Partial correction of the CFTR-dependent ABPA mouse model with recombinant adeno-associated virus gene transfer of truncated CFTR gene

ECFS standards of care on CFTR-related disorders: Identification and care of the disorders

This is the third paper in the series providing updated information and recommendations for people with cystic fibrosis transmembrane conductance regulator (CFTR)-related disorder (CFTR-RD). This paper covers the individual disorders, including the established conditions - congenital absence of the vas deferens (CAVD), diffuse bronchiectasis and chronic or acute recurrent pancreatitis - and also other conditions which might be considered a CFTR-RD, including allergic bronchopulmonary aspergillosis, chronic rhinosinusitis, primary sclerosing cholangitis and aquagenic wrinkling. The CFTR functional and genetic evidence in support of the condition being a CFTR-RD are discussed and guidance for reaching the diagnosis, including alternative conditions to consider and management recommendations, is provided. Gaps in our knowledge, particularly of the emerging conditions, and future areas of research, including the role of CFTR modulators, are highlighted.

Would it have happened without Christmas? Thoracic emphysema and allergic bronchopulmonary aspergillosis in a juvenile cystic fibrosis patient with the G551D mutation receiving ivacaftor

Potent CFTR modulators improve CF manifestations far beyond expectations, including reduction of risk of typical complications. This is the first report of a patient who developed life-threatening ABPA and emphysema after overwhelming improvement. https://bit.ly/2P96PTy.

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.

Optimization of adeno-associated virus vector-mediated gene transfer to the respiratory tract

An efficient adeno-associated virus (AAV) vector was constructed for the treatment of respiratory diseases. AAV serotypes, promoters and routes of administration potentially influencing the efficiency of gene transfer to airway cells were examined in the present study. Among the nine AAV serotypes (AAV1-9) screened in vitro and four serotypes (AAV1, 2, 6, 9) evaluated in vivo, AAV6 showed the strongest transgene expression. As for promoters, the cytomegalovirus (CMV) early enhancer/chicken β-actin (CAG) promoter resulted in more robust transduction than the CMV promoter. Regarding delivery routes, intratracheal administration resulted in strong transgene expression in the lung, whereas the intravenous and intranasal administration routes yielded negligible expression. The combination of the AAV6 capsid and CAG promoter resulted in sustained expression, and the intratracheally administered AAV6-CAG vector transduced bronchial cells and pericytes in the lung. These results suggest that AAV6-CAG vectors are more promising than the previously preferred AAV2 vectors for airway transduction, particularly when administered into the trachea. The present study offers an optimized strategy for AAV-mediated gene therapy for lung diseases, such as cystic fibrosis and pulmonary fibrosis.

Aspergillus in chronic lung disease: Modeling what goes on in the airways

Aspergillus species cause a range of respiratory diseases in humans. While immunocompromised patients are at risk for the development of invasive infection with these opportunistic molds, patients with underlying pulmonary disease can develop chronic airway infection with Aspergillus species. These conditions span a range of inflammatory and allergic diseases including Aspergillus bronchitis, allergic bronchopulmonary aspergillosis, and severe asthma with fungal sensitization. Animal models are invaluable tools for the study of the molecular mechanism underlying the colonization of airways by Aspergillus and the host response to these non-invasive infections. In this review we summarize the state-of-the-art with respect to the available animal models of noninvasive and allergic Aspergillus airway disease; the key findings of host-pathogen interaction studies using these models; and the limitations and future directions that should guide the development and use of models for the study of these important pulmonary conditions.

Development of rAAV2-CFTR: History of the First rAAV Vector Product to be Used in Humans

The first human gene therapy trials using recombinant adeno-associated virus (rAAV) vectors were performed in cystic fibrosis (CF) patients. Over 100 CF patients were enrolled in 5 separate trials of rAAV2-CFTR administration via nasal, endobronchial, maxillary sinus, and aerosol delivery. Recombinant AAV vectors were designed to deliver the CF transmembrane regulator (CFTR) gene and correct the basic CFTR defect by restoring chloride transport and reverting the upregulation of proinflammatory cytokines. However, vector DNA expression was limited in duration because of the low incidence of integration and natural airway epithelium turnover. In addition, repeated administration of AAV-CFTR vector resulted in a humoral immune response that prevented effective gene transfer from subsequent doses of vector. AAV serotype 2 was used in human trials before the comparison with other serotypes and determination that serotypes 1 and 5 not only possess higher tropism for the airway epithelium, but also are capable of bypassing the binding and trafficking processes-both were important hindrances to the effectiveness of rAAV2. Although rAAV-CFTR gene therapy does not appear likely to supplant newer small-molecule CFTR modulators in the near future, early work with rAAV-CFTR provided an important foundation for later use of rAAV in humans.

Transcomplementation by a truncation mutant of cystic fibrosis transmembrane conductance regulator (CFTR) enhances ΔF508 processing through a biomolecular interaction

We previously showed that a truncation mutant of CFTR missing the first four transmembrane segments of TMD1, Δ264 CFTR, binds to key elements in the ER quality control mechanism to increase the amounts of the mature C band of both wt and ΔF508 CFTR through transcomplementation. Here, we created a new construct, Δ27-264 CFTR. Even though Δ27-264 CFTR is rapidly degraded in the proteasome, steady state protein can be detected by Western blot. Δ27-264 CFTR can also increase the amounts of the mature C band of both wt and ΔF508 CFTR through transcomplementation. Electrophysiology experiments show that Δ27-264 CFTR can restore chloride channel currents. Further experiments with the conduction mutant S341A show conclusively that currents are indeed generated by rescued channel function of ΔF508 CFTR. Immunoprecipitation studies show that Δ27-264 binds to ΔF508-CFTR, suggesting a bimolecular interaction. Thus the adeno-associated viral vector, rAAV-Δ27-264 CFTR, is a highly promising CF gene therapy vector, because it increases the amount of mature band C protein both from wt and ΔF508 CFTR, and rescues channel activity of ΔF508 CFTR.

Gene and cell therapy for cystic fibrosis: from bench to bedside

Clinical trials in cystic fibrosis (CF) patients established proof-of-principle for transfer of the wild-type cystic fibrosis transmembrane conductance regulator (CFTR) gene to airway epithelial cells. However, the limited efficacy of gene transfer vectors as well as extra- and intracellular barriers have prevented the development of a gene therapy-based treatment for CF. Here, we review the use of new viral and nonviral gene therapy vectors, as well as human artificial chromosomes, to overcome barriers to successful CFTR expression. Pre-clinical studies will surely benefit from novel animal models, such as CF pigs and ferrets. Prenatal gene therapy is a potential alternative to gene transfer to fully developed lungs. However, unresolved issues, including the possibility of adverse effects on pre- and postnatal development, the risk of initiating oncogenic or degenerative processes and germ line transmission require further investigation. Finally, we discuss the therapeutic potential of stem cells for CF lung disease.

Impact of Aspergillus fumigatus in allergic airway diseases

For decades, fungi have been recognized as associated with asthma and other reactive airway diseases. In contrast to type I-mediated allergies caused by pollen, fungi cause a large number of allergic diseases such as allergic bronchopulmonary mycoses, rhinitis, allergic sinusitis and hypersensitivity pneumonitis. Amongst the fungi, Aspergillus fumigatus is the most prevalent cause of severe pulmonary allergic disease, including allergic bronchopulmonary aspergillosis (ABPA), known to be associated with chronic lung injury and deterioration in pulmonary function in people with chronic asthma and cystic fibrosis (CF). The goal of this review is to discuss new understandings of host-pathogen interactions in the genesis of allergic airway diseases caused by A. fumigatus. Host and pathogen related factors that participate in triggering the inflammatory cycle leading to pulmonary exacerbations in ABPA are discussed.

Lack of cystic fibrosis transmembrane conductance regulator in CD3+ lymphocytes leads to aberrant cytokine secretion and hyperinflammatory adaptive immune responses

Cystic fibrosis (CF), the most common fatal monogenic disease in the United States, results from mutations in CF transmembrane conductance regulator (CFTR), a chloride channel. The mechanisms by which CFTR mutations cause lung disease in CF are not fully defined but may include altered ion and water transport across the airway epithelium and aberrant inflammatory and immune responses to pathogens within the airways. We have shown that Cftr(-/-) mice mount an exaggerated IgE response toward Aspergillus fumigatus, with higher levels of IL-13 and IL-4, mimicking both the T helper cell type 2-biased immune responses seen in patients with CF. Herein, we demonstrate that these aberrations are primarily due to Cftr deficiency in lymphocytes rather than in the epithelium. Adoptive transfer experiments with CF splenocytes confer a higher IgE response to Aspergillus fumigatus compared with hosts receiving wild-type splenocytes. The predilection of Cftr-deficient lymphocytes to mount T helper cell type 2 responses with high IL-13 and IL-4 was confirmed by in vitro antigen recall experiments. Conclusive data on this phenomenon were obtained with conditional Cftr knockout mice, where mice lacking Cftr in T cell lineages developed higher IgE than their wild-type control littermates. Further analysis of Cftr-deficient lymphocytes revealed an enhanced intracellular Ca(2+) flux in response to T cell receptor activation. This was accompanied by an increase in nuclear localization of the calcium-sensitive transcription factor, nuclear factor of activated T cell, which could drive the IL-13 response. In summary, our data identified that CFTR dysfunction in T cells can lead directly to aberrant immune responses. These findings implicate the lymphocyte population as a potentially important target for CF therapeutics.

Mixed bacterial-fungal infections in the CF respiratory tract

Cystic fibrosis (CF) is a common genetic disease whose major clinical manifestations include repeated episodes of airway infection and inflammation that ultimately result in premature death from respiratory failure. The consequences of infection by individual bacteria have been well studied and the evidence is building that fungal pathogens may be playing an important role in lung disease progression. In contrast, though many CF patients have airway infections characterized by the presence of both bacteria and fungi, our understanding of the impact of such polymicrobial infections on the host is limited. In this review, we discuss what is currently known about incidence of mixed bacterial-fungal infections, and the potential consequences of these mixed infections on the progression of CF lung disease.

N-glycosylation augmentation of the cystic fibrosis epithelium improves Pseudomonas aeruginosa clearance

Chronic lung colonization with Pseudomonas aeruginosa is anticipated in cystic fibrosis (CF). Abnormal terminal glycosylation has been implicated as a candidate for this condition. We previously reported a down-regulation of mannose-6-phosphate isomerase (MPI) for core N-glycan production in the CFTR-defective human cell line (IB3). We found a 40% decrease in N-glycosylation of IB3 cells compared with CFTR-corrected human cell line (S9), along with a threefold-lower surface attachment of P. aeruginosa strain, PAO1. There was a twofold increase in intracellular bacteria in S9 cells compared with IB3 cells. After a 4-hour clearance period, intracellular bacteria in IB3 cells increased twofold. Comparatively, a twofold decrease in intracellular bacteria occurred in S9 cells. Gene augmentation in IB3 cells with hMPI or hCFTR reversed these IB3 deficiencies. Mannose-6-phosphate can be produced from external mannose independent of MPI, and correction in the IB3 clearance deficiencies was observed when cultured in mannose-rich medium. An in vivo model for P. aeruginosa colonization in the upper airways revealed an increased bacterial burden in the trachea and oropharynx of nontherapeutic CF mice compared with mice treated either with an intratracheal delivery adeno-associated viral vector 5 expressing murine MPI, or a hypermannose water diet. Finally, a modest lung inflammatory response was observed in CF mice, and was partially corrected by both treatments. Augmenting N-glycosylation to attenuate colonization of P. aeruginosa in CF airways reveals a new therapeutic avenue for a hallmark disease condition in CF.

Gene therapy for cystic fibrosis lung disease

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

Modulation of exaggerated-IgE allergic responses by gene transfer-mediated antagonism of IL-13 and IL-17e

Asthma and allergic rhinitis are almost invariable accompanied by elevated levels of immunoglobin E (IgE), and more importantly a genetic link between IgE levels and airway hyper-responsiveness has been established. We hypothesized that expression of soluble receptors directed against interleukin (IL)-13 and IL-17e would prevent the cytokines from engaging the cell-bound receptors and therefore help to attenuate allergic responses in a Cftr(-/-)-dependent mouse model of exaggerated-IgE responses. Cftr(-/-) mice were injected with recombinant adeno-associated virus 1 (rAAV1) intramuscularly expressing soluble receptors to IL-17e (IL-17Rh1fc) or IL-13 (IL-13Ralpha2Fc). Total IgE levels, in mice receiving the IL-17Rh1fc and IL-13Ralpha2Fc therapy, were lower than in the control group. Interestingly Aspergillus fumigatus (Af)-specific IgE levels were undetectable in both the mice receiving the IL-17Rh1fc and IL-13Ralpha2Fc therapies. Further flow cytometry analysis of intracellular gene expression suggests that blocking IL-17e may be interfering with signaling upstream of CD4+ and CD11b+ cells and reducing IgE levels by affecting signaling on these cell populations. In contrast it appears that IL-13 blockade acts downstream to reduce IgE levels probably by directly affecting B-cell maturation. These studies demonstrate the feasibility of targeting T helper 2 (Th2) cytokines with rAAV-delivered fusion proteins as a means to treat aberrant immune responses.

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.

Cystic fibrosis transmembrane regulator missing the first four transmembrane segments increases wild type and DeltaF508 processing

We previously generated an adenoassociated viral gene therapy vector, rAAV-Delta264 cystic fibrosis transmembrane conductance regulator (CFTR), missing the first four transmembrane domains of CFTR. When infected into monkey lungs, Delta264 CFTR increased the levels of endogenous wild type CFTR protein. To understand this process, we transfected Delta264 CFTR plasmid cDNA into COS7 cells, and we noted that protein expression from the truncation mutant is barely detectable when compared with wild type or DeltaF508 CFTR. Delta264 CFTR protein expression increases dramatically when cells are treated with proteasome inhibitors. Cycloheximide experiments show that Delta264 CFTR is degraded faster than DeltaF508 CFTR. VCP and HDAC6, two proteins involved in retrograde translocation from endoplasmic reticulum to cytosol for proteasomal and aggresomal degradation, coimmunoprecipitate with Delta264 CFTR. In cotransfection studies in COS7 cells and in transfection of Delta264 CFTR into cells stably expressing wild type and DeltaF508 CFTR, Delta264 CFTR increases wild type CFTR protein and increases levels of maturation of immature band B to mature band C of DeltaF508 CFTR. Thus the adenoassociated viral vector, rAAV-Delta264 CFTR, is a highly promising cystic fibrosis gene therapy vector because it increases the amount of mature band C protein both from wild type and DeltaF508 CFTR and associates with key elements in quality control mechanism of CFTR.