Selective expansion of alveolar macrophages in vivo by adenovirus-mediatedtransfer of the murine granulocyte-macrophage colony-stimulating factor cDNA

Based on the hypothesis that genetic modification of freshly isolated alveo lar macrophages (AM) with the granulocyte-macrophage colony-stimulating fac tor (GM-CSF) cDNA would induce AM to proliferate, this study focuses on the ability of adenoviral (Ad) vectors to transfer and efficiently express the murine (m) GM-CSF cDNA in murine AM with consequent expansion in the numbe r of AM in vitro and in vivo. To demonstrate that an Ad vector can effectiv ely transfer and express genes in AM, murine AM recovered by bronchoalveola r lavage from the lung of Balb/c mice were infected with an Ad vector codin g for green fluorescent protein (GFP) in vitro and expressed GFP in a dose- dependent fashion. Infection of AM with an Ad vector containing an expressi on cassette coding for mGM-CSF led to GM-CSF expression and to AM prolifera tion in vitro. When AM infected with AdGFP were returned to the respiratory tract of syngeneic recipient mice, GFP-expressing cells could still be rec overed by bronchoalveolar lavage 2 weeks later. In vitro infection of AM wi th AdmGM-CSF and subsequent transplantation of the genetically modified AM to the lungs of syngeneic recipients led to GM-CSF expression in vivo. Stri kingly, the AM recovered by lavage 5 weeks after transplantation demonstrat ed an increased rate of proliferation, and the total number of alveolar mac rophages was 1.9-fold greater than controls. importantly the increase in th e numbers of AM was selective (ie, other inflammatory cell numbers were unc hanged), end there was no modification to the lung architecture. Thus, it i s feasible to genetically modify AM with Ad vectors and to use this strateg y to modify the behavior of AM in vivo. Based on the importance of AM in th e primary defense of the respiratory epithelial surface, this strategy may be useful in enhancing pulmonary defenses in immunodeficiency states. (C) 1 999 by The American Society of Hematology.