A phase I study of adenovirus-mediated transfer of the human cystic fibrosis transmembrane conductance regulator gene to a lung segment of individuals with cystic fibrosis

mRNA therapies: Pioneering a new era in rare genetic disease treatment

Rare genetic diseases, often referred to as orphan diseases due to their low prevalence and limited treatment options, have long posed significant challenges to our medical system. In recent years, Messenger RNA (mRNA) therapy has emerged as a highly promising treatment approach for various diseases caused by genetic mutations. Chemically modified mRNA is introduced into cells using carriers like lipid-based nanoparticles (LNPs), producing functional proteins that compensate for genetic deficiencies. Given the advantages of precise dosing, biocompatibility, transient expression, and minimal risk of genomic integration, mRNA therapies can safely and effectively correct genetic defects in rare diseases and improve symptoms. Currently, dozens of mRNA drugs targeting rare diseases are undergoing clinical trials. This comprehensive review summarizes the progress of mRNA therapy in treating rare genetic diseases. It introduces the development, molecular design, and delivery systems of mRNA therapy, highlighting their research progress in rare genetic diseases based on protein replacement and gene editing. The review also summarizes research progress in various rare disease models and clinical trials. Additionally, it discusses the challenges and future prospects of mRNA therapy. Researchers are encouraged to join this field and collaborate to advance the clinical translation of mRNA therapy, bringing hope to patients with rare genetic diseases.

Backbone cationized highly branched poly(β-amino ester)s as enhanced delivery vectors in non-viral gene therapy

Gene therapy holds great potential for treating Lung Cystic Fibrosis (CF) which is a fatal hereditary condition arising from mutations in the CF transmembrane conductance regulator (CFTR) gene, resulting in dysfunctional CFTR protein. However, the advancement and clinical application of CF gene therapy systems have been hindered due to the absence of a highly efficient delivery vector. In this work, we introduce a new generation of highly branched poly(β-amino ester) (HPAE) gene delivery vectors for CF treatment. Building upon the classical chemical composition of HPAE, a novel backbone cationization strategy was developed to incorporate additional functional amine groups into HPAE without altering their branching degree. By carefully adjusting the type, proportion, and backbone distribution of the added cationic groups, a series of highly effective HPAE gene delivery vectors were successfully constructed for CF disease gene therapy. In vitro assessment results showed that the backbone cationized HPAEs with randomly distributed 10% proportion of 1-(3-aminopropyl)-4-methylpiperazine (E7) amine groups exhibited superior transfection performance than their counterparts. Furthermore, the top-performed backbone cationized HPAEs, when loaded with therapeutic plasmids, successfully reinstated CFTR protein expression in the CFBE41o- disease model, achieving levels 20-23 times higher than that of normal human bronchial epithelial (HBE) cells. Their therapeutic effectiveness significantly surpassed that of the currently advanced commercial vectors, Xfect and Lipofectamine 3000.

Gene Therapy for Cystic Fibrosis: Recent Advances and Future Prospects

Gene replacement therapies are novel therapeutic approaches that seek to tackle hereditary diseases caused by a congenital deficiency in a particular gene, when a functional copy of a gene can be delivered to the cells and tissues using various delivery systems. To do this, viral particles carrying a functional copy of the gene of interest and various nonviral gene delivery systems, including liposomes, nanoparticles, etc., can be used. In this review, we discuss the state of current knowledge regarding the molecular mechanisms and types of genetic mutations that lead to cystic fibrosis and highlight recent developments in gene therapy that can be leveraged to correct these mutations and to restore the physiological function of the carrier protein transporting sodium and chlorine ions in the airway epithelial cells. Restoration of carrier protein expression could lead to the normalization of ion and water transport across the membrane and induce a decrease in the viscosity of airway surface fluid, which is one of the pathological manifestations of this disease. This review also summarizes recently published preclinical and clinical data for various gene therapies to allow one to make some conclusions about future prospects for gene therapy in cystic fibrosis treatment.

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.

The use of adenoviral vectors in gene therapy and vaccine approaches

Adenovirus was first identified in the 1950s and since then this pathogenic group of viruses has been explored and transformed into a genetic transfer vehicle. Modification or deletion of few genes are necessary to transform it into a conditionally or non-replicative vector, creating a versatile tool capable of transducing different tissues and inducing high levels of transgene expression. In the early years of vector development, the application in monogenic diseases faced several hurdles, including short-term gene expression and even a fatality. On the other hand, an adenoviral delivery strategy for treatment of cancer was the first approved gene therapy product. There is an increasing interest in expressing transgenes with therapeutic potential targeting the cancer hallmarks, inhibiting metastasis, inducing cancer cell death or modulating the immune system to attack the tumor cells. Replicative adenovirus as vaccines may be even older and date to a few years of its discovery, application of non-replicative adenovirus for vaccination against different microorganisms has been investigated, but only recently, it demonstrated its full potential being one of the leading vaccination tools for COVID-19. This is not a new vector nor a new technology, but the result of decades of careful and intense work in this field.

Toward Gene Transfer Nanoparticles as Therapeutics

Genetic medicine has great potential to treat the underlying causes of many human diseases with exquisite precision, but the field has historically been stymied by delivery as the central challenge. Nanoparticles, engineered constructs the size of natural viruses, are being designed to more closely mimic the delivery efficiency of viruses, while enabling the advantages of increased safety, cargo-carrying flexibility, specific targeting, and ease in manufacturing. The speed in which nonviral gene transfer nanoparticles are making progress in the clinic is accelerating, with clinical validation of multiple nonviral nucleic acid delivery nanoparticle formulations recently FDA approved for both expression and for silencing of genes. While much of this progress has been with lipid nanoparticle formulations, significant development is being made with other nanomaterials for gene transfer as well, with favorable attributes such as biodegradability, scalability, and cell targeting. This review highlights the state of the field, current challenges in delivery, and opportunities for engineered nanomaterials to meet these challenges, including enabling long-term therapeutic gene editing. Delivery technology utilizing different kinds of nanomaterials and varying cargos for gene transfer (DNA, mRNA, and ribonucleoproteins) are discussed. Clinical applications are presented, including for the treatment of genetic diseases such as cystic fibrosis.

The ZAR1 protein in cancer; from epigenetic silencing to functional characterisation and epigenetic therapy of tumour suppressors

ZAR1, zygote arrest 1, is a zinc finger protein (C-terminus), which was initially identified in mouse oocytes. Later it was found that its expression is present in various human tissues e.g. lung and kidney. Interestingly, it was observed that in various tumour types the ZAR1 transcript is missing due to hypermethylation of its CpG island promoter, but not ZAR2. Since methylation of the ZAR1 promoter is described as a frequent event in tumourigenesis, ZAR1 could serve as a useful diagnostic marker in cancer screens. ZAR1 was described as a useful prognostic/diagnostic cancer marker for lung cancer, kidney cancer, melanoma and possibly liver carcinoma. Furthermore, ZAR1 was reactivated as a tumour suppressor by epigenetic therapy using CRISPR-dCas9 method. This method holds the potential to precisely target not only ZAR1 and reactivate tumour suppressors in a tailored cancer therapy. ZAR1 is highly conserved amongst vertebrates, especially its zinc finger, which is the relevant domain for its protein and RNA binding ability. ZAR1 is implicated in various cellular mechanisms including regulation of oocyte/embryo development, cell cycle control and mRNA binding, though little was known about the underlying mechanisms. ZAR1 was reported to regulate and activate translation through the binding to TCS translation control sequences in the 3'UTRs of its target mRNA the kinase WEE1. ZAR1 has a tumour suppressing function by inhibiting cell cycle progression. Here we review the current literature on ZAR1 focusing on structural, functional and epigenetic aspects. Characterising the cellular mechanisms that regulate the signalling pathways ZAR1 is involved in, could lead to a deeper understanding of tumour development and, furthermore, to new strategies in cancer treatment.

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.

A review of 65 years of human adenovirus seroprevalence

Introduction: Human adenovirus (HAdV)-derived vectors have been used in numerous pre-clinical and clinical trials during the last 40 years. Current research in HAdV-based vaccines focuses on improving transgene immunogenicity and safety. Because pre-existing humoral immunity against HAdV types correlate with reduced vaccine efficacy and safety, many groups are exploring the development of HAdV types vectors with lower seroprevalence. However, global seroepidemiological data are incomplete. Areas covered: The goal of this review is to centralize 65 years of research on (primarily) HAdV epidemiology. After briefly addressing adenovirus biology, we chronical HAdV seroprevalence studies and highlight major milestones. Finally, we analyze data from about 50 studies with respect to HAdVs types that are currently used in the clinic, or are in the developmental pipeline. Expert opinion: Vaccination is among the most efficient tools to prevent infectious disease. HAdV-based vaccines have undeniable potential, but optimization is needed and antivector immunity remains a challenge if the same vectors are to be administrated to different populations. Here, we identify gaps in our knowledge and the need for updated worldwide epidemiological data.

Targeted Gene Delivery through the Respiratory System: Rationale for Intratracheal Gene Transfer

Advances in DNA- and RNA-based technologies have made gene therapy suitable for many lung diseases, especially those that are hereditary. The main objective of gene therapy is to deliver an adequate amount of gene construct to the intended target cell, achieve stable transduction in target cells, and to produce a clinically therapeutic effect. This review focuses on the cellular organization in the normal lung and how gene therapy targets the specific cell types that are affected by pulmonary disorders caused by genetic mutations. Furthermore, it examines the pulmonary barriers that can compromise the absorption and transduction of viral vectors and genetic agents by the lung. Finally, it discusses the advantages and limitations of direct intra-tracheal gene delivery with different viral vectors in small and large animal models and in clinical trials.

Understanding Gene Therapy in Acute Respiratory Distress Syndrome

Acute Respiratory Distress Syndrome (ARDS) and its complications remain lifethreatening conditions for critically ill patients. The present therapeutic strategies such as prone positioning ventilation strategies, nitric oxide inhalation, restrictive intravenous fluid management, and extracorporeal membrane oxygenation (ECMO) do not contribute much to improving the mortality of ARDS. The advanced understanding of the pathophysiology of acute respiratory distress syndrome suggests that gene-based therapy may be an innovative method for this disease. Many scientists have made beneficial attempts to regulate the immune response genes of ARDS, maintain the normal functions of alveolar epithelial cells and endothelial cells, and inhibit the fibrosis and proliferation of ARDS. Limitations to effective pulmonary gene therapy still exist, including the security of viral vectors and the pulmonary defense mechanisms against inhaled particles. Here, we summarize and review the mechanism of gene therapy for acute respiratory distress syndrome and its application.

Chemically modified hCFTR mRNAs recuperate lung function in a mouse model of cystic fibrosis

Gene therapy has always been a promising therapeutic approach for Cystic Fibrosis (CF). However, numerous trials using DNA or viral vectors encoding the correct protein resulted in a general low efficacy. In the last years, chemically modified messenger RNA (cmRNA) has been proven to be a highly potent, pulmonary drug. Consequently, we first explored the expression, function and immunogenicity of human (h)CFTR encoded by cmRNA^hCFTR in vitro and ex vivo, quantified the expression by flow cytometry, determined its function using a YFP based assay and checked the immune response in human whole blood. Similarly, we examined the function of cmRNA^hCFTR in vivo after intratracheal (i.t.) or intravenous (i.v.) injection of the assembled cmRNA^hCFTR together with Chitosan-coated PLGA (poly-D, L-lactide-co-glycolide 75:25 (Resomer RG 752 H)) nanoparticles (NPs) by FlexiVent. The amount of expression of human hCFTR encoded by cmRNA^hCFTR was quantified by hCFTR ELISA, and cmRNA^hCFTR values were assessed by RT-qPCR. Thereby, we observed a significant improvement of lung function, especially in regards to FEV_0.1, suggesting NP-cmRNA^hCFTR as promising therapeutic option for CF patients independent of their CFTR genotype.

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.

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.

Topical cystic fibrosis transmembrane conductance regulator gene replacement for cystic fibrosis-related lung disease

BACKGROUND

Cystic fibrosis is caused by a defective gene encoding a protein called the cystic fibrosis transmembrane conductance regulator (CFTR), and is characterised by chronic lung infection resulting in inflammation and progressive lung damage that results in a reduced life expectancy.

OBJECTIVES

To determine whether topical CFTR gene replacement therapy to the lungs in people with cystic fibrosis is associated with improvements in clinical outcomes, and to assess any adverse effects.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group Trials Register comprising references identified from comprehensive electronic database searches, handsearching relevant journals and abstract books of conference proceedings.Date of most recent search: 05 May 2016.An additional search of the National Institutes for Health (NIH) Genetic Modification Clinical Research Information System (GeMCRIS) was also performed for the years 1992 to 2015.Date of most recent search: 20 April 2016.

SELECTION CRITERIA

Randomised controlled studies comparing topical CFTR gene delivery to the lung, using either viral or non-viral delivery systems, with placebo or an alternative delivery system in people with confirmed cystic fibrosis.

DATA COLLECTION AND ANALYSIS

The authors independently extracted data and assessed study quality. Authors of included studies were contacted and asked for any available additional data. Meta-analysis was limited due to differing study designs.

MAIN RESULTS

Four randomised controlled studies met the inclusion criteria for this review, involving a total of 302 participants lasting from 29 days to 13 months; 14 studies were excluded. The included studies differed in terms of CFTR gene replacement agent and study design, which limited the meta-analysis. One study only enrolled adult males, the remaining studies included both males and females aged 12 years and over.Risk of bias in the studies was moderate. Random sequence generation and allocation concealment was only described in the more recent study; the remaining three studies were judged to have an unclear risk of bias. All four studies documented double-blinding to the intervention, but there is some uncertainty with regards to participant blinding in one study. Some outcome data were missing from all four studies.There were no differences in either the number of respiratory exacerbations or the number of participants with an exacerbation between replacement therapy or placebo groups at any time point. Meta-analysis of most respiratory function tests showed no difference between treatment and placebo groups, but the smallest study (n = 16) reported forced vital capacity (litres) increased more in the placebo group at up to 24 hours. A further study reported a significant improvement in forced expiratory volume at one second (litres) at 30 days after participants had received their first dose of favouring the gene therapy agent, but this finding was not confirmed when combined with at second study in the meta-analysis. The more recent study (n = 140) demonstrated a small improvement in forced vital capacity (per cent predicted) at two and three months and again at 11 and 12 months for participants receiving CFTR gene replacement therapy compared to those receiving placebo. The same study reported a significant difference in the relative change in forced expiratory volume at one second (per cent predicted) at two months, three months and 12 months.One small study reported significant concerns with "influenza-like" symptoms in participants treated with CFTR gene replacement therapy; this was not reported on repeated use of the same agent in a larger recent study.There was no other evidence of positive impact on outcomes, in particular improved quality of life or reduced treatment burden.Two studies measured ion transport in the lower airways; one (n = 16) demonstrated significant changes toward normal values in the participants who received gene transfer agents (P < 0.0001), mean difference 6.86 (95% confidence interval 3.77 to 9.95). The second study (n = 140) also reported significant changes toward normal values (P = 0.032); however, aggregate data were not available for analysis. In the most recent study, there was also evidence of increased salt transport in cells obtained by brushing the lower airway. These outcomes, whilst important, are not of direct clinical relevance.

AUTHORS' CONCLUSIONS

One study of liposome-based CFTR gene transfer therapy demonstrated some improvements in respiratory function in people with CF, but this limited evidence of efficacy does not support this treatment as a routine therapy at present. There was no evidence of efficacy for viral-mediated gene delivery.Future studies need to investigate clinically important outcome measures.

Strategies in early clinical development for the treatment of basic defects of cystic fibrosis

INTRODUCTION

Twenty-six years after the identification of the gene responsible for cystic fibrosis (CF), controversies still surround the pathogenesis of the disease that continues to burden and shorten lives. Therefore, finding effective therapeutic strategies that target the basic defect of CF is crucially needed.

AREAS COVERED

This review offers a comprehensive survey of fundamental therapies in early stages of development for the treatment of CF. The first part describes recent strategies targeting the basic defect either at the gene or at the transcript level. The second part summarizes a panel of novel strategies targeting protein repair. The third part reports strategies targeting non-CFTR channels.

EXPERT OPINION

Recent major breakthroughs in CF therapy have been made, raising hope to find a cure for CF. Apart from Vertex corrector and potentiator molecules (lumacaftor, ivacaftor, VX-661) and from ataluren, used to correct nonsense mutations, most compounds being currently tested are in very early (I-II) phases of development and definitive clinical results are keenly expected. Among the broad list of molecules and strategies being tested, the QR-010 compound and inhibitors of phosphodiesterase type 5 (sildenafil, vardenafil) could reveal a strong potentiality as therapeutic candidates to cure CF.

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.

A nonhuman primate toxicology and immunogenicity study evaluating aerosol delivery of AERAS-402/Ad35 vaccine: Evidence for transient t cell responses in peripheral blood and robust sustained responses in the lungs

Bacille Calmette-Guérin (BCG), the only licensed vaccine for the prevention of tuberculosis (TB), provides only limited protection against certain forms of Mycobacterium tuberculosis (Mtb) infection. While infection with Mtb can be treated with antibiotics, the therapy is expensive, toxic, and requires several months for treatment. In addition, the emergence of drug resistant strains limits the impact of antibiotics and underlines the importance of developing a more effective vaccine to control this disease. Given that pulmonary TB is the most common form of the disease, a vaccine capable of inducing lung-resident immunity may be advantageous for combating this infection. New advances in pulmonary delivery make this route of vaccination feasible and affordable. Here, we evaluate the safety and immunogenicity of an aerosolized Ad35-based vaccine, AERAS-402, delivered to the lungs in nonhuman primates as part of a GLP acute and chronic toxicology and safety study. In this study, animals received three high doses (1 x 10(11) vp) of AERAS-402 by inhalation via a nebulizer at 1-week intervals. Aerosol delivery of AERAS-402 resulted in an increase in relative lung weights as well as microscopic findings in the lungs, mediastinal lymph nodes, bronchus-associated lymphatic tissue, and the naso-oropharynx that were consistent with the induction of an immune response during the acute phase. These findings resolved by the chronic phase and were considered to be non-adverse. Furthermore, we observed transient vaccine-specific immune responses in the peripheral blood as well as sustained high-level polyfunctional CD4(+) and CD8(+) T cell responses in the bronchoalveolar lavage fluid of vaccinated nonhuman primates. The data suggest that pulmonary delivery of Ad35-based vaccines can be safe and can induce potent lung-resident immunity.

Ferret and pig models of cystic fibrosis: prospects and promise for gene therapy

Large animal models of genetic diseases are rapidly becoming integral to biomedical research as technologies to manipulate the mammalian genome improve. The creation of cystic fibrosis (CF) ferrets and pigs is an example of such progress in animal modeling, with the disease phenotypes in the ferret and pig models more reflective of human CF disease than mouse models. The ferret and pig CF models also provide unique opportunities to develop and assess the effectiveness of gene and cell therapies to treat affected organs. In this review, we examine the organ disease phenotypes in these new CF models and the opportunities to test gene therapies at various stages of disease progression in affected organs. We then discuss the progress in developing recombinant replication-defective adenoviral, adeno-associated viral, and lentiviral vectors to target genes to the lung and pancreas in ferrets and pigs, the two most affected organs in CF. Through this review, we hope to convey the potential of these new animal models for developing CF gene and cell therapies.

Stent-mediated gene delivery for site-specific transgene administration to the airway epithelium and management of tracheobronchial tumors

BACKGROUND

Gene therapy is currently under investigation as a means of managing a variety of pulmonary diseases. Unfortunately, gene transfer to bronchial epithelium has been hampered by the lack of stable and efficient transduction. Recent studies have shown that gene vectors could be tethered to the metallic surfaces of intra-arterial stents. This approach enables efficacious and site-specific adenoviral gene delivery to the vascular endothelium.

OBJECTIVES

We hypothesized that airway mesh stents impregnated with viral gene vectors could be used for local gene delivery to benign and malignant bronchial epithelium.

METHODS

Serotype 5 adenoviral vectors (Ad5, E1-/E3-) containing the reporter genes green fluorescent protein (Ad.GFP) or β-galactoside/LacZ (Ad.LacZ), or a therapeutic gene, Ad.INF-β, were coupled to either metallic mesh disks or stents via anti-Ad knob antibodies. These platforms were assessed for their ability to transfect bronchial epithelial cells from both rats and humans, as well as murine (L1C2) and human (A549) lung cancer cell lines. Gene transfer was quantified by fluorescent microscopy, scanning fluorimetry for Ad.GFP, and light microscopy studies assessing β-galactosidase staining for Ad.LacZ. Metallic mesh and stent-mediated gene transfer was also performed in a murine flank tumor model and in a rat endotracheal tumor model in order to evaluate the therapeutic potential.

RESULTS

In these studies, murine and human non-small cell lung cancer (NSCLC) cells were successfully transfected with reporter genes in vitro. Ad.LacZ-complexed mesh successfully transfected reporter genes into established murine flank NSCLC tumors. In addition, Ad.LacZ-tethered stents could effectively transfect both tracheobronchial epithelium and submucosal glands in rats. Similar epithelial transfection was achieved in ex vivo human bronchial epithelium. Pilot in vivo experimentation provided data supporting the concept that therapeutic genes could also be delivered with this technology. In additional pilot in vivo experiments, the growth of murine flank tumors was inhibited by placement of mesh disks coupled with Ad.muINF-β, and rats bearing endotracheal tumors demonstrated a trend towards prolonged survival with insertion of Ad.ratINF-β-tethered stents.

CONCLUSIONS

Stent-mediated gene delivery successfully enabled site-specific vector administration to target rat and human airway cells in cell culture, organ culture and in vivo. Local tracheobronchial gene delivery via stents could provide a viable clinical solution for overcoming the difficulties encountered with vector delivery within the lungs, in particular by lowering requisite vector titers and by directing desired vectors to areas of interest. This strategy may prove valuable for treating tumors involving the tracheobronchial tree, as well as other nonmalignant tracheobronchial disorders.

Cellular unfolded protein response against viruses used in gene therapy

Viruses are excellent vehicles for gene therapy due to their natural ability to infect and deliver the cargo to specific tissues with high efficiency. Although such vectors are usually "gutted" and are replication defective, they are subjected to clearance by the host cells by immune recognition and destruction. Unfolded protein response (UPR) is a naturally evolved cyto-protective signaling pathway which is triggered due to endoplasmic reticulum (ER) stress caused by accumulation of unfolded/misfolded proteins in its lumen. The UPR signaling consists of three signaling pathways, namely PKR-like ER kinase, activating transcription factor 6, and inositol-requiring protein-1. Once activated, UPR triggers the production of ER molecular chaperones and stress response proteins to help reduce the protein load within the ER. This occurs by degradation of the misfolded proteins and ensues in the arrest of protein translation machinery. If the burden of protein load in ER is beyond its processing capacity, UPR can activate pro-apoptotic pathways or autophagy leading to cell death. Viruses are naturally evolved in hijacking the host cellular translation machinery to generate a large amount of proteins. This phenomenon disrupts ER homeostasis and leads to ER stress. Alternatively, in the case of gutted vectors used in gene therapy, the excess load of recombinant vectors administered and encountered by the cell can trigger UPR. Thus, in the context of gene therapy, UPR becomes a major roadblock that can potentially trigger inflammatory responses against the vectors and reduce the efficiency of gene transfer.

Gene therapy in cystic fibrosis

The principal cause of morbidity and mortality in cystic fibrosis (CF) is pulmonary disease, so the focus of new treatments in this condition is primarily targeted at the lungs. Since the cloning of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene in 1989, there has been significant interest in the possibility of gene therapy as a treatment for CF. Early studies using viral vectors carrying a healthy CFTR plasmid highlighted the difficulties with overcoming the body's host defences. This article reviews the work on gene therapy in CF to date and describes the ongoing work of the UK CF Gene Therapy Consortium in investigating the potential of gene therapy as a treatment for patients with CF.

Feasibility of Applying Helper-Dependent Adenoviral Vectors for Cancer Immunotherapy

Adenoviruses (Ads) infect a broad range of tissue types, and derived vectors have been extensively used for gene therapy. Helper-dependent Ad vectors (HDAds), devoid of viral coding sequences, allow for insertion of large or multiple transgenes in a single vector and have been preclinically used for the study of genetic disorders. However, the clinical application of Ad vectors including HDAds for genetic disorders has been hampered by an acute toxic response. This characteristic, while disadvantageous for gene replacement therapy, could be strategically advantageous for the activation of an immune response if HDAds were used as an adjunct treatment in cancer. Cancer treatments including immunotherapy are frequently limited by the inhibitory environment produced by both tumors and their stroma, each of which express numerous inhibitory molecules. Hence, multiple inhibitory mechanisms must be overcome for development of anti-tumor immunity. The large coding capacity of HDAds can accommodate multiple immune modulating transgenes that could produce a combined effect to overcome tumor-derived inhibition and ensure intratumoral effector T-cell proliferation and function. In this review, we discuss the potential advantages of HDAds to cancer immunotherapy based on potent host immune responses to Ads.

Topical cystic fibrosis transmembrane conductance regulator gene replacement for cystic fibrosis-related lung disease

BACKGROUND

Cystic fibrosis is caused by a defective gene encoding a protein called the cystic fibrosis transmembrane conductance regulator (CFTR), and is characterised by chronic lung infection resulting in inflammation and progressive lung damage that results in a reduced life expectancy.

OBJECTIVES

To determine whether topical CFTR gene replacement therapy to the lungs in people with cystic fibrosis is associated with improvements in clinical outcomes, and to assess any adverse effects.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group Trials Register comprising references identified from comprehensive electronic database searches, handsearching relevant journals and abstract books of conference proceedings.Date of most recent search: 22 August 2013.An additional search of the National Institutes for Health (NIH) Genetic Modification Clinical Research Information System (GeMCRIS) was also performed for the years 1992 to 2013.Date of most recent search: 04 September 2013.

SELECTION CRITERIA

Randomised controlled trials comparing topical CFTR gene delivery to the lung, using either viral or non-viral delivery systems, with placebo or an alternative delivery system in people with confirmed cystic fibrosis.

DATA COLLECTION AND ANALYSIS

The authors independently extracted data and assessed study quality. Authors of included studies were contacted and asked for any available additional data. Meta-analysis was limited due to differing study designs.

MAIN RESULTS

Three randomised controlled trials met the inclusion criteria for this review, involving a total of 155 participants. Fourteen studies were excluded. The included studies differed in terms of CFTR gene replacement agent and study design, which limited the meta-analysis.Although the first Moss study reported a significant improvement in respiratory function (forced expiratory volume at one second) 30 days after participants had received their first dose of gene therapy agent, this finding was not confirmed in their larger second study or in our meta-analysis.In participants who received the CFTR gene transfer agents in the Alton study, "influenza-like" symptoms were found (risk ratio 7.00 (95% confidence interval 1.10 to 44.61)). There were no other significant increases in adverse events in any of the studies.Alton measured ion transport in the lower airways and demonstrated significant changes toward normal values in the participants who received gene transfer agents (P < 0.0001), mean difference 6.86 (95% confidence interval 3.77 to 9.95). In these participants there was also evidence of increased salt transport in cells obtained by brushing the lower airway. These outcomes, whilst important, are not of direct clinical relevance.

AUTHORS' CONCLUSIONS

There is currently no evidence to support the use of CFTR gene transfer agents as a treatment for lung disease in people with cystic fibrosis. Future studies need to investigate clinically important outcome measures.

Nanotechnology approaches for inhalation treatment of fibrosis

Cystic fibrosis (CF) is an autosomal recessive monogenetic disease that afflicts nearly 70 000 patients worldwide. The mutation results in the accumulation of viscous mucus in multiple organs especially in the lungs, liver and pancreas. High associated morbidity and mortality is caused by CF due to the lack of effective therapies. It is widely accepted that morbidity and mortality caused by CF is primarily due to the respiratory manifestations of the disease. Consequently, several approaches were recently developed for treatment of lung complications of CF. However, the lack of effective methods for delivery and especially targeted delivery of therapeutics specifically to lung tissues and cells limits the efficiency of the therapy. Local pulmonary delivery of therapeutics has two major advantages over systemic application. First, it enhances the accumulation of therapeutics specifically in the lungs and therefore increases the efficiency of the treatment. Second, local lung delivery substantially prevents the penetration of the delivered drug into the systemic circulation limiting adverse side effects of the treatment on other organs and tissues. This review is focused on different approaches to the treatment of respiratory manifestations of CF as well as on methods of pulmonary delivery of therapeutics.

Gene therapy in cystic fibrosis

Cystic fibrosis (CF) is an autosomal recessive disease caused by mutations in the cystic fibrosis transmembrane regulator (CFTR) gene and is the most common life-shortening genetic defect in Caucasians. Life expectancy in CF has improved substantially over the last 75 years because of treatments aimed at end-organ complications. Since the CFTR gene was discovered in 1989 more than 1900 mutations have been reported to cause CF and significant effort has been put forth into gene therapy to find a mutation independent "cure" for CF. Gene-based approaches have not yet led to a viable therapy but have provided insights into hurdles that limit the efficacy of gene therapy. This review will address the nomenclature of CFTR mutations, attempts at viral and nonviral gene therapy, and recent advances in mutation-specific molecules.

Adenoviral gene transfer corrects the ion transport defect in the sinus epithelia of a porcine CF model

Cystic fibrosis (CF) pigs spontaneously develop sinus and lung disease resembling human CF. The CF pig presents a unique opportunity to use gene transfer to test hypotheses to further understand the pathogenesis of CF sinus disease. In this study, we investigated the ion transport defect in the CF sinus and found that CF porcine sinus epithelia lack cyclic AMP (cAMP)-stimulated anion transport. We asked whether we could restore CF transmembrane conductance regulator gene (CFTR) current in the porcine CF sinus epithelia by gene transfer. We quantified CFTR transduction using an adenovirus expressing CFTR and green fluorescent protein (GFP). We found that as little as 7% of transduced cells restored 6% of CFTR current with 17-28% of transduced cells increasing CFTR current to 50% of non-CF levels. We also found that we could overcorrect cAMP-mediated current in non-CF epithelia. Our findings indicate that CF porcine sinus epithelia lack anion transport, and a relatively small number of cells expressing CFTR are required to rescue the ion transport phenotype. These studies support the use of the CF pig as a preclinical model for future gene therapy trials in CF sinusitis.

Early responses to adenoviral-mediated transfer of the aquaporin-1 cDNA for radiation-induced salivary hypofunction

No conventional therapy exists for salivary hypofunction in surviving head and neck cancer patients with Radiation Therapy Oncology Group late grade 2-3 toxicity. We conducted a phase I clinical trial to test the safety and biologic efficacy of serotype 5, adenoviral-mediated aquaporin-1 cDNA transfer to a single previously irradiated parotid gland in 11 subjects using an open label, single-dose, dose-escalation design (AdhAQP1 vector; four dose tiers from 4.8 × 10(7) to 5.8 × 10(9) vector particles per gland). Treated subjects were followed at scheduled intervals. Multiple safety parameters were measured and biologic efficacy was evaluated with measurements of parotid salivary flow rate. Symptoms were assessed with a visual analog scale. All subjects tolerated vector delivery and study procedures well over the 42-d study period reported. No deaths, serious adverse events, or dose-limiting toxicities occurred. Generally, few adverse events occurred, and all were considered mild or moderate. No consistent changes were found in any clinical chemistry and hematology parameters measured. Objective responses were seen in six subjects, all at doses <5.8 × 10(9) vector particles per gland. Five of these six subjects also experienced subjective improvement in xerostomia. AdhAQP1 vector delivery to a single parotid gland was safe and transfer of the hAQP1 cDNA increased parotid flow and relieved symptoms in a subset of subjects.

Topical cystic fibrosis transmembrane conductance regulator gene replacement for cystic fibrosis-related lung disease

BACKGROUND

Cystic fibrosis is caused by a defective gene encoding a protein called the cystic fibrosis transmembrane conductance regulator (CFTR), and is characterised by chronic lung infection resulting in inflammation and progressive lung damage that results in a reduced life expectancy.

OBJECTIVES

To determine whether topical CFTR gene replacement therapy to the lungs in people with cystic fibrosis is associated with improvements in clinical outcomes, and to assess any adverse effects.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group Trials Register comprising references identified from comprehensive electronic database searches, handsearching relevant journals and abstract books of conference proceedings.Date of most recent search: 19 July 2012.An additional search of the National Institutes for Health (NIH) Genetic Modification Clinical Research Information System (GeMCRIS) was also performed for the years 1992 to 2012.Date of most recent search: 25 July 2012.

SELECTION CRITERIA

Randomised controlled trials comparing topical CFTR gene delivery to the lung, using either viral or non-viral delivery systems, with placebo or an alternative delivery system in people with confirmed cystic fibrosis.

DATA COLLECTION AND ANALYSIS

The authors independently extracted data and assessed study quality. Authors of included studies were contacted and asked for any available additional data. Meta-analysis was limited due to differing study designs.

MAIN RESULTS

Three randomised controlled trials met the inclusion criteria for this review, involving a total of 155 participants. Fourteen studies were excluded. The included studies differed in terms of CFTR gene replacement agent and study design, which limited the meta-analysis.Although the first Moss study reported a significant improvement in respiratory function (forced expiratory volume at one second) 30 days after participants had received their first dose of gene therapy agent, this finding was not confirmed in their larger second study or in our meta-analysis.In participants who received the CFTR gene transfer agents in the Alton study, "influenza-like" symptoms were found (risk ratio 7.00 (95% confidence interval 1.10 to 44.61)). There were no other significant increases in adverse events in any of the studies.Alton measured ion transport in the lower airways and demonstrated significant changes toward normal values in the participants who received gene transfer agents (P < 0.0001), mean difference 6.86 (95% CI of 3.77 to 9.95). In these participants there was also evidence of increased salt transport in cells obtained by brushing the lower airway. These outcomes, whilst important, are not of direct clinical relevance.

AUTHORS' CONCLUSIONS

There is currently no evidence to support the use of CFTR gene transfer reagents as a treatment for lung disease in people with cystic fibrosis. Future studies need to investigate clinically important outcome measures.

Pseudotyped AAV vector-mediated gene transfer in a human fetal trachea xenograft model: implications for in utero gene therapy for cystic fibrosis

Background

Lung disease including airway infection and inflammation currently causes the majority of morbidities and mortalities associated with cystic fibrosis (CF), making the airway epithelium and the submucosal glands (SMG) novel target cells for gene therapy in CF. These target cells are relatively inaccessible to postnatal gene transfer limiting the success of gene therapy. Our previous work in a human-fetal trachea xenograft model suggests the potential benefit for treating CF in utero. In this study, we aim to validate adeno-associated virus serotype 2 (AAV2) gene transfer in a human fetal trachea xenograft model and to compare transduction efficiencies of pseudotyping AAV2 vectors in fetal xenografts and postnatal xenograft controls.

Methodology/Principal Findings

Human fetal trachea or postnatal bronchus controls were xenografted onto immunocompromised SCID mice for a four-week engraftment period. After injection of AAV2/2, 2/1, 2/5, 2/7 or 2/8 with a LacZ reporter into both types of xenografts, we analyzed for transgene expression in the respiratory epithelium and SMGs. At 1 month, transduction by AAV2/2 and AAV2/8 in respiratory epithelium and SMG cells was significantly greater than that of AAV2/1, 2/5, and 2/7 in xenograft tracheas. Efficiency in SMG transduction was significantly greater in AAV2/8 than AAV2/2. At 3 months, AAV2/2 and AAV2/8 transgene expression was >99% of respiratory epithelium and SMG. At 1 month, transduction efficiency of AAV2/2 and AAV2/8 was significantly less in adult postnatal bronchial xenografts than in fetal tracheal xenografts.

Conclusions/Significance

Based on the effectiveness of AAV vectors in SMG transduction, our findings suggest the potential utility of pseudotyped AAV vectors for treatment of cystic fibrosis. The human fetal trachea xenograft model may serve as an effective tool for further development of fetal gene therapy strategies for the in utero treatment of cystic fibrosis.

Current Status of Gene Therapy for Cystic Fibrosis Pulmonary Disease

Cystic fibrosis (CF) is a common lethal genetic disorder that affects all ethnic populations; however, it is most prevalent in Caucasians. Intensive basic research over the last 20 years has resulted in a wealth of information regarding the CF gene, its protein product and the mutational basis of disease. This increased understanding has lead to the development of gene therapy for the treatment of CF pulmonary disease. Delivery of the CF gene to the airway requires direct in vivo transfer using vectors encoding for normal CF transmembrane regulator (CFTR) protein. Several vectors are currently available for CF gene transfer and include both viral (adenoviruses, adeno-associated viruses) and non-viral (liposomal) systems. Initial clinical trials with each of these vectors have demonstrated that gene transfer to the CF airway is possible. The efficiency of transfer and duration of expression, however, have been limited. The effects of gene transfer on correction of the basic ion transport defects have also been highly variable and inconsistent, irrespective of the vector. Currently, the risk of severe immunological reactions is the primary factor limiting the clinical advancement of gene therapy. Both the adenoviral and liposomal vectors are associated with significant acute inflammatory reactions. The adenoviruses and adeno-associated viruses also elicit humoral immune responses that significantly reduce the efficiency of transgene expression and increase the risk of readministration. Several strategies are under investigation to improve the efficiency of gene transfer to the CF airway. These include overcoming local barriers in the lung, circumventing the immune response and improving vector internalization and/or uptake. Application of gene transfer in the child and possibly the fetus are also potential future clinical applications of gene therapy. However, despite considerable research with gene therapy, there is little evidence to suggest that a well tolerated and effective gene transfer method is imminent and aggressive use of conventional pharmacological therapies currently offer the greatest promise in the treatment of patients with CF.

Gene therapy for the treatment of cystic fibrosis

Gene therapy is being developed as a novel treatment for cystic fibrosis (CF), a condition that has hitherto been widely-researched yet for which no treatment exists that halts the progression of lung disease. Gene therapy involves the transfer of correct copies of cystic fibrosis transmembrane conductance regulator (CFTR) DNA to the epithelial cells in the airways. The cloning of the CFTR gene in 1989 led to proof-of-principle studies of CFTR gene transfer in vitro and in animal models. The earliest clinical trials in CF patients were conducted in 1993 and used viral and non-viral gene transfer agents in both the nasal and bronchial airway epithelium. To date, studies have focused largely on molecular or bioelectric (chloride secretion) outcome measures, many demonstrating evidence of CFTR expression, but few have attempted to achieve clinical efficacy. As CF is a lifelong disease, turnover of the airway epithelium necessitates repeat administration. To date, this has been difficult to achieve with viral gene transfer agents due to host recognition leading to loss of expression. The UK Cystic Fibrosis Gene Therapy Consortium (Imperial College London, University of Edinburgh and University of Oxford) is currently working on a large and ambitious program to establish the clinical benefits of CF gene therapy. Wave 1, which has reached the clinic, uses a non-viral vector. A single-dose safety trial is nearing completion and a multi-dose clinical trial is shortly due to start; this will be powered for clinically-relevant changes. Wave 2, more futuristically, will look at the potential of lentiviruses, which have long-lasting expression. This review will summarize the current status of translational research in CF gene therapy.

Clinical review: gene-based therapies for ALI/ARDS: where are we now?

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) confer substantial morbidity and mortality, and have no specific therapy. The accessibility of the distal lung epithelium via the airway route, and the relatively transient nature of ALI/ARDS, suggest that the disease may be amenable to gene-based therapies. Ongoing advances in our understanding of the pathophysiology of ALI/ARDS have revealed multiple therapeutic targets for gene-based approaches. Strategies to enhance or restore lung epithelial and/or endothelial cell function, to strengthen lung defense mechanisms against injury, to speed clearance of infection and to enhance the repair process following ALI/ARDS have all demonstrated promise in preclinical models. Despite three decades of gene therapy research, however, the clinical potential for gene-based approaches to lung diseases including ALI/ARDS remains to be realized. Multiple barriers to effective pulmonary gene therapy exist, including the pulmonary architecture, pulmonary defense mechanisms against inhaled particles, the immunogenicity of viral vectors and the poor transfection efficiency of nonviral delivery methods. Deficits remain in our knowledge regarding the optimal molecular targets for gene-based approaches. Encouragingly, recent progress in overcoming these barriers offers hope for the successful translation of gene-based approaches for ALI/ARDS to the clinical setting.

Improvement of adenoviral vector-mediated gene transfer to airway epithelia by folate-modified anionic liposomes

Despite remarkable progress in the development of both viral and nonviral gene delivery vectors for airway disease treatment, poor gene transfer efficiency to the airway epithelium is a major obstacle in clinical application. To take advantage of the unique features of viral and nonviral vectors, we have developed complexes of adenovirus vector and anionic liposomes (AL-Ad5) by the calcium-induced phase change method. In the current study, based on the fact that there are overexpressed folate receptors on the surface of airway epithelia, we further modified the AL-Ad5 complexes with folate (F-AL-Ad5) to improve the transduction ability of Ad5 in airway epithelia. The transduction efficiencies of the obtained F-AL-Ad5 and AL-Ad5 complexes were assessed in primary-cultured airway epithelia in vitro. Our results indicated that compared with naked adenovirus vector, both AL-Ad5 and F-AL-Ad5 could significantly enhance the gene transduction efficiency of adenovirus vector in primary-cultured airway epithelial cells. Moreover, the enhancement mediated by F-AL-Ad5 was more dramatic than that by AL-Ad5. These results suggested that F-AL-Ad5 may be a useful strategy to deliver therapeutic genes to the airway epithelia and is promising in clinical application.

Challenges and advances in the development of inhalable drug formulations for cystic fibrosis lung disease

INTRODUCTION

Cystic fibrosis (CF) is a multisystem genetic disorder, which usually results in significant respiratory dysfunction. At present there is no cure for CF, but advances in pharmacotherapy have gradually increased the life expectancy of CF patients. As many drugs used in the therapy of CF are delivered by inhalation, the demand for effective and convenient inhalational CF drug formulations will grow as CF patients live longer. Knowledge of the current limitations in inhalational CF drug delivery is critical in identifying new opportunities and designing rational delivery strategies.

AREAS COVERED

This review discusses current and emerging therapeutic agents for CF therapy, selected physiological challenges to effective inhalational medication delivery, and various approaches to overcoming these challenges. The reader will find an integrated view of the known inhalational drug delivery challenges and the rationales for recent investigational inhalational drug formulations.

EXPERT OPINION

An ideal drug/gene delivery system to CF airways should overcome the tenacious sputum, which presents physical, chemical and biological barriers to effective transport of therapeutic agents to the targets and various cellular challenges.

Design of gene therapy trials in CF patients

The report of the first CF patients to receive CFTR gene therapy appeared in 1993; since then, there have been over 20 clinical trials of both viral and non-viral gene transfer agents. These have largely been single dose to either nose or lower airway and have been designed around molecular or bioelectrical outcome measures. Both transgene mRNA and partial correction of chloride secretion have been reported, although sodium hyperabsorption has not been improved. The UK CF Gene Therapy Consortium is focussed on a clinical programme to establish whether these proof-of-principle measures translate into clinical benefit. Here, we discuss the considerations in designing such a programme, focusing in particular on our choice of the optimal, currently available delivery method and established and novel outcome measures. We highlight the logistic and regulatory complexities of such a clinical programme and finally, we look to the future and consider possible alternative strategies.

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.

Vectors for pulmonary gene therapy

The success of gene transfer in preclinical animal models and proof of principle clinical studies has made gene therapy an attractive concept for disease treatment. A variety of diseases affecting the lung are candidates for gene therapy. Delivery of genes to the lungs seems to be straightforward, because of the easy accessibility of epithelial cells via the airways. However, efficient delivery and expression of the therapeutic transgene at levels sufficient to result in phenotypic correction of the diseased state have proven elusive. This review presents a brief summary about current status and future prospects in the development of viral and non-viral strategies for pulmonary gene therapy.

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.

Gene therapy for cystic fibrosis

Cystic Fibrosis (CF) is an autosomal recessive disorder due to mutations in the CF transmembrane conductance regulator (CFTR) gene that lead to defective ion transport in the conducting pulmonary airways and exocrine glands. Through a process that is not fully understood, CFTR defects predispose affected patients to chronic endobronchial infections with organisms such as Pseudomonas aeruginosa and Staphylococcus aureus. Following the discovery of the CFTR gene in 1989, CF became one of the primary targets for gene therapy research. Early enthusiasm surrounded the new field of gene therapy during most of the 1990s and it led academics and clinicians on a big effort to apply gene therapy for cystic fibrosis. Clinical studies have been pursued using recombinant adenovirus, recombinant adeno-associated virus, cationic liposomes, and cationic polymer vectors. Although to this date no dramatic therapeutic benefits have been observed, a lot of information has been gained from the pre-clinical and clinical studies that were performed. This learning curve has led to the optimization of vector technology and an appreciation of immune and mechanical barriers that have to be overcome for successful delivery.

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

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