Recombinant baculoviruses as mammalian cell gene-delivery vectors

BacMam Platform for Vaccine Antigen Delivery

Recombinant baculo viruses based on Autographa californica multiple nuclear polyhedrosis virus carrying vertebrate cell active expression cassettes, so-called BacMam viruses, are increasingly used as gene delivery vectors for vaccination of animals against pathogens. Different approaches for generation of BacMams exist and a variety of transfer vectors to improve target protein expression in vivo have been constructed. Here we describe a use of transfer vector which contains an insect cell-restricted expression cassette for the green fluorescent protein and thus enables easy monitoring of BacMam virus rescue, fast plaque purification of recombinants and their convenient titer determination and which has been proven to be efficacious for gene delivery in vaccination/challenge experiments.

Gene Expression in Mammalian Cells Using BacMam, a Modified Baculovirus System

BacMams are modified baculoviruses that contain mammalian expression cassettes for gene delivery and expression in mammalian cells. BacMams have become an integral part of the recombinant mammalian gene expression toolbox in research labs worldwide. Construction of transfer vectors is straightforward using basic molecular biology protocols. Virus generation is based on common methods used with the baculovirus insect cell expression system. BacMam transduction of mammalian cells requires minimal modifications to familiar cell culture methods. This chapter highlights the BacMam transfer vector pHTBV.

cAMP assay for GPCR ligand characterization: application of BacMam expression system

Cyclic adenosine monophosphate (cAMP) is a second messenger of many G-protein-coupled receptors. The change in cellular cAMP level has widely been used to estimate the biological activity of various GPCR-specific agents. Förster resonance energy transfer (FRET) biosensors have been around for almost 10 years and became increasingly popular for cAMP detection. Ratiometric sensitized emission assay of a FRET biosensor can easily be implemented on fluorescence plate reader platforms. For such assays a considerable amount of cells expressing the desired biosensor is needed. A method to achieve sufficient and reproducible level of cAMP biosensor protein expression with the means of BacMam transduction system is the subject of this chapter.

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.

Effect of the peak cell density of recombinant AcMNPV-infected Hi5 cells on baculovirus yields

The phenomenon of the cell density effect is not readily explained by an obvious nutrient limitation, and a recent study has suggested that for recombinant Autographa californica multiple nucleopolyhedrovirus (rAcMNPV)-infected Sf9 cells, a drop in messenger RNA (mRNA) levels may be sufficient to explain the cell density effect for this system. The current study aims to investigate the response in cell-specific yields (viral DNA (vDNA), LacZ mRNA and β-galactosidase (β-Gal) protein) with increasing infection cell density (ICD) for rAcMNPV-infected Hi5 cells, where the rAcMNPV expresses the β-Gal gene under control of the polyhedral promoter. Hi5 cells in suspension culture of Express Five® medium were synchronously infected with a rAcMNPV at multiple ICDs between 0.5 and 6 × 10(6) cells/mL and a multiplicity of infection of 10 plaque-forming units (PFU)/cell either in the original or fresh medium conditions. There were negative correlations between the three key virus infection indicators (vDNA, mRNA and β-Gal) and the peak cell density (PCD). However, unlike infected Sf9 cells, the yield decline started at the lowest PCD investigated (0.6 × 10(6) cells/mL). Generally, the yield decline with increasing PCD was most pronounced for β-Gal followed by mRNA and was more moderate for vDNA. The decline was significantly reduced but not totally arrested when fresh medium replacement was used. The results suggest that the reduction in recombinant protein-specific yields at high PCDs is associated with limitations during the up-stream processes of replication and transcription rather than entirely caused by limitations during translation. In addition, low production rates at late infection stages of moderate to high ICDs are a probable cause of the cell density effect.

Immunostaining and time-lapse analysis of vinblastine-induced paracrystal formation in human A549 cells

Vinblastine is a vinca alkaloid that binds to tubulin and inhibits microtubule formation in cells. Vinblastine treatment results in the formation of paracrystalline aggregates in the cells, which are formed from tightly packed tubulin molecules. Mitotic spindle assemblies in treated cells are disrupted and cell cycle progression is arrested at the mitosis phase. Vinblastine is therefore widely used for cancer treatment. However, the mechanism underlying paracrystal formation has not been fully elucidated. The present study attempted to observe paracrystal formation in human A549 cells. Initally, paracrystal formation was detected using the anti-tubulin antibody. Secondly, the exogenousuly expressed RFP-conjugated tubulin also formed paracrystals. Additionally, immunostaining with the anti-RBM8A antibody overlapped with paracrystal images obtained from RFP conjugated tubulin. This suggested that the localization of the RBM8A proteins was adjacent to the tubulin molecules prior to vinblastine treatment. Furthermore, a time-lapse analysis was developed for paracrystal formation in viable human A549 cells. This was achieved using exogenous expression of fluorescent proteins conjugated with tubulin and time-lapse microscopy. It may be concluded that the indicated method was successful for the real-time analysis of paracrystal formation in human cells.

High-level protein expression following single and dual gene cloning of infectious bronchitis virus N and S genes using baculovirus systems

Baculovirus is an efficient system for the gene expression that can be used for gene transfer to both insect and different vertebrate hosts. The nucleocapsid gene (N) of the infectious bronchitis virus was cloned in a baculovirus expression system for insect cell expression. Dual expression vectors containing IBV N and spike (S) proteins of the avian infectious bronchitis virus were engineered under the control of human and murine cytomegalovirus immediate-early enhancer/promoter elements in combination with the baculoviral polyhedrin and p10 promoters for simultaneous expression in both vertebrate and insect cells. Transduction of the N gene in the insect Sf9 cells revealed a high level of protein expression. The expressed protein, used in ELISA, effectively detected chicken anti-IBV antibodies with high specificity. Transduction of mammalian and avian cells with BacMam viruses revealed that dual expression cassettes yielded high levels of protein from both transcription units.

Virus-vectored influenza virus vaccines

Despite the availability of an inactivated vaccine that has been licensed for >50 years, the influenza virus continues to cause morbidity and mortality worldwide. Constant evolution of circulating influenza virus strains and the emergence of new strains diminishes the effectiveness of annual vaccines that rely on a match with circulating influenza strains. Thus, there is a continued need for new, efficacious vaccines conferring cross-clade protection to avoid the need for biannual reformulation of seasonal influenza vaccines. Recombinant virus-vectored vaccines are an appealing alternative to classical inactivated vaccines because virus vectors enable native expression of influenza antigens, even from virulent influenza viruses, while expressed in the context of the vector that can improve immunogenicity. In addition, a vectored vaccine often enables delivery of the vaccine to sites of inductive immunity such as the respiratory tract enabling protection from influenza virus infection. Moreover, the ability to readily manipulate virus vectors to produce novel influenza vaccines may provide the quickest path toward a universal vaccine protecting against all influenza viruses. This review will discuss experimental virus-vectored vaccines for use in humans, comparing them to licensed vaccines and the hurdles faced for licensure of these next-generation influenza virus vaccines.

Targeted transgene insertion into the AAVS1 locus driven by baculoviral vector-mediated zinc finger nuclease expression in human-induced pluripotent stem cells

BACKGROUND

The AAVS1 locus is viewed as a 'safe harbor' for transgene insertion into human genome. In the present study, we report a new method for AAVS1 targeting in human-induced pluripotent stem cells (hiPSCs).

METHODS

We have developed two baculoviral transduction systems: one to deliver zinc finger nuclease (ZFN) and a DNA donor template for site-specific gene insertion and another to mediate Cre recombinase-mediated cassette exchange system to replace the inserted transgene with a new transgene.

RESULTS

Our ZFN system provided the targeted integration efficiency of a Neo-EGFP cassette of 93.8% in G418-selected, stable hiPSC colonies. Southern blotting analysis of 20 AASV1 targeted colonies revealed no random integration events. Among 24 colonies examined for mono- or biallelic AASV1 targeting, 25% of them were biallelically modified. The selected hiPSCs displayed persistent enhanced green fluorescent protein expression and continued the expression of stem cell pluripotency markers. The hiPSCs maintained the ability to differentiate into three germ lineages in derived embryoid bodies and transgene expression was retained in the differentiated cells. After pre-including the loxP-docking sites into the Neo-EGFP cassette, we demonstrated that a baculovirus-Cre/loxP system could be used to facilitate the replacement of the Neo-EGFP cassette with another transgene cassette at the AAVS1 locus.

CONCLUSIONS

Given high targeting efficiency, stability in expression of inserted transgene and flexibility in transgene exchange, the approach reported in the present study holds potential for generating genetically-modified human pluripotent stem cells suitable for developmental biology research, drug development, regenerative medicine and gene therapy.

Immunogenicity of a trivalent human papillomavirus L1 DNA-encapsidated, non-replicable baculovirus nanovaccine

Previously, we developed a non-replicating recombinant baculovirus coated with human endogenous retrovirus envelope protein (AcHERV) for enhanced cellular delivery of human papillomavirus (HPV) 16L1 DNA. Here, we report the immunogenicity of an AcHERV-based multivalent HPV nanovaccine in which the L1 segments of HPV 16, 18, and 58 genes were inserted into a single baculovirus genome of AcHERV. To test whether gene expression levels were affected by the order of HPV L1 gene insertion, we compared the efficacy of bivalent AcHERV vaccines with the HPV 16L1 gene inserted ahead of the 18L1 gene (AcHERV-HP16/18L1) with that of AcHERV with the HPV 18L1 gene inserted ahead of the 16L1 gene (AcHERV-HP18/16L1). Regardless of the order, the bivalent AcHERV DNA vaccines retained the immunogenicity of monovalent AcHERV-HP16L1 and AcHERV-HP18L1 DNA vaccines. Moreover, the immunogenicity of bivalent AcHERV-HP16/18L1 was not significantly different from that of AcHERV-HP18/16L1. In challenge tests, both bivalent vaccines provided complete protection against HPV 16 and 18 pseudotype viruses. Extending these results, we found that a trivalent AcHERV nanovaccine encoding HPV 16L1, 18L1, and 58L1 genes (AcHERV-HP16/18/58L1) provided high levels of humoral and cellular immunogenicity against all three subtypes. Moreover, mice immunized with the trivalent AcHERV-based nanovaccine were protected from challenge with HPV 16, 18, and 58 pseudotype viruses. These results suggest that trivalent AcHERV-HPV16/18/58L1 could serve as a potential prophylactic baculoviral nanovaccine against concurrent infection with HPV 16, 18, and 58.

Visualization of intracellular pathways of engineered baculovirus in mammalian cells

Baculoviruses are a promising gene delivery vector. They have the ability to express large transgenes in mammalian cells without displaying pathogenicity in humans; however, little is known about their transduction mechanisms in target cells. In this study, we use colocalization and live-cell imaging studies to elucidate the internalization and intracellular trafficking pathways of baculoviruses through direct visualization of VP39-GFP-labeled viral particles and various endocytic structures within target cells. Drug inhibition and confocal microscopy results suggested that baculoviruses enter the cells via clathrin-mediated endocytosis in a dynamin-dependent manner. Viral particles were shown to traffic through early endosomes, triggering a low-pH-dependent endosomal fusion process of viruses. Suppressed autophagy activity enhanced viral transduction and overexpression of autophagosomes reduced viral transduction, suggesting that autophagy is involved in degradation process of viral particles. Actin filaments were involved in the viral transduction, while microtubules negatively regulated viral transduction by facilitating the fusion of autophagosomes with lysosomes to form autolysosomes, where degradation of viral particles occurs. These results shed some light on the essential cellular factors limiting viral transduction, which can be used to improve the use of baculoviral vectors in cell and gene therapy.

Optimization of eGFP expression using a modified baculovirus expression system

The baculovirus gene expression system is an efficient and safe protein expression system, since baculoviruses cannot replicate in mammalian cells. In order to improve the transduction efficiency and increase the reporter gene expression levels delivered by baculoviruses, we tested in the baculovirus expression cassette the Woodchuck hepatitis virus response element (WPRE), and AAV-derived inverted terminal repeats (ITRs) and the truncated vesicular stomatitis virus G protein (VSV-GED). The results showed that WPRE and VSV-GED have synergistic effects and could enhance the expression efficiency of enhanced green fluorescence protein (eGFP), and that ITRs effectively extended the duration of eGFP expression. We also demonstrated that the efficiency of eGFP expression varied under the control of the CMV, CBA, EF1-α or WSSV ie1 promoters in different cell lines.

A novel method using Autographa californica multiple nucleopolyhedrovirus for increasing the sensitivity of insecticide through calcium influx in insect cell line

Due to an intensive use of chemical insecticides, resistance mechanisms to insecticides together with adverse effects on non-target organisms have been largely reported. Improvement in pest control strategy represents an urgent need to optimize efficiency in the control of pest insects. In this context, a novel method based on the use of insect specific virus applied in combination with chemical insecticide, which could lead to sensitization of the insect target to insecticides is described. Insect virus, the baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV), applied onto Sf9 cells induces an increase of intracellular calcium concentration via extracellular calcium influx. Co-application of AcMNPV with chlorpyrifos-ethyl onto Sf9 cells expressing the key enzyme acetylcholinesterase (AChE), known to be targeted by organophosphate insecticides, increases 1.5-fold the sensitivity of AChE to the insecticide. This effect is correlated with intracellular calcium concentration rise since AcMNPV-induced potentiating insecticide effect is counteracted by pretreatment with the calcium channel blocker, cadmium chloride. Increasing insecticide target sensitivity through intracellular calcium modulation by using insect virus co-applied with a chemical insecticide is a very promising strategy allowing optimization of insecticide treatment while reducing the concentration of insecticides used.

Intradermal immunization with combined baculovirus and tumor cell lysate induces effective antitumor immunity in mice

Although tumor lysate contains all the potential helper and killer epitopes capable of stimulating T cells, it is difficult to use as a cancer vaccine because it suppresses dendritic cell (DC) function. We report that wild-type baculovirus possesses an adjuvant effect to improve the immunogenicity of tumor lysate. When mice were administered CT26 tumor cell lysate combined with baculovirus intradermally, antitumor immunity was induced and rejection of CT26 tumor growth was observed in 40% of the immunized mice. In contrast, such antitumor immunity was not elicited in mice inoculated with tumor cell lysate or baculovirus alone. In tumor-bearing mice, which had previously received the combined baculovirus and tumor lysate vaccine, the established tumors were completely eradicated by administering a booster dose of the combined vaccine. This antitumor effect was attributed to tumor-specific T cell immunity mediated primarily by CD8⁺ T cells. Baculovirus also strongly activated DCs loaded with tumor lysate. Increased interleukin (IL)-6 and IL-12p70 production were also observed in DCs co-cultured with tumor cell lysate and baculovirus. Our study demonstrates that combined baculovirus and tumor lysate vaccine can effectively stimulate DCs to induce acquired antitumor immunity.

Mos1 transposon-based transformation of fish cell lines using baculoviral vectors

Drosophila Mos1 belongs to the mariner family of transposons, which are one of the most ubiquitous transposons among eukaryotes. We first determined nuclear transportation of the Drosophila Mos1-EGFP fusion protein in fish cell lines because it is required for a function of transposons. We next constructed recombinant baculoviral vectors harboring the Drosophila Mos1 transposon or marker genes located between Mos1 inverted repeats. The infectivity of the recombinant virus to fish cells was assessed by monitoring the expression of a fluorescent protein encoded in the viral genome. We detected transgene expression in CHSE-214, HINAE, and EPC cells, but not in GF or RTG-2 cells. In the co-infection assay of the Mos1-expressing virus and reporter gene-expressing virus, we successfully transformed CHSE-214 and HINAE cells. These results suggest that the combination of a baculovirus and Mos1 transposable element may be a tool for transgenesis in fish cells.

Baculoviral transduction facilitates TALEN-mediated targeted transgene integration and Cre/LoxP cassette exchange in human-induced pluripotent stem cells

Safety and reliability of transgene integration in human genome continue to pose challenges for stem cell-based gene therapy. Here, we report a baculovirus-transcription activator-like effector nuclease system for AAVS1 locus-directed homologous recombination in human induced pluripotent stem cells (iPSCs). This viral system, when optimized in human U87 cells, provided a targeted integration efficiency of 95.21% in incorporating a Neo-eGFP cassette and was able to mediate integration of DNA insert up to 13.5 kb. In iPSCs, targeted integration with persistent transgene expression was achieved without compromising genomic stability. The modified iPSCs continued to express stem cell pluripotency markers and maintained the ability to differentiate into three germ lineages in derived embryoid bodies. Using a baculovirus-Cre/LoxP system in the iPSCs, the Neo-eGFP cassette at the AAVS1 locus could be replaced by a Hygro-mCherry cassette, demonstrating the feasibility of cassette exchange. Moreover, as assessed by measuring γ-H2AX expression levels, genome toxicity associated with chromosomal double-strand breaks was not detectable after transduction with moderate doses of baculoviral vectors expressing transcription activator-like effector nucleases. Given high targeted integration efficiency, flexibility in transgene exchange and low genome toxicity, our baculoviral transduction-based approach offers great potential and attractive option for precise genetic manipulation in human pluripotent stem cells.

Cell susceptibility to baculovirus transduction and echovirus infection is modified by protein kinase C phosphorylation and vimentin organization

Some cell types are more susceptible to viral gene transfer or virus infection than others, irrespective of the number of viral receptors or virus binding efficacy on their surfaces. In order to characterize the cell-line-specific features contributing to efficient virus entry, we studied two cell lines (Ea.hy926 and MG-63) that are nearly nonpermissive to insect-specific baculovirus (BV) and the human enterovirus echovirus 1 (EV1) and compared their characteristics with those of a highly permissive (HepG2) cell line. All the cell lines contained high levels of viral receptors on their surfaces, and virus binding was shown to be efficient. However, in nonpermissive cells, BV and its receptor, syndecan 1, were unable to internalize in the cells and formed large aggregates near the cell surface. Accordingly, EV1 had a low infection rate in nonpermissive cells but was still able to internalize the cells, suggesting that the postinternalization step of the virus was impaired. The nonpermissive and permissive cell lines showed differential expression of syntenin, filamentous actin, vimentin, and phosphorylated protein kinase C subtype α (pPKCα). The nonpermissive nature of the cells could be modulated by the choice of culture medium. RPMI medium could partially rescue infection/transduction and concomitantly showed lower syntenin expression, a modified vimentin network, and altered activities of PKC subtypes PKCα and PKCε. The observed changes in PKCα and PKCε activation caused alterations in the vimentin organization, leading to efficient BV transduction and EV1 infection. This study identifies PKCα, PKCε, and vimentin as key factors affecting efficient infection and transduction by EV1 and BV, respectively.

Immunological effects of Anticarsia gemmatalis multiple nucleopolyhedrovirus (AgMNPV) by stimulation of mice in vivo and in vitro

Baculoviruses are highly specific and only capable of replication in arthropod hosts. The Autographa californica multiple nucleopolyhedrovirus (AcMNPV) is the most studied baculovirus at the molecular level and the Anticarsia gemnatalis multiple nucleopolyhedrovirus (AgMNPV) is the most used viral insecticide worldwide. AcMNPV have also been shown to stimulate the mammalian immune response acting as an adjuvant. In order to evaluate the effects of AgMNPV in modulating macrophage and lymphocyte activation, we have stimulated these cells in vitro and inoculated BALB/c mice intranasally with the two viral phenotypes (PIBs and BVs) and compared with the response induced by the same phenotypes of AcMNPV. Our results showed that baculoviruses are able to modulate mammalian immune response; in vitro they increase phagocytosis, NO2 production and Th1 cells response. In vivo, AgMNPV BVs or PIBs do not induce an inflammatory reaction in normal lung but during a fungal lung infection they can change the type of adaptive response developed. Considering our data, AgMNPV can be considered more useful as a vaccine vector or immune adjuvant than AcMNPV.

Viral-mediated gene delivery for cell-based assays in drug discovery

BACKGROUND

Adenovirus, retrovirus and lentivirus-based vectors, originally engineered and optimized for in vivo and ex vivo gene therapy, have become increasingly useful for viral-mediated gene delivery to support in vitro cell-based assays. Viral vectors underpin functional genomics screening of cDNA, shRNA and aptamer libraries, are used for a variety of target validation studies and importantly, for high-throughput cell-based drug discovery and compound profiling assays. The baculovirus/insect cell expression system had gained prevalence as a tool for recombinant protein production when it was observed that recombinant baculovirus vectors too could serve as efficient gene delivery vehicles for a wide range of mammalian cells. Although the use of baculovirus vectors in vivo has lagged behind retroviral, adenoviral and lentiviral vectors, they have gained prominence for development of in vitro cell-based assays due to the ease of generation, broad host range and excellent biosafety profile. There is an increasing emphasis on cell-based assays in high-throughput automated drug discovery laboratories and a variety of commercially available viral-vectors can be used for supporting these assays.

OBJECTIVE

We compare and contrast the current viral-mediated gene delivery vector systems and highlight their suitability for cell-based drug discovery assays.

CONCLUSION

Viral-mediated gene delivery is increasingly being used in support of genome scale target validation studies and cell-based assay development for specific drug target genes such as ion channels, G protein-coupled receptors and intracellular enzymes. The choice of a delivery system over another for a particular application is largely dictated by the cell types and cell lines in use, virus cellular tropism, assay throughput, safety requirements and ease/cost of reagent generation.

BacMam immunization partially protects pigs against sublethal challenge with African swine fever virus

Lack of vaccines and efficient control measures complicate the control and eradication of African swine fever (ASF). Limitations of conventional inactivated and attenuated virus-based vaccines against African swine fever virus (ASFV) highlight the need to use new technologies to develop efficient and safe vaccines against this virus. With this aim in mind, in this study we have constructed BacMam-sHAPQ, a baculovirus based vector for gene transfer into mammalian cells, expressing a fusion protein comprising three in tandem ASFV antigens: p54, p30 and the extracellular domain of the viral hemagglutinin (secretory hemagglutinin, sHA), under the control of the human cytomegalovirus immediate early promoter (CMVie). Confirming its correct in vitro expression, BacMam-sHAPQ induced specific T-cell responses directly after in vivo immunization. Conversely, no specific antibody responses were detectable prior to ASFV challenge. The protective potential of this recombinant vaccine candidate was tested by a homologous sublethal challenge with ASFV following immunization. Four out of six immunized pigs remained viremia-free after ASFV infection, while the other two pigs showed similar viremic titres to control animals. The protection afforded correlated with the presence of a large number of virus-specific IFNγ-secreting T-cells in blood at 17 days post-infection. In contrast, the specific antibody levels observed after ASFV challenge in sera from BacMam-sHAPQ immunized pigs were indistinguishable from those found in control pigs. These results highlight the importance of the cellular responses in protection against ASFV and point towards BacMam vectors as potential tools for future vaccine development.

Recombinant baculovirus associated with bilosomes as an oral vaccine candidate against HEV71 infection in mice

BACKGROUND

Human enterovirus 71 (HEV71) is one of the major pathogen responsible for hand, foot and mouth disease (HFMD). Currently no effective vaccine or antiviral drugs are available. Like poliovirus, EV71 is transmitted mainly by the feco-oral route. To date the majority of the studied EV71 vaccine candidates are administered parenterally. Injectable vaccines induce good systemic immunity but mucosal responses are often unsatisfactory, whereas mucosal vaccines provide both systemic and mucosal immunity. Therefore, oral immunization appears to be an attractive alternative to parenteral immunization.

METHODOLOGY/PRINCIPAL FINDINGS

In this report, we studied the efficacy of an orally administered vaccine candidate developed using recombinant baculovirus displaying VP1 (Bac-VP1) in a murine model. Gastrointestinal delivery of Bac-VP1 significantly induced VP1-specific humoral (IgG) and mucosal (IgA) immune responses. Further, we studied the efficacy of the Bac-VP1 associated with bilosomes and observed that the Bac-VP1 associated with bilosomes elicited significantly higher immune responses compared to bilosomes non-associated with Bac-VP1. However, mice immunized subcutaneously with live Bac-VP1 had significantly enhanced VP1 specific serum IgG levels and higher neutralizing antibody titers compared with mice orally immunized with live Bac-VP1 alone or associated with bilosomes.

CONCLUSION

Bilosomes have been shown to possess inherent adjuvant properties when associated with antigen. Therefore Bac-VP1 with bilosomes could be a promising oral vaccine candidate against EV71 infections. Thus, Bac-VP1 loaded bilosomes may provide a needle free, painless approach for immunization against EV71, thereby increasing patient compliance and consequently increasing vaccination coverage.

Cross-protective efficacy of bivalent recombinant baculoviral vaccine against heterologous influenza H5N1 challenge

The present study demonstrates the cross-protective efficacy of baculovirus displayed HAs of A/Indonesia/669/06 and A/Anhui/01/05 against heterologous H5N1 challenges in a mouse model. Mice orally or subcutaneously immunized with live bivalent-BacHA vaccine significantly induced higher HA-specific humoral and cellular immune responses when compared with inactivated bivalent-BacHA. In addition, oral administration of live bivalent-BacHA vaccine was able to induce significant level of antigen-specific mucosal IgA levels. Microneutralization assay indicated that live bivalent-BacHA vaccine was able to induce strong cross-clade neutralization titer against distinct H5N1 clades (1, 2.1.3, 2.2.1.1, 2.3.2, 2.3.4, 4, 7 and 9). The production of both interferon-gamma (IFN-γ) and interleukin-4 (IL-4) by splenocytes from vaccinated mice indicated that mice vaccinated orally or subcutaneously with live bivalent-BacHA stimulated both IFN-γ secreting Th1 cells and IL-4 secreting Th2 cells, whereas mice immunized subcutaneously with inactive adjuvanted bivalent-BacHA stimulated only IL-4 secreting Th2 cells. Cross-protective immunity study also showed that mice immunized either orally or subcutaneously with live bivalent-BacHA were completely protected against 5MLD50 of clade 1 and clade 2.2.1.1 H5N1 viral infections. The protective immune response elicited by bivalent-BacHA vaccine against H5N1 variants demonstrates the possibility of protection against a broad range of H5N1 strains.

Enhanced immunogenicity induced by an alphavirus replicon-based pseudotyped baculovirus vaccine against porcine reproductive and respiratory syndrome virus

Pseudotyped baculovirus has emerged as a promising vector for vaccine development and gene therapy. Alphaviruses, such as Semliki Forest virus (SFV), have also received considerable attention for use as expression vectors because of their self-replicating properties. In this study, pseudotyped baculovirus containing the hybrid cytomegalovirus (CMV) promoter/SFV replicon was used as a vector to co-express the GP5 and M proteins of porcine reproductive and respiratory syndrome virus (PRRSV). The immunogenicity of the resulting recombinant baculovirus (BV-SFV-5m6) was compared with the pseudotyped baculovirus vaccine (BV-CMV-5m6), in which the expression of GP5 and M were driven by the CMV promoter only. In vitro, BV-SFV-5m6 exhibited enhanced expression of foreign proteins and also caused apoptosis in transduced cells. After immunization in BALB/c mice, BV-SFV-5m6 induced strong GP5-specific ELISA antibodies and neutralizing antibodies against homologous and heterologous viruses, along with dose sparing. Further analysis of the cell-mediated immune response showed that BV-SFV-5m6 elicited a Th1-dominant immune response that was greater than that elicited by BV-CMV-5m6. Taken together, the results of this study indicate that a baculovirus containing the hybrid CMV promoter/alphavirus replicon can be utilized as an alternative strategy to develop an efficacious vaccine against PRRSV infection.

Incorporation of GP64 into Helicoverpa armigera nucleopolyhedrovirus enhances virus infectivity in vivo and in vitro

The envelope fusion proteins of baculoviruses, glycoprotein GP64 from group I nucleopolyhedrovirus (NPV) or the F protein from group II NPV and granulovirus, are essential for baculovirus morphogenesis and infectivity. The F protein is considered the ancestral baculovirus envelope fusion protein, while GP64 is a more recent evolutionary introduction into baculoviruses and exhibits higher fusogenic activity than the F protein. Each of the fusion proteins is required by the respective virus to spread infection within larval tissues. A recombinant Helicoverpa armigera NPV (HearNPV) expressing GP64 from Autographa californica multiple nucleopolyhedrovirus, vHaBac-gp64-egfp, was constructed, which still retained the native F protein, and its infectivity was assayed in vivo and in vitro. Analyses by one-step growth curve to determine viral titre and by quantitative PCR to determine viral DNA copy number showed that vHaBac-gp64-egfp was more infectious in vitro than the control, vHaBac-egfp. The polyhedrin gene (polh) was reintroduced into the recombinant viruses and bioassays showed that vHaBac-gp64-polh accelerated the mortality of infected larvae compared with the vHaBac-egfp-polh control, and the LC(50) (median lethal concentration) of vHaBac-gp64-polh was reduced to approximately 20 % of that of vHaBac-egfp-polh. Therefore, incorporation of GP64 into HearNPV budded virions improved virus infectivity both in vivo and in vitro. The construction of this bivalent virus with a more efficient fusion protein could improve the use of baculoviruses in different areas such as gene therapy and biocontrol.

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

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

BacMam system for FRET-based cAMP sensor expression in studies of melanocortin MC1 receptor activation

Cyclic adenosine monophosphate (cAMP) is a second messenger of many G-protein-coupled receptors (GPCRs) and a useful readout molecule to estimate the biological activity of various GPCR-specific agents. Here we report the development and use of a Förster resonance energy transfer (FRET) biosensor for cAMP (Epac2-camps) combined with a baculovirus-based BacMam transduction system. The constructed BacMam-Epac2-camps viral transduction system is a simple and robust tool for ligand screening at the second-messenger level in a variety of mammalian cell lines. The level of biosensor protein expression can easily be adjusted in a dose-dependent manner depending on the multiplicity of viral infection. For setting up the assay, we used a B16F10 murine melanoma cell line with endogenous expression of melanocortin-1 receptor (MC(1)R). The receptor activation was characterized by a set of MC(1)R full and partial agonists. Bivalent ions Ca(2+) as well as Mg(2+) modulated ligand potencies, whereas the effect was ligand and ion specific. Results obtained for MC(1)R indicate that the BacMam-Epac2-camps system may also be applicable for studying the activation of other GPCRs and may be implemented in routine analysis as well as in high-throughput screening.

Characterization of the immune responses elicited by baculovirus-based vector vaccines against influenza virus hemagglutinin

AIM

To compare the specific immune responses elicited by different baculovirus vectors in immunized mice.

METHODS

We constructed and characterized two recombinant baculoviruses carrying the expression cassette for the H5N1 influenza virus hemagglutinin (HA) gene driven by either an insect cell promoter (vAc-HA) or a dual-promoter active both in insect and mammalian cells (vAc-HA-DUAL). Virus without the HA gene (vAc-EGFP) was used as a control. These viruses were used to immunize mice subcutaneously and intraperitoneally. The production of total and specific antibodies was determined by ELISA and competitive ELISA. Cytokine production by the spleen cells of immunized mice was studied using the ELISPOT assay.

RESULTS

Both the vAc-HA and vAc-HA-DUAL vectors expressed HA proteins in insect Sf9 cells, and HA antigen was present in progeny virions. The vAc-HA-DUAL vector also mediated HA expression in virus-transduced mammalian cell lines (BHK and A547). Both vAc-HA and vAc-HA-DUAL exhibited higher transduction efficiencies than vAc-EGFP in mammalian cells, as shown by the expression of the reporter gene egfp. Additionally, both vAc-HA and vAc-HA-DUAL induced high levels of HA-specific antibody production in immunized mice; vAc-HA-DUAL was more efficient in inducing IFN-γ and IL-2 upon stimulation with specific antigen, whereas vAc-HA was more efficient in inducing IL-4 and IL-6.

CONCLUSION

Baculovirus vectors elicited efficient, specific immune responses in immunized mice. The vector displaying the HA antigen on the virion surface (vAc-HA) elicited a Th2-biased immune response, whereas the vector displaying HA and mediating HA expression in the cell (vAc-HA-DUAL) elicited a Th1-biased immune response.

Pharmacological characterization of GSK1004723, a novel, long-acting antagonist at histamine H(1) and H(3) receptors

BACKGROUND AND PURPOSE

Preclinical pharmacological characterization of GSK1004723, a novel, dual histamine H(1) and H(3) receptor antagonist.

EXPERIMENTAL APPROACH

GSK1004723 was characterized in vitro and in vivo using methods that included radioligand binding, intracellular calcium mobilization, cAMP production, GTPγS binding, superfused human bronchus and guinea pig whole body plethysmography.

KEY RESULTS

In cell membranes over-expressing human recombinant H(1) and H(3) receptors, GSK1004723 displayed high affinity, competitive binding (H(1) pKi = 10.2; H(3) pKi = 10.6). In addition, GSK1004723 demonstrated slow dissociation from both receptors with a t(1/2) of 1.2 and 1.5 h for H(1) and H(3) respectively. GSK1004723 specifically antagonized H(1) receptor mediated increases in intracellular calcium and H(3) receptor mediated increases in GTPγS binding. The antagonism exerted was retained after cell washing, consistent with slow dissociation from H(1) and H(3) receptors. Duration of action was further evaluated using superfused human bronchus preparations. GSK1004723 (100 nmol·L(-1) ) reversed an established contractile response to histamine. When GSK1004723 was removed from the perfusate, only 20% recovery of the histamine response was observed over 10 h. Moreover, 21 h post-exposure to GSK1004723 there remained almost complete antagonism of responses to histamine. In vivo pharmacology was studied in conscious guinea pigs in which nasal congestion induced by intranasal histamine was measured indirectly (plethysmography). GSK1004723 (0.1 and 1 mg·mL(-1) intranasal) antagonized the histamine-induced response with a duration of up to 72 h.

CONCLUSIONS AND IMPLICATIONS

GSK1004723 is a potent and selective histamine H(1) and H(3) receptor antagonist with a long duration of action and represents a potential novel therapy for allergic rhinitis.

Baculovirus GP64-mediated entry into mammalian cells

The baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) serves as an efficient viral vector, not only for abundant gene expression in insect cells, but also for gene delivery into mammalian cells. Lentivirus vectors pseudotyped with the baculovirus envelope glycoprotein GP64 have been shown to acquire more potent gene transduction than those with vesicular stomatitis virus (VSV) envelope glycoprotein G. However, there are conflicting hypotheses about the molecular mechanisms of the entry of AcMNPV. Moreover, the mechanisms of the entry of pseudotyped viruses bearing GP64 into mammalian cells are not well characterized. Determination of the entry mechanisms of AcMNPV and the pseudotyped viruses bearing GP64 is important for future development of viral vectors that can deliver genes into mammalian cells with greater efficiency and specificity. In this study, we generated three pseudotyped VSVs, NPVpv, VSVpv, and MLVpv, bearing envelope proteins of AcMNPV, VSV, and murine leukemia virus, respectively. Depletion of membrane cholesterol by treatment with methyl-β-cyclodextrin, which removes cholesterol from cellular membranes, inhibited GP64-mediated internalization in a dose-dependent manner but did not inhibit attachment to the cell surface. Treatment of cells with inhibitors or the expression of dominant-negative mutants for dynamin- and clathrin-mediated endocytosis abrogated the internalization of AcMNPV and NPVpv into mammalian cells, whereas inhibition of caveolin-mediated endocytosis did not. Furthermore, inhibition of macropinocytosis reduced GP64-mediated internalization. These results suggest that cholesterol in the plasma membrane, dynamin- and clathrin-dependent endocytosis, and macropinocytosis play crucial roles in the entry of viruses bearing baculovirus GP64 into mammalian cells.

Optogenetic excitation of neurons with channelrhodopsins: light instrumentation, expression systems, and channelrhodopsin variants

Classically, temporally precise excitation of membrane potential in neurons within intact tissue can be achieved by direct electrical stimulation or indirect electrical stimulation induced by changing magnetic fields. Both of these approaches have a predetermined selectivity based on the biophysical properties of the nervous tissue and membrane in the region of the stimulation. A recent advance in selective excitation of neurons is the "optogenetic" approach utilizing channelrhodopsins (ChRs). By expressing the light-responsive ChR in neurons using cell-type selective promoters or other methods, specific neurons can be depolarized by light in a temporally precise manner with millisecond resolution even if their membrane biophysical properties are less favorable for electrical stimulation. In addition, ChRs can be used to depolarize nonneuronal cells in the nervous tissue, and to sustain depolarization over a prolonged period of time, both of which cannot be achieved with electrical or magnetic stimulations. To conduct an experiment with ChR, experimenters need to make the correct choices on the three main components to such an experiment: the expression system, the illumination source, and the ChR variant used. This chapter aims to provide some discussions on the current developments of these aspects of the experiments. To express ChR in neurons, the common expression systems include viral vectors, in utero electroporation, and transgenic animals, each with their advantages and limitations regarding the cost, expression pattern, and the required effort. In terms of the instrumentation, an illumination source that is capable of providing the desired wavelength with high intensity is crucial for the success of the experiment. The important factors regarding the light source used include the cost, light density output, efficiency for fiber coupling for in vivo rodent experiments, and the available methods to control light intensity and onset/termination. The third component of the experiment is the choice of the appropriate variants of ChR. Many novel ChR variants with unique properties have been engineered, and it can be difficult for the experimenters to choose the right variant with the desired properties for their experiments, as some information necessary for the experimenter to make the right selection is often incomplete or unavailable. Currently, the available variants for neuroscientific research are wild-type ChR2, ChR2+H134R, ChETA, VChR1, SFO, ChD, ChEF, ChIEF, ChRGR, CatCh, and TC. The features and limitations of these different variants are presented here. Lastly, this chapter will provide some suggestion for the future development of the light source, expression system, and the development of the "next" generation of ChRs.

Why proteins in mammalian cells?

Producing recombinant mammalian proteins in native or near-native conformation is fundamental to many aspects of biology. Unfortunately, it is also a task whose outcome is extremely unpredictable. A protein that has been shaped over millions of generations of evolution for expression at a level appropriate to a specific cell type or in a particular developmental stage, may be toxic to a new host cell, or become insoluble (among many possible obstacles) when overexpressed in vitro. The object of this volume, "Protein Expression in Mammalian Cells," is to offer guidance for those who wish (or who have been forced by circumstance) to overexpress a mammalian protein in mammalian cells.

Stable protein expression in mammalian cells using baculoviruses

The baculovirus Autographa californica multiple nuclear polyhedrosis virus (AcMNPV) has been widely used in biotechnology for protein expression in insect cells. Baculoviruses use arthropods as their natural hosts and are unable to replicate in mammalian cells. However, AcMNPV is able to enter many mammalian cell types and can be used for transgene expression if engineered to contain suitable expression cassettes. In this chapter, we describe the construction and application of a recombinant baculovirus containing a bicistronic expression cassette that can be used for stable protein expression in mammalian cells. As an example, the generation of glioblastoma and hepatocellular carcinoma cell lines stably expressing green fluorescent protein after puromycin selection is shown.

Baculovirus-produced influenza virus-like particles in mammalian cells protect mice from lethal influenza challenge

Influenza virus-like particles (VLPs) are effective vaccines against influenza infection, which can be produced either in insect cells by recombinant baculovirus (BV) infection or in mammalian cells by DNA plasmid transfection. However, VLPs produced from baculovirus/insect cells are difficult to purify due to baculovirus contamination; VLPs produced by plasmid transfection are limited by scale-up capability. In this study, a BacMam BV, in which three CMV-promoters drive the hemagglutinin, neuraminidase, and matrix of influenza virus was constructed. This baculovirus can deliver these genes into mammalian cells/hosts and subsequently influenza VLPs can be produced and secreted from transduced cells. Transduction conditions were optimized and influenza VLPs were purified from transduced 293T cells. Mice were vaccinated with BV transduction-produced VLPs, plasmid transfection-produced VLPs, and BacMam BV. Two vaccinations of each vaccine induced high hemagglutination-inhibition (HAI) titers and prevented influenza virus infection. In contrast, following a single vaccination, all mice vaccinated with each vaccine had significantly lower lung viral titers compared to unvaccinated mice. Remarkably, mice vaccinated with a single dose of BV transduction-produced VLPs survived challenge, whereas mice vaccinated with one dose of BacMam BV- or plasmid transfection-produced VLPs had 60-80% survival. This finding is particularly significant for producing easily purified VLPs. The BacMam system is an alternative strategy for VLP production, which is easy to scale up and purify. Besides, BacMam BV can be used as a gene delivery vector to produce VLPs in vivo, to stimulate immune responses.

A pH-sensitive heparin-binding sequence from Baculovirus gp64 protein is important for binding to mammalian cells but not to Sf9 insect cells

Binding to heparan sulfate is essential for baculovirus transduction of mammalian cells. Our previous study shows that gp64, the major glycoprotein on the virus surface, binds to heparin in a pH-dependent way, with a stronger binding at pH 6.2 than at 7.4. Using fluorescently labeled peptides, we mapped the pH-dependent heparin-binding sequence of gp64 to a 22-amino-acid region between residues 271 and 292. Binding of this region to the cell surface was also pH dependent, and peptides containing this sequence could efficiently inhibit baculovirus transduction of mammalian cells at pH 6.2. When the heparin-binding peptide was immobilized onto the bead surface to mimic the high local concentration of gp64 on the virus surface, the peptide-coated magnetic beads could efficiently pull down cells expressing heparan sulfate but not cells pretreated with heparinase or cells not expressing heparan sulfate. Interestingly, although this heparin-binding function is essential for baculovirus transduction of mammalian cells, it is dispensable for infection of Sf9 insect cells. Virus infectivity on Sf9 cells was not reduced by the presence of heparin or the identified heparin-binding peptide, even though the peptide could bind to Sf9 cell surface and be efficiently internalized. Thus, our data suggest that, depending on the availability of the target molecules on the cell surface, baculoviruses can use two different methods, electrostatic interaction with heparan sulfate and more specific receptor binding, for cell attachment.

Light it up: highly efficient multigene delivery in mammalian cells

Multigene delivery and expression systems are emerging as key technologies for many applications in contemporary biology. We have developed new methods for multigene delivery and expression in eukaryotic hosts for a variety of applications, including production of protein complexes for structural biology and drug development, provision of multicomponent protein biologics, and cell-based assays. We implemented tandem recombineering to facilitate rapid generation of multicomponent gene expression constructs for efficient transformation of mammalian cells, resulting in homogenous cell populations. Analysis of multiple parameters in living cells may require co-expression of fluorescently tagged sensors simultaneously in a single cell, at defined and ideally controlled ratios. Our method enables such applications by overcoming currently limiting challenges. Here, we review recent multigene delivery and expression strategies and their exploitation in mammalian cells. We discuss applications in drug discovery assays, interaction studies, and biologics production, which may benefit in the future from our novel approach.

Generation of iPS cells using a BacMam multigene expression system

Generation of iPS cells from mouse embryonic fibroblasts (MEF) was achieved using a BacMam transduction system containing a polycistronic plasmid expression vector for coincident and optimized expression of four defined reprogramming transcription factors. The sequences for Oct4, Klf4, Sox2 and c-Myc, were cloned as a fusion gene (OKSM) in a single open reading frame (ORF) via self-cleaving 2A peptides and expressed under the control of the CAG promoter. The transduction efficiency of primary MEF cells with BacMam particles carrying CAG-directed Venus reporter gene is 64-98%. After three successive transductions (at intervals of 3 days) of MEF cells with BacMam particles carrying a OKSM or OSKM cassette, the iPS cell colonies are observed in 15-24 days. A single transduction of MEF cells is also effective in generating sufficiently reprogrammed iPS cell lines. The iPS cell lines from colonies picked were positively stained by Nanog, SSEA-1 immunofluorescence and alkaline phosphatase substrate markers. The advantage of using the EOS-S(4+)-EmGFP reporter to identify sufficiently reprogrammed iPS cell lines is discussed by representing experimental results obtained with electroporated plasmids, such as a mixture of 2 tandem OS and KM plasmids and a polycistronic OKSM expression plasmid.

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.

Potential of adenovirus and baculovirus vectors for the delivery of shRNA against morbilliviruses

Morbilliviruses are important pathogens of humans, ruminants, carnivores and marine mammals. Although good vaccines inducing long-term immunity are available, recurrent outbreaks of measles, canine distemper and peste des petits ruminants (PPR) are observed. In control strategies, antivirals thus could be useful to confine virus spread and application of interfering RNAs is a promising approach, provided they can be delivered efficiently into the host cells. We have constructed recombinant adenovirus and baculovirus vectors expressing short hairpin RNAs (shRNAs) against the PPR virus (PPRV) and compared them in vitro. It was found that both recombinant viruses inhibited PPRV replication with the baculovirus vector, which inhibited generation of infectious progeny by more than 2 log10 and the nucleoprotein expression of PPRV by 73%, being the more efficient. The results show that baculoviral shRNA-expressing vectors have the potential for therapeutic use against morbillivirus infections.

Hybrid metabolic flux analysis: combining stoichiometric and statistical constraints to model the formation of complex recombinant products

Background

Stoichiometric models constitute the basic framework for fluxome quantification in the realm of metabolic engineering. A recurrent bottleneck, however, is the establishment of consistent stoichiometric models for the synthesis of recombinant proteins or viruses. Although optimization algorithms for in silico metabolic redesign have been developed in the context of genome-scale stoichiometric models for small molecule production, still rudimentary knowledge of how different cellular levels are regulated and phenotypically expressed prevents their full applicability for complex product optimization.

Results

A hybrid framework is presented combining classical metabolic flux analysis with projection to latent structures to further link estimated metabolic fluxes with measured productivities. We first explore the functional metabolic decomposition of a baculovirus-producing insect cell line from experimental data, highlighting the TCA cycle and mitochondrial respiration as pathways strongly associated with viral replication. To reduce uncertainty in metabolic target identification, a Monte Carlo sampling method was used to select meaningful associations with the target, from which 66% of the estimated fluxome had to be screened out due to weak correlations and/or high estimation errors. The proposed hybrid model was then validated using a subset of preliminary experiments to pinpoint the same determinant pathways, while predicting the productivity of independent cultures.

Conclusions

Overall, the results indicate our hybrid metabolic flux analysis framework is an advantageous tool for metabolic identification and quantification in incomplete or ill-defined metabolic networks. As experimental and computational solutions for constructing comprehensive global cellular models are in development, the contribution of hybrid metabolic flux analysis should constitute a valuable complement to current computational platforms in bridging the metabolic state with improved cell culture performance.

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.

Gene editing of human embryonic stem cells via an engineered baculoviral vector carrying zinc-finger nucleases

Human embryonic stem (hES) cells are renewable cell sources that have potential applications in regenerative medicine. The development of technologies to produce permanent and site-specific genome modifications is in demand to achieve future medical implementation of hES cells. We report herein that a baculoviral vector (BV) system carrying zinc-finger nucleases (ZFNs) can successfully modify the hES cell genome. BV-mediated transient expression of ZFNs specifically disrupted the CCR5 locus in transduced cells and the modified cells exhibited resistance to HIV-1 transduction. To convert the BV to a gene targeting vector, a DNA donor template and ZFNs were incorporated into the vector. These hybrid vectors yielded permanent site-specific gene addition in both immortalized human cell lines (10%) and hES cells (5%). Modified hES cells were both karyotypically normal and pluripotent. These results suggest that this baculoviral delivery system can be engineered for site-specific genetic manipulation in hES cells.

Engineered biological entities for drug delivery and gene therapy protein nanoparticles

The development of genetic engineering techniques has speeded up the growth of the biotechnological industry, resulting in a significant increase in the number of recombinant protein products on the market. The deep knowledge of protein function, structure, biological interactions, and the possibility to design new polypeptides with desired biological activities have been the main factors involved in the increase of intensive research and preclinical and clinical approaches. Consequently, new biological entities with added value for innovative medicines such as increased stability, improved targeting, and reduced toxicity, among others have been obtained. Proteins are complex nanoparticles with sizes ranging from a few nanometers to a few hundred nanometers when complex supramolecular interactions occur, as for example, in viral capsids. However, even though protein production is a delicate process that imposes the use of sophisticated analytical methods and negative secondary effects have been detected in some cases as immune and inflammatory reactions, the great potential of biodegradable and tunable protein nanoparticles indicates that protein-based biotechnological products are expected to increase in the years to come.

BacMam-mediated gene delivery into multipotent mesenchymal stromal cells

Baculoviruses have been used over the last several decades for high-level protein production in insect cells. Recently, modified baculovirus containing a mammalian promoter, known as BacMam virus, has been shown to give high transduction efficiencies across several cell types with minimal cytopathic effects. Cell types amenable to BacMam transduction include primary and adult stem cells. The shuttle vectors used in the construction of BacMam viruses can hold gene fragments up to 38 kb in size, and multiple BacMam viruses can be used in a single transduction for the delivery of more than one gene. BacMam technology has been used in the delivery and expression of targeted fluorescent protein cellular markers, small interfering RNAi, and extensively in the development of cell-based assays. BacMam offers an ideal method for the delivery and expression of large genes in hard-to-transfect cells such as primary and adult stem cells. In this chapter, we describe methods of generating high titer stocks of BacMam for transducing MSC and their derivatives.