EGTA enhancement of adenovirus-mediated gene transfer to mouse tracheal epithelium in vivo

Effective viral-mediated lung gene therapy: is airway surface preparation necessary?

Gene-based therapeutics are actively being pursued for the treatment of lung diseases. While promising advances have been made over the last decades, the absence of clinically available lung-directed genetic therapies highlights the difficulties associated with this effort. Largely, progress has been hindered by the presence of inherent physical and physiological airway barriers that significantly reduce the efficacy of gene transfer. These barriers include surface mucus, mucociliary action, cell-to-cell tight junctions, and the basolateral cell membrane location of viral receptors for many commonly used gene vectors. Accordingly, airway surface preparation methods have been developed to disrupt these barriers, creating a more conducive environment for gene uptake into the target airway cells. The two major approaches have been chemical and physical methods. Both have proven effective for increasing viral-mediated gene transfer pre-clinically, although with variable effect depending on the specific strategy employed. While such methods have been explored extensively in experimental settings, they have not been used clinically. This review covers the airway surface preparation strategies reported in the literature, the advantages and disadvantages of each method, as well as a discussion about applying this concept in the clinic.

Breaching the Delivery Barrier: Chemical and Physical Airway Epithelium Disruption Strategies for Enhancing Lentiviral-Mediated Gene Therapy

The lungs have evolved complex physical, biological and immunological defences to prevent foreign material from entering the airway epithelial cells. These mechanisms can also affect both viral and non-viral gene transfer agents, and significantly diminish the effectiveness of airway gene-addition therapies. One strategy to overcome the physical barrier properties of the airway is to transiently disturb the integrity of the epithelium prior to delivery of the gene transfer vector. In this study, chemical (lysophosphatidylcholine, LPC) and physical epithelium disruption using wire abrasion were compared for their ability to improve airway-based lentiviral (LV) vector mediated transduction and reporter gene expression in rats. When luciferase expression was assessed at 1-week post LV delivery, LPC airway conditioning significantly enhanced gene expression levels in rat lungs, while a long-term assessment in a separate cohort of rats at 12 months revealed that LPC conditioning did not improve gene expression longevity. In rats receiving physical perturbation to the trachea prior to gene delivery, significantly higher LacZ gene expression levels were found when compared to LPC-conditioned or LV-only control rats when evaluated 1-week post gene transfer. This proof-of-principle study has shown that airway epithelial disruption strategies based on physical perturbation substantially enhanced LV-mediated airway gene transfer in the trachea.

Widespread airway distribution and short-term phenotypic correction of cystic fibrosis pigs following aerosol delivery of piggyBac/adenovirus

Cystic fibrosis (CF) is a common genetic disease caused by mutations in the gene coding for cystic fibrosis transmembrane conductance regulator (CFTR). Although CF affects multiple organ systems, chronic bacterial infections and inflammation in the lung are the leading causes of morbidity and mortality in people with CF. Complementation with a functional CFTR gene repairs this defect, regardless of the disease-causing mutation. In this study, we used a gene delivery system termed piggyBac/adenovirus (Ad), which combines the delivery efficiency of an adenoviral-based vector with the persistent expression of a DNA transposon-based vector. We aerosolized piggyBac/Ad to the airways of pigs and observed widespread pulmonary distribution of vector. We quantified the regional distribution in the airways and observed transduction of large and small airway epithelial cells of non-CF pigs, with ∼30–50% of surface epithelial cells positive for GFP. We transduced multiple cell types including ciliated, non-ciliated, basal, and submucosal gland cells. In addition, we phenotypically corrected CF pigs following delivery of piggyBac/Ad expressing CFTR as measured by anion channel activity, airway surface liquid pH, and bacterial killing ability. Combining an integrating DNA transposon with adenoviral vector delivery is an efficient method for achieving functional CFTR correction from a single vector administration.

Cystic Fibrosis Gene Therapy: Looking Back, Looking Forward

Cystic fibrosis (CF) is an autosomal recessive disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene that encodes a cAMP-regulated anion channel. Although CF is a multi-organ system disease, most people with CF die of progressive lung disease that begins early in childhood and is characterized by chronic bacterial infection and inflammation. Nearly 90% of people with CF have at least one copy of the ΔF508 mutation, but there are hundreds of CFTR mutations that result in a range of disease severities. A CFTR gene replacement approach would be efficacious regardless of the disease-causing mutation. After the discovery of the CFTR gene in 1989, the in vitro proof-of-concept for gene therapy for CF was quickly established in 1990. In 1993, the first of many gene therapy clinical trials attempted to rescue the CF defect in airway epithelia. Despite the initial enthusiasm, there is still no FDA-approved gene therapy for CF. Here we discuss the history of CF gene therapy, from the discovery of the CFTR gene to current state-of-the-art gene delivery vector designs. While implementation of CF gene therapy has proven more challenging than initially envisioned; thanks to continued innovation, it may yet become a reality.

Modeling pulmonary alveolar microlithiasis by epithelial deletion of the Npt2b sodium phosphate cotransporter reveals putative biomarkers and strategies for treatment

Pulmonary alveolar microlithiasis (PAM) is a rare, autosomal recessive lung disorder associated with progressive accumulation of calcium phosphate microliths. Inactivating mutations in SLC34A2, which encodes the NPT2b sodium-dependent phosphate cotransporter, has been proposed as a cause of PAM. We show that epithelial deletion of Npt2b in mice results in a progressive pulmonary process characterized by diffuse alveolar microlith accumulation, radiographic opacification, restrictive physiology, inflammation, fibrosis, and an unexpected alveolar phospholipidosis. Cytokine and surfactant protein elevations in the alveolar lavage and serum of PAM mice and confirmed in serum from PAM patients identify serum MCP-1 (monocyte chemotactic protein 1) and SP-D (surfactant protein D) as potential biomarkers. Microliths introduced by adoptive transfer into the lungs of wild-type mice produce marked macrophage-rich inflammation and elevation of serum MCP-1 that peaks at 1 week and resolves at 1 month, concomitant with clearance of stones. Microliths isolated by bronchoalveolar lavage readily dissolve in EDTA, and therapeutic whole-lung EDTA lavage reduces the burden of stones in the lungs. A low-phosphate diet prevents microlith formation in young animals and reduces lung injury on the basis of reduction in serum SP-D. The burden of pulmonary calcium deposits in established PAM is also diminished within 4 weeks by a low-phosphate diet challenge. These data support a causative role for Npt2b in the pathogenesis of PAM and the use of the PAM mouse model as a preclinical platform for the development of biomarkers and therapeutic strategies.

Entry of PIP3-containing polyplexes into MDCK epithelial cells by local apical-basal polarity reversal

The polarized architecture of epithelium presents a barrier to therapeutic drug/gene carriers, which is mainly due to a limited (apical) internalization of the carrier systems. The bacterium Pseudomonas aeruginosa invades epithelial cells by inducing production of apical phosphatidylinositol-3, 4, 5-triphosphate (PIP3), which results in the recruitment of basolateral receptors to the apical membrane. Since basolateral receptors are known receptors for gene delivery vectors, apical PIP3 may improve the internalization of such vectors into epithelial cells. PIP3 and nucleic acids were complexed by the cationic polymer polyethylenimine (PEI), forming PEI/PIP3 polyplexes. PEI/PIP3 polyplexes showed enhanced internalization compared to PEI polyplexes in polarized MDCK cells, while basolateral receptors were found to redistribute and colocalize with PEI/PIP3 polyplexes at the apical membrane. Following their uptake via endocytosis, PEI/PIP3 polyplexes showed efficient endosomal escape. The effectiveness of the PIP3-containing delivery system to generate a physiological effect was demonstrated by an essentially complete knock down of GFP expression in 30% of GFP-expressing MDCK cells following anti-GFP siRNA delivery. Here, we demonstrate that polyplexes can be successfully modified to mimic epithelial entry mechanisms used by Pseudomonas aeruginosa. These findings encourage the development of pathogen-inspired drug delivery systems to improve drug/gene delivery into and across tissue barriers.

Lung gene therapy-How to capture illumination from the light already present in the tunnel

Gene therapy has been considered as the most ideal medical intervention for genetic diseases because it is intended to target the cause of diseases instead of disease symptoms. Availability of techniques for identification of genetic mutations and for in vitro manipulation of genes makes it practical and attractive. After the initial hype in 1990s and later disappointments in clinical trials for more than a decade, light has finally come into the tunnel in recent years, especially in the field of eye gene therapy where it has taken big strides. Clinical trials in gene therapy for retinal degenerative diseases such as Leber's congenital amaurosis (LCA) and choroideremia demonstrated clear therapeutic efficacies without apparent side effects. Although these successful examples are still rare and sporadic in the field, they provide the proof of concept for harnessing the power of gene therapy to treat genetic diseases and to modernize our medication. In addition, those success stories illuminate the path for the development of gene therapy treating other genetic diseases. Because of the differences in target organs and cells, distinct barriers to gene delivery exist in gene therapy for each genetic disease. It is not feasible for authors to review the current development in the entire field. Thus, in this article, we will focus on what we can learn from the current success in gene therapy for retinal degenerative diseases to speed up the gene therapy development for lung diseases, such as cystic fibrosis.

Gene therapy: light is finally in the tunnel

After two decades of ups and downs, gene therapy has recently achieved a milestone in treating patients with Leber's congenital amaurosis (LCA). LCA is a group of inherited blinding diseases with retinal degeneration and severe vision loss in early infancy. Mutations in several genes, including RPE65, cause the disease. Using adeno-associated virus as a vector, three independent teams of investigators have recently shown that RPE65 can be delivered to retinal pigment epithelial cells of LCA patients by subretinal injections resulting in clinical benefits without side effects. However, considering the whole field of gene therapy, there are still major obstacles to clinical applications for other diseases. These obstacles include innate and immune barriers to vector delivery, toxicity of vectors and the lack of sustained therapeutic gene expression. Therefore, new strategies are needed to overcome these hurdles for achieving safe and effective gene therapy. In this article, we shall review the major advancements over the past two decades and, using lung gene therapy as an example, discuss the current obstacles and possible solutions to provide a roadmap for future gene therapy research.

Perfluorochemical liquid-adenovirus suspensions enhance gene delivery to the distal lung

WE COMPARED LUNG DELIVERY METHODS OF RECOMBINANT ADENOVIRUS (RAD): (1) rAd suspended in saline, (2) rAd suspended in saline followed by a pulse-chase of a perfluorochemical (PFC) liquid mixture, and (3) a PFC-rAd suspension. Cell uptake, distribution, and temporal expression of rAd were examined using A549 cells, a murine model using luciferase bioluminescence, and histological analyses. Relative to saline, a 4X increase in transduction efficiency was observed in A549 cells exposed to PFC-rAd for 2-4 h. rAd transgene expression was improved in alveolar epithelial cells, and the level and distribution of luciferase expression when delivered in PFC-rAd suspensions consistently peaked at 24 h. These results demonstrate that PFC-rAd suspensions improve distribution and enhance rAd-mediated gene expression which has important implications in improving lung function by gene therapy.

Anionic liposomes enhance and prolong adenovirus-mediated gene expression in airway epithelia in vitro and in vivo

Adenoviral vector mediated gene therapy has received extensive attention in airway disease treatment. However, the lack of the requisite coxsackie-adenovirus receptor (CAR) on the apical surface of airway epithelium and the host immune response to adenoviruses limit their in vivo application. In our study, we developed for the first time a novel formulation composed of anionic liposomes and adenoviruses (AL-Ad5) using a calcium-induced phase change method. The obtained formulation was employed to enhance the transduction efficiency of airway gene delivery. Our results indicated that primary cultured airway epithelial cells infected by AL-Ad5 displayed higher LacZ gene expression compared to naked adenovirus. Importantly, AL-Ad5 significantly improved and prolonged LacZ gene expression in murine airway tissues when delivered in vivo by intratracheal instillation. Additionally, it was found that anionic liposomes provided immunoprotection to the adenovirus from neutralizing antibody, thus slowing down the elimination of Ad5 particles meanwhile reducing the inflammatory reaction caused by the Ad5 vector. These results suggested that the combination of anionic liposomes with adenovirus may be a useful strategy to deliver therapeutic genes into the airway epithelia and is promising in clinical application.

Enhanced expression of adenovirus encoding rhEPO assisted by BAPTA

Infection efficiency is the key issue for gene delivery using adenovirus vector and usually unsatisfactory. In this study, recombinant adenoviruses encoding recombinant human EPO were prepared using the Adeasy system, and injected into the mammary gland of goats via the teat canal. BAPTA was used to treat the mammary gland to facilitate adenoviruses infection compared with EGTA. Milk serum was collected from the infected mammary gland and characterized by ELISAs and Western blotting. Expression level of rhEPO from the group treated by BAPTA was higher than that treated by EGTA.

Gene therapy with helper-dependent adenoviral vectors: current advances and future perspectives

Recombinant Adenoviral vectors represent one of the best gene transfer platforms due to their ability to efficiently transduce a wide range of quiescent and proliferating cell types from various tissues and species. The activation of an adaptive immune response against the transduced cells is one of the major drawbacks of first generation Adenovirus vectors and has been overcome by the latest generation of recombinant Adenovirus, the Helper-Dependent Adenoviral (HDAd) vectors. HDAds have innovative features including the complete absence of viral coding sequences and the ability to mediate high level transgene expression with negligible chronic toxicity. This review summarizes the many aspects of HDAd biology and structure with a major focus on in vivo gene therapy application and with an emphasis on the unsolved issues that these vectors still presents toward clinical application.

Efficient, specific and targeted delivery of genes to the lung

Many inherited and acquired pulmonary disorders without satisfactory therapies may be amenable to gene therapy. Despite numerous advances, efficient delivery and expression of the therapeutic transgene at physiological levels for phenotypic correction of disease has proved elusive. This article focuses on various strategies aimed at achieving targeted delivery to the lungs. Both physical methods and biological targeting have been successfully applied in various gene delivery systems. Targeting of different cell types has been achieved by pseudotyping of viral vectors with capsids from different serotypes and modification of nonviral vectors with targeting ligands. Both classes of vectors are discussed with respect to their gene delivery and expression efficiencies, longevity of expression and immunogenicity. Moreover, gene therapy clinical trials for different lung diseases are discussed.

Anionic liposomes increase the efficiency of adenovirus-mediated gene transfer to coxsackie-adenovirus receptor deficient cells

Despite remarkable progress in the research of both viral and nonviral gene delivery vectors, the drawbacks in each delivery system have limited their clinical applications. Therefore, one of the concepts for developing novel vectors is to overcome the limitations of individual vectors by combining them. In the current study, adenoviral vectors were formulated with anionic liposomes to protect them from neutralizing antibodies and to improve their transduction efficiency in Coxsackievirus-adenovirus receptor (CAR) deficient cells. A calcium-induced phase change method was applied to encapsulate adenovirus 5 (Ad5) into anionic liposomes to formulate the complexes of Ad5 and anionic liposomes (Ad5-AL). Meanwhile, the complexes of Ad5 and cationic liposomes (Ad5-CL) were also prepared as controls. LacZ gene expression in CAR overexpressing cells (A549) and CAR deficient cells (CHO and MDCK) was measured by either qualitative or quantitative detection. Confocal laser scanning microscopy was performed to determine intracellular location of Ad5 after their infection. Human sera with a high titer of antiadenovirus antibody were used to assess the neutralizing antibody protection ability of the complexed vectors. Accompanying the enhanced gene expression, a high ability to introduce Ad5 into cytoplasm and nucleus mediated by Ad5-AL was also observed in CAR deficient cells. Additionally, antibody neutralizing assay indicated that neutralizing serum inhibited naked Ad5 and Ad5-CL at rather higher dilution than Ad5-AL, which demonstrated Ad5-AL was more capable of protecting Ad5 from neutralizing than Ad5-CL. In conclusion, anionic liposomes prepared by the calcium-induced phase change method could significantly enhance the transduction ability of Ad5 in CAR deficient cells.

Sendai virus-mediated CFTR gene transfer to the airway epithelium

The potential for gene therapy to be an effective treatment for cystic fibrosis has been hampered by the limited gene transfer efficiency of current vectors. We have shown that recombinant Sendai virus (SeV) is highly efficient in mediating gene transfer to differentiated airway epithelial cells, because of its capacity to overcome the intra- and extracellular barriers known to limit gene delivery. Here, we have identified a novel method to allow the cystic fibrosis transmembrane conductance regulator (CFTR) cDNA sequence to be inserted within SeV (SeV-CFTR). Following in vitro transduction with SeV-CFTR, a chloride-selective current was observed using whole-cell and single-channel patch-clamp techniques. SeV-CFTR administration to the nasal epithelium of cystic fibrosis (CF) mice (Cftr(G551D) and Cftr(tm1Unc)TgN(FABPCFTR)#Jaw mice) led to partial correction of the CF chloride transport defect. In addition, when compared to a SeV control vector, a higher degree of inflammation and epithelial damage was found in the nasal epithelium of mice treated with SeV-CFTR. Second-generation transmission-incompetent F-deleted SeV-CFTR led to similar correction of the CF chloride transport defect in vivo as first-generation transmission-competent vectors. Further modifications to the vector or the host may make it easier to translate these studies into clinical trials of cystic fibrosis.

Novel Therapies for the Treatment of Cystic Fibrosis: New Developments in Gene and Stem Cell Therapy

Cystic fibrosis (CF) was one of the first target diseases for lung gene therapy. Studies of lung gene transfer for CF have provided many insights into the necessary components of successful gene therapy for lung diseases. Many advancements have been achieved with promising results in vitro and in small animal models. However, studies in primate models and patients have been discouraging despite a large number of clinical trials. This reflects a number of obstacles to successful, sustained, and repeatable gene transfer in the lung. Cell-based therapy with embryonic stem cells and adult stem cells (bone marrow or cord blood), have been investigated recently and may provide a viable therapeutic approach in the future. In this article, the authors review CF pathophysiology with a focus on specific targets in the lung epithelium for gene transfer and summarize the current status and future directions of gene- and cell-based therapies.

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.

Using magnetic forces to enhance non-viral gene transfer to airway epithelium in vivo

We have assessed whether magnetic forces (magnetofection) can enhance non-viral gene transfer to the airways. TransMAG(PEI), a superparamagnetic particle was coupled to Lipofectamine 2000 or cationic lipid 67 (GL67)/plasmid DNA (pDNA) liposome complexes. In vitro transfection with these formulations resulted in approximately 300- and 30-fold increase in reporter gene expression, respectively, after exposure to a magnetic field, but only at suboptimal pDNA concentrations. Because GL67 has been formulated for in vivo use, we next assessed TransMAG(PEI) in the murine nasal epithelium in vivo, and compared this to naked pDNA. At the concentrations required for in vivo experiments, precipitation of magnetic complexes was seen. After extensive optimization, addition of non-precipitated magnetic particles resulted in approximately seven- and 90-fold decrease in gene expression for naked pDNA and GL67/pDNA liposome complexes, respectively, compared to non-magnetic particles. Thus, whereas exposure to a magnetic field improved in vitro transfection efficiency, translation to the in vivo setting remains difficult.

Activators of viral gene expression in polarized epithelial monolayers identified by rapid-throughput drug screening

Epithelial polarity and tight junction formation limit the ability of adenovirus, retrovirus and adeno-associated virus (AAV) to deliver and express virally encoded genes. Using an extended half-life luciferase assay and high-throughput luminometry, we screened 23 000 compounds and natural product extracts as potentiators to overcome this barrier. Seven strong activators were discovered (up to several hundred fold above control) and two of these exhibited spectrum of activity in multiple cell types (HeLa (human cervical carcinoma), cystic fibrosis bronchial epithelial (human bronchial), HT29 (human colonic carcinoma), Calu3 (airway serous glandular)). Enhanced transduction by unrelated gene transfer vectors (adenovirus, lentivirus, AAV, liposomal) was also observed. These results establish a strategy for identifying compounds that improve viral gene transfer to resistant cell types, and provide new tools for examining epithelial defense against viral infection. The compounds should have broad usefulness in experimental therapies for cancer and genetic diseases.

Factors influencing adenovirus-mediated airway transduction in fetal mice

Intra-amniotic injection of adenovirus allows transduction of the fetal airways following natural fetal breathing movements. This administration method is promising for use in gene therapy for cystic fibrosis and other diseases for which the main target for exogenous gene expression is the lung. Here we have investigated factors that may affect the efficacy of gene transfer to the murine fetal lung. We examined marker compound distribution and transgene expression (from a first-generation adenoviral vector) at different stages of development. This demonstrated that fetal breathing movements at 15-16 days of gestation are of sufficient intensity to carry marker/vector into the fetal lungs. These movements can be significantly stimulated by the combination of intra-amniotic theophylline administration and postoperative exposure of the dam to elevated CO(2) levels. However, the most important factor for efficient and consistent pulmonary transgene delivery is the dose of adenoviral vector used, as both the degree of transduction and the percentage of lungs transduced increases with escalating viral dose.

Specific modulation of airway epithelial tight junctions by apical application of an occludin peptide

Tight junctions are directly involved in regulating the passage of ions and macromolecules (gate functions) in epithelial and endothelial cells. The modulation of these gate functions to transiently regulate the paracellular permeability of large solutes and ions could increase the delivery of pharmacological agents or gene transfer vectors. To reduce the inflammatory responses caused by tight junction-regulating agents, alternative strategies directly targeting specific tight junction proteins could prove to be less toxic to airway epithelia. The apical delivery of peptides corresponding to the first extracellular loop of occludin to transiently modulate apical paracellular flux has been demonstrated in intestinal epithelia. We hypothesized that apical application of these occludin peptides could similarly modulate tight junction permeability in airway epithelia. Thus, we investigated the effects of apically applied occludin peptide on the paracellular permeability of molecular tracers and viral vectors in well differentiated human airway epithelial cells. The effects of occludin peptide on cellular toxicity, tight junction protein expression and localization, and membrane integrity were also assessed. Our data showed that apically applied occludin peptide significantly reduced transepithelial resistance in airway epithelia and altered tight junction permeability in a concentration-dependent manner. These alterations enhanced the paracellular flux of dextrans as well as gene transfer vectors. The occludin peptide redistributed occludin but did not alter the expression or distribution of ZO-1, claudin-1, or claudin-4. These data suggest that specific targeting of occludin could be a better-suited alternative strategy for tight junction modulation in airway epithelial cells compared with current agents that modulate tight junctions.

Aerosolized nanogram quantities of plasmid DNA mediate highly efficient gene delivery to mouse airway epithelium

The lung is an important target of gene therapeutic interventions. In contrast to intratracheal instillation, inhalation would be the most practical route of administration in clinical applications. Here we show that aerosolized nanogram quantities of pDNA complexed to PEI (350 ng) yielded transfection levels 15-fold higher than a 140-fold higher dose (50 microg) of the same vector applied directly to the lungs of mice via intratracheal intubation. An important efficacy parameter is the osmolarity of the aerosol and not biophysical properties of the nebulized vector. Vectors formulated and nebulized in hypoosmotic distilled water yielded 57- and 185-fold higher expression levels than those in isotonic 5% glucose or Hepes-buffered saline, respectively. Pretreatment of mice with nebulized indomethacin, which prevents water-induced airway alteration, resulted in lower gene expression, whereas pretreatment with EGTA or polidocanol, which modulate tight-junction activity, had no effect. These results, together with histological analysis of regional lung deposition and gene expression, suggest that a temporary water-induced hypoosmotic shock permeabilizes the epithelium sufficiently to allow vector uptake. The so far observed inefficiency of nonviral gene delivery to the airways may be the result of an inappropriate method of vector administration.

Delivery systems for pulmonary gene therapy

Delivery of therapeutic genes to the lungs is an attractive strategy to correct a variety of pulmonary dysfunctions such as cystic fibrosis, alpha-1 antitrypsin deficiency, pulmonary hypertension, asthma, and lung cancer. Different delivery routes such as intratracheal instillation, aerosol and intravenous injection have been utilized with varying degrees of efficiency. Both viral and non-viral vectors, with their respective strengths and weaknesses, have achieved significant levels of transgene expression in the lungs. However, the application of gene therapy for the treatment of pulmonary disease has been handicapped by various barriers to the delivery vectors such as serum proteins during intravenous delivery, and surfactant proteins and mucus in the airway lumen during topical application of therapeutic genes. Immune and cytokine responses against the delivery vehicle are also major problems encountered in pulmonary gene therapy. Despite these shortcomings much progress has been made to enhance the efficiency, as well as lower the toxicity of gene therapy vehicles in the treatment of pulmonary disorders such as cystic fibrosis, lung cancer and asthma.

Viscoelastic gel formulations enhance airway epithelial gene transfer with viral vectors

Advances in gene transfer to the conducting airways for the treatment of pulmonary diseases such as cystic fibrosis have identified several vector classes that transduce airway epithelia in vitro and in animal models. One barrier to epithelial gene transfer is the rapid removal of materials from the airway surface via mucociliary clearance. This host defense mechanism limits gene transfer efficiency to airway epithelial cells. Here we show that formulation of gene transfer vectors with viscoelastic gels provides longer epithelial residence time and increases vector-mediated gene transfer efficiency. Gene transfer with adenoviral, adeno-associated, and lentiviral vectors all significantly improved after formulation with viscoelastic gels designed to slow mucociliary clearance. Importantly, viscoelastic gel formulations enhanced vector transduction to the conducting airways, the desired treatment target for diseases such as cystic fibrosis.

A defective nontransmissible recombinant Sendai virus mediates efficient gene transfer to airway epithelium in vivo

Recombinant Sendai virus (SeV)-mediated gene transfer to differentiated airway epithelial cells has shown to be very efficient, because of its ability to overcome the intra- and extracellular barriers known to limit gene delivery. However, this virus is transmission competent and therefore unlikely to be suitable for use in clinical trials. A nontransmissible, replication-competent recombinant SeV has recently been developed by deleting the envelope Fusion (F) protein gene (SeV/DeltaF). Here we show that SeV/DeltaF is able to mediate beta-galactosidase reporter gene transfer to the respiratory tract of mice in vivo, as well as to human nasal epithelial cells in vitro. Further, in an ex vivo model of differentiated airway epithelium, SeV/DeltaF gene transfer was not importantly inhibited by native mucus. When compared to the transmission-competent SeV in vivo, no difference in gene expression was observed at the time of peak expression. The development of an F-defective nontransmissible SeV, which can still efficiently mediate gene transfer to the airway epithelium, represents the first important step towards the use of a cytoplasmic RNA viral vector in clinical trials of gene therapy.

Protection of Cftr knockout mice from acute lung infection by a helper-dependent adenoviral vector expressing Cftr in airway epithelia

We developed a helper-dependent adenoviral vector for cystic fibrosis lung gene therapy. The vector expresses cystic fibrosis transmembrane conductance regulator (Cftr) using control elements from cytokeratin 18. The vector expressed properly localized CFTR in cultured cells and in the airway epithelia of mice. Cftr RNA and protein were present in whole lung and bronchioles, respectively, for 28 days after a vector dose. Acute inflammation was minimal to moderate. To test the therapeutic potential of the vector, we challenged mice with a clinical strain of Burkholderia cepacia complex (Bcc). Cftr knockout mice (but not Cftr+/+ littermates) challenged with Bcc developed severe lung histopathology and had high lung bacteria counts. Cftr knockout mice receiving gene therapy 7 days before Bcc challenge had less severe histopathology, and the number of lung bacteria was reduced to the level seen in Cftr+/+ littermates. These data suggest that gene therapy could benefit cystic fibrosis patients by reducing susceptibility to opportunistic pathogens.

Transient increase in lung epithelial tight junction permeability: an additional mechanism for enhancement of lung transgene expression by perfluorochemical liquids

Intratracheal instillation of perfluorochemical (PFC) liquids enhances lung epithelial transgene expression by improved vector propulsion throughout lung airways. We now demonstrate that PFC liquids also facilitate gene transfer by increasing transepithelial permeability. Apical application of PFC liquid to well-differentiated human airway epithelial cells resulted in a transient decrease in transepithelial resistance peaking approximately 2 h after PFC liquid administration and returning to normal approximately 24 h later. The permeability change was sufficient to enhance access of apically applied 100-nm latex beads and adenoviral vectors to the basolateral side of the culture. Adenovirus-mediated gene expression was concurrently enhanced. Following intratracheal instillation of PFC liquid into mouse lungs, tight junction permeability, as assessed by electron microscopic evaluation of lanthanum deposition, was increased with peak effect between 6 h and 1 day after instillation. Importantly, alveolar-capillary permeability remained unchanged with the treatment. Administration of PFC liquid 6 h or 1 day, but not 3 days, prior to instillation of a recombinant adenovirus vector enhanced gene expression comparable to that observed with concurrent administration of PFC liquid and vector. We conclude that transient increase in epithelial permeability after PFC liquid administration contributes to the enhancement of adenovirus vector-mediated gene expression in lung epithelium.

Safety and efficiency of modulating paracellular permeability to enhance airway epithelial gene transfer in vivo

We evaluated the safety of agents that enhance gene transfer by modulating paracellular permeability. Lactate dehydrogenase (LDH) and cytokine release were measured in polarized primary human airway epithelial (HAE) cells after lumenal application of vehicle, ethyleneglycol-bis-(beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA), sodium caprate (C10), or sodium laurate (C12). Lung toxicity was assessed after tracheobronchial instillation to murine airways and the relative ability of these agents to enhance in vivo adenoviral gene transfer was evaluated. Lumenal C12 increased LDH release in vitro, but C10 and EGTA did not. Increased levels of interleukin 8 (IL-8) were secreted from EGTA-pretreated cystic fibrosis HAE cells after apical application of Pseudomonas aeruginosa (10(8) CFU/ml), whereas IL-8 secretion from C10- and C12-pretreated cells was not different from controls. In vivo toxicity studies demonstrated no effect of EGTA, C10, or C12 on weight gain, lung edema, or bronchoalveolar lavage fluid (BALF) albumin. EGTA increased BALF cell counts, neutrophils, and murine (m) macrophage inflammatory protein 2, mKC, mIL-6, and mIL-1 beta levels. C10 had no effect on BALF cell counts or LDH, but increased murine tumor necrosis factor alpha. C12 increased BALF LDH, neutrophils, and mIL-6 levels. Histopathological analysis revealed mild focal lung inflammation more frequently in the EGTA, C10, and C12 groups than in vehicle controls, with greater intensity in the C12 group relative to the other groups. C10 and C12 also increased airway responsiveness to methacholine challenge compared with control and EGTA groups. Adenoviral gene transfer to murine trachea in vivo was enhanced more efficiently by C10 than by C12 or EGTA. Thus, the different toxicities may permit the selection of agents that enhance gene transfer with minimal adverse effects.

Reduced inflammation and improved airway expression using helper-dependent adenoviral vectors with a K18 promoter

Efforts have been made to deliver transgenes to the airway epithelia of laboratory animals and humans to develop gene therapy for cystic fibrosis. These investigations have been disappointing due to combinations of transient and low-level gene expression, acute toxicity, and inflammation. We have developed new helper-dependent adenoviral vectors to deliver an epithelial cell-specific keratin 18 expression cassette driving the beta-galactosidase (beta-gal) or human alpha-fetoprotein (AFP) reporter genes. Following intranasal administration to mice, we found that the reporter genes were widely expressed in airway epithelial and submucosal cells, and secreted human AFP was also detectable in serum. In contrast to a first-generation adenoviral vector, inflammation was negligible at doses providing efficient transduction, and expression lasted longer than typically reported-up to 28 days with beta-gal and up to 15 weeks with human AFP. These results suggest that delivery to the airway of helper-dependent adenoviral vectors utilizing a tissue-specific promoter could be a significant advance in the development of gene therapy for cystic fibrosis.

Current status of gene therapy for inherited lung diseases

Gene therapy as a treatment modality for pulmonary disorders has attracted significant interest over the past decade. Since the initiation of the first clinical trials for cystic fibrosis lung disease using recombinant adenovirus in the early 1990s, the field has encountered numerous obstacles including vector inflammation, inefficient delivery, and vector production. Despite these obstacles, enthusiasm for lung gene therapy remains high. In part, this enthusiasm is fueled through the diligence of numerous researchers whose studies continue to reveal great potential of new gene transfer vectors that demonstrate increased tropism for airway epithelia. Several newly identified serotypes of adeno-associated virus have demonstrated substantial promise in animal models and will likely surface soon in clinical trials. Furthermore, an increased understanding of vector biology has also led to the development of new technologies to enhance the efficiency and selectivity of gene delivery to the lung. Although the promise of gene therapy to the lung has yet to be realized, the recent concentrated efforts in the field that focus on the basic virology of vector development will undoubtedly reap great rewards over the next decade in treating lung diseases.

Enhancement of adenovirus-mediated gene transfer to the airways by DEAE dextran and sodium caprate in vivo

Gene transfer to the trachea and airways by adenoviral vectors is limited by the basolateral localization of viral receptors, resulting in relatively low levels of transduction. Modification of paracellular permeability by sodium caprate, which opens tight junctions, enhances gene transfer from the apical side of cultured human airway epithelial cells. Based on this observation we investigated whether Na-caprate could also increase gene transfer when applied to the luminal surface of the airway epithelia in vivo and compared these results with EGTA, which has previously been shown to enhance adenovirus transduction. Transgene expression in the trachea and upper airways was increased 25-fold by a 10-min pretreatment with 50 mM Na-caprate, corresponding to a 3-fold improvement over EGTA. In the more peripheral airways EGTA had no effect, whereas expression of beta-gal was increased 3-fold by Na-caprate. When the adenovirus was complexed with DEAE dextran, transduction of the airway epithelia after Na-caprate pretreatment was increased 45-fold over virus alone. In conclusion, Na-caprate facilitates gene transfer to airway epithelia, particularly when adenovirus is complexed with DEAE dextran, and may in future be used in a clinical setting to enhance the efficiency of vectors for gene therapy of cystic fibrosis via airway delivery.

Aerosol gene therapy

Gene therapy is a novel field of medicine that holds tremendous therapeutic potential for a variety of human diseases. Targeting of therapeutic gene delivery vectors to the lungs can be beneficial for treatment of various pulmonary diseases such as lung cancer, cystic fibrosis, pulmonary hypertension, alpha-1 antitrypsin deficiency, and asthma. Inhalation therapy using formulations delivered as aerosols targets the lungs through the pulmonary airways. The instant access and the high ratio of the drug deposited within the lungs noninvasively are the major advantages of aerosol delivery over other routes of administration. Delivery of gene formulations via aerosols is a relatively new field, which is less than a decade old. However, in this short period of time significant developments in aerosol delivery systems and vectors have resulted in major advances toward potential applications for various pulmonary diseases. This article will review these advances and the potential future applications of aerosol gene therapy technology.

Barriers to and new approaches for gene therapy and gene delivery in cystic fibrosis

Clinical trials of gene therapy for cystic fibrosis suggest that current levels of gene transfer efficiency are probably too low to result in clinical benefit, largely as a result of the barriers faced by gene transfer vectors within the airways. The respiratory epithelium has evolved a complex series of extracellular barriers (mucus, lack of receptors, immune surveillance, etc.) aimed at preventing penetration of lumenally delivered materials, including gene therapy vectors. In addition, once in the cell, further hurdles have to be overcome, including DNA degradation, nuclear import and the ability to maintain long-term transgene expression. Strategies to overcome these barriers will be addressed in this review and include the use of: (i) clinically relevant adjuncts to overcome the extra- and intracellular barriers; (ii) less-conventional delivery routes, such as intravenous or in utero administration; (iii) more efficient non-viral vectors and 'stealth' viruses which can be re-administered; and (iv) new approaches to prolong transgene expression by means of alternative promoters or integrating vectors. These advances have the potential to improve the efficiency of gene delivery to the airway epithelium, thus making gene therapy a more realistic option for cystic fibrosis.

Recovery of airway cystic fibrosis transmembrane conductance regulator function in mice with cystic fibrosis after single-dose lentivirus-mediated gene transfer

The potential for gene therapy to be an effective treatment for cystic fibrosis (CF) airway disease has been limited by inefficient gene transfer vector particle delivery and lack of persistent gene expression. We have developed an airway conditioning process that, when combined with a human immunodeficiency virus (HIV)-derived lentivirus (LV) vector, resulted in persistent in vivo expression of transgenes in airway epithelium. Pretreatment of mouse nasal epithelium with the detergent lysophosphatidylcholine (LPC) prior to instillation of a single dose of an LV vector carrying the LacZ marker gene produced significant LacZ gene expression in nasal airway epithelium for at least 92 days. Transduction of the cystic fibrosis transmembrane conductance regulator (CFTR) gene using the same LV vector system resulted in partial recovery of electrophysiologic function in the nasal airway epithelium of CF mice (cftr(tm1Unc) knockout) for at least 110 days. This first demonstration of LV-mediated in vivo recovery of CFTR function in CF airway epithelium illustrates the potential of combining a preconditioning of the airway surface with a simple and brief LV vector exposure to produce therapeutic gene expression in airway.

Gene therapy for cystic fibrosis by means of aerosol

Gene therapy by aerosol is an attractive approach for the treatment of cystic fibrosis (CF). Clinical trials with aerosols in CF patients have been conducted by five different groups, three using adenoviral vectors and two using cationic liposomes carrying the coding sequence for the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR). These trials revealed that gene transfer from the lumen to the respiratory epithelium can currently be achieved in vivo, but only with low efficiency and for limited duration. Some of the many hurdles on the way to successful gene therapy for this disease will be discussed in this review. Innovative strategies need to be developed to reach this tantalizing goal.

Gene therapy progress and prospects: cystic fibrosis

Since the cloning of the cystic fibrosis gene (CFTR) in 1989, 18 clinical trials have been carried out, including five in the 2 years reviewed here. Most trials demonstrated proof-of-principle for gene transfer to the airway. However, gene transfer efficiency with each of the three gene transfer agents (adenovirus (Ad), adeno-associated virus 2 (AAV2) and cationic liposomes) was low, and most likely insufficient to achieve clinical benefit. Here, we will review the clinical and pre-clinical progress for the last 2 years (2000-2001) and briefly speculate on future prospects for the next 2 in CF gene therapy.

Regulator of G-protein signaling protein 2 modulates purinergic calcium and ciliary beat frequency responses in airway epithelia

In ciliated airway epithelial cells, purinergic stimulation increases both intracellular calcium ([Ca(2+)](i)) and ciliary beat frequency (CBF). Because regulator of G-protein signaling protein 2 (RGS2) terminates Galphaq-mediated phospholipase C activation, we examined its role in regulating purinergic signaling in human and ovine airway epithelial cells. RT-PCR of both human and ovine epithelial cell RNA yielded fragments of expected size ( approximately 491 bp) and sequence, confirming RGS2 message. Immunofluorescence demonstrated RGS2 protein expression in cultured airway epithelial cells of both species. Overexpression of an EGFP-RGS2 fusion protein (increasing RGS2 protein levels 1.8 times control, n = 28 cells) resulted in a reduced [Ca(2+)](i) and CBF response to 10 micro M ATP (human: 58 +/- 9% and 49 +/- 8% lower, respectively; n = 8 measurements, 4 cells; ovine: 56 +/- 12% and 53 +/- 16% lower, respectively; n = 5 measurements, 4 cells). Reducing RGS2 protein levels using antisense oligonucleotides increased the response of both [Ca(2+)](i) and CBF to ATP in human cells by 57 +/- 10% and 47 +/- 11%, respectively (n = 10 measurements, 6 cells), and in ovine cells by 88 +/- 13% and 48 +/- 9%, respectively (n = 10 measurements, 5 cells). These data provide functional evidence that RGS2 modulates purinergic signaling in human and ovine ciliated airway epithelial cells.

Bronchoalveolar fluid is not a major hindrance to virus-mediated gene therapy in cystic fibrosis

Successfully targeting the airway epithelium is essential for gene therapy of some pulmonary diseases. However, the airway epithelium is resistant to virus-mediated gene transfer with commonly used vectors. Vectors that interact with endogenously expressed receptors on the apical surface significantly increase gene transfer efficiency. However, other endogenous components involved in host immunity may hinder virus-mediated gene transfer. We tested the effect of bronchoalveolar lavage liquid (BAL) from patients with cystic fibrosis (CF), BAL from subjects without CF (non-CF BAL), Pseudomonas aeruginosa-derived proteins, and an array of inflammatory proteins on gene transfer mediated by adeno-associated virus type 5 (AAV5) and adenovirus targeted to an apically expressed glycosylphosphatidylinositol-modified coxsackie-adenovirus receptor. We found that neither CF BAL nor its components had a significant effect on gene transfer to human airway epithelium by these vectors. Non-CF BAL significantly impaired adenovirus-mediated gene transfer. Removal of immunoglobulins in non-CF BAL restored gene transfer efficiency. As virus vectors are improved and mechanisms of humoral immunity are elucidated, barriers to successful gene therapy found in the complex environment of the human lung can be circumvented.