In vivo retroviral gene transfer into human bronchial epithelia of xenografts

Impact of Peptide Sequence on Functional siRNA Delivery and Gene Knockdown with Cyclic Amphipathic Peptide Delivery Agents

Short-interfering RNA (siRNA) oligonucleotide therapeutics that modify gene expression by accessing RNA-interference (RNAi) pathways have great promise for the treatment of a range of disorders; however, their application in clinical settings has been limited by significant challenges in cellular delivery. Herein, we report a structure-function study using a series of modified cyclic amphipathic cell-penetrating peptides (CAPs) to determine the impact of peptide sequence on (1) siRNA-binding efficiency, (2) cellular delivery and knockdown efficiency, and (3) the endocytic uptake mechanism. Nine cyclic peptides of the general sequence Ac-C[XZ]4CG-NH2 in which X residues are hydrophobic/aromatic (Phe, Tyr, Trp, or Leu) and Z residues are charged/hydrophilic (Arg, Lys, Ser, or Glu) are assessed along with one acyclic peptide, Ac-(WR)4G-NH2. Cyclization is enforced by intramolecular disulfide bond formation between the flanking Cys residues. Binding analyses indicate that strong cationic character and the presence of aromatic residues that are competent to participate in CH-π interactions lead to CAP sequences that most effectively interact with siRNA. CAP-siRNA binding increases in the following order as a function of CAP hydrophobic/aromatic content: His < Phe < Tyr < Trp. Both cationic charge and disulfide-constrained cyclization of CAPs improve uptake of siRNA in vitro. Net neutral CAPs and an acyclic peptide demonstrate less-efficient siRNA translocation compared to the cyclic, cationic CAPs tested. All CAPs tested facilitated efficient siRNA target gene knockdown of at least 50% (as effective as a lipofectamine control), with the best CAPs enabling >80% knockdown. Significantly, gene knockdown efficiency does not strongly correlate with CAP-siRNA internalization efficiency but moderately correlates with CAP-siRNA-binding affinity. Finally, utilization of small-molecule inhibitors and targeted knockdown of essential endocytic pathway proteins indicate that most CAP-siRNA nanoparticles facilitate siRNA delivery through clathrin- and caveolin-mediated endocytosis. These results provide insight into the design principles for CAPs to facilitate siRNA delivery and the mechanisms by which these peptides translocate siRNA into cells. These studies also demonstrate the nature of the relationships between peptide-siRNA binding, cellular delivery of siRNA cargo, and functional gene knockdown. Strong correlations between these properties are not always observed, which illustrates the complexity in the design of optimal next-generation materials for oligonucleotide delivery.

Basic Science Perspective on Engineering and Modeling the Large Airways

The airway epithelium provides a physical and biochemical barrier playing a key role in protecting the lung from infiltration of pathogens and irritants and is, therefore, crucial in maintaining tissue homeostasis and regulating innate immunity. Due to continual inspiration and expiration of air during breathing, the epithelium is exposed to a plethora of environmental insults. When severe or persistent, these insults lead to inflammation and infection. The effectiveness of the epithelium as a barrier is reliant upon its capacity for mucociliary clearance, immune surveillance, and regeneration upon injury. These functions are accomplished by the cells that comprise the airway epithelium and the niche in which they reside. Engineering of new physiological and pathological models of the proximal airways requires the generation of complex structures comprising the surface airway epithelium, submucosal gland epithelium, extracellular matrix, and niche cells, including smooth muscle cells, fibroblasts, and immune cells. This chapter focuses on the structure-function relationships in the airways and the challenges of developing complex engineered models of the human airway.

RNAi therapeutic strategies for acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS), replacing the clinical term acute lung injury, involves serious pathophysiological lung changes that arise from a variety of pulmonary and nonpulmonary injuries and currently has no pharmacological therapeutics. RNA interference (RNAi) has the potential to generate therapeutic effects that would increase patient survival rates from this condition. It is the purpose of this review to discuss potential targets in treating ARDS with RNAi strategies, as well as to outline the challenges of oligonucleotide delivery to the lung and tactics to circumvent these delivery barriers.

Rapid Expansion of Human Epithelial Stem Cells Suitable for Airway Tissue Engineering

RATIONALE

Stem cell-based tracheal replacement represents an emerging therapeutic option for patients with otherwise untreatable airway diseases including long-segment congenital tracheal stenosis and upper airway tumors. Clinical experience demonstrates that restoration of mucociliary clearance in the lungs after transplantation of tissue-engineered grafts is critical, with preclinical studies showing that seeding scaffolds with autologous mucosa improves regeneration. High epithelial cell-seeding densities are required in regenerative medicine, and existing techniques are inadequate to achieve coverage of clinically suitable grafts.

OBJECTIVES

To define a scalable cell culture system to deliver airway epithelium to clinical grafts.

METHODS

Human respiratory epithelial cells derived from endobronchial biopsies were cultured using a combination of mitotically inactivated fibroblasts and Rho-associated protein kinase (ROCK) inhibition using Y-27632 (3T3+Y). Cells were analyzed by immunofluorescence, quantitative polymerase chain reaction, and flow cytometry to assess airway stem cell marker expression. Karyotyping and multiplex ligation-dependent probe amplification were performed to assess cell safety. Differentiation capacity was tested in three-dimensional tracheospheres, organotypic cultures, air-liquid interface cultures, and an in vivo tracheal xenograft model. Ciliary function was assessed in air-liquid interface cultures.

MEASUREMENTS AND MAIN RESULTS

3T3-J2 feeder cells and ROCK inhibition allowed rapid expansion of airway basal cells. These cells were capable of multipotent differentiation in vitro, generating both ciliated and goblet cell lineages. Cilia were functional with normal beat frequency and pattern. Cultured cells repopulated tracheal scaffolds in a heterotopic transplantation xenograft model.

CONCLUSIONS

Our method generates large numbers of functional airway basal epithelial cells with the efficiency demanded by clinical transplantation, suggesting its suitability for use in tracheal reconstruction.

Wnt Signaling Regulates Airway Epithelial Stem Cells in Adult Murine Submucosal Glands

Wnt signaling is required for lineage commitment of glandular stem cells (SCs) during tracheal submucosal gland (SMG) morphogenesis from the surface airway epithelium (SAE). Whether similar Wnt-dependent processes coordinate SC expansion in adult SMGs following airway injury remains unknown. We found that two Wnt-reporters in mice (BAT-gal and TCF/Lef:H2B-GFP) are coexpressed in actively cycling SCs of primordial glandular placodes and in a small subset of adult SMG progenitor cells that enter the cell cycle 24 hours following airway injury. At homeostasis, these Wnt reporters showed nonoverlapping cellular patterns of expression in the SAE and SMGs. Following tracheal injury, proliferation was accompanied by dynamic changes in Wnt-reporter activity and the analysis of 56 Wnt-related signaling genes revealed unique temporal changes in expression within proximal (gland-containing) and distal (gland-free) portions of the trachea. Wnt stimulation in vivo and in vitro promoted epithelial proliferation in both SMGs and the SAE. Interestingly, slowly cycling nucleotide label-retaining cells (LRCs) of SMGs were spatially positioned near clusters of BAT-gal positive serous tubules. Isolation and culture of tet-inducible H2B-GFP LRCs demonstrated that SMG LRCs were more proliferative than SAE LRCs and culture expanded SMG-derived progenitor cells outcompeted SAE-derived progenitors in regeneration of tracheal xenograft epithelium using a clonal analysis competition assay. SMG-derived progenitors were also multipotent for cell types in the SAE and formed gland-like structures in xenografts. These studies demonstrate the importance of Wnt signals in modulating SC phenotypes within tracheal niches and provide new insight into phenotypic differences of SMG and SAE SCs. Stem Cells 2016;34:2758-2771.

Airway Gland Structure and Function

Submucosal glands contribute to airway surface liquid (ASL), a film that protects all airway surfaces. Glandular mucus comprises electrolytes, water, the gel-forming mucin MUC5B, and hundreds of different proteins with diverse protective functions. Gland volume per unit area of mucosal surface correlates positively with impaction rate of inhaled particles. In human main bronchi, the volume of the glands is ∼ 50 times that of surface goblet cells, but the glands diminish in size and frequency distally. ASL and its trapped particles are removed from the airways by mucociliary transport. Airway glands have a tubuloacinar structure, with a single terminal duct, a nonciliated collecting duct, then branching secretory tubules lined with mucous cells and ending in serous acini. They allow for a massive increase in numbers of mucus-producing cells without replacing surface ciliated cells. Active secretion of Cl(-) and HCO3 (-) by serous cells produces most of the fluid of gland secretions. Glands are densely innervated by tonically active, mutually excitatory airway intrinsic neurons. Most gland mucus is secreted constitutively in vivo, with large, transient increases produced by emergency reflex drive from the vagus. Elevations of [cAMP]i and [Ca(2+)]i coordinate electrolyte and macromolecular secretion and probably occur together for baseline activity in vivo, with cholinergic elevation of [Ca(2+)]i being mainly responsive for transient increases in secretion. Altered submucosal gland function contributes to the pathology of all obstructive diseases, but is an early stage of pathogenesis only in cystic fibrosis.

Cell surface marker profiling of human tracheal basal cells reveals distinct subpopulations, identifies MST1/MSP as a mitogenic signal, and identifies new biomarkers for lung squamous cell carcinomas

BACKGROUND

The large airways of the lungs (trachea and bronchi) are lined with a pseudostratified mucociliary epithelium, which is maintained by stem cells/progenitors within the basal cell compartment. Alterations in basal cell behavior can contribute to large airway diseases including squamous cell carcinomas (SQCCs). Basal cells have traditionally been thought of as a uniform population defined by basolateral position, cuboidal cell shape, and expression of pan-basal cell lineage markers like KRT5 and TP63. While some evidence suggests that basal cells are not all functionally equivalent, few heterogeneously expressed markers have been identified to purify and study subpopulations. In addition, few signaling pathways have been identified that regulate their cell behavior. The goals of this work were to investigate tracheal basal cell diversity and to identify new signaling pathways that regulate basal cell behavior.

METHODS

We used flow cytometry (FACS) to profile cell surface marker expression at a single cell level in primary human tracheal basal cell cultures that maintain stem cell/progenitor activity. FACS results were validated with tissue staining, in silico comparisons with normal basal cell and lung cancer datasets, and an in vitro proliferation assay.

RESULTS

We identified 105 surface markers, with 47 markers identifying potential subpopulations. These subpopulations generally fell into more (~ > 13%) or less abundant (~ < 6%) groups. Microarray gene expression profiling supported the heterogeneous expression of these markers in the total population, and immunostaining of large airway tissue suggested that some of these markers are relevant in vivo. 24 markers were enriched in lung SQCCs relative to adenocarcinomas, with four markers having prognostic significance in SQCCs. We also identified 33 signaling receptors, including the MST1R/RON growth factor receptor, whose ligand MST1/MSP was mitogenic for basal cells.

CONCLUSION

This work provides the largest description to date of molecular diversity among human large airway basal cells. Furthermore, these markers can be used to further study basal cell function in repair and disease, and may aid in the classification and study of SQCCs.

Gene delivery to the airway

This unit describes generation of and gene transfer to several commonly used airway models. Isolation and transduction of primary airway epithelial cells are first described. Next, the preparation of polarized airway epithelial monolayers is outlined. Transduction of these polarized cells is also described. Methods are presented for generation of tracheal xenografts, as well as both ex vivo and in vivo gene transfer to these xenografts. Finally, a method for in vivo gene delivery to the lungs of rodents is included. Methods for evaluating transgene expression are given in the support protocols.

PGE2 through the EP4 receptor controls smooth muscle gene expression patterns in the ductus arteriosus critical for remodeling at birth

The ductus arteriosus (DA) is a fetal shunt that directs right ventricular outflow away from pulmonary circulation and into the aorta. Critical roles for prostaglandin E(2) (PGE(2)) and the EP4 receptor (EP4) have been established in maintaining both the patency of the vessel in utero and in its closure at birth. Here we have generated mice in which loss of EP4 expression is limited to either the smooth muscle (SMC) or endothelial cells and demonstrated that SMC, but not endothelial cell expression of EP4 is required for DA closure. The genome wide expression analysis of full term wild type and EP4(-/-) DA indicates that PGE(2)/EP4 signaling modulates expression of a number of unique pathways, including those involved in SMC proliferation, cell migration, and vascular tone. Together this supports a mechanism by which maturation and increased contractility of the vessel is coupled to the potent smooth muscle dilatory actions of PGE(2).

Novel stem/progenitor cell population from murine tracheal submucosal gland ducts with multipotent regenerative potential

The airway epithelium is in direct contact with the environment and therefore constantly at risk for injury. Basal cells (BCs) have been found to repair the surface epithelium (SE), but the contribution of other stem cell populations to airway epithelial repair has not been identified. We demonstrated that airway submucosal gland (SMG) duct cells, in addition to BCs, survived severe hypoxic-ischemic injury. We developed a method to isolate duct cells from the airway. In vitro and in vivo models were used to compare the self-renewal and differentiation potential of duct cells and BCs. We found that only duct cells were capable of regenerating SMG tubules and ducts, as well as the SE overlying the SMGs. SMG duct cells are therefore a multipotent stem cell for airway epithelial repair This is of importance to the field of lung regeneration as determining the repairing cell populations could lead to the identification of novel therapeutic targets and cell-based therapies for patients with airway diseases.

Gene therapy for ALI/ARDS

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are characterized by acute respiratory failure and are associated with diverse disorders. Gene therapy is a potentially powerful approach to treat diseases related to ALI/ARDS, and numerous viral and nonviral methods for gene delivery to the lung have been developed. Discussed are recent advances in the development of more efficient viral and nonviral gene transfer systems, and the current status of gene therapy applied to ALI/ARDS-associated pulmonary diseases is reviewed. With the development of more efficient gene therapy vectors, gene therapy is a promising strategy for clinical application.

Developing cell therapy techniques for respiratory disease: intratracheal delivery of genetically engineered stem cells in a murine model of airway injury

Interest has increased in the use of exogenous stem cells to optimize lung repair and serve as carriers of a therapeutic gene for genetic airway diseases such as cystic fibrosis. We investigated the survival and engraftment of exogenous stem cells after intratracheal injection, in a murine model of acute epithelial airway injury already used in gene therapy experiments on cystic fibrosis. Embryonic stem cells and mesenchymal stem cells were intratracheally injected 24 hr after 2% polidocanol administration, when epithelial airway injury was maximal. Stem cells were transfected with reporter genes immediately before administration. Reporter gene expression was analyzed in trachea-lungs and bronchoalveolar lavage, using nonfluorescence, quantitative, and sensitive methods. Enzyme-linked immunosorbent assay quantitative results showed that 0.4 to 5.5% of stem cells survived in the injured airway. Importantly, no stem cells survived in healthy airway or in the epithelial lining fluid. Using 5-bromo-4-chloro-3-indolyl-beta-d-galactopyranoside staining, transduced mesenchymal stem cells were detected in injured trachea and bronchi lumen. When the epithelium was spontaneously regenerated, the in vivo amount of engrafted mesenchymal stem cells from cell lines decreased dramatically. No stem cells from primary culture were located within the lungs at 7 days. This study demonstrated the feasibility of intratracheal cell delivery for airway diseases with acute epithelial injury.

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.

Toward gene therapy for cystic fibrosis using a lentivirus pseudotyped with Sendai virus envelopes

Gene therapy for cystic fibrosis (CF) is making encouraging progress into clinical trials. However, further improvements in transduction efficiency are desired. To develop a novel gene transfer vector that is improved and truly effective for CF gene therapy, a simian immunodeficiency virus (SIV) was pseudotyped with envelope proteins from Sendai virus (SeV), which is known to efficiently transduce unconditioned airway epithelial cells from the apical side. This novel vector was evaluated in mice in vivo and in vitro directed toward CF gene therapy. Here, we show that (i) we can produce relevant titers of an SIV vector pseudotyped with SeV envelope proteins for in vivo use, (ii) this vector can transduce the respiratory epithelium of the murine nose in vivo at levels that may be relevant for clinical benefit in CF, (iii) this can be achieved in a single formulation, and without the need for preconditioning, (iv) expression can last for 15 months, (v) readministration is feasible, (vi) the vector can transduce human air-liquid interface (ALI) cultures, and (vii) functional CF transmembrane conductance regulator (CFTR) chloride channels can be generated in vitro. Our data suggest that this lentiviral vector may provide a step change in airway transduction efficiency relevant to a clinical programme of gene therapy for CF.

The roles of antimicrobial peptides in innate host defense

Antimicrobial peptides (AMPs) are multi-functional peptides whose fundamental biological role in vivo has been proposed to be the elimination of pathogenic microorganisms, including Gram-positive and -negative bacteria, fungi, and viruses. Genes encoding these peptides are expressed in a variety of cells in the host, including circulating phagocytic cells and mucosal epithelial cells, demonstrating a wide range of utility in the innate immune system. Expression of these genes is tightly regulated; they are induced by pathogens and cytokines as part of the host defense response, and they can be suppressed by bacterial virulence factors and environmental factors which can lead to increased susceptibility to infection. New research has also cast light on alternative functionalities, including immunomodulatory activities, which are related to their unique structural characteristics. These peptides represent not only an important component of innate host defense against microbial colonization and a link between innate and adaptive immunity, but also form a foundation for the development of new therapeutic agents.

Methods for studying stem cells: adult stem cells for lung repair

Recent progress in lung biology includes the description of a series of pulmonary stem and progenitor cells involved in homeostasis and regeneration of the respiratory system. Moreover, the contribution of extrapulmonary stem cells to healthy and pathological lung tissue has been observed and the developmental biology of such processes should provide important hints for understanding maintenance and repair of adult lung structure and function. Despite such remarkable advances, the phenotypic and especially the functional characterization of these stem and progenitor cells, and their derivatives, along with an understanding of the molecular cues and pathways underlying differentiation into specific respiratory lineages is still in its infancy. Accordingly, the role of endogenous and extrapulmonary stem cells in normal tissue repair and pathogenesis is still largely mysterious and added basic knowledge is required in order to explore their potential for novel regenerative therapies. This review provides an overview of the current state of the art in adult lung stem cell biology including technical aspects of isolation, characterization and differentiation, and a discussion of perspectives for future regenerative therapies.

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.

A three-dimensional model of differentiation of immortalized human bronchial epithelial cells

A therapeutic approach being investigated for a variety of pathologies is tissue regeneration using a patient's own cells. Such studies have been hampered due to the difficulty in growing epithelial cells for prolonged periods in culture. Replicative senescence due to short telomeres and p16 induced by culture stress work together to inhibit cell growth. Forced expression of telomerase (hTERT) can prevent replicative senescence, and expression of the cell cycle protein cdk4 can sequester p16, thereby immortalizing epithelial cells in culture. In the present study, we used this method to immortalize human bronchial epithelial cells (HBECs) to determine whether immortalized HBECs retain the ability to differentiate normally. HBECs were plated atop contracted collagen gels containing lung fibroblasts. This three-dimensional (3D) tissue model was cultured initially submerged, then raised to the air/liquid interface for up to 28 days. Normal differentiation was assessed by the presence of ciliated cells, goblet (mucin-producing) cells, and basal epithelial cells. Scanning electron microscopic observations revealed both ciliated and non-ciliated cells in these 3D tissues. Histological examination revealed the presence of mucin-producing cells, and immunohistochemistry using antibodies against p63 and keratin 14 showed the presence of basal cells. These results demonstrate that immortalized HBECs retain the capacity to differentiate into each of three cell types: basal, mucin-producing, and columnar ciliated epithelial cells. Such cells will be useful cellular reagents for research in aging, cancer progression, as well as normal bronchial epithelial differentiation and will help progress the use of engineered cells to enhance tissue regeneration.

Antimicrobial peptides in the airway

The airway provides numerous defense mechanisms to prevent microbial colonization by the large numbers of bacteria and viruses present in ambient air. An important component of this defense is the antimicrobial peptides and proteins present in the airway surface fluid (ASF), the mucin-rich fluid covering the respiratory epithelium. These include larger proteins such as lysozyme and lactoferrin, as well as the cationic defensin and cathelicidin peptides. While some of these peptides, such as human beta-defensin (hBD)-1, are present constitutively, others, including hBD2 and -3 are inducible in response to bacterial recognition by Toll-like receptor-mediated pathways. These peptides can act as microbicides in the ASF, but also exhibit other activities, including potent chemotactic activity for cells of the innate and adaptive immune systems, suggesting they play a complex role in the host defense of the airway. Inhibition of antimicrobial peptide activity or gene expression can result in increased susceptibility to infections. This has been observed with cystic fibrosis (CF), where the CF phenotype leads to reduced antimicrobial capacity of peptides in the airway. Pathogenic virulence factors can inhibit defensin gene expression, as can environmental factors such as air pollution. Such an interference can result in infections by airway-specific pathogens including Bordetella bronchiseptica, Mycobacterium tuberculosis, and influenza virus. Research into the modulation of peptide gene expression in animal models, as well as the optimization of peptide-based therapeutics shows promise for the treatment and prevention of airway infectious diseases.

Stem cells in the lung

The lung is composed of two major anatomically distinct regions-the conducting airways and gas-exchanging airspaces. From a cell biology standpoint, the conducting airways can be further divided into two major compartments, the tracheobronchial and bronchiolar airways, while the alveolar regions of the lung make up the gas-exchanging airspaces. Each of these regions consists of distinct epithelial cell types with unique cellular physiologies and stem cell compartments. This chapter focuses on model systems with which to study stem cells in the adult tracheobronchial airways, also referred to as the proximal airway of the lung. Important in such models is an appreciation for the diversity of stem cell niches in the conducting airways that provide localized environmental signals to both maintain and mobilize stem cells in the setting of airway injury and normal cellular turnover. Because cellular turnover in airways is relatively slow, methods for analysis of stem cells in vivo have required prior injury to the lung. In contrast, ex vivo and in vitro models for analysis of airway stem cells have used genetic markers to track lineage relationships together with reconstitution systems that mimic airway biology. Over the past decades, several widely acceptable methods have been developed and used in the characterization of adult airway stem/progenitor cells. These include localization of label-retaining cells (LRCs), retroviral tagging of epithelial cells seeded into xenografts, air-liquid interface cultures to track clonal proliferative potential, and multiple transgenic mouse models. This chapter reviews the biologic context and use of these models while providing detailed methods for several of the more broadly useful models for studying adult airway stem/progenitor cell types.

Reconstitution of human airway tissue in the humanized xenograft model

Normal human airway epithelial tissue may be reconstituted in the humanized xenograft model in immunodeficient NUDE mice. Epithelial cells dissociated from human fetal or adult tissue are seeded on a denuded rat trachea and implanted in the NUDE mice. After a first step of dedifferentiation, the human epithelial cells adhere on the denuded basal lamina of the rat host trachea and progressively reconstitute a normal well-differentiated epithelium after several steps of migration, proliferation, stratification and redifferentiation.

Lentivirus-mediated gene transfer to the respiratory epithelium: a promising approach to gene therapy of cystic fibrosis

Gene therapy of cystic fibrosis (CF) lung disease needs highly efficient delivery and long-lasting complementation of the CFTR (cystic fibrosis transmembrane conductance regulator) gene into the respiratory epithelium. The development of lentiviral vectors has been a recent advance in the field of gene transfer and therapy. These integrating vectors appear to be promising vehicles for gene delivery into respiratory epithelial cells by virtue of their ability to infect nondividing cells and mediate long-term persistence of transgene expression. Studies in human airway tissues and animal models have highlighted the possibility of achieving gene expression by lentiviral vectors, which outlasted the normal lifespan of the respiratory epithelium, indicating targeting of a 'stem cell' compartment. Modification of the paracellular permeability and pseudotyping with heterologous envelopes are the strategies currently used to overcome the paucity of specific viral receptors on the apical surface of airway epithelial cells and to reach the basolateral surface receptors. Preclinical studies on CF mice, demonstrating complementation of the CF defect, offer hope that lentivirus gene therapy can be translated into an effective treatment of CF lung disease. Besides a direct targeting of the stem/progenitor niche(s) in the CF airways, an alternative approach may envision homing of hematopoietic stem cells engineered to express the CFTR gene by lentiviral vectors. In the context of lentivirus-mediated CFTR gene transfer to the CF airways, biosafety aspects should be of primary concern.

Wnt-responsive element controls Lef-1 promoter expression during submucosal gland morphogenesis

Regulated expression of lymphoid enhancer factor 1 (Lef-1) plays an obligatory role in the transcriptional control of epithelial bud formation during airway submucosal gland and mammary gland development. However, regions of the Lef-1 promoter required for spatial and temporal regulation during glandular development have yet to be defined. We hypothesized that a previously reported 110-bp Wnt-responsive element (WRE) in the Lef-1 promoter, which can be induced by Wnt-3a/beta-catenin signals, may also play a role in regulating Lef-1 expression during airway and mammary gland development. Here we show that the Lef-1 promoter is also responsive to Wnt-1 signals in both airway and mammary epithelial cell lines. To better understand the importance of the WRE in dynamically regulating Lef-1 promoter activation in these two types of epithelia in vivo, we utilized LacZ reporter transgenic mice to evaluate the significance of Wnt-responsive sequences in the Lef-1 promoter during glandular bud formation. A 2.5-kb Lef-1 promoter fragment partially reproduced endogenous Lef-1 expression patterns in a subset of cell types involved in both mammary gland and submucosal glandular bud development. Interestingly, removal of the 110-bp WRE from the Lef-1 promoter ablated expression in nasal and tracheal submucosal glandular buds while having no significant effect on developmental expression in mammary glandular buds. These findings suggest that Wnt regulation of the Lef-1 promoter at the WRE may play an important role during airway submucosal glandular bud formation.

Jaagsiekte sheep retrovirus envelope efficiently pseudotypes human immunodeficiency virus type 1-based lentiviral vectors

Jaagsiekte sheep retrovirus (JSRV) infects lung epithelial cells in sheep, and oncoretroviral vectors bearing JSRV Env can mediate transduction of human cells, suggesting that such vectors might be useful for lung-directed gene therapy. Here we show that JSRV Env can also efficiently pseudotype a human immunodeficiency virus type 1-based lentiviral vector, a more suitable vector for transduction of slowly dividing lung epithelial cells. We created several chimeric Env proteins that, unlike the parental Env, do not transform rodent fibroblasts but are still capable of pseudotyping lentiviral and oncoretroviral vectors.

Inefficient transduction of sheep in utero after intra-amniotic injection of retroviral producer cells

OBJECTIVE

Our purpose was to test the hypothesis that the intra-amniotic injection of a retroviral vector producer cell line into pregnant sheep will result in retrovirus-mediated transduction and stable gene transfer to the ovine fetus.

STUDY DESIGN

Thirteen pregnant ewes at various gestational ages underwent amniocentesis and injection of cells producing the retrovirus vector LIRESgeo, which is derived from Maloney murine leukemia virus and encodes Escherichia coli LacZ (beta-galactosidase) as a marker gene. Pregnant ewes and fetuses were killed, and amniotic fluid, placenta, and fetal tissues were collected and assayed for transgene expression 7 to 77 days after intraamniotic injection. In addition, serum was collected and analyzed for evidence of specific immune responses against the producer cells, and amniotic fluid was collected and analyzed for deleterious effects on producer cell viability, vector production, and vector transduction.

RESULTS

Only 1 of 10 fetuses exposed to the retroviral producer cells demonstrated beta-galactosidase activity that correlated with positive immunohistochemistry for LacZ in lung, trachea, pancreas, and small intestine. However, the presence of the LacZ gene could not be confirmed by polymerase chain reaction. Thus, we could not confirm transduction after any of the injections. The retroviral producer cells survived well in amniotic fluid and continued to produce high levels of retroviral vector after intra-amniotic injection, although amniotic fluid inhibited the transducing activity of the vector in a manner dependent on gestational age.

CONCLUSIONS

Intra-amniotic retroviral gene transfer with the use of these amphotropic producer cells does not result in reproducible gene transfer in the ovine fetus although amniotic fluid sustains producer cell viability and vector production. Possible reasons for the inefficient transduction are discussed.

Vesicular stomatitis virus G-pseudotyped lentivirus vectors mediate efficient apical transduction of polarized quiescent primary alveolar epithelial cells

We investigated the use of lentivirus vectors for gene transfer to quiescent alveolar epithelial cells. Primary rat alveolar epithelial cells (AEC) grown on plastic or as polarized monolayers on tissue culture-treated polycarbonate semipermeable supports were transduced with a replication-defective human immunodeficiency virus-based lentivirus vector pseudotyped with the vesicular stomatitis virus G (VSV-G) protein and encoding an enhanced green fluorescent protein reporter gene. Transduction efficiency, evaluated by confocal microscopy and quantified by fluorescence-activated cell sorting, was dependent on the dose of vector, ranging from 4% at a multiplicity of infection (MOI) of 0.1 to 99% at an MOI of 50 for AEC grown on plastic. At a comparable titer and MOI, transduction of these cells by a similarly pseudotyped murine leukemia virus vector was approximately 30-fold less than by the lentivirus vector. Importantly, comparison of lentivirus-mediated gene transfer from the apical or basolateral surface of confluent AEC monolayers (R(t) > 2 kOmega. cm(2); MOI = 10) revealed efficient transduction only when VSV-G-pseudotyped lentivirus was applied apically. Furthermore, treatment with EGTA to increase access to the basolateral surface did not increase transduction of apically applied virus, indicating that transduction was primarily via the apical membrane domain. In contrast, differentiated tracheal epithelial cells were transduced by apically applied lentivirus only in the presence of EGTA and at a much lower overall efficiency (approximately 15-fold) than was observed for AEC. Efficient transduction of AEC from the apical cell surface supports the feasibility of using VSV-G-pseudotyped lentivirus vectors for gene transfer to the alveolar epithelium and suggests that differences exist between upper and lower airways in the polarity of available receptors for the VSV-G protein.

Salt-independent abnormality of antimicrobial activity in cystic fibrosis airway surface fluid

The link between the genetic defect in cystic fibrosis (CF) and the recently described breach in pulmonary host defense has focused on the role of salt and water metabolism in the airways. Using a human bronchial xenograft model we demonstrate a salt-independent abnormality in bacterial killing in CF airway surface fluid (ASF). Biochemical characterization implicates the absence or dysfunction of a molecule critical to the constitution of normal bacterial killing. Our study suggests that CF transmembrane conductance regulator (CFTR) deficiency causes a primary abnormality in the composition of ASF that leads to a salt-independent defect in host defense. Importantly, this defect is corrected by adenovirus-mediated gene transfer of CFTR.

Filovirus-pseudotyped lentiviral vector can efficiently and stably transduce airway epithelia in vivo

Traditional gene therapy vectors have demonstrated limited utility for treatment of chronic lung diseases such as cystic fibrosis (CF). Herein we describe a vector based on a Filovirus envelope protein-pseudotyped HIV vector, which we chose after systematically evaluating multiple strategies. The vector efficiently transduces intact airway epithelium from the apical surface, as demonstrated in both in vitro and in vivo model systems. This shows the potential of pseudotyping in expanding the utility of lentiviral vectors. Pseudotyped lentiviral vectors may hold promise for the treatment of CF.

Repair of CFTR mRNA by spliceosome-mediated RNA trans-splicing

Most messenger RNA precursors (pre-mRNA) undergo cis-splicing in which introns are excised and the adjoining exons from a single pre-mRNA are ligated together to form mature messenger RNA. This reaction is driven by a complex known as the spliceosome. Spliceosomes can also combine sequences from two independently transcribed pre-mRNAs in a process known as trans-splicing. Spliceosome-mediated RNA trans-splicing (SMaRT) is an emerging technology in which RNA pre-therapeutic molecules (PTMs) are designed to recode a specific pre-mRNA by suppressing cis-splicing while enhancing trans-splicing between the PTM and its pre-mRNA target. This study examined the feasibility of SMaRT as a potential therapy for genetic diseases to correct mutations using cystic fibrosis (CF) as an example. We used several versions of a cystic fibrosis transmembrane conductance regulator (CFTR) mini-gene expressing mutant (deltaF508) pre-mRNA targets and tested this against a number of PTMs capable of binding to the CFTR target intron 9 and trans-splicing in the normal coding sequences for exons 10-24 (containing F508). When 293T cells were cotransfected with both constructs, they produced a trans-spliced mRNA in which normal exon 10-24 replaced mutant exon 10. To test whether SMaRT produced mature CFTR protein, proteins were immunoprecipitated from lysates of cotransfected cells and detected by Western blotting and PKA-phosphorylation. Tryptic phosphopeptide mapping confirmed the identity of CFTR. This proof-of-concept study demonstrates that exon replacement by SMaRT can repair an abnormal pre-mRNA associated with a genetic disease.

A murine tracheal culture system to investigate parameters affecting gene therapy for cystic fibrosis

Cystic fibrosis (CF) is a life-threatening condition caused by mutations in the cystic fibrosis transmembrane conductance regulator gene (CFTR). Delivery of the CFTR gene to the airways offers a potential treatment for CF but requires improvement in efficiency to obtain clinical benefit. We have developed a murine tracheal culture system that maintains tissue integrity as judged by normal histological appearance, high transepithelial resistance and electrophysiological responses similar to fresh tissue. This ex vivo system allows precise control of gene delivery parameters to a structure that retains the in vivo cellular architecture. We have demonstrated correction of CFTR-dependent Cl- secretion following ex vivo delivery of the CFTR gene to tracheas from CF null mice. We have used this system to examine parameters affecting liposome-mediated gene delivery to the upper airway such as plasmid dose. We have also found that a contact time of 1 min for the transfection mixture is sufficient to achieve significant DNA binding and maximal reporter gene expression.

Epithelial stem cell-mediated development of the human respiratory mucosa in SCID mice

We have developed an in vivo assay for progenitor cells of the human tracheobronchial epithelium relying on the transplantation of human prenatal respiratory tissues into severe combined immunodeficiency mice. Engrafted embryonic or fetal open tracheobronchial rudiments are rapidly closed at each end by a neoformed membrane that we named the operculum. After 2–4 weeks, differentiated human respiratory epithelium covers both the native airway matrix and the new operculum. Human epithelial cells dissociated from either emerging embryonic lung primordia or mature xenografts were seeded in host human airway grafts, of which native epithelium had been eliminated by several cycles of freezing and thawing. All grafts seeded with donor epithelial cells and implanted back into SCID mice recovered a surface mucociliary epithelium expressing expected markers and secreting mucus. Spontaneous epithelium regrowth was never observed in control unseeded, denuded grafts. In some experiments, donor epithelial cells and host denuded airway were sex-mismatched and the donor origin of newly formed epithelial structures was confirmed by sex chromosome detection. After two rounds of seeding and reimplantation, a normal epithelium was observed to line the 3rd generation operculum. These observations substantiate a functional assay for human candidate airway epithelium stem cells.

Substance P and neurokinin-1 receptor expression by intrinsic airway neurons in the rat

Tachykinins and their receptors are involved in the amplification of inflammation in the airways. We analyzed the expression of preprotachykinin-A (PPT-A) and neurokinin-1 (NK-1) receptor genes by intrinsic airway neurons in the rat. We also tested the hypothesis that PPT-A-encoded peptides released by these neurons fulfill the requisite role of substance P in immune complex injury of the lungs. We found that ganglion neurons in intact and denervated airways or in primary culture coexpress PPT-A and NK-1 receptor mRNAs and their protein products. Denervated ganglia from tracheal xenografts (nu/nu mice) or syngeneic lung grafts had increased PPT-A mRNA contents, suggesting preganglionic regulation. Formation of immune complexes in the airways induced comparable inflammatory injuries in syngeneic lung grafts, which lack peptidergic sensory fibers, and control lungs. The injury was attenuated in both cases by pretreatment with the NK-1 receptor antagonist LY-306740. We conclude that tachykinins released by ganglia act as a paracrine or autocrine signal in the airways and may contribute to NK-1 receptor-mediated amplification of immune injury in the lungs.

Human airway xenograft models of epithelial cell regeneration

Regeneration and restoration of the airway epithelium after mechanical, viral or bacterial injury have a determinant role in the evolution of numerous respiratory diseases such as chronic bronchitis, asthma and cystic fibrosis. The study in vivo of epithelial regeneration in animal models has shown that airway epithelial cells are able to dedifferentiate, spread, migrate over the denuded basement membrane and progressively redifferentiate to restore a functional respiratory epithelium after several weeks. Recently, human tracheal xenografts have been developed in immunodeficient severe combined immunodeficiency (SCID) and nude mice. In this review we recall that human airway cells implanted in such conditioned host grafts can regenerate a well-differentiated and functional human epithelium; we stress the interest in these humanized mice in assaying candidate progenitor and stem cells of the human airway mucosa.

Differentiated and functional human airway epithelium regeneration in tracheal xenografts

To investigate the regeneration process of a well-differentiated and functional human airway epithelium, we adapted an in vivo xenograft model in which adult human nasal epithelial cells adhere and progressively repopulate denuded rat tracheae grafted in nude mice. The proliferating activity, the degree of differentiation, and the barrier integrity of the repopulated epithelium were studied during the regeneration process at optical and ultrastructural levels with immunocytochemistry and a permeability tracer. Three days after implantation in nude mice, tracheal xenografts were partially repopulated with a flattened nonciliated and poorly differentiated leaky epithelium. By the end of the first week after the graft, cell proliferation produced on the entire surface of the rat trachea an epithelium that was stratified into multiple layers and tightly sealed. During successive weeks, cell proliferation dramatically decreased. Moreover, the epithelium became progressively columnar, secretory, ciliated, and transiently leaky. At 4-5 wk, a fully differentiated pseudostratified functional epithelial barrier impermeable to a low-molecular-weight tracer was reconstituted. The regeneration of a well-differentiated and functional human airway epithelium in rat tracheae grafted in nude mice includes several steps that mimic the regeneration dynamics of airway epithelium after injury.

Keratinocyte growth factor stimulates transduction of the respiratory epithelium by retroviral vectors

Cell proliferation is required for transduction by standard retrovirus vectors derived from viruses in the murine leukemia virus (MuLV) group. Since proliferation rates are low in the mature pulmonary epithelium, we tested the hypothesis that the efficiency of retrovirus-mediated transduction of respiratory epithelial cells can be enhanced by stimulation of cell proliferation with recombinant human keratinocyte growth factor (rhKGF). A marked increase in proliferation of bronchiolar and alveolar epithelial cells was observed after intratracheal administration of rhKGF (30 mg/kg) to adult FVB/N mice. Two days after rhKGF or saline treatment, 10(7) AP+ FFU of LAPSN, a recombinant amphotropic retrovirus that expresses human placental alkaline phosphatase (AP), was instilled intratracheally into the mice. Transduction efficiency, measured 2 days after infection, was increased approximately 70-fold by rhKGF pretreatment. However, even after KGF treatment the total numbers of AP-expressing cells were few. Transduction efficiency was similar using either LAPSN packaged by amphotropic host range packaging cells or LAPSN pseudotyped with 10A1 MuLV envelope protein (0.091 +/- 0.006 versus 0.094 +/- 0.028 transduction events/mm2, respectively). Amphotropic vectors use Pit-2 for cell entry, while 10A1 MuLV vectors can use Pit-1 or Pit-2 for cell entry. By in situ hybridization the retroviral receptor Pit-2 (Ram-1) mRNA was expressed only in the pulmonary vasculature, and Pit-1 (Glvr-1) mRNA was expressed at low levels throughout the lung. In vitro studies demonstrated that retrovirus was inactivated by pulmonary surfactant. Stimulating proliferation of the respiratory epithelium increased retroviral transduction in vivo, but the paucity of retroviral receptors and inactivation by surfactant are additional barriers to high-level retroviral gene transfer in the lung.

Influence of cell polarity on retrovirus-mediated gene transfer to differentiated human airway epithelia

Gene transfer with recombinant murine leukemia viruses (MuLV) provides the potential to permanently correct inherited lung diseases, such as cystic fibrosis (CF). Several problems prevent the application of MuLV-based recombinant retroviruses to lung gene therapy: (i) the lack of cell proliferation in mature pulmonary epithelia, (ii) inefficient gene transfer with a vector applied to the apical surface, and (iii) low titers of many retroviral preparations. We found that keratinocyte growth factor (KGF) stimulated proliferation of differentiated human tracheal and bronchial epithelia. Approximately 50% of epithelia divided in response to KGF as assessed by bromodeoxyuridine histochemistry. In airway epithelia stimulated to divide with KGF, high-titer ampho- and xenotropic enveloped vectors preferentially infected cells from the basal side. However, treatment with hypotonic shock or EGTA transiently increased transepithelial permeability, enhancing gene transfer with the vector applied to the mucosal surfaces of KGF-stimulated epithelia. Up to 35% of cells expressed the transgene after gene transfer. By using this approach, cells throughout the epithelial sheet, including basal cells, were targeted. Moreover, the Cl- transport defect in differentiated CF airway epithelia was corrected. These findings suggest that barriers to apical infection with MuLV can be overcome.

The relationship of chronic mucin secretion to airway disease in normal and CFTR-deficient mice

In the cystic fibrosis (CF) patient, lung function decreases throughout life as a result of continuous cycles of infection, particularly with Pseudomonas aeruginosa and Staphylococcus aureus. The mechanism underlying the pathophysiology of the disease in humans has not been established. However, it has been suggested that abnormal, tenacious mucus, resulting perhaps from improper hydration from loss of Cl- secretion via the cystic fibrosis transmembrane conductance regulator (CFTR) protein, impairs clearance of bacteria from the CF airway and provides an environment favorable to bacterial growth. If this hypothesis is correct, it could explain the absence of respiratory disease in CFTR-deficient mice, since mice have only a single submucosal gland and display few goblet cells in their lower airways, even when exposed to bacteria. To test this hypothesis further, we induced allergic airway disease in CFTR-deficient mice. We found that induction of allergic airway disease in mice, unlike bacterial infection, results in an inflammatory response characterized by goblet cell hyperplasia, increased mucin gene expression, and increased production of mucus. However, we also found that disease progression and resolution is identical in Cftr-/- mice and control animals. Furthermore, we show that the presence of mucus in the Cftr-/- airway does not lead to chronic airway disease, even upon direct inoculation with S. aureus and P. aeruginosa. Therefore, factors in addition to the absence of high levels of mucus secretion protect the mouse from the airway disease seen in human CF patients.

Three-dimensional xenograft model of dysplastic human laryngeal mucosa

OBJECTIVE

Development of new therapeutic interventions in head and neck squamous cell carcinoma (HNSCC) will be facilitated by a model system that incorporates the ease of manipulation found in current tissue culture systems while retaining the three dimensional architecture that defines these malignancies.

STUDY DESIGN

Original scientific investigation.

METHODS

We describe a modification of a normal respiratory mucosa model system which recreates premalignant mucosal histology. Grossly normal appearing human mucosa is harvested from laryngectomy specimens, the mucosal epithelium selectively removed by protease treatment and placed in conventional tissue culture. After 7 days, the cells are seeded into denuded rat tracheas, which are in turn implanted in flank pockets of athymic nu/nu mice. The tracheas are incubated for three weeks, removed and the mucosa examined histologically.

RESULTS

As originally described, normal pseudostratified squamous epithelium can be re-established in this system. Using human dysplastic mucosa as a starting material, mucosal histologies of respiratory dysplasia, squamous metaplasia, squamous dysplasia and squamous carcinoma in situ can be established.

CONCLUSION

This system will provide a paradigm for future therapeutic interventions to modify the progression of squamous metaplasia to dysplasia, carcinoma in situ and invasive squamous cell carcinoma.

Lef1 transcription factor expression defines airway progenitor cell targets for in utero gene therapy of submucosal gland in cystic fibrosis

Cystic fibrosis (CF) has emerged as a paradigm disorder for assessing the utility of gene therapy in the treatment of genetic diseases. It is hypothesized that submucosal glands may play an important role in the pathophysiology of CF lung disease. However, this region poses several significant obstacles for gene therapy due to its inaccessibility from the lumen of adult proximal airways. In utero gene therapy to correct submucosal gland dysfunction in CF provides an attractive alternative strategy to target gland progenitor cells prior to gland formation and morphogenesis. Such approaches will require the use of integrating vectors capable of transducing expanding stem-cell/progenitor-cell populations in the lung. We described a newborn-ferret model of the proximal airway which was used to evaluate the phenotypic characteristics of submucosal gland progenitors and to test gene therapy strategies for targeting these cell types. To this end, we have isolated the ferret cDNA to the lymphoid enhancing factor 1 (Lef1) and have demonstrated that its mRNA expression specifically defines a subset of surface airway epithelial progenitor cells involved in the formation of primordial submucosal gland buds and subsequent gland morphogenesis. Such findings suggest that the transcriptional switch regulating activation of Lef1 expression defines the phenotype of early submucosal gland progenitor cells. In an effort to prove the principle of gene targeting to this progenitor-cell population, we evaluated the efficiency of recombinant retroviral vectors to target submucosal glands in a xenograft model system. Findings from these studies demonstrated successful gene targeting to progenitor cells of submucosal gland buds which was stable throughout subsequent gland development. In summary, these studies have provided evidence for the existence of phenotypically distinct submucosal gland progenitor cells which represent appropriate targets for gene therapy of submucosal glands in CF.

Toxin gene-mediated growth inhibition of lung adenocarcinoma in an animal model of pleural malignancy

Transduction of malignant cells with toxin genes provides a novel strategy by which to promote tumor cell destruction. Whereas the capacity of the toxin gene/prodrug combination cytosine deaminase/fluorocytosine to inhibit growth of human metastatic pulmonary adenocarcinoma cell lines in vitro is established, the in vivo efficacy of this binary system has not yet been determined. For the development of toxin gene therapy for the treatment of lung adenocarcinoma metastatic to the pleural space, a reliable, disease-specific model is required. The serosa of the rat small intestine resembles the basal lamina of the pleura and provides the basis for a more convenient model than direct injection of tumor into the pleural space. Adenocarcinoma cells are inoculated into everted denuded rat intestine configured as a sac. Immunocytochemical and histological analyses show rapid cell growth with characteristics that mimic nodular metastatic intrapleural disease. In the context of this model, systemically delivered fluorocytosine significantly inhibits the growth of cytosine deaminase-expressing human lung adenocarcinoma cells. The dosing schedule required 30 days; neither addition of an enzyme inhibitor that increases the half-life of fluorocytosine nor intralumenal drug delivery is effective in shortening (to 15 days) the protocol. We conclude that CD continues to hold promise as a toxin gene for lung adenocarcinoma gene therapy, and that prolonged prodrug administration may be required for maximum efficacy.

The prostaglandin receptor EP4 triggers remodelling of the cardiovascular system at birth

Survival of newborn placental mammals depends on closure of the ductus arteriosus (DA), an arterial connection in the fetus which directs blood away from the pulmonary circulation and towards the placenta where oxygenation occurs. Here we show that morphological changes resulting in closure of the DA in mice are virtually identical to those observed in larger mammals, including humans, and that maintenance of the DA in the open, or patent, state in fetal mice is dependent on prostaglandin synthesis. This requirement is absent in mice lacking the prostaglandin E2 EP4 receptor (EP4(-/-) mice). In EP4(-/-) mice of the 129 strain, remodelling of the DA fails to occur after birth, resulting in a left-to-right shunt of blood and subsequently in death. This suggests that the neonatal drop in prostaglandin E2 that triggers ductal closure is sensed through the EP4 receptor. In contrast, 5% of EP4(-/-) mice of mixed genetic background survive, and selective breeding of these mice leads to a 21% survival rate, suggesting that alleles at other loci can provide an alternative mechanism for ductal closure.

Human beta-defensin-1 is a salt-sensitive antibiotic in lung that is inactivated in cystic fibrosis

A human bronchial xenograft model was used to characterize the molecular basis for the previously described defect in bacterial killing that is present in the cystic fibrosis (CF) lung. Airway surface fluid from CF grafts contained abnormally high NaCl and failed to kill bacteria, defects that were corrected with adenoviral vectors. A full-length clone for the only known human beta-defensin (i.e., hBD-1) was isolated. This gene is expressed throughout the respiratory epithelia of non-CF and CF lungs, and its protein product shows salt-dependent antimicrobial activity to P. aeruginosa. Antisense oligonucleotides to hBD-1 ablated the antimicrobial activity in airway surface fluid from non-CF grafts. These data suggest that hBD-1 plays an important role in innate immunity that is compromised in CF by its salt-dependent inactivation.

Stem cells of the respiratory epithelium and their in vitro cultivation

Parenchymal (epithelial or mesenchyma) stem cells are rapidly drawing both scientific and clinical attention in solid organs like the liver, skin, intestine and abdominal mesothelium, just as has been the case in the hematopoietic system. For the stem cells of these organs various definitions, markers for identification, methods of isolation and in vitro cultivation, and lineage mechanisms have been proposed and some of them are now proven to be valid and useful. In this article attempts will be made to explore whether there are stem cells in the lower respiratory system (from the trachea to the lung periphery) and what they look like. Because of its anatomical and functional complexity the stem cell concept for the respiratory system has been developing rather slowly. Nevertheless, the data available seem to indicate that in analogy to the above mentioned organs there is only one type of epithelial stem cells throughout all sections of the lower respiratory system during fetal through adult stages. They are multipotent for cell differentiation and able to yield lineage progenitors for ciliated, goblet, basal. Clara neuroendocrine, alveolar type 1 and alveolar type 2 cells.

In vivo analysis of fluid transport in cystic fibrosis airway epithelia of bronchial xenografts

An in vivo human bronchial xenograft model system was used to simultaneously analyze electrolyte and fluid transport defects in fully differentiated human cystic fibrosis (CF) and non-CF proximal airways. CF airways demonstrated three discernible defects when compared with non-CF, including 1) a lack of adenosine 3',5'-cylic monophosphate (cAMP)-inducible Cl- secretion, 2) a fourfold higher basal fluid absorption rate, and 3) an altered regulation of fluid absorption in response to amiloride-stimulated changes in Na+ transport. A unique finding in this study demonstrated that treatment of epithelia with amiloride led to a greater than threefold decrease in the rate of fluid absorption in CF tissues as contrasted to a greater than threefold increase in the rate of fluid absorption in non-CF tissues. The removal of apical Na+ from amiloride-treated non-CF xenografts was capable of ablating this amiloride-induced increase in fluid absorption. In light of the recent interactions demonstrated between CF transmembrane conductance regulator (CFTR) and the rat epithelial, amiloride-sensitive Na+ channel, these findings implicate additional complexities between the Na+ conductance pathways and fluid transport in normal and CF proximal airways. Such findings suggest that CFTR may also regulate amiloride-insensitive Na+ channels.

Genotypic analysis of respiratory mucous sulfation defects in cystic fibrosis

Intracellular dysfunction of the cystic fibrosis transmembrane conductance regulator (CFTR) has been proposed to alter endosomal acidification. The most widely studied consequence of this defect has been alterations in the biochemical properties of cystic fibrosis (CF) respiratory mucus glycoproteins. However, studies confirming the existence of mucous processing defects in CF have been hindered by the lack of in vivo animal models by which to test these hypotheses in the absence of secondary effects of chronic bacterial infection. The human bronchial xenograft model has been useful in evaluating the pathophysiologic differences between CF and non-CF airway epithelium, in the absence of secondary disease effects such as goblet cell hyperplasia. In this study we sought to compare the extent of sulfation within secreted mucus glycoproteins from CF and non-CF human bronchial xenografts. Cumulative results of xenografts generated from 13 independent CF tissue samples demonstrated a statistically significant higher level of sulfation (1.7 +/- 0.18, P < 0.026) as compared to non-CF paired controls. Such findings add to the growing body of knowledge that primary defects in sulfation exist in CF respiratory mucin. Correlation of genotype with the extent of mucus sulfation revealed two categories of CF tissues with statistically different mucus sulfation profiles. Results from these studies demonstrated a 2.0 +/- 0.15-fold higher level of mucus sulfation produced from xenografts of five defined CF genotypes as compared to non-CF controls (P < 0.004, n= 10). Interestingly, three CF samples for which one mutant allele remained undefined (deltaoff8/unknown or G551D/unknown) demonstrated no statistical difference in the level of sulfation as compared with matched non-CF controls (n= 3). This as yet unknown allele was not identified within a screen for the 26 most common CF mutations. These results provide preliminary evidence for allelic variation within the CF population which may begin to elucidate the structure-function of CFTR with regards to intracellular mucus processing defects.

A controlled study of adenoviral-vector-mediated gene transfer in the nasal epithelium of patients with cystic fibrosis

BACKGROUND

Cystic fibrosis is a monogenic disease that deranges multiple systems of ion transport in the airways, culminating in chronic infection and destruction of the lung. The introduction of a normal copy of the cystic fibrosis transmembrane conductance regulator (CFTR) gene into the airway epithelium through gene transfer is an attractive approach to correcting the underlying defects in patients with cystic fibrosis. We tested the feasibility of gene therapy using adenoviral vectors in the nasal epithelium of such patients.

METHODS

An adenoviral vector containing the normal CFTR complementary DNA in four logarithmically increasing doses (estimated multiplicity of infection, 1, 10, 100, and 1000), or vehicle alone, was administered in a randomized, blinded fashion to the nasal epithelium of 12 patients with cystic fibrosis. Gene transfer was quantitated by molecular techniques that detected the expression of CFTR messenger RNA and by functional measurements of transepithelial potential differences (PDs) to assess abnormalities of ion transport specific to cystic fibrosis. The safety of this treatment was monitored by nasal lavage and biopsy to assess inflammation and vector replication.

RESULTS

The adenoviral vector was detected in nasal-lavage fluid by culture, the polymerase chain reaction (PCR), or both in a dose-dependent fashion for up to eight days after vector administration. There was molecular evidence of gene transfer by reverse-transcriptase PCR assays or in situ hybridization in five of six patients treated at the two highest doses. However, the percentage of epithelial cells transfected by the vector was very low (< 1 percent), and measurement of PD across the epithelium revealed no significant restoration of chloride transport or normalization of sodium transport. At the lower doses of vector, there were no toxic effects. However, at the highest dose there was mucosal inflammation in two of three patients.

CONCLUSIONS

In patients with cystic fibrosis, adenoviral-vector-mediated transfer of the CFTR gene did not correct functional defects in nasal epithelium, and local inflammatory responses limited the dose of adenovirus that could be administered to overcome the inefficiency of gene transfer.

Regenerating cells in human airway surface epithelium represent preferential targets for recombinant adenovirus

To investigate the efficiency of adenovirus-mediated gene delivery in regenerating human respiratory epithelium, we have performed infections with an E1- and E3-deleted type 5 recombinant adenovirus containing the Escherichia coli LacZ reporter gene on different culture models of regenerating human nasal polyp surface epithelium. These models included: (i) an ex vivo organ culture of nasal polyp tissue, (ii) an explant outgrowth cell culture, and (iii) an in vitro wound repair model, on dissociated cells. In ex vivo nasal polyp tissue, transduced cells were not detected in normal pseudostratified areas, but were found in areas of the surface epithelium with a morphology reminiscent of regenerating airway tissue. In the explant outgrowth cell culture, adenovirus-infected cells were preferentially detected at the periphery of the outgrowth. These transducible epithelial cells, representative of epithelial cells present in vivo during the process of surface airway epithelium regeneration, were shown to be migrating and poorly differentiated cells, which were proliferating or not. In the in vitro wound repair model, the efficiency of cell transduction was much higher in cells present in the wound area than in those far from the wound area. These results indicate that regenerating cells from human airway surface epithelium represent preferential targets for transgene expression, and suggest that efficiency of CFTR gene transfer by recombinant adenovirus vectors may be higher in regenerating CF airway mucosa than in normal tissue. However, since these cells do not show endogenous CFTR expression, the relevance of their preferential transduction for the functional correction of the ion transport defect in cystic fibrosis needs further investigations.