Keratinocyte growth factor augments pulmonary innate immunity through epithelium-driven, GM-CSF-dependent paracrine activation of alveolar macrophages

IGFBP-6 Network in Chronic Inflammatory Airway Diseases and Lung Tumor Progression

The lung is an accomplished organ for gas exchanges and directly faces the external environment, consequently exposing its large epithelial surface. It is also the putative determinant organ for inducing potent immune responses, holding both innate and adaptive immune cells. The maintenance of lung homeostasis requires a crucial balance between inflammation and anti-inflammation factors, and perturbations of this stability are frequently associated with progressive and fatal respiratory diseases. Several data demonstrate the involvement of the insulin-like growth factor (IGF) system and their binding proteins (IGFBPs) in pulmonary growth, as they are specifically expressed in different lung compartments. As we will discuss extensively in the text, IGFs and IGFBPs are implicated in normal pulmonary development but also in the pathogenesis of various airway diseases and lung tumors. Among the known IGFBPs, IGFBP-6 shows an emerging role as a mediator of airway inflammation and tumor-suppressing activity in different lung tumors. In this review, we assess the current state of IGFBP-6's multiple roles in respiratory diseases, focusing on its function in the inflammation and fibrosis in respiratory tissues, together with its role in controlling different types of lung cancer.

Mesenchymal Stromal Cells: an Antimicrobial and Host-Directed Therapy for Complex Infectious Diseases

There is an urgent need for new antimicrobial strategies for treating complex infections and emerging pathogens. Human mesenchymal stromal cells (MSCs) are adult multipotent cells with antimicrobial properties, mediated through direct bactericidal activity and modulation of host innate and adaptive immune cells. More than 30 in vivo studies have reported on the use of human MSCs for the treatment of infectious diseases, with many more studies of animal MSCs in same-species models of infection. MSCs demonstrate potent antimicrobial effects against the major classes of human pathogens (bacteria, viruses, fungi, and parasites) across a wide range of infection models. Mechanistic studies have yielded important insight into their immunomodulatory and bactericidal activity, which can be enhanced through various forms of preconditioning. MSCs are being investigated in over 80 clinical trials for difficult-to-treat infectious diseases, including sepsis and pulmonary, intra-abdominal, cutaneous, and viral infections. Completed trials consistently report MSCs to be safe and well tolerated, with signals of efficacy against some infectious diseases. Although significant obstacles must be overcome to produce a standardized, affordable, clinical-grade cell therapy, these studies suggest that MSCs may have particular potential as an adjunct therapy in complex or resistant infections.

FGF2, an Immunomodulatory Factor in Asthma and Chronic Obstructive Pulmonary Disease (COPD)

The fibroblast growth factor 2 (FGF2) is a potent mitogenic factor belonging to the FGF family. It plays a role in airway remodeling associated with chronic inflammatory airway diseases, including asthma and chronic obstructive pulmonary disease (COPD). Recently, research interest has been raised in the immunomodulatory function of FGF2 in asthma and COPD, through its involvement in not only the regulation of inflammatory cells but also its participation as a mediator between immune cells and airway structural cells. Herein, this review provides the current knowledge on the biology of FGF2, its expression pattern in asthma and COPD patients, and its role as an immunomodulatory factor. The potential that FGF2 is involved in regulating inflammation indicates that FGF2 could be a therapeutic target for chronic inflammatory diseases.

Using toponomics to characterize phenotypic diversity in alveolar macrophages from male mice treated with exogenous SP-A1

Background

We used the Toponome Imaging System (TIS) to identify “patterns of marker expression”, referred to here as combinatorial molecular phenotypes (CMPs) in alveolar macrophages (AM) in response to the innate immune molecule, SP-A1.

Methods

We compared 114 AM from male SP-A deficient mice. One group (n = 3) was treated with exogenous human surfactant protein A1 (hSP-A1) and the other with vehicle (n = 3). AM obtained by bronchoalveolar lavage were plated onto slides and analyzed using TIS to study the AM toponome, the spatial network of proteins within intact cells. With TIS, each slide is sequentially immunostained with multiple FITC-conjugated antibodies. Images are analyzed pixel-by-pixel identifying all of the proteins within each pixel, which are then designated as CMPs. CMPs represent organized protein clusters postulated to contribute to specific functions.

Results

1) We compared identical CMPs in KO and SP-A1 cells and found them to differ significantly (p = 0.0007). Similarities between pairs of markers in the two populations also differed significantly (p < 0.0001). 2) Focusing on the 20 most abundant CMPs for each cell, we developed a method to generate CMP “signatures” that characterized various groups of cells. Phenotypes were defined as cells exhibiting similar signatures of CMPs. i) AM were extremely diverse and each group contained cells with multiple phenotypes. ii) Among the 114 AM analyzed, no two cells were identical. iii) However, CMP signatures could distinguish among cell subpopulations within and between groups. iv) Some cell populations were enriched with SP-A1 treatment, some were more common without SP-A1, and some seemed not to be influenced by the presence of SP-A1. v) We also found that AM were more diverse in mice treated with SP-A1 compared to those treated with vehicle.

Conclusions

AM diversity is far more extensive than originally thought. The increased diversity of SP-A1-treated mice points to the possibility that SP-A1 enhances or activates several pathways in the AM to better prepare it for its innate immune functions and other functions shown previously to be affected by SP-A treatment. Future studies may identify key protein(s) responsible for CMP integrity and consequently for a given function, and target it for therapeutic purposes.

Mitogenic stimulation accelerates influenza-induced mortality by increasing susceptibility of alveolar type II cells to infection

Development of pneumonia is the most lethal consequence of influenza, increasing mortality more than 50-fold compared with uncomplicated infection. The spread of viral infection from conducting airways to the alveolar epithelium is therefore a pivotal event in influenza pathogenesis. We found that mitogenic stimulation with keratinocyte growth factor (KGF) markedly accelerated mortality after infectious challenge with influenza A virus (IAV). Coadministration of KGF with IAV markedly accelerated the spread of viral infection from the airways to alveoli compared with challenge with IAV alone, based on spatial and temporal analyses of viral nucleoprotein staining of lung tissue sections and dissociated lung cells. To better define the temporal relationship between KGF administration and susceptibility to IAV infection in vivo, we administered KGF 120, 48, 24, and 0 h before intrapulmonary IAV challenge and assessed the percentages of proliferating and IAV-infected, alveolar type II (AECII) cells in dispersed lung cell populations. Peak AECII infectivity coincided with the timing of KGF administration that also induced peak AECII proliferation. AECII from mice that were given intrapulmonary KGF before isolation and then infected with IAV ex vivo exhibited the same temporal pattern of proliferation and infectious susceptibility. KGF-induced increases in mortality, AECII proliferation, and enhanced IAV susceptibility were all reversed by pretreatment of the animals with the mTOR inhibitor rapamycin before mitogenic stimulation. Taken together, these data suggest mTOR signaling-dependent, mitogenic conditioning of AECII is a determinant of host susceptibility to infection with IAV.

Pharmacological Targeting of the Host-Pathogen Interaction: Alternatives to Classical Antibiotics to Combat Drug-Resistant Superbugs

The rise of multidrug-resistant pathogens and the dearth of new antibiotic development place an existential strain on successful infectious disease therapy. Breakthrough strategies that go beyond classical antibiotic mechanisms are needed to combat this looming public health catastrophe. Reconceptualizing antibiotic therapy in the richer context of the host-pathogen interaction is required for innovative solutions. By defining specific virulence factors, the essence of a pathogen, and pharmacologically neutralizing their activities, one can block disease progression and sensitize microbes to immune clearance. Likewise, host-directed strategies to boost phagocyte bactericidal activity, enhance leukocyte recruitment, or reverse pathogen-induced immunosuppression seek to replicate the success of cancer immunotherapy in the field of infectious diseases. The answer to the threat of multidrug-resistant pathogens lies 'outside the box' of current antibiotic paradigms.

Keratinocyte growth factor supports pulmonary innate immune defense through maintenance of alveolar antimicrobial protein levels and macrophage function

Keratinocyte growth factor (KGF) is an epithelial mitogen that has been reported to protect the lungs from a variety of toxic and infectious insults. In prior studies we found that recombinant human KGF accelerates clearance of bacteria from the murine lung by augmenting the function of alveolar macrophages (AM). In this study we tested the hypothesis that endogenous KGF plays a role in the maintenance of innate pulmonary defense against gram-negative bacterial infections. KGF-deficient mice exhibited delayed clearance of Escherichia coli from the lungs, attenuated phagocytosis by AM, and decreased antimicrobial activity in bronchoalveolar lavage (BAL) fluid, due in part to reductions in levels of surfactant protein A, surfactant protein D, and lysozyme. These immune deficits were accompanied by lower alveolar type II epithelial cell counts and reduced alveolar type II epithelial cell expression of collectin and lysozyme genes on a per cell basis. No significant between-group differences were detected in selected inflammatory cytokines or BAL inflammatory cell populations at baseline or after bacterial challenge in the wild-type and KGF-deficient mice. A single intranasal dose of recombinant human KGF reversed defects in bacterial clearance, AM function, and BAL fluid antimicrobial activity. We conclude that KGF supports alveolar innate immune defense through maintenance of alveolar antimicrobial protein levels and functions of AM. Together these data demonstrate a role for endogenous KGF in maintenance of normal pulmonary innate immune function.

Therapeutic targeting of acute lung injury and acute respiratory distress syndrome

There is no Food and Drug Administration-approved treatment for acute respiratory distress syndrome (ARDS), in spite of the relatively large number of patients with the diagnosis. In this report, we provide an overview of preclinical studies and a description of completed and future clinical trials in humans with ARDS. Preclinical studies dealing with acute lung injury have suggested roles for complement and complement receptors, as well as the evolving role of histones, but details of these pathways are inadequately understood. Anti-inflammatory interventions have not been convincingly effective. Various cell growth factors are being considered for clinical study. Interventions to block complement activation or its products are under consideration. Stem cell therapies have shown efficacy in preclinical studies, which have motivated phase I/II trials in humans with ARDS.

Keratinocyte growth factor-2 inhibits bacterial infection with Pseudomonas aeruginosa pneumonia in a mouse model

To determine protective effects of concurrent administration of Keratinocyte growth factor-2 (KGF-2) with Pseudomonas aeruginosa (P. aeruginosa) inoculation on the induced pneumonia. KGF-2 (5 mg/kg) was concurrently administered into the left lobe of 55 mice with P. aeruginosa PAO1 (5 × 10(6) CFU, half-lethal dose); 55 mice in the control group were concurrently administered PBS with the PAO1. We detected and analyzed: body temperature; amount of P. aeruginosa in homogenates; count of total number of nucleated cells and of mononuclear macrophages; protein concentration in bronchoalveolar lavage fluid (BALF); lung wet-to-dry weight ratio; cytokines in BALF and blood; and lung morphology. To study survival rate, concurrent administration of KGF-2 (experimental group) versus PBS (control) with a lethal dose of PAO1 (1 × 10(7) CFU was performed, and survivorship was documented for 7 days post-inoculation. The bacterial CFU in lung homogenates was significantly decreased in the KGF-2 group compared to the control group. There were significantly more mononuclear macrophages in the BALF from the KGF-2 group than from the control group (p < 0.05). KGF-2 increased the surfactant protein and GM-CSF mRNA in lung at 6 h and 72 h after inoculation. Significant reduction of lung injury scores, protein concentrations, lung wet-to-dry weight ratio, and IL-6 and TNF-α levels was noted in the KGF-2 treated rats at 72 h after inoculation (p < 0.05). The 7-day survival rate of the KGF-2 group was significantly higher than that of the control group (p < 0.05). Concurrent administration of KGF-2 facilitates the clearance of P. aeruginosa from the lungs, attenuates P. aeruginosa-induced lung injury, and extends the 7-day survival rate in mice model with P. aeruginosa pneumonia.

Influenza induces IL-8 and GM-CSF secretion by human alveolar epithelial cells through HGF/c-Met and TGF-α/EGFR signaling

The most severe complication of influenza is viral pneumonia, which can lead to the acute respiratory distress syndrome. Alveolar epithelial cells (AECs) are the first cells that influenza virus encounters upon entering the alveolus. Infected epithelial cells produce cytokines that attract and activate neutrophils and macrophages, which in turn induce damage to the epithelial-endothelial barrier. Hepatocyte growth factor (HGF)/c-Met and transforming growth factor-α (TGF-α)/epidermal growth factor receptor (EGFR) are well known to regulate repair of damaged alveolar epithelium by stimulating cell migration and proliferation. Recently, TGF-α/EGFR signaling has also been shown to regulate innate immune responses in bronchial epithelial cells. However, little is known about whether HGF/c-Met signaling alters the innate immune responses and whether the innate immune responses in AECs are regulated by HGF/c-Met and TGF-α/EGFR. We hypothesized that HGF/c-Met and TGF-α/EGFR would regulate innate immune responses to influenza A virus infection in human AECs. We found that recombinant human HGF (rhHGF) and rhTGF-α stimulated primary human AECs to secrete IL-8 and granulocyte macrophage colony-stimulating factor (GM-CSF) strongly and IL-6 and monocyte chemotactic protein 1 moderately. Influenza infection stimulated the secretion of IL-8 and GM-CSF by AECs plated on rat-tail collagen through EGFR activation likely by TGF-α released from AECs and through c-Met activated by HGF secreted from lung fibroblasts. HGF secretion by fibroblasts was stimulated by AEC production of prostaglandin E₂ during influenza infection. We conclude that HGF/c-Met and TGF-α/EGFR signaling enhances the innate immune responses by human AECs during influenza infections.

Keratinocyte growth factor administration attenuates murine pulmonary mycobacterium tuberculosis infection through granulocyte-macrophage colony-stimulating factor (GM-CSF)-dependent macrophage activation and phagolysosome fusion

Augmentation of innate immune defenses is an appealing adjunctive strategy for treatment of pulmonary Mycobacterium tuberculosis infections, especially those caused by drug-resistant strains. The effect of intranasal administration of keratinocyte growth factor (KGF), an epithelial mitogen and differentiation factor, on M. tuberculosis infection in mice was tested in prophylaxis, treatment, and rescue scenarios. Infection of C57BL6 mice with M. tuberculosis resulted in inoculum size-dependent weight loss and mortality. A single dose of KGF given 1 day prior to infection with 10(5) M. tuberculosis bacilli prevented weight loss and enhanced pulmonary mycobacterial clearance (compared with saline-pretreated mice) for up to 28 days. Similar effects were seen when KGF was delivered intranasally every third day for 15 days, but weight loss and bacillary growth resumed when KGF was withdrawn. For mice with a well established M. tuberculosis infection, KGF given every 3 days beginning on day 15 postinoculation was associated with reversal of weight loss and an increase in M. tuberculosis clearance. In in vitro co-culture experiments, M. tuberculosis-infected macrophages exposed to conditioned medium from KGF-treated alveolar type II cell (MLE-15) monolayers exhibited enhanced GM-CSF-dependent killing through mechanisms that included promotion of phagolysosome fusion and induction of nitric oxide. Alveolar macrophages from KGF-treated mice also exhibited enhanced GM-CSF-dependent phagolysosomal fusion. These results provide evidence that administration of KGF promotes M. tuberculosis clearance through GM-CSF-dependent mechanisms and enhances host defense against M. tuberculosis infection.

Human mesenchymal stem cell microvesicles for treatment of Escherichia coli endotoxin-induced acute lung injury in mice

We previously found that human mesenchymal stem cells (MSC) or its conditioned medium restored lung protein permeability and reduced alveolar inflammation following Escherichia coli endotoxin-induced acute lung injury (ALI) in an ex vivo perfused human lung in part through the secretion of soluble factors such as keratinocyte growth factor (KGF). Recently, MSC were found to release microvesicles (MVs) that were biologically active because of the presence of mRNA or miRNA with reparative properties. MVs are circular fragments of membrane released from the endosomal compartment as exosomes or shed from the surface membranes. These studies were designed to determine if MVs released by human bone marrow derived MSCs would be effective in restoring lung protein permeability and reducing inflammation in E. coli endotoxin-induced ALI in C57BL/6 mice. The intratracheal instillation of MVs improved several indices of ALI at 48 hours. Compared to endotoxin-injured mice, MVs reduced extravascular lung water by 43% and reduced total protein levels in the bronchoalveolar lavage (BAL) fluid by 35%, demonstrating a reduction in pulmonary edema and lung protein permeability. MVs also reduced the influx of neutrophils and macrophage inflammatory protein-2 levels in the BAL fluid by 73% and 49%, respectively, demonstrating a reduction in inflammation. KGF siRNA-pretreatment of MSC partially eliminated the therapeutic effects of MVs released by MSCs, suggesting that KGF protein expression was important for the underlying mechanism. In summary, human MSC-derived MVs were therapeutically effective following E. coli endotoxin-induced ALI in mice in part through the expression of KGF mRNA in the injured alveolus.

Keratinocyte growth factor promotes epithelial survival and resolution in a human model of lung injury

RATIONALE

Increasing epithelial repair and regeneration may hasten resolution of lung injury in patients with the acute respiratory distress syndrome (ARDS). In animal models of ARDS, keratinocyte growth factor (KGF) reduces injury and increases epithelial proliferation and repair. The effect of KGF in the human alveolus is unknown.

OBJECTIVES

To test whether KGF can attenuate alveolar injury in a human model of ARDS.

METHODS

Volunteers were randomized to intravenous KGF (60 μg/kg) or placebo for 3 days, before inhaling 50 μg LPS. Six hours later, subjects underwent bronchoalveolar lavage (BAL) to quantify markers of alveolar inflammation and cell-specific injury.

MEASUREMENTS AND MAIN RESULTS

KGF did not alter leukocyte infiltration or markers of permeability in response to LPS. KGF increased BAL concentrations of surfactant protein D, matrix metalloproteinase (MMP)-9, IL-1Ra, granulocyte-macrophage colony-stimulating factor (GM-CSF), and C-reactive protein. In vitro, BAL fluid from KGF-treated subjects inhibited pulmonary fibroblast proliferation, but increased alveolar epithelial proliferation. Active MMP-9 increased alveolar epithelial wound repair. Finally, BAL from the KGF-pretreated group enhanced macrophage phagocytic uptake of apoptotic epithelial cells and bacteria compared with BAL from the placebo-treated group. This effect was blocked by inhibiting activation of the GM-CSF receptor.

CONCLUSIONS

KGF treatment increases BAL surfactant protein D, a marker of type II alveolar epithelial cell proliferation in a human model of acute lung injury. Additionally, KGF increases alveolar concentrations of the antiinflammatory cytokine IL-1Ra, and mediators that drive epithelial repair (MMP-9) and enhance macrophage clearance of dead cells and bacteria (GM-CSF). Clinical trial registered with ISRCTN 98813895.

Palifermin for the protection and regeneration of epithelial tissues following injury: new findings in basic research and pre-clinical models

Keratinocyte growth factor (KGF) is a paracrine-acting epithelial mitogen produced by cells of mesenchymal origin, that plays an important role in protecting and repairing epithelial tissues. Pre-clinical data initially demonstrated that a recombinant truncated KGF (palifermin) could reduce gastrointestinal injury and mortality resulting from a variety of toxic exposures. Furthermore, the use of palifermin in patients with hematological malignancies reduced the incidence and duration of severe oral mucositis experienced after intensive chemoradiotherapy. Based upon these findings, as well as the observation that KGF receptors are expressed in many, if not all, epithelial tissues, pre-clinical studies have been conducted to determine the efficacy of palifermin in protecting different epithelial tissues from toxic injury in an attempt to model various clinical situations in which it might prove to be of benefit in limiting tissue damage. In this article, we review these studies to provide the pre-clinical background for clinical trials that are described in the accompanying article and the rationale for additional clinical applications of palifermin.

Ovalbumin enhances YKL-40, IL-5, GM-CSF, and eotaxin expression simultaneously in primarily cultured mouse tracheal epithelial cells

Epithelial inflammation and eosinophil infiltration are crucial for the pathogenesis of asthma. Many inflammatory mediators, such as YKL-40, interleukin -5 (IL-5), granulocyte-macrophage colony-stimulating factor (GM-CSF), and eotaxin, are important for the development of allergic airway inflammation. This study is aimed at investigating the impact of treatment with ovalbumin (OVA) on the levels of those inflammatory mediators in primarily cultured mouse tracheal epithelial cells. Mouse tracheal epithelial cells were isolated and identified by immunofluorescent staining; the isolated mouse tracheal epithelial cells expressed cytokeratins. Treatment with OVA for 24 or 48 h significantly increased the relative levels of YKL-40, IL-5, GM-CSF, and eotaxin mRNA transcripts and YKL-40, IL-5, GM-CSF, and eotaxin proteins secreted in the supernatants of cultured cells, as compared with that in the untreated control cells (P < 0.01, P < 0.05, respectively). The levels of YKL-40 expression were correlated positively with the levels of IL-5, GM-CSF, and eotaxin expression in the OVA-treated cells. These data indicated that treatment with OVA simultaneously enhanced YKL-40, IL-5, GM-CSF, and eotaxin expression in the cultured mouse tracheal epithelial cells in vitro. These inflammatory mediators may synergistically contribute to the pathogenesis of allergic inflammation, and this study may help to understand the role of YKL-40 in the pathogenesis of asthma.

Therapeutic effects of human mesenchymal stem cells in ex vivo human lungs injured with live bacteria

RATIONALE

Mesenchymal stem cells secrete paracrine factors that can regulate lung permeability and decrease inflammation, making it a potentially attractive therapy for acute lung injury. However, concerns exist whether mesenchymal stem cells' immunomodulatory properties may have detrimental effects if targeted toward infectious causes of lung injury.

OBJECTIVES

Therefore, we tested the effect of mesenchymal stem cells on lung fluid balance, acute inflammation, and bacterial clearance.

METHODS

We developed an Escherichia coli pneumonia model in our ex vivo perfused human lung to test the therapeutic effects of mesenchymal stem cells on bacterial-induced acute lung injury.

MEASUREMENTS AND MAIN RESULTS

Clinical-grade human mesenchymal stem cells restored alveolar fluid clearance to a normal level, decreased inflammation, and were associated with increased bacterial killing and reduced bacteremia, in part through increased alveolar macrophage phagocytosis and secretion of antimicrobial factors. Keratinocyte growth factor, a soluble factor secreted by mesenchymal stem cells, duplicated most of the antimicrobial effects. In subsequent in vitro studies, we discovered that human monocytes expressed the keratinocyte growth factor receptor, and that keratinocyte growth factor decreased apoptosis of human monocytes through AKT phosphorylation, an effect that increased bacterial clearance. Inhibition of keratinocyte growth factor by a neutralizing antibody reduced the antimicrobial effects of mesenchymal stem cells in the ex vivo perfused human lung and monocytes grown in vitro injured with E. coli bacteria.

CONCLUSIONS

In E. coli-injured human lungs, mesenchymal stem cells restored alveolar fluid clearance, reduced inflammation, and exerted antimicrobial activity, in part through keratinocyte growth factor secretion.

Cathepsin G and neutrophil elastase play critical and nonredundant roles in lung-protective immunity against Streptococcus pneumoniae in mice

Neutrophil serine proteases cathepsin G (CG), neutrophil elastase (NE), and proteinase 3 (PR3) have recently been shown to contribute to killing of Streptococcus pneumoniae in vitro. However, their relevance in lung-protective immunity against different serotypes of S. pneumoniae in vivo has not been determined so far. Here, we examined the effect of CG and CG/NE deficiency on the lung host defense against S. pneumoniae in mice. Despite similar neutrophil recruitment, both CG knockout (KO) mice and CG/NE double-KO mice infected with focal pneumonia-inducing serotype 19 S. pneumoniae demonstrated a severely impaired bacterial clearance, which was accompanied by lack of CG and NE but not PR3 proteolytic activity in recruited neutrophils, as determined using fluorescence resonance energy transfer (FRET) substrates. Moreover, both CG and CG/NE KO mice but not wild-type mice responded with increased lung permeability to infection with S. pneumoniae, resulting in severe respiratory distress and progressive mortality. Both neutrophil depletion and ablation of hematopoietic CG/NE in bone marrow chimeras abolished intra-alveolar CG and NE immunoreactivity and led to bacterial outgrowth in the lungs of mice, thereby identifying recruited neutrophils as the primary cellular source of intra-alveolar CG and NE. This is the first study showing a contribution of neutrophil-derived neutral serine proteases CG and NE to lung-protective immunity against focal pneumonia-inducing serotype 19 S. pneumoniae in mice. These data may be important for the development of novel intervention strategies to improve lung-protective immune mechanisms in critically ill patients suffering from severe pneumococcal pneumonia.

Local delivery of GM-CSF protects mice from lethal pneumococcal pneumonia

The growth factor GM-CSF has an important role in pulmonary surfactant metabolism and the regulation of antibacterial activities of lung sentinel cells. However, the potential of intra-alveolar GM-CSF to augment lung protective immunity against inhaled bacterial pathogens has not been defined in preclinical infection models. We hypothesized that transient overexpression of GM-CSF in the lungs of mice by adenoviral gene transfer (Ad-GM-CSF) would protect mice from subsequent lethal pneumococcal pneumonia. Our data show that intra-alveolar delivery of Ad-GM-CSF led to sustained increased pSTAT5 expression and PU.1 protein expression in alveolar macrophages during a 28-d observation period. Pulmonary Ad-GM-CSF delivery 2-4 wk prior to infection of mice with Streptococcus pneumoniae significantly reduced mortality rates relative to control vector-treated mice. This increased survival was accompanied by increased inducible NO synthase expression, antibacterial activity, and a significant reduction in caspase-3-dependent apoptosis and secondary necrosis of lung sentinel cells. Importantly, therapeutic treatment of mice with rGM-CSF improved lung protective immunity and accelerated bacterial clearance after pneumococcal challenge. We conclude that prophylactic delivery of GM-CSF triggers long-lasting immunostimulatory effects in the lung in vivo and rescues mice from lethal pneumococcal pneumonia by improving antibacterial immunity. These data support use of novel antibiotic-independent immunostimulatory therapies to protect patients against bacterial pneumonias.