Abstract: Disclosed herein are packaging cell lines, in which adenovirus (Ad) E1A is constitutively expressed, that also contain integrated AAV rep and cap genes. The packaging cell lines exhibit little to no expressed Rep protein until helper virus function, such as adenovirus (Ad) E4, E2A and/or VA RNA are provided by, for example, transduction of the cells with a virus, vector or plasmid, such as an Ad-AAV hybrid virus. The promoter driving expression of AAV rep gene can be positioned far enough upstream (5?) of the rep coding sequence that E1A is unable to activate the promoter, activate substantial transcription of the rep gene and in turn produce Rep protein. Introduction of helper virus function, such as E2A, E4 and/or VA RNA into these packaging cells is able to drive AAV rep gene transcription, subsequent Rep protein expression and production of rAAV vector particles.