Expression of hepatitis B virus core antigen gene in Saccharomyces cerevisiae: synthesis of two polypeptides translated from different initiation codons

Cell Culture Systems for Studying Hepatitis B and Hepatitis D Virus Infections

The hepatitis B virus (HBV) and hepatitis D virus (HDV) infections cause liver disease, including hepatitis, cirrhosis, and hepatocellular carcinoma (HCC). HBV infection remains a major global health problem. In 2019, 296 million people were living with chronic hepatitis B and about 5% of them were co-infected with HDV. In vitro cell culture systems are instrumental in the development of therapeutic targets. Cell culture systems contribute to identifying molecular mechanisms for HBV and HDV propagation, finding drug targets for antiviral therapies, and testing antiviral agents. Current HBV therapeutics, such as nucleoside analogs, effectively suppress viral replication but are not curative. Additionally, no effective treatment for HDV infection is currently available. Therefore, there is an urgent need to develop therapies to treat both viral infections. A robust in vitro cell culture system supporting HBV and HDV infections (HBV/HDV) is a critical prerequisite to studying HBV/HDV pathogenesis, the complete life cycle of HBV/HDV infections, and consequently identifying new therapeutics. However, the lack of an efficient cell culture system hampers the development of novel antiviral strategies for HBV/HDV infections. In vitro cell culture models have evolved with significant improvements over several decades. Recently, the development of the HepG2-NTCP sec+ cell line, expressing the sodium taurocholate co-transporting polypeptide receptor (NTCP) and self-assembling co-cultured primary human hepatocytes (SACC-PHHs) has opened new perspectives for a better understanding of HBV and HDV lifecycles and the development of specific antiviral drug targets against HBV/HDV infections. We address various cell culture systems along with different cell lines and how these cell culture systems can be used to provide better tools for HBV and HDV studies.

Hepatitis B core-based virus-like particles: A platform for vaccine development in plants

Virus-like particles (VLPs) are a class of structures formed by the self-assembly of viral capsid protein subunits and contain no infective viral genetic material. The Hepatitis B core (HBc) antigen is capable of assembling into VLPs that can elicit strong immune responses and has been licensed as a commercial vaccine against Hepatitis B. The HBc VLPs have also been employed as a platform for the presentation of foreign epitopes to the immune system and have been used to develop vaccines against, for example, influenza A and Foot-and-mouth disease. Plant expression systems are rapid, scalable and safe, and are capable of providing correct post-translational modifications and reducing upstream production costs. The production of HBc-based virus-like particles in plants would thus greatly increase the efficiency of vaccine production. This review investigates the application of plant-based HBc VLP as a platform for vaccine production.

Production of the HBc Protein from Different HBV Genotypes in E. coli. Use of Reassociated HBc VLPs for Packaging of ss- and dsRNA

The core proteins (HBc) of the hepatitis B virus (HBV) genotypes A, B, C, D, E, F, and G were cloned and expressed in Escherichia coli (E. coli), and HBc-formed virus-like particles (VLPs) were purified with ammonium sulfate precipitation, gel filtration, and ion exchange chromatography (IEX). The best VLP yield was found for the HBc of the HBV genotypes D and G. For the HBc of the HBV genotypes D, F, and G, the possibility of dissociation and reassociation maintaining the native HBc structure was demonstrated. Single-stranded (ss) and double-stranded (ds) ribonucleic acid (RNA) was successfully packed into HBc VLPs for the HBV genotypes D and G.

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.

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.

Chemokine receptor interactions with virus-like particles

Virus-like particles (VLPs) presenting conformational envelope proteins on their surface represent an invaluable tool to study molecular interactions between viruses and cellular receptors/co-receptors, eliminating biological risks associated with working with live native viruses. The availability of target cells expressing specific chemokine receptors facilitates the dissection of specific interactions between human immunodeficiency virus (HIV) viral envelope proteins and these receptors in the laboratory. Here, we describe a method to evaluate HIV-VLP binding to cellular chemokine co-receptors, by carboxyfluorescein succinimidyl ester labeling and cellular uptake.

VLPs and particle strategies for cancer vaccines

Effective delivery of tumor antigens to APCs is one of the key steps for eliciting a strong and durable immune response to tumors. Several cancer vaccines have been evaluated in clinical trials, based on soluble peptides, but results have not been fully satisfactory. To improve immunogenicity particles provide a valid strategy to display and/or incorporate epitopes which can be efficiently targeted to APCs for effective induction of adaptive immunity. In the present review, we report some leading technologies for developing particulate vaccines employed in cancer immunotherapy, highlighting the key parameters for a rational design to elicit both humoral and cellular responses.

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.

Fluorosomes: fluorescent virus-like nanoparticles that represent a convenient tool to visualize receptor-ligand interactions

Viruses are the smallest life forms and parasitize on many eukaryotic organisms, including humans. Consequently, the study of viruses and viral diseases has had an enormous impact on diverse fields of biology and medicine. Due to their often pathogenic properties, viruses have not only had a strong impact on the development of immune cells but also on shaping entire immune mechanisms in their hosts. In order to better characterize virus-specific surface receptors, pathways of virus entry and the mechanisms of virus assembly, diverse methods to visualize virus particles themselves have been developed in the past decades. Apart from characterization of virus-specific mechanisms, fluorescent virus particles also serve as valuable platforms to study receptor-ligand interactions. Along those lines the authors have developed non-infectious virus-like nanoparticles (VNP), which can be decorated with immune receptors of choice and used for probing receptor-ligand interactions, an especially interesting application in the field of basic but also applied immunology research. To be able to better trace receptor-decorated VNP the authors have developed technology to introduce fluorescent proteins into such particles and henceforth termed them fluorosomes (FS). Since VNP are assembled in a simple expression system relying on HEK-293 cells, gene-products of interest can be assembled in a simple and straightforward fashion—one of the reasons why the authors like to call fluorosomes ‘the poor-man's staining tool’. Within this review article an overview on virus particle assembly, chemical and recombinant methods of virus particle labeling and examples on how FS can be applied as sensors to monitor receptor-ligand interactions on leukocytes are given.

Developments in virus-like particle-based vaccines for HIV

Virus-like particles (VLPs) hold great promise for the development of effective and affordable vaccines. VLPs, indeed, are suitable for presentation and efficient delivery to antigen-presenting cells of linear as well as conformational antigens. This will ultimately result in a crosspresentation with both MHC class I and II molecules to prime CD4(+) T-helper and CD8(+) cytotoxic T cells. This review describes an update on the development and use of VLPs as vaccine approaches for HIV.

Developments in virus-like particle-based vaccines for infectious diseases and cancer

Virus-like particles hold great promise for the development of effective and affordable vaccines. Indeed, virus-like particles are suitable for presentation and efficient delivery of linear as well as conformational antigens to antigen-presenting cells. This will ultimately result in optimal B-cell activation and cross-presentation with both MHC class I and II molecules to prime CD4(+) T-helper as well as CD8(+) cytotoxic T cells. This article provides an update on the development and use of virus-like particles as vaccine approaches for infectious diseases and cancer.

Light it up: highly efficient multigene delivery in mammalian cells

Multigene delivery and expression systems are emerging as key technologies for many applications in contemporary biology. We have developed new methods for multigene delivery and expression in eukaryotic hosts for a variety of applications, including production of protein complexes for structural biology and drug development, provision of multicomponent protein biologics, and cell-based assays. We implemented tandem recombineering to facilitate rapid generation of multicomponent gene expression constructs for efficient transformation of mammalian cells, resulting in homogenous cell populations. Analysis of multiple parameters in living cells may require co-expression of fluorescently tagged sensors simultaneously in a single cell, at defined and ideally controlled ratios. Our method enables such applications by overcoming currently limiting challenges. Here, we review recent multigene delivery and expression strategies and their exploitation in mammalian cells. We discuss applications in drug discovery assays, interaction studies, and biologics production, which may benefit in the future from our novel approach.

Generation of HIV-1 Virus-Like Particles expressing different HIV-1 glycoproteins

Elicitation of a potent and broadly neutralizing antibody response is the main goal of an effective preventive HIV-1 vaccine. It has been shown by us and others that the expression of Env glycoproteins on the surface of particulate structures, such as Virus-Like Particles (VLPs), could be a more efficient strategy to deliver conformational epitopes to the immune system. To this aim, VLPs expressing native HIV Env gp140 or gp41 glycoproteins have been produced in insect cells using a baculovirus expression system and characterized for appropriate protein expression. VLP-bound HIV gp140 glycoprotein showed the appropriate expression and trimeric conformation. Immunogenicity studies have been performed in BALB/C mice by intra-peritoneal administration and sera from immunized mice have been tested in ELISA assays, for their reactivity with HIV specific antigens, as well as in ex vivo neutralization assay. Sera from immunized animals showed a high reactivity with individual HIV proteins expressed in VLPs. Results of TZM-bl based neutralization assay show that combined sera from animals independently immunized with gp140- or full-length-gp41-expressing VLPs have an additive/synergistic effect in the neutralization activity of HIV pseudoviruses. In conclusion, novel VLPs expressing different HIV Env glycoproteins with native trimeric conformation have been generated, showing the induction of effective antibody response with neutralization activity in TZM-bl neutralization assay. These results confirm the effectiveness of VLPs as presentation and delivery system for conformational proteins and show the improved neutralization activity upon the combination of anti-sera elicited by different HIV envelope antigens, suggesting the possibility of broadening the spectrum of viral epitopes targeted by immune response.

Conformational HIV-1 envelope on particulate structures: a tool for chemokine coreceptor binding studies

The human immunodeficiency virus type 1 (HIV-1) external envelope glycoprotein gp120 presents conserved binding sites for binding to the primary virus receptor CD4 as well as the major HIV chemokine coreceptors, CCR5 and CXCR4.

Concerted efforts are underway to understand the specific interactions between gp120 and coreceptors as well as their contribution to the subsequent membrane fusion process.

The present review summarizes the current knowledge on this biological aspect, which represents one of the key and essential points of the HIV-host cell interplay and HIV life cycle. The relevance of conformational HIV-1 Envelope proteins presented on Virus-like Particles for appropriate assessment of this molecular interaction, is also discussed.

Management of hepatitis B: Consensus of the Japan Society of Hepatology 2009

Recently, much progress has been made in the field of hepatitis B, such as natural history of the disease in relation to the amount of hepatitis B virus (HBV) DNA, genotypes of HBV influencing the natural course and treatment effects, mutations of HBV influencing the severity of the disease and development of hepatocellular carcinoma, and antiviral treatment such as nucleos(t)ide analogues and pegylated interferon. To make the consensus for the diagnosis, management and treatment of hepatitis B, a meeting was held during 45th annual meeting of Japan Society of Hepatology (JSH) in June 2009. In the meeting, recommendations and informative statements were discussed on the following subjects: (i) natural history of HBV infection; (ii) clinical implication of HBV genotypes; (iii) HBV mutations and their potential impact on pathogenesis of HBV infection; (iv) indications for antiviral treatment of chronic hepatitis B; (v) nucleos(t)ide analogues for chronic hepatitis B; and (vi) interferon therapy for chronic hepatitis B. The presenters reviewed the data on these subjects and proposed the consensus statements and recommendations. These statements were discussed among the organizers and presenters, and were approved by the participants of the meeting. In the current report, the relevant data were reviewed and the 12 consensus statements and nine recommendations on chronic hepatitis B were described.

Viral nanoparticles and virus-like particles: platforms for contemporary vaccine design

Current vaccines that provide protection against infectious diseases have primarily relied on attenuated or inactivated pathogens. Virus‐like particles (VLPs), comprised of capsid proteins that can initiate an immune response but do not include the genetic material required for replication, promote immunogenicity and have been developed and approved as vaccines in some cases. In addition, many of these VLPs can be used as molecular platforms for genetic fusion or chemical attachment of heterologous antigenic epitopes. This approach has been shown to provide protective immunity against the foreign epitopes in many cases. A variety of VLPs and virus‐based nanoparticles are being developed for use as vaccines and epitope platforms. These particles have the potential to increase efficacy of current vaccines as well as treat diseases for which no effective vaccines are available. WIREs Nanomed Nanobiotechnol 2011 3 174–196 DOI: 10.1002/wnan.119

This article is categorized under: 1

Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease

Virus-like particles as a vaccine delivery system: myths and facts

Vaccines against viral disease have traditionally relied on attenuated virus strains or inactivation of infectious virus. Subunit vaccines based on viral proteins expressed in heterologous systems have been effective for some pathogens, but have often suffered from poor immunogenicity due to incorrect protein folding or modification. In this chapter we focus on a specific class of viral subunit vaccine that mimics the overall structure of virus particles and thus preserves the native antigenic conformation of the immunogenic proteins. These virus-like particles (VLPs) have been produced for a wide range of taxonomically and structurally distinct viruses, and have unique advantages in terms of safety and immunogenicity over previous approaches. With new VLP vaccines for papillomavirus beginning to reach the market place we argue that this technology has now ‘come-of-age’ and must be considered a viable vaccine strategy.

Viral nanoparticles as macromolecular devices for new therapeutic and pharmaceutical approaches

Viral nanoparticles are molecular cages derived from the assembly of viral structural proteins. They bear several peculiar features as proper dimensions for nanoscale applications, size homogeneity, an intrinsic robustness, a large surface area to mass ratio and a defined, repetitive and symmetric macromolecular organization. A number of expression strategies, using various biological systems, efficiently enable the production of significant quantities of viral nanoparticles, which can be easily purified. Genetic engineering and in vitro chemical modification consent to manipulate of the outer and inner surface of these nanocages, allowing specific changes of the original physico-chemical and biological properties. Moreover, several studies have focused on the in vitro disassembly/reassembly and gating of viral nanoparticles, with the aim of encapsulating exogenous molecules inside and therefore improving their potential as containment delivery devices. These technological progresses have led research to a growing variety of applications in different fields such as biomedicine, pharmacology, separation science, catalytic chemistry, crop pest control and material science. In this review we will focus on the strategies used to modify the characteristics of viral nanoparticles and on their use in biomedicine and pharmacology.

Virus-like particle vaccines and adjuvants: the HPV paradigm

Complex antigen structures currently represent the most-studied approach for prophylactic as well as therapeutic vaccines. Different types of complex vaccines, including virus-like particles and virosomes, have been developed depending on the nature of the viral pathogen they are trying to replicate (enveloped vs naked) or the modality to express antigenic epitopes (i.e., the binding of envelope protein on liposomic structures). The complex structure of these vaccines provides them with some adjuvanted properties, not uniformly present for all virus-like particle types. The further inclusion of specific adjuvants in vaccine preparations can modify the presentation modality of such particles to the immune system with a specific Th1 versus Th2 polarization efficacy. A paradigm of the relevance of these new adjuvants are the immunological results obtained with the inclusion of monophosphoryl lipid A adjuvant in the formulation of L1-based human papillomavirus-naked virus-like particles to reduce a Th1 cellular immunity impairment, peculiar for alum-derived adjuvants, along with the induction of highly enhanced humoral and memory B-cellular immunity.

Efficient induction of human T-cell leukemia virus-1-specific CTL by chimeric particle without adjuvant as a prophylactic for adult T-cell leukemia

Adult T-cell leukemia-lymphoma (ATL) is an aggressive peripheral T-cell neoplasm that develops after long-term infection with the human T-cell leukemia virus-1 (HTLV-1). HTLV-1-specific cytotoxic T lymphocytes (CTLs) play an important role in suppressing proliferation of HTLV-1-infected or transformed T-cells in vitro. Efficient induction of antigen-specific CTLs is important for immunologic suppression of oncogenesis, but has evaded strategies utilizing poorly immunogenic free synthetic peptides. In the present study, we examined the efficient induction of HTLV-1-specific CD8+ T-cell response by an HTLV-1/hepatitis B virus core (HBc) chimeric particle incorporating the HLA-A*0201-restricted HTLV-1 Tax-epitope. The immunization of HLA-A*0201-transgenic mice with the chimeric particle induced antigen-specific gamma-interferon reaction, whereas immunization with epitope peptide only induced no reaction as assessed by enzyme-linked immunospot assay. Immunization with the chimeric particle also induced HTLV-1-specific CD8+ T-cells in spleen and inguinal lymph nodes. Furthermore, upon exposure of dendritic cells from HLA-A*0201-transgenic mice to the chimeric particle, the expression of CD86, HLA-A02, TLR4 and MHC class II was increased. Additionally, our results show that HTLV-1-specific CD8+ T-cells can be induced by peptide with HTLV-1/HBc particle from ATL patient, but not by peptide only and these HTLV-1-specific CD8+ T-cells were able to lyse cells presenting the peptide. These results suggest that HTLV-1/HBc chimeric particle is capable of inducing strong cellular immune responses without adjuvants via effective maturation of dendritic cells and is potentially useful as an effective carrier for therapeutic vaccines in tumors, or in infectious diseases by substituting the epitope peptide.

Short communication: limited induction of IL-10 in PBMCs from HIV-infected subjects treated with HIV-VLPs

We have recently shown that HIV-1 Pr55gag virus-like particles (HIV-VLPs), produced in a baculovirus expression system and presenting a gp120 molecule from a Ugandan HIV-1 isolate of clade A (HIV-VLP(A)s), induce maturation and activation of antigen-presenting cells (APCs) in fresh peripheral blood mononuclear cells (PBMCs) from seronegative as well as seropositive, with either low or high viremia, HIV-1 subjects. A Th2 polarization has been observed in both HIV seropositive groups, which is efficiently boosted by HIV-VLP induction and does not switch into a Th1 pattern. Here we show that the production of the known immune-suppressive IL-10 is induced in both HIV-seropositive groups at a significantly lower level by HIV-VLPs compared to LPS. These levels, however, appear to still negatively interfere with the innate as well as adaptive Th1-polarized response observed in HIV-seropositive groups. These results indicate that vaccines and novel adjuvants (i.e., TLR agonists, such as LPS) must be evaluated not only for their immunogenicity but also for their potential immune-suppressive effects. In this perspective, fresh ex vivo PBMCs can be of high value for screening the responses as well as eventual failures of vaccinees enrolled in clinical trials.

Th2 polarization in peripheral blood mononuclear cells from human immunodeficiency virus (HIV)-infected subjects, as activated by HIV virus-like particles

We have recently shown that human immunodeficiency virus type 1 (HIV-1) Pr55(gag) virus-like particles (HIV-VLPs), produced in a baculovirus expression system and presenting a gp120 molecule from a Ugandan HIV-1 isolate of clade A, induce maturation and activation of monocyte-derived dendritic cells (MDDCs) with a production of Th1- and Th2-specific cytokines. Furthermore, HIV-VLP-loaded MDDCs are able to induce a primary and secondary response in autologous human CD4(+) T cells in an ex vivo immunization assay. In the present study, we show that similar data can be obtained directly with fresh peripheral blood mononuclear cells (PBMCs), and the HIV-1 seropositivity status, with either low or high viremia, does not significantly impair the immune activation status and the responsiveness of circulating monocyte CD14(+) cell populations to an immunogenic stimulus. Some HIV-1-seropositive subjects, however, show a complete lack of maturation induced by HIV-VLPs in CD14(+) circulating cells, which does not consistently correlate with an advanced status of HIV-1 infection. The established Th2 polarization in both HIV-seropositive groups is efficiently boosted by HIV-VLP induction and does not switch into a Th1 pattern, strongly suggesting that specific Th1 adjuvants would be required for therapeutic effectiveness in HIV-1-infected subjects. These results indicate the possibility of screening PBMCs for donor susceptibility to an immunogen treatment, which would greatly simplify the identification of "responsive" vaccinees as well as the understanding of eventual failures in individuals enrolled in clinical trials.

Generation of chimeric HBc proteins with epitopes in E.coli: formation of virus-like particles and a potent inducer of antigen-specific cytotoxic immune response and anti-tumor effect in vivo

The major aim of the project was to develop the virus-like particles (VLPs) displaying single or multi-epitope of hepatocellular carcinomas (HCC) in Escherichia coli and to evaluate the effect on inducing Ag-specific CD8(+) T cell response and antitumor efficacy as candidate vaccines. To this end, hepatitis B virus core (HBc) particles were used as a carrier of HCC epitopes. Four HCC epitopes MAGE-1(278-286aa), MAGE-3(271-279aa), AFP1 (158-166aa) or AFP2 (542-550aa) were fused to the 3' terminus of the truncated HBV core gene, respectively, or conjunctively. Not all recombinant plasmids led to expression of chimeric proteins in expression strain E. coli BL21 (DE3), but chimeric proteins which are expressed in inclusion bodies resulted in the formation of complete "mature" VLPs. E. coli-derived truncated HBc(1-144) chimeric protein self-assembled into VLPs that both morphologically and physically are similar to the wild-type ones and they still remained activity after purification and refolding from 6M urea solution. We also showed that they could be internalized and presented by DCs in vitro. Additionally, DCs pulsed with the chimeric HBc-VLPs could induce stronger CTL activity and greater IFN-gamma secretion by responding T cells compared with peptid-pulsed DCs. In the B16-pIR-HH tumor therapy model, the growth of established tumors was significantly inhibited by immunization using VLP-pulsed DCs, resulting in significantly higher survival rate of immunized animals. Thus, the results of the current study have demonstrated the principal possibility of using VLP on the basis of HBcAg for creation of a new type of HCC-specific immunogen.

Baculovirus-derived human immunodeficiency virus type 1 virus-like particles activate dendritic cells and induce ex vivo T-cell responses

We have recently developed a candidate human immunodeficiency virus type 1 (HIV-1) vaccine model based on HIV-1 Pr55(gag) virus-like particles (HIV-VLPs), produced in a baculovirus expression system and presenting a gp120 molecule from a Ugandan HIV-1 isolate of clade A (HIV-VLP(A)s). The HIV-VLP(A)s show the induction in BALB/c mice of systemic and mucosal neutralizing antibodies as well as cytotoxic T lymphocytes, by intraperitoneal as well as intranasal administration. In the present article, the effects of the baculovirus-expressed HIV-VLPs on human immature monocyte-derived dendritic cells (MDDCs) have been evaluated. The HIV-VLPs efficiently induce maturation and activation of MDDCs and are incorporated into MDDCs preferentially via an actin-dependent macropinocytosis and endocytosis. The HIV-VLP-activated MDDCs show enhanced Th1- and Th2-specific cytokine production, and the effects of HIV-VLPs on MDDCs are not mediated through Toll-like receptors 2 and 4 (TLR2 and -4) signaling. Finally, HIV-VLP-loaded MDDCs are able to induce a primary and secondary response in autologous human CD4(+) T cells in an ex vivo immunization assay. Our results on the interaction and processing of baculovirus HIV-VLPs by MDDCs give an insight into the mechanisms underlying the immune response induced by HIV-VLP(A)s in vivo.

Clathrin-mediated endocytosis and lysosomal cleavage of hepatitis B virus capsid-like core particles

The hepatitis B virus (HBV) core particle serves as a protective capsid shell for the viral genome and is highly immunogenic. Recombinant capsid-like core particles are used as effective carriers of foreign T and B cell epitopes and as delivery vehicles for oligonucleotides. The core monomer contains an arginine-rich C terminus that directs core particle attachment to cells via membrane heparan sulfate proteoglycans. Here we investigated the mechanism of recombinant core particle uptake and its intracellular fate following heparan sulfate binding. We found that the core particles are internalized in an energy-dependent manner. Core particle uptake is inhibited by chlorpromazine and by cytosol acidification known to block clathrin-mediated endocytosis but not by nystatin, which blocks lipid raft endocytosis. Particle uptake is abolished by expression of dominant negative forms of eps15 and Rab5, adaptors involved in clathrin-mediated endocytosis and early endosome transport, respectively. Endocytosed particles are transported to lysosomes where the core monomer is endoproteolytically cleaved into its distinct domains. Using protease inhibitors, cathepsin B was identified as the enzyme responsible for core monomer cleavage. Finally we found that monomer cleavage promotes particle dissociation within cells. Together, our results show that HBV capsid-like core particles are internalized through clathrin-mediated endocytosis, leading to lysosomal cleavage of the core monomer and particle dissociation.

Assembly of bacteriophage Qbeta virus-like particles in yeast Saccharomyces cerevisiae and Pichia pastoris

Recombinant bacteriophage Qbeta coat protein (CP), which has been proposed as a promising carrier of foreign epitopes via their incorporation either by gene engineering techniques or by chemical coupling, efficiently self-assembles into virus-like particles (VLPs) when expressed in Escherichia coli. Here, we demonstrate expression and self-assembly of Qbeta CP in yeast Saccharomyces cerevisiae and Pichia pastoris. Production reached 3-4 mg/1g of wet cells for S. cerevisiae and 4-6 mg for P. pastoris, which was about 15-20% and 20-30% of the E. coli expression level, respectively. Qbeta VLPs were easily purified by size-exclusion chromatography in both cases and contained nucleic acid, shown by native agarose gel electrophoresis. The obtained particles were highly immunogenic in mice and the resulting sera recognized both E. coli- and yeast-derived Qbeta VLPs equally well.

Immature monocyte derived dendritic cells gene expression profile in response to Virus-Like Particles stimulation

We have recently developed a candidate HIV-1 vaccine model based on HIV-1 Pr55gag Virus-Like Particles (HIV-VLPs), produced in a baculovirus expression system and presenting a gp120 molecule from an Ugandan HIV-1 isolate of the clade A (HIV-VLPAs). The HIV-VLPAs induce in Balb/c mice systemic and mucosal neutralizing Antibodies as well as cytotoxic T lymphocytes, by intra-peritoneal as well as intra-nasal administration. Moreover, we have recently shown that the baculovirus-expressed HIV-VLPs induce maturation and activation of monocyte-derived dendritic cells (MDDCs) which, in turn, produce Th1- and Th2-specific cytokines and stimulate in vitro a primary and secondary response in autologous CD4+ T cells. In the present manuscript, the effects of the baculovirus-expressed HIV-VLPAs on the genomic transcriptional profile of MDDCs obtained from normal healthy donors have been evaluated. The HIV-VLPA stimulation, compared to both PBS and LPS treatment, modulate the expression of genes involved in the morphological and functional changes characterizing the MDDCs activation and maturation. The results of gene profiling analysis here presented are highly informative on the global pattern of gene expression alteration underlying the activation of MDDCs by HIV-VLPAs at the early stages of the immune response and may be extremely helpful for the identification of exclusive activation markers.

Hepatitis B virus DNA-negative dane particles lack core protein but contain a 22-kDa precore protein without C-terminal arginine-rich domain

DNA-negative Dane particles have been observed in hepatitis B virus (HBV)-infected sera. The capsids of the empty particles are thought to be composed of core protein but have not been studied in detail. In the present study, the protein composition of the particles was examined using new enzyme immunoassays for the HBV core antigen (HBcAg) and for the HBV precore/core proteins (core-related antigens, HBcrAg). HBcrAg were abundant in fractions slightly less dense than HBcAg and HBV DNA. Three times more Dane-like particles were observed in the HBcrAg-rich fraction than in the HBV DNA-rich fraction by electron microscopy. Western blots and mass spectrometry identified the HBcrAg as a 22-kDa precore protein (p22cr) containing the uncleaved signal peptide and lacking the arginine-rich domain that is involved in binding the RNA pregenome or the DNA genome. In sera from 30 HBV-infected patients, HBcAg represented only a median 10.5% of the precore/core proteins in enveloped particles. These data suggest that most of the Dane particles lack viral DNA and core capsid but contain p22cr. This study provides a model for the formation of the DNA-negative Dane particles. The precore proteins, which lack the arginine-rich nucleotide-binding domain, form viral RNA/DNA-negative capsid-like particles and are enveloped and released as empty particles.

A hantavirus nucleocapsid protein segment exposed on hepatitis B virus core particles is highly immunogenic in mice when applied without adjuvants or in the presence of pre-existing anti-core antibodies

Hepatitis B virus (HBV) core particles carrying the amino-terminal 120 amino acids (aa) of the nucleocapsid (N) protein of the hantaviruses Dobrava, Hantaan or Puumala have been demonstrated to be highly immunogenic in mice when complexed with adjuvants. Here we demonstrate that even without adjuvant, these chimeric particles induced high-titered, and strongly cross-reactive N-specific antibody responses in BALB/c and C57BL/6 mice. The induced N-specific antibodies represented all IgG subclasses. Pre-existing core-specific antibodies did not abrogate the induction of an N-specific immune response by a hantavirus N insert presented on core particles. Therefore, chimeric core particles should represent promising vaccine candidates even for anti-core positive humans.

Hemagglutinating virus of Japan protein is efficient for induction of CD4+ T-cell response by a hepatitis B core particle-based HIV vaccine

By using the hepatitis B core (HBc) protein gene as a carrier, HIV-1 env V3 gene was inserted into the carrier gene, and the HIV gene was expressed inside a chimeric HIV-HBc particle (HIV-HBc), which was a unique candidate for induction of HIV-specific CTL activity. This was seen significantly in mice without the need of an adjuvant, because other responses specific for the HIV peptide such as T-cell proliferation and antibody production were not induced. However, when hemagglutinating virus of Japan (HVJ) protein was incorporated into an anionic liposome containing HIV peptide (HIV-HVJ-liposome) and was used as a booster immunization in HIV-HBc primed animals, the HIV-specific T-cell response and enhanced CTL activity were clearly induced in consecutively immunized animals. Furthermore, the HIV-specific humoral immune response was also induced and a neutralization activity was detected in the immune sera. Thus, when an HIV peptide antigen is expressed inside the virus like a particle of HBc, it can induce both cellular and humoral immunities when an HVJ-HIV-liposome, but not an HIV-liposome, is inoculated as the booster antigen. The HVJ-stimulated splenocytes secreted IL-18 and IL-12 to synergistically enhance the secretion of IFN-gamma in vitro. These findings suggest that the HVJ protein is effective at inducing the HIV-specific immunities, if used as part of a booster antigen in the consecutive immunization regimen.

Purification of the recombinant hepatitis B virus core antigen (rHBcAg) produced in the yeast Saccharomyces cerevisiae and comparative observation of its particles by transmission electron microscopy (TEM) and atomic force microscopy (AFM)

Hepatitis B virus core antigen (HBcAg) gene (C gene) was expressed in Saccharomyces cerevisiae and the products (rHBcAg or core particles) were purified from a crude lysate of the yeast by three steps: Sephrose CL-4B chromatography, Sucrose step-gradient ultracentrifugation and CsCl-isopycnic ultracentrifugation. It has been observed that HBcAg was synthesized in yeast cells as a particle consisting of polypeptides with a molecular weight of 21.5 kDa (p21.5). Results of ELISA test and density analysis of CsCl-isopycnic ultracentrifugation indicated that the purified products (rHBcAg particles) with HBcAg antigenicity mainly located at the densities of 1.27 and 1.40 g ml(-1), respectively. Observation and analysis of the purified rHBcAg products by TEM indicated that rHBcAg peptides could mainly self-assemble into two size classes of core particles. The larger particles were approximately 30.1 nm and the smaller were approximately 21.5 nm in mean diameter. Further observation and analysis of the same rHBcAg (core) particles by AFM also indicated that rHBcAg (core) particles were similar to the native HBcAg (core) particles from infected human hepatocytes and mainly composed of two size classes of partides core. The larger particles were approximately 31.3 nm and the smaller were approximately 22.5 nm in mean diameter which was similar to the results obtained by TEM. All results from both TEM and AFM suggested that core particles (capsids) produced in S. cerevisiae possessed dimorphism.

Synthesis of the measles virus nucleoprotein in yeast Pichia pastoris and Saccharomyces cerevisiae

The development of a simple, efficient and cost-effective system for generation of measles virus nucleoprotein might help to upgrade reagents for measles serology. The gene encoding measles nucleoprotein was successfully expressed in two different yeast genera, Pichia pastoris and Saccharomyces cerevisiae, respectively. Both yeast genera synthesized a high level of nucleoprotein, up to 29 and 18% of total cell protein, in P. pastoris and S. cerevisiae, respectively. This protein is one of most abundantly expressed in yeast. After purification nucleocapsid-like particles (NLPs) derived from both yeast genera appeared to be similar to those detected in mammalian cells infected with measles virus. A spontaneous assembly of nucleoprotein into nucleocapsid-like particles in the absence of the viral leader RNA or viral proteins has been shown. Compartmentalisation of recombinant protein into large compact inclusions in the cytoplasm of yeast S. cerevisiae by green fluorescence protein (GFP) fusion has been demonstrated. Sera from measles patients reacted with the recombinant protein expressed in both yeast genera and a simple diagnostic assay to detect measles IgM could be designed on this basis.

Virus-like particles as immunogens

Subunit vaccines based on recombinant proteins can suffer from poor immunogenicity owing to incorrect folding of the target protein or poor presentation to the immune system. Virus-like particles (VLPs) represent a specific class of subunit vaccine that mimic the structure of authentic virus particles. They are recognized readily by the immune system and present viral antigens in a more authentic conformation than other subunit vaccines. VLPs have therefore shown dramatic effectiveness as candidate vaccines. Here, we review the current status of VLPs as vaccines, and discuss the characteristics and problems associated with producing VLPs for different viruses.

Synthesis of mumps virus nucleocapsid protein in yeast Pichia pastoris

The expression of mumps virus nucleocapsid protein in yeast Pichia pastoris was investigated. Viral nucleocapsid proteins usually elicit a strong long-term humoral immune response in patients and experimental animals. Therefore, the detection of antibodies specific to mumps virus nucleoprotein can play an important role in immunoassays for mumps diagnosis. For producing a high-level of recombinant mumps virus nucleoprotein the expression system of yeast P. pastoris was employed. The recombinant nucleocapsid protein was purified by cesium chloride ultracentrifugation of yeast lysates. Electron microscopy of the purified recombinant nucleocapsid protein revealed a herring-bone structure similar to the one discovered in mammalian cells infected with mumps virus. The yield of purified nucleocapsid-like particles from P. pastoris constituted 2.1 mg per 1 g of wet biomass and was considerably higher in comparison to the other expression systems.

Purification of recombinant HBc antigen expressed in Escherichia coli and Pichia pastoris: comparison of size-exclusion chromatography and ultracentrifugation

Hepatitis B virus core protein (HBc) is an important serology marker of hepatitis B infection and patient follow-up. It is an M, 21,000 protein, which has the intrinsic capacity to self-assemble as a capsid-like particle. The hepatitis B core protein has been expressed in Escherichia coli and Pichia pastoris (three different constructions) in order to select a HBc recombinant antigen suitable for serodiagnosis requirements with a cost effective downstream strategy. The expression and purification of the different forms of recombinant HBc have been described. For the last step, ultracentrifugation and size-exclusion chromatography were compared. The morphology of these capsids was observed using an electron microscope. Our data shows that HBc antigen is produced in large quantities in E. coli but some contaminants remained which were associated with the E. coli HBc protein after ultracentrifugation or size-exclusion chromatography. The ultracentrifugation enables a higher purity of HBc antigen to be obtained than size-exclusion chromatography but the latter enables a higher recovery rate. P. pastoris enables the expression and extraction of a highly purified HBc antigen suitable for diagnostic purposes.

Interaction between hepatitis B virus core protein and reverse transcriptase

Previous mutagenesis studies with hepatitis B virus (HBV) suggest that continued interactions with core are required for several steps in genomic replication. To examine core-polymerase (Pol) interactions, insect cells were coinfected with baculovirus constructs that independently expressed core and Pol. The results demonstrated several features with implications that core plays an interactive role with HBV Pol: (i) core coprecipitated with constructs expressing full-length Pol as well as the terminal protein (TP), reverse transcriptase (RT) and RNase H domains of Pol, independently; (ii) coprecipitation of core was not dependent on the presence of an epsilon stem-loop sequence; and (iii) core-Pol complexes migrated as intact capsid particles, as detected by sucrose gradient analysis. To analyze the structural and sequence requirements of core in recognition of Pol, a series of core mutants with two- to four-amino-acid insertions or carboxy-terminal deletions were assessed for Pol interaction. The results indicated that capsid formation is required but not sufficient for interaction with Pol and that the TP and RT domains of Pol have different requirements for interaction with core. To map the core binding sites on Pol, a panel of amino- and carboxy-terminal deletion mutants of the TP and RT domains of Pol were analyzed for interaction with core. At least three separate core binding sites on Pol were detected. This analysis begins to define basic requirements for core-Pol interactions, but further study is necessary to delineate the effects of these interactions on encapsidation and genome replication.

Studies on the structures and antigenic properties of rabies virus glycoprotein analogues produced in yeast cells

We investigated two forms (designated as yGI and yGII) of rabies virus glycoprotein (G) analogues produced in the G cDNA-transfected yeast cells. Molecular weights of yGI and yGII were estimated as 66 and 56 kDa, respectively, according to their relative mobility in SDS-PAGE. Although being produced in large amounts, yGI was present mostly in insoluble forms and hardly extractable with non-ionic detergents. The yGI reacted with polyclonal anti-G antibodies, but did not react with our conformational epitope-specific anti-G monoclonal antibodies (G-MAbs). No protective immunity was induced by yGI in guinea pigs nor in mice. On the other hand, yGII was Triton-soluble, but was only small in amount (at most 1% of total G proteins) and was shown to lack the cytoplasmic domain. The yGII, however, reacted with the G-MAbs and induced protective immunity in guinea pigs as well. When the G-cDNA was expressed in animal cells in culture, a single form (about 66 kDa) of G protein was produced, which displayed similar behaviors as seen in its reactivity with the MAbs and intracellular distribution as seen in the virus-infected cells. These results suggest that most G protein molecules were not processed normally in yeast cells, resulting in abnormal folding and multimer formation, while only a small fraction were occasionally folded normally to have conformational epitopes but were mostly deprived of the C-terminal portion.

Localization of the N terminus of hepatitis B virus capsid protein by peptide-based difference mapping from cryoelectron microscopy

Recently, cryoelectron microscopy of isolated macromolecular complexes has advanced to resolutions below 10 A, enabling direct visualization of alpha-helical secondary structure. To help correlate such density maps with the amino acid sequences of the component proteins, we advocate peptide-based difference mapping, i. e., insertion of peptides, approximately 10 residues long, at targeted points in the sequence and visualization of these peptides as bulk labels in cryoelectron microscopy-derived difference maps. As proof of principle, we have appended an extraneous octapeptide at the N terminus of hepatitis B virus capsid protein and determined its location on the capsid surface by difference imaging at 11 A resolution. Hepatitis B virus capsids are icosahedral particles, approximately 300 A in diameter, made up of T-shaped dimers (subunit Mr, 16-21 kDa, depending on construct). The stems of the Ts protrude outward as spikes, whereas the crosspieces pack to form the contiguous shell. The two N termini per dimer reside on either side of the spike-stem, at the level at which it enters the shell. This location is consistent with formation of the known intramolecular disulfide bond between the cysteines at positions 61 and -7 (in the residual propeptide) in the "e-antigen" form of the capsid protein and has implications for why this clinically important antigen remains unassembled in vivo.

Core particles of hepatitis B virus as carrier for foreign epitopes

To be effective as vaccines, most monomeric proteins and peptides either require chemical coupling to high molecular weight carriers or application together with adjuvants. More recently, recombinant DNA techniques have been used to insert foreign epitopes into proteins with inherent multimerization capacity, such as particle-forming viral capsid or envelope proteins. The core protein of hepatitis B virus (HBcAg), because of its unique structural and immunological properties, has gained widespread interest as a potential antigen carrier. Foreign sequences of up to approximately 40 amino acid residues at the N terminus, 50 or 100 amino acids in the central immunodominant c/e 1 epitope region of HBcAg, and up to 100 or even more residues at the C terminus, did not interfere with particle formation. The humoral immunogenicity of inserted epitopes is determined by the immunogenicity of the peptide itself and its surface exposure, and is influenced by the route of application. The probably flexible and surface-exposed c/e1 region emerged as the most promising insertion site. When applied together with adjuvants approved for human and veterinary use, or even without adjuvants, such chimeric particles induced B and T cell immune responses against the inserted epitopes. In some cases neutralizing antibodies, cytotoxic T cells and protection against challenge with the intact pathogen were demonstrated. Major factors for the potentiated immune response against the foreign epitopes are the multimeric structure of chimeric HBcAg that results in a high epitope density per particle, and the provision of T cell help by the carrier moiety. Beyond its use as subunit vaccine, chimeric HBcAg produced in attenuated Salmonella strains may be applicable as live vaccine.

Effects of mutations within and adjacent to the terminal repeats of hepatitis B virus pregenomic RNA on viral DNA synthesis

The viral polymerase and several cis-acting sequences are essential for hepadnaviral DNA replication, but additional host factors are likely to be involved in this process. We previously identified two sequences, UBS and DBS (upstream and downstream binding sites), present in multiple copies in and adjacent to the pregenomic RNA (pgRNA) terminal redundancy, that were specifically recognized by a 65-kDa host factor, p65. The possible roles of these two sequences in hepatitis B virus (HBV) replication were investigated in the context of the intact viral genome. UBS is contained within the terminal redundancy of pgRNA, and the 5' copy of this sequence is essential for viral replication. Mutations within the central core of UBS ablate p65 binding and selectively block synthesis of plus-strand DNA, without affecting RNA packaging or minus-strand synthesis. The DBS sequence, which is located downstream of the pgRNA polyadenylation site, overlaps the core (C) protein coding region. All mutations introduced into this site severely affected viral replication. However, these effects were shown to result from dominant negative effects of mutant core polypeptides rather than from cis-acting effects on RNA recognition. Thus, the 5' UBS but not DBS sites play important cis-acting roles in HBV DNA replication; however, the involvement of p65 in these roles remains a matter for investigation.

Bactericidal action of lysozymes attached with various sizes of hydrophobic peptides to the C-terminal using genetic modification

The genetic modification of lysozyme was attempted to improve the bactericidal activity against Gram-negative bacteria E. coli. The different lengths of hydrophobic peptides were attached to the C-terminus of the hen egg white lysozyme to investigate the most effective length of the hydrophobic peptides for killing bacteria. The oligonucleotides encoding Phe-Val-Pro (H3), Phe-Phe-Val-Ala-Pro (H5) and Phe-Phe-Val-Ala-Ile-Ile-Pro (H7) were fused to the C-terminus Leu 129 of lysozyme cDNA. The reconstructed cDNAs were inserted into the yeast expression vector. The hydrophobic peptide-fused lysozymes were secreted in the yeast carrying the reconstructed cDNA. Although the hydrophobic peptide-fused lysozymes retained 75 80% lytic activity of the wild-type protein, the bactericidal action to E. coli was greatly increased with the length of hydrophobic peptides. These results suggest that the hydrophobic peptides play an important role in killing Gram-negative bacteria. To elucidate the role of catalytic domain in bactericidal action of the hydrophobic fusion lysozyme (H5-Lz), the mutant hydrophobic lysozyme (H5/E35A-Lz) whose glutamic acid was substituted with alanine at the position 35 was constructed to diminish the catalytic activity. The mutant hydrophobic lysozyme (H5/E35A-Lz) was greatly lost the bactericidal action to E. coli, suggesting that not only the length of hydrophobic peptide fused to C-terminus but also the catalytic domain is important for the bactericidal action of the hydrophobic peptide-fused lysozyme.