Transduction of vertebrate cells with Spodoptera exigua multiple nucleopolyhedrovirus F protein-pseudotyped gp64-null Autographa californica multiple nucleopolyhedrovirus

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 the Nucleopolyhedrovirus of Anticarsia gemmatalis as a Vector for Gene Therapy in Mammals

BACKGROUND

Baculoviruses are insect pathogens with important biotechnological applications that transcend their use as biological controllers of agricultural pests. One species, Autographa californica multiple nucleopolhyedrovirus (AcMNPV), has been extensively exploited as a molecular platform to produce recombinant proteins and as a delivery vector for genes in mammals because it can transduce a wide range of mammalian cells and tissues without replicating or producing progeny.

METHOD

To investigate if the budded virions of Anticarsia gemmatalis multiple nucleopolhyedrovirus (AgMNPV) species has the same ability, the viral genome was modified by homologous recombination into susceptible insect cells to integrate reporter genes and then it was evaluated on mammalian cell lines in a comparative form with respect to equivalent viruses derived from AcMNPV. Besides, the replicative capacity of AgMNPV´s virions in mammals was determined.

RESULTS

The experiments carried out showed that the recombinant variant of AgMNPV transduces and support the expression of delivered genes but not replicates in mammalian cells.

CONCLUSION

Consequently, this insect pathogen is proposed as an alternative to non-infectious viruses in humans to explore new approaches in gene therapy and other applications based on the use of mammalian cells.

Baculovirus as a Tool for Gene Delivery and Gene Therapy

Based on its ability to express high levels of protein, baculovirus has been widely used for recombinant protein production in insect cells for more than thirty years with continued technical improvements. In addition, baculovirus has been successfully applied for foreign gene delivery into mammalian cells without any viral replication. However, several CpG motifs are present throughout baculoviral DNA and induce an antiviral response in mammalian cells, resulting in the production of pro-inflammatory cytokines and type I interferon through a Toll-like receptor (TLR)-dependent or -independent signaling pathway, and ultimately limiting the efficiency of transgene expression. On the other hand, by taking advantage of this strong adjuvant activity, recombinant baculoviruses encoding neutralization epitopes can elicit protective immunity in mice. Moreover, immunodeficient cells, such as hepatitis C virus (HCV)- or human immunodeficiency virus (HIV)-infected cells, are more susceptible to baculovirus infection than normal cells and are selectively eliminated by the apoptosis-inducible recombinant baculovirus. Here, we summarize the application of baculovirus as a gene expression vector and the mechanism of the host innate immune response induced by baculovirus in mammalian cells. We also discuss the future prospects of baculovirus vectors.

Genome Characteristics of the Cyclophragma Undans Nucleopolyhedrovirus: A Distinct Species in Group I of Alphabaculovirus

The Cyclophragma undans nucleopolyhedrovirus (CyunNPV), a potential pest control agent, was isolated from Cyclophragma undans (Lepidoptera: Lasiocampidae), an important forest pest. In the present study, we performed detailed genome analysis of CyunNPV and compared its genome to those of other Group I alphabaculoviruses. Sequencing of the CyunNPV genome using the Roche 454 sequencing system generated 142,900 bp with a G + C content of 45%. Genome analysis predicted a total of 147 hypothetical open reading frames comprising 38 baculoviral core genes, 24 lepidopteran baculovirus conserved genes, nine Group I Alphabaculovirus conserved genes, 71 common genes, and five genes that are unique to CyunNPV. In addition, the genome contains 13 homologous repeated sequences (hrs). Phylogenetic analysis groups CyunNPV under a distinct branch within clade "a" of Group I in the genus Alphabaculovirus. Unlike other members of Group I, CyunNPV harbors only nine of the 11 genes previously determined to be specific to Group I viruses. Furthermore, the CyunNPV lacks the tyrosine phosphatase gene and the ac30 gene. The CyunNPV F-like protein contains two insertions of continuous polar amino acids, one at the conventional fusion peptide and a second insertion at the pre-transmembrane domain. The insertions are likely to affect the fusion function and suggest an evolutionary process that led to inactivation of the F-like protein. The above findings imply that CyunNPV is a distinct species under Group I Alphabaculovirus.

A betabaculovirus encoding a gp64 homolog

Background

A betabaculovirus (DisaGV) was isolated from Diatraea saccharalis (Lepidoptera: Crambidae), one of the most important insect pests of the sugarcane and other monocot cultures in Brazil.

Results

The complete genome sequence of DisaGV was determined using the 454-pyrosequencing method. The genome was 98,392 bp long, which makes it the smallest lepidopteran-infecting baculovirus sequenced to date. It had a G + C content of 29.7 % encoding 125 putative open reading frames (ORF). All the 37 baculovirus core genes and a set of 19 betabaculovirus-specific genes were found. A group of 13 putative genes was not found in any other baculovirus genome sequenced so far. A phylogenetic analysis indicated that DisaGV is a member of Betabaculovirus genus and that it is a sister group to a cluster formed by ChocGV, ErelGV, PiraGV isolates, ClanGV, CaLGV, CpGV, CrleGV, AdorGV, PhopGV and EpapGV. Surprisingly, we found in the DisaGV genome a G protein-coupled receptor related to lepidopteran and other insect virus genes and a gp64 homolog, which is likely a product of horizontal gene transfer from Group 1 alphabaculoviruses.

Conclusion

DisaGV represents a distinct lineage of the genus Betabaculovirus. It is closely related to the CpGV-related group and presents the smallest genome in size so far. Remarkably, we found a homolog of gp64, which was reported solely in group 1 alphabaculovirus genomes so far.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2408-9) contains supplementary material, which is available to authorized users.

A Betabaculovirus-Encoded gp64 Homolog Codes for a Functional Envelope Fusion Protein

The GP64 envelope fusion protein is a hallmark of group I alphabaculoviruses. However, the Diatraea saccharalis granulovirus genome sequence revealed the first betabaculovirus species harboring a gp64 homolog (disa118). In this work, we have shown that this homolog encodes a functional envelope fusion protein and could enable the infection and fusogenic abilities of a gp64-null prototype baculovirus. Therefore, GP64 may complement or may be in the process of replacing F protein activity in this virus lineage.

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.

Baculovirus as a vaccine vector

Baculovirus is extensively utilized as an excellent tool for production of recombinant protein in insect cells. Baculovirus infects insects in nature and is non-pathogenic to humans. In addition to insect cells, baculovirus is capable of transducing a broad range of animal cells. Due to its 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 been utilized as RNA interference mediators, gene delivery vectors, and vaccine vectors for a wide variety of applications. This article focuses on the utilization of baculoviruses as vaccine vectors to prepare antigen or subunit vaccines.

Seamless replacement of Autographa californica multiple nucleopolyhedrovirus gp64 with each of five novel type II alphabaculovirus fusion sequences generates pseudotyped virus that fails to transduce mammalian cells

Autographa californica multiple nucleopolyhedrovirus (AcMNPV), a member of the type I alphabaculoviruses, is able to transduce and deliver a functional gene to a range of non-host cells, including many mammalian lines and primary cells, a property mediated by the envelope fusion protein GP64. AcMNPV is non-cytopathic and inherently replication deficient in non-host cells. As such, AcMNPV represents a possible new class of gene therapy vector with potential future clinical utility. Whilst not a problem for in vitro gene delivery, the broad tropism displayed for non-host cells is less desirable in a gene therapy vector. The fusion protein F of type II alphabaculoviruses can substitute functionally for GP64, and such pseudotyped viruses display a severely impaired capacity for non-host-cell transduction. Thus, surface decoration of such an F-pseudotyped AcMNPV with cell-binding ligands may restore transduction competence and generate vectors with desirable cell-targeting characteristics. By seamlessly swapping the native gp64 coding sequence with each of five sequences encoding different F proteins, a set of F-pseudotyped AcMNPV was generated. This report details their relative abilities both to functionally replace GP64 in viral growth and to transduce human Saos-2 and HeLa cells. All five supported viable infections in insect cell cultures and one, the Mamestra configurata NPV (MacoNPV) F pseudotype, could be amplified to titres close to those of native AcMNPV. In contrast, none was able to transduce the Saos-2 and HeLa cell lines. The robust support provided by MacoNPV F in virus production makes the corresponding pseudotype a viable scaffold to display surface ligands to direct selective mammalian cell targeting.

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.

Counter-selection recombineering of the baculovirus genome: a strategy for seamless modification of repeat-containing BACs

Recombineering is employed to modify large DNA clones such as fosmids, BACs and PACs. Subtle and seamless modifications can be achieved using counter-selection strategies in which a donor cassette carrying both positive and negative markers inserted in the target clone is replaced by the desired sequence change. We are applying counter-selection recombineering to modify bacmid bMON14272, a recombinant baculoviral genome, as we wish to engineer the virus into a therapeutically useful gene delivery vector with cell targeting characteristics. Initial attempts to replace gp64 with Fusion (F) genes from other baculoviruses resulted in many rearranged clones in which the counter-selection cassette had been deleted. Bacmid bMON14272 contains nine highly homologous regions (hrs) and deletions were mapped to recombination between hr pairs. Recombineering modifications were attempted to decrease intramolecular recombination and/or increase recombineering efficiency. Of these only the use of longer homology arms on the donor molecule proved effective permitting seamless modification. bMON14272, because of the presence of the hr sequences, can be considered equivalent to a highly repetitive BAC and, as such, the optimized method detailed here should prove useful to others applying counter-selection recombineering to modify BACs or PACs containing similar regions of significant repeating homologies.