An LASV GPC pseudotyped virus based reporter system enables evaluation of vaccines in mice under non-BSL-4 conditions

Structure-guided design of a prefusion GPC trimer induces neutralizing responses against LASV

Lassa virus (LASV) belongs to the Arenaviridae family and causes severe hemorrhagic fever in humans. Although many vaccine candidates for Lassa fever exist, no vaccines have been approved for clinical use currently. The precursor glycoprotein complex (GPC), which is expressed as a trimer on the viral surface, is the main target for vaccine development. However, it has been a significant challenge to elicit effective neutralizing antibodies against LASV. In this study, we designed and produced a prefusion GPC trimer antigen of LASV, named GPCv2. Based on the structural information of GPC, we made modifications by replacing the amino acid at position 328 with proline and appending the trimerization domain. This resulted in a highly expressed prefusion trimeric form of GPCv2 that retained important conformational epitopes and stimulated higher levels of neutralizing antibodies. Moreover, vaccination with GPCv2 protected mice from LASV pseudovirus challenge. Additionally, immune repertoire sequencing showed that the induced immune clones in the trimeric group were more convergent and has its own unique V-J pairing bias compared with monomeric group. These findings demonstrate the potential of GPCv2 as a promising candidate antigen for an effective vaccine against LASV.

A potential broad-spectrum neutralizing antibody against Betacoronavirus

Three pandemics caused by human Betacoronavirus had broken out in the past two decades. Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) was one of the novel epidemic strains which caused the third pandemic, coronavirus disease 2019 (COVID-19), a global public health crisis. So far, more than millions of people have been infected. Considering the public health and economic impact of Betacoronavirus pandemic, drugs with broad-spectrum activity against these coronaviruses are urgently needed. In this study, two monoclonal antibodies targeting SARS-CoV-2 spike protein receptor-binding domain (RBD) with good neutralizing activity were used to construct a novel immunoglobulin-like bispecific antibody BI31. The neutralizing effect of BI31 against the pseudovirus and the authentic virus is better than that of its parent antibodies alone and in combination. What surprised us most was that the newly constructed bispecific antibody also had the neutralizing activity against SARS-CoV and Middle East respiratory syndrome coronavirus (MERS-CoV) that the parent antibodies did not have. These suggested that the BI31 can not only be developed as a therapeutic drug against COVID-19 but it could also become a broad-spectrum therapeutic antibody against Betacoronavirus.

Development of a Bioluminescent Imaging Mouse Model for SARS-CoV-2 Infection Based on a Pseudovirus System

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), remains widely pandemic around the world. Animal models that are sensitive to the virus are therefore urgently needed to evaluate potential vaccines and antiviral agents; however, SARS-CoV-2 requires biosafety level 3 containment. To overcome this, we developed an animal model using the intranasal administration of SARS-CoV-2 pseudovirus. As the pseudovirus contains the firefly luciferase reporter gene, infected tissues and the viral load could be monitored by in vivo bioluminescent imaging. We used the model to evaluate the protective efficacy of monoclonal antibodies and the tissue tropism of different variants. The model may also be a useful tool for the safe and convenient preliminary evaluation of the protective efficacy of vaccine candidates against SARS-CoV-2, as well as the treatment efficacy of anti-viral drugs.

Pseudotyped Viruses for Lyssavirus

Lyssaviruses, which belong to the family Rhabdoviridae, are enveloped and bullet-shaped ssRNA viruses with genetic diversity. All members of Lyssavirus genus are known to infect warm-blooded animals and cause the fatal disease rabies. The rabies virus (RABV) in lyssavirus is the major pathogen to cause fatal rabies. The pseudotyped RABV is constructed to study the biological functions of G protein and evaluation of anti-RABV products including vaccine-induced antisera, rabies immunoglobulins (RIG), neutralizing mAbs, and other antiviral inhibitors. In this chapter, we focus on RABV as a representative and describe the construction of RABV G protein bearing pseudotyped virus and its applications. Other non-RABV lyssaviruses are also included.

Production and characterization of lentivirus vector-based SARS-CoV-2 pseudoviruses with dual reporters: Evaluation of anti-SARS-CoV-2 viral effect of Korean Red Ginseng

Background

Pseudotyped virus systems that incorporate viral proteins have been widely employed for the rapid determination of the effectiveness and neutralizing activity of drug and vaccine candidates in biosafety level 2 facilities. We report an efficient method for producing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pseudovirus with dual luciferase and fluorescent protein reporters. Moreover, using the established method, we also aimed to investigate whether Korean Red Ginseng (KRG), a valuable Korean herbal medicine, can attenuate infectivity of the pseudotyped virus.

Methods

A pseudovirus of SARS-CoV-2 (SARS-2pv) was constructed and efficiently produced using lentivirus vector systems available in the public domain by the introduction of critical mutations in the cytoplasmic tail of the spike protein. KRG extract was dose-dependently treated to Calu-3 cells during SARS2-pv treatment to evaluate the protective activity against SARS-CoV-2.

Results

The use of Calu-3 cells or the expression of angiotensin-converting enzyme 2 (ACE2) in HEK293T cells enabled SARS-2pv infection of host cells. Coexpression of transmembrane protease serine subtype 2 (TMPRSS2), which is the activator of spike protein, with ACE2 dramatically elevated luciferase activity, confirming the importance of the TMPRSS2-mediated pathway during SARS-CoV-2 entry. Our pseudovirus assay also revealed that KRG elicited resistance to SARS-CoV-2 infection in lung cells, suggesting its beneficial health effect.

Conclusion

The method demonstrated the production of SARS-2pv for the analysis of vaccine or drug candidates. When KRG was assessed by the method, it protected host cells from coronavirus infection. Further studies will be followed for demonstrating this potential benefit.

Pseudotyped Viruses for Mammarenavirus

Mammarenaviruses are classified into New World arenaviruses (NW) and Old World arenaviruses (OW). The OW arenaviruses include the first discovered mammarenavirus-lymphocytic choriomeningitis virus (LCMV) and the highly lethal Lassa virus (LASV). Mammarenaviruses are transmitted to human by rodents, resulting in severe acute infections and hemorrhagic fever. Pseudotyped viruses have been widely used as a tool in the study of mammarenaviruses. HIV-1, SIV, FIV-based lentiviral vectors, VSV-based vectors, MLV-based vectors, and reverse genetic approaches have been applied in the construction of pseudotyped mammarenaviruses. Pseudotyped mammarenaviruses are commonly used in receptor research, neutralizing antibody detection, inhibitor screening, viral virulence studies, functional analysis of N-linked glycans, and studies of viral infection, endocytosis, and fusion mechanisms.

Visualizing lymphocytic choriomeningitis virus infection in cells and living mice

Mammarenavirus are a large family of enveloped negative-strand RNA viruses that include several agents responsible for severe hemorrhagic fevers. Until now, no FDA-licensed drug has been admitted for treating an arenavirus infection, and only few effective anti-arenavirus drugs have been tested in vivo. In this work, we designed a recombinant reporter arenavirus lymphocytic choriomeningitis virus that stably expressed nanoluciferase (LCMV-Nluc). The LCMV-Nluc was proved to share similar biological properties with wild-type LCMV and the Nluc intensity reliably reflected viral replication both in vitro and in vivo. Replication of the Nluc-encoding virus in living mice can be visualized by real-time bioluminescent imaging, and bioluminescence can be detected in a variety of organs of infected mice. This work provides a novel approach that enables real-time study of the arenavirus infection and is a convenient and valuable tool for screening of compounds that are active against arenaviruses in vitro and in living mice.

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LCMV-Nluc was constructed and shared similar biological properties with LCMV-WT

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Replication of the LCMV-Nluc can be visualized by real-time bioluminescent imaging

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LCMV-Nluc is a valuable tool for screening antiviral compounds in vitro

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LCMV-Nluc is successfully applied for screening antiviral compounds in vivo

Pseudovirus-Based Assays for the Measurement of Antibody-Mediated Neutralization of SARS-CoV-2

SARS-CoV-2 has emerged as a significant cause of morbidity and mortality worldwide. Virus neutralization assays are critical for the development and evaluation of vaccines and immunotherapeutics, as well as for conducting basic research into the immune response, spread, and pathogenesis of this disease. However, neutralization assays traditionally require the use of infectious virus which must be carefully handled in a BSL-3 setting, thus complicating the assay and restricting its use to labs with access to BSL-3 facilities. Pseudovirus-based assays are an alternative to the use of infectious virus. SARS-CoV-2 pseudovirus contains only the spike structural protein, and infection results in a single round of replication, thus allowing for the assay to be run safely under BSL-2 conditions. In this chapter, we describe protocols and considerations for the production and titration of lentivirus-based SARS-CoV-2 pseudovirus, as well as for running and analysis of FACS-based pseudovirus neutralization assays.

SARS-CoV-2 Spike Pseudoviruses: A Useful Tool to Study Virus Entry and Address Emerging Neutralization Escape Phenotypes

SARS-CoV-2 genetic variants are emerging around the globe. Unfortunately, several SARS-CoV-2 variants, especially variants of concern (VOCs), are less susceptible to neutralization by the convalescent and post-vaccination sera, raising concerns of increased disease transmissibility and severity. Recent data suggests that SARS-CoV-2 neutralizing antibody levels are a reliable correlate of vaccine-mediated protection. However, currently used BSL3-based virus micro-neutralization (MN) assays are more laborious, time-consuming, and expensive, underscoring the need for BSL2-based, cost-effective neutralization assays against SARS-CoV-2 variants. In light of this unmet need, we have developed a BSL-2 pseudovirus-based neutralization assay (PBNA) in cells expressing the human angiotensin-converting enzyme-2 (hACE2) receptor for SARS-CoV-2. The assay is reproducible (R2 = 0.96), demonstrates a good dynamic range and high sensitivity. Our data suggest that the biological Anti-SARS-CoV-2 research reagents such as NIBSC 20/130 show lower neutralization against B.1.351 SA (South Africa) and B.1.1.7 UK (United Kingdom) VOC, whereas a commercially available monoclonal antibody MM43 retains activity against both these variants. SARS-CoV-2 spike PBNAs for VOCs would be useful tools to measure the neutralization ability of candidate vaccines in both preclinical models and clinical trials and would further help develop effective prophylactic countermeasures against emerging neutralization escape phenotypes.

Human Cathelicidin Inhibits SARS-CoV-2 Infection: Killing Two Birds with One Stone

SARS-CoV-2 infection begins with the association of its spike 1 (S1) protein with host angiotensin-converting enzyme-2 (ACE2). Targeting the interaction between S1 and ACE2 is a practical strategy against SARS-CoV-2 infection. Herein, we show encouraging results indicating that human cathelicidin LL37 can simultaneously block viral S1 and cloak ACE2. LL37 binds to the receptor-binding domain (RBD) of S1 with high affinity (11.2 nM) and decreases subsequent recruitment of ACE2. Owing to the RBD blockade, LL37 inhibits SARS-CoV-2 S pseudovirion infection, with a half-maximal inhibitory concentration of 4.74 μg/mL. Interestingly, LL37 also binds to ACE2 with an affinity of 25.5 nM and cloaks the ligand-binding domain (LBD), thereby decreasing S1 adherence and protecting cells against pseudovirion infection in vitro. Intranasal administration of LL37 to C57 mice infected with adenovirus expressing human ACE2 either before or after pseudovirion invasion decreased lung infection. The study identified a versatile antimicrobial peptide in humans as an inhibitor of SARS-CoV-2 attachment using dual mechanisms, thus providing a potential candidate for coronavirus disease 2019 (COVID-19) prevention and treatment.

Deletion of the SARS-CoV-2 Spike Cytoplasmic Tail Increases Infectivity in Pseudovirus Neutralization Assays

Pseudotyped viruses are valuable tools for studying virulent or lethal viral pathogens that need to be handled in biosafety level 3 (BSL-3) or higher facilities. With the explosive spread of the coronavirus disease 2019 (COVID-19) pandemic, the establishment of a BSL-2 adapted SARS-CoV-2 pseudovirus neutralization assay is needed to facilitate the development of countermeasures. Here we describe an approach to generate a single-round lentiviral vector-based SARS-CoV-2 pseudovirus, which produced a signal more than 2 logs above background. Specifically, a SARS-CoV-2 spike variant with a cytoplasmic tail deletion of 13 amino acids, termed SΔCT13, conferred enhanced spike incorporation into pseudovirions and increased viral entry into cells as compared with full-length spike (S). We further compared S and SΔCT13 in terms of their sensitivity to vaccine sera, purified convalescent IgG, hACE2-mIgG, and the virus entry inhibitor BafA1. We developed a SΔCT13-based pseudovirus neutralization assay and defined key assay characteristics, including linearity, limit of detection, and intra- and intermediate-assay precision. Our data demonstrate that the SΔCT13-based pseudovirus shows enhanced infectivity in target cells, which will facilitate the assessment of humoral immunity to SARS-CoV-2 infection, antibody therapeutics, and vaccination. This pseudovirus neutralization assay can also be readily adapted to SARS-CoV-2 variants that emerge.IMPORTANCESARS-CoV-2 is the etiologic agent of the COVID-19 pandemic. The development of a high throughput pseudovirus neutralization assay is critical for the development of vaccines and immune-based therapeutics. In this study, we show that deletion of the cytoplasmic tail of the SARS-CoV-2 spike leads to pseudoviruses with enhanced infectivity. This SΔCT13-based pseudovirus neutralization assay should be broadly useful for the field.

Membrane Nanoparticles Derived from ACE2-Rich Cells Block SARS-CoV-2 Infection

The ongoing COVID-19 pandemic worldwide necessitates the development of therapeutics against SARS-CoV-2. ACE2 is the main receptor of SARS-CoV-2 S1 and mediates viral entry into host cells. Herein, membrane nanoparticles (NPs) prepared from ACE2-rich cells were discovered to have potent capacity to block SARS-CoV-2 infection. The membranes of human embryonic kidney-239T cells highly expressing ACE2 were applied to prepare NPs using an extrusion method. The nanomaterials, termed ACE2-NPs, contained 265.1 ng mg-1 ACE2 on the surface and acted as baits to trap S1 in a dose-dependent manner, resulting in reduced recruitment of the viral ligand to HK-2 human renal tubular epithelial cells. Aside from affecting receptor recongnition, S1 translocated to the cytoplasm and induced apoptosis by reducing optic atrophy 1 expression and increasing cytochrome c release, which was also inhibited by ACE2-NPs. Further investigations revealed that ACE2-NPs efficiently suppressed SARS-CoV-2 S pseudovirions entry into host cells and blocked viral infection in vitro and in vivo. This study characterizes easy-to-produce memrbane nanoantagonists of SARS-CoV-2 that enrich the existing antiviral arsenal and provide possibilities for COVID-19 treatment.

Membrane Nanoparticles Derived from ACE2-Rich Cells Block SARS-CoV-2 Infection

The ongoing COVID-19 pandemic worldwide necessitates the development of therapeutics against SARS-CoV-2. ACE2 is the main receptor of SARS-CoV-2 S1 and mediates viral entry into host cells. Herein, membrane nanoparticles (NPs) prepared from ACE2-rich cells were discovered to have potent capacity to block SARS-CoV-2 infection. The membranes of human embryonic kidney-239T cells highly expressing ACE2 were applied to prepare NPs using an extrusion method. The nanomaterials, termed ACE2-NPs, contained 265.1 ng mg^-1 ACE2 on the surface and acted as baits to trap S1 in a dose-dependent manner, resulting in reduced recruitment of the viral ligand to HK-2 human renal tubular epithelial cells. Aside from affecting receptor recongnition, S1 translocated to the cytoplasm and induced apoptosis by reducing optic atrophy 1 expression and increasing cytochrome c release, which was also inhibited by ACE2-NPs. Further investigations revealed that ACE2-NPs efficiently suppressed SARS-CoV-2 S pseudovirions entry into host cells and blocked viral infection in vitro and in vivo. This study characterizes easy-to-produce memrbane nanoantagonists of SARS-CoV-2 that enrich the existing antiviral arsenal and provide possibilities for COVID-19 treatment.

Dromedary camels as a natural source of neutralizing nanobodies against SARS-CoV-2

The development of prophylactic and therapeutic agents for coronavirus disease 2019 (COVID-19) is a current global health priority. Here, we investigated the presence of cross-neutralizing antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in dromedary camels that were Middle East respiratory syndrome coronavirus (MERS-CoV) seropositive but MERS-CoV free. The tested 229 dromedaries had anti–MERS-CoV camel antibodies with variable cross-reactivity patterns against SARS-CoV-2 proteins, including the S trimer and M, N, and E proteins. Using SARS-CoV-2 competitive immunofluorescence immunoassays and pseudovirus neutralization assays, we found medium-to-high titers of cross-neutralizing antibodies against SARS-CoV-2 in these animals. Through linear B cell epitope mapping using phage immunoprecipitation sequencing and a SARS-CoV-2 peptide/proteome microarray, we identified a large repertoire of Betacoronavirus cross-reactive antibody specificities in these dromedaries and demonstrated that the SARS-CoV-2–specific VHH antibody repertoire is qualitatively diverse. This analysis revealed not only several SARS-CoV-2 epitopes that are highly immunogenic in humans, including a neutralizing epitope, but also epitopes exclusively targeted by camel antibodies. The identified SARS-CoV-2 cross-neutralizing camel antibodies are not proposed as a potential treatment for COVID-19. Rather, their presence in nonimmunized camels supports the development of SARS-CoV-2 hyperimmune camels, which could be a prominent source of therapeutic agents for the prevention and treatment of COVID-19.

A neutralizing human antibody binds to the N-terminal domain of the Spike protein of SARS-CoV-2

A key target for therapeutic antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the spike protein, a trimeric protein complex with each monomer comprising an S1 and an S2 domain that mediate binding to host cells and membrane fusion, respectively. In addition to the receptor binding domain (RBD), S1 has an N-terminal domain (NTD). In searching for neutralizing antibodies, there has been a focus on the RBD. Chi et al. isolated antibodies from 10 convalescent patients and identified an antibody that potently neutralizes the virus but does not bind the RBD. Cryo–electron microscopy revealed the epitope as the NTD. This NTD-targeting antibody may be useful to combine with RBD-targeting antibodies in therapeutic cocktails.

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Developing therapeutics against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) could be guided by the distribution of epitopes, not only on the receptor binding domain (RBD) of the Spike (S) protein but also across the full Spike (S) protein. We isolated and characterized monoclonal antibodies (mAbs) from 10 convalescent COVID-19 patients. Three mAbs showed neutralizing activities against authentic SARS-CoV-2. One mAb, named 4A8, exhibits high neutralization potency against both authentic and pseudotyped SARS-CoV-2 but does not bind the RBD. We defined the epitope of 4A8 as the N-terminal domain (NTD) of the S protein by determining with cryo–eletron microscopy its structure in complex with the S protein to an overall resolution of 3.1 angstroms and local resolution of 3.3 angstroms for the 4A8-NTD interface. This points to the NTD as a promising target for therapeutic mAbs against COVID-19.

Assessing the application of a pseudovirus system for emerging SARS-CoV-2 and re-emerging avian influenza virus H5 subtypes in vaccine development

Background

Highly pathogenic emerging and re-emerging viruses continuously threaten lives worldwide. In order to provide prophylactic prevention from the emerging and re-emerging viruses, vaccine is suggested as the most efficient way to prevent individuals from the threat of viral infection. Nonetheless, the highly pathogenic viruses need to be handled in a high level of biosafety containment, which hinders vaccine development. To shorten the timeframe of vaccine development, the pseudovirus system has been widely applied to examine vaccine efficacy or immunogenicity in the emerging and re-emerging viruses.

Methods

We developed pseudovirus systems for emerging SARS coronavirus 2 (SARS-CoV-2) and re-emerging avian influenza virus H5 subtypes which can be handled in the biosafety level 2 facility. Through the generated pseudovirus of SARS-CoV-2 and avian influenza virus H5 subtypes, we successfully established a neutralization assay to quantify the neutralizing activity of antisera against the viruses.

Results

The result of re-emerging avian influenza virus H5Nx pseudoviruses provided valuable information for antigenic evolution and immunogenicity analysis in vaccine candidate selection. Together, our study assessed the potency of pseudovirus systems in vaccine efficacy, antigenic analysis, and immunogenicity in the vaccine development of emerging and re-emerging viruses.

Conclusion

Instead of handling live highly pathogenic viruses in a high biosafety level facility, using pseudovirus systems would speed up the process of vaccine development to provide community protection against emerging and re-emerging viral diseases with high pathogenicity.

Lassa Virus Genetics

In a pattern repeated across a range of ecological niches, arenaviruses have evolved a compact four-gene genome to orchestrate a complex life cycle in a narrow range of susceptible hosts. A number of mammalian arenaviruses cross-infect humans, often causing a life-threatening viral hemorrhagic fever. Among this group of geographically bound zoonoses, Lassa virus has evolved a unique niche that leads to significant and sustained human morbidity and mortality. As a biosafety level 4 pathogen, direct study of the pathogenesis of Lassa virus is limited by the sparse availability, high operating costs, and technical restrictions of the high-level biocontainment laboratories required for safe experimentation. In this chapter, we introduce the relationship between genome structure and the life cycle of Lassa virus and outline reverse genetic approaches used to probe and describe functional elements of the Lassa virus genome. We then review the tools used to obtain viral genomic sequences used for phylogeny and molecular diagnostics, before shifting to a population perspective to assess the contributions of phylogenetic analysis in understanding the evolution and ecology of Lassa virus in West Africa. We finally consider the future outlook and clinical applications for genetic study of Lassa virus.

Establishment and validation of a pseudovirus neutralization assay for SARS-CoV-2

Pseudoviruses are useful virological tools because of their safety and versatility, especially for emerging and re-emerging viruses. Due to its high pathogenicity and infectivity and the lack of effective vaccines and therapeutics, live SARS-CoV-2 has to be handled under biosafety level 3 conditions, which has hindered the development of vaccines and therapeutics. Based on a VSV pseudovirus production system, a pseudovirus-based neutralization assay has been developed for evaluating neutralizing antibodies against SARS-CoV-2 in biosafety level 2 facilities. The key parameters for this assay were optimized, including cell types, cell numbers, virus inoculum. When tested against the SARS-CoV-2 pseudovirus, SARS-CoV-2 convalescent patient sera showed high neutralizing potency, which underscore its potential as therapeutics. The limit of detection for this assay was determined as 22.1 and 43.2 for human and mouse serum samples respectively using a panel of 120 negative samples. The cutoff values were set as 30 and 50 for human and mouse serum samples, respectively. This assay showed relatively low coefficient of variations with 15.9% and 16.2% for the intra- and inter-assay analyses respectively. Taken together, we established a robust pseudovirus-based neutralization assay for SARS-CoV-2 and are glad to share pseudoviruses and related protocols with the developers of vaccines or therapeutics to fight against this lethal virus.

Crystal Structure of Refolding Fusion Core of Lassa Virus GP2 and Design of Lassa Virus Fusion Inhibitors

The envelope glycoproteins GP1 and GP2 of Lassa virus (LASV) bind to the host cell receptors to mediate viral infection. So far, no approved vaccines and specific treatment options against LASV exist. To develop specific fusion inhibitors against LASV, we solved the crystal structure of the post-fusion 6 helix bundle (6-HB) formed by two heptad repeat domains (HR1 and HR2) of GP2. This fusion core contains a parallel trimeric coiled-coil of three HR1 helices, around which three HR2 helices are entwined in an antiparallel manner. Various hydrophobic and charged interactions form between HR1 and HR2 domains to stabilize the overall conformation of GP2 fusion core. Based on the structure, we designed several peptides spanning the HR2 domain and tested their antiviral activities. We found that the longer HR2 peptides were effective in inhibiting LASV GPC protein-mediated cell–cell fusion under low pH condition. These results not only suggest that LASV infects the target cell mainly through endocytosis, including micropinocytosis, and membrane fusion at low pH, but also provide an important basis for rational design of LASV fusion inhibitors.

Nipah pseudovirus system enables evaluation of vaccines in vitro and in vivo using non-BSL-4 facilities

Because of its high infectivity in humans and the lack of effective vaccines, Nipah virus is classified as a category C agent and handling has to be performed under biosafety level 4 conditions in non-endemic countries, which has hindered the development of vaccines. Based on a highly efficient pseudovirus production system using a modified HIV backbone vector, a pseudovirus-based mouse model has been developed for evaluating the efficacy of Nipah vaccines in biosafety level 2 facilities. For the first time, the correlates of protection have been identified in a mouse model. The limited levels of neutralizing antibodies against immunogens fusion protein (F), glycoprotein (G), and combination of F and G (FG) were found to be 148, 275, and 115, respectively, in passive immunization. Relatively lower limited levels of protection of 52, and 170 were observed for immunogens F, and G, respectively, in an active immunization model. Although the minimal levels for protection of neutralizing antibody in passive immunization were slightly higher than those in active immunization, neutralizing antibody played a key role in protection against Nipah virus infection. The immunogens F and G provided similar protection, and the combination of these immunogens did not provide better outcomes. Either immunogen F or G would provide sufficient protection for Nipah vaccine. The Nipah pseudovirus mouse model, which does not involve highly pathogenic virus, has the potential to greatly facilitate the standardization and implementation of an assay to propel the development of NiV vaccines.

Recombinant Lassa Virus Expressing Green Fluorescent Protein as a Tool for High-Throughput Drug Screens and Neutralizing Antibody Assays

Lassa virus (LASV), a mammarenavirus, infects an estimated 100,000–300,000 individuals yearly in western Africa and frequently causes lethal disease. Currently, no LASV-specific antivirals or vaccines are commercially available for prevention or treatment of Lassa fever, the disease caused by LASV. The development of medical countermeasure screening platforms is a crucial step to yield licensable products. Using reverse genetics, we generated a recombinant wild-type LASV (rLASV-WT) and a modified version thereof encoding a cleavable green fluorescent protein (GFP) as a reporter for rapid and quantitative detection of infection (rLASV-GFP). Both rLASV-WT and wild-type LASV exhibited similar growth kinetics in cultured cells, whereas growth of rLASV-GFP was slightly impaired. GFP reporter expression by rLASV-GFP remained stable over several serial passages in Vero cells. Using two well-characterized broad-spectrum antivirals known to inhibit LASV infection, favipiravir and ribavirin, we demonstrate that rLASV-GFP is a suitable screening tool for the identification of LASV infection inhibitors. Building on these findings, we established a rLASV-GFP-based high-throughput drug discovery screen and an rLASV-GFP-based antibody neutralization assay. Both platforms, now available as a standard tool at the IRF-Frederick (an international resource), will accelerate anti-LASV medical countermeasure discovery and reduce costs of antiviral screens in maximum containment laboratories.

Non-neutralizing antibodies elicited by recombinant Lassa-Rabies vaccine are critical for protection against Lassa fever

Lassa fever (LF), caused by Lassa virus (LASV), is a viral hemorrhagic fever for which no approved vaccine or potent antiviral treatment is available. LF is a WHO priority disease and, together with rabies, a major health burden in West Africa. Here we present the development and characterization of an inactivated recombinant LASV and rabies vaccine candidate (LASSARAB) that expresses a codon-optimized LASV glycoprotein (coGPC) and is adjuvanted by a TLR-4 agonist (GLA-SE). LASSARAB elicits lasting humoral response against LASV and RABV in both mouse and guinea pig models, and it protects both guinea pigs and mice against LF. We also demonstrate a previously unexplored role for non-neutralizing LASV GPC-specific antibodies as a major mechanism of protection by LASSARAB against LF through antibody-dependent cellular functions. Overall, these findings demonstrate an effective inactivated LF vaccine and elucidate a novel humoral correlate of protection for LF.

Development and application of a bioluminescent imaging mouse model for Chikungunya virus based on pseudovirus system

Chikungunya virus (CHIKV) is an arthropod-borne virus that is transmitted to humans primarily via the bite of an infected mosquito. Infection of humans by CHIKV can cause chikungunya fever which is an acute febrile illness associated with severe, often debilitating polyarthralgias. Since a re-emergence of CHIKV in 2004, the virus has spread into novel locations in nearly 40 countries including non-endemic regions and has led to millions of cases of disease throughout countries. Handling of CHIKV is restricted to the high-containment Biosafety Level 3 (BSL-3) facilities, which greatly impede the research progress of this virus. In this study, an envelope-pseudotyped virus expressing the firefly luciferase reporter protein (pHIV-CHIKV-Fluc) was generated. An in vitro sensitive neutralizing assay and an in vivo bioluminescent-imaging-based mouse infection model had been developed based on the CHIKV pseudovirus. Utilizing the platform, protection effect of DNA vaccine was evaluated. Therefore, this study provides a safe, sensitive and visualizing model for evaluating vaccines and antiviral therapies against CHIKV in low containment BSL-2 laboratories.