Lower respiratory tract delivery, airway clearance, and preclinical efficacy of inhaled GM-CSF in a postinfluenza pneumococcal pneumonia model

Abstract

Inhaled granulocyte/macrophage colony-stimulating factor (GM-CSF) shows promise as a therapeutic to treat viral and bacterial pneumonia, but no mouse model of inhaled GM-CSF has been described. We sought to 1) develop a mouse model of aerosolized recombinant mouse GM-CSF administration and 2) investigate the protection conferred by inhaled GM-CSF during influenza A virus (IAV) infection against secondary bacterial infection with pneumococcus. To assess lower respiratory tract delivery of aerosolized therapeutics, mice were exposed to aerosolized fluorescein (FITC)-labeled dextran noninvasively via an aerosolization tower or invasively using a rodent ventilator. The efficiency of delivery to the lower respiratory tracts of mice was 0.01% noninvasively compared with 0.3% invasively. The airway pharmacokinetics of inhaled GM-CSF fit a two-compartment model with a terminal phase half-life of 1.3 h. To test if lower respiratory tract levels were sufficient for biological effect, mice were infected intranasally with IAV, treated with aerosolized recombinant mouse GM-CSF, and then secondarily infected with Streptococcus pneumoniae. Inhaled GM-CSF conferred a significant survival benefit to mice against secondary challenge with S. pneumoniae ( P < 0.05). Inhaled GM-CSF did not reduce airway or lung parenchymal bacterial growth but significantly reduced the incidence of S. pneumoniae bacteremia ( P < 0.01). However, GM-CSF overexpression during influenza virus infection did not affect lung epithelial permeability to FITC-dextran ingress into the bloodstream. Therefore, the mechanism of protection conferred by inhaled GM-CSF appears to be locally mediated improved lung antibacterial resistance to systemic bacteremia during IAV infection.

GM-CSF-based treatments in COVID-19: reconciling opposing therapeutic approaches

“…Pretreatment with intranasally administered GM-CSF protected mice from lethal influenza-induced lung injury 56,60 , and lung-specific overexpression of GM-CSF after influenza viral infection in an inducible transgenic mouse model significantly increased survival 61 . Inhaled GM-CSF also protected against secondary bacterial infection in a postinfluenza pneumococcal pneumonia mouse model 62 . Conversely, GM-CSF-deficient mice showed no survival 48 hours after intratracheal inoculation with Gram-negative bacteria (compared with 100% survival in controls) due to impaired alveolar macrophage bactericidal function 63 .…”

“…Across many preclinical models of viral and bacterial pneumonia, GM-CSF expression in the lung has been shown to serve a beneficial role by enhancing repair of injured lung tissue and by activating innate and adaptive immune responses to clear pathogens 19,50,[56][57][58][59][60][61][62][63] . In this context, GM-CSF is thought to act mainly on alveolar macrophages and tissue-resident CD103 + dendritic cells, and there is even evidence that GM-CSF directly modulates alveolar epithelial cells 19,50,64 .…”

Genomic and epigenomic adaptation in SP-R210 (Myo18A) isoform-deficient macrophages

“…PU.1 is critical for the terminal differentiation of alveolar macrophages downstream from GM- CSF receptor signaling in the local microenvironment (Carey, et al, 2007). In turn, alveolar macrophages are essential for host survival from severe influenza A virus (IAV) infection (Halstead, et al, 2018, Sever-Chroneos, et al, 2011, Umstead, et al, 2020, Huang, et al, 2011). Raw264.7 cells have been extensively utilized as a surrogate in vitro model to study IAV infection in macrophages with all known IAV strains (Marvin, et al, 2017, Cline, et al, 2017).…”

Macrophage-derived cytokines in pneumonia: Linking cellular immunology and genetics

“…Moreover, infiltrated monocytes are exposed to local cytokines such as granulocyte-macrophage colony-stimulating factor (GMCSF) within the lung tissue, undergo transcriptional reprogramming, and become functionally indistinguishable from resident cell populations, once inflammation is completely resolved [ 51 , 74 ]. Indeed, increased levels or externally (intranasal) delivered GMCSF are protective against viral and bacterial pneumonia, first of all during the most severe pneumonia cases, including COVID19 [ 51 , [75] , [76] , [77] , [78] , [79] ]. Interestingly, Ly6Clo lung MՓs exhibit even higher proinflammatory activities in the absence of type I interferons deactivating stimulus, than newly infiltrated Ly6Chi monocytes during influenza A and SARS-CoV-2 [ 80 , 81 ].…”