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

Gene therapy for cystic fibrosis: Challenges and prospects

Cystic fibrosis (CF) is a life-threatening autosomal-recessive disease caused by mutations in a single gene encoding cystic fibrosis transmembrane conductance regulator (CFTR). CF effects multiple organs, and lung disease is the primary cause of mortality. The median age at death from CF is in the early forties. CF was one of the first diseases to be considered for gene therapy, and efforts focused on treating CF lung disease began shortly after the CFTR gene was identified in 1989. However, despite the quickly established proof-of-concept for CFTR gene transfer in vitro and in clinical trials in 1990s, to date, 36 CF gene therapy clinical trials involving ∼600 patients with CF have yet to achieve their desired outcomes. The long journey to pursue gene therapy as a cure for CF encountered more difficulties than originally anticipated, but immense progress has been made in the past decade in the developments of next generation airway transduction viral vectors and CF animal models that reproduced human CF disease phenotypes. In this review, we look back at the history for the lessons learned from previous clinical trials and summarize the recent advances in the research for CF gene therapy, including the emerging CRISPR-based gene editing strategies. We also discuss the airway transduction vectors, large animal CF models, the complexity of CF pathogenesis and heterogeneity of CFTR expression in airway epithelium, which are the major challenges to the implementation of a successful CF gene therapy, and highlight the future opportunities and prospects.

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.

Gene therapy for cystic fibrosis: new tools for precision medicine

The discovery of the Cystic fibrosis (CF) gene in 1989 has paved the way for incredible progress in treating the disease such that the mean survival age of individuals living with CF is now ~58 years in Canada. Recent developments in gene targeting tools and new cell and animal models have re-ignited the search for a permanent genetic cure for all CF. In this review, we highlight some of the more recent gene therapy approaches as well as new models that will provide insight into personalized therapies for CF.

A helper-dependent adenoviral vector rescues CFTR to wild-type functional levels in cystic fibrosis epithelial cells harbouring class I mutations

Cystic fibrosis (CF) is a genetic disorder affecting multiple organs, including the pancreas, hepatobiliary system and reproductive organs; however, lung disease is responsible for the majority of morbidity and mortality. Management of CF involves CF transmembrane conductance regulator (CFTR) modulator agents including corrector drugs to augment cellular trafficking of mutant CFTR as well as potentiators that open defective CFTR channels. These therapies are poised to help most individuals with CF, with the notable exception of individuals with class I mutations where full-length CFTR protein is not produced. For these mutations, gene replacement has been suggested as a potential solution.In this work, we used a helper-dependent adenoviral vector (HD-CFTR) to express CFTR in nasal epithelial cell cultures derived from CF subjects with class I CFTR mutations.CFTR function was significantly restored in CF cells by HD-CFTR and reached healthy control functional levels as detected by Ussing chamber and membrane potential (FLIPR) assay. A dose-response relationship was observed between the amount of vector used and subsequent functional outcomes; small amounts of HD-CFTR were sufficient to correct CFTR function. At higher doses, HD-CFTR did not increase CFTR function in healthy control cells above baseline values. This latter observation allowed us to use this vector to benchmark in vitro efficacy testing of CFTR-modulator drugs.In summary, we demonstrate the potential for HD-CFTR to inform in vitro testing and to restore CFTR function to healthy control levels in airway cells with class I or CFTR nonsense mutations.

In Vitro Validation of a CRISPR-Mediated CFTR Correction Strategy for Preclinical Translation in Pigs

Early efforts in cystic fibrosis (CF) gene therapy faced major challenges in delivery efficiency and sustained therapeutic gene expression. Recent advancements in engineered site-specific endonucleases such as clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 make permanent CF transmembrane conductance regulator (CFTR) gene correction possible. However, because of safety concerns of the CRISPR/Cas9 system and challenges in in vivo delivery to inflamed CF airway, CRISPR-based gene correction strategies need to be tested in proper animal models. In this study, we aimed at creating vectors for testing CFTR gene correction in pig models. We constructed helper-dependent adenoviral (HD-Ad) vectors to deliver CRISPR/Cas9 and a donor template (a 6 kb LacZ or 8.7 kb human CFTR expression cassette) into cultured pig cells. We demonstrated precise integration of each donor into the GGTA1 safe harbor through Cas9-induced homology directed repair with 3 kb homology arms. In addition, we showed that both LacZ and hCFTR were persistently expressed in transduced cells. Furthermore, we created a CFTR-deficient cell line for testing CFTR correction. We detected hCFTR mRNA and protein expression in cells transduced with the hCFTR vector. We also demonstrated CFTR function in the CF cells transduced with the HD-Ad delivering the CRISPR-Cas9 system and hCFTR donor at late cellular passages using the membrane potential sensitive dye-based assay (FLIPR^®). Combined with our previous report on gene delivery to pig airway basal cells, these data provide the feasibility of testing CRISPR/Cas9-mediated permanent human CFTR correction through HD-Ad vector delivery in pigs.

TALEN-Mediated Gene Targeting for Cystic Fibrosis-Gene Therapy

Cystic fibrosis (CF) is an inherited monogenic disorder, amenable to gene-based therapies. Because CF lung disease is currently the major cause of mortality and morbidity, and the lung airway is readily accessible to gene delivery, the major CF gene therapy effort at present is directed to the lung. Although airway epithelial cells are renewed slowly, permanent gene correction through gene editing or targeting in airway stem cells is needed to perpetuate the therapeutic effect. Transcription activator-like effector nuclease (TALEN) has been utilized widely for a variety of gene editing applications. The stringent requirement for nuclease binding target sites allows for gene editing with precision. In this study, we engineered helper-dependent adenoviral (HD-Ad) vectors to deliver a pair of TALENs together with donor DNA targeting the human AAVS1 locus. With homology arms of 4 kb in length, we demonstrated precise insertion of either a LacZ reporter gene or a human cystic fibrosis transmembrane conductance regulator (CFTR) minigene (cDNA) into the target site. Using the LacZ reporter, we determined the efficiency of gene integration to be about 5%. In the CFTR vector transduced cells, we were able to detect CFTR mRNA expression using qPCR and function correction using fluorometric image plate reader (FLIPR) and iodide efflux assays. Taken together, these findings suggest a new direction for future in vitro and in vivo studies in CF gene editing.

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.

Overcoming the Undesirable CRISPR-Cas9 Expression in Gene Correction

The CRISPR-Cas9 system is attractive for gene therapy, as it allows for permanent genetic correction. However, as a new technology, Cas9 gene editing in clinical applications faces major challenges, such as safe delivery and gene targeting efficiency. Cas9 is a foreign protein to recipient cells; thus, its expression may prompt the immune system to eliminate gene-edited cells. To overcome these challenges, we have engineered a novel delivery system based on the helper-dependent adenoviral (HD-Ad) vector, which is capable of delivering genes to airway basal stem cells in vivo. Using this system, we demonstrate the successful co-delivery of both CRISPR-Cas9/single-guide RNA and the LacZ reporter or CFTR gene as donor DNA to cultured cells. HD-Ad vector genome integrity is compromised following donor DNA integration, and because the CRISPR-Cas9/single-guide RNA and donor DNA are carried on the same vector, CRISPR-Cas9 expression is concurrently eliminated. Thus, we show the feasibility of site-specific gene targeting with limited Cas9 expression. In addition, we achieved stable CFTR expression and functional correction in cultured cells following successful gene integration.

Genetic Modification of the Lung Directed Toward Treatment of Human Disease

Genetic modification therapy is a promising therapeutic strategy for many diseases of the lung intractable to other treatments. Lung gene therapy has been the subject of numerous preclinical animal experiments and human clinical trials, for targets including genetic diseases such as cystic fibrosis and α1-antitrypsin deficiency, complex disorders such as asthma, allergy, and lung cancer, infections such as respiratory syncytial virus (RSV) and Pseudomonas, as well as pulmonary arterial hypertension, transplant rejection, and lung injury. A variety of viral and non-viral vectors have been employed to overcome the many physical barriers to gene transfer imposed by lung anatomy and natural defenses. Beyond the treatment of lung diseases, the lung has the potential to be used as a metabolic factory for generating proteins for delivery to the circulation for treatment of systemic diseases. Although much has been learned through a myriad of experiments about the development of genetic modification of the lung, more work is still needed to improve the delivery vehicles and to overcome challenges such as entry barriers, persistent expression, specific cell targeting, and circumventing host anti-vector responses.

Long-Term Expression of the Human CFTR Gene in Mouse Airway via Helper-Dependent Adenoviral Vector Delivery and Transient Immunosuppression

Sustained expression of the CFTR gene is a major challenge to gene therapy with either viral or nonviral vectors with immune response to vector and transgene products. One strategy to achieve sustained CFTR expression is to modulate the host immune system through transient immunosuppression. In this study, we examined cyclophosphamide (cytoxan), dexamethasone (Dex), and a combination of cyclosporin, methylprednisolone, and azathioprine (combination) for their effects on long-term expression of the human CFTR delivered with helper-dependent adenoviral vectors in mouse airways. We found that cyclophosphamide significantly enhanced long-term expression of the transgenic human CFTR and the reporter gene LacZ by reducing host immune responses. Dex administration greatly reduced neutralizing antibody production but had no effect on transgene expression. Treatment with a combination of cyclosporin A, azathioprine, and methylprednisolone affected neither CFTR gene expression nor inflammation. Our data suggest that transient immunosuppression might be a strategy to improve sustained expression in gene therapy.

Burkholderia cepacia Complex Vaccines: Where Do We Go from here?

Burkholderia comprises a wide variety of environmental Gram-negative bacteria. Burkholderia cepacia complex (Bcc) includes several Burkholderia species that pose a health hazard as they are able to cause respiratory infections in patients with chronic granulomatous disease and cystic fibrosis. Due to the intrinsic resistance to a wide array of antibiotics and naturally occurring immune evasion strategies, treatment of Bcc infections often proves to be unsuccessful. To date, limited work related to vaccine development has been performed for Bcc pathogens. In this review, we have gathered key aspects of Bcc research that have been reported in recent years related to vaccine efforts, virulence, immune responses, and animal models, and use this information to inform the research community of areas of opportunity toward development of a viable Bcc vaccine.

Targeted CFTR gene disruption with zinc-finger nucleases in human intestinal epithelial cells induces oxidative stress and inflammation

Cystic fibrosis (CF) is a multisystemic pathology caused by mutations of the CF transmembrane conductance regulator (CFTR) gene.

OBJECTIVES

As the intestine harbors the greatest number of CFTR transcripts after birth and since CFTR plays a role in glutathione transport, we hypothesized that CFTR deletion might produce oxidative stress (OxS) and inflammation in CF intestinal epithelial cell.

METHODS

CFTR gene was abrogated in Caco-2/15 enterocytes through the zinc-finger nuclease system. Their oxidative and inflammatory characteristics were appreciated under basal conditions and after the treatment with the pro-oxidant iron-ascorbate (Fe/Asc) complex and pro-inflammatory lipopolysaccharide (LPS).

RESULTS

Intestinal epithelial cells with CFTR knockout spontaneously exhibited an increased lipid peroxidation level, reflected by malondialdehyde overproduction and reduced antioxidant defense characterized by low enzymatic activities of glutathione peroxidase and catalase. CFTR silencing also resulted in elevated protein expression of pro-inflammatory tumor necrosis Factor-α, interleukin-6, cyclooxygenase-2, and the transcription factor nuclear factor-κB. Moreover, exaggerated OxS and inflammation processes occurred in CFTR(-/-) cells in response to the addition of Fe/Asc and LPS, respectively.

CONCLUSIONS

Intestinal Caco-2/15 cells with CFTR deletion, display innate oxidative and inflammatory features while being more sensitive to pro-oxidant and pro-inflammatory stimuli. These two pathophysiological processes could be implicated in CF-related intestinal disorders.

Cystic Fibrosis Gene Therapy in the UK and Elsewhere

The cystic fibrosis transmembrane conductance regulator (CFTR) gene was identified in 1989. This opened the door for the development of cystic fibrosis (CF) gene therapy, which has been actively pursued for the last 20 years. Although 26 clinical trials involving approximately 450 patients have been carried out, the vast majority of these trials were short and included small numbers of patients; they were not designed to assess clinical benefit, but to establish safety and proof-of-concept for gene transfer using molecular end points such as the detection of recombinant mRNA or correction of the ion transport defect. The only currently published trial designed and powered to assess clinical efficacy (defined as improvement in lung function) administered AAV2-CFTR to the lungs of patients with CF. The U.K. Cystic Fibrosis Gene Therapy Consortium completed, in the autumn of 2014, the first nonviral gene therapy trial designed to answer whether repeated nonviral gene transfer (12 doses over 12 months) can lead to clinical benefit. The demonstration that the molecular defect in CFTR can be corrected with small-molecule drugs, and the success of gene therapy in other monogenic diseases, is boosting interest in CF gene therapy. Developments are discussed here.

Testing gene therapy vectors in human primary nasal epithelial cultures

Cystic fibrosis (CF) results from mutations in the CF transmembrane conductance regulator (CFTR) gene, which codes for a chloride/bicarbonate channel in the apical epithelial membranes. CFTR dysfunction results in a multisystem disease including the development of life limiting lung disease. The possibility of a cure for CF by replacing defective CFTR has led to different approaches for CF gene therapy; all of which ultimately have to be tested in preclinical model systems. Primary human nasal epithelial cultures (HNECs) derived from nasal turbinate brushing were used to test the efficiency of a helper-dependent adenoviral (HD-Ad) vector expressing CFTR. HD-Ad-CFTR transduction resulted in functional expression of CFTR at the apical membrane in nasal epithelial cells obtained from CF patients. These results suggest that HNECs can be used for preclinical testing of gene therapy vectors in CF.

Transient blocking of NK cell function with small molecule inhibitors for helper dependant adenoviral vector-mediated gene delivery

One major challenge in gene therapy is the host immune responses against viral vectors. Previous studies indicate the involvement of NK cells in stunted gene expression in viral vector mediated gene therapy. To understand the problem of the immune responses, we have developed an in-vitro co-culture system with human NK cell line, macrophages and airway epithelial cells. We showed that small molecule blockers, CAPE and ruxolitinib, for NF-κB and JAK-STAT pathways, respectively, significantly inhibited cytokine secretion by macrophages. When NK cells are co-cultured with helper-dependent adenoviral (HD-Ad) vector activated macrophages, IFN-γ cytokine expression by NK cells increased significantly, which was inhibited effectively by ruxolitinib and CAPE, and there was an additive effect when both inhibitors were used. We demonstrated that NK cells activated by cytokines produced by HD-Ad-activated macrophages kill HD-Ad vector transduced bronchial epithelial cells. This cell killing activity was significantly reduced by CAPE and ruxolitinib. Combination of these two inhibitors had an additive effect on inhibiting NK cell mediate killing of gene transduced cells. Transient inhibition of NK cell response at its peak may enhance sustained gene expression. Our data suggest that combination of CAPE and ruxolitinib may help in protecting gene transduced airway epithelial cells to prolong transgene expression.

Modulation of Alloimmune Responses by Interleukin-10 Prevents Rejection of Implanted Allogeneic Smooth Muscle Cells and Restores Postinfarction Ventricular Function

Interleukin-10 (IL-10) gene transduction into allogeneic smooth muscle cells (SMCs) was evaluated to improve the long-term benefits of allogeneic cell transplantation into infarcted myocardium. Allogeneic cells, including SMCs, have been demonstrated to restore cardiac function and repair the infarcted myocardium, but late rejection of the transplanted cells by the host immune system may reverse the benefits of cell therapy. In a rat myocardial infarction model, three groups of rats were injected with either unmodified autologous, unmodified allogeneic, or allogeneic + IL-10 SMCs into the infarct region. Three weeks later, most of the allogeneic cells were rejected, whereas autologous cells were engrafted in the myocardium. IL-10 gene transduction of the allogeneic SMCs significantly improved the cell survival. To understand the mechanism of this improved survival, we evaluated the host immune responses against the SMCs. Allogeneic SMCs expressing IL-10 decreased leukocyte-mediated cytotoxicity in coculture, decreased the number of cytotoxic CD8+ T-cells, and increased the number of CD4+CD25+ regulatory T-cells in vitro and in vivo. Furthermore, IL-10 prevented the production of antidonor antibodies by the recipients against the allogeneic SMCs. Transplantation of unmodified autologous SMCs, but not unmodified allogeneic SMCs, significantly improved fractional shortening and left ventricular dimensions compared to the media-injected control group. However, IL-10 gene-enhanced allogeneic SMCs improved ventricular function, increased wall thickness, and decreased scar length in association with their enhanced survival. We conclude that IL-10 gene-enhanced cell therapy with allogeneic SMCs prevents detrimental alloimmune responses in the recipient, thereby increasing the survival of transplanted allogeneic SMCs and more effectively restoring cardiac function.

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.

Efficient gene delivery to pig airway epithelia and submucosal glands using helper-dependent adenoviral vectors

Airway gene delivery is a promising strategy to treat patients with life-threatening lung diseases such as cystic fibrosis (CF). However, this strategy has to be evaluated in large animal preclinical studies in order to translate it to human applications. Because of anatomic and physiological similarities between the human and pig lungs, we utilized pig as a large animal model to examine the safety and efficiency of airway gene delivery with helper-dependent adenoviral vectors. Helper-dependent vectors carrying human CFTR or reporter gene LacZ were aerosolized intratracheally into pigs under bronchoscopic guidance. We found that the LacZ reporter and hCFTR transgene products were efficiently expressed in lung airway epithelial cells. The transgene vectors with this delivery can also reach to submucosal glands. Moreover, the hCFTR transgene protein localized to the apical membrane of both ciliated and nonciliated epithelial cells, mirroring the location of wild-type CF transmembrane conductance regulator (CFTR). Aerosol delivery procedure was well tolerated by pigs without showing systemic toxicity based on the limited number of pigs tested. These results provide important insights into developing clinical strategies for human CF lung gene therapy.Molecular Therapy-Nucleic Acids (2013) 2, e127; doi:10.1038/mtna.2013.55; published online 8 October 2013.

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.

Chemopreventive efficacy and mechanism of licofelone in a mouse lung tumor model via aspiration

Our previous study comparing inhalation and aspiration to administer agents directly to lung indicated that aspiration route is as effective as inhalation while reducing costs for equipment and chemopreventive agent. This study evaluated the chemopreventive efficacy and mechanism of licofelone, a dual inhibitor of COX-2 and 5-lipoxygenase (5-Lox), via oropharyngeal aspiration against mouse lung adenoma. Eight-week-old female A/J mice were given three doses of benzo[a]pyrene (B[a]P; 2 mg/dose, gavage) to induce lung adenomas. After dysplasia developed, the mice were given licofelone (0, 0.03, 0.1, or 0.3 mg/kg) for 16 weeks, and tumor incidence and multiplicity in lung were measured. In addition, the expression of a series of biomarkers in lung cancer progression was evaluated at 2 and 16 weeks. Licofelone showed dose-related inhibition of B[a]P-induced tumor incidence and multiplicity at 0.03 and 0.1 mg/kg following 16-week treatment. Licofelone also showed dose-dependent inhibition of COX-2 (25%-41%) and 5-Lox (35%-61%) at 2 and 16 weeks and proliferating cell nuclear antigen (PCNA; 41%-61%) at 16 weeks. A dose-dependent increase in apoptosis (1.5- to 2.4-fold) was also observed in licofelone groups. A marginal inhibition of survivin was observed at one dose. In conclusion, this study showed that licofelone via aspiration showed chemopreventive efficacy against mouse lung adenoma with good correlation to early and late biomarkers of lung cancer progression. This is the first study to show that the aspiration route can be an excellent inexpensive alternative to inhalation for direct delivery of drugs to rodent lungs for efficacy testing of potential chemopreventive agents.

Toxicity Profile of Solvents by Aspiration Approach for Topical Agent Delivery to Respiratory Tract Epithelium

Agent solubility is a problem for aspiration of agents into lungs for chemopreventive efficacy evaluation, since many agents have to be dissolved in solvents. These solvents may be toxic to the lung epithelium. A study was conducted in female A/J mice to determine toxicity of different solvent concentrations by using saline, dimethyl sulfoxide (DMSO), ethanol, polyethylene glycol 400 (PEG-400), and labrasol for 1, 5, and 28 days via aspiration route. Toxicity was determined by measuring changes in body weight and bronchoalveolar lavage fluid (BALF). No significant difference was observed in body weight, differential cell counts, lactate dehydrogenase (LDH) and total protein in all solvent groups compared to saline by 28 days except 50% ethanol. However, myeloperoxidase (MPO) and macrophage inflammatory protein-2 (MIP-2) showed significant increase in 2% and 10% DMSO, 10% ethanol, 0.1% and 2% PEG-400, and 1% labrasol by longer dosing. All solvents except for 10% ethanol and 2% PEG-400 are suitable for agent aspiration.

Subretinal gene delivery using helper-dependent adenoviral vectors

This study describes the successful delivery of helper-dependent adenoviral vectors to the mouse retina with long term and robust levels of reporter expression in the retina without apparent adverse effects. Since these vectors have a large cloning capacity, they have great potential to extend the success of gene therapy achieved using the adeno-associated viral vector.

Helper-Dependent Adenoviral Vectors

Helper-dependent adenoviral vectors are devoid of all viral coding sequences, possess a large cloning capacity, and can efficiently transduce a wide variety of cell types from various species independent of the cell cycle to mediate long-term transgene expression without chronic toxicity. These non-integrating vectors hold tremendous potential for a variety of gene transfer and gene therapy applications. Here, we review the production technologies, applications, obstacles to clinical translation and their potential resolutions, and the future challenges and unanswered questions regarding this promising gene transfer technology.

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.

Identification of specific and universal virulence factors in Burkholderia cenocepacia strains by using multiple infection hosts

Over the past few decades, strains of the Burkholderia cepacia complex have emerged as important pathogens for patients suffering from cystic fibrosis. Identification of virulence factors and assessment of the pathogenic potential of Burkholderia strains have increased the need for appropriate infection models. In previous studies, different infection hosts, including mammals, nematodes, insects, and plants, have been used. At present, however, the extent to which the virulence factors required to infect different hosts overlap is not known. The aim of this study was to analyze the roles of various virulence factors of two closely related Burkholderia cenocepacia strains, H111 and the epidemic strain K56-2, in a multihost pathogenesis system using four different model organisms, namely, Caenorhabditis elegans, Galleria mellonella, the alfalfa plant, and mice or rats. We demonstrate that most of the identified virulence factors are specific for one of the infection models, and only three factors were found to be essential for full pathogenicity in several hosts: mutants defective in (i) quorum sensing, (ii) siderophore production, and (iii) lipopolysaccharide biosynthesis were attenuated in at least three of the infection models and thus may represent promising targets for the development of novel anti-infectives.

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.

Characterization of pulmonary T cell response to helper-dependent adenoviral vectors following intranasal delivery

In spite of the extensive research in the field of gene therapy, host immune responses continue to be the major barrier in translating basic research to clinical practice. Helper-dependent adenoviral (HD-Ad) vectors show great potential for pulmonary gene therapy, but the knowledge of pulmonary immune responses toward these vectors is very limited. In this study, we show that HD-Ad vectors are potent stimulators of dendritic cell (DC) maturation, thus leading to stimulation of T cell proliferation with approximately 6% of naive CD4(+) T cells from pulmonary mediastinal lymph node responding to HD-Ad-treated DCs. In contrast to the belief that HD-Ad vectors are unable to prime adaptive immune response, we show for the first time, through in vivo pulmonary studies in mice, that HD-Ad vectors can prime CD4(+) and CD8(+) T cell responses in the lung at high and substantially low doses. This indicates cross-presentation of HD-Ad-derived epitopes by DCs to prime CD8(+) T cell responses. To assess the basis of pulmonary T cell response against HD-Ad vectors, we examined the response of conventional DCs (cDCs) and plasmacytoid DCs (pDCs) in the lung. In response to HD-Ad delivery, there is induction of maturation in both cDC and pDC subsets, but it is the cDCs, not pDCs, that migrate rapidly to draining lymph nodes within the first 2 days after vector delivery to prime adaptive immune response against these vectors. These findings have implications for development of strategies to prevent adaptive immune responses against gene therapy vectors.

Efficient and rapid osteoinduction in an immune-competent host

Osteoinductive systems to induce targeted rapid bone formation hold clinical promise, but development of technologies for clinical use that must be tested in animal models is often a difficult challenge. We previously demonstrated that implantation of human cells transduced with Ad5F35BMP2 to express high levels of bone morphogenetic protein-2 (BMP2) resulted in rapid bone formation at targeted sites. Inclusion of human cells in this model precluded us from testing this system in an immune-competent animal model, thus limiting information about the efficacy of this approach. Here, for the first time we demonstrate the similarity between BMP2-induced endochondral bone formation in a system using human cells in an immune-incompetent mouse and a murine cell-based BMP2 gene therapy system in immune-competent animals. In both cases the delivery cells are rapidly cleared, within 5 days, and in neither case do they appear to contribute to any of the structures forming in the tissues. Endochondral bone formation progressed through a highly ordered series of stages that were both morphologically and temporally indistinguishable between the two models. Even longterm analysis of the heterotopic bone demonstrated similar bone volumes and the eventual remodeling to form similar structures. The results suggest that the ability of BMP2 to rapidly induce bone formation overrides contributions from either immune status or the nature of delivery cells.

Virulence of Burkholderia cepacia complex strains in gp91phox-/- mice

In cystic fibrosis (CF), infection with Burkholderia cepacia complex (Bcc) strains may cause long-term asymptomatic airway colonization, or severe lung infection leading to rapid pulmonary decline. To assess the virulence of Bcc strains, we established a lung infection model in mice with a null allele of the gene involved in X-linked chronic granulomatous disease (CGD). CGD mice, challenged intratracheally with 10(3) cells of the epidemic Burkholderia cenocepacia strain J2315, died within 3 days from sepsis after bacteria had multiplied to 3.3 x 10(8) cells. Infected mice developed neutrophil-dominated lung abscesses. Other B. cenocepacia strains and a B. cepacia strain were less virulent and one B. multivorans and one B. vietnamensis CF isolate were both avirulent. Bcc mutants, defective in exopolysaccharide synthesis or quorum sensing revealed diminished or no abscess formation and mortality. Immunofluorescence staining of Bcc-infected murine and CF lung tissues revealed colocalization of Bcc and neutrophils, suggesting Bcc persistence within neutrophils in CGD and CF. In vitro, Bcc cells were rapidly killed during aerobic neutrophil phagocytosis; however, the pathogens survived in neutrophils with blocked nicotinamide adenine dinucleotide phosphate oxidase activity and under anaerobic conditions. We conclude that the Bcc infection model in CGD mice is well suited for the assessment of Bcc virulence.

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.

Nacystelyn enhances adenoviral vector-mediated gene delivery to mouse airways

Adenoviral vector-mediated gene delivery has been vastly investigated for cystic fibrosis (CF) gene therapy; however, one of its drawbacks is the low efficiency of gene transfer, which is due to basolateral colocalization of viral receptors, immune responses to viral vectors and the presence of a thick mucus layer in the airways of CF patients. Therefore, enhancement of gene transfer can lead to reduction in the viral dosage, which could further reduce the acute toxicity associated with the use of adenoviral vectors. Nacystelyn (NAL) is a mucolytic agent with anti-inflammatory and antioxidant properties, and has been used clinically in CF patients to reduce mucus viscosity in the airways. In this study, we show that pretreatment of the airways with NAL followed by administration of adenoviral vectors in complex with DEAE-Dextran can significantly enhance gene delivery to the airways of mice without any harmful effects. Moreover, NAL pretreatment can reduce the airway inflammation, which is normally observed after delivery of adenoviral particles. Taken together, these results indicate that NAL pretreatment followed by adenoviral vector-mediated gene delivery can be beneficial to CF patients by increasing the efficiency of gene transfer to the airways, and reducing the acute toxicity associated with the administration of adenoviral vectors.

Therapeutic and prophylactic potential of small interfering RNAs against severe acute respiratory syndrome: progress to date

Severe acute respiratory syndrome (SARS), caused by the novel coronavirus SARS-CoV, produced a scare when it appeared in 2003 in China and later quickly spread to other countries around the world. Although it has since disappeared, its threat to human health remains. Therefore, studies on the prevention and treatment of SARS are important for dealing with epidemics of this and other infectious diseases. The most promising newly developed technology for intervention in SARS may be RNA interference, an endogenous cellular process for the inhibition of gene expression mediated by sequence-specific double-stranded RNAs. Numerous studies have reported the therapeutic potential of RNA interference for the treatment of various human diseases ranging from cancers to infectious diseases such as HIV and hepatitis. To date, most studies on inhibition of SARS-CoV replication using small interfering RNAs (siRNAs) have been conducted in cell lines in vitro. One study using siRNAs to inhibit SARS-CoV infection in Rhesus macaques demonstrated that siRNAs were effective both prophylactically and therapeutically with no adverse effects in the animals. Challenges remaining for the application of siRNA in vivo for SARS prevention and treatment include the specificity of the siRNAs and the efficiency of delivery. However, with improvements in siRNA design and delivery methods, RNA interference has the potential to become another major weapon for combating dangerous infections due to viruses such as SARS-CoV.

The mink as an animal model for Pseudomonas aeruginosa adhesion: binding of the bacterial lectins (PA-IL and PA-IIL) to neoglycoproteins and to sections of pancreas and lung tissues from healthy mink

Lung infection with Pseudomonas aeruginosa, leading to chronic lung disease with impaired function, is the major course of morbidity and mortality among cystic fibrosis patients. The bacterium produces two lectins that bind to alpha-D-galactose (PA-IL) and L-fucose (PA-IIL), respectively, and lectin-carbohydrate interactions may be involved in microbial pathogenicity by creating bacterial adherence to epithelial and endothelial cells. An ideal animal model for P. aeruginosa infection has until now not been established, but the mink seems to be the only animal that has been reported to develop spontaneous P. aeruginosa infections in the airways. Since cystic fibrosis also severely may affect pancreatic function, we incubated sections from mink lungs and pancreas with a medium containing Pseudomonas lectins in order to detect in situ binding of the bacterial lectins. In the lungs, both lectins adhered to seromucinous glands located in the submucosa of the larger bronchi. Additionally, PA-IL reacted with the capillaries in the alveolar walls and with the small blood vessels forming the vasa vasorum around the larger vessels, while PA-IIL marked the goblet cells in the bronchial surface epithelium. In the pancreas, both lectins bound to the epithelium in the excretory ducts, and additionally, PA-IL strongly stained the pancreatic capillaries while PA-IIL staining was noticed in the apical part of acinar cells in the exocrine part of the gland while no lectin reaction could be recorded in the endocrine cells. Judging from the results in the present paper the mink should be considered a suitable model to study P. aeruginosa adherence.

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.

Gene therapy progress and prospects: cystic fibrosis

Our first review on progress and prospects in cystic fibrosis (CF) gene therapy was published in this series in October 2002. We now summarize the progress made since then and comment on the prospects for CF gene therapy over the next couple of years. Three clinical trials have been carried out, further supporting the proof-of-principle that gene transfer to the airway epithelium is feasible. Developments in viral and non-viral vectors, as well as recent alternative strategies such as gene repair, trans-splicing and stem cell therapy will be reviewed.

Gene delivery to human sweat glands: a model for cystic fibrosis gene therapy

Gene therapy vectors are mostly studied in cultured cells, rodents, and sometimes in non-human primates, but it is useful to test them in human tissue prior to clinical trials. In this study, we investigated the possibility of using human sweat glands as a model for testing cystic fibrosis (CF) gene therapy vectors. Human sweat glands are relatively easy to obtain from skin biopsy, and can be tested for CFTR function. Using patients' sweat glands could provide a safe model to study the efficacy of CF gene therapy. As the first step to explore using sweat glands as a model for CF gene therapy, we examined various ex vivo gene delivery methods for a helper-dependent adenovirus (HD-Ad) vector. Gene delivery to sweat glands in skin organ culture was studied by topical application, intradermal injection or submerged culture. We found that transduction efficiency can be enhanced by pretreating isolated sweat glands with dispase, which suggests that the basement membrane is a critical barrier to gene delivery by adenoviral vectors. Using this approach, we showed that Cftr could be efficiently delivered to and expressed by the epithelial cells of sweat glands with our helper-dependent adenoviral vector containing cytokeratin 18 regulatory elements. Based on this study we propose that sweat glands might be used as an alternative model to study CF gene therapy in humans.

Gutless adenovirus: last-generation adenovirus for gene therapy

Last-generation adenovirus vectors, also called helper-dependent or gutless adenovirus, are very attractive for gene therapy because the associated in vivo immune response is highly reduced compared to first- and second-generation adenovirus vectors, while maintaining high transduction efficiency and tropism. Nowadays, gutless adenovirus is administered in different organs, such as the liver, muscle or the central nervous system achieving high-level and long-term transgene expression in rodents and primates. However, as devoid of all viral coding regions, gutless vectors require viral proteins supplied in trans by a helper virus. To remove contamination by a helper virus from the final preparation, different systems based on the excision of the helper-packaging signal have been generated. Among them, Cre-loxP system is mostly used, although contamination levels still are 0.1-1% too high to be used in clinical trials. Recently developed strategies to avoid/reduce helper contamination were reviewed.

Readministration of helper-dependent adenovirus to mouse lung

Adenovirus vectors (Ad) are widely used in gene therapy studies, including those aimed at treating cystic fibrosis lung disease. Various approaches have been investigated to blunt the host immune response to Ad, including development of helper-dependent (HD) Ad. The host cytotoxic T-cell response to HD-Ad is generally lower than to earlier-generation Ad. However, antibodies are formed which could inhibit the efficacy of HD-Ad readministration. In this first study of HD-Ad readministration to the lung, we found that a second administration of HD-Ad to mice was possible with minimal loss of transgene expression. In contrast, when first-generation (FG) Ad was administered initially, followed by HD-Ad or FG-Ad, transgene expression was reduced. Significantly lower concentrations of antibodies against Ad were found in lung lavage fluid and serum from mice that received two doses of HD-Ad (when the initial HD-Ad lacked a transgene), compared to mice that received FG-Ad followed by HD-Ad. These data suggest that readministration of HD-Ad for lung gene therapy may be feasible.

Pre-clinical and clinical endpoint assays for cystic fibrosis gene therapy

The credibility and hence value of pre-clinical and clinical cystic fibrosis gene therapy studies depend on the assays used to evaluate gene transfer. Awareness of assay suitability, sensitivity and variability is therefore crucial to the design of experimental programmes. Here, we review the assays that are in use to assess the efficacy of gene transfer in pre-clinical and clinical CF gene therapy research, highlight their weaknesses and suggest possible new strategies that may help to overcome current limitations.

Response to acute lung infection with mucoid Pseudomonas aeruginosa in cystic fibrosis mice

RATIONALE

Cystic fibrosis is caused by defects in the cystic fibrosis transmembrane conductance regulator gene, which codes for a chloride channel, but the role of this chloride channel in inflammation induced by lung infection with Pseudomonas aeruginosa remains to be defined.

OBJECTIVES

We tested the hypothesis that loss of this chloride channel alone is sufficient to cause excessive inflammation in response to inflammatory stimuli.

METHODS

We investigated the response of cystic fibrosis and wild-type mice to mucoid P. aeruginosa administered by insufflation.

MEASUREMENTS

The host responses measured included survival, weight change, lung morphometry, bacterial clearance, and inflammatory mediators, and cell counts were assessed in bronchoalveolar lavage fluid.

MAIN RESULTS

Depending on the dose administered and frequency of dosing, cystic fibrosis mice experienced significantly higher mortality rates, greater weight loss, higher lung pathology scores, and higher inflammatory mediator and neutrophil levels compared with wild-type mice, even after the bacteria had been cleared. Surprisingly, bacteria were cleared just as rapidly in cystic fibrosis mice as in wild-type mice, and sepsis was not observed. Chronic lung infections could not be established with mucoid P. aeruginosa in either cystic fibrosis or wild-type mice.

CONCLUSIONS

Absence of this chloride channel alone appears sufficient for exaggerated inflammation and excess mortality compared with wild-type controls in the face of mucoid P. aeruginosa lung infection. To establish chronic infection, additional factors such as bacterial trapping or poor clearance may be required.

Gene transfer of CFTR to airway epithelia: low levels of expression are sufficient to correct Cl- transport and overexpression can generate basolateral CFTR

Gene transfer of CFTR cDNA to airway epithelia is a promising approach to treat cystic fibrosis (CF). Most gene transfer vectors use strong viral promoters even though the endogenous CFTR promoter is very weak. To learn whether expressing CFTR at a low level in a fraction of cells would correct Cl(-) transport, we mixed freshly isolated wild-type and CF airway epithelial cells in varying proportions and generated differentiated epithelia. Epithelia with approximately 20% wild-type cells generated approximately 70% the transepithelial Cl(-) current of epithelia containing 100% wild-type cells. These data were nearly identical to those previously obtained with CFTR expressed under control of a strong promoter in a CF epithelial cell line. We also tested high level CFTR expression using the very strong cytomegalovirus (CMV) promoter as well as the cytokeratin-18 (K18) promoter. In differentiated airway epithelia, the CMV promoter generated 50-fold more transgene expression than the K18 promoter, but the K18 promoter generated more transepithelial Cl(-) current at high vector doses. Using functional studies, we found that with marked overexpression, some CFTR channels were present in the basolateral membrane where they shunted Cl(-) flow, thereby reducing net transepithelial Cl(-) transport. These results suggest that very little CFTR is required in a fraction of CF epithelial cells to complement Cl(-) transport because transepithelial Cl(-) flow is limited at the basolateral membrane. Thus they suggest a broad leeway in promoter strength for correcting the CF gene transfer, although at very high expression levels CFTR may be mislocalized to the basolateral membrane.

Down-regulation of IL-8 expression in human airway epithelial cells through helper-dependent adenoviral-mediated RNA interference

Interleukin (IL)-8 is a potent neutrophil chemotactic factor and a crucial mediator in neutrophil-dependent inflammation. Various cell types produce IL-8, either in response to external stimuli such as cytokines or bacterial infection, or after malignant transformation. Anti-IL-8 strategies have been considered for anti-inflammatory therapy. In this paper we demonstrate that the RNA interference technique can be used to efficiently down-regulate IL-8 protein expression in airway epithelial cells. We used a helper-dependent adenoviral vector to express a small hairpin (sh)RNA targeting human IL-8 in cultured airway epithelial cells (IB3-1, Cftr-/-; C38, Cftr-corrected) stimulated with TNF-alpha, IL-1beta or heat-inactivated Burkholderia cenocepacia. Stimulated IL-8 expression in IB3-1 and C38 cells was significantly reduced by shRNA expression. The shRNA targeting IL-8 had no effect on the activation of NF-kappaB, or on the protein levels of IkappaB or IL-6, suggesting that this anti-IL-8 strategy was highly specific, and therefore may offer potential for the treatment of inflammatory diseases.

Progress towards gene therapy for cystic fibrosis

A decade ago it was widely anticipated that cystic fibrosis would be one of the first diseases to be treated by gene therapy. The difficult hurdle of cloning the responsible gene had been accomplished, its function was established and the lung appeared readily accessible for gene replacement. Since the first clinical trials for cystic fibrosis lung disease in the early 1990s it has become increasingly apparent that successful lung-directed gene therapy is significantly more complex than was first envisioned. Numerous obstacles including vector toxicity, inefficient transgene expression and limited vector production have delayed progress. An increased understanding of vector biology and host interaction has led to the development of novel strategies to enhance the efficiency and selectivity of gene delivery to the lung. Although significant challenges remain, there is now a realistic prospect of a clinically effective treatment in the next 10 years.

Advances in cystic fibrosis gene therapy

PURPOSE OF REVIEW

The first cystic fibrosis gene therapy trials were carried out in 1993, and although proof-of-principle for gene transfer to the lungs was established, efficiency was generally low. The authors review the most recent advances in preclinical airway gene transfer and summarize the results from the latest clinical trials.

RECENT FINDINGS

Recent clinical trials report encouraging results. Repeat administration of adeno-associated virus to the lung was safe. Nonviral nanoparticles used, for the first time, in the nose of cystic fibrosis patients were also safe and led to partial correction of the chloride transport defect in nasal epithelium. Important advances have been made in preclinical research, including the development of new viral and nonviral gene transfer agents and improved plasmid DNA. In addition, physical delivery methods, such a magnetofection and electroporation, are being assessed to improve nonviral gene transfer.

SUMMARY

Considerable progress has been made in understanding and overcoming the problems associated with gene transfer to airway epithelial cells, the target cells for cystic fibrosis gene therapy. It has also been recognized that novel preclinical and clinical assays are crucial for the success of cystic fibrosis gene therapy, and considerable effort is currently being put into assay development and trial designs.