The present invention relates to a novel Ad based packaging system that can be used for incorporation of heterologous DNA into infectious but replication defective viral particles. The components of the invention include an "artificial genome", i.e., a recombinant vector which contains elements that function as adenovirus replication and packaging signals flanking an intervening DNA sequence. The elements may comprise the minimum genomic Ad sequences required to direct replication of heterologous DNA and packaging into viral particles. The system also includes a means for expressing complementing helper functions to provide in trans viral proteins required for replication and packaging of recombinant viral vectors, but without contaminating the stock of recombinant, trans-packaged viral particles.