Sustained baculovirus-mediated expression in myogenic cells

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.

Genetic manipulation of myoblasts and a novel primary myosatellite cell culture system: comparing and optimizing approaches

The genetic manipulation of skeletal muscle cells in vitro is notoriously difficult, especially when using undifferentiated muscle cell lines (myoblasts) or primary muscle stem cells (myosatellites). We therefore optimized methods of gene transfer by overexpressing green fluorescent protein (GFP) in mouse C2C12 cells and in a novel system, primary rainbow trout myosatellite cells. A common lipid-based transfection reagent was used (Lipofectamine 2000) along with three different viral vectors: adeno-associated virus serotype 2 (AAV2), baculovirus (BAC) and lentivirus. Maximal transfection efficiencies of 49% were obtained in C2C12 cells after optimizing cell density and reagent : DNA ratio, although the GFP signal rapidly dissipated with proliferation and was not maintained with differentiation. The transduction efficiency of AAV2 was optimized to 65% by extending incubation time and decreasing cell density, although only 30% of cells retained expression after passing. A viral comparison revealed that lentivirus was most efficient at transducing C2C12 myoblasts as 97% of cells were transduced with only 10(6) viral genomes (vg) compared to 54% with 10(8) vg AAV2 and 23% with 10(9) vg BAC. Lentivirus also transduced 90% of primary trout myosatellites compared to 1-10% with AAV2 and BAC. The phosphoglycerate kinase 1 (pgk) promoter was 10-fold more active than the cytomegalovirus immediate-early promoter in C2C12 cells and both were effective in trout myosatellites. Maximal transduction of C2C12 myotubes was achieved by differentiating myoblasts previously transduced with lentivirus and the pgk promoter. Thus, our optimized protocol proved highly effective in diverse muscle cell systems and could therefore help overcome a common technological barrier.

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.

Efficient gene delivery into fish cells by an improved recombinant baculovirus

Studies on transduction of mammalian cells have shown that baculovirus can be used as an effective vector for gene delivery. However, previous studies have found the gene delivery efficiency to be very low in differentiated fish cells. In this study, an improved recombinant baculovirus, containing cytomegalovirus immediate-early (CMV-IE) promoter and an enhanced green fluorescent protein (EGFP) gene as the reporter gene, was constructed. The transduction efficiency of recombinant baculovirus in several fish cell lines was measured by flow cytometry (FCM) and the persistence of EGFP was monitored by fluorescence microscopy. The results demonstrated that baculovirus can mediate the high efficiency of gene delivery into differentiated fish cells. Furthermore, it was found that growth medium is superior to PBS as the surrounding solution to enhance the transduction efficiency in some fish cells. In addition, transgene expression can persist for a lengthy period in fish cells, and attained highest level several days later after transduction. This study suggest that the improved recombinant baculovirus can be an excellent gene delivery vector for fish cells and also providing new insights into the transduction of vertebrate cells with baculovirus.

Baculovirus as an avian influenza vaccine vector: differential immune responses elicited by different vector forms

Baculovirus is an enveloped virus that infects insects in nature and has emerged as a novel vaccine vector. We previously constructed a recombinant baculovirus displaying the hemagglutinin protein (HA) of avian influenza virus (AIV) on the viral envelope (Bac-HA64), and demonstrated the induction of humoral responses in immunized mice. To improve the vector design and explore how the vector forms influence the vaccine efficacy, we constructed two more baculoviruses Bac-CHA and Bac-CHA/HA64. Bac-CHA expressed HA after transducing the host cells while Bac-CHA/HA64 not only expressed HA but also displayed HA on the envelope. After administration into BALB/c mice, all three vectors elicited HA-specific humoral (IgG1, IgG2a and hemagglutination inhibition titers), mucosal (IgA titers) and cellular (interferon (IFN)-γ and IL-4 producing T cells and IFN-γ(+)/CD8(+) T cells) immune responses. Intriguingly, the magnitudes and types of responses hinged on the vaccine form and administration route. Via intranasal (i.n.) and subcutaneous (s.c.) inoculation, the HA-displaying vectors Bac-HA64 and Bac-CHA/HA64 triggered stronger humoral and mucosal responses than Bac-CHA, but upon intramuscular (i.m.) injection the HA-expressing vectors (Bac-CHA and Bac-CHA/2HA64) elicited more robust humoral and cellular responses than Bac-HA64. Via either administration route, the dual form vaccine Bac-CHA/HA64 gave rise to superior or at least comparable HA-specific immune responses than the other two vaccine forms, implicating the potential of Bac-CHA/HA64 as a vaccine candidate against AIV infection.