Presentation of antigenic sites from foot-and-mouth disease virus on the surface of baculovirus and in the membrane of infected cells

Baculovirus Display of Peptides and Proteins for Medical Applications

Baculoviridae is a large family of arthropod-infective viruses. Recombinant baculoviruses have many applications, the best known is as a system for large scale protein production in combination with insect cell cultures. More recently recombinant baculoviruses have been utilized for the display of proteins of interest with applications in medicine. In the present review we analyze the different strategies for the display of proteins and peptides on the surface of recombinant baculoviruses and provide some examples of the different proteins displayed. We analyze briefly the commercially available systems for recombinant baculovirus production and display and discuss the future of this emerging and powerful technology.

Two Distinctive Phenotypes of AcMNPV Display Different Immune Abilities and Intracellular Destiny

The budded phenotype (BV) of the baculovirus AcMNPV has been demonstrated to have strong immunostimulatory properties that are relevant for the development of vaccines and antiviral therapies. Although the occluded phenotype (ODV) shares the main structural proteins and its genome with BV, it has been poorly studied in mammals. In this study, we assessed the capacity of ODV to induce immune responses in mice. In contrast to BVs, ODVs failed to promote the secretion of IFN-gamma, IL-6 and Il-12 and to induce antiviral activity against VSV in the short term. Furthermore, ODVs were unable to induce cellular immunity against a coadministered antigen 7 days after inoculation. By analyzing the interaction of ODVs with BMDCs, we observed that although ODVs entered the cells reaching late and acidic endosomes, they did not induce their maturation. Finally, we also analyzed if BVs and ODVs followed different routes in the cell during the infection. BVs, but not ODVs, colocalized with the protein ovalbumin in compartments with the presence of proteases. The results suggest that structural differences could be responsible for their different destinies in the dendritic cell and this could lead to a different impact on the immune response.

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.

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.

Display of the VP1 epitope of foot-and-mouth disease virus on bacteriophage T7 and its application in diagnosis

Foot-and-mouth disease (FMD) is a highly contagious epidemic disease threatening the cattle industry since the sixteenth century. In recent years, the development of diagnostic assays for FMD has benefited considerably from the advances of recombinant DNA technology. In this study, the immunodominant region of the capsid protein VP1 of the foot-and-mouth disease virus (FMDV) was fused to the T7 bacteriophage and expressed on the surface of the bacteriophage capsid protein. The recombinant protein of about 42 kDa was detected by the anti-T7 tag monoclonal antibody in Western blot analysis. Phage ELISA showed that both the vaccinated and positive infected bovine sera reacted significantly with the recombinant T7 particle. This study demonstrated the potential of the T7 phage displaying the VP1 epitope as a diagnostic reagent.

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.

Surface display of AcMNPV occlusion-derived P74 does not enhance oral infectivity of budded viruses

Baculovirus occlusion-derived viruses (ODVs) and budded viruses (BVs) are morphologically and functionally distinct. ODVs are responsible for primary infection in insect hosts because of their high per os infectivity. On the contrary, BVs poorly infect endothelial gut cells, but propagate the infection in the tissues of insects with a high efficiency. P74 is one of the most important proteins from ODVs, and it participates in the attachment of this viral phenotype to endothelial cells in the midgut. We evaluated the possibility of pseudotyping BVs of Autographa californica multiple nucleopolyhedrovirus with two versions of P74 and its effect on their oral infectivity. Both recombinant BVs contained P74 and replicated similarly to wild-type viruses. Nevertheless, the presence of P74 on the BV's surface does not enhance the oral infectivity of this phenotype, suggesting that the presence of P74 in the membrane of budded virions interferes with their mechanism of infecting midgut cells.

Baculovirus expression systems for production of recombinant proteins in insect and mammalian cells

Baculovirus vector systems are extensively used for the expression of foreign gene products in insect and mammalian cells. New advances increase the possibilities and applications of the baculovirus expression system, which makes it possible to express multiple genes simultaneously within a single infected insect cell and to obtain multimeric proteins functionally similar to their natural analogs. Recombinant viruses with expression cassettes active in mammalian cells are used to deliver and express genes in mammalian cells in vitro and in vivo. Further improvement of the baculovirus expression system and its adaptation to specific target cells can open up a wide variety of applications. The review considers recent achievements in the use of modified baculoviruses to express recombinant proteins in eukaryotic cells, advantages and drawbacks of the baculovirus expression system, and ways to optimize the expression of recombinant proteins in both insect and mammalian cell lines.

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.

A chimeric baculovirus displaying bovine herpesvirus-1 (BHV-1) glycoprotein D on its surface and their immunological properties

The ability of a recombinant baculovirus containing the ectodomain of the mature sequence of glycoprotein D (gD) fused to the amino-terminus of baculoviral glycoprotein gp64 to display gD on its surface and to serve as an improved immunogen against bovine herpesvirus-1 was tested. The gD-gp64 fusion protein was correctly expressed on the virus particles as revealed by immunomicroscopy assays. Mice immunized with 5 x 10(8) plaque forming units developed antibodies that specifically reacted in an enzyme-linked immunosorbent assay with recombinant gD and whole bovine herpesvirus-1. These antibodies were able to neutralize bovine herpesvirus-1 in vitro, whereas those elicited by a version of gD expressed in Escherichia coli did not. Our data demonstrated that the display on the virion surface of recombinant baculovirus can provide a tool for the development of recombinant vaccines against bovine herpesvirus-1.

Baculovirus display: a multifunctional technology for gene delivery and eukaryotic library development

For over a decade, phage display has proven to be of immense value, allowing selection of a large variety of genes with novel functions from diverse libraries. However, the folding and modification requirements of complex proteins place a severe constraint on the type of protein that can be successfully displayed using this strategy, a restriction that could be resolved by similarly engineering a eukaryotic virus for display purposes. The quite recently established eukaryotic molecular biology tool, the baculovirus display vector system (BDVS), allows combination of genotype with phenotype and thereby enables presentation of eukaryotic proteins on the viral envelope or capsid. Data have shown that the baculovirus, Autographa californica multiple nucleopolyhedrovirus (AcMNPV), is a versatile tool for eukaryotic virus display. Insertion of heterologous peptides and/or proteins into the viral surface by utilizing the major envelope glycoprotein gp64, or foreign membrane-derived counterparts, allows incorporation of the sequence of interest onto the surface of infected cells and virus particles. A number of strategies are being investigated in order to further develop the display capabilities of AcMNPV and improve the complexity of a library that may be accommodated. Numerous expression vectors for various approaches of surface display have already been developed. Further improvement of both insertion and selection strategies toward development of a refined tool for use in the creation of useful eukaryotic libraries is, however, needed. Here, the status of baculovirus display with respect to alteration of virus tropism, antigen presentation, transgene expression in mammalian cells, and development of eukaryotic libraries will be reviewed.

RGD motifs on the surface of baculovirus enhance transduction of human lung carcinoma cells

Baculovirus vectors have been shown to enter a variety of mammalian cell lines and gene transfer with wild-type baculovirus (WT) has been demonstrated both in vitro and in vivo. Different protein motifs have been displayed on the viral surface to serve as ligands for cell-specific receptor molecules. We have generated recombinant baculovirus vectors displaying an RGD-motif, recognized by alphaV integrin, on the viral surface. The RGD motifs within the C-terminus of coxsackie virus A9 and human parechovirus 1 VP1 proteins were fused to the N-terminus of the major envelope glycoprotein, gp64, of Autographa californica multiple nucleopolyhedrovirus. The recombinant RGD-presenting viruses bound more efficiently to the surface of human lung carcinoma cells (A549), known to contain alphaV integrins, as compared to WT baculovirus. In addition, the binding pattern of the RGD-displaying baculovirus showed extensive clustering. This most likely represents clustering of the integrin molecules on the cell surface, induced by binding of the RGD-displaying baculovirus. Finally, the transduction efficiency of an RGD-representing virus increased by almost three-fold as monitored by light emission measurements. In conclusion, these results suggest that the RGD-motif is functional on the surface of baculovirus and thereby these tropism-modified viruses bind more efficiently as well as enhance the transduction efficiency of human cancer cells expressing alphaV integrins.

Baculovirus vectors for gene therapy

Since the discovery that baculoviruses can efficiently transduce mammalian cells, baculoviruses have been extensively studied as potential vectors for both in vitro and in vivo gene therapy. This chapter reviews the history of this research area, cells permissive to baculovirus transduction, factors influencing transduction and transgene expression, efforts to improve transduction, mechanisms of virus entry and intracellular trafficking, applications for in vivo and ex vivo gene therapy, as well as advantages, limitations, and safety issues concerning use of baculoviruses as gene therapy vectors. Recent progress and efforts directed toward overcoming existing bottlenecks are emphasized.

Baculovirus as a highly efficient expression vector in insect and mammalian cells

Baculovirus has been widely used for the production of recombinant proteins in insect cells. Since the finding that baculovirus can efficiently transduce mammalian cells, the applications of baculovirus have been greatly expanded. The prospects and drawbacks of baculovirus-mediated gene expression, either in insect or in mammalian cells, are reviewed. Recent progresses in expanding the applications to studies of gene regulation, viral vector preparation, in vivo and ex vivo gene therapy studies, generation of vaccine vectors, etc are discussed and the efforts directed towards overcoming the existing bottlenecks are particularly emphasized.

Amino-terminal anchored surface display in insect cells and budded baculovirus using the amino-terminal end of neuraminidase

Methods currently used for surface display on insect cells and budded baculovirus, all utilize the sequences from class I transmembrane proteins. This gives rise to some problems when handling unknown genes or cDNAs encoding full-length proteins. First, the stop codon from the cloned gene will be located upstream of the sequence for the transmembrane region. Second, the chance of getting the sequences encoding the signal peptide and the transmembrane region in frame with the cloned gene is small. To minimize these problems, we here present a method by which cDNAs or genes of interest can be cloned and fused to the codons for the signal peptide and transmembrane region of neuraminidase (NA), a class II transmembrane protein of the influenza virus. By placing both the signal peptide and transmembrane region at the amino-terminal, potential problems regarding stop codons are eliminated and errors in frame-shift minimized. To obtain proof of principle, the gene encoding enhanced green fluorescent protein, EGFP, was subcloned into a shuttle vector downstream of the neuraminidase sequence and the fusion product was then transferred to a baculovirus vector and transfected into insect cells (Sf9). Using this method, EGFP was found to be expressed on the surface of both infected cells and budded virus in an accessible manner.

Immunological properties of FMDV-gP64 fusion proteins expressed on SF9 cell and baculovirus surfaces

In the present report, we characterized the immune response and the protection conferred by recombinant baculoviruses or infected insect cells expressing the fusions gp64-P1 and gp64-site A FMDV antigens. Mice, vaccinated intraperitoneally with gp64-P1 immunogens, showed a low-antibody response and a variable degree of protection. However, when mice received recombinant baculoviruses or infected insect cells expressing the fusion protein gp64-site A, high-ELISA and seroneutralizing titers (SNT) against FMDV were elicited. All mice immunized with Sf9 cells expressing FMDV site A developed a protective immune response against challenge with virulent FMDV, indicating that the baculovirus display of foreign epitopes is a promising approach to biosynthetic vaccines.

Improved display of synthetic IgG-binding domains on the baculovirus surface

Improved display of foreign protein moieties in combination with beneficial alteration of the viral surface properties should be of value for targeted and enhanced gene delivery. Here, we describe a vector based on Autographa californica multiple nucleopolyhedrovirus (AcMNPV) displaying synthetic IgG-binding domains (ZZ) of protein A fused to the transmembrane anchor of vesicular stomatitis virus (VSV) G protein. This display vector was equipped with a GFP/EGFP expression cassette enabling fluorescent detection in both insect and mammalian cells. The virus construct displayed the biologically active fusion protein efficiently and showed increased binding capacity to IgG. As the display is carried out using a membrane anchor of foreign origin, gp64 is left intact for virus entry, which may increase gene expression in the transduced mammalian cells. In addition, the viral vector can be targeted to any desired cell type via binding of ZZ domains when an appropriate IgG antibody is available.

Baculovirus virions displaying Plasmodium berghei circumsporozoite protein protect mice against malaria sporozoite infection

The display of foreign proteins on the surface of baculovirus virions has provided a tool for the analysis of protein-protein interactions and for cell-specific targeting in gene transfer applications. To evaluate the baculovirus display system as a vaccine vehicle, we have generated a recombinant baculovirus (AcNPV-CSPsurf) that displays rodent malaria Plasmodium berghei circumsporozoite protein (PbCSP) on the virion surface as a fusion protein with the major baculovirus envelope glycoprotein gp64. The PbCSP-gp64 fusion protein was incorporated and oligomerized on the virion surface and led to a 12-fold increase in the binding activity of AcNPV-CSPsurf virions to HepG2 cells. Immunization with adjuvant-free AcNPV-CSPsurf virions induced high levels of antibodies and gamma interferon-secreting cells against PbCSP and protected 60% of mice against sporozoite challenge. These data demonstrate that AcNPV-CSPsurf displays sporozoite-like PbCSP on the virion surface and possesses dual potentials as a malaria vaccine candidate and a liver-directed gene delivery vehicle.

Bombyx mori nucleopolyhedrovirus-based surface display system for recombinant proteins

We describe here the development of a 'eukaryotic display system' for heterologous proteins on the viral and host cell surfaces using Bombyx mori nucleopolyhedrovirus (BmNPV). The reporter gene gfp (green fluorescent protein) was fused to either the gp64 gene encoding the full-length BmNPV envelope protein GP64 or to its 5' region encoding only the N-terminal domain harbouring the signal sequence, and recombinant viruses expressing the corresponding fusion proteins under the strong viral polyhedrin promoter were generated. On infection of the host insect B. mori or the host-derived BmN cells with the full-length GP64-GFP virus, abundant expression of the recombinant protein and its display on the cell surface were achieved. The fusion protein was also a component of the budded virions. Thus, the BmNPV-based display system provides an alternative to the previously established Autographa californica multinucleocapsid nucleopolyhedrovirus display system. The recombinant virus expressing GFP has also been used in preliminary pathological investigations on virus infection in B. mori and provides a simple method for screening for antiviral agents.

Baculovirus surface display of Theileria parva p67 antigen preserves the conformation of sporozoite-neutralizing epitopes

Theileria parva is an intracellular protozoan parasite that causes East Coast fever, a severe lymphoproliferative disease in cattle. Previous attempts to produce recombinant sporozoite surface antigen (p67) in bacterial or insect cells for vaccine purposes have not resulted in a correctly folded protein. Here, we report the expression of N- and C-terminal domains of p67 fused to the baculovirus envelope glycoprotein GP64 by cloning the appropriate p67 cDNA segments between the signal sequence and the major portion of GP64. To further advance the generation of such recombinants, existing surface display techniques were combined with bacmid technology. Chimeric proteins were present on the surface of budded viruses as judged by immunogold labelling and were exposed on the surface of insect cells, as concluded from immunofluorescence studies of infected, non-fixed insect cells. In non-denaturing dot blot experiments, a strong reaction was obtained between monoclonal TpM12 and baculovirus particles displaying the p67N-GP64 chimeric protein. This antibody, raised against native p67, also specifically recognized the surface of recombinant-infected cells. Apparently, a more native conformation was achieved than when p67 was expressed in E.coli or in conventional baculovirus expression systems. The baculovirus surface expression system, therefore, provides an improved way of expressing this T.parva sporozoite surface protein.