Persistent gene expression in mouse nasal epithelia following feline immunodeficiency virus-based vector gene transfer

Air-assisted intranasal instillation enhances adenoviral delivery to the olfactory epithelium and respiratory tract

Intranasal instillation is used to deliver adenoviral vectors to the olfactory epithelium and respiratory tract. The success of this approach, however, has been tempered by inconsistent infectivity in both the epithelium and lungs. Infection of the epithelium may be hampered in part by the convoluted structure of the cavity, the presence of mucus or poor airflow in the posterior cavity. Delivery of adenovirus to the lungs can be uneven in the various lobes and distal bronchioles may be poorly infected. Current approaches to circumvent these issues rely principally on intubation or intratracheal instillation. Here we describe a technique that significantly improves adenoviral infectivity rates without requiring surgical intervention. We use compressed air to increase circulation of instilled adenovirus, resulting in enhanced infection in both the epithelium and lungs. This procedure is straightforward, simple to perform and requires no specialized equipment. In the epithelium, neurons and sustentacular cells are both labeled. In the lungs, all lobes can be infected, with penetration to the most distal bronchioles. The use of compressed air will likely also be useful for enhancing the distribution of other, desired agents within the epithelium, central nervous system and respiratory tract.

A VSV-G Pseudotyped Last Generation Lentiviral Vector Mediates High Level and Persistent Gene Transfer in Models of Airway Epithelium In Vitro and In Vivo

The aim of this work was to evaluate the efficiency and duration of gene expression mediated by a VSV-G pseudotyped last generation lentiviral (LV) vector. We studied LV efficiency in ex-vivo models of respiratory epithelial cells, obtained from bronchial biopsies and nasal polyps, by GFP epifluorescence and cytofluorimetry. In vivo efficiency and persistence of gene expression was investigated by GFP immunohistochemistry and luciferase activity in lung cryosections and homogenates, respectively, upon intranasal and intratracheal administration protocols in C57Bl/6 mice. Both primary bronchial and nasal epithelial cells were transduced up to 70–80% 72 hr after the LV infection. In vivo nasal luciferase expression was increased by lysophosphatidylcholine pre-treatment of the nose. Conversely, the bronchial epithelium was transduced in the absence of any pre-conditioning treatment and luciferase expression lasted for at least 6 months without any decline. We conclude that a last generation LV vector is a promising gene transfer agent in the target organ of genetic and acquired lung diseases, as in the case of cystic fibrosis.

Stem cell therapy for cystic fibrosis: current status and future prospects

Although cystic fibrosis (CF), an autosomal recessive disease caused by mutations in the gene encoding for the CF transmembrane conductance regulator (CFTR), seems a good candidate for gene therapy, 15 years of intense investigation and a number of clinical trials have not yet produced a viable clinical gene-therapy strategy. In addition, the duration of gene expression has been shown to be limited, only lasting 1-4 weeks. Therefore, alternative approaches involve the search for, and use of, stem cell populations. Bone marrow contains different stem cell types, including hematopoietic stem cells and multipotent mesenchymal stromal cells. Numerous studies have now demonstrated the ability of hematopoietic stem cells and mesenchymal stromal cells to home to the lung and differentiate into epithelial cells of both the conducting airways and the alveolar region. However, engraftment of bone marrow-derived stem cells into the airways is a very inefficient process. Detailed knowledge of the cellular and molecular determinants governing homing to the lung and transformation of marrow cells into lung epithelial cells would benefit this process. Despite a very low level of engraftment of donor cells into the nose and gut, significant CFTR mRNA expression and a measurable level of correction of the electrophysiological defect were observed after transplantation of wild-type marrow cells into CF mice. It is uncertain whether this effect is due to the presence of CFTR-expressing epithelial cells derived from donor cells or to the immunomodulatory role of transplanted cells. Finally, initial studies on the usefulness of umbilical cord blood and embryonic stem cells in the generation of airway epithelial cells will be discussed in this review.

Lysophosphatidylcholine as an adjuvant for lentiviral vector mediated gene transfer to airway epithelium: effect of acyl chain length

BACKGROUND

Poor gene transfer efficiency has been a major problem in developing an effective gene therapy for cystic fibrosis (CF) airway disease. Lysophosphatidylcholine (LPC), a natural airway surfactant, can enhance viral gene transfer in animal models. We examined the electrophysiological and physical effect of airway pre-treatment with variants of LPC on lentiviral (LV) vector gene transfer efficiency in murine nasal airways in vivo.

METHODS

Gene transfer was assessed after 1 week following nasal instillations of a VSV-G pseudotype LV vector pre-treated with a low and high dose of LPC variants. The electrophysiological effects of a range of LPC variants were assessed by nasal transepithelial potential difference measurements (TPD) to determine tight junction permeability. Any physical changes to the epithelium from administration of the LPC variants were noted by histological methods in airway tissue harvested after 1 hour.

RESULTS

Gene transduction was significantly greater compared to control (PBS) for our standard LPC (palmitoyl/stearoyl mixture) treatment and for the majority of the other LPC variants with longer acyl chain lengths. The LPC variant heptadecanoyl also produced significantly greater LV gene transfer compared to our standard LPC mixture. LV gene transfer and the transepithelial depolarization produced by the 0.1% LPC variants at 1 hour were strongly correlated (r2 = 0.94), but at the 1% concentration the correlation was less strong (r2 = 0.59). LPC variants that displayed minor to moderate levels of disruption to the airway epithelium were clearly associated with higher LV gene transfer.

CONCLUSIONS

These findings show the LPC variants effect on airway barrier function and their correlation to the effectiveness of gene expression. The enhanced expression produced by a number of LPC variants should provide new options for preclinical development of efficient airway gene transfer techniques.

Impact of lentiviral vector-mediated transduction on the tightness of a polarized model of airway epithelium and effect of cationic polymer polyethylenimine

Lentiviral (LV) vectors are promising agents for efficient and long-lasting gene transfer into the lung and for gene therapy of genetically determined pulmonary diseases, such as cystic fibrosis, however, they have not been evaluated for cytotoxicity and impact on the tightness of the airway epithelium. In this study, we evaluated the transduction efficiency of a last-generation LV vector bearing Green Fluorescent Protein (GFP) gene as well as cytotoxicity and tight junction (TJ) integrity in a polarized model of airway epithelial cells. High multiplicities of infection (MOI) showed to be cytotoxic, as assessed by increase in propidium iodide staining and decrease in cell viability, and harmful for the epithelial tightness, as demonstrated by the decrease of transepithelial resistance (TER) and delocalization of occludin from the TJs. To increase LV efficiency at low LV:cell ratio, we employed noncovalent association with the polycation branched 25 kDa polyethylenimine (PEI). Transduction of cells with PEI/LV particles resulted in 2.5–3.6-fold increase of percentage of GFP-positive cells only at the highest PEI:LV ratios (1×10⁷ PEI molecules/transducing units with 50 MOI LV) as compared to plain LV. At this dose PEI/LV transduction resulted in 6.5 ± 2.4% of propidium iodide-positive cells. On the other hand, PEI/LV particles did not determine any alteration of TER and occludin localization. We conclude that PEI may be useful for improving the efficiency of gene transfer mediated by LV vectors in airway epithelial cells, in the absence of high acute cytotoxicity and alteration in epithelial tightness.

Respiratory syncytial virus engineered to express the cystic fibrosis transmembrane conductance regulator corrects the bioelectric phenotype of human cystic fibrosis airway epithelium in vitro

Cystic fibrosis (CF) is the most common lethal recessive genetic disease in the Caucasian population. It is caused by mutations in the CF transmembrane conductance regulator (CFTR) gene that is normally expressed in ciliated airway epithelial cells and the submucosal glands of the lung. Since the CFTR gene was first characterized in 1989, a major goal has been to develop an effective gene therapy for CF lung disease, which has the potential to ameliorate morbidity and mortality. Respiratory syncytial virus (RSV) naturally infects the ciliated cells in the human airway epithelium. In addition, the immune response mounted against an RSV infection does not prevent subsequent infections, suggesting that an RSV-based vector might be effectively readministered. To test whether the large 4.5-kb CFTR gene could be expressed by a recombinant RSV and whether infectious virus could be used to deliver CFTR to ciliated airway epithelium derived from CF patients, we inserted the CFTR gene into four sites in a recombinant green fluorescent protein-expressing RSV (rgRSV) genome to generate virus expressing four different levels of CFTR protein. Two of these four rgRSV-CFTR vectors were capable of expressing CFTR with little effect on viral replication. rgRSV-CFTR infection of primary human airway epithelial cultures derived from CF patients resulted in expression of CFTR protein that was properly localized at the luminal surface and corrected the chloride ion channel defect in these cells.

Use of the piggyBac transposon to create HIV-1 gag transgenic insect cell lines for continuous VLP production

BACKGROUND

Insect baculovirus-produced Human immunodeficiency virus type 1 (HIV-1) Gag virus-like-particles (VLPs) stimulate good humoral and cell-mediated immune responses in animals and are thought to be suitable as a vaccine candidate. Drawbacks to this production system include contamination of VLP preparations with baculovirus and the necessity for routine maintenance of infectious baculovirus stock. We used piggyBac transposition as a novel method to create transgenic insect cell lines for continuous VLP production as an alternative to the baculovirus system.

RESULTS

Transgenic cell lines maintained stable gag transgene integration and expression up to 100 cell passages, and although the level of VLPs produced was low compared to baculovirus-produced VLPs, they appeared similar in size and morphology to baculovirus-expressed VLPs. In a murine immunogenicity study, whereas baculovirus-produced VLPs elicited good CD4 immune responses in mice when used to boost a prime with a DNA vaccine, no boost response was elicited by transgenically produced VLPs.

CONCLUSION

Transgenic insect cells are stable and can produce HIV Pr55 Gag VLPs for over 100 passages: this novel result may simplify strategies aimed at making protein subunit vaccines for HIV. Immunogenicity of the Gag VLPs in mice was less than that of baculovirus-produced VLPs, which may be due to lack of baculovirus glycoprotein incorporation in the transgenic cell VLPs. Improved yield and immunogenicity of transgenic cell-produced VLPs may be achieved with the addition of further genetic elements into the piggyBac integron.

Lentiviral vectors and cystic fibrosis gene therapy

Cystic fibrosis (CF) is a chronic autosomic recessive syndrome, caused by mutations in the CF Transmembrane Conductance Regulator (CFTR) gene, a chloride channel expressed on the apical side of the airway epithelial cells. The lack of CFTR activity brings a dysregulated exchange of ions and water through the airway epithelium, one of the main aspects of CF lung disease pathophysiology. Lentiviral (LV) vectors, of the Retroviridae family, show interesting properties for CF gene therapy, since they integrate into the host genome and allow long-lasting gene expression. Proof-of-principle that LV vectors can transduce the airway epithelium and correct the basic electrophysiological defect in CF mice has been given. Initial data also demonstrate that LV vectors can be repeatedly administered to the lung and do not give rise to a gross inflammatory process, although they can elicit a T cell-mediated response to the transgene. Future studies will clarify the efficacy and safety profile of LV vectors in new complex animal models with CF, such as ferrets and pigs.

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.

Gene therapy for cystic fibrosis lung disease

Cystic fibrosis (CF) is characterised by respiratory and pancreatic deficiencies that stem from the loss of fully functional CFTR (CF transmembrane conductance regulator) at the membrane of epithelial cells. Current treatment modalities aim to delay the deterioration in lung function, Which is mostly responsible for the relatively short life expectancy of CF sufferers; however none have so far successfully dealt with the underlying molecular defect. Novel pharmacological approaches to ameliorate the lack of active CFTR in respiratory epithelial cells are beginning to address more of the pathophysiological defects caused by CFTR mutations. However, CFTR gene replacement by gene therapy remains the most likely option for addressing the basic defects, including ion transport and inflammatory functions of CFTR. In this chapter, We will review the latest preclinical and clinical advances in pharmacotherapy and gene therapy for CF lung disease.

Single-dose lentiviral gene transfer for lifetime airway gene expression

BACKGROUND

Cystic fibrosis (CF) is caused by a defect in cystic fibrosis transmembrane conductance regulator (CFTR) activity, often resulting in an incurable airway disease. Gene therapy into the conducting airway epithelium is a potential cure for CF; however, most gene vectors do not result in long-lived expression, and require re-dosing. Perversely, intrinsic host immune responses can then block renewed gene transfer.

METHODS

To investigate whether persistent gene expression could be achieved after a single dosing event, thus avoiding the issue of blocking host responses, we used a gene transfer protocol that combined an airway pretreatment using lysophosphatidylcholine with a human immunodeficiency virus type-1 (vesicular stomatitis virus G pseudotype) derived lentiviral vector to test whether an integrating vector could produce gene expression able to last for a substantial part of the lifetime of the laboratory mouse.

RESULTS

We found that a single dose of LV-LacZ produced immediate as well as lifetime mouse airway expression, confirming our hypothesis that use of an integrating vector extends transgene expression. Importantly, LV-CFTR dosing achieved at least 12 months of CFTR expression, representing partial functional correction of the CFTR defect in CF-null mice.

CONCLUSIONS

These findings validate the potential of this methodology for developing a gene transfer treatment for CF airway disease.

RNA interference technologies and therapeutics: from basic research to products

RNA interference (RNAi) is a natural cellular process that regulates gene expression by a highly precise mechanism of sequence-directed gene silencing at the stage of translation by degrading specific messenger RNAs or blocking translation. In recent years, the use of RNAi for therapeutic applications has gained considerable momentum. It has been suggested that most of the novel disease-associated targets that have been identified are not ‘druggable’ with conventional approaches. However, any disease-causing gene and any cell type or tissue can potentially be targeted with RNAi.

This review focuses on the current knowledge of RNAi mechanisms and the safety issues associated with its potential use in a therapeutic setting. Some of the most important aspects to consider when working towards the application of RNAi-based products in a clinical setting have been related to achieving high efficacies and enhanced stability profiles through a careful design of the nucleic acid sequence and the introduction of chemical modifications, but most of all, to developing improved delivery systems, both viral and non-viral. These new delivery systems allow for these products to reach the desired target cells, tissues or organs in a highly specific manner and after administration of the lowest possible doses. Various routes of application and target locations are currently being addressed in order to develop effective delivery systems for different targets and pathologies, including infectious pathologies, genetic pathologies and diseases associated with dysregulation of endogenous microRNAs. As with any new technology, several challenges and important aspects to be considered have risen on the road to clinical intervention, e.g. correct design of preclinical toxicology studies, regulatory concerns, and intellectual property protection. The main advantages related to the use of RNAi-based products in a clinical setting, and the latest clinical and preclinical studies using these compounds, are reviewed.

Progress and prospects: immune responses to viral vectors

Viral vectors are potent gene delivery platforms used for the treatment of genetic and acquired diseases. However, just as viruses have evolved to infect cells efficiently, the immune system has evolved to fight off what it perceives as invading pathogens. Therefore, innate immunity and antigen-specific adaptive immune responses against vector-derived antigens reduce the efficacy and stability of in vivo gene transfer. In addition, a number of vectors are derived from parent viruses that humans encounter through natural infection, resulting in preexisting antibodies and possibly in memory responses against vector antigens. Similarly, antibody and T-cell responses may be directed against therapeutic gene products that often differ from the endogenous nonfunctional or absent protein that is being replaced. As details and mechanisms of such immune reactions are uncovered, novel strategies are being developed, and vectors are being specifically engineered to avoid, suppress or manipulate the response, ideally resulting in sustained expression and immune tolerance to the transgene product. This review provides a summary of our current knowledge of the interactions between the immune system adeno-associated virus, adenoviral and lentiviral vectors, and their transgene products.

Activation of transgene-specific T cells following lentivirus-mediated gene delivery to mouse lung

Integrating lentiviral vectors based on the human immunodeficiency virus type-1 (HIV-1) can transduce quiescent cells, which in lung account for almost 95% of the epithelial cell population. Pseudotyping lentiviral vectors with the envelope glycoprotein from the Ebola Zaire virus, the lymphocytic choriomeningitis virus (LCMV), the Mokola virus, and the vesicular stomatitis virus (VSV-G) resulted in transduction of mouse alveolar epithelium, but gene expression in the lung of C57BL/6 and BALB/c mice waned within 90 days of vector injection. Intratracheal delivery of the four pseudotyped lentiviral vectors resulted in transgene-specific T-cell activation in both mouse strains, albeit lower than that achieved by intramuscular injection of the vectors. We performed an adoptive transfer of luciferase-specific T cells, isolated from spleen or lung of donor mice injected with VSV-G-pseudotyped lentivirus vector expressing luciferase into the muscle or lung, respectively, into recipient recombination-activating gene (RAG)–deficient mice transduced in lung with adenovirus expressing firefly luciferase (ffluc2). Gene expression declined within 7 days of adoptive transfer approaching background levels by day 36. Taken together, our results suggest that the loss of transduced cells in lung is due to VSV-G.HIV vector–mediated activation of transgene-specific T cells rather than as result of normal turnover of airway cells.

CFTR delivery to 25% of surface epithelial cells restores normal rates of mucus transport to human cystic fibrosis airway epithelium

Delivering CFTR to ciliated cells of cystic fibrosis (CF) patients fully restores ion and fluid transport to the lumenal surface of airway epithelium and returns mucus transport rates to those of non-CF airways.

Dysfunction of CFTR in cystic fibrosis (CF) airway epithelium perturbs the normal regulation of ion transport, leading to a reduced volume of airway surface liquid (ASL), mucus dehydration, decreased mucus transport, and mucus plugging of the airways. CFTR is normally expressed in ciliated epithelial cells of the surface and submucosal gland ductal epithelium and submucosal gland acinar cells. Critical questions for the development of gene transfer strategies for CF airway disease are what airway regions require CFTR function and how many epithelial cells require CFTR expression to restore normal ASL volume regulation and mucus transport to CF airway epithelium? An in vitro model of human CF ciliated surface airway epithelium (CF HAE) was used to test whether a human parainfluenza virus (PIV) vector engineered to express CFTR (PIVCFTR) could deliver sufficient CFTR to CF HAE to restore mucus transport, thus correcting the CF phenotype. PIVCFTR delivered CFTR to >60% of airway surface epithelial cells and expressed CFTR protein in CF HAE approximately 100-fold over endogenous levels in non-CF HAE. This efficiency of CFTR delivery fully corrected the basic bioelectric defects of Cl⁻ and Na⁺ epithelial ion transport and restored ASL volume regulation and mucus transport to levels approaching those of non-CF HAE. To determine the numbers of CF HAE surface epithelial cells required to express CFTR for restoration of mucus transport to normal levels, different amounts of PIVCFTR were used to express CFTR in 3%–65% of the surface epithelial cells of CF HAE and correlated to increasing ASL volumes and mucus transport rates. These data demonstrate for the first time, to our knowledge, that restoration of normal mucus transport rates in CF HAE was achieved after CFTR delivery to 25% of surface epithelial cells. In vivo experimentation in appropriate models will be required to determine what level of mucus transport will afford clinical benefit to CF patients, but we predict that a future goal for corrective gene transfer to the CF human airways in vivo would attempt to target at least 25% of surface epithelial cells to achieve mucus transport rates comparable to those in non-CF airways.

The ciliated epithelium that lines the conducting airways of the lung normally functions to transport hydrated mucus secretions out of the airways to maintain respiratory sterility. Cystic fibrosis (CF) lung disease results from reduced airway surface hydration leading to decreased mucus clearance that precipitates bacterial infection and progressive obstructive lung disease. CF is a genetic disease, and the mutant protein is a chloride ion channel (CFTR) that normally regulates ion and fluid transport on the airway surface. Restoration of corrected CFTR function to the airway epithelium of CF patients by delivering a new CFTR gene to airway epithelial cells has long been envisioned as a therapeutic strategy for CF lung disease. Towards this goal, we use a novel viral vector to deliver CFTR to a culture model that represents the ciliated airway epithelium of CF patients and show that this strategy restores airway surface hydration and mucus transport to levels of that in non-CF individuals. This study demonstrates efficient and efficacious CFTR delivery to CF ciliated airway epithelium and that CFTR delivered to approximately 25% of the surface epithelial cells restores normal levels of airway surface hydration and mucus transport. These studies serve as a benchmark for the efficiency of CFTR gene delivery to CF airways for future CF gene therapy studies in vivo.

(Strept)avidin-displaying lentiviruses as versatile tools for targeting and dual imaging of gene delivery

Lentiviruses have shown great promise for human gene therapy. However, no optimal strategies are yet available for noninvasive imaging of virus biodistribution and subsequent transduction in vivo. We have developed a dual-imaging strategy based on avidin-biotin system allowing easy exchange of the surface ligand on HIV-derived lentivirus envelope. This was achieved by displaying avidin or streptavidin fused to the transmembrane anchor of vesicular stomatitis virus G protein on gp64-pseudotyped envelopes. Avidin and streptavidin were efficiently incorporated on virus particles, which consequently showed binding to biotin in ELISA. These vectors, conjugated to biotinylated radionuclides and engineered to express a ferritin transgene, enabled for the first-time dual imaging of virus biodistribution and transduction pattern by single-photon emission computed tomography and magnetic resonance imaging after stereotactic injection into rat brain. In addition, vector retargeting to cancer cells overexpressing CD46, epidermal growth factor and transferrin receptors using biotinylated ligands and antibodies was demonstrated in vitro. In conclusion, we have generated novel lentivirus vectors for noninvasive imaging and targeting of lentivirus-mediated gene delivery. This study suggests that these novel vectors could be applicable for the treatment of central nervous system disorders and cancer.

Luciferin detection after intranasal vector delivery is improved by intranasal rather than intraperitoneal luciferin administration

In vivo bioimaging of transgenic luciferase in the lung and nose is an expedient method by which to continually measure expression of this marker gene after gene transduction. Its substrate, luciferin, is typically injected into the peritoneal cavity before bioimaging. Here we demonstrate that, compared with intraperitoneal injection, intranasal instillation of luciferin confers approximately an order of magnitude increase in luciferase bioluminescence detection in both lung and nose. This effect was observed after administration of viral vectors based on adenovirus type 5, adeno-associated virus type 8, and gp64-pseudotyped HIV lentivirus and, to a lesser extent, after nonviral polyethylenimine (PEI)-DNA delivery. Detection increased relative to the concentration of luciferin; however, a standard concentration of 15 mg/ml was well beyond the saturation point. Compared with intraperitoneal injection, intranasal instillation yields about a 10-fold increase in sensitivity with an approximate 30-fold reduction in luciferin usage when bioimaging in the nasal and pulmonary airways of mice.

Gene transfer to the lung: lessons learned from more than 2 decades of CF gene therapy

Gene therapy is currently being developed for a wide range of acute and chronic lung diseases. The target cells, and to a degree the extra and intra-cellular barriers, are disease-specific and over the past decade the gene therapy community has recognized that no one vector is good for all applications, but that the gene transfer agent (GTA) has to be carefully matched to the specific disease target. Gene therapy is particularly attractive for diseases that currently do not have satisfactory treatment options and probably easier for monogenic disorders than for complex diseases. Cystic fibrosis (CF) fulfils these criteria and is, therefore, a good candidate for gene therapy-based treatment. This review will focus on CF as an example for lung gene therapy, but lessons learned may be applicable to other target diseases.

Involvement of glycosaminoglycans in vesicular stomatitis virus G glycoprotein pseudotyped lentiviral vector-mediated gene transfer into airway epithelial cells

BACKGROUND

The involvement of surface molecules in HIV-1-derived lentivirus (LV)-mediated transduction of airway epithelial cells has not been studied so far. The present study aimed to evaluate the role of glycosaminoglycans (GAGs) in gene transfer mediated by a third generation vesicular stomatitis virus G glycoprotein (VSV-G) pseudotyped LV vector in an in vitro model of polarized airway epithelial cells.

METHODS

Human bronchial (16HBE-S1) and tracheal (CFT1-C2) epithelial cells were grown either on plastic or on filters and transduced with the LV vector polypurine tract (PPT)-green fluoresecent protein (GFP). Zonula Occludens (ZO)-1, a marker of tight junction, and GAG localization were assessed by cytofluorimetry and confocal microscopy. Soluble GAGs and removal of cell surface GAGs were used to affect LV-mediated transduction.

RESULTS

Extensive optimization of experimental parameters (presence of polybrene during the infection, the incubation time in the presence of LV particles, period of time intercurring between infection and gene expression analysis) was carried out in plastic-adherent cells. Polybrene resulted to be cytotoxic and was not further used. In CFT1-C2 polarized cells, EGTA treatment determined a 20% decrease in transepithelial resistance, a diminished ZO-1 localization at the tight junction location and a 31% increase in GFP positive cells. Heparane sulfate was distributed evenly on the cell surface. Heparin and soluble chondroitin sulfate A and B inhibited LV-mediated transduction in a dose-dependent fashion. These results were confirmed upon enzymatic removal of GAGs from the cell surface.

CONCLUSIONS

Taken together, these results show that GAGs are involved in VSV-G LV transduction of airway epithelial cells.

Lentivirus vector can be readministered to nasal epithelia without blocking immune responses

For many envisioned applications of lentivirus vectors as tools in respiratory biology and therapeutic gene delivery, the efficiency of gene transfer must be improved. We previously demonstrated stable, persistent (>11 months) in vivo expression following a single application of a feline immunodeficiency virus (FIV)-based lentivirus vector (GP64-FIV) to murine nasal epithelia. Here we investigate the efficacy of repeated administration of lentivirus vectors to the airways. Using quantitative bioluminescent imaging, we found that consecutive daily dosing achieved a linear increase in gene expression and greatly increased the number of epithelial cells targeted. Surprisingly, reporter gene expression also increased additively following each of seven doses of FIV delivered over consecutive weeks (1 dose/week), without the development of systemic or local neutralizing antibodies. This approach enhanced expression of both reporter and therapeutic transgenes. Transduction efficiency achieved following a single dose of FIV expressing mouse erythropoietin was insufficient to increase hematocrit, whereas seven consecutive daily doses significantly increased hematocrit. These unexpected results contrast strikingly with findings reported for adenovirus vectors. Prolonged gene expression has been observed in vivo following a single dose of virus vector; however, depending on the application, repeated administration of vector may be necessary to achieve stable, therapeutic gene expression.

Lentiviral transduction of the murine lung provides efficient pseudotype and developmental stage-dependent cell-specific transgene expression

Gene transfer for cystic fibrosis (CF) airway disease has been hampered by the lung's innate refractivity to pathogen infection. We hypothesized that early intervention with an integrating gene transfer vector capable of transducing the lung via the lumen may be a successful therapeutic approach. An HIV-based lentiviral vector pseudotyped with the baculovirus gp64 envelope was applied to the fetal, neonatal or adult airways. Fetal intra-amniotic administration resulted in transduction of approximately 14% of airway epithelial cells, including both ciliated and non-ciliated epithelia of the upper, mid and lower airways; there was negligible alveolar or nasal transduction. Following neonatal intra-nasal administration we observed significant transduction of the airway epithelium (approximately 11%), although mainly in the distal lung, and substantial alveolar transduction. This expression was still detectable at 1 year after application. In the adult, the majority of transduction was restricted to the alveoli. In contrast, vesicular stomatitis virus glycoprotein pseudotyped virus transduced only alveoli after adult and neonatal application and no transduction was observed after fetal administration. Repeat administration did not increase transduction levels of the conducting airway epithelia. These data demonstrate that application at early developmental stages in conjunction with an appropriately pseudotyped virus provides efficient, high-level transgene expression in the murine lung. This may provide a modality for treatment for lung disease in CF.

Lentiviruses inefficiently incorporate human parainfluenza type 3 envelope proteins

We have previously shown that the envelope glycoproteins of human parainfluenza type 3 (HPIV3), F and HN, are able to pseudotype lentiviruses, but the titers of these viruses are too low for use in clinical gene transfer. In this study we investigated the cause of these low titers. We compared the mRNA and protein expression levels of HN and F in transfected cells and in cells infected with wild-type HPIV3. Transfected cells contained similar levels of HN and F cytosolic mRNA, but fewer cell-surface HN and F proteins (3.8- and 1.3-fold less, respectively), than cells infected with wild-type HPIV3. To increase expression of HN in transfected cells, we codon-optimized HN and used it to transfect lentivirus producer cells. Cell surface expression of HN, as well as the amount of HN incorporated into virus particles, increased two- to threefold. Virus titers increased 1.2- to 6.4-fold, and the transduction efficiency of polarized MDCK cells via their apical surfaces increased 1.4-fold. Interestingly, even though codon optimization improved the expression levels of HN and virus titers, we found that HPIV3 pseudotyped viruses contained about 14-fold fewer envelope proteins than lentiviruses pseudotyped with the amphotropic envelope protein. Taken together, our findings suggest that titers are low, not because virus producer cells express levels of HPIV3 envelope proteins that are too low, but because too few of these proteins are incorporated by the lentiviruses for them to be able to efficiently transduce cells.

Identification of a GP64 subdomain involved in receptor binding by budded virions of the baculovirus Autographica californica multicapsid nucleopolyhedrovirus

Enveloped virus entry into host cells is typically initiated by an interaction between a viral envelope glycoprotein and a host cell receptor. For budded virions of the baculovirus Autographa californica multicapsid nucleopolyhedrovirus, the envelope glycoprotein GP64 is involved in host cell receptor binding, and GP64 is sufficient to mediate low-pH-triggered membrane fusion. To better define the role of GP64 in receptor binding, we generated and characterized a panel of antisera against subdomains of GP64. Eight subdomain-specific antisera were generated, and their reactivities with GP64 proteins and neutralization of virus infectivity and binding were examined. Antibodies directed against the N-terminal region of GP64 (amino acids 21 to 159) showed strong neutralization of infectivity and effectively inhibited binding of (35)S-labeled budded virions to Sf9 cells. In addition, we generated virions displaying truncated GP64 constructs. A construct displaying the N-terminal 274 amino acids (residues 21 to 294) of the ectodomain was sufficient to mediate virion binding. Additional studies of antisera directed against small subdomains revealed that an antiserum against a 40-amino-acid region (residues 121 to 160) neutralized virus infectivity. Site-directed mutagenesis was subsequently used for functional analysis of that region. Recombinant viruses expressing GP64 proteins with single amino acid substitutions within amino acids 120 to 124 and 142 to 148 replicated to high titers, suggesting that those amino acids were not critical for receptor binding or other important GP64 functions. In contrast, GP64 proteins with single amino acid substitutions of residues 153 and 156 were unable to substitute for wild-type GP64 and did not rescue a gp64 knockout virus. Further analysis showed that these substitutions substantially reduced binding of recombinant virus to Sf9 cells. Thus, the amino acid region from positions 21 to 159 was identified as a putative receptor binding domain, and amino acids 153 and 156 appear to be important for receptor binding.

Enhanced gene expression conferred by stepwise modification of a nonprimate lentiviral vector

The practical application of gene transfer as a treatment for genetic diseases such as cystic fibrosis or hemophilia has been hindered, in part, by low efficiencies of vector delivery and transgene expression. We demonstrated that a feline immunodeficiency virus (FIV)-based lentiviral vector pseudotyped with the envelope glycoprotein from the baculovirus Autographa californica (GP64) efficiently transduces and persistently expresses a reporter gene in respiratory epithelium in the absence of agents that disrupt cellular tight junction integrity. GP64-pseudotyped FIV also efficiently transduced murine hepatocytes after tail vein delivery. To improve the FIV-based vector, we tested the contribution of a series of modifications to luciferase expression in vitro and in vivo. These modifications included the addition of spleen necrosis virus U5 (SNV U5) and mutation of the major splice donor and gag start codon located in the packaging region of the FIV transgene plasmid. After vector modification, we observed significantly enhanced expression of luciferase in respiratory epithelia after nasal application and in the liver after tail vein delivery. In addition, we observed significantly enhanced human factor VIII production after tail vein delivery. These sequential modifications provide an improved FIV lentivirus platform for gene therapy applications and may be applied to other retroviral vectors.

Baculovirus vector for gene delivery and vaccine development

The baculovirus Autographa californica multiple nucleopolyhedrovirus has been widely used not only to acheive a high level of foreign gene expression in insect cells, but also for efficient gene transduction into mammalian cells. Recombinant and pseudotyped baculoviruses possessing chimeric or foreign ligands have been constructed to improve the efficiency of gene transduction and to confer specificity for gene delivery into mammalian cells, respectively. Baculoviral DNA CpG motifs induce proinflammatory cytokines through a Toll-like receptor (TLR9)/MyD88-dependent signaling pathway. Other baculovirus components produce type I interferons via a TLR-independent pathway. Baculovirus exhibits a strong adjuvant property and recombinant baculoviruses encoding microbial antigens elicit antibodies to the antigens and provide protective immunity in mice. This review deals with recent progress in the application of baculovirus vectors to gene delivery and vaccine development, and discusses the future prospects of baculovirus vectors.

In vivo imaging of gene transfer to the respiratory tract

Imaging of in vivo gene expression using luciferase expression in various organs has been used for several years. In contrast to other organs, in vivo imaging of the lung, particularly after non-viral gene transfer has not been extensively studied. The aim of this study was to address several questions: (1) Does in vivo light emission correlate with standard tissue homogenate-based luciferase detection in a dose-dependent manner? Recombinant Sendai virus (SeV) transduces airway epithelial cells very efficiently and was used to address this question, (2) Is the sensitivity of the assay sufficient to detect non-viral gene transfer? We treated mice with SeV-Lux vector using our standard "sniffing" protocol, a method that predominantly results in lung deposition. Dose-related in vivo light emission was visible in all animals. Importantly, there was a significant correlation (r>0.90, p<0.0001) between the in vivo and ex vivo assays in both the left and right lung. We next transfected the nasal epithelium via nasal perfusion or the lungs ("sniffing") of mice with a luciferase plasmid (pCIKLux) complexed to the cationic lipid GL67 (n=25-27/group) and imaged luciferase expression in vivo 24h after transfection. Gene expression was detectable in both organs. Correlation between the in vivo and ex vivo assays was significant (r=0.52, p<0.005) in the left, but not the right lung. The correlation in the nose was weaker (r=0.45, p<0.05). To our knowledge these studies show for the first time that this non-invasive method of assessing pulmonary gene transfer is viable for evaluating non-viral gene transfer agents.

Ion-exchange membrane chromatography method for rapid and efficient purification of recombinant baculovirus and baculovirus gp64 protein

Significant progress in the application of baculoviral vectors for gene delivery into mammalian cells calls for the development of powerful methods for virus purification and concentration. We report here a novel and efficient method based on membrane chromatography to prepare baculoviral stocks. On a strong cation-exchange membrane unit, baculovirus in insect cell culture supernatants was captured at a flow rate of 3 ml/min and efficiently eluted at the same flow rate with a physiological buffer containing 150 mM NaCl as a desorption reagent. The procedure allowed for a final recovery of 78% of infective viral particles from the original supernatant and 30-fold enrichment. The high purity of the viral preparation was demonstrated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. Baculovirus gp64 proteins could be purified by the same method, indicating the importance of the protein in mediating the binding of baculovirus to the cation-exchange membrane. The method developed should be suitable for preparing baculoviral stocks, and probably other gp64-pseudotyped viral vectors, for gene therapy applications.

Gene delivery to airway epithelial cells in vivo: a direct comparison of apical and basolateral transduction strategies using pseudotyped lentivirus vectors

Lentivirus vectors are being investigated as gene delivery vehicles for cystic fibrosis airway gene therapy. Vesicular stomatitis virus G glycoprotein (VSV-G)-pseudotyped vectors transduce airway epithelia via receptors that are located predominantly on the basolateral surface of the airway epithelium. Effective transduction with VSV-G-pseudotyped vectors requires the use of a pre-treatment that disrupts epithelial tight junctions, allowing access to these basolateral receptors. In contrast, it has been reported that apically targeted lentiviral vectors allow efficient gene transfer in the absence of any pre-treatment. In a direct comparison of transduction by a VSV-G-pseudotyped vector, in combination with a pre-treatment with lysophosphatidylcholine (LPC), and the same vector pseudotyped with the apically targeted baculovirus GP64 envelope (without any pre-treatment), the GP64 vector was found to be significantly less efficient. However, when a pre-treatment with LPC was used the level of transduction with the GP64-pseudotyped lentiviral vector was not significantly different to that resulting from the VSV-G-pseudotyped vector. The cell types transduced with each vector were essentially the same, with the majority of cells transduced being respiratory (ciliated cells). However, unlike the VSV-G-pseudotyped vector, which results in persisting gene expression, transduction with the GP64-pseudotyped vector resulted in gene expression that declined to undetectable levels over six months, whether or not an LPC pre-treatment was used.

Development of lentiviral vectors with regulated respiratory epithelial expression in vivo

Development of gene transfer vectors with regulated, lung-specific expression will be a useful tool for studying lung biology and developing gene therapies. In this study we constructed a series of lentiviral vectors with regulatory elements predicted to produce lung-specific transgene expression: the surfactant protein C promoter (SPC) for alveolar epithelial type II cell (AECII) expression, the Clara cell 10-kD protein (CC10) for Clara cell expression in the airway, and the Jaagskiete sheep retrovirus (JSRV) promoter for expression in both cell types. Transgene expression from the SPC and CC10 vectors was restricted to AECII and Clara cell lines, respectively, while expression from the JSRV vector was observed in multiple respiratory and nonrespiratory cell types. After intratracheal delivery of lentivector supernatant to mice, transgene expression was observed in AECII from the SPC lentivector, and in Clara cells from the CC10-promoted lentivector. Transgene expression was not detected in nonrespiratory tissues after intravenous delivery of CC10 and SPC lentiviral vectors to murine recipients. In summary, incorporation of genomic regulatory elements from the SPC and CC10 genes resulted in respiratory specific transgene expression in vitro and in vivo. These vectors will provide a useful tool for the study of lung biology and the development of gene therapies for lung disorders.

The stability of human respiratory syncytial virus is enhanced by incorporation of the baculovirus GP64 protein

Current efforts to develop a vaccine against human respiratory syncytial virus (HRSV) are focused on live attenuated strains. However, the unstable nature of HRSV is a major challenge for the preparation, storage and distribution of live vaccine candidates. We report here that the stability of HRSV can be improved by incorporation of the GP64 glycoprotein from baculovirus Autographa californica multiple nucleopolyhedrovirus. GP64 was incorporated in place of or in addition to the homologous HRSV glycoproteins and was either expressed from the HRSV genome or provided by propagating the virus in a Vero cell line constitutively expressing GP64 (Vbac cells). The infectivity of the different virus stocks was monitored after storage at 4 degrees, 22 degrees or 37 degrees C, over a period of 8 weeks. The results showed that the infectivity of HRSV could be stabilized by up to 10,000-fold by the GP64 protein, when stored at 22 degrees C for 6 weeks. This approach for stabilizing live HRSV may be important for vaccine development and may also prove useful for stabilizing other enveloped viruses.

SPECT/CT imaging of baculovirus biodistribution in rat

Non-invasive imaging provides essential information regarding the biodistribution of gene therapy vectors and it can also be used for the development of targeted vectors. In this study, we have utilized micro Single-photon emission computed tomography to visualize biodistribution of a (99m)Tc-polylys-ser-DTPA-biotin-labelled avidin-displaying baculovirus, Baavi, after intrafemoral (i.f.), intraperitoneal (i.p.), intramuscular (i.m.) and intracerebroventricular (i.c.v.) administration. The imaging results suggest that the virus can spread via the lymphatic network after different administration routes, also showing accumulation in the nasal area after systemic administration. Extensive expression in the kidneys and spleen was seen after i.p. administration, which was confirmed by reverse transcriptase-polymerase chain reaction and immunohistochemistry. Additionally, transduction of kidneys was seen with i.m. and i.f. administrations. We conclude that baculovirus may be beneficial for the treatment of kidney diseases after i.p. administration route.

Viral Vector–mediated and Cell-based Therapies for Treatment of Cystic Fibrosis

Gene and cell-based therapies are considered to be potentially powerful new approaches for the management of cystic fibrosis (CF) lung disease. Despite tremendous efforts that have been made, especially in studies to understand the obstacles to gene delivery, major challenges to the application of these approaches remain to be solved. This article will review the advancements made and challenges remaining in the development of viral vector-mediated and cell-based approaches to treat patients with CF.