Generation of hepatitis C virus-like particles by use of a recombinant vesicular stomatitis virus vector

Harnessing Nanovaccines for Effective Immunization─A Special Concern on COVID-19: Facts, Fidelity, and Future Prospective

Nanotechnology has emerged as a transformative pathway in vaccine research and delivery. Nanovaccines, encompassing lipid and nonlipid formulations, exhibit considerable advantages over traditional vaccine techniques, including enhanced antigen stability, heightened immunogenicity, targeted distribution, and the potential for codelivery with adjuvants or immune modulators. This review provides a comprehensive overview of the latest advancements and applications of lipid and non-lipid-based nanovaccines in current vaccination strategies for immunization. The review commences by outlining the fundamental concepts underlying lipid and nonlipid nanovaccine design before delving into the diverse components and production processes employed in their development. Subsequently, a comparative analysis of various nanocarriers is presented, elucidating their distinct physicochemical characteristics and impact on the immune response, along with preclinical and clinical studies. The discussion also highlights how nanotechnology enables the possibility of personalized and combined vaccination techniques, facilitating the creation of tailored nanovaccines to meet the individual patient needs. The ethical aspects concerning the use of nanovaccines, as well as potential safety concerns and public perception, are also addressed. The study underscores the gaps and challenges that must be overcome before adopting nanovaccines in clinical practice. This comprehensive analysis offers vital new insights into lipid and nonlipid nanovaccine status. It emphasizes the significance of continuous research, collaboration among interdisciplinary experts, and regulatory measures to fully unlock the potential of nanotechnology in enhancing immunization and ensuring a healthier, more resilient society.

A vesicular stomatitis virus-based African swine fever vaccine prototype effectively induced robust immune responses in mice following a single-dose immunization

Introduction

African swine fever (ASF) is a highly contagious hemorrhagic fever disease in pigs caused by African swine fever virus (ASFV). It is very difficult to control and prevent ASF outbreaks due to the absence of safe and effective vaccines.

Methods

In order to develop a safe and effective ASF vaccine for the control and prevention of ASF, two ASFV recombinant vesicular stomatitis virus (VSV) live vector vaccine prototypes, containing the gene of p72, and a chimera of p30 and p54, were developed based on the replication-competent VSV, and named VSV-p72 and VSV-p35. The immune potency of VSV-p72 or VSV-p35 alone and in combination was evaluated in BALB/c mice via intramuscular and intranasal vaccination.

Results

The results indicated that whether administered alone or in combination, the two vaccine prototypes showed acceptable safety in mice and, more importantly, induced high-level specific antibodies against p72, p30, and p54 of ASFV and a strong cellular immune response 28 days after vaccination. The sera from mice vaccinated with the vaccine prototypes significantly inhibited ASFV from infecting porcine alveolar macrophages (PAMs) in vitro. Most notably, the immunized sera from a mixture of VSV-p35 and VSV-p72 inhibited ASFV from infecting PAMs, with an inhibition rate of up to 78.58%.

Conclusion

Overall, our findings suggest that ASFV recombinant VSV live vector vaccine prototypes may become a promising candidate vaccine for the control and prevention of ASF.

Optimal Expression, Function, and Immunogenicity of an HIV-1 Vaccine Derived from the Approved Ebola Vaccine, rVSV-ZEBOV

Vesicular stomatitis virus (VSV) remains an attractive platform for a potential HIV-1 vaccine but hurdles remain, such as selection of a highly immunogenic HIV-1 Envelope (Env) with a maximal surface expression on recombinant rVSV particles. An HIV-1 Env chimera with the transmembrane domain (TM) and cytoplasmic tail (CT) of SIVMac239 results in high expression on the approved Ebola vaccine, rVSV-ZEBOV, also harboring the Ebola Virus (EBOV) glycoprotein (GP). Codon-optimized (CO) Env chimeras derived from a subtype A primary isolate (A74) are capable of entering a CD4+/CCR5+ cell line, inhibited by HIV-1 neutralizing antibodies PGT121, VRC01, and the drug, Maraviroc. The immunization of mice with the rVSV-ZEBOV carrying the CO A74 Env chimeras results in anti-Env antibody levels as well as neutralizing antibodies 200-fold higher than with the NL4-3 Env-based construct. The novel, functional, and immunogenic chimeras of CO A74 Env with the SIV_Env-TMCT within the rVSV-ZEBOV vaccine are now being tested in non-human primates.

A tool with many applications: vesicular stomatitis virus in research and medicine

INTRODUCTION

Vesicular stomatitis virus (VSV) has long been a useful research tool in virology and recently become an essential part of medicinal products. Vesiculovirus research is growing quickly following its adaptation to clinical gene and cell therapy and oncolytic virotherapy.

AREAS COVERED

This article reviews the versatility of VSV as a research tool and biological reagent, its use as a viral and vaccine vector delivering therapeutic and immunogenic transgenes and an oncolytic virus aiding cancer treatment. Challenges such as the immune response against such advanced therapeutic medicinal products and manufacturing constraints are also discussed.

EXPERT OPINION

The field of in vivo gene and cell therapy is advancing rapidly with VSV used in many ways. Comparison of VSV's use as a versatile therapeutic reagent unveils further prospects and problems for each application. Overcoming immunological challenges to aid repeated administration of viral vectors and minimizing harmful host-vector interactions remains one of the major challenges. In the future, exploitation of reverse genetic tools may assist the creation of recombinant viral variants that have improved onco-selectivity and more efficient vaccine vector activity. This will add to the preferential features of VSV as an excellent advanced therapy medicinal product (ATMP) platform.

Hepatitis C virus: Morphogenesis, infection and therapy

Hepatitis C virus (HCV) is a major cause of liver diseases including liver cirrhosis and hepatocellular carcinoma. Approximately 3% of the world population is infected with HCV. Thus, HCV infection is considered a public healthy challenge. It is worth mentioning, that the HCV prevalence is dependent on the countries with infection rates around 20% in high endemic countries. The review summarizes recent data on HCV molecular biology, the physiopathology of infection (immune-mediated liver damage, liver fibrosis and lipid metabolism), virus diagnostic and treatment. In addition, currently available in vitro, ex vivo and animal models to study the virus life cycle, virus pathogenesis and therapy are described. Understanding of both host and viral factors may in the future lead to creation of new approaches in generation of an efficient therapeutic vaccine.

Preclinical Development and Production of Virus-Like Particles As Vaccine Candidates for Hepatitis C

Hepatitis C Virus (HCV) infects 2% of the world’s population and is the leading cause of liver disease and liver transplantation. It poses a serious and growing worldwide public health problem that will only be partially addressed with the introduction of new antiviral therapies. However, these treatments will not prevent re-infection particularly in high risk populations. The introduction of a HCV vaccine has been predicted, using simulation models in a high risk population, to have a significant effect on reducing the incidence of HCV. A vaccine with 50 to 80% efficacy targeted to high-risk intravenous drug users could dramatically reduce HCV incidence in this population. Virus like particles (VLPs) are composed of viral structural proteins which self-assemble into non-infectious particles that lack genetic material and resemble native viruses. Thus, VLPs represent a safe and highly immunogenic vaccine delivery platform able to induce potent adaptive immune responses. Currently, many VLP-based vaccines have entered clinical trials, while licensed VLP vaccines for hepatitis B virus (HBV) and human papilloma virus (HPV) have been in use for many years. The HCV core, E1 and E2 proteins can self-assemble into immunogenic VLPs while inclusion of HCV antigens into heterogenous (chimeric) VLPs is also a promising approach. These VLPs are produced using different expression systems such as bacterial, yeast, mammalian, plant, or insect cells. Here, this paper will review HCV VLP-based vaccines and their immunogenicity in animal models as well as the different expression systems used in their production.

Development of an HIV vaccine using a vesicular stomatitis virus vector expressing designer HIV-1 envelope glycoproteins to enhance humoral responses

Vesicular stomatitis virus (VSV), like many other Rhabdoviruses, have become the focus of intense research over the past couple of decades based on their suitability as vaccine vectors, transient gene delivery systems, and as oncolytic viruses for cancer therapy. VSV as a vaccine vector platform has multiple advantages over more traditional viral vectors including low level, non-pathogenic replication in diverse cell types, ability to induce both humoral and cell-mediate immune responses, and the remarkable expression of foreign proteins cloned into multiple intergenic sites in the VSV genome. The utility and safety of VSV as a vaccine vector was recently demonstrated near the end of the recent Ebola outbreak in West Africa where VSV pseudotyped with the Ebola virus (EBOV) glycoprotein was proven safe in humans and provided protective efficacy against EBOV in a human phase III clinical trial. A team of Canadian scientists, led by Dr. Gary Kobinger, is now working with International AIDS Vaccine Initiative (IAVI) in developing a VSV-based HIV vaccine that will combine unique Canadian research on the HIV-1 Env glycoprotein and on the VSV vaccine vector. The goal of this collaboration is to develop a vaccine with a robust and potent anti-HIV immune response with an emphasis on generating quality antibodies to protect against HIV challenges.

A vesicular stomatitis virus-based mucosal vaccine promotes dendritic cell maturation and elicits preferable immune response against coxsackievirus B3 induced viral myocarditis

Recombinant vesicular stomatitis virus (VSV) is widely used as a vaccine platform. However, the capacity of VSV-based vaccines to induce mucosal immunity has not been fully investigated. In the present study, a recombinant VSV expressing coxsackievirus B3 (CVB3) major immunogen VP1 has been generated and the immune protection elicited by VSV-VP1 was evaluated. We demonstrated that intranasal delivery of VSV-VP1 can induce a potent antigen-specific mucosal immune response as well as a systemic immune response, particularly the induction of polyfunctional T cells. Importantly, mice immunized with VSV-VP1 were better protected against CVB3-induced viral myocarditis than those receiving a chitosan-formulated DNA vaccine. Increased dendritic cell (DC) maturation in the mesenteric lymph node (MLN) was observed in the mice vaccinated with VSV-VP1, which could be a potential mechanism for the protective immune response. These findings support VSV as a viral delivery vector that can induce robust mucosal immunity that should be considered for further vaccine development.

Enhanced virus-specific CD8+ T cell responses by Listeria monocytogenes-infected dendritic cells in the context of Tim-3 blockade

In this study, we engineered Listeria monocytogens (Lm) by deleting the LmΔactA/ΔinlB virulence determinants and inserting HCV-NS5B consensus antigens to develop a therapeutic vaccine against hepatitis C virus (HCV) infection. We tested this recombinant Lm-HCV vaccine in triggering of innate and adaptive immune responses in vitro using immune cells from HCV-infected and uninfected individuals. This live-attenuated Lm-HCV vaccine could naturally infect human dendritic cells (DC), thereby driving DC maturation and antigen presentation, producing Th1 cytokines, and triggering CTL responses in uninfected individuals. However, vaccine responses were diminished when using DC and T cells derived from chronically HCV-infected individuals, who express higher levels of inhibitory molecule Tim-3 on immune cells. Notably, blocking Tim-3 signaling significantly improved the innate and adaptive immune responses in chronically HCV-infected patients, indicating that novel strategies to enhance the potential of antigen presentation and cellular responses are essential for developing an effective therapeutic vaccine against HCV infection.

Progress in research of genotypes of hepatitis C virus

Hepatitis C virus (HCV), belonging to the Flaviviridae family, is divided into six genotypes and different subtypes. There are four nomenclatures for HCV, of which the nomenclature system proposed by Simmonds et al. is widely applied overseas in recent years. HCV genotypes have obvious geographical variation and show significant epidemiological differences. Five methods are currently available for genotyping HCV, and each has its own advantages and disadvantages. HCV genotypes closely correlate with the severity, course, progression, treatment, and outcome of hepatitis C. The therapeutic effect for different HCV genotypes varies, and IL-28B polymorphism is a predictor of sustained virological response to treatment among various HCV genotypes. The diversity of HCV genotypes brings certain difficulty to vaccine development. Some success has been achieved in the development of HCV vaccine in animals. The main purpose of the present article is to review the recent progress in research of genotypes of HCV in terms of genotyping methods, associations between genotypes and epidemiological significance, severity of disease, and antiviral treatment response, and vaccine development.

The immune response to a vesicular stomatitis virus vaccine vector is independent of particulate antigen secretion and protein turnover rate

Vesicular stomatitis virus (VSV) is a highly cytopathic virus being developed as a vaccine vector due to its ability to induce strong protective T cell and antibody responses after a single dose. However, little is known regarding the mechanisms underlying the potent immune responses elicited by VSV. We previously generated a VSV vector expressing the hepatitis B virus middle envelope surface glycoprotein (MS) that induces strong MS-specific T cell and antibody responses in mice. After synthesis in the cytoplasm, the MS protein translocates to the endoplasmic reticulum, where it forms subviral particles that are secreted from the cell. To better understand the contributions of secreted and intracellular protein to the VSV-induced immune response, we produced a vector expressing a secretion-deficient MS mutant (MS(C69A)) and compared the immunogenicity of this vector to that of the wild-type VSV-MS vector in mice. As expected, the MS(C69A) protein was not secreted from VSV-infected cells and displayed enhanced proteasome-mediated degradation. Surprisingly, despite these differences in intracellular protein processing, the T cell and antibody responses generated to MS(C69A) were comparable to those elicited by virus expressing wild-type MS protein. Therefore, when it is expressed from VSV, the immune responses to MS are independent of particulate antigen secretion and the turnover rate of cytoplasmic protein. These results are consistent with a model in which the immune responses to VSV are strongly influenced by the replication cycle of the vector and demonstrate that characteristics of the vector have the capacity to affect vaccine efficacy more than do the properties of the antigen itself.

Vesicular stomatitis virus as a vector to deliver virus-like particles of human norovirus: a new vaccine candidate against an important noncultivable virus

Human norovirus (HuNoV) is a major causative agent of food-borne gastroenteritis worldwide. Currently, there are no vaccines or effective therapeutic interventions for this virus. Development of an attenuated vaccine for HuNoV has been hampered by the inability to grow the virus in cell culture. Thus, a vector-based vaccine may be ideal. In this study, we constructed a recombinant vesicular stomatitis virus (rVSV-VP1) expressing VP1, the major capsid protein of HuNoV. Expression of the capsid protein by VSV resulted in the formation of HuNoV virus-like particles (VLPs) that are morphologically and antigenically similar to native virions. Recombinant rVSV-VP1 was attenuated in cultured mammalian cells as well as in mice. Mice inoculated with a single dose of rVSV-VP1 through intranasal and oral routes stimulated a significantly stronger humoral and cellular immune response than baculovirus-expressed VLP vaccination. Moreover, we demonstrated that mice inoculated with rVSV-VP1 triggered a comparable level of fecal and vaginal IgA antibody. Taken together, the VSV recombinant system not only provides a new approach to generate HuNoV VLPs in vitro but also a new avenue for the development of vectored vaccines against norovirus and other noncultivable viruses.

A vesicular stomatitis virus-based hepatitis B virus vaccine vector provides protection against challenge in a single dose

As one of the world's most common infectious diseases, hepatitis B virus (HBV) is a serious worldwide public health problem, with HBV-associated liver disease accounting for more than half a million deaths each year. Although there is an effective prophylactic vaccine currently available to prevent infection, it has a number of characteristics that are suboptimal: multiple doses are needed to induce long-lasting immunity, immunity declines over time, it does not elicit protection in some individuals, and it is not effective therapeutically. We produced a recombinant vesicular stomatitis virus (VSV)-based vaccine vector expressing the HBV middle envelope surface protein (MS) and found that this vector was able to efficiently generate a strong HBs-specific antibody response following a single immunization in mice. A single immunization with the VSV-MS vector also induced robust CD8 T-cell activation. The CD8 T-cell response was greater in magnitude and broader in specificity than the response generated by a vaccinia virus-based vaccine vector or by recombinant protein immunization. Furthermore, a single VSV-MS immunization provided protection against virus challenge in mice. Given the similar antibody titers and superior T-cell responses elicited from a single immunization, a VSV-based HBV vaccine may have advantages over the current recombinant protein vaccine.

Characterization of hepatitis C virus core protein multimerization and membrane envelopment: revelation of a cascade of core-membrane interactions

The molecular basis underlying hepatitis C virus (HCV) core protein maturation and morphogenesis remains elusive. We characterized the concerted events associated with core protein multimerization and interaction with membranes. Analyses of core proteins expressed from a subgenomic system showed that the signal sequence located between the core and envelope glycoprotein E1 is critical for core association with endoplasmic reticula (ER)/late endosomes and the core's envelopment by membranes, which was judged by the core's acquisition of resistance to proteinase K digestion. Despite exerting an inhibitory effect on the core's association with membranes, (Z-LL)(2)-ketone, a specific inhibitor of signal peptide peptidase (SPP), did not affect core multimeric complex formation, suggesting that oligomeric core complex formation proceeds prior to or upon core attachment to membranes. Protease-resistant core complexes that contained both innate and processed proteins were detected in the presence of (Z-LL)(2)-ketone, implying that core envelopment occurs after intramembrane cleavage. Mutations of the core that prevent signal peptide cleavage or coexpression with an SPP loss-of-function D219A mutant decreased the core's envelopment, demonstrating that SPP-mediated cleavage is required for core envelopment. Analyses of core mutants with a deletion in domain I revealed that this domain contains sequences crucial for core envelopment. The core proteins expressed by infectious JFH1 and Jc1 RNAs in Huh7 cells also assembled into a multimeric complex, associated with ER/late-endosomal membranes, and were enveloped by membranes. Treatment with (Z-LL)(2)-ketone or coexpression with D219A mutant SPP interfered with both core envelopment and infectious HCV production, indicating a critical role of core envelopment in HCV morphogenesis. The results provide mechanistic insights into the sequential and coordinated processes during the association of the HCV core protein with membranes in the early phase of virus maturation and morphogenesis.

Cellular models for the screening and development of anti-hepatitis C virus agents

Investigations on the biology of hepatitis C virus (HCV) have been hampered by the lack of small animal models. Efforts have therefore been directed to designing practical and robust cellular models of human origin able to support HCV replication and production in a reproducible, reliable and consistent manner. Many different models based on different forms of virions and hepatoma or other cell types have been described including virus-like particles, pseudotyped particles, subgenomic and full length replicons, virion productive replicons, immortalised hepatocytes, fetal and adult primary human hepatocytes. This review focuses on these different cellular models, their advantages and disadvantages at the biological and experimental levels, and their respective use for evaluating the effect of antiviral molecules on different steps of HCV biology including virus entry, replication, particles generation and excretion, as well as on the modulation by the virus of the host cell response to infection.

Antigen delivery systems for veterinary vaccine development. Viral-vector based delivery systems

The recent advances in molecular genetics, pathogenesis and immunology have provided an optimal framework for developing novel approaches in the rational design of vaccines effective against viral epizootic diseases. This paper reviews most of the viral-vector based antigen delivery systems (ADSs) recently developed for vaccine testing in veterinary species, including attenuated virus and DNA and RNA viral vectors. Besides their usefulness in vaccinology, these ADSs constitute invaluable tools to researchers for understanding the nature of protective responses in different species, opening the possibility of modulating or potentiating relevant immune mechanisms involved in protection.

Association between expression of the H histo-blood group antigen, alpha1,2fucosyltransferases polymorphism of wild rabbits, and sensitivity to rabbit hemorrhagic disease virus

RHDV (rabbit hemorrhagic disease virus) is a highly virulent calicivirus that has become a major cause of mortality in wild rabbit populations (Oryctolagus cuniculus). It binds to the histo-blood group antigen (HBGA) H type 2 which requires an alpha1,2fucosyltransferase for its synthesis. In rabbit, three alpha1,2fucosyltransferases genes are known, Fut1, Fut2, and Sec1. Nonfunctional alleles at any of these loci could potentially confer resistance to RHDV, similar to human FUT2 alleles that determine the nonsecretor phenotype and resistance to infection by various NoV strains. In this study, we looked for the presence of H type 2 on buccal epithelial cells of wild rabbits from two geographic areas under RHDV pressure and from one RHDV-free area. Some animals with diminished H type 2 expression were found in the three populations (nonsecretor-like phenotype). Their frequency markedly increased according to the RHDV impact, suggesting that outbreaks selected survivors with low expression of the virus ligand. Polymorphisms of the Fut1, Fut2, and Sec1 coding regions were determined among animals that either died or survived outbreaks. The Fut2 and Sec1 genes presented a high polymorphism and the frequency of one Sec1 allele was significantly elevated, over 6-fold, among survivors. Sec1 enzyme variants showed either moderate, low, or undetectable catalytic activity, whereas all variant Fut2 enzymes showed strong catalytic activity. This functional analysis of the enzymes encoded by each Fut2 and Sec1 allele suggests that the association between one Sec1 allele and survival might be explained by a deficit of alpha1,2fucosyltransferase expression rather than by impaired catalytic activity.

Recombinant vesicular stomatitis virus-based west Nile vaccine elicits strong humoral and cellular immune responses and protects mice against lethal challenge with the virulent west Nile virus strain LSU-AR01

Vesicular stomatitis virus (VSV) has been extensively utilized as a viral vector system for the induction of protective immune responses against a variety of pathogens. We constructed recombinant VSVs specifying either the Indiana or Chandipura virus G glycoprotein and expressing the West Nile virus (WNV) envelope (E) glycoprotein. Mice were intranasally vaccinated using a prime (Indiana)-boost (Chandipura) immunization approach and challenged with the virulent WNV-LSU-AR01. Ninety-percent (9 of 10) of the vaccinated mice survived as compared to 10% of the mock-vaccinated mice after WNV lethal challenge. Histopathological examination of brain tissues revealed neuronal necrosis in mock-vaccinated mice but not in vaccinated mice, and vaccinated, but not mock-vaccinated mice developed a strong neutralizing antibody response against WNV. Extensive immunological analysis using polychromatic flow cytometry staining revealed that vaccinated, but not mock-vaccinated mice developed robust cellular immune responses as evidenced by up-regulation of CD4⁺ CD154⁺ IFNγ⁺ T cells in vaccinated, but not mock-vaccinated mice. Similarly, vaccinated mice developed robust E-glycoprotein-specific CD8⁺ T cell immune responses as evidenced by the presence of a high percentage of CD8⁺ CD62L^low IFNγ⁺ cells. In addition, a sizeable population of CD8⁺ CD69⁺ cells was detected indicating E-specific activation of mature T cells and CD4⁺ CD25⁺ CD127^low T regulatory (T reg) cells were down-regulated. These results suggest that VSV-vectored vaccines administered intranasally can efficiently induce protective humoral and cellular immune responses against WNV infections.

Vesicular stomatitis virus: re-inventing the bullet

As our understanding of the molecular aspects of human disease increases, it is becoming possible to create designer therapeutics that are exquisitely targeted and have greater efficacy and fewer side effects. One class of targeted biological agents that has benefited from recent advances in molecular biology is designer viruses. Vesicular stomatitis virus (VSV) is normally relatively innocuous but can be engineered to target cancer cells or to stimulate immunity against diseases such as AIDS or influenza. Strains of VSV that induce or direct the production of interferon are superior to wild-type strains of the virus for inducing oncolysis. These strains might also make better vaccine vectors. In this review, some of the features that make VSV an excellent platform for the development of a range of viral therapeutics are discussed.

Trans-encapsidation of hepatitis C virus subgenomic replicon RNA with viral structure proteins

A trans-packaging system for hepatitis C virus (HCV) subgenomic replicon RNAs was developed. HCV subgenomic replicon was efficiently encapsidated by the HCV structural proteins that were stably expressed in trans under the control of a mammalian promoter. Infectious HCV-like particles (HCV-LPs), established a single-round infection, were produced and released into culture medium in titers of up to 10(3) focus forming units/ml. Expression of NS2 protein with structural proteins (core, E1, E2, and p7) was shown to be critical for the infectivity of HCV-LPs. Anti-CD81 treatment decreased the number of infected cells, suggesting that HCV-LPs infected cells in a CD81-dependent manner. The packaging cell line should be useful both for the production of single-round infectious HCV-LPs to elucidate the mechanisms of HCV assembly, particle formation and infection to host cells, and for the development of HCV replicon-based vaccines.

Critical role of virion-associated cholesterol and sphingolipid in hepatitis C virus infection

In this study, we establish that cholesterol and sphingolipid associated with hepatitis C virus (HCV) particles are important for virion maturation and infectivity. In a recently developed culture system enabling study of the complete life cycle of HCV, mature virions were enriched with cholesterol as assessed by the molar ratio of cholesterol to phospholipid in virion and cell membranes. Depletion of cholesterol from the virus or hydrolysis of virion-associated sphingomyelin almost completely abolished HCV infectivity. Supplementation of cholesterol-depleted virus with exogenous cholesterol enhanced infectivity to a level equivalent to that of the untreated control. Cholesterol-depleted or sphingomyelin-hydrolyzed virus had markedly defective internalization, but no influence on cell attachment was observed. Significant portions of HCV structural proteins partitioned into cellular detergent-resistant, lipid-raft-like membranes. Combined with the observation that inhibitors of the sphingolipid biosynthetic pathway block virion production, but not RNA accumulation, in a JFH-1 isolate, our findings suggest that alteration of the lipid composition of HCV particles might be a useful approach in the design of anti-HCV therapy.

Hepatitis C viral life cycle

Hepatitis C virus (HCV) has been recognized as a major cause of chronic liver diseases worldwide. Molecular studies of the virus became possible with the successful cloning of its genome in 1989. Although much work remains to be done regarding early and late stages of the HCV life cycle, significant progress has been made with respect to the molecular biology of HCV, especially the viral protein processing and the genome replication. This review summarizes our current understanding of genomic organization of HCV, features of the viral protein characteristics, and the viral life cycle.

Lifestyle-related diseases of the digestive system: a new in vitro model of hepatitis C virion production: application of basic research on hepatitis C virus to clinical medicine

The hepatitis C virus (HCV) is an enveloped virus with a single positive-strand RNA genome of about 9.6 kb. It is a major cause of liver disease worldwide. Clear understanding of the viral life cycle has been hampered by the lack of a robust cell culture system. While the development of the HCV replicon system was a major breakthrough, infectious virions could not be produced with the replicon system. Recently, several groups have reported producing HCV virions using in vitro systems. One of these is a replicon system, but with the special genotype 2a strain JFH-1. Another is a DNA transfection system, with the construct containing the cDNA of the known infectious HCV genotype 1b flanked by two ribozymes. The development of these models further extends the repertoire of tools available for the study of HCV biology, and in particular, they may help to elucidate the molecular details of hepatitis C viral assembly and release. This review discusses the progression of experimental strategies related to HCV and how these strategies may be applied to clinical medicine.

Molecular biology of hepatitis C virus

Infection with hepatitis C virus (HCV), which is distributed worldwide, often becomes persistent, causing chronic hepatitis, cirrhosis, and hepatocellular carcinoma. For many years, the characterization of the HCV genome and its products has been done by heterologous expression systems because of the lack of a productive cell culture system. The development of the HCV replicon system is a highlight of HCV research and has allowed examination of the viral RNA replication in cell culture. Recently, a robust system for production of recombinant infectious HCV has been established, and classical virological techniques are now able to be applied to HCV. This development of reverse genetics-based experimental tools in HCV research can bring a greater understanding of the viral life cycle and pathogenesis of HCV-induced diseases. This review summarizes the current knowledge of cell culture systems for HCV research and recent advances in the investigation of the molecular virology of HCV.

The hepatitis C virus life cycle as a target for new antiviral therapies

The burden of disease consequent to hepatitis C virus (HCV) infection has been well described and is expected to increase dramatically over the next decade. Current approved antiviral therapies are effective in eradicating the virus in approximately 50% of infected patients. However, pegylated interferon and ribavirin-based therapy is costly, prolonged, associated with significant adverse effects, and not deemed suitable for many HCV-infected patients. As such, there is a clear and pressing need for the development of additional agents that act through alternate or different mechanisms, in the hope that such regimens could lead to enhanced response rates more broadly applicable to patients with hepatitis C infection. Recent basic science enhancements in HCV cell culture systems and replication assays have led to a broadening of our understanding of many of the mechanisms of HCV replication and, therefore, potential novel antiviral targets. In this article, we have attempted to highlight important new information as it relates to our understanding of the HCV life cycle. These steps broadly encompass viral attachment, entry, and fusion; viral RNA translation; posttranslational processing; HCV replication; and viral assembly and release. In each of these areas, we present up-to-date knowledge of the relevant aspects of that component of the viral life cycle and then describe the preclinical and clinical development targets and pathways being explored in the translational and clinical settings.

Structural requirements for assembly and homotypic interactions of the hepatitis C virus core protein

The hepatitis C virus (HCV) core protein is involved in the assembly of nucleocapsid particles, as well as regulation of cellular and viral gene expression. To investigate the biological properties of the viral core protein and viral RNA assembly, two recombinant core proteins, the mature core protein (named C179) and a C-terminal truncated protein (named C124), were expressed and purified. To confirm their ability to generate viral particles, the production of nucleocapsid-like particles was monitored using transmission electron microscopy (EM). The EM analysis revealed that exposure of these proteins to the 5' untranslated region (5' UTR) of the viral RNA resulted in generation of spherical particles of 30-140nm in diameter. Interestingly, a cross-linking analysis revealed that C124 required an RNA component for homotypic interactions. In contrast, C179 successfully assembled in the absence of nucleic acids. Additionally, RNA-mediated conversion of the C124 structure into a more stable state was maintained even after RNase treatment. Therefore, our results indicate that the basic N-terminal domain of the viral core protein utilizes RNA components to induce conformational changes or efficient homotypic interactions, while the C-terminal domain may contain key peptide sequences for initiating spontaneous multimerization at the early stages of viral assembly.

Recombinant vesicular stomatitis virus as an HIV-1 vaccine vector

Recombinant vesicular stomatitis virus (rVSV) is currently under evaluation as a human immunodeficiency virus (HIV)-1 vaccine vector. The most compelling reasons to develop rVSV as a vaccine vector include a very low seroprevalence in humans, the ability to infect and robustly express foreign antigens in a broad range of cells, and vigorous growth in continuous cell lines used for vaccine manufacture. Numerous preclinical studies with rVSV vectors expressing antigens from a variety of human pathogens have demonstrated the versatility, flexibility, and potential efficacy of the rVSV vaccine platform. When administered to nonhuman primates (NHPs), rVSV vectors expressing HIV-1 Gag and Env elicited robust HIV-1-specific cellular and humoral immune responses, and animals immunized with rVSV vectors expressing simian immunodeficiency virus (SIV) Gag and HIV Env were protected from AIDS after challenge with a pathogenic SIV/HIV recombinant. However, results from an exploratory neurovirulence study in NHPs indicated that these prototypic rVSV vectors might not be adequately attenuated for widespread use in human populations. To address this safety concern, a variety of different attenuation strategies, designed to produce a range of further attenuated rVSV vectors, are currently under investigation. Additional modifications of further attenuated rVSV vectors to upregulate expression of HIV-1 antigens and coexpress molecular adjuvants are also being developed in an effort to balance immunogenicity and attenuation.

Evaluating replication-defective vesicular stomatitis virus as a vaccine vehicle

We have generated replication-competent (VSV-C/E1/E2) and nonpropagating (VSVDeltaG-C/E1/E2) vesicular stomatitis virus (VSV) contiguously expressing the structural proteins of hepatitis C virus (HCV; core [C] and glycoproteins E1 and E2) and report on their immunogenicity in murine models. VSV-C/E1/E2 and VSVDeltaG-C/E1/E2 expressed high levels of HCV C, E1, and E2, which were authentically posttranslationally processed. Both VSV-expressed HCV E1-E2 glycoproteins were found to form noncovalently linked heterodimers and appeared to be correctly folded, as confirmed by coimmunoprecipitation analysis using conformationally sensitive anti-HCV-E2 monoclonal antibodies (MAbs). Intravenous or intraperitoneal immunization of BALB/c mice with VSV-C/E1/E2 or VSVDeltaG-C/E1/E2 resulted in significant and surprisingly comparable HCV core or E2 antibody responses compared to those of control mice. In addition, both virus types generated HCV C-, E1-, or E2-specific gamma interferon (IFN-gamma)-producing CD8(+) T cells, as determined by enzyme-linked immunospot (ELISPOT) analysis. Mice immunized with VSVDeltaG-C/E1/E2 were also protected against the formation of tumors expressing HCV E2 (CT26-hghE2t) and exhibited CT26-hghE2t-specific IFN-gamma-producing and E2-specific CD8(+) T-cell activity. Finally, recombinant vaccinia virus (vvHCV.S) expressing the HCV structural proteins replicated at significantly lower levels when inoculated into mice immunized with VSV-C/E1/E2 or VSVDeltaG-C/E1/E2, but not with control viruses. Our data therefore illustrate that potentially safer replication-defective VSV can be successfully engineered to express high levels of antigenically authentic HCV glycoproteins. In addition, this strategy may therefore serve in effective vaccine and immunotherapy-based approaches to the treatment of HCV-related disease.

Development of prophylactic and therapeutic vaccines against hepatitis C virus

The hepatitis C virus was discovered 15 years ago as the agent responsible for most cases of transfusion-associated hepatitis non-A, non-B. At present, 180 million people worldwide are estimated to be infected with the virus, producing severe and progressive liver disease in millions and representing the most common reason for liver transplantation in adults. Although the spread of the virus can be halted by the application of primary prevention strategies, such as routine testing of blood donations, inactivation of blood products and systematic use of disposable needles and syringes, the development of a prophylactic vaccine could facilitate the control of this infection and protect those at high risk of being infected with hepatitis C virus. As the present therapy of chronic hepatitis C virus infections, consisting of a combined administration of pegylated interferon-alpha and ribavirin, is only successful in 50% of patients infected with genotype 1, and is costly and associated with serious side effects, there is an urgent need for better tolerated and more effective treatment modalities, and a therapeutic vaccine may be the solution. This review first provides an overview of the present knowledge regarding the interaction between the virus and immune system of the infected host, with special attention given to the possible mechanisms responsible for chronic evolution of the infection. The numerous candidate vaccines that have been developed in the past 10 years are discussed, including the studies in which their immunogenicity has been examined in rodents and chimpanzees. Finally, the only studies of therapeutic vaccines performed in humans to date are considered.

Virus morphogenesis and viral entry as alternative targets for novel hepatitis C antivirals

Hepatitis C virus (HCV) infection is a major public health concern. New antiviral drugs are required urgently to complement and improve the efficacy of current chemotherapies. Molecules specifically targeting viral enzymes are the most attractive in terms of drug development and are, therefore, the most studied. However, an antiviral strategy based uniquely on the utilization of this type of target is expected to encounter problems caused by the emergence of viral escape mutants as has already been widely described for HIV and hepatitis B virus. HCV morphogenesis and viral entry represent interesting, and yet unexploited, novel molecular targets. Inhibitors of morphogenesis have recently been identified and studied in different virus–cell systems. Some of these are currently being evaluated in clinical trials against HCV. This review focuses on HCV morphogenesis, viral entry and inhibition and presents clinical development perspectives of this new generation of antivirals.

Characterization of HCV-like particles produced in a human hepatoma cell line by a recombinant baculovirus

Although processing of the hepatitis C virus (HCV) polyprotein and characterization of each of its viral proteins have been described in detail, analysis of the structure and assembly of HCV particles has been hampered by the lack of a robust cell culture system to support efficient replication of HCV. In this study, we generated HCV-like particles (HCV-LP) using a recombinant baculovirus encoding structural and a part of non-structural proteins in a human hepatoma cell line. The HCV-LP exhibited a buoyant density of 1.17 g/ml in CsCl equilibrium gradient and particles of 40 to 50 nm in diameter. Binding of the HCV-LP to human hepatoma cells was partially inhibited by the treatment with anti-hCD81 antibody, in contrast to the hCD81-independent binding of HCV-LP produced in insect cells. These results indicate that HCV-LP generated in different types of cells exhibit different cellular tropism for binding to target cells.

Signal peptide peptidase promotes the formation of hepatitis C virus non-enveloped particles and is captured on the viral membrane during assembly

The maturation of the core protein (C) of Hepatitis C virus (HCV) is controlled by the signal peptidase (sp) and signal peptide peptidase (spp) of the host. To date, it remains unknown whether spp cleavage influences viral infectivity and/or the assembly process. Here, evidence is provided that cleavage by spp is not required for assembly of nucleocapsid-like particles (NLPs) in yeast (Pichia pastoris). The immature NLPs (not processed by spp) show a density of 1.11 g ml(-1) on sucrose gradients and a diameter of 50 nm. Co-expression of human spp (hspp) with C generates the 21 kDa mature form of the protein and promotes the accumulation of non-enveloped particles. The amount of non-enveloped particles accumulating in the cell was correlated directly with the expression level of hspp. Furthermore, immunocapture studies showed that hspp was embedded in the membranes of enveloped particles. These results suggest that maturation of the C protein can occur after formation of the enveloped particles and that the abundance of hspp influences the types of particle accumulating in the cells.

Recombinant rhabdoviruses: vectors for vaccine development and gene therapy

The establishment of methods to recover rhabdoviruses from cDNA, so-called reverse genetics systems, has made it possible to genetically engineer rhabdoviruses and to study all aspects of the virus life cycle by introducing defined mutations into the viral genomes. It has also opened the way to make use of the viruses in biomedical applications such as vaccination, gene therapy, or oncolytic virotherapy. The typical gene expression mode of rhabdoviruses, a high genetic stability, and the propensity to tolerate changes in the virus envelope have made rhabdoviruses attractive, targetable gene expression vectors. This chapter provides an overview on the possibilities to manipulate biological properties of the rhabdoviruses that may be important for further development of vaccine vectors and examples of recombinant rhabdoviruses expressing foreign genes and antigens.

Efficient formation of vesicular stomatitis virus pseudotypes bearing the native forms of hepatitis C virus envelope proteins detected after sonication

Hepatitis C virus (HCV) causes chronic hepatitis, liver cirrhosis and hepatocellular carcinoma in addition to acute hepatitis. The HCV genome encodes two envelope glycoproteins, E1 and E2. To investigate the role of E1 and E2 in HCV infection, we used a recombinant vesicular stomatitis virus (VSV), VSVdeltaG*, harboring the green fluorescent protein gene instead of the VSV G envelope protein gene. It was complemented with the native form of E1 and E2, or E1 or E2 alone, to make HCV pseudotypes VSVdeltaG*(HCV), VSVdeltaG*(E1), and VSVdeltaG*(E2). Neither E1 nor E2 expression was detected on the cell surface, as reported. Unlike previous reports, infectious activities of VSVdeltaG*(HCV), VSVdeltaG*(E1) and VSVdeltaG*(E2) pseudotypes were detected under conditions where VSV was completely neutralized by anti-VSV. We could enhance the infectious titers 100-fold by sonication upon virus harvest. Bovine lactoferrin efficiently inhibited infection by VSVdeltaG*(HCV) as well as VSVdeltaG*(E2), as the interaction between E2 and lactoferrin has been thought to contribute to the inhibition of HCV infectivity. VSVdeltaG*(HCV) infected many adherent cell lines, including hepatic cell lines, but not most hematopoietic cell lines. Treatment of cells with trypsin, tunicamycin, or sulfated polysaccharides before infection reduced the infectivity of VSVdeltaG*(HCV) by about 90%, suggesting that a cell surface protein(s) with sugar chains plays an important role in HCV infection. The VSV pseudotypes developed here would be useful for analyzing the early stages of HCV infection.

Membrane binding properties and terminal residues of the mature hepatitis C virus capsid protein in insect cells

The immature core protein (p23, residues 1 to 191) of hepatitis C virus undergoes posttranslational modifications including intramembranous proteolysis within its C-terminal signal sequence by signal peptide peptidase to generate the mature form (p21). In this study, we analyzed the cleavage site and other amino acid modifications that occur on the core protein. To produce the posttranslationally modified core protein, we used a baculovirus-insect cell expression model system. As previously reported, p23 is processed to form p21 in insect as well as in mammalian cells. p21 was found to be associated with the cytoplasmic membrane, and its significant portion behaved as an integral membrane protein. The protein was purified from the membrane by a simple and unique procedure on the basis of its membrane-binding properties and solubility in detergents. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) analysis of purified p21 showed that the average molecular mass (m/z 19,307) of its single-charged ion differs by m/z 1,457 from that calculated for p23. To determine the posttranslational modifications, tryptic p21 peptides were analyzed by MALDI-TOF MS. We found three peptides that did not match the theoretically derived peptides of p23. Analysis of these peptides by MALDI-TOF tandem MS revealed that they correspond to N-terminal peptides (residues 2 to 9 and 2 to 10) starting with alpha-N-acetylserine and C-terminal peptide (residues 150 to 177) ending with phenylalanine. These results suggest that the mature core protein (molecular mass of 19,306 Da) includes residues 2 to 177 and that its N terminus is blocked with an acetyl group.

Involvement of a bovine viral diarrhea virus NS5B locus in virion assembly

A novel mutant of bovine viral diarrhea virus (BVDV) was found with a virion assembly phenotype attributable to an insertion into the NS5B polymerase locus. This mutant, termed 5B-741, was engineered by reverse genetics to express NS5B with a C-terminal peptide tag of 22 amino acids. Electroporation of bovine cells with genomic RNA from this mutant showed levels RNA synthesis which were regarded as sufficient for infectivity, yet infectious virions were not produced. Pseudorevertants of mutant 5B-741 that released infectious virions and formed plaques revealed a single nucleotide change (T12369C). This change resulted in a leucine-to-proline substitution within the NS5B tag (L726P). Genetic analysis revealed that indeed a single nucleotide change encoding proline at NS5B position 726 in the pseudorevertant polyprotein mediated recovery of virion assembly function without improving genomic RNA accumulation levels. A subgenomic BVDV reporter replicon (rNS3-5B) was used to analyze the consequences of alterations of the genomic region encoding the NS5B C terminus on replication and assembly. Interestingly, rNS3-5B-L726P (revertant) replicated with the same efficiency as the rNS3-5B-741 mutant but produced 10 times more virions in a trans-packaging assay. These results indicated that impairment of assembly function in 5B-741 was independent of RNA accumulation levels and agreed with the observations from the full-length mutant and revertant genomes. Finally, we recapitulated the packaging defect of 5B-741 with a vaccinia virus expression system to eliminate possible unwanted interactions between the helper virus and the packaged replicon. Taken together, these studies revealed an unexpected role of NS5B in infectious virion assembly.

Inhibition of hepatitis C virus-like particle binding to target cells by antiviral antibodies in acute and chronic hepatitis C

Hepatitis C virus (HCV) is a leading cause of chronic viral hepatitis worldwide. The study of antibody-mediated virus neutralization has been hampered by the lack of an efficient and high-throughput cell culture system for the study of virus neutralization. The HCV structural proteins have been shown to assemble into noninfectious HCV-like particles (HCV-LPs). Similar to serum-derived virions, HCV-LPs bind and enter human hepatocytes and hepatoma cell lines. In this study, we developed an HCV-LP-based model system for a systematic functional analysis of antiviral antibodies from patients with acute or chronic hepatitis C. We demonstrate that cellular HCV-LP binding was specifically inhibited by antiviral antibodies from patients with acute or chronic hepatitis C in a dose-dependent manner. Using a library of homologous overlapping envelope peptides covering the entire HCV envelope, we identified an epitope in the N-terminal E2 region (SQKIQLVNTNGSWHI; amino acid positions 408 to 422) as one target of human antiviral antibodies inhibiting cellular particle binding. Using a large panel of serum samples from patients with acute and chronic hepatitis C, we demonstrated that the presence of antibodies with inhibition of binding activity was not associated with viral clearance. In conclusion, antibody-mediated inhibition of cellular HCV-LP binding represents a convenient system for the functional characterization of human anti-HCV antibodies, allowing the mapping of envelope neutralization epitopes targeted by naturally occurring antiviral antibodies.

Unique features of hepatitis C virus capsid formation revealed by de novo cell-free assembly

The assembly of hepatitis C virus (HCV) is poorly understood, largely due to the lack of mammalian cell culture systems that are easily manipulated and produce high titers of virus. This problem is highlighted by the inability of the recently established HCV replicon systems to support HCV capsid assembly despite high levels of structural protein synthesis. Here we demonstrate that up to 80% of HCV core protein synthesized de novo in cell-free systems containing rabbit reticulocyte lysate or wheat germ extracts assembles into HCV capsids. This contrasts with standard primate cell culture systems, in which almost no core assembles into capsids. Cell-free HCV capsids, which have a sedimentation value of approximately 100S, have a buoyant density (1.28 g/ml) on cesium chloride similar to that of HCV capsids from other systems. Capsids produced in cell-free systems are also indistinguishable from capsids isolated from HCV-infected patient serum when analyzed by transmission electron microscopy. Using these cell-free systems, we show that HCV capsid assembly is independent of signal sequence cleavage, is dependent on the N terminus but not the C terminus of HCV core, proceeds at very low nascent chain concentrations, is independent of intact membrane surfaces, and is partially inhibited by cultured liver cell lysates. By allowing reproducible and quantitative assessment of viral and cellular requirements for capsid formation, these cell-free systems make a mechanistic dissection of HCV capsid assembly possible.

A candidate DNA vaccine elicits HCV specific humoral and cellular immune responses

AIM: To investigate the immunogenicity of candidate DNA vaccine against hepatitis C virus (HCV) delivered by two plasmids expressing HCV envelope protein 1 (E1) and envelope protein 2 (E2) antigens respectively and to study the effect of CpG adjuvant on this candidate vaccine.

METHODS: Recombinant plasmids expressing HCV E1 and E2 antigens respectively were used to simultaneously inoculate mice with or without CpG adjuvant. Antisera were then collected and titers of anti-HCV antibodies were analyzed by ELISA. One month after the last injection, animals were sacrificed to prepare single-cell suspension of splenocytes. These cells were subjected to HCV antigen specific proliferation assays and cytokine secretion assays to evaluate the cellular immune responses of the vaccinated animals.

RESULTS: Antibody responses to HCV E1 and E2 antigens were detected in vaccinated animals. Animals receiving CpG adjuvant had slightly lower titers of anti-HCV antibodies in the sera, while the splenocytes from these animals showed higher HCV-antigen specific proliferation. Analysis of cytokine secretion from the splenocytes was consistent with the above results. While no antigen-specific IL-4 secretion was detected for all vaccinated animals, HCV antigen-specific INF-γ secretion was detected for the splenocytes of vaccinated animals. CpG adjuvant enhanced the secretion of INF-γ but did not change the profile of IL-4 secretion.

CONCLUSION: Vaccination of mice with plasmids encoding HCV E1 and E2 antigens induces humoral and cellular immune responses. CpG adjuvant significantly enhances the cellular immune response.

Recombinant replication-restricted VSV as an expression vector for murine cytokines

Vesicular stomatitis virus (VSV) is a prototypic non-segmented, negative-strand RNA virus that rapidly and efficiently shuts down the production of host cell-encoded proteins and utilizes the cell's protein production machinery to express high levels of virally encoded proteins. In an effort to take advantage of this characteristic of VSV, we have employed a reverse genetics system to create recombinant forms of VSV encoding a variety of murine cytokines. Previous studies have revealed that cells infected with recombinant VSV that lack expression of the surface glycoprotein (G protein), designated deltaG-VSV, more efficiently express and secrete recombinant proteins than do recombinant "wild-type" VSV. Therefore, murine cytokine-expressing recombinants were produced as deltaG viruses. Propagation of these deltaG viruses in cells that transiently express G protein in vitro results in G-complemented virions that can infect cells, shut down host protein synthesis, and express at high levels each virally encoded protein (including the designated cytokine). We assessed the ability of each deltaG-VSV construct to express recombinant cytokine by infecting BHK cells and then monitoring/measuring the production of the desired cytokine. When possible, the bioactivity of the cytokine products was also measured. The results presented here reveal that large quantities of bioactive cytokines can be produced rapidly and inexpensively using deltaG-VSV as a protein expression system.

Histo-blood group antigen and human milk oligosaccharides: genetic polymorphism and risk of infectious diseases

ABH and Lewis antigens are carbohydrates present on gut epithelial cells. These antigens provide diversity within the human population. Their biosynthesis largely is controlled by the enzyme products of alleles at the ABO, FUT2 and FUT3 loci. We have shown that Norwalk virus (NV) uses structures based on H type 1 as its primary receptor. Norwalk virus is the prototype of human caliciviruses, which collectively are responsible for the majority of gastroenteritis outbreaks in people of all ages. Individuals with two mutated FUT2 alleles, and therefore devoid of H type 1 epitopes on their gut epithelial cells, are called nonsecretors and are resistant to infection by NV. This genetically controlled mechanism of resistance to NV also might be important in the protection of infants by human milk, yet in an inverse manner since, unlike milk from secretors, the milk from nonsecretor mothers does not inhibit attachment of recombinant NV particles to their primary receptor. This suggests that breastfeeding by a secretor mother should protect a secretor child from NV infection, whereas breastfeeding by a nonsecretor mother should not.

Cellular binding of hepatitis C virus envelope glycoprotein E2 requires cell surface heparan sulfate

The conservation of positively charged residues in the N terminus of the hepatitis C virus (HCV) envelope glycoprotein E2 suggests an interaction of the viral envelope with cell surface glycosaminoglycans. Using recombinant envelope glycoprotein E2 and virus-like particles as ligands for cellular binding, we demonstrate that cell surface heparan sulfate proteoglycans (HSPG) play an important role in mediating HCV envelope-target cell interaction. Heparin and liver-derived highly sulfated heparan sulfate but not other soluble glycosaminoglycans inhibited cellular binding and entry of virus-like particles in a dose-dependent manner. Degradation of cell surface heparan sulfate by pretreatment with heparinases resulted in a marked reduction of viral envelope protein binding. Surface plasmon resonance analysis demonstrated a high affinity interaction (KD 5.2 x 10-9 m) of E2 with heparin, a structural homologue of highly sulfated heparan sulfate. Deletion of E2 hypervariable region-1 reduced E2-heparin interaction suggesting that positively charged residues in the N-terminal E2 region play an important role in mediating E2-HSPG binding. In conclusion, our results demonstrate for the first time that cellular binding of HCV envelope requires E2-HSPG interaction. Docking of E2 to cellular HSPG may be the initial step in the interaction between HCV and the cell surface resulting in receptor-mediated entry and initiation of infection.

Hepatitis C virus infection: when silence is deception

Hepatitis C virus (HCV) uses complex and unique mechanisms to prevent, evade or subvert innate and adaptive immune responses and to establish persistent infection and chronic hepatitis. Recently developed experimental systems have significantly facilitated the analysis of HCV replication, virus-host interaction and pathogenesis of chronic hepatitis and have provided new insights into the mechanisms of HCV clearance and persistence.

Topology of hepatitis C virus envelope glycoproteins

Hepatitis C virus encodes two envelope glycoproteins, E1 and E2, that are released from a polyprotein precursor after cleavage by host signal peptidase(s). These proteins contain a large N-terminal ectodomain and a C-terminal transmembrane domain, and they assemble as a noncovalent heterodimer. The transmembrane domains of hepatitis C virus envelope glycoproteins have been shown to be multifunctional: (1) they are membrane anchors, (2) they bear ER retention signals, (3) they contain a signal sequence function, and (4) they are involved in E1-E2 heterodimerisation. Due to these multiple functions, the topology adopted by these transmembrane domains has given rise to much controversy. They are less than 30 amino acid residues long and are composed of two stretches of hydrophobic residues separated by a short segment containing one or two fully conserved positively charged residues. The presence of a signal sequence function in the C-terminal half of the transmembrane domains of E1 and E2 had suggested that these domains are composed of two membrane spanning segments. However, the two hydrophobic stretches are too short to make two membrane spanning alpha-helices. These discrepancies can now be explained by a dynamic model, based on experimental data, describing the early steps of the biogenesis of hepatitis C virus envelope glycoproteins. In this model, the transmembrane domains of E1 and E2 form a hairpin structure before cleavage by a signal peptidase, and a reorientation of the second hydrophobic stretch occurs after cleavage to produce a single membrane spanning domain.