cm in diameter, and the presence of microvascular invasion were independent risk factors for tumor recurrence. HBV pre-S deletions were found to be clustered primarily in the 5' end of pre-S2 region and were more often found between amino acids 120 and 142 of the pre-S2 domain. The domains most frequently potentially involved were the transactivator domain in pre-S2 and polymerized human serum albumin binding site.Our cohort showed that pre-S deletions at the time of resection could predict tumor recurrence in HCC patients after curative resection.

Ceruloplasmin inhibits the production of extracellular hepatitis B virions by targeting its middle surface protein

Ceruloplasmin (CP) is mainly synthesized by hepatocytes and plays an essential role in iron metabolism. Previous reports have shown that CP levels correlate negatively with disease progression in patients with chronic hepatitis B. However, the function of CP in the hepatitis B virus (HBV) life cycle and the mechanism underlying the above correlation remain unclear. Here, we report that CP can selectively inhibit the production of extracellular HBV virions without altering intracellular viral replication. HBV expression can also downregulate the expression of CP. Knockdown of CP using small interfering RNA significantly increased the level of extracellular HBV virions in both Huh7 and HepG2.2.15 cells, while overexpression of CP decreased this level. Mechanistically, CP could specifically interact with the HBV middle surface protein (MHB). Using an HBV replication-competent clone unable to express MHBs, we demonstrated that the overexpression of CP did not affect the production of extracellular HBV virions in the absence of MHBs. Furthermore, introduction of an MHB expression construct could rescue the impairment in virion production caused by CP. Taken together, our results suggest that CP may be an important host factor that targets MHBs during the envelopment and/or release of virions.

Different pre-S deletion patterns and their association with hepatitis B virus genotypes

AIM

To investigate the associations of different types of pre-S deletions with hepatitis B virus (HBV) genotypes.

METHODS

The sequences of the pre-S region, basal core promoter (BCP) mutation, and precore (PC) mutation were examined through direct DNA sequencing or clonal analysis and sequencing in 273 HBV carriers, namely 55 asymptomatic carriers, 55 carriers with chronic hepatitis (CH), 55 with liver cirrhosis (LC), 53 with liver cirrhotic hepatocellular carcinoma (LC-HCC), and 55 with noncirrhotic HCC. A total of 126 HBV carriers (46.2%) harbored pre-S deletions. The DNA sequences of pre-S deletion mutants from 43 age-matched genotype B (HBV/B)-infected carriers and 43 age-matched genotype C (HBV/C)-infected carriers were further examined, aligned, and compared.

RESULTS

No significant difference was observed in the mean age distribution (P = 0.464), male sex (P = 0.805), viral load (P = 0.635), or BCP mutation (P = 0.117) between the HBV/B and HBV/C groups. However, the rate of PC mutation was significantly higher in the HBV/B-infected carriers than in the HBV/C-infected carriers (P = 0.003). Both genotypes exhibited a high rate of deletion in the C-terminal half of the pre-S1 region and N-terminus of the pre-S2 region (86.0% and 79.1% in the HBV/B group; 69.8% and 72.1% in the HBV/C group, respectively). Epitope mapping showed that deletion in several epitope sites was frequent in both genotypes, particularly pS1-BT and pS2-B2. Conversely, the rate of pS2-B1 deletion was significantly higher in the HBV/B group (72.1% vs 37.2%, P = 0.002), and the rate of pS2-T deletion was significantly higher in the HBV/C group (48.8% vs 25.6%, P = 0.044). Functional mapping showed that the rate of deletion in three functional sites (the nucleocapsid binding site, start codon of M, and site for viral secretion) located in the N-terminus of the pre-S2 region was significantly higher in the HBV/B group (P < 0.05). One type of N-terminus pre-S1 deletion mutant with deletion of the start codon of the L protein was frequently observed in the HBV/C group (20.9% vs 9.3%, P = 0.228), particularly in the LC patients (42.9% vs 12.5%). Different patterns of pre-S deletions were also found between the HBV/B and HBV/C groups according to different clinical outcomes. In CH patients, deletion in the site for polymerized human serum albumin was more frequent in the HBV/B group (88.9% vs 36.4%, P = 0.028). In the LC-HCC patients, the rate of deletion in the pre-S2 region was significantly higher in the HBV/B group than in the HBV/C group (P < 0.05).

CONCLUSION

HBV/B- and HBV/C-infected carriers exhibit different patterns of pre-S deletion, which may be associated with the progression of liver diseases.

Different pre-S deletion patterns and their association with hepatitis B virus genotypes

AIM

To investigate the associations of different types of pre-S deletions with hepatitis B virus (HBV) genotypes.

METHODS

The sequences of the pre-S region, basal core promoter (BCP) mutation, and precore (PC) mutation were examined through direct DNA sequencing or clonal analysis and sequencing in 273 HBV carriers, namely 55 asymptomatic carriers, 55 carriers with chronic hepatitis (CH), 55 with liver cirrhosis (LC), 53 with liver cirrhotic hepatocellular carcinoma (LC-HCC), and 55 with noncirrhotic HCC. A total of 126 HBV carriers (46.2%) harbored pre-S deletions. The DNA sequences of pre-S deletion mutants from 43 age-matched genotype B (HBV/B)-infected carriers and 43 age-matched genotype C (HBV/C)-infected carriers were further examined, aligned, and compared.

RESULTS

No significant difference was observed in the mean age distribution (P = 0.464), male sex (P = 0.805), viral load (P = 0.635), or BCP mutation (P = 0.117) between the HBV/B and HBV/C groups. However, the rate of PC mutation was significantly higher in the HBV/B-infected carriers than in the HBV/C-infected carriers (P = 0.003). Both genotypes exhibited a high rate of deletion in the C-terminal half of the pre-S1 region and N-terminus of the pre-S2 region (86.0% and 79.1% in the HBV/B group; 69.8% and 72.1% in the HBV/C group, respectively). Epitope mapping showed that deletion in several epitope sites was frequent in both genotypes, particularly pS1-BT and pS2-B2. Conversely, the rate of pS2-B1 deletion was significantly higher in the HBV/B group (72.1% vs 37.2%, P = 0.002), and the rate of pS2-T deletion was significantly higher in the HBV/C group (48.8% vs 25.6%, P = 0.044). Functional mapping showed that the rate of deletion in three functional sites (the nucleocapsid binding site, start codon of M, and site for viral secretion) located in the N-terminus of the pre-S2 region was significantly higher in the HBV/B group (P < 0.05). One type of N-terminus pre-S1 deletion mutant with deletion of the start codon of the L protein was frequently observed in the HBV/C group (20.9% vs 9.3%, P = 0.228), particularly in the LC patients (42.9% vs 12.5%). Different patterns of pre-S deletions were also found between the HBV/B and HBV/C groups according to different clinical outcomes. In CH patients, deletion in the site for polymerized human serum albumin was more frequent in the HBV/B group (88.9% vs 36.4%, P = 0.028). In the LC-HCC patients, the rate of deletion in the pre-S2 region was significantly higher in the HBV/B group than in the HBV/C group (P < 0.05).

CONCLUSION

HBV/B- and HBV/C-infected carriers exhibit different patterns of pre-S deletion, which may be associated with the progression of liver diseases.

Evolutionary Changes of Hepatitis B Virus Pre-S Mutations Prior to Development of Hepatocellular Carcinoma

BACKGROUND AND AIMS

Deletions/mutations in the hepatitis B virus (HBV) pre-S region have been associated with hepatocellular carcinoma (HCC). We aimed to study the evolutionary changes of pre-S mutations prior to HCC development.

METHODS

We studied the HBV pre-S sequences at 1 to 10 years preceding diagnosis of HCC in 74 patients with HBV-related HCC (HCC group). 148 chronic hepatitis B patients matched for sex and age in 2:1 ratio, who had been followed up for at least 3 years without HCC (HCC-free group) were recruited as controls. 56 and 47 patients of HCC and HCC-free groups respectively had serially stored sera for longitudinally examination at 1-3 years, 4-6 years, 7-9 years and ≥10 years prior to the recruitment of the study.

RESULTS

Compared to the HCC-free group, higher frequencies of pre-S deletions and point mutations (at 11 codons) were observed in the HCC group (p<0.05). Multiple logistic regression analysis showed that pre-S deletions, point mutations at codon 51 and 167 were independent factors associated with HCC. Longitudinal observation showed that pre-S deletions and most of the 11 HCC-associated pre-S point mutations existed at least 10 years before HCC development, and were more prevalent preceding HCC development in patients from HCC groups than HCC-free group. The number of HCC-associated pre-S point mutations increased over time preceding HCC development, and correlated positively with the time to HCC diagnosis (r = 0.220, p = 0.005).

CONCLUSIONS

High prevalence and cumulative evolution of pre-S mutations preceding HCC development suggested a possible carcinogenic role of pre-S mutations and their potential application in HCC risk prediction.

Evolutionary Changes of Hepatitis B Virus Pre-S Mutations Prior to Development of Hepatocellular Carcinoma

BACKGROUND AND AIMS

Deletions/mutations in the hepatitis B virus (HBV) pre-S region have been associated with hepatocellular carcinoma (HCC). We aimed to study the evolutionary changes of pre-S mutations prior to HCC development.

METHODS

We studied the HBV pre-S sequences at 1 to 10 years preceding diagnosis of HCC in 74 patients with HBV-related HCC (HCC group). 148 chronic hepatitis B patients matched for sex and age in 2:1 ratio, who had been followed up for at least 3 years without HCC (HCC-free group) were recruited as controls. 56 and 47 patients of HCC and HCC-free groups respectively had serially stored sera for longitudinally examination at 1-3 years, 4-6 years, 7-9 years and ≥10 years prior to the recruitment of the study.

RESULTS

Compared to the HCC-free group, higher frequencies of pre-S deletions and point mutations (at 11 codons) were observed in the HCC group (p<0.05). Multiple logistic regression analysis showed that pre-S deletions, point mutations at codon 51 and 167 were independent factors associated with HCC. Longitudinal observation showed that pre-S deletions and most of the 11 HCC-associated pre-S point mutations existed at least 10 years before HCC development, and were more prevalent preceding HCC development in patients from HCC groups than HCC-free group. The number of HCC-associated pre-S point mutations increased over time preceding HCC development, and correlated positively with the time to HCC diagnosis (r = 0.220, p = 0.005).

CONCLUSIONS

High prevalence and cumulative evolution of pre-S mutations preceding HCC development suggested a possible carcinogenic role of pre-S mutations and their potential application in HCC risk prediction.

Studies of nosocomial outbreaks of hepatitis B in nursing homes in Germany suggest a major role of hepatitis B e antigen expression in disease severity and progression

Hepatitis B virus (HBV) causes acute or chronic hepatitis B. Local outbreaks of HBV infections in skilled nursing facilities is a matter of growing concern in developed countries. Here, we investigated two outbreaks of hepatitis B that recently occurred in nursing homes in Germany. The outbreak at location A was associated with acute fulminant hepatitis with fatal outcome in several cases, while individuals infected at location B developed asymptomatic or mild hepatitis B. Sequence analysis of viruses involved in these outbreaks revealed different, but unique HBV strains for each location. Each of the strains produced high viremia of more than 10(9) virions/mL serum. We found that the mild course of hepatitis B at location B was caused by a circulating wild-type HBV genotype A2 strain, which is commonly found in Central Europe. Complete genome sequences of isolates obtained from infected patients revealed nearly 100% sequence identity at the nucleotide level as well as expression of HBV e protein (HBeAg), a known T cell tolerogen in the incubation or chronic phases of HBV infection. By contrast, the outbreak at location A was associated with an HBV genotype D2 variant that lacked HBeAg expression, suggesting that immunopathology and selection of specific HBV variants played a major role in the severe (or even fulminant) acute hepatitis observed at location A. Importantly, all patients were diagnosed with type 2 diabetes mellitus, a known risk factor for healthcare-associated transmission of HBV. The study leads us to suggest that, besides strict adherence to hygiene standards, additional efforts are required to reduce the risk of HBV transmission and fulminant disease progression in healthcare settings and nursing homes. In this context, a general screening for HBsAg and active hepatitis B vaccination should be considered for people living in nursing homes, especially for those with diagnosed diabetes or other predisposing factors for HBV transmission.

Prophylactic vaccination against hepatitis B: achievements, challenges and perspectives

Large-scale vaccination against hepatitis B virus (HBV) infection started in 1984 with first-generation vaccines made from plasma of chronic carriers containing HBV surface antigen (HBsAg). Thereafter, it was replaced in most countries by second-generation vaccines manufactured in yeast cells transformed with gene S encoding HBsAg. Both generations of vaccines have been applied for universal neonate and early childhood vaccination worldwide and have led to a 70-90 % decrease in chronic HBV carrier rates. However, 10-30% of newborns from HBsAg/HBeAg-positive mothers cannot be protected by passive/active vaccination alone and become chronic HBV carriers themselves. Asymptomatic occult HBV infections are frequent even in those who have protective levels of anti-HBs. Suboptimal protection may be due to heterologous HBsAg subtypes that are present in 99% of HBV carriers worldwide. Second-generation vaccines contain partially misfolded HBsAg and lack preS1 antigen that carries the major HBV attachment site and neutralizing epitopes. Third-generation vaccines produced in mammalian cells contain correctly folded HBsAg and neutralizing epitopes of the preS antigens, induce more rapid protection, overcome nonresponse to second-generation vaccines and, most importantly, may provide better protection for newborns of HBV-positive mothers. PreS/S vaccines expressed in mammalian cells are more expensive to manufacture, but introduction of more potent HBV vaccines should be considered in regions with a high rate of vertical transmission pending assessment of health economics and healthcare priorities. With optimal vaccines and vaccination coverage, eradication of HBV would be possible.

Modification of the hepatitis B virus envelope protein glycosylation pattern interferes with secretion of viral particles, infectivity, and susceptibility to neutralizing antibodies

The envelope proteins of hepatitis B virus (HBV) bear an N-linked glycosylation site at N146 within the immunodominant a-determinant in the antigenic loop (AGL) region. This glycosylation site is never fully functional, leading to a nearly 1/1 ratio of glycosylated/nonglycosylated isoforms in the viral envelope. Here we investigated the requirement for a precise positioning of N-linked glycan at amino acid 146 and the functions associated with the glycosylated and nonglycosylated isoforms. We observed that the removal of the N146 glycosylation site by mutagenesis was permissive to envelope protein synthesis and stability and to secretion of subviral particles (SVPs) and hepatitis delta virus (HDV) virions, but it was detrimental to HBV virion production. Several positions in the AGL could substitute for position 146 as the glycosylation acceptor site. At position 146, neither a glycan chain nor asparagine was absolutely required for infectivity, but there was a preference for a polar residue. Envelope proteins bearing 5 AGL glycosylation sites became hyperglycosylated, leading to an increased capacity for SVP secretion at the expense of HBV and HDV virion secretion. Infectivity-compatible N-glycosylation sites could be inserted at 3 positions (positions 115, 129, and 136), but when all three positions were glycosylated, the hyperglycosylated mutant was substantially attenuated at viral entry, while it acquired resistance to neutralizing antibodies. Taken together, these findings suggest that the nonglycosylated N146 is essential for infectivity, while the glycosylated form, in addition to its importance for HBV virion secretion, is instrumental in shielding the a-determinant from neutralizing antibodies.

IMPORTANCE

At the surface of HBV particles, the immunodominant a-determinant is the main target of neutralizing antibodies and an essential determinant of infectivity. It contains an N-glycosylation site at position 146, which is functional on only half of the envelope proteins. Our data suggest that the coexistence of nonglycosylated and glycosylated N146 at the surface of HBV reflects the dual function of this determinant in infectivity and immune escape. Hence, a modification of the HBV glycosylation pattern affects not only virion assembly and infectivity but also immune escape.

Fine mapping of hepatitis B virus pre-S deletion and its association with hepatocellular carcinoma

BACKGROUND

Naturally occurring pre-S deletion mutants have been identified in hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC).

AIMS

This study investigated whether specific deletions within the pre-S region were associated with HCC development.

METHODS

The virologic characteristics of 56 HBV chronic carriers and 112 age-matched patients with HBV-related HCC were examined.

RESULTS

The HCC patients had a significantly higher frequency of high viral load, basal core promoter mutation and pre-S deletion than chronic carriers. Sequencing analysis showed that the deleted regions were clustered mainly in the C terminus of pre-S1 (70.5%) and the N terminus of pre-S2 (72.7%) in HCC patients. Immuno-epitope mapping of these pre-S deletion sequences showed that all the deletion regions encompassed T- and B- cell epitopes and the B-cell epitope at amino acid 1-6 of pre-S2 was significantly deleted in HCC patients (60.0% vs. 0.0%; P = 0.036). Functional mapping of these deletion mutants showed that most of HCC patients lost one or more functional sites and the deletion of site for viral secretion (aa 1-5 of pre-S2 domain) was significantly detected in HCC patients than chronic carriers (62.5% vs. 0.0%; P = 0.029). Computational protein function prediction indicated that these mutants may have different molecular functions and participate in other biological processes compared with wild-type pre-S.

CONCLUSIONS

Deletion of B-cell epitope at amino acid 1-6 of pre-S2 region and the site for virion secretion are significantly associated with the development of HCC in HBV carriers.

Functional analysis of hepatitis B virus pre-s deletion variants associated with hepatocellular carcinoma

BACKGROUND

Naturally occurring pre-S deletion mutants have been identified in hepatitis B carriers and shown to be associated with the development of hepatocellular carcinoma. The phenotypes of these pre-S deletion genomes remain unclear, and they were investigated in this study.

METHODS

The pre-S deletion genomes: (1) pre-S1 deletion, (2) deletion spanning pre-S1 and pre-S2, (3) pre-S2 N-terminal deletion, and (4) pre-S2 internal deletion were constructed and analyzed by transfection into Huh-7 cells.

RESULTS

Functional analyses reveal that these mutants were divided into two groups: S promoter deletion and non-S promoter deletion variants. Compared with the wild-type genome, S promoter deletion variants led to an inverse ratio of pre-S1 mRNA and pre-S2/S mRNA, and intracellular accumulation of surface proteins. An interesting finding is that a small amount of L proteins was detected in the medium from S promoter deletion variant-transfected cells. Non-S promoter deletion variants conversely displayed a wild-type like mRNA and protein pattern. The secretion of surface proteins from non-S promoter deletion variants was inhibited less than from S promoter deletion variant. Immunofluorescence analysis showed mutant surface proteins colocalized with ER and exhibited an atypical distribution: granular staining pattern in the S-promoter deletion variants and perinuclear staining pattern in the non-S promoter deletion variants.

CONCLUSION

This study shows that these pre-S deletion genomes exhibit two different phenotypes in mRNA transcription, surface protein expression and secretion. This diversity seems to result from the deletion of S promoter rather than result from the deletion of pre-S1 or pre-S2.

Differential pattern of pre-S mutations/deletions and its association with hepatitis B virus genotypes in Eastern India

The presence of three different HBV genotypes (A, C and D) in Eastern India provided us a unique opportunity to study HBV pre-S mutants in these genotypes and subtypes among the same ethnic population. Furthermore, we also aimed to investigate the association of the HBV pre-S mutation with clinical outcome. Pre-S1-S2 and S gene was amplified and sequenced from 86 HBsAg positive study subjects with varying clinical manifestation. The genetic variability in the pre-S region (mutations) was studied with respect to different HBV genotypes, subtypes and different clinical categories. Six different types of HBV pre-S mutations were detected in 25 cases (29.07%), among which pre-S2 start codon mutation (28.0%) and pre-S2 deletion (24.0%) were most common. Pre-S mutation was highest in HBV/C (7/18; 38.89%) followed by HBV/A (9/27; 33.33%) and HBV/D (9/40; 22.50%). Pre-S1 deletion is common in HBV/D, whereas pre-S2 start codon mutation and pre-S2 deletions are frequent among HBV/A and HBV/C, respectively. Interestingly, in HBV/A and HBV/C the tendency of mutation/deletion increases from pre-S1 to pre-S2 region while in HBV/D the opposite tendency was observed. A significantly higher association of pre-S mutation (p=0.013) and pre-S2 deletion/ablation (p=0.016) was found among the HBeAg negative cases. Pre-S1 deletion and pre-S2 deletion were common among the ASC and CLD cases respectively, while pre-S2 start codon mutation was significantly associated with cirrhosis (p<0.05). The study underscores the association of types of pre-S mutations with particular HBV genotype and clinical outcome in the study population.

Transient occult hepatitis B virus infection in a blood donor with high viremia

BACKGROUND

Screening of blood donors for viral nucleic acids has recently been introduced in several countries. With the use of transcription-mediated amplification, a blood donor was detected who had 90,000 copies of hepatitis B virus (HBV) DNA/mL but no hepatitis B surface antigen (HBsAg) or antibody to hepatitis B core antigen (anti-HBc). One month later, anti-HBc and hepatitis B surface antibody (anti-HBs) appeared; HBV DNA disappeared after 2 months. This study asked why HBsAg was undetectable in this rare case of transient occult HBV infection.

STUDY DESIGN AND METHODS

The HBV DNA in the first sample was cloned and sequenced to identify mutations. The physical nature of the virus was examined by polyethylene glycol precipitation, DNase digestion, density gradient centrifugation, and immunoprecipitation.

RESULTS

Several mutations were found all over the genome, but the HBs antigen loop was unchanged. A stop mutation in the precore region led to loss of hepatitis B e antigen (HBeAg) expression. No HBV DNA–containing immune complexes were present. The plasma did not contain nonencapsidated HBV DNA that could explain the absence of HBsAg. The virus was immune precipitated by antibodies against HBsAg or preS1 antigen. The ratio of HBV to HBsAg subviral particles was estimated to be 1 in less than 20 whereas in overt cases the ratio is 1 in more than 1000.

CONCLUSION

The acute resolving occult HBV infection was caused by an HBeAg-negative variant, which otherwise was almost normal. The negative HBsAg result was probably due to an unusually low production of surplus HBsAg. The absence of the viral immunomodulator HBeAg and the early appearance of anti-HBs suggested a rapid noncytolytic HBsAg-specific T-cell response leading to low expression of HBsAg.

PreS deletion mutations of hepatitis B virus in chronically infected patients with simultaneous seropositivity for hepatitis-B surface antigen and anti-HBS antibodies

Hepatitis B surface antigen (HBsAg) and anti-HBs antibodies (anti-HBs) may coexist in certain chronic hepatitis B (CHB) patients. This study was designed to further explore the relationship between this coexistence and hepatitis B Virus (HBV) preS deletions. Sera of 28 patients carrying both HBsAg and anti-HBs (Group I) and those of another 28 HBsAg positive but anti-HBs negative patients (Group II) were collected from CHB patients. Direct sequencing of polymerase chain reaction products or sequencing of clones was applied to both groups to determine sequences of HBV preS and S genes. Genotyping of the S gene indicated that all sampled HBVs were either Genosubtype Ba or Genosubtype Ce. Seven samples in Group I harbored HBV preS deletion mutations. Three of the seven samples showed large deletion mutations in 3' terminus of preS1 and co-existence of the mutant type and the full-length wild type, and the remaining four samples showed deletion mutations in 5' terminus of preS2. All mutant strains were found to be genosubtype Ce. Only two samples in Group I showed G145R/A mutation. Only one sample in Group II contained preS deletion mutation. It is therefore concluded that HBV preS deletion mutations are likely to be related to the coexistence of HBsAg and anti-HBs in CHB patients (P-value = 0.024). Some immune reactions may select for the preS deletion in CHB patients with anti-HBs, the possible marker for immune selection.

Antigenic and physicochemical characterization of the 2nd International Standard for hepatitis B virus surface antigen (HBsAg)

BACKGROUND

Standard preparations for HBsAg are required for quality control of test kits and clinical studies on HBsAg quantitation. WHO provides purified heat inactivated HBsAg diluted in negative defribinated plasma as 2nd International Standard (IS) for quality control of tests.

OBJECTIVE

Study of possible alterations of antigenicity, protein composition, size and density of the heat inactivated source material (SM) for the 2nd IS.

STUDY DESIGN

Native HBsAg and SM were examined by quantitative immune electrophoresis (QIE), SDS-PAGE, ultracentrifugation and gel chromatography. HBV DNA was sequenced and the HBsAg geno/subtype derived.

RESULTS

The SM contained 97,600 International Units HBsAg/ml in QIE which agreed very well with the previous evaluations by WHO using 10 different assays. In SDS-PAGE, SM showed on a strong background the small HBs proteins but no preS proteins. SM had a more heterogeneous density than native HBsAg and contained particle aggregates. The HBsAg geno/subtype of SM was A2/adw2.

CONCLUSIONS

The IS has very good HBs antigenicity, but it lacks the preS domains, has modified HBs proteins and is partially aggregated. While it has been proven very useful for quality control of tests, certain inconsistencies due to the altered structure of its HBsAg cannot be excluded.

Pre-S2 deletions of hepatitis B virus and hepatocellular carcinoma in children

The cause of early oncogenesis in hepatitis B virus (HBV)-related childhood hepatocellular carcinoma (HCC) remains unclear. This study investigated whether pre-S deletion of HBV is related to childhood HCC. By using nested polymerase chain reaction, we compared the pre-S sequence of HBV from sera of children with HCC against control children with similar chronic HBV infection. The HBV in sera of children with HCC had a significantly higher rate of pre-S deletion than that of children with chronic HBV infection (p = 0.008). All except one of the pre-S deletions from the HCC group involved the pre-S2 region, whereas no pre-S2 deletion was found in the chronic HBV group (p = 0.003). There was a trend whereby genotype-C sera had a higher rate of pre-S2 deletion than genotype-B sera (p = 0.11). A multivariate logistic regression model revealed that pre-S deletion was an independent risk factor for HCC in children (odds ratio: 36.69, p = 0.015). In conclusion, pre-S2 deletion does not need to take decades to occur; its presence in nearly half of children with HCC, in contrast to its absence in children with chronic HBV infection, suggests a link between pre-S2 deletion and HCC development in children.

Anti-preS responses influence the anti-HBs response in newborns after vaccination with the third generation Sci-B-Vac vaccine

We analysed the specificity and significance of the antibody response towards the linear preS1 sequence that has been shown to represent the "hepatocyte binding site" comprising amino acids preS1 (21-47) or the specific preS2 (131-140) antibody response to the "polymerised albumin receptor" in relation to the antibody response to hepatitis B surface antigen during immunisation of healthy children with the preS-containing Sci-B-Vac vaccine. Twenty-eight healthy newborns received three doses of the Sci-B-Vac vaccine according to a 0-, 1-, and 6-month scheme. Seventeen (61%) of the 28 newborns had detectable levels of anti-preS1 (21-47) antibodies and 14 (50%) were anti-preS2 (131-140) reactive at 6 and/or 9 months after initiation of the vaccination. The mean levels of anti-HBs were significantly higher in the anti-preS2 (131-140) non-reactive (24580+/-7815IU/l, mean+SEM) compared with the reactive sera (7287+/-2317IU/l, p<0.025). The highest anti-HBs levels were found in newborns who exhibited reactivity towards the aa 21-47 of the preS1 but lacked anti-preS2 (131-140) reactivity.

Genetic study of hepatitis B virus in Indonesia reveals a new subgenotype of genotype B in east Nusa Tenggara

The hepatitis B virus (HBV) genotype is associated with viral anthropological history, clinical outcome of disease and response to treatment. This study examines the HBV genotypes in Indonesia. HBV genotypes were determined by whole-genome sequencing and from the sequence of the Pre-S2 and S regions in a larger series. Two HBV genotypes, B (HBV/B) and C (HBV/C), were predominant. Three previously reported HBV/B subgenotypes were identified, with certain population association: HBV/B2 (HBV/Ba) was found mostly in Indonesians of Chinese ethnic origin, HBV/B3 was dominant among the Javanese, and HBV/B5, reported earlier from the Philippines, was also discovered, albeit at low frequency. Two other subgenotypes, HBV/B4 from Vietnam and HBV/B6, recently reported from the Arctic region, were not found. A novel subgenotype, HBV/B7, was recognized, associated with populations of the Nusa Tenggara islands in eastern Indonesia. Characteristic differences in HBsAg serotype and single nucleotide polymorphisms (SNPs) in the Pre-S2 region distinguish HBV/B7 from other HBV/B subgenotypes and further establish the new HBV subgenotype.

Pre-S deletion and complex mutations of hepatitis B virus related to advanced liver disease in HBeAg-negative patients

BACKGROUND & AIMS

This longitudinal study investigated the interactions and roles of hepatitis B virus (HBV) genotypes, pre-S deletions, and core promoter and precore mutations on the progression of liver disease in hepatitis B e antigen (HBeAg)-negative patients.

METHODS

A total of 141 HBeAg-negative patients without liver cirrhosis or hepatocellular carcinoma at study entry were recruited for this study, including 45 inactive HBV carriers and 96 patients with HBeAg-negative chronic hepatitis B. The HBV genotypes and the sequences of pre-S, core promoter, and precore regions were determined.

RESULTS

Compared with patients without developing liver cirrhosis, patients with the development of liver cirrhosis had higher rates of genotype C; pre-S deletions; C or G1753, T1762/A1764, T1766, and/or A1768 mutants; and G1799 variant. Cox regression analysis showed that older age, higher total bilirubin and HBV DNA levels, pre-S deletions, and T1766 and/or A1768 mutants were significantly associated with the development of liver cirrhosis. HBV with a complex mutation pattern (pre-S deletion, T1762/A1764, and T1766 and/or A1768 mutants) rather than a single mutation was associated with the development of liver cirrhosis, and the patterns of mutation combinations differed between HBV genotype B and C. Moreover, pre-S deletion was a significant risk factor for hepatocellular carcinoma.

CONCLUSIONS

This study indicated that pre-S deletion and combined mutations of HBV are useful molecular markers for predicting the clinical outcomes of HBeAg-negative patients.

Myristoylation signal transfer from the large to the middle or the small HBV envelope protein leads to a loss of HDV particles infectivity

A myristate linked to the N-terminus of the large hepatitis B virus (HBV) envelope protein was found to be required for infectivity of the hepatitis delta virus (HDV). Myristoylation of the large HBV envelope protein being known as indispensable for HBV infectivity, this result further demonstrates the similarities between the HBV and HDV entry pathways. In addition, the transfer of the N-myristoylation signal from the large to the middle or the small HBV envelope protein led in both cases to a loss of HDV infectivity. Hence, it is suggested that viral entry could depend on a physical link, or a spatial association, between the N-terminal receptor-binding polypeptide of the large protein and the myristoyl anchor linked to glycine-2.

Viral and cellular determinants involved in hepadnaviral entry

Hepadnaviridae is a family of hepatotropic DNA viruses that is divided into the genera orthohepadnavirus of mammals and avihepadnavirus of birds. All members of this family can cause acute and chronic hepatic infection, which in the case of human hepatitis B virus (HBV) constitutes a major global health problem. Although our knowledge about the molecular biology of these highly liver-specific viruses has profoundly increased in the last two decades, the mechanisms of attachment and productive entrance into the differentiated host hepatocytes are still enigmatic. The difficulties in studying hepadnaviral entry were primarily caused by the lack of easily accessible in vitro infection systems. Thus, for more than twenty years, differentiated primary hepatocytes from the respective species were the only in vitro models for both orthohepadnaviruses (e.g. HBV) and avihepadnaviruses (e.g. duck hepatitis B virus [DHBV]). Two important discoveries have been made recently regarding HBV: (1) primary hepatocytes from tree-shrews; i.e., Tupaia belangeri, can be substituted for primary human hepatocytes, and (2) a human hepatoma cell line (HepaRG) was established that gains susceptibility for HBV infection upon induction of differentiation in vitro. A number of potential HBV receptor candidates have been described in the past, but none of them have been confirmed to function as a receptor. For DHBV and probably all other avian hepadnaviruses, carboxypeptidase D (CPD) has been shown to be indispensable for infection, although the exact role of this molecule is still under debate. While still restricted to the use of primary duck hepatocytes (PDH), investigations performed with DHBV provided important general concepts on the first steps of hepadnaviral infection. However, with emerging data obtained from the new HBV infection systems, the hope that DHBV utilizes the same mechanism as HBV only partially held true. Nevertheless, both HBV and DHBV in vitro infection systems will help to: (1) functionally dissect the hepadnaviral entry pathways, (2) perform reverse genetics (e.g. test the fitness of escape mutants), (3) titrate and map neutralizing antibodies, (4) improve current vaccines to combat acute and chronic infections of hepatitis B, and (5) develop entry inhibitors for future clinical applications.

Solution conformation of an immunodominant epitope in the hepatitis B virus preS2 surface antigen

We have determined the solution conformation of the major B cell epitope (residues 123-145, adrl23 hereafter) in the preS2 region of hepatitis B virus known to be associated with infection neutralization. The adrl23 shows an "L" shaped helix-turn-helix topology with two beta-turns formed by residues Ala(130)-Asp(133) and Asp(133)-Val(136) intervening the N- and C-terminal helices. The N-terminal alpha-helix consists of residues Ser(124)-Gln(129) whereas the C-terminal 3(10) helix is formed by residues Val(136)-Tyr(140). The beta-turns overlap partially with the putative "conformational" epitope. The overall topology of adrl23 is primarily maintained by hydrophobic interactions involving Phe(127), Leu(131), Leu(132), Val(136), and Tyr(140) that are clustered on one side of the molecule. An additional hydrophobic stabilization comes from Phe(141) that is buried inside the concave side of the molecule. A network of hydrogen bonds formed among Thr(125), His(128), and Arg(137) further contribute to the "boomerang-shaped" architecture of adrl23. The N-terminus of adrl23 is immobile due to a hydrogen bond between the N-terminal amide proton of Asn(123) and the hydroxyl oxygen of Thr(126). The side chains of Asp(133), Arg(135), Val(136), Leu(139), and Tyr(140) that were shown to be important for binding to a monoclonal antibody H8 mAb are surface exposed.

High prevalence and mapping of pre-S deletion in hepatitis B virus carriers with progressive liver diseases

BACKGROUND & AIMS

The interactions among pre-S deletion, precore (PC) mutation, and basal core promoter (BCP) mutation in various stages of chronic hepatitis B virus (HBV) infection remain unclear and were thus investigated in this study.

METHODS

The sequences of the pre-S region and the BCP (A1762T, G1764A) and PC (G1896A) mutations were determined in 46 HBV chronic carriers (CC) and 106 age-matched carriers with different stages of liver diseases, including 38 chronic hepatitis (CH), 18 cirrhosis (LC), and 50 hepatocellular carcinoma (HCC).

RESULTS

A higher prevalence of pre-S deletion and BCP and PC mutations was found in carriers with progressive liver diseases compared with the CC group. By logistic regression analysis, patients with pre-S deletion and BCP mutation were significantly associated with the development of progressive liver diseases than those without. Combination of mutations rather than single mutation was associated with the development of progressive liver diseases, especially in combination with pre-S deletion. Sequencing analysis showed that the deleted regions were more often in the 3' terminus of pre-S1 and the 5' terminus of pre-S2. Further mapping of these pre-S deletion sequences found that all the deletion regions encompassed T- and B-cell epitopes, and most of them lost 1 or more functional sites.

CONCLUSIONS

Our data indicate that patients with progressive liver diseases have a higher frequency of pre-S deletion.

Evolution of Hepatitis B virus in an acute hepatitis B patient co-infected with genotypes B and C

The interactions between different genotypes of Hepatitis B virus (HBV) in co-infected patients remain largely unknown, especially in acute infection. Here, the evolution of HBV strains was studied in an acute, self-limited hepatitis B patient co-infected with genotypes Ba (B2) and C. Virological analyses were performed at four time points after admission: T1 (5 days), T2 (11 days), T3 (22 days) and T4 (260 days). A dominant-genotype change from genotype C to Ba was found after anti-HBV e antigen (anti-HBe) seroconversion. Further clonal and phylogenetic analyses of the pre-S and pre-core/core regions of HBV were carried out to clarify the interactions between genotypes Ba and C. All clones propagated from T1 and T2 were of genotype C. In contrast, clones propagated from T3 (after anti-HBe seroconversion) were of genotype Ba, C and/or recombinant within the pre-S region. At T4, all clones were of genotype Ba with a 123 bp (from nt 3147 of the pre-S1 region to nt 54 of the pre-S2 region) in-frame pre-S deletion and had lost the start codon of the middle envelope protein and the nucleocapsid-binding site. Phylogenetic analysis showed that genetic distance was greater at T3 after seroconversion to anti-HBe. By using SimPlot, the breakpoint of one pre-S recombinant was located at nt 3069-3100 and the other two at nt 49-87. In conclusion, HBV genotype Ba may overtake genotype C as the predominant strain after anti-HBe seroconversion in acute hepatitis B. Recombination within the pre-S region emerged transiently and the pre-S deletion mutant was finally cleared.

The design and implementation of the immune epitope database and analysis resource

Epitopes are defined as parts of antigens interacting with receptors of the immune system. Knowledge about their intrinsic structure and how they affect the immune response is required to continue development of techniques that detect, monitor, and fight diseases. Their scientific importance is reflected in the vast amount of epitope-related information gathered, ranging from interactions between epitopes and major histocompatibility complex molecules determined by X-ray crystallography to clinical studies analyzing correlates of protection for epitope based vaccines. Our goal is to provide a central resource capable of capturing this information, allowing users to access and connect realms of knowledge that are currently separated and difficult to access. Here, we portray a new initiative, "The Immune Epitope Database and Analysis Resource." We describe how we plan to capture, structure, and store this information, what query interfaces we will make available to the public, and what additional predictive and analytical tools we will provide.

Structure of pre-S2 N- and O-linked glycans in surface proteins from different genotypes of hepatitis B virus

The middle-sized (M) surface proteins of hepatitis B virus (HBV) and other orthohepadnaviruses contain a conserved N-glycan in their pre-S2 domain, which is essential for the secretion of viral particles. Recently, we also found O-glycans in the pre-S2 domain of M protein from woodchuck hepatitis virus (WHV) and HBV genotype D. Since the O-glycosylation motif is not conserved in all genotypes of HBV, the glycosylation patterns of HBV genotypes A and C were analysed. Pre-S2 (glyco)peptides were released from HBV-carrier-derived HBV subviral particles by tryptic digestion, purified by reversed-phase HPLC and identified by amino acid and amino-terminal sequence analysis as well as matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Pre-S2 N-glycans were characterized by anion-exchange chromatography, methylation analysis and on-target sequential exoglycosidase digestions in combination with MALDI-TOF-MS, demonstrating the presence of partially sialylated diantennary complex-type oligosaccharides in all genotypes examined. Pre-S2 O-glycans were characterized by on-target sequential exoglycosidase digestions in combination with MALDI-TOF-MS. The pre-S2 domain of M protein and, to a minor extent, of L (large) protein from HBV genotype C and D was partially O-glycosylated by Neu5Ac(alpha2-3)Gal(beta1-3)GalNAcalpha- or Gal(beta1-3)GalNAcalpha-units at Thr-37 within a conserved sequence context. Genotype A, containing no Thr at position 37 or 38, was not O-glycosylated. Analytical data further revealed that M protein is mostly amino-terminally acetylated in all examined genotypes and that the terminal methionine is partially oxidized. The findings may be relevant for the secretion and the immunogenicity of HBV.

Structure of pre-S2 N- and O-linked glycans in surface proteins from different genotypes of hepatitis B virus

The middle-sized (M) surface proteins of hepatitis B virus (HBV) and other orthohepadnaviruses contain a conserved N-glycan in their pre-S2 domain, which is essential for the secretion of viral particles. Recently, we also found O-glycans in the pre-S2 domain of M protein from woodchuck hepatitis virus (WHV) and HBV genotype D. Since the O-glycosylation motif is not conserved in all genotypes of HBV, the glycosylation patterns of HBV genotypes A and C were analysed. Pre-S2 (glyco)peptides were released from HBV-carrier-derived HBV subviral particles by tryptic digestion, purified by reversed-phase HPLC and identified by amino acid and amino-terminal sequence analysis as well as matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Pre-S2 N-glycans were characterized by anion-exchange chromatography, methylation analysis and on-target sequential exoglycosidase digestions in combination with MALDI-TOF-MS, demonstrating the presence of partially sialylated diantennary complex-type oligosaccharides in all genotypes examined. Pre-S2 O-glycans were characterized by on-target sequential exoglycosidase digestions in combination with MALDI-TOF-MS. The pre-S2 domain of M protein and, to a minor extent, of L (large) protein from HBV genotype C and D was partially O-glycosylated by Neu5Ac(α2–3)Gal(β1–3)GalNAcα- or Gal(β1–3)GalNAcα-units at Thr-37 within a conserved sequence context. Genotype A, containing no Thr at position 37 or 38, was not O-glycosylated. Analytical data further revealed that M protein is mostly amino-terminally acetylated in all examined genotypes and that the terminal methionine is partially oxidized. The findings may be relevant for the secretion and the immunogenicity of HBV.

Pre-s1 antigen-dependent infection of Tupaia hepatocyte cultures with human hepatitis B virus

The susceptibility of the tree shrew Tupaia belangeri to human hepatitis B virus (HBV) has been demonstrated both in vivo and in vitro. In this study, we show that purified HBV infects primary T. belangeri hepatocyte cultures in a very specific manner, as detected by HBV covalently closed circular DNA, mRNA, HBV e antigen, and HBsAg production. A monoclonal antibody (MAb), MA18/7, directed against the pre-S1 domain of the large HBs protein, which has been shown to neutralize infectivity of HBV for primary human hepatocytes, also blocked infection of primary Tupaia hepatocytes. MAbs against the pre-S2 domain of HBs inhibited infection only partially, whereas an S MAb and polyvalent anti-HBs antibodies neutralized infection completely. Thus, both pre-S1 and S antigens are necessary for infection in the tupaia. Using subviral particles, >70% of primary Tupaia hepatocytes are capable of specific binding of pre-S1-rich HBsAg, showing localization in distinct membrane areas. The data show that the early steps of HBV infection in Tupaia hepatocyte cultures are comparable to those in the human system.

Screening and identification of a novel gene coding for hepatitis B virus pre-S2 antigen interacting protein S2-29

AIM

The Pre-S2 region of hepatitis B virus (HBV) has been reported to have complex biological functions. It has human polymerized albumin receptor (PAR) activity, which correlates with viral replication, and it can induce neutralization antibody. As an important part of truncated middle surface proteins (MHBs), the Pre-S2 domain binds PKC alpha/beta and triggers a PKC-dependent activation of the c-Raf-1/MAP2-kinase signal transduction cascade, resulting in activation of transcription factors such as AP-1 and NF-kB. To investigate the biological function of hepatitis B virus (HBV) Pre-S2 protein, we used yeast two-hybrid technique to screen proteins interacting with HBV Pre-S2 antigen in hepatocytes.

METHODS

The HBV Pre-S2 gene was amplified by polymerase chain reaction (PCR) and cloned into yeast expression vector PGBKT7 to construct HBV Pre-S2 bait plasmid. The bait plasmid was transformed into yeast AH109 and mated with yeast Y187 containing liver cDNA library plasmid in 2×YPDA medium. Diploid yeast was plated on synthetic dropout nutrient medium (SD/-Trp-Leu-His-Ade) and synthetic dropout nutrient medium (SD/-Trp-Leu-His-Ade) containing X-α-gal for selection and screening. After being extracted and sequenced, genes were analyzed by bioinformatics. The complete sequence of new gene S2-29 was amplified from the mRNA of HepG2 cell by reverse transcription polymerase chain reaction (RT-PCR) and cloned into pGADT7, then translated by using reticulocyte lysate and analysed by immunoprecipitation technique in vitro.

RESULTS

Twenty-six colonies were obtained, among them two colonies were new genes with unknown function and no homeobox genes were found in Genbank by blast. The complete sequence of new gene S2-29 could be amplified from the mRNA of HepG2 cell and the interaction between HBV Pre-S2 antigen and S2-29 was further confirmed by coimmunoprecipitation technique.

CONCLUSION

Genes of HBV Pre-S2 interacting proteins were successfully screened. A novel gene S2-29 was cloned and could express in HepG2 cell. The HBV Pre-S2 antigen could interact with S2-29, which brings new clues for studying the biological functions of HBV Pre-S2 and the pathogenesis of HBV infection.

Targeted destruction of the polymerized human serum albumin binding site within the preS2 region of the HBV surface antigen while retaining full immunogenicity for this epitope

The 55-amino acid (a.a.) preS2 region of the hepatitis B virus (HBV) envelope protein is highly immunogenic, and antibodies against this epitope confer seroprotection against HBV infections. Accordingly, various experimental and clinical studies for developing and evaluating HBV vaccines that include this particular epitope have been reported. However, a pitfall in using preS2 epitopes as part of a vaccinating antigen is that polymerized human serum albumin (pHSA), which is a normal constituent of the human serum, binds to and makes complexes with this particular region. Consequently, it is most likely that the antigen epitope is masked by serum pHSA and subsequently not detected by the immune system. To overcome these limitations, a novel single a.a substitute of the preS2 region was designed that corresponds to a tyrosine to serine exchange at position 140 of preS2. Competitive enzyme-linked immunosorbent assay showed that this substitution completely abolishes pHSA-binding activities in the mutated preS2 peptide, and CD spectra analysis revealed that this property might have been induced by slight conformational changes in its secondary structure. Nevertheless, the original B-cell epitope was still preserved in the mutated preS2 as determined by experimental immunization in mice. In this regard, the preS2(120-145/Y140S) sequence may be an HBV vaccine where epitopes, with intrinsic properties have been deleted without affecting the immunogenicity of the epitope itself. It is expected that the inclusion of this point mutated preS2 epitope will improve the efficacy of conventional preS2-containing HBV vaccines.

Fine-mapping of the B-cell epitope domain at the N-terminus of the preS2 region of the hepatitis B surface antigen

In this study, we report the exact localization and substitutional characterization of a B-cell epitope domain at the N-terminus of the preS2 region of the hepatitis B surface antigen. A set of deletion variants containing preS2 sequences of different length was generated on the basis of frCP as a carrier. It was found after Western blot analysis that three monoclonal antibodies (MAbs) (2-11B1, 3-11C2, HB.OT10) recognized the linear preS2 sequence within the amino acid (aa) stretch 3-WNSTTFHQTLQDP-13. The importance of each aa residue of the epitope was proved by comparison of antibody binding to alanine-substituted peptides in both free-peptide and Pepscan variants.

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.

Antibody responses to preS components after immunization of children with low doses of BioHepB

BioHepB is a recombinant, hepatitis B vaccine derived from a mammalian cell line and containing HBs as well as preS1 and preS2 antigens, in their glycosylated and non-glycosylated forms. The vaccine was administered intramuscularly to 18 children aged 5 months to 11 years at 0, 1 and 6 months. One hundred percent seroconversion and seroprotection rates were achieved after primary and secondary immunization with the 2.5 microg doses of BioHepB. Ten out of the 18 children (56%) responded with the appearance of anti-preS1 and/or anti-preS2 antibodies in circulation, when analyzed 1, 2, 6, 7 and 12 months after the initiation of vaccination. In comparison with the emergence of the anti-HBs response, early (month 2, after two injections) or late (month 7, after three injections) peak responses were noted for the kinetics of anti-preS1 and anti-preS2 production during the course of immunization, demonstrating that the anti-preS1 and anti-preS2 responses are differently regulated, compared with the anti-HBs response. At month 6, just prior to the final injection, BioHepB caused significantly higher anti-HBs responses (GMT) in preS1-reactive children than in children without preS1 antibodies (P<0.005). Moreover, a significantly higher, anti-HBs response in GMT was also noted for anti-preS2-reactive children compared with anti-preS2-negative children (P<0.05). These findings demonstrated that recognition of the preS epitopes contained in the experimental preS1/preS2/S vaccine is accompanied by a more rapid onset and pronounced antibody response to the S-gene-derived protein in healthy children.