RECOMBINANT ADENOASSOCIATED VIRUS-MEDIATED HIGH-EFFICIENCY, TRANSIENTEXPRESSION OF THE MURINE CATIONIC AMINO-ACID TRANSPORTER (ECOTROPIC RETROVIRAL RECEPTOR) PERMITS STABLE TRANSDUCTION OF HUMAN HELA-CELLS BYECOTROPIC RETROVIRAL VECTORS

Adeno-associated virus has a broad host range, is nonpathogenic, and i ntegrates into a preferred location on chromosome 19, features that ha ve fostered development of recombinant adeno-associated viruses (rAAV) as gene transfer vectors for therapeutic applications. We have used a n rAAV to transfer and express the murine cationic amino acid transpor ter which functions as the ecotropic retroviral receptor, thereby rend ering human cells conditionally susceptible to infection by an ecotrop ic retroviral vector, The proportion of human HeLa cells expressing th e receptor at 60 h varied as a function of the multiplicity of infecti on (MOI) with the rAAV, Cells expressing the ecotropic receptor were e fficiently transduced with an ecotropic retroviral vector encoding a n ucleus-localized form of beta-galactosidase. Cells coexpressing the ec otropic receptor and nucleus-localized beta-galactosidase were isolate d by fluorescence-activated cell sorting, and cell lines were recovere d by cloning at limiting dilution. After growth in culture, all clones contained the retroviral vector genome, but fewer than 10% (3 of 47) contained the rAAV genome and continued to express the ecotropic recep tor. The ecotropic receptor coding sequences in the rAAV genome were u nder the control of a tetracycline-modulated promoter. In the presence of tetracycline, receptor expression was low and the proportion of ce lls transduced by the ecotropic retroviral vector was decreased, Modul ation of receptor expression was achieved with both an episomal and an integrated form of the rAAV genome. These data establish that functio nal gene expression from an rAAV genome can occur transiently without genome integration.