Incorporation of decay-accelerating factor into the baculovirus envelope generates complement-resistant gene transfer vectors

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.

Highly efficient CRISPR-mediated large DNA docking and multiplexed prime editing using a single baculovirus

CRISPR-based precise gene-editing requires simultaneous delivery of multiple components into living cells, rapidly exceeding the cargo capacity of traditional viral vector systems. This challenge represents a major roadblock to genome engineering applications. Here we exploit the unmatched heterologous DNA cargo capacity of baculovirus to resolve this bottleneck in human cells. By encoding Cas9, sgRNA and Donor DNAs on a single, rapidly assembled baculoviral vector, we achieve with up to 30% efficacy whole-exon replacement in the intronic β-actin (ACTB) locus, including site-specific docking of very large DNA payloads. We use our approach to rescue wild-type podocin expression in steroid-resistant nephrotic syndrome (SRNS) patient derived podocytes. We demonstrate single baculovirus vectored delivery of single and multiplexed prime-editing toolkits, achieving up to 100% cleavage-free DNA search-and-replace interventions without detectable indels. Taken together, we provide a versatile delivery platform for single base to multi-gene level genome interventions, addressing the currently unmet need for a powerful delivery system accommodating current and future CRISPR technologies without the burden of limited cargo capacity.

Baculoviruses in Gene Therapy and Personalized Medicine

This review will outline the role of baculoviruses in gene therapy and future potential in personalized medicine. Baculoviruses are a safe, non-toxic, non-integrative vector with a large cloning capacity. Baculoviruses are also a highly adaptable, low-cost vector with a broad tissue and host tropism due to their ability to infect both quiescent and proliferating cells. Moreover, they only replicate in insect cells, not mammalian cells, improving their biosafety. The beneficial properties of baculoviruses make it an attractive option for gene delivery. The use of baculoviruses in gene therapy has advanced significantly, contributing to vaccine production, anti-cancer therapies and regenerative medicine. Currently, baculoviruses are primarily used for recombinant protein production and vaccines.  This review will also discuss methods to optimize baculoviruses protein production and mammalian cell entry, limitations and potential for gene therapy and personalized medicine. Limitations such as transient gene expression, complement activation and virus fragility are discussed in details as they can be overcome through further genetic modifications and other methods. This review concludes that baculoviruses are an excllent candidate for gene therapy, personalized medicine and other biotherapeutic applications.

Evaluation of Combinatory Effects of Plasmodium Circumsporozoite Protein and Complement Regulatory Protein Expression of Recombinant Baculovirus Vectors

Baculovirus vectors (BVs) are safely able to transduce foreign genes and express them in mammalian cells. However, the transduction activity of BVs is strongly reduced by the attack of serum complement, which is one of the major obstacles in the use of BVs for in vivo gene transfer. One strategy to overcome this problem is the display of complement regulatory proteins (CRPs) on BV virions. We previously developed CD46-decay accelerating factor (DAF)-CD59 triple fusion type BV showing potent complement resistance. We also developed BVs expressing Plasmodium circumsporozoite protein (CSP) to enhance transduction efficacy in hepatic cells. In this study, we investigated the combination of CSP and CRPs in a BV system to evaluate transduction efficacy along with complement resistance. To accomplish the combination of CSP and CRPs, we generated insect Sf9 cells stably expressing CRPs, to which CSP type BV was infected. The BVs collected from these infected cells were confirmed to possess both CSP and CRPs in virions. We demonstrated that CSP-CD46-DAF-CD59 type BV, containing both CSP and CD46-DAF-CD59, showed a significant increase in transduction efficacy in human hepatoma HepG2 cells under intact serum exposure compared with control type BV or CSP type BV, retaining both advantages of CSP and CD46-DAF-CD59. Collectively, these results demonstrated that the utilization of stably expressing Sf9 cells to introduce the protein products of interest, e.g., CRPs into BVs, would be useful strategy to generate BVs with novel functions such as resistance against serum complement attack.

Synthetic Virus-Derived Nanosystems (SVNs) for Delivery and Precision Docking of Large Multifunctional DNA Circuitry in Mammalian Cells

DNA delivery is at the forefront of current research efforts in gene therapy and synthetic biology. Viral vectors have traditionally dominated the field; however, nonviral delivery systems are increasingly gaining traction. Baculoviruses are arthropod-specific viruses that can be easily engineered and repurposed to accommodate and deliver large sequences of exogenous DNA into mammalian cells, tissues, or ultimately organisms. These synthetic virus-derived nanosystems (SVNs) are safe, readily customized, and can be manufactured at scale. By implementing clustered regularly interspaced palindromic repeats (CRISPR) associated protein (CRISPR/Cas) modalities into this system, we developed SVNs capable of inserting complex DNAs into genomes, at base pair precision. We anticipate a major role for SVNs as an attractive alternative to viral vectors in accelerating genome engineering and gene therapy applications in the future.

Induction of mucosal immunity against pathogens by using recombinant baculoviral vectors: Mechanisms, advantages, and limitations

Over 90% of pathogens of medical importance invade the organism through mucosal surfaces, which makes it urgent to develop safe and effective mucosal vaccines and mucosal immunization protocols. Besides, parenteral immunization does not provide adequate protective immunity in mucosal surfaces. Effective mucosal vaccination could protect local and systemic compartments and favor herd immunity. Although various mucosal adjuvants and Ag-delivery systems have been developed, none has filled the gap to control diseases caused by complex mucosal pathogens. Among the strategies to counteract them, recombinant virions from the baculovirus Autographa californica multiple nucleopolyhedrovirus (rAcMNPV) are useful vectors, given their safety and efficacy to produce mucosal and systemic immunity in animal infection models. Here, we review the immunogenic properties of rAcMNPV virions from the perspectives of mucosal immunology and vaccinology. Some features, which are analyzed and extrapolated from studies with different particulate antigens, include size, shape, surface molecule organization, and danger signals, all needed to break the tolerogenic responses of the mucosal immune tissues. Also, we present a condensed discussion on the immunity provided by rAcMNPV virions against influenza virus and human papillomavirus in animal models. Through the text, we highlight the advantages and limitations of this experimental immunization platform.

Protection of Baculovirus Vectors Expressing Complement Regulatory Proteins against Serum Complement Attack

Baculovirus vectors (BVs) enable safe and efficient gene delivery to mammalian cells and are useful in a wide range of applications, including gene therapy and in vivo analysis of gene functions. We previously developed BVs expressing malaria sporozoite surface proteins for targeting liver cells or hepatocytes. However, BVs are known to be very vulnerable to complement attack and efforts to overcome their inactivation based on complement are important. In this study, BVs expressing complement regulatory proteins (CRPs) on the surfaces of virions were developed to inhibit complement reactions. Decay accelerating factor (DAF; CD55)-type BVs exhibited significantly higher complement resistance than control BVs without any CRPs in HepG2 cells transduction, although the transduction efficacy of DAF-type BV was low. In contrast, CD46-DAF-CD59 fusion type BVs showed significantly higher transduction efficacy and complement resistance than both control and DAF-type BVs. DAF-type and CD46-DAF-CD59 type BVs repressed formation of the membrane attack complex, a terminal product of complement reaction cascades, induced by BVs. These results suggest that the CD46-DAF-CD59 fusion construct confers complement protection ability superior to that of the DAF construct in gene delivery under complement active serum.

Beyond the Role of CD55 as a Complement Component

The complement is a part of the immune system that plays several roles in removing pathogens. Despite the importance of the complement system, the exact role of each component has been overlooked because the complement system was thought to be a nonspecific humoral immune mechanism that worked against pathogens. Decay-accelerating factor (DAF or CD55) is a known inhibitor of the complement system and has recently attracted substantial attention due to its role in various diseases, such as cancer, protein-losing enteropathy, and malaria. Some protein-losing enteropathy cases are caused by CD55 deficiency, which leads to complement hyperactivation, malabsorption, and angiopathic thrombosis. In addition, CD55 has been reported to be an essential host receptor for infection by the malaria parasite. Moreover, CD55 is a ligand of the seven-span transmembrane receptor CD97. Since CD55 is present in various cells, the functional role of CD55 has been expanded by showing that CD55 is associated with a variety of diseases, including cancer, malaria, protein-losing enteropathy, paroxysmal nocturnal hemoglobinuria, and autoimmune diseases. This review summarizes the current understanding of CD55 and the role of CD55 in these diseases. It also provides insight into the development of novel drugs for the diagnosis and treatment of diseases associated with CD55.

Malaria sporozoite protein expression enhances baculovirus-mediated gene transfer to hepatocytes

BACKGROUND

Baculovirus vector (BV) is able to transduce foreign genes into mammalian cells efficiently and safely by incorporating a mammalian promoter. In the present study, we tailored the surface proteins expressed by malaria sporozoites to enhance hepatocyte transduction. Sporozoites infect hepatocytes within minutes of initial entry into the blood circulation. Infectivity and hepatocyte-specific selectivity are mediated by the interplay between hepatocytes and sporozoite surface proteins. The circumsporozoite protein (CSP) and the thrombospondin-related anonymous protein (TRAP) bind to the heparan sulfate proteoglycan on the hepatocyte surface and contribute to sporozoite infection and hepatocyte selectivity.

METHODS

BVs displaying an ectodomain consisting of three different CSP variants (full-length, N-terminal and C-terminal) or TRAP on the virus envelope were constructed, and the resulting in vitro hepatocyte transduction efficiency was evaluated.

RESULTS

We demonstrated improved hepatocyte transduction efficiency in BVs expressing CSP or TRAP ectodomains compared to BVs without malaria surface proteins. In addition, gene transduction efficiencies for BVs displaying CSP or TRAP are higher than those expressing the preS1 antigen of the hepatitis B virus.

CONCLUSIONS

BVs expressing CSP or TRAP in the ectodomain could represent a promising hepatocyte-specific gene delivery methodology. Copyright © 2016 John Wiley & Sons, Ltd.

Gene delivery and gene expression in vertebrate using baculovirus Bombyx mori nucleopolyhedrovirus vector

The baculovirus Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) has been investigated as a possible tool for gene therapy, but its inhibition by complement proteins in human serum limits its applicability. Here, we used the baculovirus Bombyx mori nucleopolyhedrovirus (BmNPV) to construct a gene delivery vector in which a reporter gene is driven by a cytomegalovirus IE promoter. Enhanced green fluorescent protein (EGFP) and luciferase reporter genes were used to test the efficiency of gene delivery. In vitro complement inactivation data showed that the recombinant BmNPV vector was more stable in human serum than the recombinant AcMNPV vector. The recombinant BmNPV vector successfully delivered the reporter genes into different tissues and organs in mice and chicks. These results demonstrate that the BmNPV vector is more stability against complement inactivation in human serum than the AcMNPV vector, and indicate that it may be useful as an effective gene delivery vector for gene therapy in vertebrates.

DAF-shielded baculovirus-vectored vaccine enhances protection against malaria sporozoite challenge in mice

Background

Previous studies have shown that the baculovirus-vectored vaccine based on the “baculovirus dual expression system (BDES)” is an effective vaccine delivery platform for malaria. However, a point of weakness remaining for use of this vaccine platform in vivo concerns viral inactivation by serum complement. In an effort to achieve complement resistance, the gene encoding the human decay-accelerating factor (hDAF) was incorporated into the BDES malaria vaccine expressing the Plasmodium falciparum circumsporozoite protein (PfCSP).

Results

The newly-developed BDES vaccine, designated BDES-sPfCSP2-Spider, effectively displayed hDAF and PfCSP on the surface of the viral envelope, resulting in complement resistance both in vitro and in vivo. Importantly, upon intramuscular inoculation into mice, the BDES-sPfCSP2-Spider vaccine had a higher protective efficacy (60%) than that of the control vaccine BDES-sPfCSP2-Spier (30%) against challenge with transgenic Plasmodium berghei sporozoites expressing PfCSP.

Conclusion

DAF-shielded BDES-vaccines offer great potential for development as a new malaria vaccine platform against the sporozoite challenge.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-017-2039-x) contains supplementary material, which is available to authorized users.

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.

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.

Sleeping Beauty-baculovirus hybrid vectors for long-term gene expression in the eye

BACKGROUND

A baculovirus vector is capable of efficiently transducing many nondiving and diving cell types. However, the potential of baculovirus is restricted for many gene delivery applications as a result of the transient gene expression that it mediates. The plasmid-based Sleeping Beauty (SB) transposon system integrates transgenes into target cell genome efficiently with a genomic integration pattern that is generally considered safer than the integration of many other integrating vectors; yet efficient delivery of therapeutic genes into cells of target tissues in vivo is a major challenge for nonviral gene therapy. In the present study, SB was introduced into baculovirus to obtain novel hybrid vectors that would combine the best features of the two vector systems (i.e. effective gene delivery and efficient integration into the genome), thus circumventing the major limitations of these vectors.

METHODS

We constructed and optimized SB-baculovirus hybrid vectors that bear either SB100x transposase or SB transposon in the forward or reverse orientations with respect to the viral backbone The functionality of the novel hybrid vectors was investigated in cell cultures and in a proof-of-concept study in the mouse eye.

RESULTS

The hybrid vectors showed high and sustained transgene expression that remained stable and demonstrated no signs of decline during the 2 months follow-up in vitro. These results were verified in the mouse eye where persistent transgene expression was detected two months after intravitreal injection.

CONCLUSIONS

Our results confirm that (i) SB-baculovirus hybrid vectors mediate long-term gene expression in vitro and in vivo, and (ii) the hybrid vectors are potential new tools for the treatment of ocular diseases.

Bioengineered baculoviruses as new class of therapeutics using micro and nanotechnologies: principles, prospects and challenges

Designing a safe and efficient gene delivery system is required for success of gene therapy trials. Although a wide variety of viral, non-viral and polymeric nanoparticle based careers have been widely studied, the current gene delivery vehicles are limited by their suboptimal, non-specific therapeutic efficacy and acute immunological reactions, leading to unwanted side effects. Recently, there has been a growing interest in insect-cell-originated baculoviruses as gene delivery vehicles for diverse biomedical applications. Specifically, the emergence of diverse types of surface functionalized and bioengineered baculoviruses is posed to edge over currently available gene delivery vehicles. This is primarily because baculoviruses are comparatively non-pathogenic and non-toxic as they cannot replicate in mammalian cells and do not invoke any cytopathic effect. Moreover, emerging advanced studies in this direction have demonstrated that hybridizing the baculovirus surface with different kinds of bioactive therapeutic molecules, cell-specific targeting moieties, protective polymeric grafts and nanomaterials can significantly improve the preclinical efficacy of baculoviruses. This review presents a comprehensive overview of the recent advancements in the field of bioengineering and biotherapeutics to engineer baculovirus hybrids for tailored gene therapy, and articulates in detail the potential and challenges of these strategies for clinical realization. In addition, the article illustrates the rapid evolvement of microfluidic devices as a high throughput platform for optimizing baculovirus production and treatment conditions.

Potential Usefulness of Baculovirus-Mediated Sodium-Iodide Symporter Reporter Gene as Non-Invasively Gene Therapy Monitoring in Liver Cancer Cells: An In Vitro Evaluation

Primary liver cancer has one of the highest mortality rates of all cancers, and the main current treatments have a poor prognosis. This study aims to examine the efficiency of baculovirus vectors for transducing target gene into liver cancer cells and to evaluate the feasibility of using baculovirus vectors to deliver the sodium-iodide symporter (NIS) gene as a reporter gene through co-vector administration approach to monitor the expression of the target therapeutic gene in liver cancer gene therapy. We constructed (green fluorescent protein) GFP- and NIS-expressing baculovirus vectors (Bac-GFP and Bac-NIS), and measured the baculovirus transduction efficiency in HepG2 cells and other tumor cells (A549, SW1116 and 8505C), and it showed that the transduction efficiency and target gene expression level rose with increasing viral multiplicity of infection (MOI) in HepG2 cells, and HepG2 cells had a significantly higher transduction efficiency (60.8% at MOI = 200) than other tumor cells. Moreover, the baculovirus transduction was not cytotoxic to HepG2 cells at a higher MOI (MOI = 400). We also performed dynamic iodide uptake trials, and found that Bac-NIS-transduced HepG2 cells exhibited efficient iodide uptake which could be inhibited by sodium perchlorate (NaClO4). And we measured the correlation of fluorescent intensities and 125 I uptake amount in HepG2 cells after co-vector administration with Bac-NIS and Bac-GFP at different MOIs, and found a high correlation coefficient ( r2 = 0.8447), which provides a good basis for successfully evaluating the feasibility of baculovirus-mediated NIS reporter gene monitoring target gene expression in liver cancer therapy. Therefore, this study indicates that baculovirus vector is a potential vehicle for delivering therapeutic genes in studying liver cancer cells. And it is feasible to use a baculovirus vector to deliver NIS gene as a reporter gene to monitor the expression of target genes. It therefore provides an effective approach and a good basis for future baculovirus-mediated therapeutic gene delivering or therapeutic gene expression monitoring in liver cancer cells studies.

Evaluating baculovirus as a vector for human prostate cancer gene therapy

Gene therapy represents an attractive strategy for the non-invasive treatment of prostate cancer, where current clinical interventions show limited efficacy. Here, we evaluate the use of the insect virus, baculovirus (BV), as a novel vector for human prostate cancer gene therapy. Since prostate tumours represent a heterogeneous environment, a therapeutic approach that achieves long-term regression must be capable of targeting multiple transformed cell populations. Furthermore, discrimination in the targeting of malignant compared to non-malignant cells would have value in minimising side effects. We employed a number of prostate cancer models to analyse the potential for BV to achieve these goals. In vitro, both traditional prostate cell lines as well as primary epithelial or stromal cells derived from patient prostate biopsies, in two- or three-dimensional cultures, were used. We also evaluated BV in vivo in murine prostate cancer xenograft models. BV was capable of preferentially transducing invasive malignant prostate cancer cell lines compared to early stage cancers and non-malignant samples, a restriction that was not a function of nuclear import. Of more clinical relevance, primary patient-derived prostate cancer cells were also efficiently transduced by BV, with robust rates observed in epithelial cells of basal phenotype, which expressed BV-encoded transgenes faster than epithelial cells of a more differentiated, luminal phenotype. Maximum transduction capacity was observed in stromal cells. BV was able to penetrate through three-dimensional structures, including in vitro spheroids and in vivo orthotopic xenografts. BV vectors containing a nitroreductase transgene in a gene-directed enzyme pro-drug therapy approach were capable of efficiently killing malignant prostate targets following administration of the pro-drug, CB1954. Thus, BV is capable of transducing a large proportion of prostate cell types within a heterogeneous 3-D prostate tumour, can facilitate cell death using a pro-drug approach, and shows promise as a vector for the treatment of prostate cancer.

Hepatitis C virus infection upregulates CD55 expression on the hepatocyte surface and promotes association with virus particles

CD55 limits excessive complement activation on the host cell surface by accelerating the decay of C3 convertases. In this study, we observed that hepatitis C virus (HCV) infection of hepatocytes or HCV core protein expression in transfected hepatocytes upregulated CD55 expression at the mRNA and protein levels. Further analysis suggested that the HCV core protein or full-length (FL) genome enhanced CD55 promoter activity in a luciferase-based assay, which was further augmented in the presence of interleukin-6. Mutation of the CREB or SP-1 binding site on the CD55 promoter impaired HCV core protein-mediated upregulation of CD55. HCV-infected or core protein-transfected Huh7.5 cells displayed greater viability in the presence of CD81 and CD55 antibodies and complement. Biochemical analysis revealed that CD55 was associated with cell culture-grown HCV after purification by sucrose density gradient ultracentrifugation. Consistent with this, a polyclonal antibody to CD55 captured cell culture-grown HCV. Blocking antibodies against CD55 or virus envelope glycoproteins in the presence of normal human serum as a source of complement inhibited HCV infection. The inhibition was enhanced in the presence of both the antibodies and serum complement. Collectively, these results suggest that HCV induces and associates with a negative regulator of the complement pathway, a likely mechanism for immune evasion.

Strategies for local gene therapy of corneal allograft rejection

Penetrating keratoplasty is the most common type of tissue transplant in humans. Irreversible immune rejection leads to loss of vision and graft failure. This complex immune response further predisposes future corneal transplants to rejection and failure. A diverse armamentarium of surgical and pharmacologic tools is available to improve graft survival. In this review, we will discuss the various gene therapeutic strategies aimed at potentiating the anterior chamber-associated immune deviation to extend graft survival.

Baculovirus-mediated vascular endothelial growth factor-D(ΔNΔC) gene transfer induces angiogenesis in rabbit skeletal muscle

BACKGROUND

Occluded arteries and ischemic tissues cannot always be treated by angioplasty, stenting or by-pass-surgery. Under such circumstances, viral gene therapy may be useful in inducing increased blood supply to ischemic area. There is evidence of improved blood flow in ischemic skeletal muscle and myocardium in both animal and human studies using adenoviral vascular endothelial growth factor (VEGF) gene therapy. However, the expression is transient and repeated gene transfers with the same vector are inefficient due to immune responses.

METHODS

Different baculoviral vectors pseudotyped with or without vesicular stomatitis virus glycoprotein (VSV-G) and/or carrying woodchuck hepatitis virus post-transcriptional regulatory element (Wpre) were tested both in vitro and in vivo. VEGF-D(ΔNΔC) was used as therapeutic transgene and lacZ as a control. In vivo efficacy was evaluated as capillary enlargement and transgene expression in New Zealand White (NZW) rabbit skeletal muscle.

RESULTS

A statistically significant capillary enlargement was detected 6 days after gene transfer in transduced areas compared to the control gene transfers with baculovirus and adenovirus encoding β-galactosidase (lacZ). Substantially improved gene transfer efficiency was achieved with a modified baculovirus pseudotyped with VSV-G and carrying Wpre. Dose escalation experiments revealed that either too large volume or too many virus particles caused inflammation and necrosis in the target tissue, whereas 10(9) plaque forming units injected in multiple aliquots resulted in transgene expression with only mild immune reactions.

CONCLUSIONS

We show the first evidence of biologically significant baculoviral gene transfer in skeletal muscle of NZW rabbits using VEGF-D(ΔNΔC) as a therapeutic transgene.

Microfibers fabricated by non-covalent assembly of peptide and DNA for viral vector encapsulation and cancer therapy

Self-assembled amphiphilic peptide units and supercoiled, circular double-stranded plasmid DNA are used as building blocks to form peptide/DNA fibers for virus encapsulation. Since the fiber formation process takes place under ambient conditions and is aqueous-based without the use of denaturing organic solvents, the bioactivity of viruses is well preserved.

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.

Baculoviruses as gene therapy vectors for human prostate cancer

Prostate cancer is the most commonly diagnosed cancer in ageing men in the western world. While the primary cancers can be treated with androgen ablation, radiotherapy and surgery, recurrent castration resistant cancers have an extremely poor prognosis, hence promoting research that could lead to a better treatment. Targeted therapeutic gene therapy may provide an attractive option for these patients. By exploiting the natural ability of viruses to target and transfer their genes into cancer cells, either naturally or after genetic manipulation, new generations of biological control can be developed. In this review we present the advantages and practicalities of using baculovirus as a vector for prostate cancer gene therapy and provide evidence for the potential of the baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) as a safer alternative vehicle for targeting cancer cells. Strategies to target baculovirus binding specifically to prostate cell surfaces are also presented. The large insertion capacity of baculoviruses also permits restricted, prostate-specific gene expression of therapeutic genes by cloning extended human transcriptional control sequences into the baculovirus genome.

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 vectors for antiangiogenesis-based cancer gene therapy

Baculovirus is an insect virus that is non-pathogenic to humans and has emerged as a promising gene therapy vector. Since solid tumor growth/metastasis critically relies on angiogenesis and hEA, a fusion protein comprising human endostatin and angiostatin, exhibits potent antiangiogenic and antitumor efficacy in mouse models; this study aimed to evaluate the feasibility of baculovirus for hEA expression and antiangiogenesis-based cancer gene therapy. Toward this end, we constructed Bac-hEA that mediated transient hEA expression and Bac-ITR-hEA that exploited the adeno-associated virus inverted terminal repeats (ITRs) for prolonged hEA expression. Western blot and ELISA analyses showed that both Bac-hEA and Bac-ITR-hEA expressed hEA in transduced mammalian cells, yet Bac-ITR-hEA only marginally prolonged the hEA expression. In comparison with Bac-hEA, nonetheless, Bac-ITR-hEA significantly enhanced the hEA expression level that concurred with augmented antiangiogenic properties, as demonstrated by cell proliferation, migration and tubule network formation assays. Importantly, intratumoral injection of Bac-ITR-hEA into prostate cancer mouse models, when compared with Bac-hEA, exerted stronger antiangiogenic effects in vivo, more potently inhibited tumor growth and significantly prolonged mouse survival. This study collectively supported the notion that hEA is an effective antiangiogenic protein and proved the potential of baculovirus as a vector for antiangiogenesis-based cancer therapy, which may be combined with chemotherapy, radiotherapy or gene therapies using other vectors.

Baculovirus as a gene delivery vector: recent understandings of molecular alterations in transduced cells and latest applications

Baculovirus infects insects in nature and is non-pathogenic to humans, but can transduce a broad range of mammalian and avian cells. Thanks to the biosafety, large cloning capacity, low cytotoxicity and non-replication nature in the transduced cells as well as the ease of manipulation and production, baculovirus has gained explosive popularity as a gene delivery vector for a wide variety of applications. This article extensively reviews the recent understandings of the molecular mechanisms pertinent to baculovirus entry and cellular responses, and covers the latest advances in the vector improvements and applications, with special emphasis on antiviral therapy, cancer therapy, regenerative medicine and vaccine.

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.

Introduction to viral vectors

Viral vector is the most effective means of gene transfer to modify specific cell type or tissue and can be manipulated to express therapeutic genes. Several virus types are currently being investigated for use to deliver genes to cells to provide either transient or permanent transgene expression. These include adenoviruses (Ads), retroviruses (γ-retroviruses and lentiviruses), poxviruses, adeno-associated viruses, baculoviruses, and herpes simplex viruses. The choice of virus for routine clinical use will depend on the efficiency of transgene expression, ease of production, safety, toxicity, and stability. This chapter provides an introductory overview of the general characteristics of viral vectors commonly used in gene transfer and their advantages and disadvantages for gene therapy use.

Baculovirus vector-mediated transfer of NIS gene into colon tumor cells for radionuclide therapy

AIM: To investigate the feasibility of radionuclide therapy of colon tumor cells by baculovirus vector-mediated transfer of the sodium/iodide symporter (NIS) gene.

METHODS: A recombinant baculovirus plasmid carrying the NIS gene was constructed, and the viruses (Bac-NIS) were prepared using the Bac-to-Bac system. The infection efficiency in the colon cancer cell line SW1116 of a green fluorescent protein (GFP) expressing baculovirus (Bac-GFP) at different multiplicities of infection (MOI) with various concentrations of sodium butyrate was determined by flow cytometry. An in vitro cytotoxicity assay was also conducted after infection of SW1116 cells with Bac-NIS. Iodine uptake of Bac-NIS infected SW1116 cells and inhibition of this uptake by sodium perchlorate was examined, and the effect of Bac-NIS-mediated ¹³¹I in killing tumor cells was evaluated by cell colony formation tests.

RESULTS: Infection and transgene expression in SW1116 with Bac-GFP were significantly enhanced by sodium butyrate, as up to 72% of SW1116 cells were infected with the virus at MOI of 400 and sodium butyrate at 0.5 mmol/L. No obvious cytotoxicity was observed under these conditions. Infection of SW1116 with Bac-NIS allowed uptake of ¹³¹I in these tumor cells, which could be inhibited by sodium perchlorate. The viability of SW1116 cells infected with Bac-NIS was significantly lower than with Bac-GFP, suggesting that NIS gene-mediated ¹³¹I uptake could specifically kill tumor cells.

CONCLUSION: Baculovirus vector-mediated NIS gene therapy is a potential approach for treatment of colon cancer.

Indications for cell stress in response to adenoviral and baculoviral gene transfer observed by proteome profiling of human cancer cells

Gene transfer to cultured cells is an important tool for functional studies in many areas of biomedical research and vector systems derived from adenoviruses and baculoviruses are frequently used for this purpose. In order to characterize how viral gene transfer vectors affect the functional state of transduced cells, we applied 2-D PAGE allowing quantitative determination of protein amounts and synthesis rates of metabolically labeled cells and shotgun proteomics. Using HepG2 human hepatoma cells we show that both vector types can achieve efficient expression of green fluorescent protein, which accounted for about 0.1% of total cellular protein synthesis 72 h after transduction. No evidence in contrast was found for expression of proteins from the viral backbones. With respect to the host cell response, both vectors induced a general increase in protein synthesis of about 50%, which was independent of green fluorescent protein expression. 2-D PAGE autoradiographs identified a 3.6-fold increase of gamma-actin synthesis in adenovirus transduced cells. In addition shotgun proteomics of cytoplasmic and nuclear extract fractions identified a slight induction of several proteins related to inflammatory activation, cell survival and chromatin function by both virus types. These data demonstrate that commonly used gene transfer vectors induce a response reminiscent of stress activation in host cells, which needs to be taken into account when performing functional assays with transduced cells.

Recombinant baculovirus as a highly potent vector for gene therapy of human colorectal carcinoma: molecular cloning, expression, and in vitro characterization

Present therapeutic strategies for most cancers are restricted mainly to the primary tumors and are also not very effective in controlling metastatic states. Alternatively, gene therapy can be a potential option for treating such cancers. Currently mammalian viral-based cancer gene therapy is the most popular approach, but the efficacy has been shown to be quite low in clinical trials. In this study, for the first time, the insect cell-specific baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) has been evaluated as a vector for gene delivery to colorectal cancer cells. Experiments involving factorial design were employed to study the individual and combined effects of different parameters such as multiplicity of infection (MOI), viral incubation time and epigenetic factors on transduction efficiency. The results demonstrate that baculovirus gene delivery system holds immense potential for development of a new generation of highly effective virotherapy for colorectal, as well as other major carcinomas (breast, pancreas, and brain), and offers significant benefits to traditional animal virus-based vectors with respect to safety concerns.

Adenovirus capsid-display of the retro-oriented human complement inhibitor DAF reduces Ad vector-triggered immune responses in vitro and in vivo

Adenovirus (Ad) vectors are widely used in human clinical trials. However, at higher dosages, Ad vector-triggered innate toxicities remain a major obstacle to many applications. Ad interactions with the complement system significantly contribute to innate immune responses in several models of Ad-mediated gene transfer. We constructed a novel class of Ad vectors, genetically engineered to "capsid-display" native and retro-oriented versions of the human complement inhibitor decay-accelerating factor (DAF), as a fusion protein from the C-terminus of the Ad capsid protein IX. In contrast to conventional Ad vectors, DAF-displaying Ads dramatically minimized complement activation in vitro and complement-dependent immune responses in vivo. DAF-displaying Ads did not trigger thrombocytopenia, minimized endothelial cell activation, and had diminished inductions of proinflammatory cytokine and chemokine responses. The retro-oriented display of DAF facilitated the greatest improvements in vivo, with diminished activation of innate immune cells, such as dendritic and natural killer cells. In conclusion, Ad vectors can capsid-display proteins in a manner that not only retains the functionality of the displayed proteins but also potentially can be harnessed to improve the efficacy of this important gene transfer platform for numerous gene transfer applications.

Screening of complement inhibitors: shielded baculoviruses increase the safety and efficacy of gene delivery

One of the major obstacles in the use of baculovirus vectors for in vivo gene transfer is the virus inactivation by serum complement. In this study, we investigated the effect of decay-accelerating factor (DAF), factor H (FH)-like protein-1 (FHL-1), C4b-binding protein (C4BP), and membrane cofactor protein (MCP) on protection of baculovirus vectors from the complement-mediated inactivation. Complement regulatory proteins were displayed on baculovirus surface as fusions to membrane anchor of the vesicular stomatitis virus-G (VSV-G) protein. This strategy resulted in abundant expression of recombinant proteins on the viral envelope while viral titers comparable to control virus were reached. The surface-modified vectors exhibited complement resistance in vitro, DAF showing the highest level of protection. Intraportal delivery of DAF-displaying baculovirus resulted in increased survival and enhanced gene expression in immunocompetent mice. Mice receiving DAF-displaying baculovirus also exhibited lower level of liver inflammation as evidenced by aspartate aminotransferase (AST). In line with this, macrophages treated with DAF baculovirus produced lower levels of inflammatory cytokines IL-1beta, IL-6, and IL-12p40 compared to control virus. These results suggest that DAF-display can protect the vector against complement inactivation but also reduce complement-mediated inflammation injury. In conclusion, complement shielded baculovirus vectors represent attractive tools for effective in vivo gene delivery.

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.

The feasibility of using a baculovirus vector to deliver the sodium-iodide symporter gene as a reporter

PURPOSE

To evaluate the efficiency of baculovirus vectors in transducing FTC-133 cells and to examine the feasibility of using baculovirus vectors for the delivery of the sodium-iodide symporter (NIS) gene as a reporter through co-transduction to monitor the expression of the target gene.

METHOD

Two recombinant baculoviruses were constructed to express NIS and green fluorescent protein (GFP) respectively. FTC-133, 8050C, SW1116, A549 cells, were infected with Bac-GFP. The infection efficiency of Bac-GFP and the intensity of fluorescence, in either the presence or absence of sodium butyrate, were monitored by flow cytometry. The iodine uptake by FTC-133 cells infected with Bac-NIS was measured using a gamma counter. FTC-133 cells were infected with a mixture of equal amounts of Bac-NIS and Bac-GFP at different setting of multiplicity of infection (MOI). The changes of GFP fluorescence intensity and iodine uptake were monitored 24 h after infection in the coinfected cells.

RESULTS

We have successfully constructed recombinant baculoviruses carrying NIS and GFP under the control of the cytomegalovirus IE-1 promoter. We found that transduced efficiency of baculovirus in 8505C, SW1116, A549 cells are low in absence of sodium butyrate. Yet Bac-GFP infects FTC-133 cells at a high efficiency, 77.67%, 85.57% and 93.23% with MOI of 100, 200 and 400, respectively. The fluorescence intensity of the Bac-GFP infected tumor cells correlated positively with the MOI of the virus. Sodium butyrate induction increased both the infection efficiency and the fluorescence intensity, but increase of infection efficiency was insignificant in FTC-133 cells. Reporter gene (GFP) expression in FTC-133 is stable within 7 days after infection. The radioactivity incorporated by the tumor cells infected with Bac-NIS correlated positively with the MOI of Bac-NIS as well. In tumor cells co-infected with Bac-NIS and Bac-GFP, the amount of radioactivity incorporated significantly correlated with the GFP fluorescence intensity (r=0.922).

CONCLUSION

Baculovirus vectors are powerful vehicles for studying FTC-133 tumor cells in gene delivery. It is feasible to use a baculovirus vector to deliver NIS as a reporter gene to monitor the expression of target genes. This is therefore an effective approach for the detection of target gene expression in gene therapy.

Acquisition of complement resistance through incorporation of CD55/decay-accelerating factor into viral particles bearing baculovirus GP64

A major obstacle to gene transduction by viral vectors is inactivation by human complement in vivo. One way to overcome this is to incorporate complement regulatory proteins, such as CD55/decay accelerating factor (DAF), into viral particles. Lentivirus vectors pseudotyped with the baculovirus envelope protein GP64 have been shown to acquire more potent resistance to serum inactivation and longer transgene expression than those pseudotyped with the vesicular stomatitis virus (VSV) envelope protein G. However, the molecular mechanisms underlying resistance to serum inactivation in pseudotype particles bearing the GP64 have not been precisely elucidated. In this study, we generated pseudotype and recombinant VSVs bearing the GP64. Recombinant VSVs generated in human cell lines exhibited the incorporation of human DAF in viral particles and were resistant to serum inactivation, whereas those generated in insect cells exhibited no incorporation of human DAF and were sensitive to complement inactivation. The GP64 and human DAF were detected on the detergent-resistant membrane and were coprecipitated by immunoprecipitation analysis. A pseudotype VSV bearing GP64 produced in human DAF knockdown cells reduced resistance to serum inactivation. In contrast, recombinant baculoviruses generated in insect cells expressing human DAF or carrying the human DAF gene exhibited resistance to complement inactivation. These results suggest that the incorporation of human DAF into viral particles by interacting with baculovirus GP64 is involved in the acquisition of resistance to serum inactivation.

Preclinical evaluation of innate immunity to baculovirus gene therapy vectors in whole human blood

Interactions of gene therapy vectors with human blood components upon intravenous administration have a significant effect on vector efficacy and patient safety. Here we describe methods to evaluate these interactions and their effects in whole human blood, using baculovirus vectors as a model. Opsonisation of baculovirus particles by binding of IgM and C3b was demonstrated, which is likely to be the cause of the significant blood cell-associated virus that was detected. Preventing formation of the complement C5b-9 (membrane attack) complex maintained infectivity of baculovirus particles as shown by studying the effects of two specific complement inhibitors, Compstatin and a C5a receptor antagonist. Formation of macroscopic blood clots after 4h was prevented by both complement inhibitors. Pro- and anti-inflammatory cytokines Il-1beta, IL-6, IL-8 and TNF-alpha were produced at variable levels between volunteers and complement inhibitors showed patient-specific effects on cytokine levels. Whilst both complement inhibitors could play a role in protecting patients from aggressive inflammatory reactions, only Compstatin maintained virus infectivity. We conclude that this ex vivo model, used here for the first time with infectious agents, is a valuable tool in evaluating human innate immune responses to gene therapy vectors or to predict the response of individual patients as part of a clinical trial or treatment. The use of complement inhibitors for therapeutic viruses should be considered on a patient-specific basis.

Polyethylenimine coating to produce serum-resistant baculoviral vectors for in vivo gene delivery

Recombinant baculoviral vectors efficiently transduce many types of mammalian cells. However, their in vivo applications are hampered by the sensitivity of the virus to complement-mediated inactivation. Based on our observation that the surface charge of baculovirus is negative at neutral pH, we developed a procedure to coat baculoviral vectors with positively charged polyethylenimine 25 kDa, a commonly tested non-viral gene delivery vector, through electrostatic interaction. This coating was effective in protecting baculoviral vectors against human and rat serum-mediated inactivation in vitro, providing transduction efficiencies comparable with that generated by the control virus used under a serum-free condition. Enhanced in vivo gene expression in the liver and spleen was observed after tail vein injection of the coated viruses into mice. When injected directly into human tumor xenografts in nude mice, the coated viruses suppressed tumor development more effectively than uncoated viral vectors. These findings demonstrated the usefulness of using a simple coating method to circumvent a major obstacle to in vivo application of baculoviral vectors. The method may also serve as a flexible platform technology for improved use of the vectors, for example introducing a targeting ligand and minimizing immune responses.

Improved adenovirus type 5 vector-mediated transduction of resistant cells by piggybacking on coxsackie B-adenovirus receptor-pseudotyped baculovirus

Taking advantage of the wide tropism of baculoviruses (BVs), we constructed a recombinant BV (BV(CAR)) pseudotyped with human coxsackie B-adenovirus receptor (CAR), the high-affinity attachment receptor for adenovirus type 5 (Ad5), and used the strategy of piggybacking Ad5-green fluorescent protein (Ad5GFP) vector on BV(CAR) to transduce various cells refractory to Ad5 infection. We found that transduction of all cells tested, including human primary cells and cancer cell lines, was significantly improved using the BV(CAR)-Ad5GFP biviral complex compared to that obtained with Ad5GFP or BV(CAR)GFP alone. We determined the optimal conditions for the formation of the complex and found that a high level of BV(CAR)-Ad5GFP-mediated transduction occurred at relatively low adenovirus vector doses, compared with transduction by Ad5GFP alone. The increase in transduction was dependent on the direct coupling of BV(CAR) to Ad5GFP via CAR-fiber knob interaction, and the cell attachment of the BV(CAR)-Ad5GFP complex was mediated by the baculoviral envelope glycoprotein gp64. Analysis of the virus-cell binding reaction indicated that the presence of BV(CAR) in the complex provided kinetic benefits to Ad5GFP compared to the effects with Ad5GFP alone. The endocytic pathway of BV(CAR)-Ad5GFP did not require Ad5 penton base RGD-integrin interaction. Biodistribution of BV(CAR)-Ad5Luc complex in vivo was studied by intravenous administration to nude BALB/c mice and compared to Ad5Luc injected alone. No significant difference in viscerotropism was found between the two inocula, and the liver remained the preferred localization. In vitro, coagulation factor X drastically increased the Ad5GFP-mediated transduction of CAR-negative cells but had no effect on the efficiency of transduction by the BV(CAR)-Ad5GFP complex. Various situations in vitro or ex vivo in which our BV(CAR)-Ad5 duo could be advantageously used as gene transfer biviral vector are discussed.

Antigen delivery systems for veterinary vaccine development. Viral-vector based delivery systems

The recent advances in molecular genetics, pathogenesis and immunology have provided an optimal framework for developing novel approaches in the rational design of vaccines effective against viral epizootic diseases. This paper reviews most of the viral-vector based antigen delivery systems (ADSs) recently developed for vaccine testing in veterinary species, including attenuated virus and DNA and RNA viral vectors. Besides their usefulness in vaccinology, these ADSs constitute invaluable tools to researchers for understanding the nature of protective responses in different species, opening the possibility of modulating or potentiating relevant immune mechanisms involved in protection.

Biological gene delivery vehicles: beyond viral vectors

Gene therapy covers a broad spectrum of applications, from gene replacement and knockdown for genetic or acquired diseases such as cancer, to vaccination, each with different requirements for gene delivery. Viral vectors and synthetic liposomes have emerged as the vehicles of choice for many applications today, but both have limitations and risks, including complexity of production, limited packaging capacity, and unfavorable immunological features, which restrict gene therapy applications and hold back the potential for preventive gene therapy. While continuing to improve these vectors, it is important to investigate other options, particularly nonviral biological agents which include bacteria, bacteriophage, virus-like particles (VLPs), erythrocyte ghosts, and exosomes. Exploiting the natural properties of these biological entities for specific gene delivery applications will expand the repertoire of gene therapy vectors available for clinical use. Here, we review the prospects for nonviral biological delivery vehicles as gene therapy agents with focus on their unique evolved biological properties and respective limitations and potential applications. The potential of these nonviral biological entities to act as clinical gene therapy delivery vehicles has already been shown in clinical trials using bacteria-mediated gene transfer and with sufficient development, these entities will complement the established delivery techniques for gene therapy applications.

Interstitial tissue-specific gene expression in mouse testis by intra-tunica albuguineal injection of recombinant baculovirus

The purpose of this study is to establish a gene delivery system for interstitial tissue-specific protein expression in mice testes using modified recombinant baculovirus. Green fluorescent protein (GFP)-expressing recombinant baculovirus (GFP-baculovirus), in which the insect cell-specific polyhedron promoter was replaced by the cytomegalovirus (CMV)-IE promoter, was used to transfect testicular cells in vitro, and for intra-tunica albuguineal injection of the interstitial tissue of the testis. GFP expression was monitored in frozen testes sections by fluorescence microscopy. Expression of GFP in testicular tissues was also assessed by reverse transcription polymerase chain reaction (RT-PCR), and protein expression was assessed by Western blot. Testicular cells in vitro were infected efficiently by modified recombinant GFP-baculovirus. Intra-tunica albuguineal injection of GFP-baculovirus into the mouse testis resulted in a high level of GFP expression in the interstitial tissues. RT-PCR analysis clearly showed GFP gene expression in the testis, particularly interstitial tissues. Intra-tunica albuguineal injection of a modified baculovirus that encoded recombinant rat insulin-like growth factor binding protein (IGFBP)-5 resulted in an increase in IGFBP-5 in testis and semen. In conclusion, we have developed an efficient delivery system for gene expression in vivo in testicular cells, particularly cells of the interstitial tissue using intra-tunica albuguineal injection of a modified recombinant baculovirus. This method will be particularly relevant for application that requires gene delivery and protein expression in the testicular cells of the outer seminiferous tubule of the testis.

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.

Targeting and purification of metabolically biotinylated baculovirus

Targeting viral entry is one of the major goals in the development of vectors for gene therapy. Ideally, the coupling of each new targeting motif would not require changes in vector structure. To achieve this, we developed novel metabolically biotinylated baculoviral vectors by displaying a small biotin acceptor peptide (BAP) fused either to different sites in the baculovirus glycoprotein gp64 or to the transmembrane anchor of vesicular stomatitis virus G protein. Baculoviral particles were biotinylated during vector production by coexpression of Escherichia coli biotin ligase (BirA). The insertion of BAP at amino acid position 283 of gp64 resulted in the most efficient biotin display. Unlike vectors with lower biotin display, these vectors also showed improved transduction when retargeted to transferrin, epidermal growth factor, and CD46 receptors overexpressed on rat glioma and human ovarian carcinoma cells. Biotinylated baculoviral vectors could also be concentrated by one-step magnetic particle-based capture to reach titers up to 10(10) plaque-forming units/ml. These results demonstrate the utility of metabolically biotinylated baculovirus for vector targeting and viral purification applications.

Baculovirus-mediated interferon alleviates dimethylnitrosamine-induced liver cirrhosis symptoms in a murine model

The wild-type baculovirus Autographa californica multiple nuclear polyhedrosis virus (AcMNPV) infects a range of mammalian cell types in vitro but does not replicate in these cells. The current study investigated the in vivo effect of AcMNPV in the mouse model of liver cirrhosis induced by the mutagen dimethylnitrosamine. Intraperitoneal injection of AcMNPV induced an immune response. The baculovirus was taken up by the liver and spleen where it suppressed liver injury and fibrosis through the induction of interferons. This study presents the first evidence of the feasibility of using baculovirus to treat liver cirrhosis.

Characterization of the gene delivery properties of baculoviral-based virosomal vectors

The current study reports the production of baculoviral-virosomal vectors consisting of lipoplexes and of the viral glycoprotein (GP64) of baculovirus Autographa californica multiple nucleopolyhdrovirus (AcMNPV). This study demonstrates that such complexes have an increased transfection capability in a number of cells, including undifferentiated H9 human embryonic stem H9hES cells compared to lipoplexes alone. The GP64-mediated enhancement of gene transfer of lipoplexes is inhibited by the addition of anti-GP64 neutralizing antibody and by a modified GP64 protein, but is however less potent than vesicular stomatitis virus glycoprotein (VSV-G)-mediated enhancement of gene transfer of lipoplexes. This difference may be explained in part by the dissimilarity in the fusogenic properties of their respective viral glycoprotein.