Relocation of the attTn7 Transgene Insertion Site in Bacmid DNA Enhances Baculovirus Genome Stability and Recombinant Protein Expression in Insect Cells

Engineered thermoswitch in the baculovirus expression vector system for production of virus-like particle vaccines with minimized baculovirus contaminants

The baculovirus expression vector system (BEVS) is commercially used for producing recombinant (glyco)proteins, gene therapy vectors, and virus-like particles (VLPs) in insect cells. A major challenge in VLP downstream processing (DSP) is the removal of similarly sized baculovirus particle contaminants. Herein we engineered a genetic ON/OFF thermoswitch in the baculovirus vector by mutating the essential gp41 gene. This temperature-sensitive (ts) baculovirus expression system (BacFreets) produces high baculovirus titers at 27°C, while contaminating baculovirus production switches off at elevated temperatures. We demonstrate scalable VLP production for chikungunya virus (CHIKV), West Nile virus (WNV), coxsackievirus A6, and foot-and-mouth disease virus (FMDV) at 33°C, concomitant with baculovirus particle reduction up to 99.97%. However, elevated temperature moderately affected the yield of two out of four VLP designs. BacFreets is compatible with commonly used insect cells and scalable infection strategies. BacFreets effectively reduces baculovirus contaminants in the upstream VLP production phase, which will facilitate DSP of human and veterinary VLP-based vaccines.

Virus-like particle vaccine with authentic quaternary epitopes protects against Zika virus-induced viremia and testicular damage

Zika virus (ZIKV) caused unprecedented outbreaks in South America and the Caribbean in 2015-2016, leading primarily to a series of abnormalities in neonates termed congenital Zika syndrome. The threat of ZIKV reemergence has seen the development of multiple ZIKV vaccines that are at the preclinical stage or in early-stage clinical trials. Herein, we describe a pathway to the development of ZIKV vaccines generated using a baculovirus-insect cell expression system, which is widely applied for the manufacture of biologics for human use. Virus-like particle (VLP) vaccines comprising CprME and subviral particle (SVP) vaccines comprising prME were evaluated for their ability to mediate protection against ZIKV challenge in Ifnar1-/- mice. Initial attempts resulted in VLP and SVP vaccines that failed to present quaternary epitopes and did not provide effective protection. To improve the SVP vaccine, two modifications were introduced: firstly, an alanine to cysteine substitution (A264C) in the E domain II region to promote the formation of stabilized E homodimers and, secondly, the use of Spodoptera frugiperda Sf9 insect cells that had been adapted to grow and produce vaccine at a neutral pH of 7. E homodimers largely retain their pre-fusion conformation at pH 7, which is a requirement for the induction of effective neutralizing antibody responses. The stabilized SVP-A26C vaccine induced high levels of neutralizing antibodies and protected male Ifnar1-/- mice against viremia and testicular damage. Our study reiterates the need to present the immune system with E dimers arranged in authentic quaternary conformations and provides a scalable production method for this novel ZIKV vaccine.IMPORTANCEWe describe the generation of a subviral particle (SVP) vaccine comprising prME proteins of ZIKV, with an envelope protein substitution, A264C, that stabilizes E dimer formation. The SVP vaccine was produced in a novel Sf9 insect cell line adapted to grow in suspension at pH 7. The study highlights the importance of challenge experiments to ascertain whether the responses induced by an experimental vaccine actually mediate protection against virus infection and disease. The study also reiterates the contention that effective flavivirus vaccines need to present the immunogen in an authentic tertiary and quaternary structure with a pre-fusion conformation.

Continuous Production of Influenza VLPs Using IC-BEVS and Multi-Stage Bioreactors

The insect cell-baculovirus expression vector system (IC-BEVS) has been an asset to produce biologics for over 30 years. With the current trend in biotechnology shifting toward process intensification and integration, developing intensified processes such as continuous production is crucial to hold this platform as a suitable alternative to others. However, the implementation of continuous production has been hindered by the lytic nature of this expression system and the process-detrimental virus passage effect. In this study, we implemented a multi-stage bioreactor setup for continuous production of influenza hemagglutinin-displaying virus-like particles (HA-VLPs) using IC-BEVS. A setup consisting of one Cell Growth Bioreactor simultaneously feeding non-infected insect cells to three parallel Production Bioreactors operated at different residence times (RT) (18, 36, and 54 h) was implemented; Production Bioreactors were continuously harvested. Two insect cell lines (neutral pH-adapted High Five and Sf9) and two recombinant baculovirus (rBAC) constructs (one that originates from a bacmid, rBACbacmid, and another of non-bacteria origin, rBACflashbac) were tested. Combining rBACflashbac with Sf9 cells was the most efficient approach, allowing consistent HA-VLPs titers (34 ± 14 HA titer/mL) and rBAC titers (108-109 pfu/mL) throughout the period of continuous operation (20 days). Cell growth kinetics and viability varied across RT, and higher RT was associated with increased expression of HA-VLPs, independent of the cell line and rBAC used; RT of 54 h allowed to maximize titers. The presence of particles resembling HA-VLPs was confirmed by transmission electron microscopy throughout the continuous operation. This work showcases the implementation of a process for continuous production of a promising class of biotherapeutics (i.e., VLPs), and paves the way for establishing continuous, integrated setups using the IC-BEVS expression system.

Establishment & characterization of a non-adherent insect cell line for cultivated meat

This study presents a blueprint for developing, scaling, and analyzing novel insect cell lines for food. The large-scale production of cultivated meat requires the development and analysis of cell lines that are simple to grow and easy to scale. Insect cells may be a favorable cell source due to their robust growth properties, adaptability to different culture conditions, and resiliency in culture. Cells were isolated from Tobacco hornworm (Manduca sexta) embryos and subsequently adapted to single-cell suspension culture in animal-free growth media. Cells were able to reach relatively high cell densities of over 20 million cells per mL in shake flasks. Cell growth data is presented in various culture vessels and spent media analysis was performed to better understand cell metabolic processes. Finally, a preliminary nutritional profile consisting of proximate, amino acid, mineral, and fatty acid analysis is reported.

Progress in AAV-Mediated In Vivo Gene Therapy and Its Applications in Central Nervous System Diseases

As the blood-brain barrier (BBB) prevents molecules from accessing the central nervous system (CNS), the traditional systemic delivery of chemical drugs limits the development of neurological drugs. However, in recent years, innovative therapeutic strategies have tried to bypass the restriction of traditional drug delivery methods. In vivo gene therapy refers to emerging biopharma vectors that carry the specific genes and target and infect specific tissues; these infected cells and tissues then undergo fundamental changes at the genetic level and produce therapeutic proteins or substances, thus providing therapeutic benefits. Clinical and preclinical trials mainly utilize adeno-associated viruses (AAVs), lentiviruses (LVs), and other viruses as gene vectors for disease investigation. Although LVs have a higher gene-carrying capacity, the vector of choice for many neurological diseases is the AAV vector due to its safety and long-term transgene expression in neurons. Here, we review the basic biology of AAVs and summarize some key issues in recombinant AAV (rAAV) engineering in gene therapy research; then, we summarize recent clinical trials using rAAV treatment for neurological diseases and provide translational perspectives and future challenges on target selection.

From infection to remedy: Harnessing oncolytic viruses in cancer treatment

Oncolytic virus (OV) mediated immunotherapy is one of the recent techniques used to treat higher grade cancers where conventional therapies like chemotherapy, radiation fail. OVs as a therapeutic tool show high efficacy and fewer side effects than conventional methods as supported by multiple preclinical and clinical studies since they are engineered to target tumours. In this chapter, we discuss the modifications in viruses to make them oncolytic, types of strains commonly administered, mechanisms employed by viruses to specifically target and eradicate malignancy and progress achieved as reported in case studies (preclinical and clinical trials). OVs also face some unique challenges with respect to the malignancy being treated and the varied pathogen exposure of the patients, which is also highlighted here. Since pathogen exposure varies according to population dynamics worldwide, chances of generating a non-specific recall response to an OV cannot be negated. Lastly, the future perspectives and ongoing practises of combination therapies are discussed as they provide a leading edge over monotherapies in terms of tumour clearance, blocking metastasis and enhancing patient survival. Efforts undertaken to overcome current challenges are also highlighted.

Process intensification of the baculovirus expression vector system using a perfusion process with a low multiplicity of infection at high cell concentrations

The emergence of new viruses and the spread of existing pathogens necessitate efficient vaccine production methods. The baculovirus expression vector system (BEVS) is an efficient and scalable system for subunit and virus-like particle vaccine production and gene therapy vectors. However, current production processes are often limited to low cell concentrations (1-4 × 106 cells/mL) in fed-batch mode. To improve the volumetric productivity of the BEVS, a medium exchange strategy was investigated. Screening experiments were performed to test baculovirus (expressing green fluorescent protein; GFP) infection and productivity of insect cell cultures infected at high cell concentration (1-2 × 107 cells/mL), showing that infection at high cell concentrations was possible with medium exchange. Next, duplicate perfusion runs with baculovirus infection were performed using a cell concentration upon infection (CCI) of 1.2 × 107 cells/mL and a multiplicity of infection (MOI) of 0.01, reaching a maximum viable cell concentration of 2.8 × 107 cells/mL and a maximum GFP production of 263 mg/L. The volumetric productivity of these perfusion runs was 4.8 times higher than for reference batch processes with a CCI of 3 × 106 cells/mL and an MOI of 1. These results demonstrate that process intensification can be achieved for the BEVS by implementing perfusion, resulting in a higher volumetric productivity.

Efficient and accurate BmNPV bacmid editing system by two-step golden gate assembly

The silkworm-baculovirus expression vector system (silkworm-BEVS), using Bombyx mori nucleopolyhedrovirus (BmNPV) and silkworm larvae or pupae, has been used as a cost-effective expression system for the production of various recombinant proteins. Recently, several gene knockouts in baculoviruses have been shown to improve the productivity of recombinant proteins. However, the gene editing of the baculovirus genome (approximately 130 kb) remains challenging and time-consuming. In this study, we sought to further enhance the productivity of the silkworm-BEVS by synthesizing and gene editing the BmNPV bacmid from plasmids containing fragments of BmNPV genomic DNA using a two-step Golden Gate Assembly (GGA). The BmNPV genome, divided into 19 fragments, was amplified by PCR and cloned into the plasmids. From these initial plasmids, four intermediate plasmids containing the BmNPV genomic DNA were constructed by GGA with the type IIS restriction enzyme BsaI. Subsequently, the full-length bacmid was successfully synthesized from the four intermediate plasmids by GGA with another type IIS restriction enzyme PaqCI with a high efficiency of 97.2 %. Furthermore, this methodology enabled the rapid and straightforward generation of the BmNPV bacmid lacking six genes, resulting in the suppression of degradation of recombinant proteins expressed in silkworm pupae. These results indicate that the BmNPV bacmid can be quickly and efficiently edited using only simple cloning techniques and enzymatic reactions, marking a significant advancement in the improvement of the silkworm-BEVS.

A getah virus-like-particle vaccine provides complete protection from viremia and arthritis in wild-type mice

Getah virus (GETV) is an emerging mosquito-borne virus with economic impact on the livestock industry in East Asia. In this study, we successfully produced GETV virus-like particles (VLPs) in insect cells using the baculovirus expression vector system. We show that the GETV envelope glycoproteins were successfully expressed at the surface of the insect cell and were glycosylated. VLPs were isolated from the culture fluid as enveloped particles of 60-80 nm in diameter. Two 1 µg vaccinations with this GETV VLP vaccine, without adjuvant, generated neutralizing antibody responses and protected wild-type C57/BL6 mice against GETV viremia and arthritic disease. The GETV VLP vaccine may find application as a horse and/or pig vaccine in the future.

Tobacco Plant: A Novel and Promising Heterologous Bioreactor for the Production of Recombinant Bovine Chymosin

The natural source of chymosin, a key enzyme in the dairy industry, is insufficient for rapidly growing cheese industries. Large-scale production of recombinant proteins in heterologous hosts provides an efficient alternative solution. Here, the codon-optimized synthetic prochymosin gene, which has a CAI index of 0.926, was subcloned from a cloning vector (pUC57-bCYM) into the pBI121 vector, resulting in the construct named pBI121-bCYM. CAI ranges from 0 to 1 and higher CAI improves gene expression in heterologous hosts. The overexpression of the prochymosin gene was under the control of constitutive CaMV 35S promoter and NOS terminator and was transferred into the tobacco via A. tumefaciens strain LBA4404. Explant type, regeneration method, inoculation temperature, cell density (OD600) of Agrobacterium for inoculation, and acetosyringone concentration were leaf explants, direct somatic embryogenesis, 19 °C, 0.1, and 100 µM, respectively. The successful integration and expression of the prochymosin gene, along with the bioactivity of recombinant chymosin, were confirmed by PCR, RT-PCR, and milk coagulation assay, respectively. Overall, this study reports the first successful overexpression of the codon-optimized prochymosin form of the bovine chymosin enzyme in the tobacco via indirect transformation. Production of recombinant bovine chymosin in plants can be an easy-to-scale-up, safe, and inexpensive platform.

Adeno-associated virus as a delivery vector for gene therapy of human diseases

Adeno-associated virus (AAV) has emerged as a pivotal delivery tool in clinical gene therapy owing to its minimal pathogenicity and ability to establish long-term gene expression in different tissues. Recombinant AAV (rAAV) has been engineered for enhanced specificity and developed as a tool for treating various diseases. However, as rAAV is being more widely used as a therapy, the increased demand has created challenges for the existing manufacturing methods. Seven rAAV-based gene therapy products have received regulatory approval, but there continue to be concerns about safely using high-dose viral therapies in humans, including immune responses and adverse effects such as genotoxicity, hepatotoxicity, thrombotic microangiopathy, and neurotoxicity. In this review, we explore AAV biology with an emphasis on current vector engineering strategies and manufacturing technologies. We discuss how rAAVs are being employed in ongoing clinical trials for ocular, neurological, metabolic, hematological, neuromuscular, and cardiovascular diseases as well as cancers. We outline immune responses triggered by rAAV, address associated side effects, and discuss strategies to mitigate these reactions. We hope that discussing recent advancements and current challenges in the field will be a helpful guide for researchers and clinicians navigating the ever-evolving landscape of rAAV-based gene therapy.

Genetically Engineered Microorganisms and Their Impact on Human Health

The emergence of antibiotic-resistant strains, the decreased effectiveness of conventional therapies, and the side effects have led researchers to seek a safer, more cost-effective, patient-friendly, and effective method that does not develop antibiotic resistance. With progress in synthetic biology and genetic engineering, genetically engineered microorganisms effective in treatment, prophylaxis, drug delivery, and diagnosis have been developed. The present study reviews the types of genetically engineered bacteria and phages, their impacts on diseases, cancer, and metabolic and inflammatory disorders, the biosynthesis of these modified strains, the route of administration, and their effects on the environment. We conclude that genetically engineered microorganisms can be considered promising candidates for adjunctive treatment of diseases and cancers.

Scarless Baculovirus Genome Editing Using Lambda-Red Recombineering in E. coli

Baculoviruses are widely used for their potential as biological pesticide and as platform for the production of recombinant proteins and gene therapy vectors. The Baculovirus Expression Vector System (BEVS) is used for high level of expression of (multiple) proteins in insect cells. Baculovirus recombinants can be quickly constructed by transposition of the gene(s) of interest into a so-called bacmid, which is a baculovirus infectious clone maintained as single-copy, bacterial artificial chromosome in Escherichia coli. A two-step homologous recombineering technique using the lambda-red system in E. coli allows for scarless editing of the bacmid with PCR products based on sequence homology. In the first step, a selection cassette with 50 bp homology arms, typically generated by PCR, is inserted into the designated locus. In the second step, the selection cassette is removed based on a negative selection marker, such as SacB or rpsL. This lambda-red recombineering technique can be used for multiple gene editing purposes, including (large) deletions, insertions, and even single point mutations. Moreover, since there are no remnants of the editing process, successive modifications of the same bacmid are possible. This chapter provides detailed instructions to design and perform two-step homologous recombineering of baculovirus bacmid DNA in E. coli. We present two case studies demonstrating the utility of this technique for creating a deletion mutant of the chitinase and cathepsin genes and for introducing a single point mutation in the baculovirus gene gp41. This scarless genome editing approach can facilitate functional studies of baculovirus genes and improve the production of recombinant proteins using the BEVS.

A sensitive assay for scrutiny of Autographa californica multiple nucleopolyhedrovirus genes using CRISPR-Cas9

Baculoviruses have very large genomes and previous studies have demonstrated improvements in recombinant protein production and genome stability through the removal of some nonessential sequences. However, recombinant baculovirus expression vectors (rBEVs) in widespread use remain virtually unmodified. Traditional approaches for generating knockout viruses (KOVs) require several experimental steps to remove the target gene prior to the generation of the virus. In order to optimize rBEV genomes by removing nonessential sequences, more efficient techniques for establishing and evaluating KOVs are required. Here, we have developed a sensitive assay utilizing CRISPR-Cas9-mediated gene targeting to examine the phenotypic impact of disruption of endogenous Autographa californica multiple nucleopolyhedrovirus (AcMNPV) genes. For validation, 13 AcMNPV genes were targeted for disruption and evaluated for the production of GFP and progeny virus - traits that are essential for their use as vectors for recombinant protein production. The assay involves transfection of sgRNA into a Cas9-expressing Sf9 cell line followed by infection with a baculovirus vector carrying the gfp gene under the p10 or p6.9 promoters. This assay represents an efficient strategy for scrutinizing AcMNPV gene function through targeted disruption, and represents a valuable tool for developing an optimized rBEV genome. KEY POINTS: [Formula: see text] A method to scrutinize the essentiality of baculovirus genes was developed. [Formula: see text] The method uses Sf9-Cas9 cells, a targeting plasmid carrying a sgRNA, and a rBEV-GFP. [Formula: see text] The method allows scrutiny by only needing to modify the targeting sgRNA plasmid.

Comparative Efficacy of Mayaro Virus-Like Particle Vaccines Produced in Insect or Mammalian Cells

Mayaro virus (MAYV) is a mosquito-transmitted alphavirus that causes often debilitating rheumatic disease in tropical Central and South America. There are currently no licensed vaccines or antiviral drugs available for MAYV disease. Here, we generated Mayaro virus-like particles (VLPs) using the scalable baculovirus-insect cell expression system. High-level secretion of MAYV VLPs in the culture fluid of Sf9 insect cells was achieved, and particles with a diameter of 64 to 70 nm were obtained after purification. We characterize a C57BL/6J adult wild-type mouse model of MAYV infection and disease and used this model to compare the immunogenicity of VLPs from insect cells with that of VLPs produced in mammalian cells. Mice received two intramuscular immunizations with 1 μg of nonadjuvanted MAYV VLPs. Potent neutralizing antibody responses were generated against the vaccine strain, BeH407, with comparable activity seen against a contemporary 2018 isolate from Brazil (BR-18), whereas neutralizing activity against chikungunya virus was marginal. Sequencing of BR-18 illustrated that this virus segregates with genotype D isolates, whereas MAYV BeH407 belongs to genotype L. The mammalian cell-derived VLPs induced higher mean neutralizing antibody titers than those produced in insect cells. Both VLP vaccines completely protected adult wild-type mice against viremia, myositis, tendonitis, and joint inflammation after MAYV challenge. IMPORTANCE Mayaro virus (MAYV) is associated with acute rheumatic disease that can be debilitating and can evolve into months of chronic arthralgia. MAYV is believed to have the potential to emerge as a tropical public health threat, especially if it develops the ability to be efficiently transmitted by urban mosquito vectors, such as Aedes aegypti and/or Aedes albopictus. Here, we describe a scalable virus-like particle vaccine against MAYV that induced neutralizing antibodies against a historical and a contemporary isolate of MAYV and protected mice against infection and disease, providing a potential new intervention for MAYV epidemic preparedness.

Homologous recombination risk in baculovirus expression vector system

The baculovirus expression vector system (BEVS) is widely used for producing recombinant proteins. To achieve high expression level of recombinant proteins, baculoviral elements, such as enhancers, promoters, signal peptide coding sequences and 3'-UTR, have been extensively employed. There is a recombination risk derived from homologous sequences between viral genome and functional baculovirus-derived elements associated with foreign genes. Although homologous recombination have distinct biological functions, these potential adverse recombination may trigger a DNA fragment being inverted or looped out, resulting in the production of defective viruses and eventual yields declines of recombinant proteins. However, the risk of such homologous recombination has not been systematically assessed. Here, we measured the recombination rate using a promoter-less fluorescent reporter integrated with various lengths homologous of p10 coding region. Homologous fragments longer than 60 bp possess sufficient recombination probability and exerts effect on purity and integrity of virus. Shortening the length of homologous fragments and separating homologous fragments by point mutations can effectively reduce unfavorable recombination. These findings reveal a homologous recombination risk resulted from genome-homologous baculoviral elements and propose reliable strategies reducing recombination rate to facilitate viral stability and integrity in baculovirus expression vector system.

Genetic engineering of baculovirus-insect cell system to improve protein production

The Baculovirus Expression Vector System (BEVS), a mature foreign protein expression platform, has been available for decades, and has been effectively used in vaccine production, gene therapy, and a host of other applications. To date, eleven BEVS-derived products have been approved for use, including four human vaccines [Cervarix against cervical cancer caused by human papillomavirus (HPV), Flublok and Flublok Quadrivalent against seasonal influenza, Nuvaxovid/Covovax against COVID-19], two human therapeutics [Provenge against prostate cancer and Glybera against hereditary lipoprotein lipase deficiency (LPLD)] and five veterinary vaccines (Porcilis Pesti, BAYOVAC CSF E2, Circumvent PCV, Ingelvac CircoFLEX and Porcilis PCV). The BEVS has many advantages, including high safety, ease of operation and adaptable for serum-free culture. It also produces properly folded proteins with correct post-translational modifications, and can accommodate multi-gene- or large gene insertions. However, there remain some challenges with this system, including unstable expression and reduced levels of protein glycosylation. As the demand for biotechnology increases, there has been a concomitant effort into optimizing yield, stability and protein glycosylation through genetic engineering and the manipulation of baculovirus vector and host cells. In this review, we summarize the strategies and technological advances of BEVS in recent years and explore how this will be used to inform the further development and application of this system.

Application of bioreactor technology for cell culture-based viral vaccine production: Present status and future prospects

Bioreactors are widely used in cell culture-based viral vaccine production, especially during the coronavirus disease 2019 (COVID-19) pandemic. In this context, the development and application of bioreactors can provide more efficient and cost-effective vaccine production to meet the global vaccine demand. The production of viral vaccines is inseparable from the development of upstream biological processes. In particular, exploration at the laboratory-scale is urgently required for further development. Therefore, it is necessary to evaluate the existing upstream biological processes, to enable the selection of pilot-scale conditions for academic and industrial scientists to maximize the yield and quality of vaccine development and production. Reviewing methods for optimizing the upstream process of virus vaccine production, this review discusses the bioreactor concepts, significant parameters and operational strategies related to large-scale amplification of virus. On this basis, a comprehensive analysis and evaluation of the various process optimization methods for the production of various viruses (SARS-CoV-2, Influenza virus, Tropical virus, Enterovirus, Rabies virus) in bioreactors is presented. Meanwhile, the types of viral vaccines are briefly introduced, and the established animal cell lines for vaccine production are described. In addition, it is emphasized that the co-development of bioreactor and computational biology is urgently needed to meet the challenges posed by the differences in upstream production scales between the laboratory and industry.

Application of Baculovirus Expression Vector system (BEV) for COVID-19 diagnostics and therapeutics: a review

BACKGROUND

The baculovirus expression vector system has been developed for expressing a wide range of proteins, including enzymes, glycoproteins, recombinant viruses, and vaccines. The availability of the SARS-CoV-2 genome sequence has enabled the synthesis of SARS-CoV2 proteins in a baculovirus-insect cell platform for various applications. The most cloned SARS-CoV-2 protein is the spike protein, which plays a critical role in SARS-CoV-2 infection. It is available in its whole length or as subunits like S1 or the receptor-binding domain (RBD). Non-structural proteins (Nsps), another recombinant SARS-CoV-2 protein generated by the baculovirus expression vector system (BEV), are used in the identification of new medications or the repurposing of existing therapies for the treatment of COVID-19. Non-SARS-CoV-2 proteins generated by BEV for SARS-CoV-2 diagnosis or treatment include moloney murine leukemia virus reverse transcriptase (MMLVRT), angiotensin converting enzyme 2 (ACE2), therapeutic proteins, and recombinant antibodies. The recombinant proteins were modified to boost the yield or to stabilize the protein.

CONCLUSION

This review covers the wide application of the recombinant protein produced using the baculovirus expression technology for COVID-19 research. A lot of improvements have been made to produce functional proteins with high yields. However, there is still room for improvement and there are parts of this field of research that have not been investigated yet.

Secreted Trimeric Chikungunya Virus Spikes from Insect Cells: Production, Purification, and Glycosylation Status

Chikungunya virus (CHIKV) is a rapidly emerging mosquito-borne virus that causes a severe febrile illness with long-lasting arthralgia in humans. As there is no vaccine to protect humans and limit CHIKV epidemics, the virus continues to be a global public health concern. The CHIKV envelope glycoproteins E1 and E2 are important immunogens; therefore, the aim of this study is to produce trimeric CHIKV spikes in insect cells using the baculovirus expression system. The CHIKV E1 and E2 ectodomains were covalently coupled by a flexible linker that replaces the 6K transmembrane protein. The C-terminal E1 transmembrane was replaced by a Strep-tag II for the purification of secreted spikes from the culture fluid. After production in Sf9 suspension cells (product yields of 5.8–7.6 mg/L), the CHIKV spikes were purified by Strep-Tactin affinity chromatography, which successfully cleared the co-produced baculoviruses. Bis(sulfosuccinimidyl)suberate cross-linking demonstrated that the spikes are secreted as trimers. PNGase F treatment showed that the spikes are glycosylated. LC–MS/MS-based glycoproteomic analysis confirmed the glycosylation and revealed that the majority are of the mannose- or hybrid-type N-glycans and <2% have complex-type N-glycans. The LC –MS/MS analysis also revealed three O-glycosylation sites in E1. In conclusion, the trimeric, glycosylated CHIKV spikes have been successfully produced in insect cells and are now available for vaccination studies.

Two-Component Nanoparticle Vaccine Displaying Glycosylated Spike S1 Domain Induces Neutralizing Antibody Response against SARS-CoV-2 Variants

Vaccines pave the way out of the SARS-CoV-2 pandemic. Besides mRNA and adenoviral vector vaccines, effective protein-based vaccines are needed for immunization against current and emerging variants. We have developed a virus-like particle (VLP)-based vaccine using the baculovirus-insect cell expression system, a robust production platform known for its scalability, low cost, and safety. Baculoviruses were constructed encoding SARS-CoV-2 spike proteins: full-length S, stabilized secreted S, or the S1 domain. Since subunit S only partially protected mice from SARS-CoV-2 challenge, we produced S1 for conjugation to bacteriophage AP205 VLP nanoparticles using tag/catcher technology. The S1 yield in an insect-cell bioreactor was ∼11 mg/liter, and authentic protein folding, efficient glycosylation, partial trimerization, and ACE2 receptor binding was confirmed. Prime-boost immunization of mice with 0.5 μg S1-VLPs showed potent neutralizing antibody responses against Wuhan and UK/B.1.1.7 SARS-CoV-2 variants. This two-component nanoparticle vaccine can now be further developed to help alleviate the burden of COVID-19.

An Overview of the Application of Viruses to Biotechnology

Viruses may cause devastating diseases in several organisms; however, they are simple systems that can be manipulated to be beneficial and useful for many purposes in different areas. In medicine, viruses have been used for a long time in vaccines and are now being used as vectors to carry materials for the treatment of diseases, such as cancer, being able to target specific cells. In agriculture, viruses are being studied to introduce desirable characteristics in plants or render resistance to biotic and abiotic stresses. Viruses have been exploited in nanotechnology for the deposition of specific metals and have been shown to be of great benefit to nanomaterial production. They can also be used for different applications in pharmacology, cosmetics, electronics, and other industries. Thus, viruses are no longer only seen as enemies. They have shown enormous potential, covering several important areas in our lives, and they are making our lives easier and better. Although viruses have already proven their potential, there is still a long road ahead. This prompt us to propose this theme in the Special Issue "The application of viruses to biotechnology". We believe that the articles gathered here highlight recent significant advances in the use of viruses in several fields, contributing to the current knowledge on virus applications.