N-terminal myristoylation-dependent masking of neutralizing epitopes in the preS1 attachment site of hepatitis B virus

The hepatitis B virus surface antigen: An evolved perfection and its unresolved mysteries

The Hepatitis B Virus has long afflicted the human race, with a widespread impact on the global health system and profound medical implications for those who are chronically infected. Despite its relatively recent discovery, over the last 50 years great advancements have been made towards the characterisation of this complex etiological agent. The virus itself has a highly evolved genome which encodes for seven viral proteins, three of which (the surface antigens) were consequential in the initial discovery and isolation of the virus. These surface antigens are ubiquitously important throughout the viral lifecycle, from capsid envelopment through to receptor-mediated invasion into the hepatocytes. The hepatitis B surface antigens (in particular, the large protein) adopt complex topological folds and tertiary structures, and it is this topological intricacy which facilitates the diverse roles the three surface antigens play in HBV maturation and infection. Here, the biochemical and topological attributes of the three surface antigens are reviewed in detail, with particular focus on their relevance to the establishment of infection. Further research is still required to elucidate the coordinates of the antigen loop and the dynamic topological changes of key motifs during entry and viral morphogenesis; these in turn may provide new leads for therapeutics which may potentiate a functional cure for chronic hepatitis B.

The PreS-Based Recombinant Vaccine VVX001 Induces Hepatitis B Virus Neutralizing Antibodies in a Low-Responder to HBsAg-Based HBV Vaccines

Background: Approximately 10-20% of subjects vaccinated with HBsAg-based hepatitis B virus (HBV) vaccines are non-responders. BM32 is a recombinant grass pollen allergy vaccine containing the HBV-derived preS surface antigen as an immunological carrier protein. PreS includes the binding site of HBV to its receptor on hepatocytes. We investigated whether immunological non-responsiveness to HBV after repeated HBsAg-based vaccinations could be overcome by immunization with VVX001 (i.e., alum-adsorbed BM325, a component of BM32). Methods: A subject failing to develop protective HBV-specific immunity after HBsAg-based vaccination received five monthly injections of 20 µg VVX001. PreS-specific antibody responses were measured by enzyme-linked immunosorbent assay (ELISA) and micro-array technology. Serum reactivity to subviral particles of different HBV genotypes was determined by sandwich ELISA. PreS-specific T cell responses were monitored by carboxyfluorescein diacetate succinimidyl ester (CFSE) staining and subsequent flow cytometry. HBV neutralization was assessed using cultured HBV-infected HepG2 cells. Results: Vaccination with VVX001 induced a strong and sustained preS-specific antibody response composed mainly of the IgG1 subclass. PreS-specific IgG antibodies were primarily directed to the N-terminal part of preS containing the sodium taurocholate co-transporting polypeptide (NTCP) attachment site. IgG reactivity to subviral particles as well as to the N-terminal preS-derived peptides was comparable for HBV genotypes A-H. A pronounced reactivity of CD3+CD4+ lymphocytes specific for preS after the complete injection course remaining up to one year after the last injection was found. Maximal HBV neutralization (98.4%) in vitro was achieved 1 month after the last injection, which correlated with the maximal IgG reactivity to the N-terminal part of preS. Conclusions: Our data suggest that VVX001 may be used as a preventive vaccination against HBV even in non-responders to HBsAg-based HBV vaccines.

A retrospective study to determine the correlation among HBV PreS1 antigen, HBV e antigen, alanine aminotransferase, and HBV DNA

BACKGROUND AND AIM

Hepatitis B virus (HBV) infection presents with indicators of varying clinical significance. We aimed to evaluate the correlation among HBV Pre-S1 antigen (HBV PreS1-Ag), HBV e antigen (HBeAg), HBV DNA, and alanine aminotransferase (ALT) levels.

METHODS

We retrospectively analyzed 6180 serum samples collected between 2020 and 2022 at the Shanghai General Hospital, China. Data regarding PreS1-Ag, HBeAg, ALT, and HBV DNA were compiled. Correlation analyses and cross-tabulations were employed to explore the diagnostic indicators.

RESULTS

The detection rates of both antigen indicators showed a proportional increase with HBV DNA loads. The correlation between PreS1-Ag and HBV DNA (r = 0.616) was stronger than that between HBeAg and HBV DNA (r = 0.391). The specificity of PreS1-Ag (84.30 %) was lower than that of HBeAg (97.44 %), whereas the sensitivity of HBeAg (91.13 %) significantly surpassed that of PreS1-Ag (29.56 %). Among the HBV DNA positive patients, 92.04 % tested positive for at least one indicator, which exceeded the rate of PreS1+HBeAg- and PreS1-HBeAg+ (52. 28 % and 68. 56 %, respectively). Only 1.75 % of the patients exhibited double negativity, which was lower than the percentage of patients with single negativity (1.95 % and 12.00 % for PreS1-Ag and HBeAg, respectively). The PreS1 levels correlated with ALT levels (r = 0.317); patients with PreS1-positive status had higher ALT levels than patients with PreS1-negative status.

CONCLUSION

PreS1-Ag is a more robust HBV replication indicator than HBeAg. PreS1-Ag displayed high sensitivity, whereas HBeAg demonstrated high specificity. Moreover, PreS1-Ag levels correlated with ALT levels. A combination of these indicators demonstrated dependable clinical value for detecting HBV infection and evaluating liver function.

PreS1 Containing HBc VLPs for the Development of a Combined Therapeutic/Prophylactic Hepatitis B Vaccine

The available HBV vaccines based on the HBV surface protein are manufactured in yeasts and demonstrate excellent prophylactic but no therapeutic activity and are thus ineffective against chronic HBV infection. Five different HBV core proteins (HBc)-full length and C-terminally truncated-were used for the insertion of the short, preS1,aa 20-47 and long, preS1phil, aa 12-60 + 89-119 fragments. Modified virus-like particles (VLPs) were compared for their biotechnological and immunological properties. The expression level of HBc-preS1 proteins was high for all investigated proteins, allowing us to obtain 10-20 mg of purified VLPs from a gram of biomass with the combination of gel filtration and ion-exchange chromatography to reach approximately 90% purity of target proteins. The immunogenicity of chimeric VLPs was tested in BALB/c mice, showing a high anti-preS1 response and substantial T-cell proliferation after stimulation with HBc protein. Targeted incorporation of oligonucleotide ODN 1668 in modified HBc-preS1 VLPs was demonstrated.

Analysis of differential metabolites and metabolic pathways in adipose tissue of tree shrews (Tupaia belangeri) under gradient cooling acclimation

In order to investigate the influence of gradient cooling acclimation on body mass regulation in tree shrews (Tupaia belangeri), white adipose tissue (WAT) and brown adipose tissue (BAT) in T. belangeri between the control group and gradient cooling acclimation group on day 56 were collected, body mass, food intake, thermogenic capacity, differential metabolites, and related metabolic pathways in WAT and BAT were measured, the changes of differential metabolites were analyzed by non-targeted metabolomics method based on liquid chromatography-mass spectrometry. The results shown that gradient cooling acclimation significantly increased body mass, food intake, resting metabolic rate (RMR), non-shivering thermogenesis (NST), and masses of WAT and BAT. 23 significant differential metabolites in WAT between the gradient cooling acclimation group and the control group, of which the relative contents of 13 differential metabolites were up-regulated and 10 differential metabolites were down-regulated. 27 significant differential metabolites in BAT, of which 18 differential metabolites decreased and 9 differential metabolites increased. 15 differential metabolic pathways in WAT, 8 differential metabolic pathways in BAT, and 4 differential metabolic pathways involved in both WAT and BAT, including Purine metabolism, Pyrimidine metabolism, Glycerol phosphate metabolism, Arginine and proline metabolism, respectively. All of the above results suggested that T. belangeri could use different metabolites of adipose tissue to withstand low temperature environments and enhance their survival.

ATP5B Is an Essential Factor for Hepatitis B Virus Entry

Elucidation of the factors responsible for hepatitis B virus (HBV) is extremely important in order to understand the viral life cycle and pathogenesis, and thereby explore potential anti-HBV drugs. The recent determination that sodium taurocholate co-transporting peptide (NTCP) is an essential molecule for the HBV entry into cells led to the development of an HBV infection system in vitro using a human hepatocellular carcinoma (HCC) cell line expressing NTCP; however, the precise mechanism of HBV entry is still largely unknown, and thus it may be necessary to elucidate all the molecules involved. Here, we identified ATP5B as another essential factor for HBV entry. ATP5B was expressed on the cell surface of the HCC cell lines and bound with myristoylated but not with non-myristoylated preS1 2-47, which supported the notion that ATP5B is involved in the HBV entry process. Knockdown of ATP5B in NTCP-expressing HepG2 cells, which allowed HBV infection, reduced HBV infectivity with less cccDNA formation. Taken together, these results strongly suggested that ATP5B is an essential factor for HBV entry into the cells.

Vaccine based on folded receptor binding domain-PreS fusion protein with potential to induce sterilizing immunity to SARS-CoV-2 variants

BACKGROUND

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for the ongoing global COVID-19 pandemic. One possibility to control the pandemic is to induce sterilizing immunity through the induction and maintenance of neutralizing antibodies preventing SARS-CoV-2 from entering human cells to replicate in.

METHODS

We report the construction and in vitro and in vivo characterization of a SARS-CoV-2 subunit vaccine (PreS-RBD) based on a structurally folded recombinant fusion protein consisting of two SARS-CoV-2 Spike protein receptor-binding domains (RBD) fused to the N- and C-terminus of hepatitis B virus (HBV) surface antigen PreS to enable the two unrelated proteins serving as immunologic carriers for each other.

RESULTS

PreS-RBD, but not RBD alone, induced a robust and uniform RBD-specific IgG response in rabbits. Currently available genetic SARS-CoV-2 vaccines induce mainly transient IgG1 responses in vaccinated subjects whereas the PreS-RBD vaccine induced RBD-specific IgG antibodies consisting of an early IgG1 and sustained IgG4 antibody response in a SARS-CoV-2 naive subject. PreS-RBD-specific IgG antibodies were detected in serum and mucosal secretions, reacted with SARS-CoV-2 variants, including the omicron variant of concern and the HBV receptor-binding sites on PreS of currently known HBV genotypes. PreS-RBD-specific antibodies of the immunized subject more potently inhibited the interaction of RBD with its human receptor ACE2 and their virus-neutralizing titers (VNTs) were higher than median VNTs in a random sample of healthy subjects fully immunized with registered SARS-CoV-2 vaccines or in COVID-19 convalescent subjects.

CONCLUSION

The PreS-RBD vaccine has the potential to serve as a combination vaccine for inducing sterilizing immunity against SARS-CoV-2 and HBV by stopping viral replication through the inhibition of cellular virus entry.

[Hepatitis B vaccines-history, achievements, challenges, and perspectives]

Die ersten Impfversuche gegen das Hepatitis-B-Virus (HBV) erfolgten 1970, noch bevor die Natur des dafür verwendeten „Australia-Antigens“ bekannt war. Bald darauf wurde dieses Antigen als Hüllprotein des HBV erkannt (HBV Surface Antigen, HBsAg), dann aus HBV-haltigem Plasma gereinigt und später gentechnisch in Hefezellen hergestellt. Die hohe Wirksamkeit des HBsAg-Impfstoffs wurde vielfach bewiesen, insbesondere bei Neugeborenen von HBV-infizierten Müttern, die sonst fast immer chronische HBV-Träger werden. Auch bei älteren Kindern und Erwachsenen schützt die Impfung und wird seit 1984 weltweit angewendet, was zu einer ungefähr 10-fachen Abnahme der HBV-Infektionen bei den Geimpften geführt hat.

Es gibt dennoch verschiedene Herausforderungen bei der Hepatitis-B-Impfung. Bei Neugeborenen von hochvirämischen Müttern kann die Impfung versagen. Bei verringerter Immunkompetenz kann die Bildung schützender Antikörper ausbleiben, aber auch bei Risikofaktoren wie höherem Alter, Rauchen oder Übergewicht. Frühe Impfstudien belegten, dass Impfstoffe mit dem HBsAg-Subtyp adw2 auch gegen HBV mit anderen HBsAg-Subtypen schützen, neuere Beobachtungen zeigen aber, dass die Schutzwirkung gegen heterologe Subtypen schwächer ist. Gelegentlich werden auch Escape-Mutationen beobachtet.

Die meisten jetzigen Impfstoffe beruhen auf dem Kenntnisstand vor 40 Jahren und könnten wesentlich verbessert werden. Eine Einbeziehung der bislang fehlenden PräS-Domänen der HBV-Hülle in die Impfstoffe würde die wichtigsten schützenden T‑ und B‑Zellepitope einbringen. Die Expression in Säugerzellkulturen verbessert die native Faltung der neutralisierenden HBsAg-Epitope und die Verwendung von regional vorherrschenden HBsAg-Subtypen würde die Schutzwirkung erhöhen. Optimale Adjuvanzien oder Epitopträger könnten die Immunogenität auch für eine HBV-Immuntherapie steigern.

A fusion peptide in preS1 and the human protein disulfide isomerase ERp57 are involved in hepatitis B virus membrane fusion process

Cell entry of enveloped viruses relies on the fusion between the viral and plasma or endosomal membranes, through a mechanism that is triggered by a cellular signal. Here we used a combination of computational and experimental approaches to unravel the main determinants of hepatitis B virus (HBV) membrane fusion process. We discovered that ERp57 is a host factor critically involved in triggering HBV fusion and infection. Then, through modeling approaches, we uncovered a putative allosteric cross-strand disulfide (CSD) bond in the HBV S glycoprotein and we demonstrate that its stabilization could prevent membrane fusion. Finally, we identified and characterized a potential fusion peptide in the preS1 domain of the HBV L glycoprotein. These results underscore a membrane fusion mechanism that could be triggered by ERp57, allowing a thiol/disulfide exchange reaction to occur and regulate isomerization of a critical CSD, which ultimately leads to the exposition of the fusion peptide.

Efficacy of Birth Dose Vaccination in Preventing Mother-to-Child Transmission of Hepatitis B: A Randomized Controlled Trial Comparing Engerix-B and Sci-B-Vac

Background and aims: Peripartum transmission of hepatitis B virus (HBV) from an infected mother to the child can be prevented in most but not all cases by immediate vaccination of the newborn. The aim of this study was to compare the efficacy of two licensed hepatitis B vaccines, Engerix-B versus Sci-B-Vac, in preventing peripartum HBV transmission. Methods: A prospective multicenter randomized controlled study in 4 delivery centers was performed from 2009 to 2014. HBsAg positive pregnant women and their newborns were recruited at the delivery rooms. All newborns received Hepatitis B Immune Globulin within 10 h after birth, as well as active HBV vaccination at 0, 1 and 6 months of age. Maternal assessment at delivery included transaminases, blood count, international normalized ratio and viral status. Infants were tested for HBsAg, anti-HBc and anti-HBs at 12 months of age. Results: In the intention to treat (ITT), 171 infant and mother pairs fulfilled the study enrollment criteria and completed follow up, 82 received Engerix-B and 89 Sci-B-Vac. Maternal parameters and viral status were similar in both groups. At 12 months of age, the Sci-B-Vac group had lower HBsAg carriage rates (1/89, 1.1%) than the Engerix-B group (5/82, 6.1%) with borderline significance (risk difference of -0.05, 95% CI -0.11-0.007, t-test = 0.05), and borderline significance lower vaccine failure rates with anti-HBs < 10 mIU/mL in the Sci-B-Vac (2/89, 2.2%) than in the Engerix-B (8/82, 9.8%, p = 0.05). Higher seroprotection rates were found in the Sci-B-Vac group with all anti-HBs titer stratifications of >10 mIU/mL (p = 0.05), >100 mIU/mL (p = 0.05) and >1000 mIU/mL (p = 0.01). Active/passive vaccination was effective in 10/13 cases with maternal HBV DNA levels > 7 log10 IU/mL up to 9.5 log10 IU/mL, but failed in 3 cases for unknown reasons. Conclusion: Sci-B-Vac was superior to Engerix-B in preventing peripartum HBV transmission in neonates from HBsAg+ mothers and induces significantly higher anti-HBs levels. NIH registration number: NCT01133184.

HBV evolution and genetic variability: Impact on prevention, treatment and development of antivirals

Hepatitis B virus (HBV) poses a major global health burden with 260 million people being chronically infected and 890,000 dying annually from complications in the course of the infection. HBV is a small enveloped virus with a reverse-transcribed DNA genome that infects hepatocytes and can cause acute and chronic infections of the liver. HBV is endemic in humans and apes representing the prototype member of the viral family Hepadnaviridae and can be divided into 10 genotypes. Hepadnaviruses have been found in all vertebrate classes and constitute an ancient viral family that descended from non-enveloped progenitors more than 360 million years ago. The de novo emergence of the envelope protein gene was accompanied with the liver-tropism and resulted in a tight virus-host association. The oldest HBV genomes so far have been isolated from human remains of the Bronze Age and the Neolithic (~7000 years before present). Despite the remarkable stability of the hepadnaviral genome over geological eras, HBV is able to rapidly evolve within an infected individual under pressure of the immune response or during antiviral treatment. Treatment with currently available antivirals blocking intracellular replication of HBV allows controlling of high viremia and improving liver health during long-term therapy of patients with chronic hepatitis B (CHB), but they are not sufficient to cure the disease. New therapy options that cover all HBV genotypes and emerging viral variants will have to be developed soon. In addition to the antiviral treatment of chronically infected patients, continued efforts to expand the global coverage of the currently available HBV vaccine will be one of the key factors for controlling the rising global spread of HBV. Certain improvements of the vaccine (e.g. inclusion of PreS domains) could counteract known problems such as low or no responsiveness of certain risk groups and waning anti-HBs titers leading to occult infections, especially with HBV genotypes E or F. But even with an optimal vaccine and a cure for hepatitis B, global eradication of HBV would be difficult to achieve because of an existing viral reservoir in primates and bats carrying closely related hepadnaviruses with zoonotic potential.

Computational Design of a Novel VLP-Based Vaccine for Hepatitis B Virus

Hepatitis B virus (HBV) is a global virus responsible for a universal disease burden for millions of people. Various vaccination strategies have been developed using viral vector, nucleic acid, protein, peptide, and virus-like particles (VLPs) to stimulate favorable immune responses against HBV. Given the pivotal role of specific immune responses of hepatitis B surface antigen (HBsAg) and hepatitis B core antigen (HBcAg) in infection control, we designed a VLP-based vaccine by placing the antibody-binding fragments of HBsAg in the major immunodominant region (MIR) epitope of HBcAg to stimulate multilateral immunity. A computational approach was employed to predict and evaluate the conservation, antigenicity, allergenicity, and immunogenicity of the construct. Modeling and molecular dynamics (MD) demonstrated the folding stability of HBcAg as a carrier in inserting Myrcludex and "a" determinant of HBsAg. Regions 1-50 and 118-150 of HBsAg were considered to have the highest stability to be involved in the designed vaccine. Molecular docking revealed appropriate interactions between the B cell epitope of the designed vaccine and the antibodies. Totally, the final construct was promising for inducing humoral and cellular responses against HBV.

Designing a therapeutic hepatitis B vaccine to circumvent immune tolerance

An effective prophylactic hepatitis B virus (HBV) vaccine has long been available but is ineffective for chronic infection. The primary cause of chronic hepatitis B (CHB) and greatest impediment for a therapeutic vaccine is the direct and indirect effects of immune tolerance to HBV antigens. The resulting defective CD4⁺/CD8⁺ T cell response, poor cytokine production, insufficient neutralizing antibody (nAb) and poor response to HBsAg vaccination characterize CHB infection. The objective of this study was to develop virus-like-particles (VLPs) that elicit nAb to prevent viral spread and prime CD4⁺/CD8⁺ T cells to eradicate intracellular HBV. Eight neutralizing B cell epitopes from the envelope PreS1 region were consolidated onto a species-variant of the HBV core protein, the woodchuck hepatitis core antigen (WHcAg). PreS1-specific B cell epitopes were chosen because of preferential expression on HBV virions. Because WHcAg and HBcAg are not crossreactive at the B cell level and only partially cross-reactive at the CD4⁺/CD8⁺ T cell level, CD4⁺ T cells specific for WHcAg-unique T cell sites can provide cognate T-B cell help for anti-PreS1 Ab production that is not curtailed by immune tolerance. Immunization of immune tolerant HBV transgenic (Tg) mice with PreS1-WHc VLPs elicited levels of high titer anti-PreS1 nAbs equivalent to wildtype mice. Passive transfer of PreS1 nAbs into human-liver chimeric mice prevented acute infection and cleared serum HBV from mice previously infected with HBV in a model of CHB. At the T cell level, PreS1-WHc VLPs and hybrid WHcAg/HBcAg DNA immunogens elicited HBcAg-specific CD4⁺ Th and CD8⁺ CTL responses.

Recapitulation of HDV infection in a fully permissive hepatoma cell line allows efficient drug evaluation

Hepatitis delta virus (HDV) depends on the helper function of hepatitis B virus (HBV), which provides the envelope proteins for progeny virus secretion. Current infection-competent cell culture models do not support assembly and secretion of HDV. By stably transducing HepG2 cells with genes encoding the NTCP-receptor and the HBV envelope proteins we produce a cell line (HepNB2.7) that allows continuous secretion of infectious progeny HDV following primary infection. Evaluation of antiviral drugs shows that the entry inhibitor Myrcludex B (IC₅₀: 1.4 nM) and interferon-α (IC₅₀: 28 IU/ml, but max. 60–80% inhibition) interfere with primary infection. Lonafarnib inhibits virus secretion (IC₅₀: 36 nM) but leads to a substantial intracellular accumulation of large hepatitis delta antigen and replicative intermediates, accompanied by the induction of innate immune responses. This work provides a cell line that supports the complete HDV replication cycle and presents a convenient tool for antiviral drug evaluation.

Hepatitis delta virus (HDV) depends on the envelope proteins of hepatitis B virus (HBV) for virion production. Here, Lempp et al. produce a cell line expressing HBV envelope proteins and their receptor, which allows continuous secretion of infectious progeny HDV and testing of antiviral drugs.

Oral administration of a chimeric Hepatitis B Virus S/preS1 antigen produced in lettuce triggers infection neutralizing antibodies in mice

Hepatitis B Virus (HBV) infection can be prevented by vaccination. Vaccines containing the small (S) envelope protein are currently used in universal vaccination programs and achieve protective immune response in more than 90% of recipients. However, new vaccination strategies are necessary for successful immunization of the remaining non- or low-responders. We have previously characterized a novel HBV chimeric antigen, which combines neutralization epitopes of the S and the preS1 domain of the large (L) envelope protein (genotype D). The S/preS121-47 chimera produced in mammalian cells and Nicotiana benthamiana plants, induced a significantly stronger immune response in parenterally vaccinated mice than the S protein. Here we describe the transient expression of the S/preS121-47 antigen in an edible plant, Lactuca sativa, for potential development of an oral HBV vaccine. Our study shows that oral administration of adjuvant-free Lactuca sativa expressing the S/preS121-47 antigen, three times, at 1 μg/dose, was sufficient to trigger a humoral immune response in mice. Importantly, the elicited antibodies were able to neutralize HBV infection in an NTCP-expressing infection system (HepG2-NTCP cell line) more efficiently than those induced by mice fed on Lactuca sativa expressing the S protein. These results support the S/preS121-47 antigen as a promising candidate for future development as an edible HBV vaccine.

3D microfluidic liver cultures as a physiological preclinical tool for hepatitis B virus infection

With more than 240 million people infected, hepatitis B virus (HBV) is a major health concern. The inability to mimic the complexity of the liver using cell lines and regular primary human hepatocyte (PHH) cultures pose significant limitations for studying host/pathogen interactions. Here, we describe a 3D microfluidic PHH system permissive to HBV infection, which can be maintained for at least 40 days. This system enables the recapitulation of all steps of the HBV life cycle, including the replication of patient-derived HBV and the maintenance of HBV cccDNA. We show that innate immune and cytokine responses following infection with HBV mimic those observed in HBV-infected patients, thus allowing the dissection of pathways important for immune evasion and validation of biomarkers. Additionally, we demonstrate that the co-culture of PHH with other non-parenchymal cells enables the identification of the cellular origin of immune effectors, thus providing a valuable preclinical platform for HBV research.

Adaptive evolution of proteins in hepatitis B virus during divergence of genotypes

Hepatitis B virus (HBV) is classified into several genotypes, correlated with different geographic distributions, clinical outcomes and susceptible human populations. It is crucial to investigate the evolutionary significance behind the diversification of HBV genotypes, because it improves our understanding of their pathological differences and pathogen-host interactions. Here, we performed comprehensive analysis of HBV genome sequences collected from public database. With a stringent criteria, we generated a dataset of 2992 HBV genomes from eight major genotypes. In particular, we applied a specified classification of non-synonymous and synonymous variants in overlapping regions, to distinguish joint and independent gene evolutions. We confirmed the presence of selective constraints over non-synonymous variants in consideration of overlapping regions. We then performed the McDonald-Kreitman test and revealed adaptive evolutions of non-synonymous variants during genotypic differentiation. Remarkably, we identified strong positive selection that drove the differentiation of PreS1 domain, which is an essential regulator involved in viral transmission. Our study presents novel evidences for the adaptive evolution of HBV genotypes, which suggests that these viruses evolve directionally for maintenance or improvement of successful infections.

Sequence analysis and functional characterization of full-length hepatitis B virus genomes from Korean cirrhotic patients with or without liver cancer

This study aimed to identify and characterize mutations in the hepatitis B virus (HBV) genome associated with advanced liver diseases. The 3.2-kb HBV genome of the C2 subgenotype was amplified from sera of 18 cirrhotic Korean patients with (10) or without (8) hepatocellular carcinoma (HCC), and two clones per patient were characterized by transient transfection experiments in human hepatoma cells. While A1762T/G1764A core promoter mutations were highly prevalent in both groups, the G1896A precore mutation to abolish hepatitis B e antigen (HBeAg) expression was more common in HCC clones (55% vs. 20%). High replication capacity was mostly found in HCC clones and associated with core promoter mutations, whereas more non-HCC clones harbored a nonfunctional core gene (34% vs. 8%). Large in-frame deletions in the preS region were found in 60% of HCC clones and 38% of non-HCC clones. They removed the first 11 residues of large envelope protein or impaired small envelope protein expression, or deleted a neutralizing epitope in the preS2 domain. Additional point mutations prevented middle envelope protein expression, or caused nonsense mutations in the preS or S region to truncate large and/or small envelope protein. Consequently, many clones were unable to express or secrete hepatitis B surface antigen (HBsAg). In conclusion, mutations associated with the advanced stage of chronic HBV infection are complex and diverse. Host immune pressure most likely selected for mutations in the HBV genome to abolish or reduce HBeAg or HBsAg production, to enhance genome replication, or to escape neutralizing antibodies. Some of these mutations may contribute to liver cirrhosis or HCC development.

The Hepatitis B Virus Core Variants that Expose Foreign C-Terminal Insertions on the Outer Surface of Virus-Like Particles

The major immunodominant region (MIR) and N-terminus of the hepatitis B virus (HBV) core (HBc) protein were used to expose foreign insertions on the outer surface of HBc virus-like particles (VLPs). The additions to the HBc positively charged arginine-rich C-terminal (CT) domain are usually not exposed on the VLP surface. Here, we constructed a set of recombinant HBcG vectors in which CT arginine stretches were substituted by glycine residues. In contrast to natural HBc VLPs and recombinant HBc VLP variants carrying native CT domain, the HBcG VLPs demonstrated a lowered capability to pack bacterial RNA during expression in Escherichia coli cells. The C-terminal addition of a model foreign epitope from the HBV preS1 sequence to the HBcG vectors resulted in the exposure of the inserted epitope on the VLP surface, whereas the same preS1 sequences added to the native CT of the natural HBc protein remained buried within the HBc VLPs. Based on the immunisation of mice, the preS1 epitope added to the HBcG vectors as a part of preS1(20-47) and preS1phil sequences demonstrated remarkable immunogenicity. The same epitope added to the original C-terminus of the HBc protein did not induce a notable level of anti-preS1 antibodies. HBcG vectors may contribute to the further development of versatile HBc VLP-based vaccine and gene therapy applications.

Immunotherapy With the PreS-based Grass Pollen Allergy Vaccine BM32 Induces Antibody Responses Protecting Against Hepatitis B Infection

Background

We have constructed and clinically evaluated a hypoallergenic vaccine for grass pollen allergy, BM32, which is based on fusion proteins consisting of peptides from the IgE binding sites of the major grass pollen allergens fused to preS (preS1 + preS2), a domain of the hepatitis B virus (HBV) large envelope protein which mediates the viral attachment and entry. Aim of this study was the characterization of the HBV-specific immune response induced by vaccination of allergic patients with BM32 and the investigation of the vaccines' potential to protect against infection with HBV.

Methods

Hepatitis B-specific antibody and T cell responses of patients vaccinated with BM32 were studied using recombinant preS and synthetic overlapping peptides spanning the preS sequence. The specificities of the antibody responses were compared with those of patients with chronic HBV infection. Furthermore, the capacity of BM32-induced antibodies, to inhibit HBV infection was investigated using HepG2-hNTCP cell-based in vitro virus neutralization assays.

Findings

IgG antibodies from BM32-vaccinated but not of HBV-infected individuals recognized the sequence motif implicated in NTCP (sodium-taurocholate co-transporting polypeptide)-receptor interaction of the hepatitis B virus and inhibited HBV infection.

Interpretation

Our study demonstrates that the recombinant hypoallergenic grass pollen allergy vaccine BM32 induces hepatitis B-specific immune responses which protect against hepatitis B virus infection in vitro.

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BM32 is a recombinant allergy vaccine consisting of the preS domain of the large envelope protein of hepatitis B virus (HBV) and allergen-derived peptides.

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Vaccination of allergic patients with BM32 induced preS-specific antibodies which inhibit hepatitis B infection in vitro.

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BM32 may be useful as therapeutic vaccine in HBV-infected patients.

Infection with HBV remains a major cause of morbidity and mortality worldwide. Conventional HBV vaccines, consisting of SHBs particles solely, do not elicit adequate antibody production in 5–10% of vaccines and there is a need for therapeutic HBV vaccines. We have engineered an allergy vaccine which consists of allergen-derived peptides fused to the preS domain of the large envelope protein of HBV. Here we show that vaccination of allergic patients with this vaccine induces antibodies which protect against HBV infection in vitro. The preS-containing allergy vaccine may thus be also useful for therapeutic vaccination of HBV-infected patients.

The Structural Biology of Hepatitis B Virus: Form and Function

Hepatitis B virus is one of the smallest human pathogens, encoded by a 3,200-bp genome with only four open reading frames. Yet the virus shows a remarkable diversity in structural features, often with the same proteins adopting several conformations. In part, this is the parsimony of viruses, where a minimal number of proteins perform a wide variety of functions. However, a more important theme is that weak interactions between components as well as components with multiple conformations that have similar stabilities lead to a highly dynamic system. In hepatitis B virus, this is manifested as a virion where the envelope proteins have multiple structures, the envelope-capsid interaction is irregular, and the capsid is a dynamic compartment that actively participates in metabolism of the encapsidated genome and carries regulated signals for intracellular trafficking.

Characterization of the 3rd International Standard for hepatitis B virus surface antigen (HBsAg)

BACKGROUND

HBsAg is the most important marker for laboratory diagnosis of HBV infection. Validation and quality control of HBsAg tests requires International Standards (IS). Recently the 2nd IS was replaced by the 3rd IS. Both IS are made from plasma-derived hepatitis B vaccines, but production and geographical origin are different.

OBJECTIVE

Characterization of the HBsAg in the source material (SM) for the 3rd IS and comparison with the 2nd IS and native HBsAg.

STUDY DESIGN

The SM was analyzed using solid-phase immunoassays, quantitative immune electrophoresis, ultracentrifugation, immunoblotting and HBV DNA sequencing.

RESULTS

The plasma-derived HBsAg of the SM originated from at least two different HBV strains, both of subgenotype (sgt) B4, typical for Vietnam. The HBsAg subtype was heterogeneous with ayw1 and adw2. The HBsAg concentration was 23,700 IU/ml as determined by solid-phase immunoassay; immune electrophoresis calibrated with sgt B2 revealed a concentration of 24,500 IU/ml while calibration with sgt D1 provided lower values. Proteins in the SM are heterogeneous in size containing only traces of preS. The protein subunits are partially cross-linked.

CONCLUSIONS

The antigenicity of the 3rd IS is suitable for HBsAg calibration in laboratory tests. In contrast to the 2nd IS, the 3rd IS is representative for a highly endemic region. Similar to the 2nd IS and different from native HBsAg, preS domains are depleted, protein subunits are partially cross-linked and the HBsAg particles are partially aggregated in the 3rd IS. The HBV subgenotype differences between the two IS may lead to variations in different quantitative assays.

Rational Basis for Optimizing Short and Long-term Hepatitis B Virus Prophylaxis Post Liver Transplantation: Role of Hepatitis B Immune Globulin

Antiviral therapy using newer nucleos(t)ide analogues with lower resistance rates, such as entecavir or tenofovir, suppress hepatitis B virus (HBV) replication, improve liver function in patients with compensated or decompensated cirrhosis, and delay or obviate the need for liver transplantation in some patients. After liver transplantation, the combination of long-term antiviral and low-dose hepatitis B Immune globulin (HBIG) can effectively prevent HBV recurrence in greater than 90% of transplant recipients. Some forms of HBV prophylaxis need to be continued indefinitely after transplantation but, in patients with a low-risk of HBV recurrence (i.e., HBV DNA levels undetectable before transplantation), it is possible to discontinue HBIG and maintain only long-term nucleos(t)ide analogue(s) therapy. A more cautious approach is necessary for those patients with high pretransplant HBV DNA levels, those with limited antiviral options if HBV recurrence occurs (i.e., HIV or hepatitis D virus coinfection, preexisting drug resistance), those with a high risk of hepatocellular carcinoma recurrence, and those at risk of noncompliance with antiviral therapy. In this group, HBIG-free prophylaxis cannot be recommended.

The combination of long-term antiviral and low-dose Hepatitis B Immune globulin (HBIG) can effectively prevent HBV recurrence in > 90% of liver transplant recipients. In patients with low HBV DNA levels, nucleos(t)ide analogue(s) treatment without HBIG is possible.

Entry of hepatitis B and hepatitis D virus into hepatocytes: Basic insights and clinical implications

For almost three decades following the discovery of the human Hepatitis B Virus (HBV) the early events of virus infection (attachment to hepatocytes, specific binding to a receptor on hepatocytes) remained enigmatic. The gradual improvement of tissue culture systems for HBV has enabled the identification of viral determinants for viral infectivity and facilitated the discovery of the human sodium taurocholate co-transporting polypeptide (hNTCP) as a liver specific receptor of HBV and its satellite, the human Hepatitis Delta Virus (HDV). These findings are currently leading basic and clinical research activities in new directions. (1) Stable hNTCP-expressing cell lines have become a valuable platform to study the full HBV replication cycle from its native template, the cccDNA. (2) The suitability of NTCP complemented cell culture systems for high throughput screening approaches will facilitate identification of novel host factors involved in HBV replication (including those that determine the peculiar host specificity of HBV infection) and will enable identification and development of novel drug candidates for improved therapeutics. (3) Since NTCP is a major host-specific restriction factor for HBV and HDV, hNTCP-expressing animals provide the basis for future susceptible in vivo models. (4) The concept obtained with the entry inhibitor Myrcludex B demonstrates that NTCP is a suitable target for clinical interference with viral entry. This will foster further clinical approaches aiming at curative combination therapies.

Construction of polyomavirus-derived pseudotype virus-like particles displaying a functionally active neutralizing antibody against hepatitis B virus surface antigen

Background

Virus-like particles (VLPs) can be efficiently produced by heterologous expression of viral structural proteins in yeast. Due to their repetitive structure, VLPs are extensively used for protein engineering and generation of chimeric VLPs with inserted foreign epitopes. Hamster polyomavirus VP1 represents a promising epitope carrier. However, insertion of large sized protein sequences may interfere with its self-assembly competence. The co-expression of polyomavirus capsid protein VP1 with minor capsid protein VP2 or its fusion protein may result in pseudotype VLPs where an intact VP1 protein mediates VLP formation. In the current study, the capacity of VP1 protein to self-assemble to VLPs and interact with the modified VP2 protein has been exploited to generate pseudotype VLPs displaying large-sized antibody molecules.

Results

Polyomavirus-derived pseudotype VLPs harbouring a surface-exposed functionally active neutralizing antibody specific to hepatitis B virus (HBV) surface antigen (HBsAg) have been generated. The pseudotype VLPs consisting of an intact hamster polyomavirus (HaPyV) major capsid protein VP1 and minor capsid protein VP2 fused with the anti-HBsAg molecule were efficiently produced in yeast Saccharomyces cerevisiae and purified by density-gradient centrifugation. Formation of VLPs was confirmed by electron microscopy. Two types of pseudotype VLPs were generated harbouring either the single-chain fragment variable (scFv) or Fc-engineered scFv on the VLP surface. The antigen-binding activity of the purified pseudotype VLPs was evaluated by ELISA and virus-neutralization assay on HBV-susceptible primary hepatocytes from Tupaia belangeri. Both types of the pseudotype VLPs were functionally active and showed a potent HBV-neutralizing activity comparable to that of the parental monoclonal antibody. The VP2-fused scFv molecules were incorporated into the VLPs with higher efficiency as compared to the VP2-fused Fc-scFv. However, the pseudotype VLPs with displayed VP2-fused Fc-scFv molecule showed higher antigen-binding activity and HBV-neutralizing capacity that might be explained by a better accessibility of the Fc-engineered scFv of the VLP surface.

Conclusions

Polyomavirus-derived pseudotype VLPs harbouring multiple functionally active antibody molecules with virus-neutralizing capability may represent a novel platform for developing therapeutic tools with a potential application for post-exposure or therapeutic treatment of viral infections.

Hepatitis B Virus and Hepatitis D Virus Entry, Species Specificity, and Tissue Tropism

Entry of hepatitis B (HBV) and hepatitis D viruses (HDV) into a host cell represents the initial step of infection. This process requires multiple steps, including the low-affinity attachment of the virus to the cell surface, followed by high-affinity attachment to specific receptor(s), and subsequent endocytosis-mediated internalization. Within the viral envelope, the preS1 region is involved in receptor binding. Recently, sodium taurocholate cotransporting polypeptide (NTCP) has been identified as an entry receptor of HBV and HDV by affinity purification using a preS1 peptide. NTCP is mainly or exclusively expressed in the liver, and this membrane protein is at least one of the factors determining the narrow species specificity and hepatotropism of HBV and HDV. However, there are likely other factors that mediate the species and tissue tropism of HBV. This review summarizes the current understanding of the mechanisms of HBV/HDV entry.

Applications of human hepatitis B virus preS domain in bio- and nanotechnology

Human hepatitis B virus (HBV) is a member of the family Hepadnaviridae, and causes acute and chronic infections of the liver. The hepatitis B surface antigen (HBsAg) contains the large (L), middle (M), and small (S) surface proteins. The L protein consists of the S protein, preS1, and preS2. In HBsAg, the preS domain (preS1 + preS2) plays a key role in the infection of hepatocytic cells by HBV and has several immunogenic epitopes. Based on these characteristics of preS, several preS-based diagnostic and therapeutic materials and systems have been developed. PreS1-specific monoclonal antibodies (e.g., MA18/7 and KR127) can be used to inhibit HBV infection. A myristoylated preS1 peptide (amino acids 2-48) also inhibits the attachment of HBV to HepaRG cells, primary human hepatocytes, and primary tupaia hepatocytes. Antibodies and antigens related to the components of HBsAg, preS (preS1 + preS2), or preS1 can be available as diagnostic markers of acute and chronic HBV infections. Hepatocyte-targeting delivery systems for therapeutic molecules (drugs, genes, or proteins) are very important for increasing the clinical efficacy of these molecules and in reducing their adverse effects on other organs. The selective delivery of diagnostic molecules to target hepatocytic cells can also improve the efficiency of diagnosis. In addition to the full-length HBV vector, preS (preS1 + preS2), preS1, and preS1-derived fragments can be useful in hepatocyte-specific targeting. In this review, we discuss the literature concerning the applications of the HBV preS domain in bio- and nanotechnology.

A Human Monoclonal Antibody against Hepatitis B Surface Antigen with Potent Neutralizing Activity

We describe the production and characterization of human monoclonal antibodies (mAb) specific for the major hepatitis B virus (HBV) S protein. The mAbs, two IgG1κ and one IgG1λ, were secreted by B-cell clones obtained from peripheral blood mononuclear cells (PBMC) of one person convalescent from acute hepatitis B and one vaccinated individual. The former recognized a denaturation-insensitive epitope within the p24 protein whereas the latter recognized a denaturation-sensitive, conformational epitope located within the HBsAg common "a" determinant. This mAb, denominated ADRI-2F3, displayed a very high protective titer of over 43,000 IU/mg mAb and showed an extremely potent neutralizing activity in the in vitro model of HBV infection using primary hepatocytes from Tupaia belangeri as target. Recombinant variable heavy and light domain sequences derived from mAb ADRI-2F3 were cloned into eukaryotic expression vectors and showed identical fine specificity and 1 log10 higher titer than the original IgG1λ. It is envisaged that such mAb will be able to efficiently prevent HBV reinfection after liver transplantation for end-stage chronic HBV infection or infection after needle-stick exposure, providing an unlimited source of valuable protective anti-HBs antibody.

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.

Enhanced humanization and affinity maturation of neutralizing anti-hepatitis B virus preS1 antibody based on antigen-antibody complex structure

To improve a previously constructed broadly neutralizing hepatitis B virus (HBV)-specific preS1 humanized antibody (HzKR127), we further humanized it through specificity-determining residue (SDR) grafting. Moreover, we improved affinity by mutating two residues in heavy-chain complementarity-determining regions (CDR), on the basis of the crystal structure of the antigen-antibody complex. HzKR127-3.2 exhibited 2.5-fold higher affinity and enhanced virus-neutralizing activity compared to the original KR127 antibody and showed less immunogenic potential than HzKR127. Enhanced virus-neutralizing activity was achieved by the increased association rate, providing insights into engineering potent antibody therapeutics for HBV immunoprophylaxis. HzKR127-3.2 may be a good candidate for HBV immunoprophylaxis.

Vaccination against infectious diseases: what is promising?

Vaccination has proven to be one of the best weapons protecting the mankind against infectious diseases. Along with the huge progress in microbiology, numerous highly efficacious and safe vaccines have been produced by conventional technology (cultivation), by the use of molecular biology (genetic modification), or by synthetic chemistry. Sterilising prevention is achieved by the stimulation of antibody production, while the stimulation of cell-mediated immune responses may prevent the outbreak of disease in consequence of an acute or reactivated infection. From several examples, two rules are deduced to evaluate the perspectives of future vaccine developments: They are promising, if (1) the natural infectious disease induces immunity or (2) passive immunisation (transfer of antibodies, adoptive transfer of lymphocytes) is successful in preventing infection.

Selected phenotypic assays used to evaluate antiviral resistance and viral fitness of hepatitis B virus and its variants

Currently available antiviral therapies specifically target viral replication by blocking reverse transcription with orally given nucleos(t)ide analogues and are able to specifically suppress viral replication. The unique replication strategy of hepatitis B virus (HBV), however, allows long-term persistence of the viral genome within infected hepatocytes in spite of successful therapy. Thus, antiviral therapy needs to be continued for years. Therapy can result either in the emergence and selection of antiviral-resistant variants or the relapse of viral replication after the termination of antiviral therapy. Resistance is a major problem for 4 of the 5 approved HBV nucleos(t)ide analogues, but it is not the only reason for therapy failure. An accurate phenotypic in vitro assay for resistance allows the identification of a viral variant selected in vivo during antiviral therapy and helps to find therapeutic alternatives. Furthermore, these assays can be used to measure viral fitness and pathogenicity in vitro. With the help of these assays, the prediction of emerging viral variants with drug resistance or increased pathogenic potential can be realized. Phenotypic resistance tests for HBV are not trivial because the virus cannot be readily grown in cell culture. This review focuses on currently available phenotypic assays to evaluate antiviral resistance of HBV and fitness of viral variants in general.

Inhibitors of hepatitis B virus attachment and entry

Inhibition of virus entry has become a major concept in the development of new antiviral drugs. Entry inhibitors can either neutralize activities of viral surface proteins or target essential host factors such as (co)receptors. Due to its distinct tissue tropism and the highly specific viral and cellular factors involved in its entry, hepatitis B virus (HBV) is an ideal candidate for entry inhibition. Hepatitis B immunoglobulins neutralize infection by binding to the S-domain of HBV surface proteins and are used to prevent reinfection of the graft after liver transplantation. Novel S or preS-specific monoclonal antibodies are currently in development. The identification of sodium-taurocholate cotransporting polypeptide (NTCP) as a bona fide receptor has revealed a suitable target for HBV entry inhibition. NTCP receptor function is blocked by a variety of different agents including Myrcludex B, a synthetic N-acylated preS1-derived lipopeptide that inhibits HBV entry in vitro and in vivo with high efficacy. Current antiviral treatment for chronic HBV-infected patients focuses on the inhibition of the viral polymerase via nucleos(t)ide analogues (NA). Entry inhibitors in combination with NAs could block reinfection and shield naive hepatocytes that emerge from natural liver turnover, opening up new therapeutic options.

Induction of a robust T- and B-cell immune response in non- and low-responders to conventional vaccination against hepatitis B by using a third generation PreS/S vaccine

Non-responsiveness to conventional hepatitis B vaccines in individuals at high risk of exposure to hepatitis B virus (HBV) is an important public health problem and of particular relevance in health care providers. Yeast-derived conventional HBsAg vaccines fail to induce protective antibody titers in up to 10% of immune competent vaccinees. Therefore, a third generation HBV vaccine, Sci-B-Vac™, was developed which contains in addition to the small S antigen the PreS1 and PreS2 antigens. This vaccine proved to induce a highly potent cellular and humoral immune response in healthy individuals as well as protective antibody levels in non- and low-responders to conventional HBV vaccines. The aim of the study was to examine whether Sci-B-Vac™ triggers cellular and humoral immunity in individuals who failed immunization with conventional vaccines. We immunized 21 volunteers (15 non- and 6 low-responders) according to the standard vaccination schedule (0, 4 and 24 weeks), determined the cellular immunity by proliferation assay and interferon (IFN)-γ ELISpot and measured the anti-HBs antibody titers prior to each vaccination and four weeks after the third vaccine dose. Following three vaccinations, PreS/S-specific T-cell proliferation was detected in 8 out of 15 non-responders and 5 out of 6 low-responders. Specific IFN-γ responses were measured in 2 out of 15 non-responders and 4 out of 6 low-responders. All but one (20/21) study participants developed anti-HBs titers ≥10IU/l after three vaccinations. Anti-HBs ≥100IU/L were detected in 12 out of 15 non-responders and in 6 out of 6 low-responders. Anti-HBs ≥10IU/l and <100IU/l were found in 2 non-responders. These results indicate that Sci-B-Vac™ induces cellular immunity as well as protective anti-HBs antibody titers in non- and low-responders. In conclusion, these results confirm that Sci-B-Vac™ should be administered to non-responders to conventional HBV vaccines and patients with impaired immune function.

Liver cell-specific peptides derived from the preS1 domain of human hepatitis B virus

The envelope of human hepatitis B virus (HBV) consists of the large (L), middle (M), and small (S) surface proteins. The preS1 domain at the N terminus of the L-protein is essential for recognizing a target cell and for viral infectivity. In the present study, peptides derived from the preS1 domain (amino acid residues 2-19) were synthesized, and their binding affinities for human hepatocellular carcinoma (HCC) cells were determined. Non-myristoylated peptides showed much lower affinity for HepG2 cells than myristoylated peptides. Although all peptides showed significantly higher affinities for two human HCC cell lines (HepG2 and HuH-7) compared with other cell lines (HeLa, B16, NMuLi, and NIH 3T3), a modified peptide exhibited the highest affinity for HCC cell lines. These results suggest that the modified peptide can target liver cells.

NTCP and beyond: opening the door to unveil hepatitis B virus entry

Chronic hepatitis B virus (HBV) infection, affecting approximately 240 million people worldwide, is a major public health problem that elevates the risk of developing liver cirrhosis and hepatocellular carcinoma. Given that current anti-HBV drugs are limited to interferon-based regimens and nucleos(t)ide analogs, the development of new anti-HBV agents is urgently needed. The viral entry process is generally an attractive target implicated in antiviral strategies. Using primary cells from humans and Tupaia belangeri, as well as HepaRG cells, important determinants of viral entry have been achieved. Recently, sodium taurocholate cotransporting polypeptide (NTCP) was identified as an HBV entry receptor and enabled the establishment of a susceptible cell line that can efficiently support HBV infection. This finding will allow a deeper understanding of the requirements for efficient HBV infection, including the elucidation of the molecular entry mechanism. In addition, pharmacological studies suggest that NTCP is able to serve as a therapeutic target. This article summarizes our current knowledge on the mechanisms of HBV entry and the role of NTCP in this process.

Metabolomics study of type 2 diabetes using ultra-performance LC-ESI/quadrupole-TOF high-definition MS coupled with pattern recognition methods

Type 2 diabetes (T2D), called the burden of the twenty-first century, is growing with an epidemic rate. Here, we explored the differences in metabolite concentrations between T2D patients and healthy volunteers. Metabolomics represents an emerging discipline concerned with comprehensive analysis of small molecule metabolites and provides a powerful approach to discover biomarkers in biological systems. The acquired data were analyzed by ultra-performance liquid chromatography-electrospray ionization/quadrupole time-of-flight high-definition mass spectrometry coupled with pattern recognition approach [principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA)] to identify potential disease-specific biomarkers. PCA showed satisfactory clustering between patients and healthy volunteers. Biomarkers reflected the biochemical events associated with early stages of T2D which were observed in PLS-DA loading plots. These urinary differential metabolites, such as adiponectin, acylcarnitines, citric acid, kynurenic acid, 3-indoxyl sulfate, urate, and glucose, were identified involving several key metabolic pathways such as taurine and hypotaurine metabolism; cysteine and methionine metabolism; valine, leucine, and isoleucine biosynthesis metabolism, etc. Our data suggest that robust metabolomics has the potential as a noninvasive strategy to evaluate the early diagnosis of T2D patients and provides new insight into pathophysiologic mechanisms and may enhance the understanding of its cause of disease.

Hepatitis B core-based virus-like particles to present heterologous epitopes

Since the first effort to recombinantly express the hepatitis B core protein (HBc) in bacteria, the remarkable virion-like structure has fuelled interest in unraveling the structural and antigenic properties of this protein. Initial studies proved HBc virus-like particles to possess strong immunogenic properties, which can be conveyed to linked antigens. More than 35 years later, numerous studies have been performed using HBc as a carrier protein for antigens derived from over a dozen different pathogens and diseases. In this review, the authors highlight the intriguing features of HBc as carrier and antigen, illustrated by some examples and experimental results that underscore the value of HBc as an antigen-presenting platform. Two of these HBc fusions, targeting influenza A and malaria, have even progressed into clinical testing. In the future, the HBc-based virus-like particles platform will probably continue to be used for the display of poorly immunogenic antigens, mainly because virus-like particle formation by HBc capsomers is compatible with nearly any available recombinant gene expression system.

Medical virology of hepatitis B: how it began and where we are now

Infection with hepatitis B virus (HBV) may lead to acute or chronic hepatitis. HBV infections were previously much more frequent but there are still 240 million chronic HBV carriers today and ca. 620,000 die per year from the late sequelae liver cirrhosis or hepatocellular carcinoma. Hepatitis B was recognized as a disease in ancient times, but its etiologic agent was only recently identified. The first clue in unraveling this mystery was the discovery of an enigmatic serum protein named Australia antigen 50 years ago by Baruch Blumberg. Some years later this was recognized to be the HBV surface antigen (HBsAg). Detection of HBsAg allowed for the first time screening of inapparently infected blood donors for a dangerous pathogen. The need to diagnose clinically silent HBV infections was a strong driving force in the development of modern virus diagnostics. HBsAg was the first infection marker to be assayed with a highly sensitive radio immune assay. HBV itself was among the first viruses to be detected by assay of its DNA genome and IgM antibodies against the HBV core antigen were the first to be selectively detected by the anti-μ capture assay. The cloning and sequencing of the HBV genome in 1978 paved the way to understand the viral life cycle, and allowed development of efficient vaccines and drugs. Today’s hepatitis B vaccine was the first vaccine produced by gene technology. Among the problems that still remain today are the inability to achieve a complete cure of chronic HBV infections, the recognition of occult HBV infections, their potential reactivation and the incomplete protection against escape mutants and heterologous HBV genotypes by HBV vaccines.

Posttranslational modifications and secretion efficiency of immunogenic hepatitis B virus L protein deletion variants

BACKGROUND

Subviral particles of hepatitis B virus (HBV) composed of L protein deletion variants with the 48 N-terminal amino acids of preS joined to the N-terminus of S protein (1-48preS/S) induced broadly neutralizing antibodies after immunization of mice with a Semliki Forest virus vector. A practical limitation for use as vaccine is the suboptimal secretion of such particles. The role of the N-terminal preS myristoylation in the cellular retention of full-length L protein is described controversially in the literature and the relation of these data to the truncated L protein was unknown. Thus, we studied the effect of preS myristoylation signal suppression on 1-48preS/S secretion efficiency, glycosylation and subcellular distribution.

FINDINGS

The findings are that 1-48preS/S is secreted, and that removal of the N-terminal myristoylation signal in its G2A variant reduced secretion slightly, but significantly. The glycosylation pattern of 1-48preS/S was not affected by the removal of the myristoylation signal (G2A mutant) but was different than natural L protein, whereby N4 of the preS and N3 of the S domain were ectopically glycosylated. This suggested cotranslational translocation of 1-48preS in contrast to natural L protein. The 1-48preS/S bearing a myristoylation signal was localized in a compact, perinuclear pattern with strong colocalization of preS and S epitopes, while the non-myristoylated mutants demonstrated a dispersed, granular cytoplasmic distribution with weaker colocalization.

CONCLUSIONS

The large deletion in 1-48preS/S in presence of the myristoylation site facilitated formation and secretion of protein particles with neutralizing preS1 epitopes at their surface and could be a useful feature for future hepatitis B vaccines.

Host factors involved in hepatitis B virus maturation, assembly, and egress

Hepatitis B virus (HBV) is a major cause of liver disease. Due to the tiny size of its genome, HBV depends on the critical interplay between viral and host factors for the generation of new viral particles from infected cells. Recent work has illuminated a multiplicity of spatially and temporally coordinated virus-host interactions that accompany HBV particle genesis. These interactions include the requirement of cellular chaperones for the maturation of the three viral envelope proteins, the cellular factors involved in dynamic modification, maturation, and intracellular trafficking of the nucleocapsids, and the host components of the multivesicular body (MVB) pathway enabling virion budding at intracellular compartments. Beside infectious virions, HBV produces at least two other types of particles, subviral empty envelope particles and subviral naked capsid particles, likely as a result of the engagement of different host factors by the viral structural proteins. Accordingly, HBV exploits distinct cellular pathways to release its particle types. Here, I review recent progress in these areas of the cell biology of HBV genesis.

Optimisation of prime-boost immunization in mice using novel protein-based and recombinant vaccinia (Tiantan)-based HBV vaccine

BACKGROUND

A therapeutic vaccine for chronic hepatitis B virus (HBV) infection that enhances virus-specific cellular immune responses is urgently needed. The "prime-boost" regimen is a widely used vaccine strategy against many persistence infections. However, few reports have addressed this strategy applying for HBV therapeutic vaccine development.

METHODOLOGY/PRINCIPAL FINDINGS

To develop an effective HBV therapeutic vaccine, we constructed a recombinant vaccinia virus (Tiantan) containing the S+PreS1 fusion antigen (RVJSS1) combined with the HBV particle-like subunit vaccine HBVSS1 to explore the most effective prime-boost regimen against HBV. The immune responses to different prime-boost regimens were assessed in C57BL/C mice by ELISA, ELISpot assay and Intracellular cytokine staining analysis. Among the combinations tested, an HBV protein particle vaccine priming and recombinant vaccinia virus boosting strategy accelerated specific seroconversion and produced high antibody (anti-PreS1, anti-S antibody) titres as well as the strongest multi-antigen (PreS1, and S)-specific cellular immune response. HBSS1 protein prime/RVJSS1 boost immunization was also generated more significant level of both CD4+ and CD8+ T cell responses for Th1 cytokines (TNF-α and IFN-γ).

CONCLUSIONS

The HBSS1 protein-vaccine prime plus RVJSS1 vector boost elicits specific antibody as well as CD4 and CD8 cells secreting Th1-like cytokines, and these immune responses may be important parameters for the future HBV therapeutic vaccines.

Recombinant Semliki Forest virus vectors encoding hepatitis B virus small surface and pre-S1 antigens induce broadly reactive neutralizing antibodies

Most hepatitis B virus (HBV) vaccines consist of viral small surface (S) protein subtype adw2 expressed in yeast cells. In spite of good efficacy, HBV-genotype and subtype differences, escape mutants and insufficient Th1 activation remain potential problems. To address these problems, we generated recombinant Semliki Forest virus (rSFV) vectors encoding S protein, subtype adw2 or ayw2, or a fragment of the large surface protein, amino acids 1-48 of the pre-S1 domain, fused to S (pre-S1.1-48/S). The antigen loop in S protein and the selected pre-S1 sequences are known targets of neutralizing antibodies. BALB/c mice were immunized intravenously with 10(7) rSFV particles and 10(8) rSFV particles 3 weeks later. Antibodies induced by rSFV encoding S proteins reacted preferentially with subtype determinants of yeast-derived S antigen but equally well with patient-derived S antigen. Immunization with rSFV encoding pre-S1.1-48/S resulted in formation of pre-S1- and S-specific immunoglobulin G (IgG), while immunization with the isogenic mutant without S start codon induced pre-S1 antibodies only. Neutralizing antibodies were determined by mixing with plasma-derived HBV/ayw2 and subsequent inoculation of susceptible primary hepatocyte cultures from Tupaia belangeri. S/adw2 antisera neutralized HBV/ayw2 as effectively as antisera raised with S/ayw2. The pre-S1 antibodies also completely neutralized HBV infectivity. The IgG1/IgG2a ratios ranged from 0.28 to 0.88 in the four immunized groups and were lowest for the pre-S1.1-48/S vector, indicating the strongest Th1 response. This vector type may induce subtype-independent and S-escape-resistant neutralizing antibodies against HBV.