Glycoprotein E of the Japanese encephalitis virus forms virus-like particles and induces syncytia when expressed by a baculovirus

Insect cell production of chimeric virus-like particles based on human immunodeficiency virus GAG proteins and yellow fever virus envelope protein

The yellow fever virus (YFV) is a single stranded RNA virus belonging to the genus Orthoflavivirus that is capable of zoonotic transmissions that infect nonhuman and human primates. It is endemic in Brazil with recurrent epidemics of the disease, and it is transmitted through mosquitoes. The detection and immunization against YFV and other flaviviruses are fundamental for the management of the impacts of the disease in human environments. In an ongoing effort to develop new approaches for diagnostics and immunizations, we expressed VLPs displaying the yellow fever virus envelope protein (YFE) using recombinant baculovirus in insect cells. By co-expressing HIV-1 Pr55Gag protein (GAG) together with YFE we were able to generate chimeric VLPs containing a GAG core together with an envelope containing the YFE protein. The YFE and the chimeric GAG-YFE VLPs have potential as vaccine candidates and as reagents for serological assays in the detection of these viruses in human sera.

Phage display and other peptide display technologies

Phage display technology, which is based on the presentation of peptide sequences on the surface of bacteriophage virions, was developed over 30 years ago. Improvements in phage display systems have allowed us to employ this method in numerous fields of biotechnology, as diverse as immunological and biomedical applications, the formation of novel materials and many others. The importance of phage display platforms was recognized by awarding the Nobel Prize in 2018 "for the phage display of peptides and antibodies". In contrast to many review articles concerning specific applications of phage display systems published in recent years, we present an overview of this technology, including a comparison of various display systems, their advantages and disadvantages, and examples of applications in various fields of science, medicine, and the broad sense of biotechnology. Other peptide display technologies, which employ bacterial, yeast and mammalian cells, as well as eukaryotic viruses and cell-free systems, are also discussed. These powerful methods are still being developed and improved; thus, novel sophisticated tools based on phage display and other peptide display systems are constantly emerging, and new opportunities to solve various scientific, medical and technological problems can be expected to become available in the near future.

Solutions against emerging infectious and noninfectious human diseases through the application of baculovirus technologies

Abstract

Baculoviruses are insect pathogens widely used as biotechnological tools in different fields of life sciences and technologies. The particular biology of these entities (biosafety viruses 1; large circular double-stranded DNA genomes, infective per se; generally of narrow host range on insect larvae; many of the latter being pests in agriculture) and the availability of molecular-biology procedures (e.g., genetic engineering to edit their genomes) and cellular resources (availability of cell lines that grow under in vitro culture conditions) have enabled the application of baculoviruses as active ingredients in pest control, as systems for the expression of recombinant proteins (Baculovirus Expression Vector Systems—BEVS) and as viral vectors for gene delivery in mammals or to display antigenic proteins (Baculoviruses applied on mammals—BacMam). Accordingly, BEVS and BacMam technologies have been introduced in academia because of their availability as commercial systems and ease of use and have also reached the human pharmaceutical industry, as incomparable tools in the development of biological products such as diagnostic kits, vaccines, protein therapies, and—though still in the conceptual stage involving animal models—gene therapies. Among all the baculovirus species, the Autographa californica multiple nucleopolyhedrovirus has been the most highly exploited in the above utilities for the human-biotechnology field. This review highlights the main achievements (in their different stages of development) of the use of BEVS and BacMam technologies for the generation of products for infectious and noninfectious human diseases.

Key points

• Baculoviruses can assist as biotechnological tools in human health problems.

• Vaccines and diagnosis reagents produced in the baculovirus platform are described.

• The use of recombinant baculovirus for gene therapy–based treatment is reviewed.

Interaction Between Virus-Like Particles (VLPs) and Pattern Recognition Receptors (PRRs) From Dendritic Cells (DCs): Toward Better Engineering of VLPs

Virus-like particles (VLPs) have been shown to be strong activators of dendritic cells (DCs). DCs are the most potent antigen presenting cells (APCs) and their activation prompts the priming of immunity mediators based on B and T cells. The first step for the activation of DCs is the binding of VLPs to pattern recognition receptors (PRRs) on the surface of DCs, followed by VLP internalization. Like wild-type viruses, VLPs use specific PRRs from the DC; however, these recognition interactions between VLPs and PRRs from DCs have not been thoroughly reviewed. In this review, we focused on the interaction between proteins that form VLPs and PRRs from DCs. Several proteins that form VLP contain glycosylations that allow the direct interaction with PRRs sensing carbohydrates, prompting DC maturation and leading to the development of strong adaptive immune responses. We also discussed how the knowledge of the molecular interaction between VLPs and PRRs from DCs can lead to the smart design of VLPs, whether based on the fusion of foreign epitopes or their chemical conjugation, as well as other modifications that have been shown to induce a stronger adaptive immune response and protection against infectious pathogens of importance in human and veterinary medicine. Finally, we address the use of VLPs as tools against cancer and allergic diseases.

Virus-Like Particle Systems for Vaccine Development against Viruses in the Flaviviridae Family

Viruses in the Flaviviridae family are important human and animal pathogens that impose serious threats to global public health. This family of viruses includes emerging and re-emerging viruses, most of which are transmitted by infected mosquito or tick bites. Currently, there is no protective vaccine or effective antiviral treatment against the majority of these viruses, and due to their growing spread, several strategies have been employed to manufacture prophylactic vaccines against these infectious agents including virus-like particle (VLP) subunit vaccines. VLPs are genomeless viral particles that resemble authentic viruses and contain critical repetitive conformational structures on their surface that can trigger the induction of both humoral and cellular responses, making them safe and ideal vaccine candidates against these viruses. In this review, we focus on the potential of the VLP platform in the current vaccine development against the medically important viruses in the Flaviviridae family.

Production and Biomedical Application of Flavivirus-like Particles

Many viruses belonging to the Flaviviridae family are transmitted by invertebrate vectors. Among those transmitted by mosquitos, there are many human pathogens of great medical importance, such as Japanese encephalitis virus, West Nile virus, dengue virus, Zika virus, or yellow fever virus. Millions of people contract mosquito-borne diseases each year, leading to thousands of deaths. Co-circulation of genetically similar flaviviruses in the same areas result in the generation of crossreactive antibodies, which is of serious concern for the development of effective vaccines and diagnostic tests. This review provides comprehensive insight into the potential use of virus-like particles as safe and effective antigens in both diagnostics tests, as well as in the development of vaccines against several mosquito-borne flaviviruses.

Establishment of Baculovirus-Expressed VLPs Induced Syncytial Formation Assay for Flavivirus Antiviral Screening

The baculovirus-insect cell expression system has been widely used for heterologous protein expression and virus-like particles (VLPs) expression. In this study, we established a new method for antiviral screening targeting to glycoprotein E of flaviviruses based on the baculovirus expression system. ZIKV is a mosquito-borne flavivirus and has posed great threat to the public health. It has been reported that ZIKV infection was associated with microcephaly and serious neurological complications. Our study showed that either ZIKV E or prME protein expressed in insect cells can form VLPs and induce membrane fusion between insect cells. Therefore, the E protein, which is responsible for receptor binding, attachment, and virus fusion during viral entry, achieved proper folding and retained its fusogenic ability in VLPs when expressed in this system. The syncytia in insect cells were significantly reduced by the anti-ZIKV-E specific polyclonal antibody in a dose-dependent manner. AMS, a thiol-conjugating reagent, was also shown to have an inhibitory effect on the E protein induced syncytia and inhibited ZIKV infection by blocking viral entry. Indeed the phenomenon of syncytial formation induced by E protein expressed VLPs in insect cells is common among flaviviruses, including Japanese encephalitis virus (JEV), Dengue virus type 2 (DENV-2), and tick-borne encephalitis virus (TBEV). This inhibition effect on syncytial formation can be developed as a novel, safe, and simple antiviral screening approach for inhibitory antibodies, peptides, or small molecules targeting to E protein of ZIKV and other flaviviruses.

Zika Virus Baculovirus-Expressed Virus-Like Particles Induce Neutralizing Antibodies in Mice

The newly emerged mosquito-borne Zika virus (ZIKV) strains pose a global challenge owing to its ability to cause microcephaly and neurological disorders. Several ZIKV vaccine candidates have been proposed, including inactivated and live attenuated virus vaccines, vector-based vaccines, DNA and RNA vaccines. These have been shown to be efficacious in preclinical studies in mice and nonhuman primates, but their use will potentially be a threat to immunocompromised individuals and pregnant women. Virus-like particles (VLPs) are empty particles composed merely of viral proteins, which can serve as a safe and valuable tool for clinical prevention and treatment strategies. In this study, we used a new strategy to produce ZIKV VLPs based on the baculovirus expression system and demonstrated the feasibility of their use as a vaccine candidate. The pre-membrane (prM) and envelope (E) proteins were co-expressed in insect cells and self-assembled into particles similar to ZIKV. We found that the ZIKV VLPs could be quickly and easily prepared in large quantities using this system. The VLPs were shown to have good immunogenicity in immunized mice, as they stimulated high levels of virus neutralizing antibody titers, ZIKV-specific IgG titers and potent memory T cell responses. Thus, the baculovirus-based ZIKV VLP vaccine is a safe, effective and economical vaccine candidate for use against ZIKV.

Japanese encephalitis virus counteracts BST2 restriction via its envelope protein E

It has been well documented that BST2 restricts the release of enveloped viruses by cross-linking newly produced virions to the cell membrane. However, it is less clear whether and how BST2 inhibits the release of enveloped viruses which bud via the secretory pathway. Here, we demonstrated that BST2 restricts the release of Japanese encephalitis virus (JEV) whose budding occurs at the ER-Golgi intermediate compartment, and in turn, JEV infection downregulates BST2 expression. We further found that the JEV envelope protein E, but not other viral components, significantly downregulates BST2 with the viral protein M playing an auxiliary role in the process. Envelope protein E-mediated BST2 downregulation appears to undergo lysosomal degradation pathway. Additional study revealed that the transmembrane domain and the coiled-coil domain (CC) of BST2 are the target domains of viral protein E and that the N- and C-terminal membrane anchors and the CC domain of BST2 are essential for blocking JEV release. Our results together indicate that the release of enveloped viruses whose budding take place in an intracellular compartment can be restricted by BST2.

Virus like particle-based vaccines against emerging infectious disease viruses

Emerging infectious diseases are major threats to human health. Most severe viral disease outbreaks occur in developing regions where health conditions are poor. With increased international travel and business, the possibility of eventually transmitting infectious viruses between different countries is increasing. The most effective approach in preventing viral diseases is vaccination. However, vaccines are not currently available for numerous viral diseases. Virus-like particles (VLPs) are engineered vaccine candidates that have been studied for decades. VLPs are constructed by viral protein expression in various expression systems that promote the selfassembly of proteins into structures resembling virus particles. VLPs have antigenicity similar to that of the native virus, but are non-infectious as they lack key viral genetic material. VLP vaccines have attracted considerable research interest because they offer several advantages over traditional vaccines. Studies have shown that VLP vaccines can stimulate both humoral and cellular immune responses, which may offer effective antiviral protection. Here we review recent developments with VLP-based vaccines for several highly virulent emerging or re-emerging infectious diseases. The infectious agents discussed include RNA viruses from different virus families, such as the Arenaviridae, Bunyaviridae, Caliciviridae, Coronaviridae, Filoviridae, Flaviviridae, Orthomyxoviridae, Paramyxoviridae, and Togaviridae families.

An in vitro recombination-based reverse genetic system for rapid mutagenesis of structural genes of the Japanese encephalitis virus

Japanese encephalitis virus (JEV) is one of the most common pathogens of severe viral encephalitis, which is a severe threat to human health. Despite instability of the JEV genome in bacteria, many strategies have been developed to establish molecular clone systems of JEV, providing convenient tools for studying the virus life cycle and virus-host interactions. In this study, we adapted an In-Fusion enzyme-based in vitro recombination method to construct a reverse genetic system of JEV, thereby providing a rapid approach to introduce mutations into the structural genes. A truncated genome without the structural genes was constructed as the backbone, and the complementary segment containing the structural genes was recombined in vitro, which was then transfected directly into virus-permissive cells. The progeny of the infectious virus was successfully detected in the supernatant of the transfected cells, and showed an identical phenotype to its parental virus. To provide a proof-of-principle, the 12 conserved cysteine residues in the envelope (E) protein of JEV were respectively mutated using this approach, and all mutations resulted in a complete failure to generate infectious virus. However, a leucine-tophenylanine mutation at amino acid 107 of the E protein did not interfere with the production of the infectious virus. These results suggested that all 12 cysteines in the E protein are essential for the JEV life cycle. In summary, a novel reverse genetic system of JEV was established for rapidly introducing mutations into structural genes, which will serve as a useful tool for functional studies.