Eukaryotic virus display: engineering the major surface glycoprotein of the Autographa californica nuclear polyhedrosis virus (AcNPV) for the presentation of foreign proteins on the virus surface

Intracellular localized heterogeneous protein franking by a transmembrane domain of GP64 is sufficient to be assembled on budded virions of Bombyx mori nucleopolyhedrovirus

Baculovirus has been widely used for foreign protein expression in biomedical studies, and budded virus (BV) surface display has developed into an important research tool for heterogenous membrane protein studies. The basic strategy of surface display is to construct a recombinant virus where the target gene is fused with a complete or partial gp64 gene. In this study, we further investigate and develop this BV surface displaying strategy. We constructed stable insect cell lines to express the target protein flanking with different regions of signal peptide (SP) and GP64 transmembrane domain (TMD). Subsequently, recombinant BmNPV was used to infect the cell, and the integration of heterogeneous protein into BV was detected. The results indicated that deletion of the n-region of SP (SPΔn) decreased the incorporation rate more than that of the full-length SP. However, the incorporation rate of the protein fused with h and c-region deletion of SP (SPΔh-c) was significantly enhanced by 35-40 times compare to full-length SP. Moreover, the foreign protein without SP and TMD failed to display on the BV, while the integration of foreign proteins with GP64 TMD fusion at the c-terminal was significantly enhanced by 12-26 times compared to the control. Thus, these new strategies developed the BV surface display system further.

Architecture of the baculovirus nucleocapsid revealed by cryo-EM

Baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) has been widely used as a bioinsecticide and a protein expression vector. Despite their importance, very little is known about the structure of most baculovirus proteins. Here, we show a 3.2 Å resolution structure of helical cylindrical body of the AcMNPV nucleocapsid, composed of VP39, as well as 4.3 Å resolution structures of both the head and the base of the nucleocapsid composed of over 100 protein subunits. AcMNPV VP39 demonstrates some features of the HK97-like fold and utilizes disulfide-bonds and a set of interactions at its C-termini to mediate nucleocapsid assembly and stability. At both ends of the nucleocapsid, the VP39 cylinder is constricted by an outer shell ring composed of proteins AC104, AC142 and AC109. AC101(BV/ODV-C42) and AC144(ODV-EC27) form a C14 symmetric inner layer at both capsid head and base. In the base, these proteins interact with a 7-fold symmetric capsid plug, while a portal-like structure is seen in the central portion of head. Additionally, we propose an application of AlphaFold2 for model building in intermediate resolution density.

Assessing developability early in the discovery process for novel biologics

Beyond potency, a good developability profile is a key attribute of a biological drug. Selecting and screening for such attributes early in the drug development process can save resources and avoid costly late-stage failures. Here, we review some of the most important developability properties that can be assessed early on for biologics. These include the influence of the source of the biologic, its biophysical and pharmacokinetic properties, and how well it can be expressed recombinantly. We furthermore present in silico, in vitro, and in vivo methods and techniques that can be exploited at different stages of the discovery process to identify molecules with liabilities and thereby facilitate the selection of the most optimal drug leads. Finally, we reflect on the most relevant developability parameters for injectable versus orally delivered biologics and provide an outlook toward what general trends are expected to rise in the development of biologics.

The Magic Staff: A Comprehensive Overview of Baculovirus-Based Technologies Applied to Human and Animal Health

Baculoviruses are enveloped, insect-specific viruses with large double-stranded DNA genomes. Among all the baculovirus species, Autographa californica multiple nucleopolyhedrovirus (AcMNPV) is the most studied. Due to its characteristics regarding biosafety, narrow host range and the availability of different platforms for modifying its genome, AcMNPV has become a powerful biotechnological tool. In this review, we will address the most widespread technological applications of baculoviruses. We will begin by summarizing their natural cycle both in larvae and in cell culture and how it can be exploited. Secondly, we will explore the different baculovirus-based protein expression systems (BEVS) and their multiple applications in the pharmaceutical and biotechnological industry. We will focus particularly on the production of vaccines, many of which are either currently commercialized or in advanced stages of development (e.g., Novavax, COVID-19 vaccine). In addition, recombinant baculoviruses can be used as efficient gene transduction and protein expression vectors in vertebrate cells (e.g., BacMam). Finally, we will extensively describe various gene therapy strategies based on baculoviruses applied to the treatment of different diseases. The main objective of this work is to provide an extensive up-to-date summary of the different biotechnological applications of baculoviruses, emphasizing the genetic modification strategies used in each field.

Harnessing coronavirus spike proteins' binding affinity to ACE2 receptor through a novel baculovirus surface display system

Coronavirus disease 2019 (COVID-19) caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a newly emerging infectious disease currently spreading across the world. The spike (S) protein plays a key role in the receptor recognition and cell membrane fusion, making it an important target for developing vaccines, therapeutic antibodies and diagnosis. In this study, we constructed a baculovirus surface display system that efficiently presents both SARS-CoV and SARS-CoV-2 S proteins (including ectodomain, S1 subunit and receptor-binding-domain, RBD) on the surface of recombinant baculoviruses, utilizing transmembrane anchors from gp64 (signal peptide) and vesicular stomatitis virus (VSV). These recombinant baculoviruses were capable of transducing engineered HEK 293T cells overexpressing ACE2 receptors with significantly higher transduction efficiencies, indicating that S proteins displayed on baculovirus surface have antigenicity and can recognize and bind ACE2 receptors. Additionally, the transduction of SARS-CoV-2 S proteins can be inhibited by an antibody against the SARS-CoV-2 RBD. These results demonstrate that this baculovirus surface display system is a promising tool for developing antibodies, vaccines and recombinant protein production.

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

Abstract

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

Key points

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

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

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

Interaction with the Receptor SLAM and Baculovirus Surface Display of Peste des petits ruminants Virus Hemagglutinin

Peste des petits ruminants (PPR) is an acute, highly infectious, and highly pathogenic disease, which mainly damages small ruminants such as goats and sheep. Hemagglutinin protein (H), the main antigenic protein of peste des petits ruminants virus (PPRV), has been a hot spot in the research of genetic engineering vaccine for PPRV. In this study, the silkworm baculovirus surface display technology is combined with the transmembrane structure of the silkworm baculovirus envelope protein GP64 and different characteristics of the promoters to display four kinds of fusion proteins, which contain Pph-H, Pph-HJ, Pie1-H, and Pie1-HJ. The fusion proteins displayed on baculovirus surface have been detected by western blotting, cell surface immunofluorescence, and immunogold electron microscopy. In addition, the dominant form of PPR H displayed on baculovirus surface has been determined which is fusion protein mediated by Pph containing the hemagglutinin protein and full-length GP64, Pph-H. Furthermore, by comparing the fluorescence intensity of binding of hemagglutinin protein and signaling lymphocyte activation molecules (SLAM) in Vero-SLAM cells by immunocytochemistry, Pph-H can be combined with the receptor protein of PPRV, SLAM. It provides technical support for displaying the different structure of hemagglutinin and exploring the key sites of hemagglutinin and SLAM binding. Meanwhile, it is important for exploring the pathogenesis and immune mechanism of PPRV.

Preincubation with a low concentration of methyl-β-cyclodextrin enhances baculovirus expression system productivity

OBJECTIVES

To enhance the productivity of foreign protein in culture cells using baculovirus expression system.

RESULTS

A low concentration of MβCD, with the optimal application concentration of 0.25 mM and the appropriate preincubation time range from 10 to 120 min, can efficiently enhance expression levels in both the AcMNPV and BmNPV expression systems.

CONCLUSIONS

Preincubation with a low concentration MβCD enhance baculovirus infection and foreign protein expression productivity.

The interaction between baculoviruses and their insect hosts

Baculoviruses are double-stranded circular DNA viruses that infect arthropods via the midgut. Because of their superiority as eukaryotic expression systems and their importance as biopesticides, extensive research on the functions of baculovirus genes as well as on the host response to baculovirus infection has been carried out, including transcriptomic and proteomic analyses of the midgut. The morphological and cellular changes caused by baculovirus infection are also important to better understand the infection pathway. Thanks to these previous studies, we now have a clearer picture of the mechanisms of action of the virus and of host immunity. In this paper, we systematically reviewed studies on the interaction between baculoviruses and their insect hosts. By better understanding these interactions, baculoviruses can be developed for use as more efficient biopesticides to improve agricultural development in the future.

Baculovirus Surface Display of Immunogenic Proteins for Vaccine Development

Vaccination is an efficient way to prevent the occurrence of many infectious diseases in humans. To date, several viral vectors have been utilized for the generation of vaccines. Among them, baculovirus-categorized as a nonhuman viral vector-has been used in wider applications. Its versatile features, like large cloning capacity, nonreplicative nature in mammalian cells, and broad tissue tropism, hold it at an excellent position among vaccine vectors. In addition to ease and safety during swift production, recent key improvements to existing baculovirus vectors (such as inclusion of hybrid promoters, immunostimulatory elements, etc.) have led to significant improvements in immunogenicity and efficacy of surface-displayed antigens. Furthermore, some promising preclinical results have been reported that mirror the scope and practicality of baculovirus as a vaccine vector for human applications in the near future. Herein, this review provides an overview of the induced immune responses by baculovirus surface-displayed vaccines against influenza and other infectious diseases in animal models, and highlights the strategies applied to enhance the protective immune responses against the displayed antigens.

Baculovirus for gene delivery to mammalian cells: Past, present and future

Baculovirus is an insect virus which has been used for more than thirty years for production of recombinant proteins in insect cells. However, baculovirus can also be harnessed for efficient gene delivery to mammalian cells if it is equipped with mammalian promoters. This technology is known as BacMam and has been used for gene delivery to immortalized cell lines, stem cells, and primary cells, as well as for gene delivery in animals. Baculovirus has unique features when compared to mammalian viruses. Besides the fact that it is replication-incompetent and does not integrate into the host genome, it has large capacity for foreign DNA. This capacity can for example be used to deliver multiple genes for reprogramming of stem cells, or for delivery of large homology constructs for genome editing. In this review, we provide a brief overview of baculovirus-based gene delivery and its recent applications in therapy and basic research. We also describe how baculovirus is manipulated for efficient transduction in mammalian cells and we highlight possible future improvements.

Immunization With Fc-Based Recombinant Epstein-Barr Virus gp350 Elicits Potent Neutralizing Humoral Immune Response in a BALB/c Mice Model

Epstein–Barr virus (EBV) was the first human virus proved to be closely associated with tumor development, such as lymphoma, nasopharyngeal carcinoma, and EBV-associated gastric carcinoma. Despite many efforts to develop prophylactic vaccines against EBV infection and diseases, no candidates have succeeded in effectively blocking EBV infection in clinical trials. Previous investigations showed that EBV gp350 plays a pivotal role in the infection of B-lymphocytes. Nevertheless, using monomeric gp350 proteins as antigens has not been effective in preventing infection. Multimeric forms of the antigen are more potently immunogenic than monomers; however, the multimerization elements used in previous constructs are not approved for human clinical trials. To prepare a much-needed EBV prophylactic vaccine that is potent, safe, and applicable, we constructed an Fc-based form of gp350 to serve as a dimeric antigen. Here, we show that the Fc-based gp350 antigen exhibits dramatically enhanced immunogenicity compared with wild-type gp350 protein. The complete or partial gp350 ectodomain was fused with the mouse IgG2a Fc domain. Fusion with the Fc domain did not impair gp350 folding, binding to a conformation-dependent neutralizing antibody (nAb) and binding to its receptor by enzyme-linked immunosorbent assay and surface plasmon resonance. Specific antibody titers against gp350 were notably enhanced by immunization with gp350-Fc dimers compared with gp350 monomers. Furthermore, immunization with gp350-Fc fusion proteins elicited potent nAbs against EBV. Our data strongly suggest that an EBV gp350 vaccine based on Fc fusion proteins may be an efficient candidate to prevent EBV infection in clinical applications.

The localization of a heterologous displayed antigen in the baculovirus-budded virion determines the type and strength of induced adaptive immune response

In the search of strategies of presentation of heterologous antigens to elicit humoral or cellular immune responses that modulate and properly potentiate each type of response, researchers have been studying baculovirus (BV) as vaccine vectors with promising results. For some years, several research groups explored different antigen presentation approaches using the BV AcNPV by expressing polypeptides on the surface of budded virions or by de novo synthesis of heterologous antigens by transduction of mammalian cells. In the case of expression on the surface of budded virions, for example, researchers have expressed polypeptides in peplomers as GP64 glycoprotein fusions or distributed throughout the entire surface by fusions to portions of the G protein of vesicular stomatitis virus, VSV. Recently, our group developed the strategy of cross-presentation of antigens by fusions of GP64 to the capsid protein VP39 (capsid display) for the generation of cytotoxic responses. While the different strategies showed to be effective in raising immune responses, the individuality of each analysis makes difficult the comparison of the results. Here, by comparing the different strategies, we show that localization of the model antigen ovalbumin (OVA) strongly determined the quality and intensity of the adaptive response to the heterologous antigen. Furthermore, surface display favored humoral responses, whereas capsid display favored cytotoxic responses. Finally, capsid display showed a much more efficient strategy to activate CD8-mediated responses than transduction. The incorporation of adjuvants in baculovirus formulations dramatically diminished the immunostimulatory properties of baculovirus.

Functional Display of an α2 Integrin-Specific Motif (RKK) on the Surface of Baculovirus Particles

The use of baculovirus vectors shows promise as a tool for gene delivery into mammalian cells. These insect viruses have been shown to transduce a variety of mammalian cell lines, and gene transfer has also been demonstrated in vivo. In this study, we generated two recombinant baculovirus vectors displaying an integrin-specific motif, RKK, as a part of two different loops of the green fluorescent protein (GFP) fused with the major envelope protein gp64 of Autographa californica M nucleopolyhedrovirus. By enzyme linked immunosorbent assays, these viruses were shown to bind a peptide representing the receptor binding site of an α2 integrin, the α2I-domain. However, the interaction was not strong enough to overcome binding of wild type gp64 to the unknown cellular receptor(s) on the surface of α2 integrin-expressing cells (CHO-α2β1) or enhance the viral uptake. After treatment of these cells with phospholipase C, internalization of all viruses was blocked or decreased significantly. However, one of the RKK displaying viruses, AcGFP(K)gp64, was still able to internalize into CHO-α2β1 cells, although at a lower level as compared to non-treated cells. This may indicate the possible utilization of a PLC independent alternative route via, in this case, the α2β1 integrin.

Generation of Envelope-Modified Baculoviruses for Gene Delivery into Mammalian Cells

Genetically modified baculoviruses can efficiently deliver and express genes in mammalian cells. The major prerequisite for the expression of a gene transferred by baculovirus is its control by a promoter that is active in mammalian cells. This chapter describes methods for producing second generation baculovirus vectors through modification of their envelope. Envelope modified baculoviruses offer additional new applications of the system, such as their use in in vivo gene delivery, targeting, and vaccination. Methods of generating a recombinant baculovirus vector with a modified envelope and its amplification and purification, including technical scale production, are discussed. A variety of notes give clues regarding specific technical procedures. Finally, methods to analyze the virus and transduction procedures are presented.

Insect Biotechnology

For the purpose of this work, insect biotechnology, which is also known as yellow biotechnology, is the use of insects as well as insect-derived cells or molecules in medical (red biotechnology), agricultural (green biotechnology), and industrial (white) biotechnology. It is based on the application of biotechnological techniques on insects or their cells to develop products or services for human use. Such products are then applied in agriculture, medicine, and industrial biotechnology. Insect biotechnology has proven to be a useful resource in diverse industries, especially for the production of industrial enzymes including chitinases and cellulases, pharmaceuticals, microbial insecticides, insect genes, and many other substances. Insect cells (ICs), and particularly lepidopteran cells, constitute a competitive strategy to mammalian cells for the manufacturing of biotechnology products. Among the wide range of methods and expression hosts available for the production of biotech products, ICs are ideal for the production of complex proteins requiring extensive posttranslational modification. The progress so far made in insect biotechnology essentially derives from scientific breakthroughs in molecular biology, especially with the advances in techniques that allow genetic manipulation of organisms and cells. Insect biotechnology has grown tremendously in the last 30 years.

Baculovirus vectors expressing F proteins in combination with virus-induced signaling adaptor (VISA) molecules confer protection against respiratory syncytial virus infection

Baculovirus has been exploited for use as a novel vaccine vector. To investigate the feasibility and efficacy of recombinant baculoviruses (rBVs) expressing respiratory syncytial virus (RSV) fusion (F) proteins, four constructs (Bac-tF/64, Bac-CF, Bac-CF/tF64 and Bac-CF/tF64-VISA) were generated. Bac-tF64 displays the F ectodomain (tF) on the envelope of rBVs, whereas Bac-CF expresses full-length F protein in transduced mammalian cells. Bac-CF/tF64 not only displays tF on the envelope but also expresses F in cells. Bac-CF/tF64-VISA comprises Bac-CF/tF64 harboring the virus-induced signaling adaptor (VISA) gene. After administration to BALB/c mice, all four vectors elicited RSV neutralizing antibody (Ab), systemic Ab (IgG, IgG1, and IgG2a), and cytokine responses. Compared with Bac-tF64, mice inoculated with Bac-CF and Bac-CF/tF64 exhibited an increased mixed Th1/Th2 cytokine response, increased ratios of IgG2a/IgG1 antibody responses, and reduced immunopathology upon RSV challenge. Intriguingly, co-expression of VISA reduced Th2 cytokine (IL-4, IL-5, and IL-10) production induced by Bac-CF/tF64, thus relieving lung pathology upon a subsequent RSV challenge. Our results indicated that the Bac-CF/tF64 vector incorporated with the VISA molecule may provide an effective vaccine strategy for protection against RSV.

Baculovirus display of functional antibody Fab fragments

The generation of a recombinant baculovirus that displays antibody Fab fragments on the surface was investigated. A recombinant baculovirus was engineered so that the heavy chain (Hc; Fd fragment) of a mouse Fab fragment was expressed as a fusion to the N-terminus of baculovirus gp64, while the light chain of the Fab fragment was simultaneously expressed as a secretory protein. Following infection of Sf9 insect cells with the recombinant baculovirus, the culture supernatant was analyzed by enzyme-linked immunosorbent assay using antigen-coated microplates and either an anti-mouse IgG or an anti-gp64 antibody. A relatively strong signal was obtained in each case, showing antigen-binding activity in the culture supernatant. In western blot analysis of the culture supernatant using the anti-gp64 antibody, specific protein bands were detected at an electrophoretic mobility that coincided with the molecular weight of the Hc-gp64 fusion protein as well as that of gp64. Flow cytometry using a fluorescein isothiocyanate-conjugated antibody specific to mouse IgG successfully detected the Fab fragments on the surface of the Sf9 cells. These results suggest that immunologically functional antibody Fab fragments can be displayed on the surface of baculovirus particles, and that a fluorescence-activated cell sorter with a fluorescence-labeled antigen can isolate baculoviruses displaying specific Fab fragments. This successful baculovirus display of antibody Fab fragments may offer a novel approach for the efficient selection of specific antibodies.

Baculovirus-mediated gene delivery and RNAi applications

Baculoviruses are widely encountered in nature and a great deal of data is available about their safety and biology. Recently, these versatile, insect-specific viruses have demonstrated their usefulness in various biotechnological applications including protein production and gene transfer. Multiple in vitro and in vivo studies exist and support their use as gene delivery vehicles in vertebrate cells. Recently, baculoviruses have also demonstrated high potential in RNAi applications in which several advantages of the virus make it a promising tool for RNA gene transfer with high safety and wide tropism.

Study on nanocomposite construction based on the multi-functional biotemplate self-assembled by the recombinant TMGMV coat protein for potential biomedical applications

Nowadays there is a growing interest in bio-scaffolded nanoarchitectures. Rapid progress in nanobiotechnology and molecular biology has allowed the engineering of inorganic-binding peptides termed as genetically engineered polypeptides for inorganics (GEPIs) into self-assembling biological structures to facilitate the design of novel biomedical or bioimaging devices. Here we introduce a novel nanocomposite comprising a self-assembled protein scaffold based on a recombinant tobacco mild green mosaic tobamovirus (TMGMV) coat protein (CP) and the photocatalytic TiO2 nanoparticles attached to it, which may provide a generic method for materials engineering. A template containing a modified TMGMV CP (mCP) gene, with the first six C-terminal amino acid residues deleted to accommodate more foreign peptides and expressing a site-directed mutation of A123C for bioconjugation utility, and two genetically engineered mutants, Escherichia coli-based P-mCP-Ti7 containing a C-terminal TiO2 GEPI sequence of seven peptides (Ti7) and Hi5 insect cells-derived E-CP-Ti7-His6 C-terminally fused with Ti7+His6 tag were created. Expression vectors and protocols for enriching of the two CP variants were established and the resultant proteins were identified by western blot analysis. Their RNA-free self-assembling structures were analyzed by transmission electron microscopy (TEM) and immuno-gold labeling TEM analysis. Adherence of nanoparticles to the P-mCP-Ti7 induced protein scaffold was visualized by TEM analysis. Also discussed is the Cysteine thiol reactivity in bioconjugation reactions with the maleimide-functionalized porphyrin photosensitizers which can function as clinical photodynamic therapy agents. This study introduced a novel approach to producing an assembly-competent recombinant TMGMV CP, examined its ability to serve as a novel platform for the multivalent display of surface ligands and demonstrated an alternative method for nanodevice synthesis for nanobiotechnological applications by combining GEPIs-mediated immobilization with the controllability of self-assembling recombinant TMGMV CP.

Generation of antibodies against membrane proteins

The monoclonal antibody has become an important therapeutic in the treatment of both hematological malignancies and solid tumors. The recent success of antibody-drug conjugates (ADCs) has broadened the extent of the potential target molecules in cancer immunotherapy. As a result, even molecules of low abundance have become targets for cytotoxic reagents. The multi-pass membrane proteins are an emerging target for the next generation antibody therapeutics. One outstanding challenge is the difficulty in preparing a sufficient amount of these membrane proteins so as to be able to generate the functional antibody. We have pursued the expression of various membrane proteins on the baculovirus particle and the utilization of displayed protein for immunization. The strong antigenicity of the virus acts either as a friend or foe in the making of an efficient antibody against an immunologically tolerant antigen. This article is part of a Special Issue entitled: Recent advances in molecular engineering of antibody.

Self-biotinylation and site-specific double labeling of baculovirus using quantum dots for single-virus in-situ tracking

Single-virus labeling and tracking represent a powerful tool to study virus-cell interactions. Using baculovirus as a model, here we developed a biochemical method for labeling both the viral envelope and the viral capsid of a virus. Viral envelope of the baculovirus AcMNPV was self-biotinylated and site-specifically conjugated with quantum dots (QDs) following one-step binding reaction, while the viral nucleocapsid was site-specifically labeled with green fluorescent protein (GFP) during viral replication. The established procedure of labeling did not affect viral infectivity, showing that the double-labeled virus retained functional structure and could be tracked for viral localization and movement in the host cells. The double-labeled virus also demonstrated the potential to be used for in-situ and real-time visualizing the internalization of a single viral particle into the host cells. Furthermore, the disassembly processes of the viral envelope and the viral nucleocapsid could be monitored for a long period of time (up to 2 h). Using the established method, several interaction details between the labeled baculoviruses and the host cells have been revealed. Given its advantages in high efficiency, high specificity, convenience and the maintenance of viral infectivity, the established approach provides a promising means for elucidating virus-cell interactions.

Site-specific labeling of baculovirus in an integrated microfluidic device

Labeling of viruses can be used to reveal viral infection pathways and screen potential anti-viral drugs. Complex procedures, including virus cultivation, purification and labeling are involved in traditional virus labeling methods. And the manipulation of living virus brings risk to researcher health. In this work, we report a general method for site-specific labeling of the envelope virus in an integrated microfluidic device with simple procedures and high security. Site-specific labeling of virus was achieved by fusing the biotin acceptor peptide (AP-tag) and the biotin ligase enzyme (BirA enzyme) with the envelope protein GP64 of baculovirus. The AP-tag could be modified by BirA enzyme to introduce the biotin moiety onto the viral envelope. Western blots and fluorescence colocalization analysis proved that the baculoviruses were biotinylated and labeled with high efficiency. The integrated device incorporated several operation steps including cell seeding, cell culture, cell transfection, virus culture and virus labeling. Since virus biotinylation was achieved during the process of virus cultivation, the complex procedures of virus labeling were simplified in our device. Furthermore the whole process could be completed in the integrated microfluidic device, and direct contact between viruses and researchers could be eliminated in our method, which could greatly reduce the risk to researcher health during living virus labeling.

Display of enterovirus 71 VP1 on baculovirus as a type II transmembrane protein elicits protective B and T cell responses in immunized mice

Human enterovirus 71 (EV71) has become a major public health threat across Asia Pacific. The virus causes hand, foot, and mouth disease which can lead to neurological complications in young children. There are no specific antivirals or vaccines against EV71 infection. The major neutralizing epitope of EV71 is located in the carboxy-terminal half of the VP1 protein at amino acid positions 215-219 (Lim et al., 2012). To study the immunogenicity of VP1 we have developed a baculovirus vector which displays VP1 as a type II transmembrane protein, providing an accessible C-terminus. Immunization of mice with this recombinant baculovirus elicited neutralizing antibodies against heterologous EV71 in an in vitro microneutralization assay. Passive protection of neonatal mice confirmed the prophylactic efficacy of the antisera. Additionally, EV71 specific T cell responses were stimulated. Taken together, our results demonstrate that the display of VP1 as a type II transmembrane protein efficiently stimulated both humoral and cellular immunities.

Induction of protective immune responses against EV71 in mice by baculovirus encoding a novel expression cassette for capsid protein VP1

EV71 is a major causative agent of hand, foot and mouth disease (HFMD) and is responsible for large outbreaks in various Asian Pacific countries. In the present study, we generated the recombinant baculovirus (Bac-VP1) encoding VP1 in a novel expression cassette. The transmembrane domain of hemagglutinin of the H3N2 influenza virus was included in the cassette as a minimal membrane anchor for VP1. The protective immunity of Bac-VP1 was investigated in a mouse model. The results showed that mice vaccinated with live Bac-VP1 had strong VP1 specific antibody responses. In an in vitro neutralization assay Bac-VP1 sera exhibited cross-neutralization against homologous and heterologous EV71 strains with a maximum titer of 1:512. Passive immunization studies confirmed that these sera were able to provide 100% protection against 5 MLD(50) of mouse adapted EV71 (B4 strain). This study revealed that baculovirus displaying VP1 with a HA transmembrane domain efficiently induced cross-neutralizing antibody responses in mice.

Genetic modification of baculovirus expression vectors

As a protein expression vector, the baculovirus demonstrates many advantages over other vectors. With the development of biotechnology, baculoviral vectors have been genetically modified to facilitate high level expression of heterologous proteins in both insect and mammalian cells. These modifications include utilization of different promoters and signal peptides, deletion or replacement of viral genes for increasing protein secretion, integration of polycistronic expression cassette for producing protein complexes, and baculovirus pseudotyping, promoter accommodation or surface display for enhancing mammalian cell targeting gene delivery. This review summarizes the development and the current state of art of the baculovirus expression system. Further development of baculovirus expression systems will make them even more feasible and accessible for advanced applications.

How to avoid complement attack in baculovirus-mediated gene delivery

Serum inactivation of baculovirus vectors is a significant barrier to the development of these highly efficient vectors for therapeutic gene delivery. In this review we will describe the efforts taken to avoid complement attack by passive or active measures. Evidently good targets for baculovirus-mediated gene delivery include immunoprivileged tissues, such as eye, brain and testis. Similarly baculovirus vectors have also proven their efficacy in an ex vivo setting for tissue engineering. Active measures to inhibit complement include the use of pharmacological inhibitors of complement as well as surface engineering of the baculoviral vectors through the use of synthetic polymers, pseudotyping or display of complement inhibitors. Lessons learned from these studies will significantly increase the possibility of using baculovirus vectors for therapeutic applications.

Baculovirus capsid display potentiates OVA cytotoxic and innate immune responses

Baculoviruses (BV) are DNA viruses that are pathogenic for insects. Although BV infect a range of mammalian cell types, they do not replicate in these cells. Indeed, the potential effects of these insect viruses on the immune responses of mammals are only just beginning to be studied. We show in this paper that a recombinant Autographa californica multiple nuclear polyhedrosis virus carrying a fragment of ovalbumin (OVA) on the VP39 capsid protein (BV-OVA) has the capacity to act as an adjuvant and vector of antigens in mice, thereby promoting specific CD4 and cytotoxic T cell responses against OVA. BV also induced in vivo maturation of dendritic cells and the production of inflammatory cytokines, thus promoting innate and adaptive immune responses. The OVA-specific response induced by BV-OVA was strong enough to reject a challenge with OVA-expressing melanoma cells (MO5 cells) and effectively prolonged survival of MO5 bearing mice. All these findings, together with the absence of pre-existing immunity to BV in humans and the lack of viral gene expression in mammalian cells, make BV a candidate for vaccination.

Generation of HIV-1 Virus-Like Particles expressing different HIV-1 glycoproteins

Elicitation of a potent and broadly neutralizing antibody response is the main goal of an effective preventive HIV-1 vaccine. It has been shown by us and others that the expression of Env glycoproteins on the surface of particulate structures, such as Virus-Like Particles (VLPs), could be a more efficient strategy to deliver conformational epitopes to the immune system. To this aim, VLPs expressing native HIV Env gp140 or gp41 glycoproteins have been produced in insect cells using a baculovirus expression system and characterized for appropriate protein expression. VLP-bound HIV gp140 glycoprotein showed the appropriate expression and trimeric conformation. Immunogenicity studies have been performed in BALB/C mice by intra-peritoneal administration and sera from immunized mice have been tested in ELISA assays, for their reactivity with HIV specific antigens, as well as in ex vivo neutralization assay. Sera from immunized animals showed a high reactivity with individual HIV proteins expressed in VLPs. Results of TZM-bl based neutralization assay show that combined sera from animals independently immunized with gp140- or full-length-gp41-expressing VLPs have an additive/synergistic effect in the neutralization activity of HIV pseudoviruses. In conclusion, novel VLPs expressing different HIV Env glycoproteins with native trimeric conformation have been generated, showing the induction of effective antibody response with neutralization activity in TZM-bl neutralization assay. These results confirm the effectiveness of VLPs as presentation and delivery system for conformational proteins and show the improved neutralization activity upon the combination of anti-sera elicited by different HIV envelope antigens, suggesting the possibility of broadening the spectrum of viral epitopes targeted by immune response.

Inorganic binding peptide-mediated immobilization based on baculovirus surface display system

The biomolecule-mediated assembly of novel composites has been the subject of numerous investigations during the last years, providing new insights into material science and engineering. Via molecular biology technology, we were able to introduce the genetically engineered polypeptide for inorganics (GEPI) as a molecular binder into biomolecules such as phage viruses, to assemble hybrid functional nanoarchitectures. In the present work, we introduced a novel nanocomposite comprising the Autographa californica nuclear polyhedrosis virus (AcNPV) and nanoparticles bound to it. Our results show that a GEPI-encoding gene was successfully introduced by recombination into a eukaryotic expression bacmid and finally displayed outside of the AcNPV after transfection into Sf9 insect cells using the Bac-to-Bac baculovirus expression system. The recombinant baculovirus maintained both the viral infectivity and the specific binding activity of the GEPI. The construction of the gene in the recombinant plasmid was examined by polymerase chain reaction analysis and enzymatic digestion identification, and verified by gene sequencing. Surface display of the fused peptide was revealed by Western blot analysis in dissolution studies and determined by immuno- gold electron microscopy. Adherence of nanoparticles to the recombinant baculovirus was visualized by transmission electron microscopy analysis. Here, we demonstrated the possibilities of combining peptide-mediated immobilization with baculovirus surface display technology.

Hemagglutinin displayed baculovirus protects against highly pathogenic influenza

Baculovirus (BV) replicating in insect cells can express a foreign gene product as part of its genome. The influenza hemagglutinin (HA) can be expressed from BV and displayed on the surface of baculovirus (HA-DBV). In this study we first generated six recombinant baculoviruses that expressed chimeric HAs with segments of the BV glycoprotein (gp64). The signal peptide (SP) and cytoplasmic tail (CT) domains of gp64 can enhance the display of HA from A/PR8/34 on BV surface, while the transmembrane (TM) domain of gp64 impairs HA display. Different doses of either live or β-propiolactone (BPL)-inactivated HA-DBV were administered to BALB/c mice. Live HA-DBV elicited higher hemagglutination-inhibition (HAI) titers than BPL-inactivated HA-DBV, and provided sterilizing protection. A second generation recombinant BV simultaneously displaying four HAs derived from four subclades of H5N1 influenza viruses was constructed. This tetravalent H5N1 HA-DBV vaccine elicited HAI titers against all four homologous H5N1 viruses, significantly decreasing viral lung titers of challenged mice and providing 100% protection against lethal doses of homologous H5N1 viruses. Moreover, mice vaccinated with HA-DBV had high levels of IFNγ-secreting and HA-specific CD8+ T cells. Taken together, this study demonstrates that HA-DBV can stimulate strong humoral, as well as cellular immune responses, and is an effective vaccine candidate for influenza.

Baculoviral capsid display of His-tagged ZnO inorganic binding peptide

Virus-templated fabrication of compound structures can be made through incorporating the specifically inorganic-binding peptide into the viral scaffold, widely used is phage display system. Compared to prokaryotic phages, insect cell-based baculovirus has some strengths such as the adaptability to the proteins' posttranslational modification and non-replication in mammalian cells. As an attempt to explore the baculovirus-mediated bioconjugates, we show in this study that a genetically engineered baculovirus, with a hexahistidine (His(6)) tagged ZnO binding peptide fused to the N-terminus of the viral capsid protein vp39 of AcNPV, was constructed. It maintains both the viral infectivity and the fusion protein's activity. The presence of the fusion protein on the baculovirus particle was demonstrated by western blot analysis of purified budded virus. Its display on the virus capsid was revealed by virus fractionation analysis. The binding of nanosized ZnO powders to the virus capsid was visualized by transmission electron microscopy (TEM). This is the first report of the display of the inorganic-binding peptide on the capsid of eukaryotic baculovirus. Aimed at the nanomaterials' application in the biological field, this research could find useful in the biotracking of the baculovirus transduction process and the preparation of novel functional nanodevices.

Silkworm expression system as a platform technology in life science

Many recombinant proteins have been successfully produced in silkworm larvae or pupae and used for academic and industrial purposes. Several recombinant proteins produced by silkworms have already been commercialized. However, construction of a recombinant baculovirus containing a gene of interest requires tedious and troublesome steps and takes a long time (3-6 months). The recent development of a bacmid, Escherichia coli and Bombyx mori shuttle vector, has eliminated the conventional tedious procedures required to identify and isolate recombinant viruses. Several technical improvements, including a cysteine protease or chitinase deletion bacmid and chaperone-assisted expression and coexpression, have led to significantly increased protein yields and reduced costs for large-scale production. Terminal N-acetyl glucosamine and galactose residues were found in the N-glycan structures produced by silkworms, which are different from those generated by insect cells. Genomic elucidation of silkworm has opened a new chapter in utilization of silkworm. Transgenic silkworm technology provides a stable production of recombinant protein. Baculovirus surface display expression is one of the low-cost approaches toward silkworm larvae-derived recombinant subunit vaccines. The expression of pharmaceutically relevant proteins, including cell/viral surface proteins, membrane proteins, and guanine nucleotide-binding protein (G protein) coupled receptors, using silkworm larvae or cocoons has become very attractive. Silkworm biotechnology is an innovative and easy approach to achieve high protein expression levels and is a very promising platform technology in the field of life science. Like the "Silkroad," we expect that the "Bioroad" from Asia to Europe will be established by the silkworm expression system.

Baculovirus-based display and gene delivery systems

The baculovirus expression vector system has been used extensively to produce numerous proteins originating from both prokaryotic and eukaryotic sources. In addition to easy cloning techniques and abundant viral propagation, the system's insect cell environment provides eukaryotic post-translational modification machinery. The recently established eukaryotic molecular biology tool, the baculovirus display vector system (BDVS), allows the combination of genotype with phenotype, enabling presentation of foreign peptides or even complex proteins on the baculoviral envelope or capsid. This strategy is important because it can be used to enhance viral binding and entry to mammalian cells as well as to produce antibodies against the displayed antigen. In addition, the technology should enable modifications of intracellular behavior, that is, trafficking of recombinant "nanoparticles," a highly relevant feature for studies of targeted gene or protein delivery. This article discusses the design and potential uses of insect-derived baculoviral display vectors.

Reduction of liver macrophage transduction by pseudotyping lentiviral vectors with a fusion envelope from Autographa californica GP64 and Sendai virus F2 domain

Background

Lentiviral vectors are well suited for gene therapy because they can mediate long-term expression in both dividing and nondividing cells. However, lentiviral vectors seem less suitable for liver gene therapy because systemically administered lentiviral vectors are preferentially sequestered by liver macrophages. This results in a reduction of available virus and might also increase the immune response to the vector and vector products.

Reduction of macrophage sequestration is therefore essential for efficient lentiviral liver gene therapy.

Results

Fusions were made of Autographa californica GP64 and the hepatocyte specific Sendai Virus envelope proteins. Lentiviral vectors were produced with either wild type GP64, Sendai-GP64, or both wild type GP64 and Sendai-GP64 and tested in vitro and in vivo for hepatocyte and macrophage gene transfer.

Sendai-GP64 pseudotyped vectors showed specific gene transfer to HepG2 hepatoma cells, with no detectable transduction of HeLa cervical carcinoma cells, and a decreased affinity for RAW mouse macrophages. Co-expression of wild type GP64 and Sendai-GP64 resulted in improved viral titers while retaining increased affinity for HepG2 cells.

In vivo, the Sendai-GP64 vectors also showed decreased transduction of murine liver macrophages.

Conclusion

We demonstrate reduced macrophage transduction in vitro and in vivo with GP64/Sendai chimeric envelope proteins.

Baculovirus surface display of NS3 nonstructural protein of classical swine fever virus

Classical swine fever virus (CSFV) causes significant losses in the pig industry in many countries. NS3 proteins of CSFV, which include serine protease and RNA helicase/nucleotide triphosphatase (NTPase) activities, are multifunctional proteins involved in polyprotein processing and viral replication. Previous reports showed that NS3 protein can induce apoptosis in host cells that present cytopathic effects (CPE). Baculovirus/insect cell systems are used widely for recombinant protein production. In this study, one recombinant baculovirus BacSC-NS3 expressing histidine-tagged NS3 with the transmembrane domain (TM) and cytoplasmic domain (CTD) derived from baculovirus envelope protein gp64 of baculovirus was constructed. After infection, NS3 was expressed and anchored to the plasma membrane of Sf-9 cells, as demonstrated by Western blot assay and confocal microscopy. Immunogold electron microscopy demonstrated that the NS3 glycoprotein successfully displayed on the baculoviral envelope. Animal vaccine tests showed that recombinant baculovirus BacSC-NS3 elicited significantly higher NS3 antibody titers in the treated mouse models than the control group. This report demonstrated the potential of NS3-pseudotyped baculovirus expression of NS3 protein successfully.

Tumor targeting of baculovirus displaying a lymphatic homing peptide

BACKGROUND

Tumor-associated cells and vasculature express attractive molecular markers for site-specific vector targeting. To attain tumor-selective tropism, we recently developed a baculovirus vector displaying the lymphatic homing peptide LyP-1, originally identified by ex vivo/in vivo screening of phage display libraries, on the viral envelope by fusion to the transmembrane anchor of vesicular stomatitis virus G-protein.

METHODS

In the present study, we explored the specificity and kinetics of viral binding and internalization as well as in vivo tumor homing of the LyP-1 displaying virus to elucidate the applicability of baculovirus for targeted therapies.

RESULTS

We demonstrated that the LyP-1 peptide contributes to saturable binding of baculovirus in human MDA-MB-435 and HepG2 carcinoma cells and escalates the kinetics of viral internalization leading to earlier nuclear accumulation and enhanced transgene expression. The LyP-1 displaying virus also showed stronger competitiveness against transduction with wild-type baculovirus, suggesting involvement of a specific receptor in cellular attachment and entry. Following intravenous injections, the modified virus accumulated within the human MDA-MB-435 and MDA-MB-231 carcinoma xenografts in mice with higher specificity and efficiency than the control virus. Targeting of the modified virus was more specific in the MDA-MB-435 than in the MDA-MB-231 xenografts as demonstrated by higher tumor accumulation and lower distribution in nontarget organs. No apparent cytotoxicity was associated with the surface modification.

CONCLUSIONS

This first demonstration of in vivo tumor targeting of a systemically administered, tropism-modified baculoviral vector highlights the potential of baculovirus-mediated targeted therapies.

Baculovirus surface display of sigmaC and sigmaB proteins of avian reovirus and immunogenicity of the displayed proteins in a mouse model

Avian reovirus (ARV), an important pathogen in poultry, causes arthritis, chronic respiratory disease, and malabsorption syndrome that cause considerable economic losses to the poultry industry. In present study, we have succeeded in construction of a universal baculovirus surface display system (UBSDS) that can display different foreign proteins on the envelope of baculovirus. Sequences encoding the signal peptide (SS), transmembrane domain (TM), and cytoplasmic domain (CTD) derived from the gp64 protein of baculovirus and histidine tag, respectively were inserted into the pBacCE vector. Four restriction enzyme sites between the histidine tag and gp64 transmembrane domain were established for expression of different foreign proteins. The transmembrane domain and CTD of gp64 in the platform were designed in order to improve stability and quantity of foreign proteins on the envelope of baculovirus. The sigmaC and sigmaB proteins of ARV are known to elicit neutralizing antibodies against ARV. The UBSDS was therefore used to express sigmaC and sigmaB proteins on the envelope of baculovirus. Two recombinant baculoviruses BacSC-sigmaC and BacSC-sigmaB have been successfully constructed. After infection, both His6-tagged recombinant sigmaC (rsigmaC) and sigmaB (rsigmaB) proteins were displayed on the envelope of recombinant baculoviruses and the recombinant viral proteins were anchored on the plasma membrane of Sf-9 cells, as revealed by immunofluorescence staining (IFS) and confocal microscopy. The antigenicity of rsigmaC and rsigmaB proteins was demonstrated by Western blotting assay. Immunogold electron microscopy demonstrated that both recombinant viruses displayed rsigmaC and rsigmaB proteins on the viral surface. Immunization of BALB/c mice with recombinant viruses, demonstrated that serum from the BacSC-sigmaC and BacSC-sigmaB treated models had significant higher levels of virus neutralization activities than the control groups. This demonstrates that the recombinant baculoviruses BacSC-sigmaC and BacSC-sigmaB can be a potential vaccine against ARV infections.

The postfusion structure of baculovirus gp64 supports a unified view of viral fusion machines

Viral fusion proteins mediate the merger of host and viral membranes during cell entry for all enveloped viruses. Baculovirus glycoprotein gp64 (gp64) is unusual in promoting entry into both insect and mammalian cells and is distinct from established class I and class II fusion proteins. We report the crystal structure of its postfusion form, which explains a number of gp64's biological properties including its cellular promiscuity, identifies the fusion peptides and shows it to be the third representative of a new class (III) of fusion proteins with unexpected structural homology with vesicular stomatitis virus G and herpes simplex virus type 1 gB proteins. We show that domains of class III proteins have counterparts in both class I and II proteins, suggesting that all these viral fusion machines are structurally more related than previously thought.

Baculovirus surface display of E(rns) envelope glycoprotein of classical swine fever virus

Classical swine fever virus (CSFV) causes significant losses in the pig industry in many countries. E(rns) is an envelope glycoprotein of CSFV which is known to induce virus-neutralizing antibodies and protective immunity in the natural host. In this study, one recombinant baculoviruses BacSC-E(rns) expressing histidine-tagged E(rns) with the transmembrane domain (TM) and cytoplasmic domain (CTD) derived from baculovirus envelope protein gp64 was constructed and its immunizing efficacy was evaluated in a mouse model. After infection, E(rns) was expressed and anchored on the plasma membrane of Sf-9 cells, as demonstrated by Western-blot and confocal microscopy. Immunogold electron microscopy demonstrated that the E(rns) glycoprotein was successfully displayed on the baculoviral envelope. Vaccine tests in animals showed that BacSC-E(rns) elicited significantly higher E(rns) antibody titers in the immunized mouse models than the control group. This demonstrates that the BacSC-E(rns) vaccine can be used potentially against CSFV infections. This is the first report demonstrating the potential of E(rns)-pseudotyped baculovirus as a CSFV vaccine.