Selective Expansion of Alveolar Macrophages In Vivo by Adenovirus-Mediated Transfer of the Murine Granulocyte-Macrophage Colony-Stimulating Factor cDNA

Understanding the Biology of Self-Renewing Macrophages

Macrophages reside in specific territories in organs, where they contribute to the development, homeostasis, and repair of tissues. Recent work has shown that the size of tissue macrophage populations has an impact on tissue functions and is determined by the balance between replenishment and elimination. Macrophage replenishment is mainly due to self-renewal of macrophages, with a secondary contribution from blood monocytes. Self-renewal is a recently discovered trait of macrophages, which can have a major impact on their physiological functions and hence on the wellbeing of the organism. In this review, I discuss our current understanding of the developmental origin of self-renewing macrophages and the mechanisms used to maintain a physiologically stable macrophage pool.

Adenoviral vectors transduce alveolar macrophages in lung cancer models

Adenoviral vectors expressing Cre recombinase are commonly used to initiate tumor formation in murine lung cancer models. While these vectors are designed to target genetic recombination to lung epithelial cells, adenoviruses can infect additional cell types that potentially influence tumor development. Our goal was to explore the consequences of adenoviral-mediated alveolar macrophage (AM) transduction in a Kras-initiated lung tumor model. As expected, treatment of animals harboring the Kras^LSL-G12D allele and an inducible green fluorescence protein (GFP) tracking allele with an adenoviral vector expressing Cre recombinase under the control of the cytomegalovirus (CMV) promoter (Ad5-CMV-Cre), caused GFP-positive lung adenocarcinomas. Surprisingly, however, up to 70% of the total GFP⁺ cells were AM, and GFP⁺ AM could be detected 6 months after tumor initiation, and transduced AM demonstrated Kras activation and increased proliferation. In contrast, recombination was not detected in other immune cell populations and AM recombination could be eliminated by tumor initiation with an adenovirus expressing Cre recombinase under the control of the surfactant protein C (SPC) promoter. In addition, AM isolated from Kras^LSL-G12D animals and transduced by Ad5-CMV-Cre ex vivo displayed prolonged survival in vitro and increased the growth of murine lung adenocarcinoma CMT/167 cells when co-injected in an orthotopic flank model. Given the importance of the immune system in tumor development and progression, inadvertent AM transduction by Ad5-CMV-Cre merits careful consideration during lung cancer model selection particularly if studies evaluating the tumor-immune interactions are planned.

Pivotal roles of GM-CSF in autoimmunity and inflammation

Granulocyte macrophage-colony stimulating factor (GM-CSF) is a hematopoietic growth factor, which stimulates the proliferation of granulocytes and macrophages from bone marrow precursor cells. In autoimmune and inflammatory diseases, Th17 cells have been considered as strong inducers of tissue inflammation. However, recent evidence indicates that GM-CSF has prominent proinflammatory functions and that this growth factor (not IL-17) is critical for the pathogenicity of CD4⁺ T cells. Therefore, the mechanism of GM-CSF-producing CD4⁺ T cell differentiation and the role of GM-CSF in the development of autoimmune and inflammatory diseases are gaining increasing attention. This review summarizes the latest knowledge of GM-CSF and its relationship with autoimmune and inflammatory diseases. The potential therapies targeting GM-CSF as well as their possible side effects have also been addressed in this review.

Mast cells: a pivotal role in pulmonary fibrosis

Pulmonary fibrosis is characterized by an inflammatory response that includes macrophages, neutrophils, lymphocytes, and mast cells. The purpose of this study was to evaluate whether mast cells play a role in initiating pulmonary fibrosis. Pulmonary fibrosis was induced with bleomycin in mast-cell-deficient WBB6F1-W/W(v) (MCD) mice and their congenic controls (WBB6F1-(+)/(+)). Mast cell deficiency protected against bleomycin-induced pulmonary fibrosis, but protection was reversed with the re-introduction of mast cells to the lungs of MCD mice. Two mast cell mediators were identified as fibrogenic: histamine and renin, via angiotensin (ANG II). Both human and rat lung fibroblasts express the histamine H1 and ANG II AT1 receptor subtypes and when activated, they promote proliferation, transforming growth factor β1 secretion, and collagen synthesis. Mast cells appear to be critical to pulmonary fibrosis. Therapeutic blockade of mast cell degranulation and/or histamine and ANG II receptors should attenuate pulmonary fibrosis.

PPARs in alveolar macrophage biology

PPARs, most notably PPAR-gamma, play a crucial role in regulating the activation of alveolar macrophages, which in turn occupy a pivotal place in the immune response to pathogens and particulates drawn in with inspired air. In this review, we describe the dual role of the alveolar macrophage as both a first-line defender through its phagocytotic activity and a regulator of the immune response. Depending on its state of activation, the alveolar macrophage may either enhance or suppress different aspects of immune function in the lung. We then review the role of PPAR-gamma and its ligands in deactivating alveolar macrophages-thus limiting the inflammatory response that, if unchecked, could threaten the essential respiratory function of the alveolus-while upregulating the cell's phagocytotic activity. Finally, we examine the role that inadequate or inappropriate PPAR-gamma responses play in specific lung diseases.

Emphysema mediated by lung overexpression of ADAM10

Cigarette smoking is the major risk factor for emphysema, a disorder of the lung parenchyma characterized by destruction of the alveolar walls. Current concepts of the pathogenesis of emphysema hold that the destruction of the lung parenchyma results, in part, from a local imbalance of proteases and antiproteases. Based on the knowledge that human alveolar macrophages express ADAM 10, a protease capable of destroying basement membrane collagen but not previously implicated in emphysema, we used adenovirus-mediated lung expression of ADAM 10 in a mouse model to assess whether an increased burden of ADAM 10 was capable of inducing emphysema. To assess this, the human ADAM 10 cDNA under control of a constitutive promoter was inserted into an adenovirus gene transfer vector (AdhADAMlO), and the vector (10(11) particle units) administered to the respiratory tract of wild type C57BI/6 mice. Lung levels of ADAM 10 mRNA and protein were upregulated following AdhADAMlO administration. After 8 weeks, quantitative morphometry of the lung parenchyma demonstrated that AdhADAMlO administration induced emphysema (mean linear intercept of 60.6 + 1.3 microm compared with 55.6 + 0.8 in mice treated with a control vector, p < 0.003). These results suggest a role of ADAM 10 in the pathogenesis of emphysema, adding to the list of proteases expressed in the lung that are capable of contributing to the development of lung destruction.

Neutralizing granulocyte/macrophage colony-stimulating factor inhibits cigarette smoke-induced lung inflammation

RATIONALE

Cigarette smoke is the major cause of chronic obstructive pulmonary disease (COPD), and there is currently no satisfactory therapy to treat people with COPD. We have previously shown that granulocyte/macrophage colony-stimulating factor (GM-CSF) regulates lung innate immunity to LPS through Akt/Erk activation of nuclear factor-kappaB and activator protein (AP)-1.

OBJECTIVES

The aim of this study was to determine whether neutralization of GM-CSF can inhibit cigarette smoke-induced lung inflammation in vivo.

METHODS

Male BALB/c mice were exposed to cigarette smoke generated from 9 cigarettes per day for 4 days. Mice were treated intranasally with 100 microg 22E9 (anti-GM-CSF mAb) and isotype control antibody on Days 2 and 4, 1 hour before cigarette smoke or sham exposure. On the fifth day mice were killed, and the lungs were lavaged with PBS and then harvested for genomic and proteomic analysis.

MEASUREMENTS AND MAIN RESULTS

Cigarette smoke-exposed mice treated with anti-GM-CSF mAb had significantly less BALF macrophages and neutrophils, whole lung TNF-alpha, macrophage inflammatory protein (MIP)-2, and matrix metalloproteinase (MMP)-12 mRNA expression and lost less weight compared with smoke-exposed mice treated with isotype control. In contrast, smoke-induced increases in MMP-9 and net gelatinase activity were unaffected by treatment with anti-GM-CSF. In addition, neutralization of GM-CSF did not affect the phagocytic function of alveolar macrophages.

CONCLUSIONS

GM-CSF is a key mediator in smoke-induced airways inflammation, and its neutralization may have therapeutic implications in diseases such as COPD.

Expression of PU.1 and terminal differentiation of alveolar macrophages in newborn rats

PU.1, which is a transcription factor, promotes the terminal differentiation of alveolar macrophages (AMs). Its expression is regulated by granulocyte/macrophage colony-stimulating factor (GM-CSF). In this study of AMs in newborn rats, we performed immunohistochemical staining, acid phosphatase staining, reverse transcriptase polymerase chain reaction (RT-PCR), quantitative real-time PCR, cytokine assay, and electron microscopy. AMs at 3 and 7 days after birth had a large foamy appearance with an intracytoplasmic accumulation of surfactants. Weak expression of PU.1 was observed in the nuclei. AMs at 15 days after birth were smaller, and PU.1 expression had increased. Ultrastructurally, AMs at 1 day after birth had a smooth surface and abundant lamellar structures in the cytoplasm, whereas AMs at 56 days after birth were characterized by (1) abundant microvillar projections on the cell surface, and (2) well-developed lysosomes and a few lamellar structures in the cytoplasm. Acid phosphatase activity and the expression of mannose receptor, scavenger receptor, and GM-CSF receptor alpha were enhanced in AMs with time after birth. These results suggest that AMs are initially immature, and that their terminal differentiation starts after birth concomitantly with an increased expression of PU.1.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) and T-cell responses: what we do and don't know

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is an important hematopoietic growth factor and immune modulator. GM-CSF also has profound effects on the functional activities of various circulating leukocytes. It is produced by a variety of cell types including T cells, macrophages, endothelial cells and fibroblasts upon receiving immune stimuli. Although GM-CSF is produced locally, it can act in a paracrine fashion to recruit circulating neutrophils, monocytes and lymphocytes to enhance their functions in host defense. Recent intensive investigations are centered on the application of GM-CSF as an immune adjuvant for its ability to increase dendritic cell (DC) maturation and function as well as macrophage activity. It is used clinically to treat neutropenia in cancer patients undergoing chemotherapy, in AIDS patients during therapy, and in patients after bone marrow transplantation. Interestingly, the hematopoietic system of GM-CSF-deficient mice appears to be normal; the most significant changes are in some specific T cell responses. Although molecular cloning of GM-CSF was carried out using cDNA library of T cells and it is well known that the T cells produce GM-CSF after activation, there is a lack of systematic investigation of this cytokine in production by T cells and its effect on T cell function. In this article, we will focus mainly on the immunobiology of GM-CSF in T cells.

Therapeutic potential of treating chronic obstructive pulmonary disease (COPD) by neutralising granulocyte macrophage-colony stimulating factor (GM-CSF)

Chronic obstructive pulmonary disease (COPD) is a major incurable global health burden and will become the third largest cause of death in the world by 2020. It is currently believed that an exaggerated inflammatory response to inhaled irritants, in particular cigarette smoke, causes progressive airflow limitation. This inflammation, where macrophages and neutrophils are prominent, leads to oxidative stress, emphysema (loss of lung structure), small airways fibrosis and mucus hypersecretion. However, COPD responds poorly to current anti-inflammatory treatments including potent glucocorticosteroids, which produce little or no benefit. In this review we consider the therapeutic potential of targeting granulocyte macrophage-colony stimulating factor (GM-CSF) for the treatment of COPD. GM-CSF is a major regulator of both macrophage and neutrophil activation and survival in the lung-these cells are intimately linked to COPD. Animal data indicates that neutralisation of GM-CSF ameliorates experimental COPD and predicts therapeutic utility in treating stable COPD and treating exacerbations. As such, GM-CSF represents an attractive therapeutic target for the treatment of COPD.

Intrapleural administration of a serotype 5 adeno-associated virus coding for α1-antitrypsin mediates persistent, high lung and serum levels of α1-antitrypsin

alpha1-Antitrypsin (alpha1AT) is a serine proteinase inhibitor that protects the lung from degradation by neutrophil proteases. In alpha1AT deficiency, an autosomal recessive disorder resulting from mutations in the alpha1AT (approved symbol SERPINA1) gene, serum alpha1AT levels of < 570 microg/ml are associated with development of emphysema. Adeno-associated virus (AAV) serotype 2 (AAV2) vectors expressing alpha1AT administered intramuscularly or intravenously mediate sustained serum levels of alpha1AT in experimental animals. Since the lung is only 2% of the body weight, AAV vector delivery to the muscle or liver is inefficient, as most of the alpha1AT does not reach the lung. The present study evaluates AAV2- and AAV5-mediated delivery of human alpha1AT (halpha1AT) to C57BL/6 mice using the intrapleural space as a platform for local production of alpha1AT. Intrapleural administration of either an AAV5-halpha1AT or an AAV2-halpha1AT vector achieves higher lung and serum levels of alpha1AT than intramuscular delivery. AAV5-mediated serum and lung alpha1AT levels were 10-fold higher than those achieved by AAV2 delivery via either route. The diaphragm, lung, and heart are the major sites of transgene expression following intrapleural administration of an AAV5 reporter vector. At 40 weeks postadministration, intrapleural administration of the AAV5-halpha1AT vector mediated serum alpha1AT levels of 900 +/- 50 microg/ml, 1.6-fold higher than the accepted therapeutic level of 570 microg/ml. In the context that the pleura is a safe site for administration, intrapleural administration using AAV5 vectors may represent an attractive gene therapy strategy for alpha1AT deficiency in humans.

New method of delivering gene-altered Kupffer cells to rat liver: studies in an ischemia-reperfusion model

BACKGROUND & AIMS

Kupffer cells play a major role in the pathogenesis of several diseases. They release physiologically active substances that often lead to localized tissue injury. Therefore, the aim of this study was to establish a model to protect the liver through supplementation of Kupffer cells that have been transduced by recombinant adenovirus.

METHODS

Optimal conditions for intravenous injection in rats were established using carbon-labeled Kupffer cells. Adenoviral-transduced Kupffer cells encoding the Cu/Zn-SOD gene (Ad.SOD1) or beta-galactosidase reporter gene (Ad.LacZ) were transplanted into recipient rats. Twenty-four hours after transplantation, 70% hepatic ischemia-reperfusion was used to induce hepatic oxidative stress, and liver injury was determined 8 or 24 hours later.

RESULTS

In initial experiments, 10%-20% of the injected carbon-labeled cells were localized in the host liver after 24 hours, representing approximately 1% of the total population of Kupffer cells. Pretreatment of the recipient with a single dose of cyclosporin A maximized Kupffer cell reseeding up to 4%-10% of the total Kupffer cell population, suggesting that efficiency is limited by host immune response. Moreover, reseeded Kupffer cells were retained in host livers for up to 14 days after transplant. In livers of animals injected with Kupffer cells transduced with Ad.LacZ, transgene expression was observed, indicating Kupffer cell functional integrity. Injection of Kupffer cells transduced with Ad.SOD1 significantly blunted the increase in serum transaminases and liver injury because of ischemia-reperfusion compared with controls.

CONCLUSIONS

This novel approach allows delivery of transduced Kupffer cells in rats, which can be used as an investigative tool as well as a therapeutic strategy against inflammatory liver diseases.

Inhibition of HIV-1 replication in alveolar macrophages by adenovirus gene transfer vectors

To assess the hypothesis that infection of alveolar macrophages (AM) with adenovirus (Ad) gene transfer vectors might prevent subsequent human immunodeficiency virus (HIV)-1 replication in AM, AM isolated from normal volunteers were infected with increasing doses of first generation (E1(-)) Ad vectors, followed 72 h later by infection with HIV-1(JRFL), an R5/M-tropic strain that preferentially uses the CCR5 coreceptor. As a measure of HIV-1 replication, p24 Ag was quantified by enzyme-linked imunosorbent assay in supernatants on Days 4 to 14 after HIV-1infection. Pretreatment of the AM with an Ad vector resulted in a dose- and time-dependent suppression of subsequent HIV-1 replication. The Ad vector inhibition of HIV-1 replication was independent of the transgene in the Ad vector expression cassette and E4 genes in the Ad backbone. Moreover, it did not appear to be secondary to a soluble factor released by the AM, nor was it overridden by the concomitant transfer of the CCR5 or CXCR4 receptors to the AM before HIV-1 infection. These observations have implications regarding pulmonary host responses associated with HIV-1 infection, as well as possibly uncovering new therapeutic strategies against HIV-1 infection.

GM-CSF expression by human lung microvascular endothelial cells: in vitro and in vivo findings

Recently, many findings indicate that granulocyte-macrophage colony-stimulating factor (GM-CSF) plays an important role in the pathogenesis of acute and chronic lung diseases. In the present paper, the production of this cytokine in human pulmonary microvascular endothelial cells (HPMEC) is investigated. In an in vitro study, quiescent HPMEC did not express GM-CSF, either at the transcriptional or at the protein level. After activation for 4 h with tumor necrosis factor (TNF)-alpha (30/300 U/ml), lipopolysaccharide (LPS; 0.1/1 microg/ml), or interleukin (IL)-1 beta (100 U/ml), a significant release of GM-CSF was measured by enzyme-linked immunosorbent assay, with a time-dependent increase over 72 h. IL-8 (4, 16, or 64 ng/ml) or IL-1 beta at a concentration of 10 U/ml did not induce the release of GM-CSF. Human umbilical vein endothelial cells (HUVEC) and the angiosarcoma cell line HAEND served as reference cell lines. GM-CSF release in HPMEC was significantly (P < 0.025-0.05) less inducible by IL-1 beta than in HUVEC. A constitutive expression of GM-CSF by HAEND was observed. Additionally, GM-CSF expression in vivo by the lung microvasculature was confirmed by immunohistochemistry in lung tissue. To our knowledge, this is the first report of the ability of human pulmonary endothelial cells to synthesize and release GM-CSF. These results support the hypothesis that the lung microvasculature via the production of GM-CSF is a potential contributor to the cytokine network in lung diseases. This could be of particular importance in the pathogenesis of the acute respiratory distress syndrome in which endothelial dysfunction plays a central pathogenetic role.

Gm-CSF regulates pulmonary surfactant homeostasis and alveolar macrophage-mediated innate host defense

Recent studies in transgenic mice have revealed important insights into the roles of GM-CSF in regulation of surfactant homeostasis and lung host defense. Interruption of the GM-CSF signaling pathway by targeted ablation of the GM-CSF gene or its receptor (GM(-/-) or GM Rbetac(-/-) mice, respectively) resulted in pulmonary alveolar proteinosis (PAP) but no hematologic abnormalities. Alveolar macrophages from GM(-/-) mice have reduced capacity for surfactant catabolism, cell adhesion, phagocytosis, bacterial killing, Toll-receptor signaling, and expression of various pathogen-associated molecular pattern recognition receptors, suggesting arrest at an early stage of differentiation. PAP and abnormalities of alveolar macrophage function were corrected by local expression of GM-CSF in the lung, and expression of the transcription factor PU.1 in alveolar macrophages of GM(-/-) mice rescued most defects. Recently, a strong association of auto-antibodies to GM-CSF or GM-CSF receptor gene mutations with PAP has implicated GM-CSF signaling abnormalities in the pathogenesis of PAP in humans. Together, these observations demonstrate that GM-CSF has a critical role in regulation of surfactant homeostasis and alveolar macrophage innate immune functions in the lung.

Reduced tissue macrophage population in the lung by anticancer agent cyclophosphamide: restoration by local granulocyte macrophage-colony-stimulating factor gene transfer

Granulocytopenia is thought to be the sole mechanism underlying the increased susceptibility to bacterial infection in hosts with anticancer chemotherapy. Little is known about the functional state of tissue macrophage populations in such hosts. Using a model of chemotherapy-induced leukopenia, the number and function of alveolar macrophages (AMS) were examined during and after multiple injections of an anticancer agent, cyclophosphamide (CP). Although CP quickly reduced peripheral blood leukocytes, the number of these cells rebounded quickly 3 to 4 days after the withdrawal of CP. Accompanying blood leukopenia was a profound reduction in the number of AMs. Contrary to the rapid onset of blood leukopenia, tissue macrophage deficiency was a more chronic process that worsened gradually as the CP regimen continued. Of importance, in contrast to blood leukopenia, which restored itself shortly after CP withdrawal, tissue macrophage deficiency was not immediately self-recoverable in spite of a restored number of circulating leukocytes. Although AMS had a decreased ability to proliferate during, but not after, the CP regimen, these cells retained a normal ability to release tumor necrosis factor-alpha and nitric oxide. To identify the potential therapeutics for recovering macrophages, a gene vector expressing granulocyte macrophage-colony-stimulating factor (GM-CSF) was delivered either systemically or locally. GM-CSF transgene was able to expand macrophage populations only when delivered to the lung after, but not during, the CP regimen. This study thus identifies tissue macrophage deficiency as a mechanism of weakened innate immunity by chemotherapy and suggests the usefulness of topical GM-CSF transgene expression for restoring innate immunity in the lung.

Impaired functional activity of alveolar macrophages from GM-CSF-deficient mice

We hypothesized that pulmonary granulocyte-macrophage colony-stimulating factor (GM-CSF) is critically involved in determining the functional capabilities of alveolar macrophages (AM) for host defense. To test this hypothesis, cells were collected by lung lavage from GM-CSF mutant mice [GM(-/-)] and C57BL/6 wild-type mice. GM(-/-) mice yielded almost 4-fold more AM than wild-type mice. The percentage of cells positive for the beta(2)-integrins CD11a and CD11c was reduced significantly in GM(-/-) AM compared with wild-type cells, whereas expression of CD11b was similar in the two groups. The phagocytic activity of GM(-/-) AM for FITC-labeled microspheres was impaired significantly compared with that of wild-type AM both in vitro and in vivo (after intratracheal inoculation with FITC-labeled beads). Stimulated secretion of tumor necrosis factor-alpha (TNF-alpha) and leukotrienes by AM from the GM(-/-) mice was greatly reduced compared with wild-type AM, whereas secretion of monocyte chemoattractant protein-1 was increased. Transgenic expression of GM-CSF exclusively in the lungs of GM(-/-) mice resulted in AM with normal or supranormal expression of CD11a and CD11c, phagocytic activity, and TNF-alpha secretion. Thus, in the absence of GM-CSF, AM functional capabilities for host defense were significantly impaired but were restored by lung-specific expression of GM-CSF.

Regulation of adenovirus-mediated elafin transgene expression by bacterial lipopolysaccharide

Lipopolysaccharide (LPS) is a mediator of inflammatory lung injury. Selective augmentation of host defense molecules such as elafin (an elastase inhibitor with antimicrobial activity) at the onset of pulmonary inflammation is an attractive potential therapeutic strategy. The aim of this study was to determine whether elafin expression could be induced by LPS administered after transfection with adenovirus (Ad) encoding human elafin downstream of the murine cytomegalovirus (CMV) promoter (known to be potentially responsive to LPS). In addition, we aimed to determine the effect of local elafin augmentation on neutrophil migration to the lung. LPS significantly up-regulated elafin expression from pulmonary epithelial cells transfected with Ad-elafin in vitro. In murine airways expression of human elafin was achieved using doses low enough (3 x 10(7) plaque forming units) to circumvent overt vector-induced inflammation. LPS significantly up-regulated human elafin secretion in murine airways treated with Ad-elafin [117 ng/ml in bronchoalveolar lavage fluid (BALF) after LPS administration, 5.9 ng/ml after PBS, p < 0.01)]. Over-expression of elafin significantly augmented LPS-mediated neutrophil migration into the airways in vivo (1.30 x 10(6) neutrophils in BALF after Ad-elafin/LPS treatment, 0.54 x 10(6) after Ad-lacZ/LPS (p < 0.05), 0.63 x 10(6) after PBS/LPS (p < 0.05)) and significantly enhanced human neutrophil migration in vitro. These data suggest novel functions for elafin in neutrophil migration, and that judicious selection of promoters may allow single, low-dose adenoviral administration to effect inflammation-specific expression of potentially therapeutic transgenes.

A mouse model for adenovirus gene delivery

The cellular attachment receptor for adenovirus (Ad), Coxsackie adenovirus receptor (CAR), required for delivery of Ad into primary cells, is not present on all cell types, thus restricting Ad-gene delivery systems. To circumvent this constrain, a transgenic mouse has been generated that expresses a truncated human CAR in all tissues analyzed. These mice allowed efficient in vitro infections at low multiplicities into lymphoid, myeloid, and endothelial cells. Furthermore, in vivo administration of Ad-vectors results in infection of macrophages, lymphocytes, and endothelial cells. In addition, tail vein injection resulted in targeting of virus into previously inaccessible areas, such as the lung and the capillaries of the brain. The CAR transgenic mice will be useful for rapid functional genomic analysis in vivo, for testing the efficacy of gene therapy procedures or as a source of easily transducible cells.

Transfer of heme oxygenase 1 cDNA by a replication-deficient adenovirus enhances interleukin 10 production from alveolar macrophages that attenuates lipopolysaccharide-induced acute lung injury in mice

By using a direct, intratracheal inoculation of an adenovirus encoding heme oxygenase 1 (Ad.HO-1), model gene therapy for acute lung injury induced by inhaled pathogen was performed. Data demonstrated that Ad.HO-1 administration is as effective as the pharmacologic upregulation of the endogenous HO-1 gene expression by hemin to attenuate neutrophilic inflammations of the lung after aerosolized lipopolysaccharide (LPS) exposure. Interestingly, immunohistochemical analysis revealed that the HO-1 gene was transferred not only to the airway epithelium, but to the alveolar macrophages (AMs). Moreover, overexpression of exogenous HO-1 in the macrophages provided a high level of endogenous interleukin 10 (IL-10) production from the macrophages, and additional experiments using IL-10 knockout mice demonstrated that the increase in IL-10 in the macrophages was critical for the resolution of neutrophilic migration in the lung after LPS exposure. These results suggest that AMs not only are barriers for efficient gene transfer to the respiratory epithelium, but also represent logical targets for Ad-mediated, direct, in vivo gene therapy strategies for inflammatory disorders in humans.

Macrophage death and the role of apoptosis in human atherosclerosis

The arterial disease atherosclerosis is responsible for severe morbidity and is the most common cause of death in the Western population. The complete pathogenesis of the disease is unknown, but multiple risk factors have been identified that correlate with the development of its complications such as heart attack and stroke. Evidence suggests that atherosclerosis is an inflammatory disease and the major cell types involved are smooth muscle cells, macrophages, and T lymphocytes. In this paper, we review the function of macrophages in the context of atherosclerosis and we also discuss the role and significance of macrophage death, including apoptosis. There is much evidence, certainly in vitro, suggesting that low-density lipoprotein becomes atherogenic when it undergoes cell-mediated oxidation within the artery wall. Besides inducing apoptosis in vitro, oxidized low-density lipoprotein may also cause extensive DNA damage in intimal cells, which might presage apoptosis. We review the results of experimental and clinical studies, which may indicate how the complications of atherosclerosis could be prevented by using different therapeutical strategies including bone marrow transplantation and gene therapy.

Lung overexpression of the vascular endothelial growth factor gene induces pulmonary edema

We hypothesized that the angiogenic mediator, vascular endothelial growth factor (VEGF), known to be expressed in the lung and to be capable of inducing local edema in skin, might evoke the development of lung edema if expressed in excess amounts. To test this hypothesis, we developed an in vivo model of VEGF overexpression in the lung on the basis of delivery to the respiratory epithelium of the VEGF165 complementary DNA by an E1(-) adenovirus vector (AdVEGF165). Administration of AdVEGF165 by the intratracheal route (10(9) plaque-forming units [pfu]) to C57Bl/6 mice showed increased expression of VEGF messenger RNA in lung tissue by Northern analysis. Overexpression of VEGF protein in the lung at Days 1 to 10 was confirmed by enzyme-linked immunosorbent assay. Intratracheal administration of AdVEGF165 resulted in a dose-dependent increase in lung wet/dry weight ratios over time, lung histology showed widespread intra- alveolar edema, and pulmonary capillary permeability was significantly increased as quantified by the Evans blue dye assay and [(131)I]albumin permeability. To confirm the specificity of these observations, mice were pretreated with intranasal administration of an adenovirus vector expressing a truncated soluble form of the VEGF receptor flt-1 (Adsflt). Adsflt (10(9) pfu) pretreatment completely abrogated the increased lung wet/dry weight ratio caused by AdVEGF165 administration, whereas an identical adenovirus vector with an irrelevant transgene had no effect upon subsequent AdVEGF165-induced pulmonary edema. Together, these data suggest that overexpression of VEGF in the lung may be one mechanism of increased pulmonary vascular permeability in the early stages of acute lung injury.

Transgenic expression of granulocyte-macrophage colony-stimulating factor induces the differentiation and activation of a novel dendritic cell population in the lung

The role of granulocyte-macrophage colony-stimulating factor (GM-CSF) in the differentiation of dendritic cells (DCs) during pulmonary viral infection was investigated by using a mouse model of GM-CSF transgene expression established with an adenoviral vector (AdGM-CSF). GM-CSF gene transfer resulted in increased levels of GM-CSF in the lung, which peaked at day 4 and remained increased up to day 19. A striking cellular response composed predominantly of macrophage-like cells was observed in the lung receiving AdGM-CSF but not control vector. By FACS analysis, the majority of these cells were identified at an early time point as macrophages and later as mature/activated myeloid DCs characterized by CD11bbright, CD11cbright, MHC class IIbright, and B7.1bright. In contrast, GM-CSF had a weak effect on a small DC population that was found present in normal lung and was characterized by CD11cbright and CD11blow. By immunohistochemistry staining for MHC II, the majority of activated antigen-presenting cells were localized to the airway epithelium and peribronchial/perivascular areas in the lung. A concurrently enhanced Th1 immune response was observed under these conditions. The number of CD4 and CD8 T cells was markedly increased in the lung expressing GM-CSF, accompanied by increased release of interferon (IFN)γ in the lung. Furthermore, lymphocytes isolated from either lung parenchyma or local draining lymph nodes of these mice but not the control mice released large amounts of IFNγ on adenoviral antigen stimulation in vitro. These findings reveal that GM-CSF promotes the differentiation and activation of a myeloid DC population primarily by acting on macrophages during pulmonary immune responses.

On the mechanism of protection of distal joints after local gene transfer in collagen-induced arthritis

Considerable interest has been generated by the observation that adenovirus-mediated gene delivery to a single arthritic joint results in suppression of arthritis in distal joints associated with the presence of small numbers of transduced cells in distal joints. It has been proposed that this is mediated by trafficking of transduced cells from the injected to distal joints. There are, however, alternative explanations that have not been explored, including the possibility that transgene protein or infectious virions circulate to distal sites. To investigate these possibilities, a replication-incompetent adenovirus encoding viral IL-10 (vIL-10) was administered to naive mice and to mice with collagen-induced arthritis by intraarticular, periarticular, or intravenous injection. In all cases, the ability to protect distal joints correlated with serum levels of vIL-10 protein. After intraarticular or intravenous injection, vIL-10 cDNA could be detected not only in distal joints, but also in the liver, which is the major target of circulating adenovirus, demonstrating that adenovirus circulating through the bloodstream is taken up by the joint tissue. Periarticular administration of adenovirus, which resulted in lower serum levels of vIL-10, protected only the injected paws and failed to induce trafficking immunoregulatory cells capable of suppressing distal disease. These observations suggest that circulating vIL-10 protein is the major mediator of distal protection. The presence of small numbers of transduced cells at distal sites can be accounted for by transduction of distal synovium after entry of adenovirus virions into the circulation.

Inflammatory thoughts about glioma gene therapy

Gene therapy for treatment of glioma often involves delivery of herpes simplex virus-1 thymidine kinase gene. A new study shows that this approach can induce chronic inflammation, and raises important questions about current adenoviral-based clinical trials (pages 1256-1263).