Mechanism of adenovirus improvement of cationic liposome-mediated gene transfer

Substantial effort has been focused on the development of highly efficient gene transfer strategies. Although viral and non-viral methods have been elaborated, mechanisms of gene delivery are still poorly understood. We exploited our recent observation that replication-deficient type 5 adenovirus dramatically enhances lipofectAMINE-mediated gene transfer (lipoadenofection) in differentiated cells to elucidate the mechanism of adenovirus action in this process. Heat-induced denaturation of viral capsid abolishes adenovirus action whereas inactivation of viral genome by short treatment with UV has no effect. Electron microscopic observations reveal the formation of a complex containing adenovirus and lipofectAMINE which probably carries DNA into cells via endocytosis. Anti-adenovirus antiserum or monoclonal anti-alpha(v)beta3 integrin antibody inhibits lipoadenofection, at least partially. Neutralization of endosomal compartments with chloroquine, ammonium chloride or monensin does not prevent adenovirus improvement of gene transfer. Hence, adenovirus-lipofectAMINE-DNA complexes in which viral particles are each encompassed by three lipid layers, penetrate cells via an endocytic pathway involving probably the adenovirus receptor and alpha(v)beta3 integrin. The resulting efficient transfer and expression of plasmid DNA proceeds from a mechanism in which adenoviral endosomolytic activity appears to be required while viral genome is not essential.