Use of baculovirus expression system for generation of virus-like particles: successes and challenges

Extracellular Vesicles based STAT3 delivery as innovative therapeutic approach to restore STAT3 signaling deficiency

Extracellular Vesicles (EVs) have been proposed as a promising tool for drug delivery because of their natural ability to cross biological barriers, protect their cargo, and target specific cells. Moreover, EVs are not recognized by the immune system as foreign, reducing the risk of an immune response and enhancing biocompatibility. Herein, we proposed an alternative therapeutic strategy to restore STAT3 signaling exploiting STAT3 loaded EVs. This approach could be useful in the treatment of Autosomal Dominant Hyper-IgE Syndrome (AD-HIES), a rare primary immunodeficiency and multisystem disorder due to the presence of mutations in STAT3 gene. These mutations alter the signal transduction of STAT3, thereby impeding Th17 CD4+ cell differentiation that leads to the failure of immune response. We set up a simple and versatile method in which EVs were loaded with fully functional STAT3 protein. Moreover, our method allows to follow the uptake of STAT3 loaded vesicles inside cells due to the presence of EGFP in the EGFP-STAT3 fusion protein construct. Taken together, the data presented in this study could provide the scientific background for the development of new therapeutic strategy aimed to restore STAT3 signaling in STAT3 misfunction associated diseases like AD-HIES. In the future, the administration of fully functional wild type STAT3 to CD4+ T cells of AD-HIES patients might compensate its loss of function and would be beneficial for these patients, lowering the risk of infections, the use of medications, and hospitalizations.

CHO cells for virus-like particle and subunit vaccine manufacturing

Chinese Hamster Ovary (CHO) cells, employed primarily for manufacturing monoclonal antibodies and other recombinant protein (r-protein) therapeutics, are emerging as a promising host for vaccine antigen production. This is exemplified by the recently approved CHO cell-derived subunit vaccines (SUV) against respiratory syncytial virus (RSV) and varicella-zoster virus (VZV), as well as the enveloped virus-like particle (eVLP) vaccine against hepatitis B virus (HBV). Here, we summarize the design, production, and immunogenicity features of these vaccine and review the most recent progress of other CHO-derived vaccines in pre-clinical and clinical development. We also discuss the challenges associated with vaccine production in CHO cells, with a focus on ensuring viral clearance for eVLP products.

Engineering strategies for enhanced heterologous protein production by Saccharomyces cerevisiae

Microbial proteins are promising substitutes for animal- and plant-based proteins. S. cerevisiae, a generally recognized as safe (GRAS) microorganism, has been frequently employed to generate heterologous proteins. However, constructing a universal yeast chassis for efficient protein production is still a challenge due to the varying properties of different proteins. With progress in synthetic biology, a multitude of molecular biology tools and metabolic engineering strategies have been employed to alleviate these issues. This review first analyses the advantages of protein production by S. cerevisiae. The most recent advances in improving heterologous protein yield are summarized and discussed in terms of protein hyperexpression systems, protein secretion engineering, glycosylation pathway engineering and systems metabolic engineering. Furthermore, the prospects for efficient and sustainable heterologous protein production by S. cerevisiae are also provided.

Overexpression of Endoplasmic Reticulum Proteins from Arabidopsis thaliana in Baculovirus

The overproduction of proteins of the endoplasmic reticulum (ER) of plant cells in prokaryotic heterologous gene expression system remains a technical challenge. Recent advances in genetically modified insect cell technology and virus engineering methods have paved the way to produce recombinant ER plant proteins, including those harboring posttranslational modifications, and therefore, to yield ER plant proteins that are natively folded and fully functional. The present contribution focuses on the baculovirus-expression system flashBAC, which overcomes certain technical hurdles found in other insect cell-based expression systems such as the generation of a bacmid and the negative selection of recombinant clones.

Challenges and Opportunities in the Process Development of Chimeric Vaccines

Vaccines are integral to human life to protect them from life-threatening diseases. However, conventional vaccines often suffer limitations like inefficiency, safety concerns, unavailability for non-culturable microbes, and genetic variability among pathogens. Chimeric vaccines combine multiple antigen-encoding genes of similar or different microbial strains to protect against hyper-evolving drug-resistant pathogens. The outbreaks of dreadful diseases have led researchers to develop economical chimeric vaccines that can cater to a large population in a shorter time. The process development begins with computationally aided omics-based approaches to design chimeric vaccines. Furthermore, developing these vaccines requires optimizing upstream and downstream processes for mass production at an industrial scale. Owing to the complex structures and complicated bioprocessing of evolving pathogens, various high-throughput process technologies have come up with added advantages. Recent advancements in high-throughput tools, process analytical technology (PAT), quality-by-design (QbD), design of experiments (DoE), modeling and simulations, single-use technology, and integrated continuous bioprocessing have made scalable production more convenient and economical. The paradigm shift to innovative strategies requires significant attention to deal with major health threats at the global scale. This review outlines the challenges and emerging avenues in the bioprocess development of chimeric vaccines.

Plant and insect virus-like particles: emerging nanoparticles for agricultural pest management

Virus-like particles (VLPs) represent a biodegradable, biocompatible nanomaterial made from viral coat proteins that can improve the delivery of antigens, drugs, nucleic acids, and other substances, with most applications in human and veterinary medicine. Regarding agricultural viruses, many insect and plant virus coat proteins have been shown to assemble into VLPs accurately. In addition, some plant virus-based VLPs have been used in medical studies. However, to our knowledge, the potential application of plant/insect virus-based VLPs in agriculture remains largely underexplored. This review focuses on why and how to engineer coat proteins of plant/insect viruses as functionalized VLPs, and how to exploit VLPs in agricultural pest control. The first part of the review describes four different engineering strategies for loading cargo at the inner or the outer surface of VLPs depending on the type of cargo and purpose. Second, the literature on plant and insect viruses the coat proteins of which have been confirmed to self-assemble into VLPs is reviewed. These VLPs are good candidates for developing VLP-based agricultural pest control strategies. Lastly, the concepts of plant/insect virus-based VLPs for delivering insecticidal and antiviral components (e.g., double-stranded RNA, peptides, and chemicals) are discussed, which provides future prospects of VLP application in agricultural pest control. In addition, some concerns are raised about VLP production on a large scale and the short-term resistance of hosts to VLP uptake. Overall, this review is expected to stimulate interest and research exploring plant/insect virus-based VLP applications in agricultural pest management. © 2023 Society of Chemical Industry.

Growth hormone receptor agonists and antagonists: From protein expression and purification to long-acting formulations

Recombinant human growth hormone (rhGH) and GH receptor antagonists (GHAs) are used clinically to treat a range of disorders associated with GH deficiency or hypersecretion, respectively. However, these biotherapeutics can be difficult and expensive to manufacture with multiple challenges from recombinant protein generation through to the development of long-acting formulations required to improve the circulating half-life of the drug. In this review, we summarize methodologies and approaches used for making and purifying recombinant GH and GHA proteins, and strategies to improve pharmacokinetic and pharmacodynamic properties, including PEGylation and fusion proteins. Therapeutics that are in clinical use or are currently under development are also discussed.

Nipah virus attachment glycoprotein ectodomain delivered by type 5 adenovirus vector elicits broad immune response against NiV and HeV

Nipah virus (NiV) and Hendra virus (HeV) are newly emerging dangerous zoonotic pathogens of the Henipavirus genus of the Paramyxoviridae family. NiV and HeV (HNVs) which are transmitted by bats cause acute respiratory disease and fatal encephalitis in humans. To date, as there is a lack of antiviral drugs or effective antiviral therapies, the development of vaccines against those two viruses is of primary importance, and the immunogen design is crucial to the success of vaccines. In this study, the full-length protein (G), the ectodomain (Ge) and the head domain (Gs) of NiV attachment glycoprotein were delivered by the replication-defective type 5 adenovirus vector (Ad5) respectively, and the recombinant Ad5-NiV vaccine candidates (Ad5-NiVG, Ad5-NiVGe and Ad5-NiVGs) were constructed and their immunogenicity were evaluated in mice. The results showed that all the vaccine candidates stimulated specific humoral and cellular immune responses efficiently and rapidly against both NiV and HeV, and the Ad5-NiVGe elicited the strongest immune responses after a single-dose immunization. Furthermore, the potent conserved T-cell epitope DTLYFPAVGFL shared by NiV and HeV was identified in the study, which may provide valid information on the mechanism of HNVs-specific cellular immunity. In summary, this study demonstrates that the Ad5-NiVGe could be a potent vaccine candidate against HNVs by inducing robust humoral and cellular immune responses.

Zika virus-like particles (VLPs) produced in insect cells

Introdutcion: The Zika virus (ZIKV) infections are a healthcare concern mostly in the Americas, Africa, and Asia but have increased its endemicity area beyond these geographical regions. Due to the advances in infections by Zika virus, it is imperative to develop diagnostic and preventive tools against this viral agent. Virus-like particles (VLPs) appear as a suitable approach for use as antiviral vaccines. Methods: In this work, a methodology was established to produce virus-like particles containing the structural proteins, C, prM, and E of Zika virus produced in insect cells using the gene expression system derived from baculovirus. The vector pFast- CprME -ZIKV was constructed containing the gene sequences of Zika virus structural proteins and it was used to generate the recombinant bacmids (Bac- CprME -ZIKV) through transformation into DH10Bac^TM cells. The Bac- CprME -ZIKV was transfected in Spodoptera frugiperda (Sf9) insect cells and batches of BV- CprME -ZIKV were obtained by infection assays using a multiplicity of infection of 2. The Sf9 cells were infected, and the supernatant was collected 96 h post-infection. The expression of the CprME -ZIKV protein on the cell surface could be observed by immunochemical assays. To concentrate and purify virus-like particles, the sucrose and iodixanol gradients were evaluated, and the correct CprME -ZIKV proteins' conformation was evaluated by the Western blot assay. The virus-like particles were also analyzed and characterized by transmission electron microscopy. Results and discussion: Spherical structures like the native Zika virus from 50 to 65 nm containing the CprME -ZIKV proteins on their surface were observed in micrographs. The results obtained can be useful in the development path for a vaccine candidate against Zika virus.

Construction, expression and assemble of EMCV VLPs and their potency evaluation

Encephalomycarditis virus (EMCV) is an essential pathogen with a broad host range and causes enormous economic losses to the pig industry worldwide. Here, we constructed and assembled the EMCV virus-like particles (VLPs) in vitro and verified high efficiency of virus protection. Results showed that the proteins auto-assembled into VLPs successfully in vitro. The animal experiments revealed that high-titer antibody production is triggered by VLPs. Meanwhile, the mice challenged with EMCV were obviously protected. The protection rate of group VLPs with the adjuvant was 75%, while that of the VLPs group was 62.5% compared to the control. These findings indicate that recombinant EMCV VLPs have a remarkable anti-EMCV effect and could be a new vaccine candidate for the control of EMCV infection.

Biochemical monitoring throughout all stages of rabies virus-like particles production by Raman spectroscopy using global models

This work aimed to quantify growth and biochemical parameters (viable cell density, Xv; cell viability, CV; glucose, lactate, glutamine, glutamate, ammonium, and potassium concentrations) in upstream stages to obtain rabies virus-like particles (rabies VLP) from insect cell-baculovirus system using on-line and off-line Raman spectra to calibrate global models with minimal experimental data. Five cultivations in bioreactor were performed. The first one comprised the growth of uninfected Spodoptera frugiperda (Sf9) cells, the second and third runs to obtain recombinant baculovirus (rBV) bearing Rabies G glycoprotein and matrix protein, respectively. The fourth one involved the generation of rabies VLP from rBVs and the last one was a repetition of the third one with cell inoculum infected by rBV. The spectra were acquired through a Raman spectrometer with a 785-nm laser source. The fitted Partial Least Square models for nutrients and metabolites were comparable with those previously reported for mammalian cell lines (Relative error < 15 %). However, the use of this chemometrics approach for Xv and CV was not as accurate as it was for other parameters. The findings from this work established the basis for bioprocess Raman spectroscopical monitoring using insect cells for VLP manufacturing, which are gaining ground in the pharmaceutical industry.

Modern vaccine strategies for emerging zoonotic viruses

INTRODUCTION

The significant increase in the emergence of notable zoonotic viruses in the previous decades has become a serious concern to global public health. Ninety-nine percent of infectious diseases have originated from zoonotic viruses with immense potential for dissemination, infecting the susceptible population completely lacking herd immunity.

AREAS COVERED

Zoonotic viruses appear in the last two decades as a major health threat either newly evolved or previously present with elevated prevalence in the last few years are selected to explain their current prophylactic measures. In this review, modern generation vaccines including viral vector vaccines, mRNA vaccines, DNA vaccines, synthetic vaccines, virus-like particles, and plant-based vaccines are discussed with their benefits and challenges. Moreover, the traditional vaccines and their efficacy are also compared with the latest vaccines.

EXPERT OPINION

The emergence and reemergence of viruses that constantly mutate themselves have greatly increased the chance of transmission and immune escape mechanisms in humans. Therefore, the only possible solution to prevent viral infection is the use of vaccines with improved safety profile and efficacy, which becomes the basis of modern generation vaccines.

Baculovirus-Free SARS-CoV-2 Virus-like Particle Production in Insect Cells for Rapid Neutralization Assessment

Virus-like particles (VLPs) resemble authentic virus while not containing any genomic information. Here, we present a fast and powerful method for the production of SARS-CoV-2 VLP in insect cells and the application of these VLPs to evaluate the inhibition capacity of monoclonal antibodies and sera of vaccinated donors. Our method avoids the baculovirus-based approaches commonly used in insect cells by employing direct plasmid transfection to co-express SARS-CoV-2 envelope, membrane, and spike protein that self-assemble into VLPs. After optimization of the expression plasmids and vector ratios, VLPs with an ~145 nm diameter and the typical "Corona" aura were obtained, as confirmed by nanoparticle tracking analysis (NTA) and transmission electron microscopy (TEM). Fusion of the membrane protein to GFP allowed direct quantification of binding inhibition to angiotensin II-converting enzyme 2 (ACE2) on cells by therapeutic antibody candidates or sera from vaccinated individuals. Neither VLP purification nor fluorescent labeling by secondary antibodies are required to perform these flow cytometric assays.

Baculovirus-Free SARS-CoV-2 Virus-like Particle Production in Insect Cells for Rapid Neutralization Assessment

Virus-like particles (VLPs) resemble authentic virus while not containing any genomic information. Here, we present a fast and powerful method for the production of SARS-CoV-2 VLP in insect cells and the application of these VLPs to evaluate the inhibition capacity of monoclonal antibodies and sera of vaccinated donors. Our method avoids the baculovirus-based approaches commonly used in insect cells by employing direct plasmid transfection to co-express SARS-CoV-2 envelope, membrane, and spike protein that self-assemble into VLPs. After optimization of the expression plasmids and vector ratios, VLPs with an ~145 nm diameter and the typical “Corona” aura were obtained, as confirmed by nanoparticle tracking analysis (NTA) and transmission electron microscopy (TEM). Fusion of the membrane protein to GFP allowed direct quantification of binding inhibition to angiotensin II-converting enzyme 2 (ACE2) on cells by therapeutic antibody candidates or sera from vaccinated individuals. Neither VLP purification nor fluorescent labeling by secondary antibodies are required to perform these flow cytometric assays.

Virus-like Particles: Fundamentals and Biomedical Applications

Nanotechnology is a fast-evolving field focused on fabricating nanoscale objects for industrial, cosmetic, and therapeutic applications. Virus-like particles (VLPs) are self-assembled nanoparticles whose intrinsic properties, such as heterogeneity, and highly ordered structural organization are exploited to prepare vaccines; imaging agents; construct nanobioreactors; cancer treatment approaches; or deliver drugs, genes, and enzymes. However, depending upon the intrinsic features of the native virus from which they are produced, the therapeutic performance of VLPs can vary. This review compiles the recent scientific literature about the fundamentals of VLPs with biomedical applications. We consulted different databases to present a general scenario about viruses and how VLPs are produced in eukaryotic and prokaryotic cell lines to entrap therapeutic cargo. Moreover, the structural classification, morphology, and methods to functionalize the surface of VLPs are discussed. Finally, different characterization techniques required to examine the size, charge, aggregation, and composition of VLPs are described.

RG203KR Mutations in SARS-CoV-2 Nucleocapsid: Assessing the Impact Using a Virus-Like Particle Model System

Since its origin in late 2019, the SARS-CoV-2 virus has been constantly mutating and evolving. Current studies mostly employ spike protein (S) pseudovirus systems to determine the effects of mutations on the infectivity and immunogenicity of variants.

Immunization with Virus-Like Particle Vaccine Protects Rabbits against Hepatitis E-3 Virus Infection

Here, rabbits were immunized with a virus-like particle (VLP) vaccine prepared by expressing 239 amino acids of the swine hepatitis E virus (HEV)-3 capsid protein using a baculovirus system. Thirty specific-pathogen-free rabbits were divided into five groups (negative and positive control and 10, 50, and 100 μg VLP-vaccinated). Positive control group rabbits showed viremia and fecal viral shedding, whereas rabbits vaccinated with 10 μg VLP showed transient fecal viral shedding, and rabbits vaccinated with 50 and 100 μg VLP did not show viremia or fecal viral shedding. Serum anti-HEV antibody titers increased in a dose-dependent manner. Anti-HEV antibody titers were significantly higher (p < 0.05) in 100 μg VLP-vaccinated rabbits than in the negative control rabbits at week 4. Anti-HEV antibody titers were significantly higher in 50 and 10 μg VLP-vaccinated rabbits than in the negative control rabbits at weeks 8 and 11, respectively. Serum IFN-γ and IL-12 levels were significantly higher (p < 0.01) in rabbits vaccinated with 50 and 100 μg VLP than in the negative control rabbits at weeks 4 and 6. Liver tissues of 50 and 100 μg VLP-vaccinated rabbits displayed significantly less (p < 0.05) fibrosis than those of the positive control rabbits. The prepared VLP vaccine demonstrated dose-dependent immunogenicity sufficient for inducing anti-HEV antibody production, thus protecting rabbits against swine HEV-3.

Live attenuated Salmonella enterica serovar Choleraesuis vector delivering a virus-like particles induces a protective immune response against porcine circovirus type 2 in mice

The virus-like particles (VLPs) of porcine circovirus type 2 (PCV2) is an attractive vaccine candidate that retains the natural conformation of the virion but lacks the viral genome to replicate, thus balancing safety and immunogenicity. However, the assembly of VLPs requires cumbersome subsequent processes, hindering the development of related vaccines. In addition, as a subunit antigen, VLPs are defective in inducing cellular and mucosal immune responses. In this study, the capsid (Cap) protein of PCV2 was synthesized and self-assembled into VLPs in the recombinant attenuated S. Choleraesuis vector, rSC0016(pS-Cap). Furthermore, rSC0016(pS-Cap) induced a Cap-specific Th1-dominant immune response, mucosal immune responses, and neutralizing antibodies against PCV2. Finally, the virus genome copies in mice immunized with the rSC0016(pS-Cap) were significantly lower than those of the empty vector control group after challenge with PCV2. In conclusion, our study demonstrates the potential of using S. Choleraesuis vectors to delivery VLPs, providing new ideas for the development of PCV2 vaccines.

Can Virus-like Particles Be Used as Synergistic Agent in Pest Management?

Among novel strategies proposed in pest management, synergistic agents are used to improve insecticide efficacy through an elevation of intracellular calcium concentration that activates the calcium-dependent intracellular pathway. This leads to a changed target site conformation and to increased sensitivity to insecticides while reducing their concentrations. Because virus-like particles (VLPs) increase the intracellular calcium concentration, they can be used as a synergistic agent to synergize the effect of insecticides. VLPs are self-assembled viral protein complexes, and by contrast to entomopathogen viruses, they are devoid of genetic material, which makes them non-infectious and safer than viruses. Although VLPs are well-known to be used in human health, we propose in this study the development of a promising strategy based on the use of VLPs as synergistic agents in pest management. This will lead to increased insecticides efficacy while reducing their concentrations.

Review: Development of SARS-CoV-2 immuno-enhanced COVID-19 vaccines with nano-platform

Vaccination is the most effective way to prevent coronavirus disease 2019 (COVID-19). Vaccine development approaches consist of viral vector vaccines, DNA vaccine, RNA vaccine, live attenuated virus, and recombinant proteins, which elicit a specific immune response. The use of nanoparticles displaying antigen is one of the alternative approaches to conventional vaccines. This is due to the fact that nano-based vaccines are stable, able to target, form images, and offer an opportunity to enhance the immune responses. The diameters of ultrafine nanoparticles are in the range of 1-100 nm. The application of nanotechnology on vaccine design provides precise fabrication of nanomaterials with desirable properties and ability to eliminate undesirable features. To be successful, nanomaterials must be uptaken into the cell, especially into the target and able to modulate cellular functions at the subcellular levels. The advantages of nano-based vaccines are the ability to protect a cargo such as RNA, DNA, protein, or synthesis substance and have enhanced stability in a broad range of pH, ambient temperatures, and humidity for long-term storage. Moreover, nano-based vaccines can be engineered to overcome biological barriers such as nonspecific distribution in order to elicit functions in antigen presenting cells. In this review, we will summarize on the developing COVID-19 vaccine strategies and how the nanotechnology can enhance antigen presentation and strong immunogenicity using advanced technology in nanocarrier to deliver antigens. The discussion about their safe, effective, and affordable vaccines to immunize against COVID-19 will be highlighted.

Two-step purification of tag-free norovirus-like particles from silkworm larvae (Bombyx mori)

Recombinantly expressed VP1 of norovirus self-assembled and formed norovirus-like particles (NoV-LPs). This native VP1 was expressed using the Bombyx mori nucleopolyhedrovirus (BmNPV) expression system in silkworm larva. NoV-LPs were collected from silkworm fat body lysate by density gradient centrifugation. To improve the purity of the NoV-LP, the proteins were further purified using immobilized metal affinity chromatography based on the surface exposed side chain of histidine residues. The additional purification led to a highly purified virus-like particle (VLP). The morphology and size of the purified VLPs were examined using a transmission electron microscope, and dynamic light scattering revealed a monodispersed spherical morphology with a diameter of 34 nm. The purified product had a purity of >90% with a recovery yield of 48.7% (equivalent to 930 μg) from crude lysate, obtained from seven silkworm larvae. In addition, the purified VLP could be recognized by antibodies against GII norovirus in sandwich enzyme-linked immunosorbent assay, which indicated that the silkworm-derived VLP is biologically functional as a NoV-LP in its native state, is structurally correct, and exerts its biological function. Our results suggest that the silkworm-derived NoV-LP may be useful for subsequent applications, such as in a vaccine platform. Moreover, the silkworm-based expression system is known for its robustness, facile up-scalability, and relatively low expense compared to insect cell systems.

Pigs Immunized with the Virus-like Particle Vaccine Are Protected against the Hepatitis E-3 Virus

In this study, we generated the HEV virus-like particle (VLP) vaccine expressing 239 amino acids (367–605 aa) of the HEV-3 ORF2 using the baculovirus expression system. The HEV-3-239-VLP vaccine efficacy was evaluated by dividing 12 pathogen-free pigs into four groups: negative control, positive control, 100 μg VLP-, and 200 μg VLP-vaccinated groups for 10 weeks. The pigs in either of the vaccinated groups were administered the corresponding first and booster doses on weeks 0 and 2. At week 4, the positive control and two vaccinated groups were challenged with 10⁶ HEV-3 genomic equivalent copies; viremia and fecal shedding of the virus were identified in pigs in the positive control and 100 μg VLP-vaccinated pigs showed transient viremia and fecal viral shedding. However, no viruses were detected in the serum or fecal samples of the 200 μg VLP-vaccinated pigs. The 100 and 200 μg VLP-vaccinated pigs had significantly higher (p < 0.01) anti-HEV antibodies than the negative control pigs from weeks 6–10 with normal levels of liver enzymes. The 200 μg VLP-vaccinated pigs showed statistically less liver tissue fibrosis (p < 0.05) than that of the positive control pigs. Thus, the novel baculovirus expression system-generated VLP vaccine dose-dependently protects against HEV-3 challenge and may be useful in other animal species, including humans.

Virus-Like Particle Vaccines Against Respiratory Viruses and Protozoan Parasites

The field of vaccinology underwent massive advances over the past decades with the introduction of virus-like particles (VLPs), a supra-molecular nanoparticle vaccine platform that resembles viral structures without the ability to replicate in hosts. This innovative approach has been remarkably effective, as evidenced by its profound immunogenicity and safety. These highly desirable intrinsic properties enabled their further development as vaccines against a multitude of diseases. To date, several VLP-based vaccines have already been commercialized and many more are undergoing clinical evaluation prior to FDA approval. However, efficacious vaccines against a plethora of pathogens are still lacking, which imposes a tremendous socioeconomic burden and continues to threaten public health throughout the globe. This is especially the case for several respiratory pathogens and protozoan parasites. In this review, we briefly describe the fundamentals of VLP vaccines and the unique properties that enable these to be such valuable vaccine candidates and summarize current advances in VLP-based vaccines targeting respiratory and parasitic diseases of global importance.

Proteome Based Approach Defines Candidates for Designing a Multitope Vaccine against the Nipah Virus

Nipah virus is one of the most harmful emerging viruses with deadly effects on both humans and animals. Because of the severe outbreaks, in 2018, the World Health Organization focused on the urgent need for the development of effective solutions against the virus. However, up to date, there is no effective vaccine against the Nipah virus in the market. In the current study, the complete proteome of the Nipah virus (nine proteins) was analyzed for the antigenicity score and the virulence role of each protein, where we came up with fusion glycoprotein (F), glycoprotein (G), protein (V), and protein (W) as the candidates for epitope prediction. Following that, the multitope vaccine was designed based on top-ranking CTL, HTL, and BCL epitopes from the selected proteins. We used suitable linkers, adjuvant, and PADRE peptides to finalize the constructed vaccine, which was analyzed for its physicochemical features, antigenicity, toxicity, allergenicity, and solubility. The designed vaccine passed these assessments through computational analysis and, as a final step, we ran a docking analysis between the designed vaccine and TLR-³ and validated the docked complex through molecular dynamics simulation, which estimated a strong binding and supported the nomination of the designed vaccine as a putative solution for Nipah virus. Here, we describe the computational approach for design and analysis of this vaccine.

Western equine encephalitis virus virus-like particles from an insect cell-baculovirus system elicit the strong immune responses in mice

Western equine encephalitis virus (WEEV) causes lethal encephalitis in humans and equines, and it poses a serious public health threat in many countries. Therefore, the development of an efficient vaccine remains an important challenge for the prevention of WEEV infection. This study presents the first description of WEEV virus-like particles (VLPs) generated from insect cells using recombinant baculoviruses. WEEV VLPs with 206 adjuvant could trigger a strong cellular immune response; increase the levels of IL-2, IL-4 and IFN-γ; and induce a high level of neutralizing antibodies against WEEV in mice. These data showed that the insect cell-baculovirus system is suitable for the production of WEEV VLPs and that these VLPs could elicit the strong immunogenicity in mice. These results suggest a new, nonreplicating, and effective vaccine candidate against WEEV infection.

Production of Rabies VLPs in Insect Cells by Two Monocistronic Baculoviruses Approach

Rabies is an ancient zoonotic disease that still causes the death of over 59,000 people worldwide each year. The rabies lyssavirus encodes five proteins, including the envelope glycoprotein and the matrix protein. RVGP is the only protein exposed on the surface of viral particle, and it can induce immune response with neutralizing antibody formation. RVM has the ability to assist with production process of virus-like particles. VLPs were produced in recombinant baculovirus system. In this work, two recombinant baculoviruses carrying the RVGP and RVM genes were constructed. From the infection and coinfection assays, we standardized the best multiplicity of infection and the best harvest time. Cell supernatants were collected, concentrated, and purified by sucrose gradient. Each step was used for protein detection through immunoassays. Sucrose gradient analysis enabled to verify the separation of VLPs from rBV. Through the negative contrast technique, we visualized structures resembling rabies VLPs produced in insect cells and rBV in the different fractions of the sucrose gradient. Using ELISA to measure total RVGP, the recovery efficiency of VLPs at each stage of the purification process was verified. Thus, these results encourage further studies to confirm whether rabies VLPs are a promising candidate for a veterinary rabies vaccine.

Characterization of alfalfa mosaic virus capsid protein using Cryo-EM

VLPs are virus-like particles that comprise viral capsid proteins that can self-assemble and mimic the shape and size of real viral particles; however, because they do not contain genetic material they cannot infect host cells. VLPs have great potential as safe drug/vehicle candidates; therefore, they are gaining popularity in the field of preventive medicine and therapeutics. Indeed, extensive studies are underway to examine their role as carriers for immunization and as vehicles for delivery of therapeutic agents. Here, we examined the possibility of developing VLP-utilizing technology based on an efficient VLP production process and high-resolution structural analysis. Nicotiana benthamiana was used as an expression platform to produce the coat protein of the alfalfa mosaic virus (AMV-CP). About 250 mg/kg of rAMV-CP was produced from Nicotiana benthamiana leaves. Structural analysis revealed that the oligomeric status of rAMV-CP changed according to the composition and pH of the buffer. Size exclusion chromatography and electron microscopy analysis confirmed the optimal conditions for rAMV-CP VLP formation, and a 2.4 Å resolution structure was confirmed by cryo-EM analysis. Based on the efficient protein production, VLP manufacturing technology, and high-resolution structure presented herein, we suggest that rAMV-CP VLP is a useful platform for development of various new drugs.

Comparison of Chicken Immune Responses after Inoculation with H5 Avian Influenza Virus-like Particles Produced by Insect Cells or Pupae

Introduction

Novel clade 2.3.4.4 H5 highly pathogenic avian influenza virus (HPAIV) outbreaks have occurred since early 2015 in Taiwan and impacted the island economically, like they have many countries. This research investigates the immunogenicity of two HPAIV-like particles to assess their promise as vaccine candidates.

Material and Methods

The haemagglutinin (HA) gene derived from clade 2.3.4.4 H5 HPAIV and matrix protein 1 (M1) gene were cloned into the pFastBac Dual baculovirus vector. The resulting recombinant viruses were expressed in Spodoptera frugiperda moth (Sf)21 cells and silkworm pupae to generate Sf21 virus-like particles (VLP) and silkworm pupa VLP. Two-week-old specific pathogen–free chickens were immunised and their humoral and cellular immune responses were analysed.

Results

The silkworm pupa VLP had higher haemagglutination competence. Both VLP types elicited haemagglutination inhibition antibodies, anti-HA antibodies, splenic interferon gamma (IFN-γ) and interleukin 4 (IL-4) mRNA expression, and CD4⁺/CD8⁺ ratio elevation. However, chickens receiving silkworm pupa VLP exhibited a significantly higher anti-HA antibody titre in ELISA after vaccination. Although Sf21 VLP recipients expressed more IFN-γ and IL-4, the increase in IFN-γ did not significantly raise the CD4⁺/CD8⁺ ratio and the increase in IL-4 did not promote anti-HA antibodies.

Conclusion

Both VLP systems possess desirable immunogenicity in vivo. However, in respect of immunogenic efficacy and the production cost, pupa VLP may be the superior vaccine candidate against clade 2.3.4.4 H5 HPAIV infection.

Effect of Posttranslational Modifications on the Structure and Activity of FTO Demethylase

The FTO protein is involved in a wide range of physiological processes, including adipogenesis and osteogenesis. This two-domain protein belongs to the AlkB family of 2-oxoglutarate (2-OG)- and Fe(II)-dependent dioxygenases, displaying N⁶-methyladenosine (N⁶-meA) demethylase activity. The aim of the study was to characterize the relationships between the structure and activity of FTO. The effect of cofactors (Fe²⁺/Mn²⁺ and 2-OG), Ca²⁺ that do not bind at the catalytic site, and protein concentration on FTO properties expressed in either E. coli (^ECFTO) or baculovirus (^BESFTO) system were determined using biophysical methods (DSF, MST, SAXS) and biochemical techniques (size-exclusion chromatography, enzymatic assay). We found that ^BESFTO carries three phosphoserines (S184, S256, S260), while there were no such modifications in ^ECFTO. The S256D mutation mimicking the S256 phosphorylation moderately decreased FTO catalytic activity. In the presence of Ca²⁺, a slight stabilization of the FTO structure was observed, accompanied by a decrease in catalytic activity. Size exclusion chromatography and MST data confirmed the ability of FTO from both expression systems to form homodimers. The MST-determined dissociation constant of the FTO homodimer was consistent with their in vivo formation in human cells. Finally, a low-resolution structure of the FTO homodimer was built based on SAXS data.

Investigation of Kluyveromyces marxianus as a novel host for large-scale production of porcine parvovirus virus-like particles

Background

Porcine Parvovirus (PPV) is a Parvovirinae virus that can cause embryonic and fetal loss and death and mummification in affected fetal pigs. Unlike conventional vaccines, virus-like particles (VLPs) inherit the natural structure of their authentic virions and highly immunostimulatory that can induce strong humoral immune and T cell responses with no risk of pathogenicity. The production of PPV VLPs is still a challenge based on traditional expression platforms due to their low yields and high culture costs. Kluyveromyces marxianus is a safe and fast-growing eukaryote that can get high biomass with low-cost cultures. In this study, we investigated the expression and downstream processes of PPV VLPs in K. marxianus, and the potential for effective stand-alone vaccines.

Results

After optimization according to the codon bias of K. marxianus, the VP2 protein from Kresse strain was highly expressed. In a 5 L fermentator, the yield of PPV VLPs reached 2.5 g/L, quantified by HPLC, using a defined mineral medium after 48 h fermentation. Two strategies were established to purify intracellular PPV VLPs: (i) Using the cation exchange chromatography coupled with Sephacryl® S-500 HR chromatography to purify VLPs from the supernatants of pH adjusted cell lysates. (ii) Using anion exchange chromatography followed by cross-flow diafiltration to recover the VLPs precipitated in pH adjusted cell lysates. The purity of PPV VLPs reached about 95%, and total recovery was more than 60%. Vaccination of mice with the purified PPV VLPs induced high titers of specific IgG antibodies in sera, and showed hemagglutination inhibitions on both swine and guinea pig erythrocytes. Spleen lymphocyte proliferation and cytokines detection suggested the PPV VLPs produced by K. marxianus provoked the cellular immune and humoral immunity responses in mice.

Conclusions

This is the highest production of recombinant PPV VLPs achieved to date. The superiorities, Generally Recognized As Safe (GRAS), high production, short lead time, and low cost, make K. marxianus a greatly competitive platform for bioproduction of PPV VLPs vaccine.

Nanoparticle vaccines against respiratory syncytial virus

Respiratory syncytial virus (RSV) is a leading cause of respiratory disease in infants, the elderly and immunocompromised individuals. Despite the global burden, there is no licensed vaccine for RSV. Recent advances in the use of nanoparticle technology have provided new opportunities to address some of the limitations of conventional vaccines. Precise control over particle size and surface properties enhance antigen stability and prolong antigen release. Particle size can also be modified to target specific antigen-presenting cells in order to induce specific types of effector T-cell responses. Numerous nanoparticle-based vaccines are currently being evaluated for RSV including inorganic, polymeric and virus-like particle-based formulations. Here, we review the potential advantages of using different nanoparticle formulations in a vaccine for RSV, and discuss many examples of safe, and effective vaccines currently in both preclinical and clinical stages of testing.

Dengue and Zika virus multi-epitope antigen expression in insect cells

Dengue virus and Zika virus are arthropod-borne flaviviruses that cause millions of infections worldwide. The co-circulation of both viruses makes serological diagnosis difficult as they share high amino acid similarities in viral proteins. Antigens are one of the key reagents in the differential diagnosis of these viruses through the detection of IgG antibodies in serological assays during the convalescent-phase of infections. Here, we report the expression of Dengue virus (DENV) and Zika virus (ZIKV) antigens containing non-conserved and immunodominant amino acid sequences using the baculovirus expression vector system in insect cells. We designed DENV and ZIKV antigens based on the domain III of the E protein (EDIII) after analyzing previously reported epitopes and by multiple alignment of the most important flaviviruses. The ZIKV and DENV multi-epitope genes were designed as tandem repeats or impaired repeats separated by tetra- or hexa-glycine linkers. The biochemical analyses revealed adequate expression of the antigens. Then, the obtained multi-epitope antigens were semi-purified in a sucrose gradient and tested using patients' sera collected during the convalescent-phase that were previously diagnosed positive for anti-DENV and -ZIKV IgG antibodies. The optimal serum dilution was 1:200, and the mean absorbance values in the preliminary tests show that multi-epitope antigens have been recognized by human sera. The production of both antigens using the multi-epitope strategy in the eukaryotic system and based on the EDIII regions provide a proof of concept for the use of antigens in the differentiation between DENV and ZIKV.

Coupling Microscopy and Flow Cytometry for a Comprehensive Characterization of Nanoparticle Production in Insect Cells

Advancements in the field of characterization techniques have broadened the opportunities to deepen into nanoparticle production bioprocesses. Gag-based virus-like particles (VLPs) have shown their potential as candidates for recombinant vaccine development. However, comprehensive characterization of the production process is still a requirement to meet the desired critical quality attributes. In this work, the production process of Gag VLPs by baculovirus (BV) infection in the reference High Five and Sf9 insect cell lines is characterized in detail. To this end, the Gag polyprotein was fused in frame to the enhanced green fluorescent protein (eGFP) to favor process evaluation with multiple analytical tools. Tracking of the infection process using confocal microscopy and flow cytometry revealed a pronounced increase in the complexity of High Five over Sf9 cells. Cryogenic transmission electron microscopy (cryo-TEM) characterization determined that changes in cell complexity could be attributed to the presence of occlusion-derived BV in High Five cells, whereas Sf9 cells evidenced a larger proportion of the budded virus phenotype (23-fold). Initial evaluation of the VLP production process using spectrofluorometry showed that higher levels of the Gag-eGFP polyprotein were obtained in High Five cells (3.6-fold). However, comparative analysis based on nanoparticle quantification by flow virometry and nanoparticle tracking analysis (NTA) proved that Sf9 cells were 1.7- and 1.5-fold more productive in terms of assembled VLPs, respectively. Finally, analytical ultracentrifugation coupled to flow virometry evidenced a larger sedimentation coefficient of High Five-derived VLPs, indicating a possible interaction with other cellular compounds. Taken together, these results highlight the combined use of microscopy and flow cytometry techniques to improve vaccine development processes using the insect cell/BV expression vector system. © 2020 International Society for Advancement of Cytometry.

Highly Pathogenic and Low Pathogenic Avian Influenza H5 Subtype Viruses in Wild Birds in Ukraine

There have been three waves of highly pathogenic avian influenza (HPAI) outbreaks in commercial, backyard poultry, and wild birds in Ukraine. The first (2005-2006) and second (2008) waves were caused by H5N1 HPAI virus, with 45 outbreaks among commercial poultry (chickens) and backyard fowl (chickens, ducks, and geese) in four regions of Ukraine (AR Crimea, Kherson, Odesa, and Sumy Oblast). H5N1 HPAI viruses were isolated from dead wild birds: cormorants (Phalacrocorax carbo) and great crested grebes (Podiceps cristatus) in 2006 and 2008. The third HPAI wave consisted of nine outbreaks of H5N8 HPAI in wild and domestic birds, beginning in November 2016 in the central and south regions (Kherson, Odesa, Chernivtsi, Ternopil, and Mykolaiv Oblast). H5N8 HPAI virus was detected in dead mute swans (Cygnus olor), peacocks (Pavo cristatus) (in zoo), ruddy shelducks (Tadorna ferruginea), white-fronted geese (Anser albifrons), and from environmental samples in 2016 and 2017. Wide wild bird surveillance for avian influenza (AI) virus was conducted from 2006 to 2016 in Ukraine regions suspected of being intercontinental (north-south and east-west) flyways. A total of 21 511 samples were collected from 105 species of wild birds representing 27 families and 11 orders. Ninety-five avian influenza (AI) viruses were isolated (including one H5N2 LPAI virus in 2010) from wild birds with a total of 26 antigenic hemagglutinin (HA) and neuraminidase (NA) combinations. Fifteen of 16 known avian HA subtypes were isolated. Two H5N8 HPAI viruses (2016-2017) and two H5N2 LPAI viruses (2016) were isolated from wild birds and environmental samples (fresh bird feces) during surveillance before the outbreak in poultry in 2016-2017. The Ukrainian H5N1, H5N8 HPAI, and H5N2 LPAI viruses belong to different H5 phylogenetic groups. Our results demonstrate the great diversity of AI viruses in wild birds in Ukraine, as well as the importance of this region for studying the ecology of avian influenza.

Efficacy of Clade 2.3.2 H5-Recombinant Baculovirus Vaccine in Protecting Muscovy and Pekin Ducks from Clade 2.3.4.4 H5N8 Highly Pathogenic Avian Influenza Infection

In late 2016, a highly pathogenic avian influenza (HPAI) virus subtype H5N8 clade 2.3.4.4 was reported in Egypt in migratory birds; subsequently, the virus spread to backyard and commercial poultry in several Egyptian governorates, causing severe economic losses to the poultry industry. Here, a recombinant subunit commercial H5 vaccine prepared from the clade 2.3.2 H5 segment on baculovirus was evaluated in Pekin ducks (Anasplatyrhynchos domesticus) and Muscovy ducks (Cairina moschata) in Biosafety Level 3 isolators by using two vaccination regimes: either a single dose on day 10 and a challenge on day 31 or a double dose on days 10 and 28 and a challenge on day 49. The protection parameters were evaluated after experimental infection with the Egyptian HPAI H5N8 isolate clade 2.3.4.4b (A/common-coot/Egypt/CA285/2016) based on mortality rate, clinical signs, gross lesions, seroconversion, virus shedding, and histopathologic changes. In the single-dose vaccination regime, the mortality rate in Muscovy and Pekin ducks was 10% and 0% vs. 40% and 0% in nonvaccinated challenged ducks, respectively. In the double-dose vaccination regime, the mortality rates in Muscovy and Pekin ducks were 0% and 0% vs. 60% and 40% in nonvaccinated challenged ducks, respectively. Muscovy ducks developed more severe clinical signs and gross lesions than Pekin ducks. In addition, tracheal viral shedding in challenged Muscovy ducks, in the single-dose vaccination regime, was 50%, 22%, and 0% at 3, 5, and 7 days postchallenge (DPC), respectively, and was 0% in all Pekin ducks vs. 100% in all challenged nonvaccinated Muscovy and Pekin ducks at 3, 5, and 7 DPC. The viral shedding in challenged Muscovy and Pekin ducks, in the double-dose vaccination regime, was 0% at 3, 5, and 7 DPC vs. 100% in nonvaccinated challenged Muscovy and Pekin ducks, respectively. The results of this study indicate that the H5 baculovirus-based vaccine can be used in ducks with better vaccination regime based on double-dose vaccination at 10 and 28 days of age. In addition, they highlight the need to evaluate the efficacy of currently used commercial vaccines against challenge with the newly emerged HPAI H5N8 clade 2.3.4.4 in the field in Egypt to ensure proper control strategy in ducks.

Baculovirus-Derived Vectors for Immunization and Therapeutic Applications

Baculoviruses are arthropod-specific, enveloped viruses with circular, supercoiled double-stranded deoxyribonucleic acid genomes. While many viruses are studied to seek solutions for their adverse impact on human, veterinary, and plant health, the study of baculoviruses was stimulated initially by their potential utility to control insect pests. Later, the utility of baculovirus as gene expression vectors was evidenced leading to numerous applications. Several strategies are employed to obtain recombinant viruses that express large quantities of heterologous proteins. A major step forward was the development of bacmid technology (the construction of bacterial artificial chromosomes containing the genome of the baculovirus) which allows the manipulation of the baculovirus genome in bacteria. With this technology, foreign genes can be introduced into the bacmid by homologous and site-directed recombination or by transposition. Baculoviruses have been used to explore fundamental questions in molecular biology such as the nature of programmed cell-death. Moreover, the ability of baculoviruses to transduce mammalian cells led to the consideration of their use as gene-therapy and vaccine vectors. Strategies for genetic engineering of baculoviruses have been developed to meet the requirements of new application areas. Display of foreign proteins on the surface of virions or in nucleocapsid structures, the assembly of expressed proteins to form virus-like particles or protein complexes have been explored and validated as vaccines. The aim of this chapter is to update the areas of application of the baculoviruses in protein expression, alternative vaccine designs and gene therapy of infectious diseases and genetic disorders. Finally, we review the baculovirus-derived products on the market and in the pipeline for biomedical and veterinary use.

Nipah virus: epidemiology, pathology, immunobiology and advances in diagnosis, vaccine designing and control strategies - a comprehensive review

Nipah (Nee-pa) viral disease is a zoonotic infection caused by Nipah virus (NiV), a paramyxovirus belonging to the genus Henipavirus of the family Paramyxoviridae. It is a biosafety level-4 pathogen, which is transmitted by specific types of fruit bats, mainly Pteropus spp. which are natural reservoir host. The disease was reported for the first time from the Kampung Sungai Nipah village of Malaysia in 1998. Human-to-human transmission also occurs. Outbreaks have been reported also from other countries in South and Southeast Asia. Phylogenetic analysis affirmed the circulation of two major clades of NiV as based on currently available complete N and G gene sequences. NiV isolates from Malaysia and Cambodia clustered together in NiV-MY clade, whereas isolates from Bangladesh and India clusterered within NiV-BD clade. NiV isolates from Thailand harboured mixed population of sequences. In humans, the virus is responsible for causing rapidly progressing severe illness which might be characterized by severe respiratory illness and/or deadly encephalitis. In pigs below six months of age, respiratory illness along with nervous symptoms may develop. Different types of enzyme-linked immunosorbent assays along with molecular methods based on polymerase chain reaction have been developed for diagnostic purposes. Due to the expensive nature of the antibody drugs, identification of broad-spectrum antivirals is essential along with focusing on small interfering RNAs (siRNAs). High pathogenicity of NiV in humans, and lack of vaccines or therapeutics to counter this disease have attracted attention of researchers worldwide for developing effective NiV vaccine and treatment regimens.

Process development for pandemic influenza VLP vaccine production using a baculovirus expression system

Background

Influenza viruses cause hundreds of thousands of respiratory diseases worldwide each year, and vaccination is considered the most effective approach for preventing influenza annual epidemics or pandemics. Since 1950, chicken embryonated eggs have been used as the main method for producing seasonal influenza vaccines. However, this platform has the main drawback of a lack of scale-up flexibility, and thus, egg-based vaccine manufacturers cannot supply sufficient doses within a short period for use for pandemic prevention. As a result, strategies for reducing the manufacturing time and increasing production capacity are urgently needed. Non-virion vaccine methods have been considered an alternative strategy against an influenza pandemic, and the purpose of maintaining an immunogenic capsule structure with infectious properties appears to be met by the virus-like particle (VLP) platform.

Results

An influenza H7N9-TW VLP production platform using insect cells, which included the expression of hemagglutinin (HA), NA, and M1 proteins, was established. To scale up H7N9-TW VLP production, several culture conditions were optimized to obtain a higher production yield. A high level of dissolved oxygen (DO) could be critical to H7N9-TW VLP production. If the DO was maintained at a high level, the HA titer obtained in the spinner flask system with ventilation was similar to that obtained in a shake flask. In this study, the HA titer in a 5-L bioreactor with a well-controlled DO level was substantially improved by 128-fold (from 4 HA units (HAU)/50 μL to 512 HAU/50 μL).

Conclusions

In this study, a multigene expression platform and an effective upstream process were developed. Notably, a high H7N9-TW VLP yield was achieved using a two-step production strategy while a high DO level was maintained. The upstream process, which resulted in high VLP titers, could be further used for large-scale influenza VLP vaccine production.

Display of malaria transmission-blocking antigens on chimeric duck hepatitis B virus-derived virus-like particles produced in Hansenula polymorpha

BACKGROUND

Malaria caused by Plasmodium falciparum is one of the major threats to human health globally. Despite huge efforts in malaria control and eradication, highly effective vaccines are urgently needed, including vaccines that can block malaria transmission. Chimeric virus-like particles (VLP) have emerged as a promising strategy to develop new malaria vaccine candidates.

METHODS

We developed yeast cell lines and processes for the expression of malaria transmission-blocking vaccine candidates Pfs25 and Pfs230 as VLP and VLP were analyzed for purity, size, protein incorporation rate and expression of malaria antigens.

RESULTS

In this study, a novel platform for the display of Plasmodium falciparum antigens on chimeric VLP is presented. Leading transmission-blocking vaccine candidates Pfs25 and Pfs230 were genetically fused to the small surface protein (dS) of the duck hepatitis B virus (DHBV). The resulting fusion proteins were co-expressed in recombinant Hansenula polymorpha (syn. Pichia angusta, Ogataea polymorpha) strains along with the wild-type dS as the VLP scaffold protein. Through this strategy, chimeric VLP containing Pfs25 or the Pfs230-derived fragments Pfs230c or Pfs230D1M were purified. Up to 100 mg chimeric VLP were isolated from 100 g dry cell weight with a maximum protein purity of 90% on the protein level. Expression of the Pfs230D1M construct was more efficient than Pfs230c and enabled VLP with higher purity. VLP showed reactivity with transmission-blocking antibodies and supported the surface display of the malaria antigens on the native VLP.

CONCLUSION

The incorporation of leading Plasmodium falciparum transmission-blocking antigens into the dS-based VLP scaffold is a promising novel strategy for their display on nano-scaled particles. Competitive processes for efficient production and purification were established in this study.

Purification and Characterization of DUOX Peroxidase Homology Domains (PHDs)

The dual oxidase (DUOX) enzymes (DUOX1 and DUOX2) are unique hydrogen peroxide (H₂O₂)-producing members of the NADPH oxidase (NOX) family, structurally distinguished from their related NOX isoforms by the presence of an additional N-terminal extracellular domain. This region has significant sequence and predicted structural homology to mammalian peroxidases, including myeloperoxidase (MPO) and lactoperoxidase (LPO), therefore justifying the nomenclature of the peroxidase homology domain (PHD). Obtaining detailed structural information and defining a function for this appended region are both critical for elucidation of the uncharacterized mechanism of H₂O₂ production by DUOX proteins. Purification strategies focused on isolated sections of each DUOX enzyme are a logical means to further characterization, particularly as isolation of the complete membrane-bound enzyme in significant quantities remains unachievable. In this chapter, a reproducible method for production of the homology domain applicable to both human DUOX isoforms is described. The approach utilizes a baculovirus expression vector in insect cell culture to produce secreted recombinant PHD; an appended C-terminal His₆ affinity tag was found to be crucial for structural stability. Finally, initial characterization of the activity of the purified PHDs is also described.

Nipah virus: epidemiology, pathology, immunobiology and advances in diagnosis, vaccine designing and control strategies - a comprehensive review

Nipah (Nee-pa) viral disease is a zoonotic infection caused by Nipah virus (NiV), a paramyxovirus belonging to the genus Henipavirus of the family Paramyxoviridae. It is a biosafety level-4 pathogen, which is transmitted by specific types of fruit bats, mainly Pteropus spp. which are natural reservoir host. The disease was reported for the first time from the Kampung Sungai Nipah village of Malaysia in 1998. Human-to-human transmission also occurs. Outbreaks have been reported also from other countries in South and Southeast Asia. Phylogenetic analysis affirmed the circulation of two major clades of NiV as based on currently available complete N and G gene sequences. NiV isolates from Malaysia and Cambodia clustered together in NiV-MY clade, whereas isolates from Bangladesh and India clusterered within NiV-BD clade. NiV isolates from Thailand harboured mixed population of sequences. In humans, the virus is responsible for causing rapidly progressing severe illness which might be characterized by severe respiratory illness and/or deadly encephalitis. In pigs below six months of age, respiratory illness along with nervous symptoms may develop. Different types of enzyme-linked immunosorbent assays along with molecular methods based on polymerase chain reaction have been developed for diagnostic purposes. Due to the expensive nature of the antibody drugs, identification of broad-spectrum antivirals is essential along with focusing on small interfering RNAs (siRNAs). High pathogenicity of NiV in humans, and lack of vaccines or therapeutics to counter this disease have attracted attention of researchers worldwide for developing effective NiV vaccine and treatment regimens.

Assembly of tomato blistering mosaic virus-like particles using a baculovirus expression vector system

The expression of several structural proteins from a wide variety of viruses in heterologous cell culture systems results in the formation of virus-like particles (VLPs). These VLPs structurally resemble the wild-type virus particles and have been used to study viral assembly process and as antigens for diagnosis and/or vaccine development. Tomato blistering mosaic virus (ToBMV) is a tymovirus that has a 6.3-kb positive-sense ssRNA genome. We have employed the baculovirus expression vector system (BEVS) for the production of tymovirus-like particles (tVLPs) in insect cells. Two recombinant baculoviruses containing the ToBMV wild-type coat protein (CP) gene or a modified short amino-terminal deletion (Δ_2-24CP) variant were constructed and used to infect insect cells. Both recombinant viruses were able to express ToBMV CP and Δ_2-24CP from infected insect cells that self-assembled into tVLPs. Therefore, the N-terminal residues (2-24) of the native ToBMV CP were shown not to be essential for self-assembly of tVLPs. We also constructed a third recombinant baculovirus containing a small sequence coding for the major epitope of the chikungunya virus (CHIKV) envelope protein 2 (E2) replacing the native CP N-terminal 2-24 amino acids. This recombinant virus also produced tVLPs. In summary, ToBMV VLPs can be produced in a baculovirus/insect cell heterologous expression system, and the N-terminal residues 2-24 of the CP are not essential for this assembly, allowing its potential use as a protein carrier that facilitates antigen purification and might be used for diagnosis.

Immunogenicity and protective efficacy of a novel foot-and-mouth disease virus empty-capsid-like particle with improved acid stability

Foot-and-mouth disease virus (FMDV) is the etiological agent of a highly contagious disease that affects cloven-hoofed animal species. The FMDV capsid is highly acid labile and viral particles lose their immunogenicity when they disassemble at mildly acidic pHs. The viral capsid of FMDV serotype O is more sensitive than those of other serotypes, making it more difficult to acquire enough empty-capsid-like particles in the acidic insect cell environment for research. In this study, novel FMDV mutants with increased acid resistance were isolated using BHK-21 cell cultured under low-pH conditions. Amino acid substitutions Q25R, K41E, and N85A in the VP1 capsid protein and K154Q in the VP3 capsid protein were detected in all six mutants. Based on these amino acid replacements, empty-capsid-like particles of FMDV serotype O, which were resistant to the acid-induced dissociation of the capsid into pentameric subunits, were produced in insect cells. We characterized the protective immunity induced by these acid-resistant empty capsid particles. Significant humoral and cellular immune responses were elicited in mice after immunization with the acid-resistant empty capsid particles. The acid-resistant empty-capsid-like particles also induced strong neutralizing antibodies in guinea pigs and protected all the guinea pigs from FMDV challenge. Our results suggest that these acid-resistant empty-capsid-like particles have potential utility as a vaccine against serotype O FMDV infection.

Characterization of native-like HIV-1 gp140 glycoprotein expressed in insect cells

The trimeric HIV-1 envelope glycoprotein (Env) is critical for vaccine development aimed at achieving broadly-neutralizing antibody responses. The use of various recombinant expression systems and construct designs are associated with the resultant nature of produced proteins, especially in terms of glycosylation, antigenicity, and immunogenicity of the glycoprotein. Here, we explored an otherwise baculovirus cassette than classical one designed to express HIV-1 Env protein, including SOSIP mutation and Foldon moiety involvement. This improved design increased the ratio of the Env trimer fraction from ∼40% to ∼60% with respect to that of prototypical design, as indicated by high-performance size-exclusion chromatography and sedimentation velocity analysis. In addition, the design prolonged cell viability and enhanced the final yield (approximately 13-15 mg/L) after affinity purification. gp140 produced from insect cells mimicked the native-like trimer and mainly adopted glycosylation pattern of oligomannose glycans. The native-like Env proteins conferred cross-clade neutralizing antibody production in BALB/c mice. In summary, the expression of Env in insect cells by optimizing the baculovirus vector provides an alternative strategy for HIV-1 immunogen production and may benefit future Env-based HIV vaccine design.

Novel coronavirus-like particles targeting cells lining the respiratory tract

Virus like particles (VLPs) produced by the expression of viral structural proteins can serve as versatile nanovectors or potential vaccine candidates. In this study we describe for the first time the generation of HCoV-NL63 VLPs using baculovirus system. Major structural proteins of HCoV-NL63 have been expressed in tagged or native form, and their assembly to form VLPs was evaluated. Additionally, a novel procedure for chromatography purification of HCoV-NL63 VLPs was developed. Interestingly, we show that these nanoparticles may deliver cargo and selectively transduce cells expressing the ACE2 protein such as ciliated cells of the respiratory tract. Production of a specific delivery vector is a major challenge for research concerning targeting molecules. The obtained results show that HCoV-NL63 VLPs may be efficiently produced, purified, modified and serve as a delivery platform. This study constitutes an important basis for further development of a promising viral vector displaying narrow tissue tropism.

Efficient production of a mature and functional gamma secretase protease

Baculoviral protein expression in insect cells has been previously used to generate large quantities of a protein of interest for subsequent use in biochemical and structural analyses. The MultiBac baculovirus protein expression system has enabled, the use of a single baculovirus to reconstitute a protein complex of interest, resulting in a larger protein yield. Using this system, we aimed to reconstruct the gamma (γ)-secretase complex, a multiprotein enzyme complex essential for the production of amyloid-β (Aβ) protein. A MultiBac vector containing all components of the γ-secretase complex was generated and expression was observed for all components. The complex was active in processing APP and Notch derived γ-secretase substrates and proteolysis could be inhibited with γ-secretase inhibitors, confirming specificity of the recombinant γ-secretase enzyme. Finally, affinity purification was used to purify an active recombinant γ-secretase complex. In this study we demonstrated that the MultiBac protein expression system can be used to generate an active γ-secretase complex and provides a new tool to study γ-secretase enzyme and its variants.

Production of Ebola virus-like particles in Drosophila melanogaster Schneider 2 cells

In this study, we generated recombinant virus-like particles (VLPs) against family Filoviridae, genus Ebolavirus, species Zaire ebolavirus, strain Makona (EBOV) in Drosophila melanogaster Schneider 2 (S2) cells using the EBOV Makona. S2 cells were cotransfected with four viral plasmids encoding EBOV Makona proteins and protein expression was analyzed by immunoblotting. We confirmed that EBOV Makona proteins were successfully expressed in S2 cells. Additionally, we further examined the formation of intracellular and extracellular VLPs by electron microscopy. eVLPs were produced by sucrose gradient ultracentrifugation of S2 cells transfected with EBOV Makona genes, and production of VLPs was confirmed by immunoblot analysis. Collectively, our findings showed that the S2 cell system could be a promising tool for efficient production of eVLPs.