Structures of hepatitis B virus cores presenting a model epitope and their complexes with antibodies

Bioengineering of virus-like particles as dynamic nanocarriers for in vivo delivery and targeting to solid tumours

Virus-like particles (VLPs) are known as self-assembled, non-replicative and non-infectious protein particles, which imitate the formation and structure of original wild type viruses, however, lack the viral genome and/or their fragments. The capacity of VLPs to encompass small molecules like nucleic acids and others has made them as novel vessels of nanocarriers for drug delivery applications. In addition, VLPs surface have the capacity to achieve variation of the surface display via several modification strategies including genetic modification, chemical modification, and non-covalent modification. Among the VLPs nanocarriers, Hepatitis B virus core (HBc) particles have been the most encouraging candidate. HBc particles are hollow nanoparticles in the range of 30-34 nm in diameter and 7 nm thick envelopes, consisting of 180 or 240 copies of identical polypeptide monomer. They also employ a distinctive position among the VLPs carriers due to the high-level synthesis, which serves as a strong protective capsid shell and efficient self-assembly properties. This review highlights on the bioengineering of HBc particles as dynamic nanocarriers for in vivo delivery and specific targeting to solid tumours.

Synergistic Effect of Two Nanotechnologies Enhances the Protective Capacity of the Theileria parva Sporozoite p67C Antigen in Cattle

East Coast fever (ECF), caused by Theileria parva, is the most important tick-borne disease of cattle in sub-Saharan Africa. Practical disadvantages associated with the currently used live-parasite vaccine could be overcome by subunit vaccines. An 80-aa polypeptide derived from the C-terminal portion of p67, a sporozoite surface Ag and target of neutralizing Abs, was the focus of the efforts on subunit vaccines against ECF and subjected to several vaccine trials with very promising results. However, the vaccination regimen was far from optimized, involving three inoculations of 450 μg of soluble p67C (s-p67C) Ag formulated in the Seppic adjuvant Montanide ISA 206 VG. Hence, an improved formulation of this polypeptide Ag is needed. In this study, we report on two nanotechnologies that enhance the bovine immune responses to p67C. Individually, HBcAg-p67C (chimeric hepatitis B core Ag virus-like particles displaying p67C) and silica vesicle (SV)-p67C (s-p67C adsorbed to SV-140-C₁₈, octadecyl-modified SVs) adjuvanted with ISA 206 VG primed strong Ab and T cell responses to p67C in cattle, respectively. Coimmunization of cattle (Bos taurus) with HBcAg-p67C and SV-p67C resulted in stimulation of both high Ab titers and CD4 T cell response to p67C, leading to the highest subunit vaccine efficacy we have achieved to date with the p67C immunogen. These results offer the much-needed research depth on the innovative platforms for developing effective novel protein-based bovine vaccines to further the advancement.

Optimization of a Soft Ensemble Vote Classifier for the Prediction of Chimeric Virus-Like Particle Solubility and Other Biophysical Properties

Chimeric virus-like particles (cVLPs) are protein-based nanostructures applied as investigational vaccines against infectious diseases, cancer, and immunological disorders. Low solubility of cVLP vaccine candidates is a challenge that can prevent development of these very substances. Solubility of cVLPs is typically assessed empirically, leading to high time and material requirements. Prediction of cVLP solubility in silico can aid in reducing this effort. Protein aggregation by hydrophobic interaction is an important factor driving protein insolubility. In this article, a recently developed soft ensemble vote classifier (sEVC) for the prediction of cVLP solubility was used based on 91 literature amino acid hydrophobicity scales. Optimization algorithms were developed to boost model performance, and the model was redesigned as a regression tool for ammonium sulfate concentration required for cVLP precipitation. The present dataset consists of 568 cVLPs, created by insertion of 71 different peptide sequences using eight different insertion strategies. Two optimization algorithms were developed that (I) modified the sEVC with regard to systematic misclassification based on the different insertion strategies, and (II) modified the amino acid hydrophobicity scale tables to improve classification. The second algorithm was additionally used to synthesize scales from random vectors. Compared to the unmodified model, Matthew’s Correlation Coefficient (MCC), and accuracy of the test set predictions could be elevated from 0.63 and 0.81 to 0.77 and 0.88, respectively, for the best models. This improved performance compared to literature scales was suggested to be due to a decreased correlation between synthesized scales. In these, tryptophan was identified as the most hydrophobic amino acid, i.e., the amino acid most problematic for cVLP solubility, supported by previous literature findings. As a case study, the sEVC was redesigned as a regression tool and applied to determine ammonium sulfate concentrations for the precipitation of cVLPs. This was evaluated with a small dataset of ten cVLPs resulting in an R² of 0.69. In summary, we propose optimization algorithms that improve sEVC model performance for the prediction of cVLP solubility, allow for the synthesis of amino acid scale tables, and further evaluate the sEVC as regression tool to predict cVLP-precipitating ammonium sulfate concentrations.

An assessment of the use of Hepatitis B Virus core protein virus-like particles to display heterologous antigens from Neisseria meningitidis

Neisseria meningitidis is the causative agent of meningococcal meningitis and sepsis and remains a significant public health problem in many countries. Efforts to develop a comprehensive vaccine against serogroup B meningococci have focused on the use of surface-exposed outer membrane proteins. Here we report the use of virus-like particles derived from the core protein of Hepatitis B Virus, HBc, to incorporate antigen domains derived from Factor H binding protein (FHbp) and the adhesin NadA. The extracellular domain of NadA was inserted into the major immunodominant region of HBc, and the C-terminal domain of FHbp at the C-terminus (CFHbp), creating a single polypeptide chain 3.7-fold larger than native HBc. Remarkably, cryoelectron microscopy revealed that the construct formed assemblies that were able to incorporate both antigens with minimal structural changes to native HBc. Electron density was weak for NadA and absent for CFHbp, partly attributable to domain flexibility. Following immunization of mice, three HBc fusions (CFHbp or NadA alone, NadA + CFHbp) were able to induce production of IgG1, IgG2a and IgG2b antibodies reactive against their respective antigens at dilutions in excess of 1:18,000. However, only HBc fusions containing NadA elicited the production of antibodies with serum bactericidal activity. It is hypothesized that this improved immune response is attributable to the adoption of a more native-like folding of crucial conformational epitopes of NadA within the chimeric VLP. This work demonstrates that HBc can incorporate insertions of large antigen domains but that maintenance of their three-dimensional structure is likely to be critical in obtaining a protective response.

Synthesis and Assembly of Hepatitis B Virus-Like Particles in a Pichia pastoris Cell-Free System

Virus-like particles (VLPs) are supramolecular protein assemblies with the potential for unique and exciting applications in synthetic biology and medicine. Despite the attention VLPs have gained thus far, considerable limitations still persist in their production. Poorly scalable manufacturing technologies and inconsistent product architectures continue to restrict the full potential of VLPs. Cell-free protein synthesis (CFPS) offers an alternative approach to VLP production and has already proven to be successful, albeit using extracts from a limited number of organisms. Using a recently developed Pichia pastoris-based CFPS system, we have demonstrated the production of the model Hepatitis B core antigen VLP as a proof-of-concept. The VLPs produced in the CFPS system were found to have comparable characteristics to those previously produced in vivo and in vitro. Additionally, we have developed a facile and rapid synthesis, assembly and purification methodology that could be applied as a rapid prototyping platform for vaccine development or synthetic biology applications. Overall the CFPS methodology allows far greater throughput, which will expedite the screening of optimal assembly conditions for more robust and stable VLPs. This approach could therefore support the characterization of larger sample sets to improve vaccine development efficiency.

Engineering Human Epidermal Growth Receptor 2-Targeting Hepatitis B Virus Core Nanoparticles for siRNA Delivery in Vitro and in Vivo

Hepatitis B virus core (HBc) particles acquire the capacity to disassemble and reassemble in a controlled manner, allowing entrapment and delivery of drugs and macromolecules to cells. HBc particles are made of 180-240 copies of 21 kDa protein monomers, assembled into 30-34 nm diameter icosahedral particles. In this study, we aimed at formulating HBc particles for the delivery of siRNA for gene silencing in vitro and in vivo. We have previously reported recombinant HBc particles expressing Z_HER2 affibodies, specifically targeting human epidermal growth receptor 2 (HER2)-expressing cancer cells (Z_HER2-ΔHBc). siRNA was encapsulated within the Z_HER2-ΔHBc particles following disassembly and reassembly. The Z_HER2-ΔHBc-siRNA hybrids were able to secure the encapsulated siRNA from serum and nucleases in vitro. Enhanced siRNA uptake in HER2-expressing cancer cells treated with Z_HER2-ΔHBc-siRNA hybrids was observed compared to the nontargeted HBc-siRNA hybrids in a time- and dose-dependent manner. A successful in vitro polo-like kinase 1 (PLK1) gene knockdown was demonstrated in cancer cells treated with Z_HER2-ΔHBc-siPLK1 hybrids, to levels comparable to commercial transfecting reagents. Interestingly, Z_HER2-ΔHBc particles exhibit intrinsic capability of reducing the solid tumor mass, independent of siPLK1 therapy, in an intraperitoneal tumor model following intraperitoneal injection.

Engineering hepatitis B virus core particles for targeting HER2 receptors in vitro and in vivo

Hepatitis B Virus core (HBc) particles have been studied for their potential as drug delivery vehicles for cancer therapy. HBc particles are hollow nano-particles of 30–34 nm diameter and 7 nm thick envelopes, consisting of 180–240 units of 21 kDa core monomers. They have the capacity to assemble/dis-assemble in a controlled manner allowing encapsulation of various drugs and other biomolecules. Moreover, other functional motifs, i.e. receptors, receptor binding sequences, peptides and proteins can be expressed. This study focuses on the development of genetically modified HBc particles to specifically recognise and target human epidermal growth factor receptor-2 (HER2)-expressing cancer cells, in vitro and in vivo, for future cancer therapy. The non-specific binding capacity of wild type HBc particles was reduced by genetic deletion of the sequence encoding arginine-rich domains. A specific HER2-targeting was achieved by expressing the Z_HER2 affibodies on the HBc particles surface. In vitro studies showed specific uptake of Z_HER2-ΔHBc particles in HER2 expressing cancer cells. In vivo studies confirmed positive uptake of Z_HER2-ΔHBc particles in HER2-expressing tumours, compared to non-targeted ΔHBc particles in intraperitoneal tumour-bearing mice models. The present results highlight the potential of these nanocarriers in targeting HER2-positive metastatic abdominal cancer following intra-peritoneal administration.

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.

Genetic variation of hepatitis B virus and its significance for pathogenesis

Hepatitis B virus (HBV) has a worldwide distribution and is endemic in many populations. Due to its unique life cycle which requires an error-prone reverse transcriptase for replication, it constantly evolves, resulting in tremendous genetic variation in the form of genotypes, sub-genotypes, and mutations. In recent years, there has been considerable research on the relationship between HBV genetic variation and HBV-related pathogenesis, which has profound implications in the natural history of HBV infection, viral detection, immune prevention, drug treatment and prognosis. In this review, we attempted to provide a brief account of the influence of HBV genotype on the pathogenesis of HBV infection and summarize our current knowledge on the effects of HBV mutations in different regions on HBV-associated pathogenesis, with an emphasis on mutations in the preS/S proteins in immune evasion, occult HBV infection and hepatocellular carcinoma (HCC), mutations in polymerase in relation to drug resistance, mutations in HBV core and e antigen in immune evasion, chronicalization of infection and hepatitis B-related acute-on-chronic liver failure, and finally mutations in HBV x proteins in HCC.

Virus-like particles presenting interleukin-33 molecules: immunization characteristics and potentials of blockingIL-33/ST2 pathway in allergic airway inflammation

We sought to develop an IL-33 vaccine and evaluate its efficacy in a mouse model of asthma. The full-length molecules of putative mature IL-33 were inserted into the immunodominant epitope region of hepatitis B core antigen using gene recombination techniques. The expressed chimeric protein presented as virus-like particles (VLPs) under observation using an electron microscopy. To investigate immunization characteristics of the VLPs, mice were immunized by using different doses, adjuvants, and routes. The VLPs induced sustained and high titers of IL-33-specific IgG and IgA even without the use of a conventional adjuvant, and the lowered ratio of IgG1/IgG2a in vaccinated mice indicated a shift from Th2 to Th1-like responses. To assess the vaccine effects on blocking the signaling of IL-33/ST2 pathway, mice receiving 3 vaccinations subjected to intraperitoneal sensitization and intranasal challenge with ovalbumin (OVA). Control animals received carrier or PBS in place of the vaccine. Immunization with the VLPs significantly suppressed inflammatory cell number and IL-33 level in BALF. OVA -induced goblet cell hyperplasia and lung tissue inflammatory cell infiltration were significantly suppressed in vaccinated mice. Our data indicate that IL-33 molecule-based vaccine, which may block IL-33/ST2 signaling pathway on a persistent basis, holds potential for treatment of asthma and, by extension, other diseases where overexpressed IL-33 plays a pivotal role in pathogenesis.

Preparation by alkaline treatment and detailed characterisation of empty hepatitis B virus core particles for vaccine and gene therapy applications

Hepatitis B virus (HBV) core (HBc) virus-like particles (VLPs) are one of the most powerful protein engineering tools utilised to expose immunological epitopes and/or cell-targeting signals and for the packaging of genetic material and immune stimulatory sequences. Although HBc VLPs and their numerous derivatives are produced in highly efficient bacterial and yeast expression systems, the existing purification and packaging protocols are not sufficiently optimised and standardised. Here, a simple alkaline treatment method was employed for the complete removal of internal RNA from bacteria- and yeast-produced HBc VLPs and for the conversion of these VLPs into empty particles, without any damage to the VLP structure. The empty HBc VLPs were able to effectively package the added DNA and RNA sequences. Furthermore, the alkaline hydrolysis technology appeared efficient for the purification and packaging of four different HBc variants carrying lysine residues on the HBc VLP spikes. Utilising the introduced lysine residues and the intrinsic aspartic and glutamic acid residues exposed on the tips of the HBc spikes for chemical coupling of the chosen peptide and/or nucleic acid sequences ensured a standard and easy protocol for the further development of versatile HBc VLP-based vaccine and gene therapy applications.

Key role of hepatitis B virus mutation in chronic hepatitis B development to hepatocellular carcinoma

Chronic hepatitis B virus (HBV) infection is a major risk factor for hepatocellular carcinoma (HCC). The HBV mutations, which include point mutation, deletion, insertion and truncation mutation of HBV gene in 4 open reading frames (S, C, P, X), are closely associated with HCC pathogenesis. Some mutations accumulated during chronic HBV infection could be regarded as a biomarker to predict the occurrence of HCC. The detection of the mutations in clinical practice could be helpful for defining better preventive and therapeutic strategies and, moreover, predicting the progression of liver disease.

A theoretical study of SRPK interaction with the flexible domains of hepatitis B capsids

Hepatitis B virus (HBV) controls genome encapsidation and reverse transcription from a single-stranded RNA to a double-stranded DNA through the flexible C-terminal domain (CTD) of the capsid proteins. Although the microscopic structure of the nucleocapsid plays a critical role in the life cycle of HBV, the location of CTD residues at different stages of viral replication remains poorly understood. In this work, we report the radial distributions of individual amino-acid residues of the CTD tails for both empty and RNA-containing HBV capsids by using a coarse-grained model for the key biological components and the classical density functional theory. The density functional theory calculations reveal substantial exposure of the CTD residues outside the capsid, in particular when it is devoid of any nucleic materials. The outermost layer of the capsid surface mainly consists of residues from (170)Ser-(175)Arg of the CTD tails, i.e., the serine-arginine protein kinase binding motif. The theoretical description corroborates recent in vitro studies that show a transient CTD distribution captured by serine-arginine protein kinase binding. We have also investigated the nucleocapsid structural changes due to phosphorylation of serine residues and shown a correlation between the CTD location and the internal distribution of RNA segments.

Silica nanoparticles as the adjuvant for the immunisation of mice using hepatitis B core virus-like particles

Advances in nanotechnology and nanomaterials have facilitated the development of silicon dioxide, or Silica, particles as a promising immunological adjuvant for the generation of novel prophylactic and therapeutic vaccines. In the present study, we have compared the adjuvanting potential of commercially available Silica nanoparticles (initial particles size of 10–20 nm) with that of aluminium hydroxide, or Alum, as well as that of complete and incomplete Freund's adjuvants for the immunisation of BALB/c mice with virus-like particles (VLPs) formed by recombinant full-length Hepatitis B virus core (HBc) protein. The induction of B-cell and T-cell responses was studied after immunisation. Silica nanoparticles were able to adsorb maximally 40% of the added HBc, whereas the adsorption capacity of Alum exceeded 90% at the same VLPs/adjuvant ratio. Both Silica and Alum formed large complexes with HBc VLPs that sedimented rapidly after formulation, as detected by dynamic light scattering, spectrophotometry, and electron microscopy. Both Silica and Alum augmented the humoral response against HBc VLPs to the high anti-HBc level in the case of intraperitoneal immunisation, whereas in subcutaneous immunisation, the Silica-adjuvanted anti-HBc level even exceeded the level adjuvanted by Alum. The adjuvanting of HBc VLPs by Silica resulted in the same typical IgG2a/IgG1 ratios as in the case of the adjuvanting by Alum. The combination of Silica with monophosphoryl lipid A (MPL) led to the same enhancement of the HBc-specific T-cell induction as in the case of the Alum and MPL combination. These findings demonstrate that Silica is not a weaker putative adjuvant than Alum for induction of B-cell and T-cell responses against recombinant HBc VLPs. This finding may have an essential impact on the development of the set of Silica-adjuvanted vaccines based on a long list of HBc-derived virus-like particles as the biological component.

Immunopathogenesis of chronic hepatitis B

Chronic hepatitis B (CHB) is a widespread infectious disease with unfavorable outcomes and life-threatening consequences for patients, in spite of modern vaccination and antiviral treatment modalities. Cutting-edge experimental approaches have demonstrated key pathways that involve cross-talk between viral particles and host immune cells. All events, including penetration of hepatitis B virus (HBV) particles into host cells, establishing persistence, and chronization of CHB infection, and possibility of complete elimination of HBV particles are controlled by the immune system. Researchers have paid special attention to the replication capacity of HBV in host cells, which is associated with cellular changes that reflect presentation of viral antigens and variability of HBV antigen features. In addition, specific HBV proteins have an immune-modulating ability to initiate molecular mechanisms that “avoid” control by the immune system. The relationship between immunological shifts and chronic infection stages has been intensively studied since it was recognized that the immune system is a direct participant in the recurrent (cyclic) nature of CHB. Understanding the wide diversity of molecular pathways and the crosstalk between innate and adaptive immune system components will provide fresh insight into CHB immune pathogenesis and the possibilities of developing new treatment strategies for this disease.

Phage display creates innovative applications to combat hepatitis B virus

Hepatitis B virus (HBV) has killed countless lives in human history. The invention of HBV vaccines in the 20^th century has reduced significantly the rate of the viral infection. However, currently there is no effective treatment for chronic HBV carriers. Newly emerging vaccine escape mutants and drug resistant strains have complicated the viral eradication program. The entire world is now facing a new threat of HBV and human immunodeficiency virus co-infection. Could phage display provide solutions to these life-threatening problems? This article reviews critically and comprehensively the innovative and potential applications of phage display in the development of vaccines, therapeutic agents, diagnostic reagents, as well as gene and drug delivery systems to combat HBV. The application of phage display in epitope mapping of HBV antigens is also discussed in detail. Although this review mainly focuses on HBV, the innovative applications of phage display could also be extended to other infectious diseases.

Potential mutations associated with occult hepatitis B virus status

CONTEXT

Occult hepatitis B virus (HBV) status (OHBS) is simply defined as the presence of HBV DNA in the liver (with or without detectable HBV DNA in the serum), in the absence of serum HBV surface antigen (HBsAg). Importance of OHBS is mostly clinical, related to its possible role in spreading through blood transfusion and liver transplantation; causing classic forms of HBV. Mechanisms underlying this entity are poorly defined. Several possibilities have been suggested, with major classification into two groups: defective host immune response and viral replication activity through mutations of HBV DNA sequence. Mutations are extensively investigated in all four overlapping open reading frames (ORFs) of HBV genome, to define their possible role in the pathogenesis of OHBS. Some of these mutations like S-escape mutants could not be detected by the routine available assays, making them difficult to diagnosis. Therefore, trying to detect this covert condition could be more helpful for defining better preventive and therapeutic strategies.

EVIDENCE ACQUISITION

In the present study we provided an in-depth review of the most important new data available on different mutations in HBV genome of patients with OHBS, which may play a role in the pathogenesis of OHBS. The data were collected through reviewing the full-text articles, identified by the PubMed search, using the following keywords and their different combinations: occult hepatitis B, HBV genome, "a" determinant, HBV open reading frames, S mutations, X mutations, P mutations and C mutations.

RESULTS

Variants within the major hydrophilic region (MHR) of the HBsAg, deletions in the pre-S1region, codon stop in the S open reading frames (ORF), sporadic non common mutations, some mutations affecting the posttranslational production of HBV proteins in the S ORF like deletion mutations, mutations in start codon and nucleotide changes in the X ORF, deletion and point mutations in P ORF and sometimes, nucleotide substitution in the C ORF are among the assumed mutations detected to have a role in OHBS appearance.

CONCLUSIONS

Studies mostly lacked a control group and the whole-length HBV sequencing was scant with conflicting results, suggesting that OHBS is often a result of multiple mechanisms. Additional studies on full-length HBV genomes from occult and non-occult HBV cases may shed more light on the interplay between different mechanisms involved in the pathogenesis of OHBS.

A VLP library of C-terminally truncated Hepatitis B core proteins: correlation of RNA encapsidation with a Th1/Th2 switch in the immune responses of mice

An efficient pBR327- and Ptrp-based E. coli expression system was used to generate a large-scale library of virus like particles (VLP) formed by recombinant hepatitis B virus (HBV) core (HBc) protein derivatives. To construct the library, the gene of HBc protein of the genotype D/subtype ayw2 virus was gradually truncated from the 3`-end and twenty-two HBc variants (with truncation up to 139 aa) were expressed at high levels. The proteins were purified by salt precipitation and gel filtration. Background RNA binding was observed for VLPs formed by HBc1-149, which lacked all C-terminal Arg blocks, and the addition of three Arg residues (HBc1-152) only slightly increased RNA binding. The presence of two Arg blocks (proteins HBc1-162 and HBc1-163) resulted in approximately half of the typical level of RNA binding, and the presence of three blocks (protein HBc1-171) led to approximately 85% of the typical level of binding. Only a small increase in the level of RNA binding was found for the HBc1-175 VLPs, which contained all four Arg blocks but lacked the last 8 aa of the full-length HBc protein. VLPs containing high levels of RNA had higher antigenicity according to an ELISA with anti-HBc mAbs than the VLPs formed by HBc variants without C-terminal Arg blocks and lacking RNA. The results indicate that the VLPs were stabilised by nucleic acids. The immunogenicity in BALB/c mice was comparable for VLPs formed by different HBc proteins, but a clear switch from a Th1 response to a Th2 response occurred after the loss of encapsidated RNA. We did not observe significant differences in lymphocyte proliferation in vitro for the tested VLP variants; however, the loss of RNA encapsidation correlated with a decreased level of IFN-γ induction, which is a measure of the potential CTL activity of immunogens.

Chimeric derivatives of hepatitis B virus core particles carrying major epitopes of the rubella virus E1 glycoprotein

Three variants of the major rubella virus (RV) E1 protein virus-neutralizing epitope from position 214 to 285 were exposed on the hepatitis B virus (HBV) C-terminally truncated core (HBcΔ) in a virus-like particle (VLP) vector and were produced in Escherichia coli. All three chimeras demonstrated VLPs in bacterial cell lysates, but only HBcΔ-E1(245-285) demonstrated the correct VLP structure after purification. The other chimeras, HBcΔ-E1(214-285) and HBcΔ-E1(214-240), appeared after purification as non-VLP aggregates of 100 to 900 nm in diameter according to dynamic light scattering data. All three variants possessed the intrinsic antigenic activity of RV E1, since they were recognized by natural human anti-RV E1 antibodies and induced an anti-RV E1 response in mice. HBcΔ-E1(214-240) and HBcΔ-E1(245-285) can be regarded as prototypes for a putative RV vaccine because they were able to induce antibodies recognizing natural RV E1 protein in RV diagnostic kits.