Abstract: An episomal vector sytem and methods for use in gene therapy in humans and animals. The vector contains a papilloma virus origin of replication, a vector maintenance sequence, a first promoter transcriptionally linked to a therapeutic nucleic acid sequence, a second promoter transcriptionally linked to a papilloma virus E1 gene sequence, and a third promoter transcriptionally linked to a papilloma virus E2 gene sequence or an E1/E2 fusion gene. The vector is capable of episomal replication in human or animal cells.