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

Pseudoviruses, a safer toolbox for vaccine development against enveloped viruses

INTRODUCTION

Pseudoviruses are recombinant, replication-incompetent, viral particles designed to mimic the surface characteristics of native enveloped viruses. They are a safer, and cost-effective research alternative to live viruses. With the potential emergence of the next major infectious disease, more vaccine scientists must become familiar with the pseudovirus platform as a vaccine development tool to mitigate future outbreaks.

AREAS COVERED

This review aims at vaccine developers to provide a basic understanding of pseudoviruses, list their production methods, and discuss their utility to assess vaccine efficacy against enveloped viral pathogens. We further illustrate their usefulness as wet-lab simulators for emerging mutant variants, and new viruses to help prepare for current and future viral outbreaks, minimizing the need for gain-of-function experiments with highly infectious or lethal enveloped viruses.

EXPERT OPINION

With this platform, researchers can better understand the role of virus-receptor interactions and entry in infections, prepare for dangerous mutations, and develop effective vaccines.

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.

Methyl brevifolincarboxylate, a novel influenza virus PB2 inhibitor from Canarium Album (Lour.) Raeusch

Methyl brevifolincarboxylate (MBC) was isolated from ethyl acetate extract of Canarium album (Lour.) Raeusch. The structure was identified, and the effect on influenza A virus infection was evaluated. MBC exhibited inhibitory activity against influenza virus A/Puerto Rico/8/34 (H1N1) and A/Aichi/2/68 (H3N2) with IC₅₀ values of 27.16 ± 1.39 μM and 33.41 ± 2.34 μM. Mechanism studies indicated that MBC inhibited the replication of influenza A virus by targeting PB2 cap-binding domain. Our results demonstrated MBC was a potent PB2 cap-binding inhibitor and represented as a new type of promising lead compound for the development of anti-influenza virus drugs from natural products.

Isocorilagin, isolated from Canarium album (Lour.) Raeusch, as a potent neuraminidase inhibitor against influenza A virus

Canarium album (Lour.) Raeusch (C. album) as a normally medicinal and edible plant has been used widely in Asian countries and is considered a source of phytochemicals that are beneficial to human health. Here, we showed at the first time isocorilagin, a polyphenolic compound isolated from C. album, displayed antiviral activity against diverse strains of influenza A virus (IAV), including A/Puerto Rico/8/34 (H1N1), A/Aichi/2/68 (H3N2) and NA-H274Y (H1N1) with IC₅₀ value of 9.19 ± 1.99, 23.72 ± 2.51 and 4.64 ± 3.01 μM, respectively. Further mechanistic studies revealed that it clearly inhibited neuraminidase activity of IAV and directly influenced the virus release. The molecular docking studies presented isocorilagin could bind to the highly conserved residues in the active sites of NA, implying that isocorilagin may be effective against various influenza strains and not susceptible to produce drug resistance. Taken together, the results strongly suggest that isocorilagin has potential to be an effective, safe and affordable neuraminidase inhibitor against a diverse panel of IAV strains. More importantly, our work expands the biological activities of C. album extracts and provide a new option for the development of anti-influenza drug.

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.

Comparative Study of Fusogenic Activity of H1 and H5 Subtypes Influenza Virus Hemagglutinins

Influenza virus hemagglutinins are surface proteins responsible for fusion of the viral and cellular membranes. Their capacity to mediate membrane fusion (fusogenic activity) is studied by various methods, including the syncytium formation and pseudovirus transduction methods. We constructed plasmids coding for genes of three H1 and one H5 hemagglutinins and compared their fusogenic activities. Hemagglutinin capacity to induce syncytium formation did not always correlate with the transduction activity of the respective pseudoviruses. Hemagglutinin H5 exhibited high fusogenic activity in studies by both methods, however, two of the studied H1 hemagglutinins induced the formation of syncytia, but did not mediate pseudovirus transduction. This could be due to different capsid sizes of influenza virus and vesicular stomatitis virus, which determines their different permeability through the fusion pore.

Characterization of Vesicular Stomatitis Virus Pseudotypes Bearing Essential Entry Glycoproteins gB, gD, gH, and gL of Herpes Simplex Virus 1

Herpes simplex viruses (HSVs) are unusual in that unlike most enveloped viruses, they require at least four entry glycoproteins, gB, gD, gH, and gL, for entry into target cells in addition to a cellular receptor for gD. The dissection of the herpes simplex virus 1 (HSV-1) entry mechanism is complicated by the presence of more than a dozen proteins on the viral envelope. To investigate HSV-1 entry requirements in a simplified system, we generated vesicular stomatitis virus (VSV) virions pseudotyped with HSV-1 essential entry glycoproteins gB, gD, gH, and gL but lacking the native VSV fusogen G. These virions, referred to here as VSVΔG-BHLD virions, infected a cell line expressing a gD receptor, demonstrating for the first time that the four essential entry glycoproteins of HSV-1 are not only required but also sufficient for cell entry. To our knowledge, this is the first time the VSV pseudotyping system has been successfully extended beyond two proteins. Entry of pseudotyped virions required a gD receptor and was inhibited by HSV-1 specific anti-gB or anti-gH/gL neutralizing antibodies, which suggests that membrane fusion during the entry of the pseudotyped virions shares common requirements with the membrane fusion involved in HSV-1 entry and HSV-1-mediated syncytium formation. The HSV pseudotyping system established in this study presents a novel tool for systematic exploration of the HSV entry and membrane fusion mechanisms.

IMPORTANCE

Herpes simplex viruses (HSVs) are human pathogens that can cause cold sores, genital herpes, and blindness. No vaccines or preventatives are available. HSV entry into cells-a prerequisite for a successful infection-is a complex process that involves multiple viral and host proteins and occurs by different routes. Detailed mechanistic knowledge of the HSV entry is important for understanding its pathogenesis and would benefit antiviral and vaccine development, yet the presence of more than a dozen proteins on the viral envelope complicates the dissection of the HSV entry mechanisms. In this study, we generated heterologous virions displaying the four essential entry proteins of HSV-1 and showed that they are capable of cell entry and, like HSV-1, require all four entry glycoproteins along with a gD receptor. This HSV pseudotyping system pioneered in this work opens doors for future systematic exploration of the herpesvirus entry mechanisms.

The application of pseudotypes to influenza pandemic preparedness

ABSTRACT 

Human and animal populations are constantly exposed to multiple influenza strains due to zoonotic spillover and rapid viral evolution driven by intrinsic error-prone replication and immunological pressure. In this context, antibody responses directed against the hemagglutinin protein on the surface of the virus are of importance since they have been shown to correlate with protective immunity. Serological techniques, detecting these responses, play a critical role in influenza pandemic preparedness in particular with regard to the measurement of vaccine immunogenicity. As the recent human pandemics (H1N1) and avian influenza outbreaks (H5 and H7) have demonstrated, there is an urgent need to be better prepared to assess the contribution of the antibody response to protection against newly emerged viruses and to evaluate the extent of pre-existing heterosubtypic immunity in populations. This review compares pseudotype-based assays with wild-type and virus-like particle virus assays and discusses their place in the pandemic preparedness against the influenza virus. It additionally addresses the state-of-the-art developments of pseudotype-based assays (chimeric hemagglutinins, multiplex and post-attachment) including the development and future deployment of assay kits and approaches toward standardization to both preclinical and clinical endpoints. Progress toward the development of an influenza pseudotype library for the purposes of pandemic preparedness is also outlined and discussed.

Pseudotype-based neutralization assays for influenza: a systematic analysis

The use of vaccination against the influenza virus remains the most effective method of mitigating the significant morbidity and mortality caused by this virus. Antibodies elicited by currently licensed influenza vaccines are predominantly hemagglutination-inhibition (HI)-competent antibodies that target the globular head of hemagglutinin (HA) thus inhibiting influenza virus entry into target cells. These antibodies predominantly confer homosubtypic/strain specific protection and only rarely confer heterosubtypic protection. However, recent academia or pharma-led R&D toward the production of a “universal vaccine” has centered on the elicitation of antibodies directed against the stalk of the influenza HA that has been shown to confer broad protection across a range of different subtypes (H1–H16). The accurate and sensitive measurement of antibody responses elicited by these “next-generation” influenza vaccines is, however, hampered by the lack of sensitivity of the traditional influenza serological assays HI, single radial hemolysis, and microneutralization. Assays utilizing pseudotypes, chimeric viruses bearing influenza glycoproteins, have been shown to be highly efficient for the measurement of homosubtypic and heterosubtypic broadly neutralizing antibodies, making them ideal serological tools for the study of cross-protective responses against multiple influenza subtypes with pandemic potential. In this review, we will analyze and compare literature involving the production of influenza pseudotypes with particular emphasis on their use in serum antibody neutralization assays. This will enable us to establish the parameters required for optimization and propose a consensus protocol to be employed for the further deployment of these assays in influenza vaccine immunogenicity studies.

A viable recombinant rhabdovirus lacking its glycoprotein gene and expressing influenza virus hemagglutinin and neuraminidase is a potent influenza vaccine

The emergence of novel influenza viruses that cause devastating human disease is an ongoing threat and serves as an impetus for the continued development of novel approaches to influenza vaccines. Influenza vaccine development has traditionally focused on producing humoral and/or cell-mediated immunity, often against the viral surface glycoproteins hemagglutinin (HA) and neuraminidase (NA). Here, we describe a new vaccine candidate that utilizes a replication-defective vesicular stomatitis virus (VSV) vector backbone that lacks the native G surface glycoprotein gene (VSVΔG). The expression of the H5 HA of an H5N1 highly pathogenic avian influenza virus (HPAIV), A/Vietnam/1203/04 (VN1203), and the NA of the mouse-adapted H1N1 influenza virus A/Puerto Rico/8/34 (PR8) in the VSVΔG vector restored the ability of the recombinant virus to replicate in cell culture, without the requirement for the addition of trypsin. We show here that this recombinant virus vaccine candidate was nonpathogenic in mice when given by either the intramuscular or intranasal route of immunization and that the in vivo replication of VSVΔG-H5N1 is profoundly attenuated. This recombinant virus also provided protection against lethal H5N1 infection after a single dose. This novel approach to vaccination against HPAIVs may be widely applicable to other emerging strains of influenza virus.

IMPORTANCE

Preparation for a potentially catastrophic influenza pandemic requires novel influenza vaccines that are safe, can be produced and administered quickly, and are effective, both soon after administration and for a long duration. We have created a new influenza vaccine that utilizes an attenuated vesicular stomatitis virus (VSV) vector, to deliver and express influenza virus proteins against which vaccinated animals develop potent antibody responses. The influenza virus hemagglutinin and neuraminidase proteins, expressed on the surface of VSV particles, allowed this vaccine to grow in cell culture and induced a potent antibody response in mice that was effective against infection with a lethal influenza virus. The mice showed no adverse reactions to the vaccine, and they were protected against an otherwise lethal influenza infection after only 14 days postvaccination and after as many as 140 days postvaccination. The ability to rapidly produce this safe and effective vaccine in cell culture is additionally advantageous.