Yellow fever virus envelope protein expressed in insect cells is capable of syncytium formation in lepidopteran cells and could be used for immunodetection of YFV in human sera

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.

Preparation and application of yellow fever virus NS1 protein-specific monoclonal antibodies

Yellow fever is an acute infectious disease that is common in Africa and South America and causes thousands of deaths annually. However, there are very few studies on yellow fever virus (YFV) antigen detection kits. As a detection target, the nonstructural protein 1 (NS1) has been successfully used in the early diagnosis of dengue virus (a member of the Flaviviridae family) infection. In this study, we used monoclonal antibody technology to prepare anti-YFV NS1 monoclonal antibodies (MAbs) and identified their immunological properties. Next, we used two mouse MAbs that can recognize different epitopes of YFV NS1 as capture and detection antibodies to establish a YFV NS1 antigen-capture enzyme-linked immunosorbent assay (ELISA). The antigen-capture ELISA displayed exclusive specificity to YFV without cross-reaction with other related members of the flavivirus family, including the dengue virus, West Nile virus, Japanese encephalitis virus. Additionally, the detection sensitivity towards the YFV culture supernatant was 103 TCID50/mL and the detection positivity rate was 95% compared with reverse transcription-polymerase chain reaction. In conclusion, this newly developed NS1 antigen-capture ELISA with high sensitivity and specificity could be used as an efficient method for the early diagnosis of YFV infection in animals or humans.

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.

Plant-Produced Subunit Vaccine Candidates against Yellow Fever Induce Virus Neutralizing Antibodies and Confer Protection against Viral Challenge in Animal Models

Yellow fever (YF) is a viral disease transmitted by mosquitoes and endemic mostly in South America and Africa with 20-50% fatality. All current licensed YF vaccines, including YF-Vax^® (Sanofi-Pasteur, Lyon, France) and 17DD-YFV (Bio-Manguinhos, Rio de Janeiro, Brazil), are based on live attenuated virus produced in hens' eggs and have been widely used. The YF vaccines are considered safe and highly effective. However, a recent increase in demand for YF vaccines and reports of rare cases of YF vaccine-associated fatal adverse events have provoked interest in developing a safer YF vaccine that can be easily scaled up to meet this increased global demand. To this point, we have engineered the YF virus envelope protein (YFE) and transiently expressed it in Nicotiana benthamiana as a stand-alone protein (YFE) or as fusion to the bacterial enzyme lichenase (YFE-LicKM). Immunogenicity and challenge studies in mice demonstrated that both YFE and YFE-LicKM elicited virus neutralizing (VN) antibodies and protected over 70% of mice from lethal challenge infection. Furthermore, these two YFE-based vaccine candidates induced VN antibody responses with high serum avidity in nonhuman primates and these VN antibody responses were further enhanced after challenge infection with the 17DD strain of YF virus. These results demonstrate partial protective efficacy in mice of YFE-based subunit vaccines expressed in N. benthamiana. However, their efficacy is inferior to that of the live attenuated 17DD vaccine, indicating that formulation development, such as incorporating a more suitable adjuvant, may be required for product development.

Crimean-Congo Hemorrhagic Fever Virus Gn Bioinformatic Analysis and Construction of a Recombinant Bacmid in Order to Express Gn by Baculovirus Expression System

Background

Crimean-Congo hemorrhagic fever virus (CCHFV) is a member of the nairovirus, a genus in the Bunyaviridae family, which causes a life threatening disease in human. Currently, there is no vaccine against CCHFV and detailed structural analysis of CCHFV proteins remains undefined. The CCHFV M RNA segment encodes two viral surface glycoproteins known as Gn and Gc. Viral glycoproteins can be considered as key targets for vaccine development.

Objectives

The current study aimed to investigate structural bioinformatics of CCHFV Gn protein and design a construct to make a recombinant bacmid to express by baculovirus system.

Materials and Methods

To express the Gn protein in insect cells that can be used as antigen in animal model vaccine studies. Bioinformatic analysis of CCHFV Gn protein was performed and designed a construct and cloned into pFastBacHTb vector and a recombinant Gn-bacmid was generated by Bac to Bac system.

Results

Primary, secondary, and 3D structure of CCHFV Gn were obtained and PCR reaction with M13 forward and reverse primers confirmed the generation of recombinant bacmid DNA harboring Gn coding region under polyhedron promoter.

Conclusions

Characterization of the detailed structure of CCHFV Gn by bioinformatics software provides the basis for development of new experiments and construction of a recombinant bacmid harboring CCHFV Gn, which is valuable for designing a recombinant vaccine against deadly pathogens like CCHFV.

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

The prM glycoprotein is thought to be a chaperone for the proper folding, membrane association and assembly of the envelope protein (E) of flaviviruses. The prM-E and E proteins of the Japanese encephalitis virus (JEV) were expressed in insect cells using both the baculovirus-expression system and the transient expression method. Protein expression was analysed by Western blotting and the cytopathic effect was observed by microscopy. In the baculovirus-expression system the E protein, with or without the prM protein, induced syncytial formation in Sf9 cells. Transient expression of prM-E also induced syncytia in Sf9 cells. Immunofluorescence revealed that in presence of prM, E proteins were endoplasmic reticulum-like in distribution, while in the absence of prM, E proteins were located on the cell surface. Sucrose gradient sedimentation and Western blot analysis indicated that the E protein expressed with or without the prM protein was secreted into the culture medium in particulate form. The formation of virus-like particles (VLPs) in the medium was confirmed by electron microscopy and immunoelectron microscopy. The results suggest that the E protein of JEV in the absence of prM, retained its fusion ability, by either cell surface expression or formation of VLPs. Moreover, based on the observation that co-expression of prM-E in Sf9 cells induced considerable syncytial formation, a novel, safe and simple antiviral screening approach is proposed for studying inhibitory antibodies, peptides or small molecules targeting the JEV E protein.

Research advances in plant-made flavivirus antigens

Outbreaks of flaviviruses such as dengue (DV), yellow fever (YFV), Japanese encephalitis (JEV), tick-borne encephalitis (TBEV) and West Nile (WNV) affect numerous countries around the world. The fast spread of these viruses is the result of increases in the human population, rapid urbanisation and globalisation. While vector control is an important preventive measure against vector-borne diseases, it has failed to prevent the spread of these diseases, particularly in developing countries where the implementation of control measures is intermittent. As antiviral drugs against flaviviruses are not yet available, vaccination remains the most important tool for prevention. Although human vaccines for YFV, TBEV and JEV are available, on-going vaccination efforts are insufficient to prevent infection. No vaccines against DENV and WNV are available. Research advances have provided important tools for flavivirus vaccine development, such as the use of plants as a recombinant antigen production platform. This review summarises the research efforts in this area and highlights why a plant system is considered a necessary alternative production platform for high-tech subunit vaccines.

Revealing the molecular signatures of host-pathogen interactions

Advances in sequencing technology and genome-wide association studies are now revealing the complex interactions between hosts and pathogen through genomic variation signatures, which arise from evolutionary co-existence.