Role of alveolar macrophages in rapid elimination of adenovirus vectors administered to the epithelial surface of the respiratory tract
To evaluate the hypothesis that innate immune mechanisms play a major role in eliminating adenovirus (Ad) vectors from the lung, the fate of adenoviral genome of an Ad vector was quantified in the first 24 h after intratracheal administration of an Ad vector coding for beta-galactosidase (beta gal) to mice. Southern analysis with an Ad specific probe showed that 70% of the Ad genome was lost within 24 h, in both immunocompetent and immunodeficient animals. When alveolar macrophages were eliminated by administration of liposomes containing dichloromethylene-biphosphanate, subsequent administration of Ad vector was associated with a 100%+/-8% increase in lung Ad DNA and 96%+/-9% rise in beta gal expression at 24 h compared to control animals. In vitro infection of mouse, rat, and human alveolar macrophages with an Ad vector resulted in 65% loss of vector genome within 24 h, whereas the vector genome was stable in lung epithelial cell lines. PCR in situ hybridization demonstrated that the Ad vector genome persisted A549 lung epithelial cell in vitro but not in alveolar macrophages. Finally, alveolar macrophages recovered from the mouse lung 30 min following intratracheal administration of an Ad vector showed large amounts of vector genome, whereas much less was evident in alveolar macrophages recovered after 24 h. These observations demonstrate that alveolar macrophages play an important role in elimination of Ad vectors from the lung and suggest that strategies to transiently suppress this major innate immune defense system might be rewarding in enhancing the efficiency Ad vectors for lung gene therapy.