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

Gene Therapeutics for Surfactant Dysfunction Disorders: Targeting the Alveolar Type 2 Epithelial Cell

Genetic disorders of surfactant dysfunction result in significant morbidity and mortality, among infants, children, and adults. Available medical interventions are limited, nonspecific, and generally ineffective. As such, the need for effective therapies remains. Pathogenic variants in the SFTPB, SFTPC, and ABCA3 genes, each of which encode proteins essential for proper pulmonary surfactant production and function, result in interstitial lung disease in infants, children, and adults, and lead to morbidity and early mortality. Expression of these genes is predominantly limited to the alveolar type 2 (AT2) epithelial cells present in the distal airspaces of the lungs, thus providing an unequivocal cellular origin of disease pathogenesis. While several treatment strategies are under development, a gene-based therapeutic holds great promise as a definitive therapy. Importantly for clinical translation, the genes associated with surfactant dysfunction are both well characterized and amenable to a gene-therapeutic-based strategy. This review focuses on the pathophysiology associated with these genetic disorders of surfactant dysfunction, and also provides an overview of the current state of gene-based therapeutics designed to target and transduce the AT2 cells.

Pseudotyped lentiviral vectors: Ready for translation into targeted cancer gene therapy?

Gene therapy holds great promise for curing cancer by editing the deleterious genes of tumor cells, but the lack of vector systems for efficient delivery of genetic material into specific tumor sites in vivo has limited its full therapeutic potential in cancer gene therapy. Over the past two decades, increasing studies have shown that lentiviral vectors (LVs) modified with different glycoproteins from a donating virus, a process referred to as pseudotyping, have altered tropism and display cell-type specificity in transduction, leading to selective tumor cell killing. This feature of LVs together with their ability to enable high efficient gene delivery in dividing and non-dividing mammalian cells in vivo make them to be attractive tools in future cancer gene therapy. This review is intended to summarize the status quo of some typical pseudotypings of LVs and their applications in basic anti-cancer studies across many malignancies. The opportunities of translating pseudotyped LVs into clinic use in cancer therapy have also been discussed.

Gene Therapy Potential for Genetic Disorders of Surfactant Dysfunction

Pulmonary surfactant is critically important to prevent atelectasis by lowering the surface tension of the alveolar lining liquid. While respiratory distress syndrome (RDS) is common in premature infants, severe RDS in term and late preterm infants suggests an underlying genetic etiology. Pathogenic variants in the genes encoding key components of pulmonary surfactant including surfactant protein B (SP-B, SFTPB gene), surfactant protein C (SP-C, SFTPC gene), and the ATP-Binding Cassette transporter A3 (ABCA3, ABCA3 gene) result in severe neonatal RDS or childhood interstitial lung disease (chILD). These proteins play essential roles in pulmonary surfactant biogenesis and are expressed in alveolar epithelial type II cells (AEC2), the progenitor cell of the alveolar epithelium. SP-B deficiency most commonly presents in the neonatal period with severe RDS and requires lung transplantation for survival. SFTPC mutations act in an autosomal dominant fashion and more commonly presents with chILD or idiopathic pulmonary fibrosis than neonatal RDS. ABCA3 deficiency often presents as neonatal RDS or chILD. Gene therapy is a promising option to treat monogenic lung diseases. Successes and challenges in developing gene therapies for genetic disorders of surfactant dysfunction include viral vector design and tropism for target cell types. In this review, we explore adeno-associated virus (AAV), lentiviral, and adenoviral (Ad)-based vectors as delivery vehicles. Both gene addition and gene editing strategies are compared to best design treatments for lung diseases resulting from pathogenic variants in the SFTPB, SFTPC, and ABCA3 genes.

ACE2-lentiviral transduction enables mouse SARS-CoV-2 infection and mapping of receptor interactions

SARS-CoV-2 uses the human ACE2 (hACE2) receptor for cell attachment and entry, with mouse ACE2 (mACE2) unable to support infection. Herein we describe an ACE2-lentivirus system and illustrate its utility for in vitro and in vivo SARS-CoV-2 infection models. Transduction of non-permissive cell lines with hACE2 imparted replication competence, and transduction with mACE2 containing N30D, N31K, F83Y and H353K substitutions, to match hACE2, rescued SARS-CoV-2 replication. Intrapulmonary hACE2-lentivirus transduction of C57BL/6J mice permitted significant virus replication in lung epithelium. RNA-Seq and histological analyses illustrated that this model involved an acute inflammatory disease followed by resolution and tissue repair, with a transcriptomic profile similar to that seen in COVID-19 patients. hACE2-lentivirus transduction of IFNAR-/- and IL-28RA-/- mouse lungs was used to illustrate that loss of type I or III interferon responses have no significant effect on virus replication. However, their importance in driving inflammatory responses was illustrated by RNA-Seq analyses. We also demonstrate the utility of the hACE2-lentivirus transduction system for vaccine evaluation in C57BL/6J mice. The ACE2-lentivirus system thus has broad application in SARS-CoV-2 research, providing a tool for both mutagenesis studies and mouse model development.

Increased CFTR expression and function from an optimized lentiviral vector for cystic fibrosis gene therapy

Despite significant advances in cystic fibrosis (CF) treatments, a one-time treatment for this life-shortening disease remains elusive. Stable complementation of the disease-causing mutation with a normal copy of the CF transmembrane conductance regulator (CFTR) gene fulfills that goal. Integrating lentiviral vectors are well suited for this purpose, but widespread airway transduction in humans is limited by achievable titers and delivery barriers. Since airway epithelial cells are interconnected through gap junctions, small numbers of cells expressing supraphysiologic levels of CFTR could support sufficient channel function to rescue CF phenotypes. Here, we investigated promoter choice and CFTR codon optimization (coCFTR) as strategies to regulate CFTR expression. We evaluated two promoters-phosphoglycerate kinase (PGK) and elongation factor 1-α (EF1α)-that have been safely used in clinical trials. We also compared the wild-type human CFTR sequence to three alternative coCFTR sequences generated by different algorithms. With the use of the CFTR-mediated anion current in primary human CF airway epithelia to quantify channel expression and function, we determined that EF1α produced greater currents than PGK and identified a coCFTR sequence that conferred significantly increased functional CFTR expression. Optimized promoter and CFTR sequences advance lentiviral vectors toward CF gene therapy clinical trials.

New Directions in Pulmonary Gene Therapy

The lung has long been a target for gene therapy, yet efficient delivery and phenotypic disease correction has remained challenging. Although there have been significant advancements in gene therapies of other organs, including the development of several ex vivo therapies, in vivo therapeutics of the lung have been slower to transition to the clinic. Within the past few years, the field has witnessed an explosion in the development of new gene addition and gene editing strategies for the treatment of monogenic disorders. In this review, we will summarize current developments in gene therapy for cystic fibrosis, alpha-1 antitrypsin deficiency, and surfactant protein deficiencies. We will explore the different gene addition and gene editing strategies under investigation and review the challenges of delivery to the lung.

Lentiviral Vectors for the Treatment and Prevention of Cystic Fibrosis Lung Disease

Despite the continued development of cystic fibrosis transmembrane conductance regulator (CFTR) modulator drugs for the treatment of cystic fibrosis (CF), the need for mutation agnostic treatments remains. In a sub-group of CF individuals with mutations that may not respond to modulators, such as those with nonsense mutations, CFTR gene transfer to airway epithelia offers the potential for an effective treatment. Lentiviral vectors are well-suited for this purpose because they transduce nondividing cells, and provide long-term transgene expression. Studies in primary cultures of human CF airway epithelia and CF animal models demonstrate the long-term correction of CF phenotypes and low immunogenicity using lentiviral vectors. Further development of CF gene therapy requires the investigation of optimal CFTR expression in the airways. Lentiviral vectors with improved safety features have minimized insertional mutagenesis safety concerns raised in early clinical trials for severe combined immunodeficiency using γ-retroviral vectors. Recent clinical trials using improved lentiviral vectors support the feasibility and safety of lentiviral gene therapy for monogenetic diseases. While work remains to be done before CF gene therapy reaches the bedside, recent advances in lentiviral vector development reviewed here are encouraging and suggest it could be tested in clinical studies in the near future.

CLDN18.1 attenuates malignancy and related signaling pathways of lung adenocarcinoma in vivo and in vitro

Claudins are a family of transmembrane proteins integral to the structure and function of tight junctions (TJ). Disruption of TJ and alterations in claudin expression are important features of invasive and metastatic cancer cells. Expression of CLDN18.1, the lung-specific isoform of CLDN18, is markedly decreased in lung adenocarcinoma (LuAd). Furthermore, we recently observed that aged Cldn18 -/- mice have increased propensity to develop LuAd. We now demonstrate that CLDN18.1 expression correlates inversely with promoter methylation and with LuAd patient mortality. In addition, when restored in LuAd cells that have lost expression, CLDN18.1 markedly attenuates malignant properties including xenograft tumor growth in vivo as well as cell proliferation, migration, invasion and anchorage-independent colony formation in vitro. Based on high throughput analyses of Cldn18 -/- murine lung alveolar epithelial type II cells, as well as CLDN18.1-repleted human LuAd cells, we hypothesized and subsequently confirmed by Western analysis that CLDN18.1 inhibits insulin-like growth factor-1 receptor (IGF-1R) and AKT phosphorylation. Consistent with recent data in Cldn18 -/- knockout mice, expression of CLDN18.1 in human LuAd cells also decreased expression of transcriptional co-activator with PDZ-binding motif (TAZ) and Yes-associated protein (YAP) and their target genes, contributing to its tumor suppressor activity. Moreover, analysis of LuAd cells in which YAP and/or TAZ are silenced with siRNA suggests that inhibition of TAZ, and possibly YAP, is also involved in CLDN18.1-mediated AKT inactivation. Taken together, these data indicate a tumor suppressor role for CLDN18.1 in LuAd mediated by a regulatory network that encompasses YAP/TAZ, IGF-1R and AKT signaling.

Cell-specific expression of aquaporin-5 (Aqp5) in alveolar epithelium is directed by GATA6/Sp1 via histone acetylation

Epigenetic regulation of differentiation-related genes is poorly understood. We previously reported that transcription factors GATA6 and Sp1 interact with and activate the rat proximal 358-bp promoter/enhancer (p358P/E) of lung alveolar epithelial type I (AT1) cell-specific gene aquaporin-5 (Aqp5). In this study, we found that histone deacetylase (HDAC) inhibitor suberoylanilide hydroxamic acid (SAHA) increased AQP5 expression and Sp1-mediated transcription of p358P/E. HDAC3 overexpression inhibited Sp1-mediated Aqp5 activation, while HDAC3 knockdown augmented AQP5 protein expression. Knockdown of GATA6 or transcriptional co-activator/histone acetyltransferase p300 decreased AQP5 expression, while p300 overexpression enhanced p358P/E activation by GATA6 and Sp1. GATA6 overexpression, SAHA treatment or HDAC3 knockdown increased histone H3 (H3) but not histone H4 (H4) acetylation within the homologous p358P/E region of mouse Aqp5. HDAC3 binds to Sp1 and HDAC3 knockdown increased interaction of GATA6/Sp1, GATA6/p300 and Sp1/p300. These results indicate that GATA6 and HDAC3 control Aqp5 transcription via modulation of H3 acetylation/deacetylation, respectively, through competition for binding to Sp1, and suggest that p300 modulates acetylation and/or interacts with GATA6/Sp1 to regulate Aqp5 transcription. Cooperative interactions among transcription factors and histone modifications regulate Aqp5 expression during alveolar epithelial cell transdifferentiation, suggesting that HDAC inhibitors may enhance repair by promoting acquisition of AT1 cell phenotype.

Rho-associated protein kinase inhibition enhances airway epithelial Basal-cell proliferation and lentivirus transduction

The identification of factors that regulate airway epithelial cell proliferation and differentiation are essential for understanding the pathophysiology of airway diseases. Rho-associated protein kinases (ROCKs) are downstream effector proteins of RhoA GTPase that direct the functions of cell cytoskeletal proteins. ROCK inhibition with Y27632 has been shown to enhance the survival and cloning of human embryonic stem cells and pluripotent cells in other tissues. We hypothesized that Y27632 treatment exerts a similar effect on airway epithelial basal cells, which function as airway epithelial progenitor cells. Treatment with Y27632 enhanced basal-cell proliferation in cultured human tracheobronchial and mouse tracheal epithelial cells. ROCK inhibition accelerated the maturation of basal cells, characterized by a diminution of the cell size associated with cell compaction and the expression of E-cadherin at cell-cell junctions. Transient treatment of cultured basal cells with Y27632 did not affect subsequent ciliated or mucous cell differentiation under air-liquid interface conditions, and allowed for the initial use of lower numbers of human or mouse primary airway epithelial cells than otherwise possible. Moreover, the use of Y27632 during lentivirus-mediated transduction significantly improved posttransduction efficiency and the selection of a transduced cell population, as determined by reporter gene expression. These findings suggest an important role for ROCKs in the regulation of proliferation and maturation of epithelial basal cells, and demonstrate that the inhibition of ROCK pathways using Y27632 provides an adjunctive tool for the in vitro genetic manipulation of airway epithelial cells by lentivirus vectors.

Analysis of ciliogenesis in primary culture mouse tracheal epithelial cells

Cell biological and molecular characterization of structural and functional ciliary components and regulators of mammalian motile ciliogenesis is made possible by the development of a robust and biologically faithful mouse tracheal epithelial cell (MTEC) culture system and complementary research techniques. Here, we describe the air-liquid interface culture of mouse airway epithelial progenitor cells that undergo motile ciliogenesis de novo. Multiciliated cells differentiate rapidly, and distinct stages of the ciliogenesis pathway can be identified and characterized with centriolar and ciliary immunofluorescence markers. Immunolabeled structures correlate with morphological features previously identified by electron microscopy, facilitating light microscopy analysis. MTEC cultures can be successfully transduced by lentiviral RNAi or epitope-tagged cDNA constructs to perturb gene expression. Also, motile ciliogenesis can be manipulated by drug treatment. Distinct cell populations can be isolated by cell sorting to facilitate comparison among the multiciliated and other cell types in the in vitro differentiated epithelium. The MTEC system uniquely offers the study of ciliogenesis in cells from genetically modified mouse strains.

A VSV-G Pseudotyped Last Generation Lentiviral Vector Mediates High Level and Persistent Gene Transfer in Models of Airway Epithelium In Vitro and In Vivo

The aim of this work was to evaluate the efficiency and duration of gene expression mediated by a VSV-G pseudotyped last generation lentiviral (LV) vector. We studied LV efficiency in ex-vivo models of respiratory epithelial cells, obtained from bronchial biopsies and nasal polyps, by GFP epifluorescence and cytofluorimetry. In vivo efficiency and persistence of gene expression was investigated by GFP immunohistochemistry and luciferase activity in lung cryosections and homogenates, respectively, upon intranasal and intratracheal administration protocols in C57Bl/6 mice. Both primary bronchial and nasal epithelial cells were transduced up to 70–80% 72 hr after the LV infection. In vivo nasal luciferase expression was increased by lysophosphatidylcholine pre-treatment of the nose. Conversely, the bronchial epithelium was transduced in the absence of any pre-conditioning treatment and luciferase expression lasted for at least 6 months without any decline. We conclude that a last generation LV vector is a promising gene transfer agent in the target organ of genetic and acquired lung diseases, as in the case of cystic fibrosis.

Impact of lentiviral vector-mediated transduction on the tightness of a polarized model of airway epithelium and effect of cationic polymer polyethylenimine

Lentiviral (LV) vectors are promising agents for efficient and long-lasting gene transfer into the lung and for gene therapy of genetically determined pulmonary diseases, such as cystic fibrosis, however, they have not been evaluated for cytotoxicity and impact on the tightness of the airway epithelium. In this study, we evaluated the transduction efficiency of a last-generation LV vector bearing Green Fluorescent Protein (GFP) gene as well as cytotoxicity and tight junction (TJ) integrity in a polarized model of airway epithelial cells. High multiplicities of infection (MOI) showed to be cytotoxic, as assessed by increase in propidium iodide staining and decrease in cell viability, and harmful for the epithelial tightness, as demonstrated by the decrease of transepithelial resistance (TER) and delocalization of occludin from the TJs. To increase LV efficiency at low LV:cell ratio, we employed noncovalent association with the polycation branched 25 kDa polyethylenimine (PEI). Transduction of cells with PEI/LV particles resulted in 2.5–3.6-fold increase of percentage of GFP-positive cells only at the highest PEI:LV ratios (1×10⁷ PEI molecules/transducing units with 50 MOI LV) as compared to plain LV. At this dose PEI/LV transduction resulted in 6.5 ± 2.4% of propidium iodide-positive cells. On the other hand, PEI/LV particles did not determine any alteration of TER and occludin localization. We conclude that PEI may be useful for improving the efficiency of gene transfer mediated by LV vectors in airway epithelial cells, in the absence of high acute cytotoxicity and alteration in epithelial tightness.

Effective in vivo and ex vivo gene transfer to intestinal mucosa by VSV-G-pseudotyped lentiviral vectors

Background

Gene transfer to the gastrointestinal (GI) mucosa is a therapeutic strategy which could prove particularly advantageous for treatment of various hereditary and acquired intestinal disorders, including inflammatory bowel disease (IBD), GI infections, and cancer.

Methods

We evaluated vesicular stomatitis virus glycoprotein envelope (VSV-G)-pseudotyped lentiviral vectors (LV) for efficacy of gene transfer to both murine rectosigmoid colon in vivo and human colon explants ex vivo. LV encoding beta-galactosidase (LV-β-Gal) or firefly-luciferase (LV-fLuc) reporter genes were administered by intrarectal instillation in mice, or applied topically for ex vivo transduction of human colorectal explant tissues from normal individuals. Macroscopic and histological evaluations were performed to assess any tissue damage or inflammation. Transduction efficiency and systemic biodistribution were evaluated by real-time quantitative PCR. LV-fLuc expression was evaluated by ex vivo bioluminescence imaging. LV-β-Gal expression and identity of transduced cell types were examined by histochemical and immunofluorescence staining.

Results

Imaging studies showed positive fLuc signals in murine distal colon; β-Gal-positive cells were found in both murine and human intestinal tissue. In the murine model, β-Gal-positive epithelial and lamina propria cells were found to express cytokeratin, CD45, and CD4. LV-transduced β-Gal-positive cells were also seen in human colorectal explants, consisting mainly of CD45, CD4, and CD11c-positive cells confined to the LP.

Conclusions

We have demonstrated the feasibility of LV-mediated gene transfer into colonic mucosa. We also identified differential patterns of mucosal gene transfer dependent on whether murine or human tissue was used. Within the limitations of the study, the LV did not appear to induce mucosal damage and were not distributed beyond the distal colon.

Amelioration of emphysema in mice through lentiviral transduction of long-lived pulmonary alveolar macrophages

Directed gene transfer into specific cell lineages in vivo is an attractive approach for both modulating gene expression and correcting inherited mutations such as emphysema caused by human alpha1 antitrypsin (hAAT) deficiency. However, somatic tissues are mainly comprised of heterogeneous, differentiated cell lineages that can be short lived and difficult to specifically transfect. Here, we describe an intratracheally instilled lentiviral system able to deliver genes selectively to as many as 70% of alveolar macrophages (AMs) in the mouse lung. Following a single in vivo lentiviral transduction, genetically tagged AMs persisted in lung alveoli and expressed transferred genes for the lifetime of the adult mouse. A prolonged macrophage lifespan, rather than precursor cell proliferation, accounted for the surprisingly sustained presence of transduced AMs. We utilized this long-lived population to achieve localized secretion of therapeutic levels of hAAT protein in lung epithelial lining fluid. In an established mouse model of emphysema, lentivirally delivered hAAT ameliorated the progression of emphysema, as evidenced by attenuation of increased lung compliance and alveolar size. After 24 weeks of sustained gene expression, no humoral or cellular immune responses to hAAT protein were detected. Our results challenge the dogma that AMs are short lived and suggest that these differentiated cells may be a possible target cell population for in vivo gene therapy applications, including the sustained correction of hAAT deficiency.

Lentiviral transduction of mammary stem cells for analysis of gene function during development and cancer

The mouse mammary gland is the only epithelial organ capable of complete regeneration upon orthotopic transplantation, making it ideally suited for in vivo gene function studies through viral-mediated gene delivery. A hurdle that has challenged the widespread adoption of this technique has been the inability to transduce mammary stem cells effectively. We have overcome this limitation by infecting total primary mammary epithelial cells in suspension with high-titer lentiviruses. Transduced cells gave rise to all major cell types of the mammary gland and were capable of clonal outgrowth and functional differentiation in serial transplants. To demonstrate that this method is a valuable alternative to developing transgenic animals, we used lentiviral-mediated Wnt-1 overexpression to replicate MMTV-Wnt-1 mammary phenotypes and used a dominant-negative Xenopus Suppressor of Hairless to reveal a requirement for Notch signaling during ductal morphogenesis. Importantly, this method is also applicable to transduction of cells from other tissues.

Effect of cell polarization on hepatitis C virus entry

The primary reservoir for hepatitis C virus (HCV) replication in vivo is believed to be hepatocytes within the liver. Three host cell molecules have been reported to be important entry factors for receptors for HCV: the tetraspanin CD81, scavenger receptor BI (SR-BI), and the tight-junction (TJ) protein claudin 1 (CLDN1). The recent discovery of a TJ protein as a critical coreceptor highlighted the importance of studying the effect(s) of TJ formation and cell polarization on HCV entry. The colorectal adenocarcinoma Caco-2 cell line forms polarized monolayers containing functional TJs and was found to express the CD81, SR-BI, and CLDN1 proteins. Viral receptor expression levels increased upon polarization, and CLDN1 relocalized from the apical pole of the lateral cell membrane to the lateral cell-cell junction and basolateral domains. In contrast, expression and localization of the TJ proteins ZO-1 and occludin 1 were unchanged upon polarization. HCV infected polarized and nonpolarized Caco-2 cells to comparable levels, and entry was neutralized by anti-E2 monoclonal antibodies, demonstrating glycoprotein-dependent entry. HCV pseudoparticle infection and recombinant HCV E1E2 glycoprotein interaction with polarized Caco-2 cells occurred predominantly at the apical surface. Disruption of TJs significantly increased HCV entry. These data support a model where TJs provide a physical barrier for viral access to receptors expressed on lateral and basolateral cellular domains.

Effects of dynamic compression on lentiviral transduction in an in vitro airway wall model

Asthmatic patients are more susceptible to viral infection, and we asked whether dynamic strain on the airway wall (such as that associated with bronchoconstriction) would influence the rate of viral infection of the epithelial and subepithelial cells. To address this, we characterized the barrier function of a three-dimensional culture model of the bronchial airway wall mucosa, modified the culture conditions for optimization of ciliogenesis, and compared epithelial and subepithelial green fluorescent protein (GFP) transduction by a pWpts-GFP lentivirus, pseudotyped with VSV-G, under static vs. dynamic conditions. The model consisted of human lung fibroblasts, bronchial epithelial cells, and a type I collagen matrix, and after 21 days of culture at air liquid interface, it exhibited a pseudostratified epithelium comprised of basal cells, mucus-secreting cells, and ciliated columnar cells with beating cilia. Microparticle tracking revealed partial coordination of mucociliary transport among groups of cells. Slow dynamic compression of the airway wall model (15% strain at 0.1 Hz over 3 days) substantially enhanced GFP transduction of epithelial cells and underlying fibroblasts. Fibroblast-only controls showed a similar degree of transduction enhancement when undergoing dynamic strain, suggesting enhanced transport through the matrix. Tight junction loss in the epithelium after mechanical stress was observed by immunostaining. We conclude that dynamic compressive strain such as that associated with bronchoconstriction may promote transepithelial transport and enhance viral transgene delivery to epithelial and subepithelial cells. This finding has significance for asthma pathophysiology as well as for designing delivery strategies of viral gene therapies to the airways.

Molecular characterization of centriole assembly in ciliated epithelial cells

Ciliated epithelial cells have the unique ability to generate hundreds of centrioles during differentiation. We used centrosomal proteins as molecular markers in cultured mouse tracheal epithelial cells to understand this process. Most centrosomal proteins were up-regulated early in ciliogenesis, initially appearing in cytoplasmic foci and then incorporated into centrioles. Three candidate proteins were further characterized. The centrosomal component SAS-6 localized to basal bodies and the proximal region of the ciliary axoneme, and depletion of SAS-6 prevented centriole assembly. The intraflagellar transport component polaris localized to nascent centrioles before incorporation into cilia, and depletion of polaris blocked axoneme formation. The centriolar satellite component PCM-1 colocalized with centrosomal components in cytoplasmic granules surrounding nascent centrioles. Interfering with PCM-1 reduced the amount of centrosomal proteins at basal bodies but did not prevent centriole assembly. This system will help determine the mechanism of centriole formation in mammalian cells and how the limitation on centriole duplication is overcome in ciliated epithelial cells.

Development of lentiviral vectors with regulated respiratory epithelial expression in vivo

Development of gene transfer vectors with regulated, lung-specific expression will be a useful tool for studying lung biology and developing gene therapies. In this study we constructed a series of lentiviral vectors with regulatory elements predicted to produce lung-specific transgene expression: the surfactant protein C promoter (SPC) for alveolar epithelial type II cell (AECII) expression, the Clara cell 10-kD protein (CC10) for Clara cell expression in the airway, and the Jaagskiete sheep retrovirus (JSRV) promoter for expression in both cell types. Transgene expression from the SPC and CC10 vectors was restricted to AECII and Clara cell lines, respectively, while expression from the JSRV vector was observed in multiple respiratory and nonrespiratory cell types. After intratracheal delivery of lentivector supernatant to mice, transgene expression was observed in AECII from the SPC lentivector, and in Clara cells from the CC10-promoted lentivector. Transgene expression was not detected in nonrespiratory tissues after intravenous delivery of CC10 and SPC lentiviral vectors to murine recipients. In summary, incorporation of genomic regulatory elements from the SPC and CC10 genes resulted in respiratory specific transgene expression in vitro and in vivo. These vectors will provide a useful tool for the study of lung biology and the development of gene therapies for lung disorders.

Permanent, lowered HLA class I expression using lentivirus vectors with shRNA constructs: Averting cytotoxicity by alloreactive T lymphocytes

Transplantation of many tissues requires histocompatibility matching of human leukocyte antigens (HLA) to prevent graft rejection, to reduce the level of immunosuppression needed to maintain graft survival, and to minimize the risk of graft-versus-host disease, particularly in the case of bone marrow transplantation. However, recent advances in fields of gene delivery and genetic regulation technologies have opened the possibility of engineering grafts that display reduced levels of HLA expression. Suppression of HLA expression could help to overcome the limitations imposed by extensive HLA polymorphisms that restrict the availability of suitable donors, necessitate the maintenance of large donor registries, and complicate the logistics of procuring and delivering matched tissues and organs to the recipient. Accordingly, we investigated whether knockdown of HLA by RNA interference (RNAi), a ubiquitous regulatory system that can efficiently and selectively inhibit the expression of specific gene products, would enable allogeneic cells to evade immune recognition. For efficient and stable delivery of short hairpin-type RNAi constructs (shRNA), we employed lentivirus-based gene transfer vectors, which provide a delivery system that can achieve integration into genomic DNA, thereby permanently modifying transduced graft cells. Our results show that lentivirus-mediated delivery of shRNA targeting pan-Class I and allele-specific HLA can achieve efficient and dose-dependent reduction in surface expression of HLA in human cells, associated with enhanced resistance to alloreactive T lymphocyte-mediated cytotoxicity, while avoiding MHC-non-restricted killing. We hypothesize that RNAi-induced silencing of HLA expression has the potential to create histocompatibility-enhanced, and, eventually, perhaps "universally" compatible cellular grafts.

Subunit-specific coordinate upregulation of sodium pump activity in alveolar epithelial cells by lentivirus-mediated gene transfer

Resolution of alveolar edema depends on active ion transport by sodium pumps located on the basolateral surface of alveolar epithelial cells (AECs), suggesting that upregulation of sodium pump activity may facilitate clearance of edema fluid. We have investigated the use of lentiviral vectors to augment sodium pump activity via gene transfer of sodium pump subunits to AECs. Full-length cDNA for the alpha(1) or beta(1) subunit of rat Na(+),K(+)-ATPase was cloned into the lentiviral vector pRRLsin.hCMV.IRES.EGFP. Rat AECs in primary culture were transduced on day 4 with lentiviral vectors pseudotyped with vesicular stomatitis virus glycoprotein G. Transduction with lentiviral vectors encoding either alpha(1) subunit (Lenti-alpha(1)-EGFP) or beta(1) subunit (Lenti-beta(1)-EGFP) led to dose-dependent increases in mRNA and protein for the corresponding subunit. Transduction with Lenti-beta(1)-EGFP was accompanied by coordinate upregulation of endogenous alpha(1) expression, whereas endogenous beta(1) expression was unchanged after transduction with Lenti-alpha(1)-EGFP. Consistent with these findings, transduction with Lenti-beta(1)-EGFP, but not Lenti-alpha(1)-EGFP, led to augmentation of sodium pump activity as a result of increases in Na(+),K(+)-ATPase holoenzyme. Sodium pump alpha(2) subunit and sodium channel protein did not change after Lenti-beta(1)-EGFP transduction. These results demonstrate that overall sodium pump activity can be efficiently upregulated in AECs specifically via gene transfer of the sodium pump beta(1) subunit and support the feasibility of lentivirus-mediated gene transfer to augment alveolar fluid clearance.

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.

Role of f-box factor foxj1 in differentiation of ciliated airway epithelial cells

Factors required for commitment of an undifferentiated airway epithelial cell to a ciliated cell are unknown. Cell ultrastructure analysis indicates ciliated cell commitment activates a multistage program involving synthesis of cilia precursor proteins and assembly of macromolecular complexes. Foxj1 is an f-box transcription factor expressed in ciliated cells and shown to be required for cilia formation by gene deletion in a mouse model. To identify a specific role for foxj1 in directing the ciliated cell phenotype, we evaluated the capacity of foxj1 to induce ciliogenesis and direct cilia assembly. In a primary culture model of wild-type mouse airway epithelial cells, foxj1 expression preceded the appearance of cilia and in cultured foxj1 null cells cilia did not develop. Delivery of foxj1 to polarized epithelial cell lines and primary cultured alveolar epithelial cells failed to promote ciliogenesis. Similarly, delivery of foxj1 to wild-type airway epithelial cells did not enhance the total number of ciliated cells. In contrast, delivery of foxj1 to null cells resulted in the appearance of cilia. Analysis revealed that, in the absence of foxj1, null cells contained cilia precursor basal bodies, indicating prior commitment to ciliogenesis. However, the basal bodies were disorganized within the apical compartment and failed to dock with the apical membrane. Reconstitution of foxj1 in null cells restored normal basal body organization, resulting in axoneme growth. Thus foxj1 functions in late-stage ciliogenesis to regulate programs promoting basal body docking and axoneme formation in cells previously committed to the ciliated cell phenotype.

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

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