Use of vesicular stomatitis virus pseudotypes bearing hantaan or seoul virus envelope proteins in a rapid and safe neutralization test

The effects of low-level laser therapy on severe acute respiratory syndrome coronavirus 2 infection in HEK293/ACE2 cells

SARS-CoV-2 is a threat to public health due to its ability to undergo crucial mutations, increasing its infectivity and decreasing the vaccine's effectiveness. There is a need to find and introduce alternative and effective methods of controlling SARS-CoV-2. LLLT treats diseases by exposing cells or tissues to low levels of red and near-infrared light. The study aims to investigate for the first time the impact of LLLT on SARS-CoV-2 infected HEK293/ACE2 cells and compare them to uninfected ones. Cells were irradiated at 640 nm, at different fluences. Subsequently, the effects of laser irradiation on the virus and cells were assessed using biological assays. Irradiated uninfected cells showed no changes in cell viability and cytotoxicity, while there were changes in irradiated infected cells. Furthermore, uninfected irradiated cells showed no luciferase activity while laser irradiation reduced luciferase activity in infected cells. Under SEM, there was a clear difference between the infected and uninfected cells.

Validation of an antigenic site targeted by monoclonal antibodies against Puumala virus

Identification of B-cell epitopes facilitates the development of vaccines, therapeutic antibodies and diagnostic tools. Previously, the binding site of the bank vole monoclonal antibody (mAb) 4G2 against Puumala virus (PUUV, an orthohantavirus in the Hantaviridae family of the Bunyavirales order) was predicted using a combination of methods, including pepscan, phage-display, and site-directed mutagenesis of vesicular stomatitis virus (VSV) particles pseudotyped with Gn and Gc glycoproteins from PUUV. These techniques led to the identification of the neutralization escape mutation F915A. To our surprise, a recent crystal structure of PUUV Gc in complex with Fab 4G2 revealed that residue F915 is distal from epitope of mAb 4G2. To clarify this issue and explore potential explanations for the inconsistency, we designed a mutagenesis experiment to probe the 4G2 epitope, with three PUUV pseudoviruses carrying amino acid changes E725A, S944F, and S946F, located within the structure-based 4G2 epitope on the Gc. These amino acid changes were able to convey neutralization escape from 4G2, and S944F and S946F also conveyed escape from neutralization by human mAb 1C9. Furthermore, our mapping of all the known neutralization evasion sites from hantaviral Gcs onto PUUV Gc revealed that over 60 % of these sites reside within or close to the epitope of mAb 4G2, indicating that this region may represent a crucial area targeted by neutralizing antibodies against PUUV, and to a lesser extent, other hantaviruses. The identification of this site of vulnerability could guide the creation of subunit vaccines against PUUV and other hantaviruses in the future.

Pseudotyped Viruses for Orthohantavirus

Orthohantaviruses, members of the Orthohantavirus genus of Hantaviridae family of the Bunyavirales order, are enveloped, negative-sense, single-stranded, tripartite RNA viruses. They are emerging zoonotic pathogens carried by small mammals including rodents, moles, shrews, and bats and are the etiologic agents of hemorrhagic fever with renal syndrome (HFRS) and hantavirus cardiopulmonary syndrome (HCPS) among humans. With the characteristics of low biological risk but strong operability, a variety of pseudotyped viruses have been constructed as alternatives to authentic orthohantaviruses to help delineate the roles of host factors in viral entry and other virus-host interactions, to assist in deciphering mechanisms of immune response and correlates of protection, to enhance our understanding of viral antigenic property, to characterize viral entry inhibitors, and to be developed as vaccines. In this chapter, we will discuss the general property of orthohantavirus, construction of pseudotyped orthohantaviruses based on different packaging systems, and their current applications.

Robust neutralization assay based on SARS-CoV-2 S-protein-bearing vesicular stomatitis virus (VSV) pseudovirus and ACE2-overexpressing BHK21 cells

The global pandemic of coronavirus disease 2019 (COVID-19) is a disaster for human society. A convenient and reliable neutralization assay is very important for the development of vaccines and novel drugs. In this study, a G protein-deficient vesicular stomatitis virus (VSVdG) bearing a truncated spike protein (S with C-terminal 18 amino acid truncation) was compared to that bearing the full-length spike protein of SARS-CoV-2 and showed much higher efficiency. A neutralization assay was established based on VSV-SARS-CoV-2-Sdel18 pseudovirus and hACE2-overexpressing BHK21 cells (BHK21-hACE2 cells). The experimental results can be obtained by automatically counting the number of EGFP-positive cells at 12 h after infection, making the assay convenient and high-throughput. The serum neutralizing titer measured by the VSV-SARS-CoV-2-Sdel18 pseudovirus assay has a good correlation with that measured by the wild type SARS-CoV-2 assay. Seven neutralizing monoclonal antibodies targeting the receptor binding domain (RBD) of the SARS-CoV-2 S protein were obtained. This efficient and reliable pseudovirus assay model could facilitate the development of new drugs and vaccines.

Comparison of VSV Pseudovirus and Focus Reduction Neutralization Assays for Measurement of Anti-Andes orthohantavirus Neutralizing Antibodies in Patient Samples

Andes orthohantavirus (ANDV) is the etiologic agent of hantavirus cardiopulmonary syndrome (HCPS), which has a case fatality rate around 35%, with no effective treatment or vaccine available. ANDV neutralizing antibody (NAb) measurements are important for the evaluation of the immune response following infection, vaccination, or passive administration of investigational monoclonal or polyclonal antibodies. The standard assay for NAb measurement is a focus reduction neutralization test (FRNT) featuring live ANDV and must be completed under biosafety level (BSL)-3 conditions. In this study, we compared neutralization assays featuring infectious ANDV or vesicular stomatitis virus (VSV) pseudovirions decorated with ANDV glycoproteins for their ability to measure anti-ANDV NAbs from patient samples. Our studies demonstrate that VSV pseudovirions effectively measure NAb from clinical samples and have greater sensitivity compared to FRNT with live ANDV. Importantly, the pseudovirus assay requires less labor and sample materials and can be conducted at BSL-2.

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.

Hantavirus entry: Perspectives and recent advances

Hantaviruses are important zoonotic pathogens of public health importance that are found on all continents except Antarctica and are associated with hemorrhagic fever with renal syndrome (HFRS) in the Old World and hantavirus pulmonary syndrome (HPS) in the New World. Despite the significant disease burden they cause, no FDA-approved specific therapeutics or vaccines exist against these lethal viruses. The lack of available interventions is largely due to an incomplete understanding of hantavirus pathogenesis and molecular mechanisms of virus replication, including cellular entry. Hantavirus Gn/Gc glycoproteins are the only viral proteins exposed on the surface of virions and are necessary and sufficient to orchestrate virus attachment and entry. In vitro studies have implicated integrins (β_1-3), DAF/CD55, and gC1qR as candidate receptors that mediate viral attachment for both Old World and New World hantaviruses. Recently, protocadherin-1 (PCDH1) was demonstrated as a requirement for cellular attachment and entry of New World hantaviruses in vitro and lethal HPS in vivo, making it the first clade-specific host factor to be identified. Attachment of hantavirus particles to cellular receptors induces their internalization by clathrin-mediated, dynamin-independent, or macropinocytosis-like mechanisms, followed by particle trafficking to an endosomal compartment where the fusion of viral and endosomal membranes can occur. Following membrane fusion, which requires cholesterol and acid pH, viral nucleocapsids escape into the cytoplasm and launch genome replication. In this review, we discuss the current mechanistic understanding of hantavirus entry, highlight gaps in our existing knowledge, and suggest areas for future inquiry.

In vitro and in vivo efficacy of a Rift Valley fever virus vaccine based on pseudovirus

Rift Valley fever virus (RVFV), a recognized category A priority pathogen, causes large outbreaks of Rift Valley fever with some fatalities in humans in humans and huge economic losses in livestock. As wild-type RVFV must be handled in BSL-3 or BSL-4 laboratories, we constructed a high-titer vesicular stomatitis virus (VSV) pseudotype bearing RVFV envelope glycoproteins to detect neutralizing antibodies in vitro under BSL-2 conditions. The neutralizing properties of 39 amino acid mutant sites that have occurred naturally over time in the RVFV envelope glycoproteins were analyzed with their corresponding pseudoviral mutants separately. Compared with the results in the primary strain, the variants showed no statistically significant differences. We next established a Balb/c mouse pseudovirus infection model for detecting neutralizing antibodies against pseudovirus. Five immunizations with pseudoviral DNA protected the mice from infection with the pseudovirus. Bioluminescence imaging, which we used to evaluate viral dissemination and distribution in the mice, showed a good relationship between the neutralizing antibodies titers in vitro. These pseudovirus methods will allow for the safe determination of neutralizing antibodies in vivo and in vitro, and will assist with studies on vaccines and drugs against RVFV with the long term objective of Rift Valley fever prevention.

Production of Pseudotyped Particles to Study Highly Pathogenic Coronaviruses in a Biosafety Level 2 Setting

The protocol aims to generate coronavirus (CoV) spike (S) fusion protein pseudotyped particles with a murine leukemia virus (MLV) core and luciferase reporter, using a simple transfection procedure of the widely available HEK-293T cell line. Once formed and released from producer cells, these pseudovirions incorporate a luciferase reporter gene. Since they only contain the heterologous coronavirus spike protein on their surface, the particles behave like their native coronavirus counterparts for entry steps. As such, they are the excellent surrogates of native virions for studying viral entry into host cells. Upon successful entry and infection into target cells, the luciferase reporter gets integrated into the host cell genome and is expressed. Using a simple luciferase assay, transduced cells can be easily quantified. An important advantage of the procedure is that it can be performed in biosafety level 2 (BSL-2) facilities instead of BSL-3 facilities required for work with highly pathogenic coronaviruses such as Middle East respiratory syndrome coronavirus (MERS-CoV) and severe acute respiratory syndrome coronavirus (SARS-CoV). Another benefit comes from its versatility as it can be applied to envelope proteins belonging to all three classes of viral fusion proteins, such as the class I influenza hemagglutinin (HA) and Ebola virus glycoprotein (GP), the class II Semliki forest virus E1 protein, or the class III vesicular stomatitis virus G glycoprotein. A limitation of the methodology is that it can only recapitulate virus entry steps mediated by the envelope protein being investigated. For studying other viral life cycle steps, other methods are required. Examples of the many applications these pseudotype particles can be used in include investigation of host cell susceptibility and tropism and testing the effects of virus entry inhibitors to dissect viral entry pathways used.

Defining of MAbs-neutralizing sites on the surface glycoproteins Gn and Gc of a hantavirus using vesicular stomatitis virus pseudotypes and site-directed mutagenesis

Earlier four monoclonal antibodies (MAbs) against surface glycoproteins Gn and Gc of puumala virus (PUUV, genus Orthohantavirus, family Hantaviridae, order Bunyavirales) were generated and for three MAbs with neutralizing capacity the localization of binding epitopes was predicted using pepscan and phage-display techniques. In this work, we produced vesicular stomatitis virus (VSV) particles pseudotyped with the Gn and Gc glycoproteins of PUUV and applied site-directed mutagenesis to dissect the structure of neutralizing epitopes. Replacement of cysteine amino acid (aa) residues with alanines resulted in pseudotype particles with diminished (16 to 18 %) neut-titres; double Cys→Ala mutants, as well as mutants with bulky aromatic and charged residues replaced with alanines, have shown even stronger reduction in neut-titres (from 25 % to the escape phenotype). In silico modelling of the neut-epitopes supported the hypothesis that these critical residues are located on the surface of viral glycoprotein molecules and thus can be recognized by the antibodies indeed. A similar pattern was observed in experiments with mutant pseudotypes and sera collected from patients suggesting that these neut-epitopes are utilized in a course of human PUUV infection. These data will help understanding the mechanisms of hantavirus neutralization and assist construction of vaccine candidates.

Two Point Mutations in Old World Hantavirus Glycoproteins Afford the Generation of Highly Infectious Recombinant Vesicular Stomatitis Virus Vectors

Human hantavirus infections cause hantavirus pulmonary syndrome in the Americas and hemorrhagic fever with renal syndrome (HFRS) in Eurasia. No FDA-approved vaccines and therapeutics exist for these deadly viruses, and their development is limited by the requirement for high biocontainment. In this study, we identified and characterized key amino acid changes in the surface glycoproteins of HFRS-causing Hantaan virus that enhance their incorporation into recombinant vesicular stomatitis virus (rVSV) particles. The replication-competent rVSVs encoding Hantaan virus and Dobrava-Belgrade virus glycoproteins described in this work provide a powerful and facile system to study hantavirus entry under lower biocontainment and may have utility as hantavirus vaccines.

Rodent-to-human transmission of hantaviruses is associated with severe disease. Currently, no FDA-approved, specific antivirals or vaccines are available, and the requirement for high biocontainment (biosafety level 3 [BSL-3]) laboratories limits hantavirus research. To study hantavirus entry in a BSL-2 laboratory, we set out to generate replication-competent, recombinant vesicular stomatitis viruses (rVSVs) bearing the Gn and Gc (Gn/Gc) entry glycoproteins. As previously reported, rVSVs bearing New World hantavirus Gn/Gc were readily rescued from cDNAs, but their counterparts bearing Gn/Gc from the Old World hantaviruses, Hantaan virus (HTNV) or Dobrava-Belgrade virus (DOBV), were refractory to rescue. However, serial passage of the rescued rVSV-HTNV Gn/Gc virus markedly increased its infectivity and capacity for cell-to-cell spread. This gain in viral fitness was associated with the acquisition of two point mutations: I532K in the cytoplasmic tail of Gn and S1094L in the membrane-proximal stem of Gc. Follow-up experiments with rVSVs and single-cycle VSV pseudotypes confirmed these results. Mechanistic studies revealed that both mutations were determinative and contributed to viral infectivity in a synergistic manner. Our findings indicate that the primary mode of action of these mutations is to relocalize HTNV Gn/Gc from the Golgi complex to the cell surface, thereby affording significantly enhanced Gn/Gc incorporation into budding VSV particles. Finally, I532K/S1094L mutations in DOBV Gn/Gc permitted the rescue of rVSV-DOBV Gn/Gc, demonstrating that incorporation of cognate mutations into other hantaviral Gn/Gc proteins could afford the generation of rVSVs that are otherwise challenging to rescue. The robust replication-competent rVSVs, bearing HTNV and DOBV Gn/Gc, reported herein may also have utility as vaccines.

Retrovirus-Based Surrogate Systems for BSL-2 High-Throughput Screening of Antivirals Targeting BSL-3/4 Hemorrhagic Fever-Causing Viruses

The majority of viruses causing hemorrhagic fever in humans are Risk Group 3 or 4 pathogens and, therefore, can only be handled in biosafety level 3 or 4 (BSL-3/4) containment laboratories. The restricted number of such laboratories, the substantial financial requirements to maintain them, and safety concerns for the laboratory workers pose formidable challenges for rapid medical countermeasure discovery and evaluation. BSL-2 surrogate systems are a less challenging, cheap, and fast alternative to the use of live high-consequence viruses for dissecting and targeting individual steps of viral lifecycles with a diminished threat to the laboratory worker. Typical surrogate systems are virion-like particles (VLPs), transcriptionally active ("infectious") VLPs, minigenome systems, recombinant heterotypic viruses encoding proteins of target viruses, and vesiculoviral or retroviral pseudotype systems. Here, we outline the use of retroviral pseudotypes for identification of antivirals against BSL-4 pathogens.

Current status on the development of pseudoviruses for enveloped viruses

Emerging and reemerging infectious diseases have a strong negative impact on public health. However, because many of these pathogens must be handled in biosafety level, 3 or 4 containment laboratories, research and development of antivirals or vaccines against these diseases are often impeded. Alternative approaches to address this issue have been vigorously pursued, particularly the use of pseudoviruses in place of wild‐type viruses. As pseudoviruses have been deprived of certain gene sequences of the virulent virus, they can be handled in biosafety level 2 laboratories. Importantly, the envelopes of these viral particles may have similar conformational structures to those of the wild‐type viruses, making it feasible to conduct mechanistic investigation on viral entry and to evaluate potential neutralizing antibodies. However, a variety of challenging issues remain, including the production of a sufficient pseudovirus yield and the inability to produce an appropriate pseudotype of certain viruses. This review discusses current progress in the development of pseudoviruses and dissects the factors that contribute to low viral yields.

Analysis of the glycoproteins of Seoul orthohantavirus strain B1 associated with fusion activity

We analyzed two virus variants (S1 and L1) from Seoul orthohantavirus strain B1. Strain B1 produces large opaque plaques when plated on Vero E6 cell monolayers. However, although the L1 variant produced the large opaque plaques common to the strain, the variant S1 produced small clear ones on Vero E6 cells. Five days after Vero E6 cells were infected with the S1 variant, polykaryons formed spontaneously. However, the cells infected with the L1 variant did not show the formation of syncytia. An analysis of the pH dependency of the cell fusion demonstrated that the L1 variant could induce cell fusion, but only at a pH that was 0.2 units lower than the pH at which the S1 variant induced it. Sequencing of the M genome segment of the two virus variants revealed amino acid substitutions at 4 positions in the Gn and Gc gene products of the S1 variant. Two of these substitutions occurred in the extracellular domain of Gn and changed the charge of the protein. Our findings suggest that these amino acid substitutions caused the S1 variant Gn protein to induce fusion at an elevated pH.

Analysis of VSV pseudotype virus infection mediated by rubella virus envelope proteins

Rubella virus (RV) generally causes a systemic infection in humans. Viral cell tropism is a key determinant of viral pathogenesis, but the tropism of RV is currently poorly understood. We analyzed various human cell lines and determined that RV only establishes an infection efficiently in particular non-immune cell lines. To establish an infection the host cells must be susceptible and permissible. To assess the susceptibility of individual cell lines, we generated a pseudotype vesicular stomatitis virus bearing RV envelope proteins (VSV-RV/CE2E1). VSV-RV/CE2E1 entered cells in an RV envelope protein-dependent manner, and thus the infection was neutralized completely by an RV-specific antibody. The infection was Ca²⁺-dependent and inhibited by endosomal acidification inhibitors, further confirming the dependency on RV envelope proteins for the VSV-RV/CE2E1 infection. Human non-immune cell lines were mostly susceptible to VSV-RV/CE2E1, while immune cell lines were much less susceptible than non-immune cell lines. However, susceptibility of immune cells to VSV-RV/CE2E1 was increased upon stimulation of these cells. Our data therefore suggest that immune cells are generally less susceptible to RV infection than non-immune cells, but the susceptibility of immune cells is enhanced upon stimulation.

Comparison of serological assays to titrate Hantaan and Seoul hantavirus-specific antibodies

BACKGROUND

Hantaan and Seoul viruses, in the Hantavirus genus, are known to cause hemorrhagic fever with renal syndrome (HFRS). The plaque reduction neutralization test (PRNT), as conventional neutralization test for hantaviruses, is laborious and time-consuming. Alternatives to PRNT for hantaviruses are required.

METHODS

In this study, the methods for Hantaan and Seoul viruses serological typing including microneutralization test (MNT), pseudoparticle neutralization test (PPNT) and immunofluorescence assay based on viral glycoproteins (IFA-GP) were developed and compared with PRNT using a panel of 74 sera including 44 convalescent sera of laboratory confirmed HFRS patients and 30 patients sera of non-hantavirus infection. Antibody titres and serotyping obtained with different methods above were analyzed by paired-t, linear correlation, McNemar χ² and Kappa agreement tests.

RESULTS

Antibody titres obtained with MNT₅₀, PPNT₅₀ and IFA-GP were significantly correlated with that obtained with PRNT₅₀ (p < 0.001). GMT determined by PPNT₅₀ was statistically higher than that determined by PRNT₅₀ (p < 0.001), while GMT determined by MNT₅₀ and IFA-GP were equal with (p > 0.05) and less than (p < 0.001) that obtained with PRNT₅₀ respectively. Serotyping obtained with MNT₅₀ and PRNT₅₀, PPNT₅₀ and PRNT₅₀ were highly consistent (p < 0.001), whereas that obtained with IFA-GP and PRNT₅₀ were moderately consistent (p < 0.001). There were no significant differences for serotyping between PRNT₅₀ and MNT₅₀, as well as PRNT₅₀ and PPNT₅₀ (p > 0.05). IFA-GP was less sensitive than PRNT₅₀ and MNT₅₀ for serotyping of hantaviruses infection (p < 0.05). However, for 79.5% (35/44) samples, serotyping determined by IFA-GP and PRNT₅₀ were consistent.

CONCLUSIONS

MNT₅₀ and PPNT₅₀ both can be used as simple and rapid alternatives to PRNT₅₀, and MNT₅₀ is more specific while PPNT₅₀ is more sensitive than other assays for neutralizing antibody determination. So far, this work has been the most comprehensive comparison of alternatives to PRNT.

Assessing the safety and immunogenicity of recombinant vesicular stomatitis virus Ebola vaccine in healthy adults: a randomized clinical trial

BACKGROUND

The 2013-2016 Ebola virus outbreak in West Africa was the most widespread in history. In response, alive attenuated recombinant vesicular stomatitis virus (rVSV) vaccine expressing Zaire Ebolavirus glycoprotein (rVSVΔG-ZEBOV-GP) was evaluated in humans.

METHODS

In a phase 1, randomized, dose-ranging, observer-blind, placebo-controlled trial, healthy adults aged 18-65 years were randomized into 4 groups of 10 to receive one of 3 vaccine doses or placebo. Follow-up visits spanned 180 days postvaccination for safety monitoring, immunogenicity testing and any rVSV virus shedding.

RESULTS

Forty participants were injected with rVSVΔG-ZEBOV-GP vaccine (n = 30) or saline placebo (n = 10). No serious adverse events related to the vaccine or participant withdrawals were reported. Solicited adverse events during the 14-day follow-up period were mild to moderate and self-limited, with the exception of injection-site pain and headache. Viremia following vaccination was transient and no longer detectable after study day 3, with no virus shedding in saliva or urine. All vaccinated participants developed serum immunoglobulin G (IgG), as measured by Ebola virus envelope glycoprotein-based enzyme-linked immunosorbent assay (ELISA). Immunogenicity was comparable across all dose groups, and sustained IgG titers were detectable through to the last visit, at study day 180.

INTERPRETATION

In this phase 1 study, there were no safety concerns after a single dose of rVSVΔG-ZEBOV-GP vaccine. IgG ELISA showed persistent high titers at 180 days postimmunization. There was a period of reactogenicity, but in general, the vaccine was well tolerated. This study provides evidence of the safety and immunogenicity of rVSVΔG-ZEBOV-GP vaccine and importance of its further investigation. Trial registration: Clinical-Trials.gov no., NCT02374385.

Production of Filovirus Glycoprotein-Pseudotyped Vesicular Stomatitis Virus for Study of Filovirus Entry Mechanisms

Members of the family Filoviridae are filamentous, enveloped, and nonsegmented negative-stranded RNA viruses that can cause severe hemorrhagic disease in humans and nonhuman primates with high mortality rates. Current efforts to analyze the structure and biology of these viruses as well as the development of antivirals have been hindered by the necessity of biosafety level 4 containment (BSL4). Here, we outline how to produce and work with Ebola virus glycoprotein bearing vesicular stomatitis virus (VSV) pseudovirions. These pseudovirions can be safely used to evaluate early steps of the filovirus life cycle without need for BSL4 containment. Virus gene expression in the transduced cells is easy to assess since the pseudovirions encode a reporter gene in place of the VSV G glycoprotein gene. Adoption of VSV for use as a pseudovirion system for filovirus GP has significantly expanded access for researchers to study specific aspects of the viral life cycle outside of BSL4 containment and has allowed substantial growth of filovirus research.

Codon-optimized filovirus DNA vaccines delivered by intramuscular electroporation protect cynomolgus macaques from lethal Ebola and Marburg virus challenges

Cynomolgus macaques were vaccinated by intramuscular electroporation with DNA plasmids expressing codon-optimized glycoprotein (GP) genes of Ebola virus (EBOV) or Marburg virus (MARV) or a combination of codon-optimized GP DNA vaccines for EBOV, MARV, Sudan virus and Ravn virus. When measured by ELISA, the individual vaccines elicited slightly higher IgG responses to EBOV or MARV than did the combination vaccines. No significant differences in immune responses of macaques given the individual or combination vaccines were measured by pseudovirion neutralization or IFN-γ ELISpot assays. Both the MARV and mixed vaccines were able to protect macaques from lethal MARV challenge (5/6 vs. 6/6). In contrast, a greater proportion of macaques vaccinated with the EBOV vaccine survived lethal EBOV challenge in comparison to those that received the mixed vaccine (5/6 vs. 1/6). EBOV challenge survivors had significantly higher pre-challenge neutralizing antibody titers than those that succumbed.

Analysis of the entry mechanism of Crimean-Congo hemorrhagic fever virus, using a vesicular stomatitis virus pseudotyping system

Crimean-Congo hemorrhagic fever (CCHF) is a tick-borne disease causing severe hemorrhagic symptoms with a nearly 30 % case-fatality rate in humans. The experimental use of CCHF virus (CCHFV), which causes CCHF, requires high-biosafety-level (BSL) containment. In contrast, pseudotyping of various viral glycoproteins (GPs) onto vesicular stomatitis virus (VSV) can be used in facilities with lower BSL containment, and this has facilitated studies on the viral entry mechanism and the measurement of neutralizing activity, especially for highly pathogenic viruses. In the present study, we generated high titers of pseudotyped VSV bearing the CCHFV envelope GP and analyzed the mechanisms involved in CCHFV infection. A partial deletion of the CCHFV GP cytoplasmic domain increased the titer of the pseudotyped VSV, the entry mechanism of which was dependent on the CCHFV envelope GP. Using the pseudotype virus, DC-SIGN (a calcium-dependent [C-type] lectin cell-surface molecule) was revealed to enhance viral infection and act as an entry factor for CCHFV.

Vaccinia virus-free rescue of fluorescent replication-defective vesicular stomatitis virus and pseudotyping with Puumala virus glycoproteins for use in neutralization tests

Puumala virus (PUUV) grows slowly in cell culture. To study antigenic properties of PUUV, an amenable method for their expression would be beneficial. To achieve this, a replication-defective recombinant vesicular stomatitis virus, rVSVΔG*EGFP, was rescued using BSRT7/5 and encephalomyocarditis virus (EMCV) internal ribosomal entry site (IRES)-enabled rescue plasmids. Using these particles, pseudotypes bearing PUUV Sotkamo strain glycoproteins were produced, with titres in the range 105-108, and were used in pseudotype focus reduction neutralization tests (pFRNTs) with neutralizing monoclonal antibodies and patient sera. The results were compared with those from orthodox focus reduction neutralization tests (oFRNTs) using native PUUV with the same samples and showed a strong positive correlation (rs = 0.82) between the methods. While developing the system we identified three amino acids which were mutated in the Vero E6 cell culture adapted PUUV prototype Sotkamo strain sequence, and changing these residues was critical for expression and neutralizing antibody binding of PUUV glycoproteins.

Preclinical Development of Inactivated Rabies Virus-Based Polyvalent Vaccine Against Rabies and Filoviruses

We previously described the generation of a novel Ebola virus (EBOV) vaccine based on inactivated rabies virus (RABV) containing EBOV glycoprotein (GP) incorporated in the RABV virion. Our results demonstrated safety, immunogenicity, and protective efficacy in mice and nonhuman primates (NHPs). Protection against viral challenge depended largely on the quality of the humoral immune response against EBOV GP.Here we present the extension and improvement of this vaccine by increasing the amount of GP incorporation into virions via GP codon-optimization as well as the addition of Sudan virus (SUDV) and Marburg virus (MARV) GP containing virions. Immunogenicity studies in mice indicate similar immune responses for both SUDV GP and MARV GP compared to EBOV GP. Immunizing mice with multiple antigens resulted in immune responses similar to immunization with a single antigen. Moreover, immunization of NHP with the new inactivated RABV EBOV vaccine resulted in high titer neutralizing antibody levels and 100% protection against lethal EBOV challenge when applied with adjuvant.Our results indicate that an inactivated polyvalent vaccine against RABV filoviruses is achievable. Finally, the novel vaccines are produced on approved VERO cells and a clinical grade RABV/EBOV vaccine for human trials has been produced.

Development of a helper cell-dependent form of peste des petits ruminants virus: a system for making biosafe antigen

Peste des petits ruminants (PPR) is a viral disease of sheep and goats that is spreading through many countries in the developing world. Work on the virus is often restricted to studies of attenuated vaccine strains or to work in laboratories that have high containment facilities. We have created a helper cell dependent form of PPR virus by removing the entire RNA polymerase gene and complementing it with polymerase made constitutively in a cell line. The resultant L-deleted virus grows efficiently in the L-expressing cell line but not in other cells. Virus made with this system is indistinguishable from normal virus when used in diagnostic assays, and can be grown in normal facilities without the need for high level biocontainment. The L-deleted virus will thus make a positive contribution to the control and study of this important disease.

Inability of rat DPP4 to allow MERS-CoV infection revealed by using a VSV pseudotype bearing truncated MERS-CoV spike protein

Middle East respiratory syndrome (MERS) coronavirus (Co-V) contains a single spike (S) protein, which binds to a receptor molecule, dipeptidyl peptidase 4 (DPP4; also known as CD26), and serves as a neutralizing antigen. Pseudotyped viruses are useful for measuring neutralization titers against highly infectious viruses as well as for studying their mechanism of entry. In this study, we constructed a series of cytoplasmic deletion mutants of MERS-CoV S and compared the efficiency with which they formed pseudotypes with vesicular stomatitis virus. A pseudotype bearing an S protein with the C-terminal 16 amino acids deleted (MERSpv-St16) reached a maximum titer that was approximately tenfold higher than that of a pseudotype bearing a non-truncated full-length S protein. Using MERSpv-St16, we demonstrated the inability of rat DPP4 to serve as a functional receptor for MERS-CoV, suggesting that rats are not susceptible to MERS-CoV infection. This study provides novel information that enhances our understanding of the host range of MERS-CoV.

Hantaviruses--globally emerging pathogens

Hantaviruses are emerging zoonotic viruses which cause human disease in Africa, America, Asia, and Europe. This review summarizes the progress in hantavirus epidemiology and diagnostics during the previous decade. Moreover, we discuss the influence of ecological factors on the worldwide virus distribution and give an outlook on research perspectives for the next years.

Crimean-Congo hemorrhagic fever virus entry into host cells occurs through the multivesicular body and requires ESCRT regulators

Crimean-Congo hemorrhagic fever virus (CCHFV) is a tick-borne bunyavirus causing outbreaks of severe disease in humans, with a fatality rate approaching 30%. There are no widely accepted therapeutics available to prevent or treat the disease. CCHFV enters host cells through clathrin-mediated endocytosis and is subsequently transported to an acidified compartment where the fusion of virus envelope with cellular membranes takes place. To better understand the uptake pathway, we sought to identify host factors controlling CCHFV transport through the cell. We demonstrate that after passing through early endosomes in a Rab5-dependent manner, CCHFV is delivered to multivesicular bodies (MVBs). Virus particles localized to MVBs approximately 1 hour after infection and affected the distribution of the organelle within cells. Interestingly, blocking Rab7 activity had no effect on association of the virus with MVBs. Productive virus infection depended on phosphatidylinositol 3-kinase (PI3K) activity, which meditates the formation of functional MVBs. Silencing Tsg101, Vps24, Vps4B, or Alix/Aip1, components of the endosomal sorting complex required for transport (ESCRT) pathway controlling MVB biogenesis, inhibited infection of wild-type virus as well as a novel pseudotyped vesicular stomatitis virus (VSV) bearing CCHFV glycoprotein, supporting a role for the MVB pathway in CCHFV entry. We further demonstrate that blocking transport out of MVBs still allowed virus entry while preventing vesicular acidification, required for membrane fusion, trapped virions in the MVBs. These findings suggest that MVBs are necessary for infection and are the sites of virus-endosome membrane fusion.

Crimean-Congo hemorrhagic fever virus (CCHFV) is the cause of a severe, often fatal disease in humans. While it has been demonstrated that CCHFV cell entry depends on clathrin-mediated endocytosis, low pH, and early endosomes, the identity of the endosomes where virus penetrates into cell cytoplasm to initiate genome replication is unknown. Here, we showed that CCHFV was transported through early endosomes to multivesicular bodies (MVBs). We also showed that MVBs were likely the last organelle virus encountered before escaping into the cytoplasm. Our work has identified new cellular factors essential for CCHFV entry and potential novel targets for therapeutic intervention against this pathogen.

A vesicular stomatitis pseudovirus expressing the surface glycoproteins of influenza A virus

Pseudotyped viruses bearing the glycoprotein(s) of a donor virus over the nucleocapsid core of a surrogate virus are widely used as safe substitutes for infectious virus in virology studies. Retroviral particles pseudotyped with influenza A virus glycoproteins have been used recently for the study of influenza hemagglutinin and neuraminidase-dependent processes. Here, we report the development of vesicular-stomatitis-virus-based pseudotypes bearing the glycoproteins of influenza A virus. We show that pseudotypes bearing the hemagglutinin and neuraminidase of H5N1 influenza A virus mimic the wild-type virus in neutralization assays and sensitivity to entry inhibitors. We demonstrate the requirement of NA for the infectivity of pseudotypes and show that viruses obtained with different NA proteins are significantly different in their transduction activities. Inhibition studies with oseltamivir carboxylate show that neuraminidase activity is required for pseudovirus production, but not for the infection of target cells with H5N1-VSV pseudovirus. The HA-NA-VSV pseudoviruses have high transduction titers and better stability than the previously reported retroviral pseudotypes and can replace live influenza virus in the development of neutralization assays, screening of potential antivirals, and the study of different HA/NA reassortants.

Development of an immunochromatography strip test based on truncated nucleocapsid antigens of three representative hantaviruses

BACKGROUND

Hantaviruses are causative agents of hemorrhagic fever with renal syndrome (HFRS) and nephropathia epidemica (NE) in the Old World and hantavirus pulmonary syndrome (HPS) in the New World. There is a need for time-saving diagnostic methods. In the present study, recombinant N antigens were used as antigens in an immunochromatography strip (ICG) test to detect specific IgG antibodies.

METHODS

The N-terminal 103 amino acids (aa) of Hantaan virus (HTNV), Puumala virus (PUUV) and Andes virus (ANDV) nucleocapsid (N) protein were expressed in E. coli as representative antigens of three groups (HFRS, NE and HPS-causing viruses) of hantavirus. Five different types of ICG test strips, one antigen line on one strip for each of the three selected hantaviruses (HTNV, PUUV and ANDV), three antigen lines on one strip and a mixed antigen line on one strip, were developed and sensitivities were compared.

RESULTS

A total of 87 convalescent-phase patient sera, including sera from 35 HFRS patients, 36 NE patients and 16 HPS patients, and 25 sera from healthy seronegative people as negative controls were used to evaluate the ICG test. Sensitivities of the three-line strip and mixed-line strip were similar to those of the single antigen strip (97.2 to 100%). On the other hand, all of the ICG test strips showed high specificities to healthy donors.

CONCLUSION

These results indicated that the ICG test with the three representative antigens is an effective serodiagnostic tool for screening and typing of hantavirus infection in humans.

Recombinant lentogenic Newcastle disease virus expressing Ebola virus GP infects cells independently of exogenous trypsin and uses macropinocytosis as the major pathway for cell entry

BACKGROUND

Using reverse genetics, we generated a recombinant low-pathogenic LaSota strain Newcastle disease virus (NDV) expressing the glycoprotein (GP) of Ebola virus (EBOV), designated rLa-EBOVGP, and evaluated its biological characteristic in vivo and in vitro.

RESULTS

The introduction and expression of the EBOV GP gene did not increase the virulence of the NDV vector in poultry or mice. EBOV GP was incorporated into the particle of the vector virus and the recombinant virus rLa-EBOVGP infected cells and spread within them independently of exogenous trypsin. rLa-EBOVGP is more resistant to NDV antiserum than the vector NDV and is moderately sensitive to EBOV GP antiserum. More importantly, infection with rLa-EBOVGP was markedly inhibited by IPA3, indicating that rLa-EBOVGP uses macropinocytosis as the major internalization pathway for cell entry.

CONCLUSIONS

The results demonstrate that EBOV GP in recombinant NDV particles functions independently to mediate the viral infection of the host cells and alters the cell-entry pathway.

Role of nucleocapsid protein of hantaviruses in intracellular traffic of viral glycoproteins

To understand the role of nucleocapsid protein (NP) of hantaviruses in viral assembly, the effect of NP on intracellular traffic of viral glycoproteins Gn and Gc was investigated. Double staining of viral and host proteins in Hantaan virus (HTNV)-infected Vero E6 cells showed that Gn and Gc were localized to cis-Golgi, in which virus particles are thought to be formed. When HTNV Gn and Gc were expressed by a plasmid encoding glycoprotein precursor (GPC), which is posttranslationally cleaved into Gn and Gc, Gn was localized to cis-Golgi, whereas Gc showed diffuse distribution in the cytoplasm in 32.9% of Gc-positive cells. The ratio of the diffused Gc-positive cells was significantly decreased to 15.0% by co-expression of HTNV NP. Co-expression of HTNV GPC with NPs of other hantaviruses, such as Seoul virus, Puumala virus and Sin Nombre virus, also reduced the ratios of diffused Gc-positive cells to 13.5%, 25.2%, and 11.6%, respectively. Among amino- and carboxyl-terminally truncated HTNV NPs, NP75-429, NP116-429, NP1-333, NP1-233, and NP1-155 possessed activity to reduce the ratio of diffused Gc-positive cells, while NP155-429 and NP1-116 did not. NP30-429 has partial activity. These results indicate that amino acid region 116-155 of NP is important for the activity, although amino acid region 1-30 is partially related. Truncation of the HTNV Gc cytoplasmic tail caused an increase in diffused Gc-positive cells. In addition, the effect of coexpression of HTNV NP was weakened. These results suggest that HTNV NP has a role to promote Golgi localization of Gc through a mechanism possibly mediated by the Gc cytoplasmic tail.

Severe fever with thrombocytopenia virus glycoproteins are targeted by neutralizing antibodies and can use DC-SIGN as a receptor for pH-dependent entry into human and animal cell lines

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a novel bunyavirus that recently emerged in China. Infection with SFTSV is associated with case-fatality rates of up to 30%, and neither antivirals nor vaccines are available at present. Development of antiviral strategies requires the elucidation of virus-host cell interactions. Here, we analyzed host cell entry of SFTSV. Employing lentiviral and rhabdoviral vectors, we found that the Gn/Gc glycoproteins (Gn/Gc) of SFTSV mediate entry into a broad range of human and animal cell lines, as well as human macrophages and dendritic cells. The Gn/Gc proteins of La Crosse virus (LACV) and Rift Valley Fever Virus (RVFV), other members of the bunyavirus family, facilitated entry into an overlapping but not identical range of cell lines, suggesting that SFTSV, LACV, and RVFV might differ in their receptor requirements. Entry driven by SFTSV Gn/Gc was dependent on low pH but did not require the activity of the pH-dependent endosomal/lysosomal cysteine proteases cathepsins B and L. Instead, the activity of a cellular serine protease was required for infection driven by SFTSV and LACV Gn/Gc. Sera from convalescent SFTS patients inhibited SFTSV Gn/Gc-driven host cell entry in a dose-dependent fashion, demonstrating that the vector system employed is suitable to detect neutralizing antibodies. Finally, the C-type lectin DC-SIGN was found to serve as a receptor for SFTSV Gn/Gc-driven entry into cell lines and dendritic cells. Our results provide initial insights into cell tropism, receptor usage, and proteolytic activation of SFTSV and will aid in the understanding of viral spread and pathogenesis.

Serological assays based on recombinant viral proteins for the diagnosis of arenavirus hemorrhagic fevers

The family Arenaviridae, genus Arenavirus, consists of two phylogenetically independent groups: Old World (OW) and New World (NW) complexes. The Lassa and Lujo viruses in the OW complex and the Guanarito, Junin, Machupo, Sabia, and Chapare viruses in the NW complex cause viral hemorrhagic fever (VHF) in humans, leading to serious public health concerns. These viruses are also considered potential bioterrorism agents. Therefore, it is of great importance to detect these pathogens rapidly and specifically in order to minimize the risk and scale of arenavirus outbreaks. However, these arenaviruses are classified as BSL-4 pathogens, thus making it difficult to develop diagnostic techniques for these virus infections in institutes without BSL-4 facilities. To overcome these difficulties, antibody detection systems in the form of an enzyme-linked immunosorbent assay (ELISA) and an indirect immunofluorescence assay were developed using recombinant nucleoproteins (rNPs) derived from these viruses. Furthermore, several antigen-detection assays were developed. For example, novel monoclonal antibodies (mAbs) to the rNPs of Lassa and Junin viruses were generated. Sandwich antigen-capture (Ag-capture) ELISAs using these mAbs as capture antibodies were developed and confirmed to be sensitive and specific for detecting the respective arenavirus NPs. These rNP-based assays were proposed to be useful not only for an etiological diagnosis of VHFs, but also for seroepidemiological studies on VHFs. We recently developed arenavirus neutralization assays using vesicular stomatitis virus (VSV)-based pseudotypes bearing arenavirus recombinant glycoproteins. The goal of this article is to review the recent advances in developing laboratory diagnostic assays based on recombinant viral proteins for the diagnosis of VHFs and epidemiological studies on the VHFs caused by arenaviruses.

Newcastle disease virus-vectored Nipah encephalitis vaccines induce B and T cell responses in mice and long-lasting neutralizing antibodies in pigs

Nipah virus (NiV), a member of the Paramyxoviridae family, causes deadly encephalitis in humans and huge economic losses to the pig industry. Here, we generated recombinant avirulent Newcastle disease virus (NDV) LaSota strains expressing the NiV G and F proteins respectively (designated as rLa-NiVG and rLa-NiVF), and evaluated their immunogenicity in mice and pigs. Both rLa-NiVG and rLa-NiVF displayed growth properties similar to those of LaSota virus in chicken eggs. Co-infection of rLa-NiVG and rLa-NiVF caused marked syncytia formation, while intracerebral co-inoculation of these viruses in mice showed they were safe in at least one mammalian species. Animal immunization studies showed rLa-NiVG and rLa-NiVF induced NiV neutralizing antibody responses in mice and pigs, and F protein-specific CD8+ T cell responses in mice. Most importantly, rLa-NiVG and rLa-NiVF administered alone or together, induced a long-lasting neutralizing antibody response in pigs. Recombinant rLa-NiVG/F thus appear to be promising NiV vaccine candidates for pigs and potentially humans.

Development of a diagnostic method applicable to various serotypes of hantavirus infection in rodents

Antigenic diversity among different hantaviruses requires a variety of reagents for diagnosis of hantavirus infection. To develop a diagnostic method applicable to various hantavirus infections with a single set of reagents, we developed an enzyme-linked immunosorbent assay (ELISA) using recombinant nucleocapsid proteins of three hantaviruses, Amur, Hokkaido, and Sin Nombre viruses. This novel cocktail antigen-based ELISA enabled detection of antibodies against Hantaan, Seoul, Amur, Puumala, and Sin Nombre viruses in immunized laboratory animals. In wild rodent species, including Apodemus, Rattus, and Myodes, our ELISA detected antibodies against hantaviruses with high sensitivity and specificity. These data suggest that our novel diagnostic ELISA is a useful tool for screening hantavirus infections and could be effectively utilized for serological surveillance and quarantine purposes.

Efficient production of Hantaan and Puumala pseudovirions for viral tropism and neutralization studies

Puumala (PUUV) and Hantaan (HTNV) viruses are hantaviruses within the family Bunyaviridae and associated with Hemorrhagic Fever with Renal Syndrome (HFRS) in humans. Little is known about how these viruses interact with host cells, though pathogenic hantaviruses interact with α(v)β(3) integrin. To study host cell interactions and rapidly test the ability of antibodies to prevent infection, we produced HTNV and PUUV pseudovirions on a vesicular stomatitis virus (VSV) core. Similar to replication-competent hantaviruses, infection was low-pH-dependent. Despite broad cell tropism, several human T cell lines were poorly permissive to hantavirus pseudovirions, compared to VSV, indicating a relative block to infection at the level of entry. Stable expression of α(v)β(3) integrin in SupT1 cells did not restore infectivity. Finally, the pseudovirion system provided a rapid, quantitative, and specific method to screen for neutralizing antibodies in immune sera.

Vesicular stomatitis virus-based vaccine protects hamsters against lethal challenge with Andes virus

Andes virus (ANDV) is a highly pathogenic South American hantavirus that causes hantavirus pulmonary syndrome (HPS). A high case fatality rate, the potential for human-to-human transmission, the capacity to infect via aerosolization, and the absence of effective therapies make it imperative that a safe, fast-acting, and effective ANDV vaccine be developed. We generated and characterized a recombinant vesicular stomatitis virus (VSV) vector expressing the ANDV surface glycoprotein precursor (VSVΔG/ANDVGPC) as a possible vaccine candidate and tested its efficacy in the only lethal-disease animal model of HPS. Syrian hamsters immunized with a single injection of VSVΔG/ANDVGPC were fully protected against disease when challenged at 28, 14, 7, or 3 days postimmunization with a lethal dose of ANDV; however, the mechanism of protection seems to differ depending on when the immunization occurs. At 28 days postimmunization, a lack of detectable ANDV RNA in lung, liver, and blood tissue samples, as well as a lack of seroconversion to the ANDV nucleocapsidprotein in nearly all animals, suggested largely sterile immunity. The vaccine was able to generate high levels of neutralizing anti-ANDV G(N)/G(C) antibodies, which seem to play a role as a mechanism of vaccine protection. Administration of the vaccine at 7 or 3 days before challenge also resulted in full protection but with no specific neutralizing humoral immune response, suggesting a possible role of innate responses in protection against challenge virus replication. Administration of the vaccine 24 h postchallenge was successful in protecting 90% of hamsters and again suggested the induction of a potent antiviral state by the recombinant vector as a potential mechanism. Overall, our data suggest the potential for the use of the VSV platform as a fast-acting and effective prophylaxis/postexposure treatment against lethal hantavirus infections.

Production of influenza pseudotyped lentiviral particles and their use in influenza research and diagnosis: an update

Pseudotyped viral particles are being used as safe surrogates to mimic the structure and surface of many viruses, including highly pathogenic viruses such as avian influenza H5N1, to investigate biological functions mediated by the envelope proteins derived from these viruses. The first part of this article evaluates and discusses the differences in the production and characterization of influenza pseudoparticles. The second part focuses on the applications that such a flexible tool can provide in modern influenza research, in particular in the fields of drug discovery, molecular biology and diagnosis.

Generation of VSV pseudotypes using recombinant ΔG-VSV for studies on virus entry, identification of entry inhibitors, and immune responses to vaccines

Vesicular stomatitis virus (VSV) is a prototypic enveloped animal virus that has been used extensively to study virus entry, replication and assembly due to its broad host range and robust replication properties in a wide variety of mammalian and insect cells. Studies on VSV assembly led to the creation of a recombinant VSV in which the glycoprotein (G) gene was deleted. This recombinant (rVSV-ΔG) has been used to produce VSV pseudotypes containing the envelope glycoproteins of heterologous viruses, including viruses that require high-level biocontainment; however, because the infectivity of rVSV-ΔG pseudotypes is restricted to a single round of replication the analysis can be performed using biosafety level 2 (BSL-2) containment. As such, rVSV-ΔG pseudotypes have facilitated the analysis of virus entry for numerous viral pathogens without the need for specialized containment facilities. The pseudotypes also provide a robust platform to screen libraries for entry inhibitors and to evaluate the neutralizing antibody responses following vaccination. This manuscript describes methods to produce and titer rVSV-ΔG pseudotypes. Procedures to generate rVSV-ΔG stocks and to quantify virus infectivity are also described. These protocols should allow any laboratory knowledgeable in general virological and cell culture techniques to produce successfully replication-restricted rVSV-ΔG pseudotypes for subsequent analysis.

Development of a lentiviral vector system to study the role of the Andes virus glycoproteins

To infect target cells, enveloped viruses use their virion surface proteins to direct cell attachment and subsequent entry via virus-cell membrane fusion. How hantaviruses enter cells has been largely unexplored. To study early steps of Andes virus (ANDV) cell infection, a lentiviral vector system was developed based on a Simian immunodeficiency virus (SIV) vector pseudotyped with the ANDV-Gn/Gc envelope glycoproteins. The incorporation of Gn and Gc onto SIV-derived vector particles was assessed using newly generated monoclonal antibodies against ANDV glycoproteins. In addition, sera of ANDV infected humans were able to block cell entry of the SIV vector pseudotyped with ANDV glycoproteins, suggesting that their antigenic conformation is similar to that in the native virus. The use of such SIV vector pseudotyped with ANDV-Gn/Gc glycoproteins should facilitate studies on ANDV cell entry. Along this line, it was found that depletion of cholesterol from target cells strongly diminished cell infection, indicating a possible role of lipid rafts in ANDV cell entry. The Gn/Gc pseudotyped SIV vector has several advantages, notably high titer vector production and easy quantification of cell infection by monitoring GFP reporter gene expression by flow cytometry. Such pseudotyped SIV vectors can be used to identify functional domains in the Gn/Gc glycoproteins and to screen for potential hantavirus cell entry inhibitors.

Study of Andes virus entry and neutralization using a pseudovirion system

Andes virus (ANDV), a member of the Hantavirus genus in the family Bunyaviridae, causes an acute disease characteristic of New-World hantaviruses called hantavirus pulmonary syndrome (HPS). HPS is a highly pathogenic disease with a case-fatality rate of 40%. ANDV is the only hantavirus reported to spread directly from human-to-human. The aim of the present study was to develop a quantitative and high-throughput pseudovirion assay to study ANDV infection and neutralization in biosafety level 2 facilities (BSL-2). This pseudovirion assay is based on incorporation of ANDV glycoproteins onto replication-defective vesicular stomatitis virus (VSV) cores in which the gene for the surface G protein has been replaced by that encoding Renilla luciferase. Infection by the pseudovirions can be quantified by luciferase activity of infected cell lysates. ANDV pseudovirions were neutralized by ANDV-specific antisera, and there was good concordance between specificity and neutralization titers of ANDV hamster sera as determined by our pseudovirion assay and a commonly used plaque reduction neutralization titer (PRNT) assay. In addition, the pseudovirions were used to evaluate the requirements for ANDV entry, like pH dependency and the role of beta3 integrin, the reported receptor for other pathogenic hantaviruses, on entry.

Viral strategies for studying the brain, including a replication-restricted self-amplifying delta-G vesicular stomatis virus that rapidly expresses transgenes in brain and can generate a multicolor golgi-like expression

Viruses have substantial value as vehicles for transporting transgenes into neurons. Each virus has its own set of attributes for addressing neuroscience-related questions. Here we review some of the advantages and limitations of herpes, pseudorabies, rabies, adeno-associated, lentivirus, and others to study the brain. We then explore a novel recombinant vesicular stomatitis virus (dG-VSV) with the G-gene deleted and transgenes engineered into the first position of the RNA genome, which replicates only in the first brain cell infected, as corroborated with ultrastructural analysis, eliminating spread of virus. Because of its ability to replicate rapidly and to express multiple mRNA copies and additional templates for more copies, reporter gene expression is amplified substantially, over 500-fold in 6 hours, allowing detailed imaging of dendrites, dendritic spines, axons, and axon terminal fields within a few hours to a few days after inoculation. Green fluorescent protein (GFP) expression is first detected within 1 hour of inoculation. The virus generates a Golgi-like appearance in all neurons or glia of regions of the brain tested. Whole-cell patch-clamp electrophysiology, calcium digital imaging with fura-2, and time-lapse digital imaging showed that neurons appeared physiologically normal after expressing viral transgenes. The virus has a wide range of species applicability, including mouse, rat, hamster, human, and Drosophila cells. By using dG-VSV, we show efferent projections from the suprachiasmatic nucleus terminating in the periventricular region immediately dorsal to the nucleus. DG-VSVs with genes coding for different color reporters allow multicolor visualization of neurons wherever applied.

A neutralization test for specific detection of Nipah virus antibodies using pseudotyped vesicular stomatitis virus expressing green fluorescent protein

Nipah virus (NiV) is a new zoonotic paramyxovirus that emerged in 1998 and is now classified in the genus Henipavirus along with the closely related Hendra virus (HeV). NiV is highly pathogenic in several vertebrate species including humans, and the lack of available vaccines or specific treatment restricts it to biosafety level 4 (BSL4) containment. A serum neutralization test was developed for measuring NiV neutralizing antibodies under BSL2 conditions using a recombinant vesicular stomatitis virus (VSV) expressing green fluorescent protein (GFP) and bearing the F and G proteins of NiV (VSV–NiV–GFP). The neutralization titers were obtained by counting GFP-expressing cells or by measuring fluorescence. The performance of this new assay was compared against the conventional test using live NiV with panels of sera from several mammalian species, including sera from NiV outbreaks, experimental infections, as well as HeV-specific sera. The results obtained with the VSV–NiV–GFP based test correlated with those obtained using live NiV. Using a 50% reduction in VSV–NiV–GFP infected cells as the cut-off for neutralization, this new assay demonstrated its potential as an effective tool for detecting NiV neutralizing antibodies under BSL2 containment with greater speed, sensitivity and safety as compared to the conventional NiV serum neutralization test.

Adenovirus vectors expressing hantavirus proteins protect hamsters against lethal challenge with andes virus

Hantaviruses infect humans following aerosolization from rodent feces and urine, producing hemorrhagic fever with renal syndrome and hantavirus pulmonary syndrome. Due to the high rates of mortality and lack of therapies, vaccines are urgently needed. Nonreplicating adenovirus (Ad) vectors that express Andes hantavirus (ANDV) nucleocapsid protein (AdN) or glycoproteins (AdG(N) and AdG(C)) were constructed. Ad vectors were tested for their ability to protect Syrian hamsters from a lethal ANDV infection that mimics the pulmonary disease seen in humans. When administered once, all three Ad vectors, individually or in combination, elicited a robust immune response that protected hamsters. No vaccinated animal died, and there were no obvious clinical signs of disease. Further, hantavirus RNA was not detected by sensitive reverse transcription-PCR in tissues and blood of hamsters immunized with both AdG(N) and AdG(C). Cellular immunity appeared to be important for protection because the AdN vector completely protected animals. All three Ad vectors produced strong cytotoxic T-lymphocyte responses directed to hantavirus proteins in mice. Moreover, hamsters vaccinated with AdN, AdG(N), or AdG(C) produced no detectable neutralizing antibodies yet were protected. These Ad vectors represent the first vaccines that prevent lethal hantavirus disease and, in some instances (AdG(N) and AdG(C)), provide sterile immunity. These observations set the stage for a more detailed characterization of the types of immunity required to protect humans from hantavirus infections.

How to diagnose hantavirus infections and detect them in rodents and insectivores

Hantaviruses are carried by rodents and insectivores in which they cause persistent and generally asymptomatic infections. Several hantaviruses can infect humans and many of them cause either haemorrhagic fever with renal syndrome (HFRS) in Eurasia or hantavirus cardiopulmonary syndrome (HCPS) in the Americas. In humans hantavirus infections are diagnosed using IgM-capture tests but also by RT-PCR detection of viral RNA. For detection of hantavirus infections in rodents and insectivores, serology followed by immunoblotting of, for example, lung tissue, and RT-PCR detection of viral RNA may be used, and if of interest followed by sequencing and virus isolation. For sero/genotyping of hantavirus infections in humans and carrier animals neutralisation tests/RNA sequencing are required. Hantaviruses are prime examples of emerging and re-emerging infections and it seems likely that many new hantaviruses will be detected in the near future.

Development of a serotyping ELISA system for Thailand virus infection

To distinguish Thailand virus infection from infections with other hantaviruses, we established an ELISA serotyping system using a truncated nucleocapsid protein of Thailand virus lacking 49 amino acids at the N-terminus. In evaluations using patient and rodent sera, Thailand virus infection was readily distinguished from Hantaan and Seoul virus infections. Therefore, this ELISA system is an effective alternative to neutralization tests.

Pseudotyped vesicular stomatitis virus for analysis of virus entry mediated by SARS coronavirus spike proteins

Severe acute respiratory syndrome (SARS) coronavirus (CoV) contains a spike (S) protein that binds to a receptor molecule (angiotensin-converting enzyme 2; ACE2), induces membrane fusion, and serves as a neutralizing epitope. To study the functions of the S protein, we describe here the generation of SARS-CoV S protein-bearing vesicular stomatitis virus (VSV) pseudotype using a VSVdeltaG*/GFP system in which the G gene is replaced by the green fluorescent protein (GFP) gene (VSV-SARS-CoV-St19/GFP). Partial deletion of the cytoplasmic domain of SARS-CoV S protein (SARS-CoV-St19) allowed efficient incorporation into the VSV particle that enabled the generation of a high titer of pseudotype virus. Neutralization assay with anti-SARS-CoV antibody revealed that VSV-SARS-St19/GFP pseudotype infection is mediated by SARS-CoV S protein. The VSVdeltaaG*/SEAP system, which secretes alkaline phosphatase instead of GFP, was also generated as a VSV pseudotype having SARS-CoV S protein (VSV-SARS-CoV-St19/SEAP). This system enabled high-throughput analysis of SARS-CoV S protein-mediated cell entry by measuring alkaline phosphatase activity. Thus, VSV pseudotyped with SARS-CoV S protein is useful for developing a rapid detection system for neutralizing antibody specific for SARS-CoV infection as well as studying the S-mediated cell entry of SARS-CoV.

Replication-competent recombinant vesicular stomatitis virus encoding hepatitis C virus envelope proteins

Although in vitro replication of the hepatitis C virus (HCV) JFH1 clone of genotype 2a (HCVcc) has been developed, a robust cell culture system for the 1a and 1b genotypes, which are the most prevalent viruses in the world and resistant to interferon therapy, has not yet been established. As a surrogate virus system, pseudotype viruses transiently bearing HCV envelope proteins based on the vesicular stomatitis virus (VSV) and retrovirus have been developed. Here, we have developed a replication-competent recombinant VSV with a genome encoding unmodified HCV E1 and E2 proteins in place of the VSV envelope protein (HCVrv) in human cell lines. HCVrv and a pseudotype VSV bearing the unmodified HCV envelope proteins (HCVpv) generated in 293T or Huh7 cells exhibited high infectivity in Huh7 cells. Generation of infectious HCVrv was limited in some cell lines examined. Furthermore, HCVrv but not HCVpv was able to propagate and form foci in Huh7 cells. The infection of Huh7 cells with HCVpv and HCVrv was neutralized by anti-hCD81 and anti-E2 antibodies and by sera from chronic HCV patients. The infectivity of HCVrv was inhibited by an endoplasmic reticulum alpha-glucosidase inhibitor, N-(n-nonyl) deoxynojirimycin (Nn-DNJ), but not by a Golgi mannosidase inhibitor, deoxymannojirimycin. Focus formation of HCVrv in Huh7 cells was impaired by Nn-DNJ treatment. These results indicate that the HCVrv developed in this study can be used to study HCV envelope proteins with respect to not only the biological functions in the entry process but also their maturation step.

Generating vesicular stomatitis virus pseudotype bearing the severe acute respiratory syndrome coronavirus spike envelope glycoprotein for rapid and safe neutralization test or cell-entry assay

abstract: We generated a recombinant vesicular stomatitis virus (VSV) pseudotype (VSV Δ G*SG) by replacing the envelope G gene with the GFP gene and complementing with spike glycoprotein (S) of SARS‐CoV in trans. The neutralization and infection blocking tests showed that the VSV Δ G*SG and SARS‐CoV reacted similarly to SARS‐CoV specific antiserum, suggesting the VSVΔ G*SG can be a safe replacement of the live SARS‐CoV for neutralization test and cell‐entry assay.