Abstract: A rolling circle DNA replicon which replicates in a host eukaryotic cell and is capable of eliciting an immunization reaction is disclosed. The rolling circle DNA replicon comprises a Rep gene open reading frame placed under transcriptional control of a promoter, which is placed 5′ of the gene. Any sequences that are required to be present in cis on the rolling circle DNA replicon in order that the Rep protein might promote replication of the rolling circle DNA replicon and elicit an immunization reaction are included. At least one expression cassette with an RNA polymerase II promoter, a multiple cloning site, and transcription termination and polyadenylation signals suitable for transcription of RNA molecules not normally intrinsic to a geminiviral, circoviral or nanoviral genome is also included.