Stable integration of transgenes delivered by a retrotransposon-adenovirushybrid vector

Helper-dependent adenoviruses show great promise as gene delivery vectors. However, because they do not integrate into the host chromosome, transgene expression cannot be maintained indefinitely. To overcome these limitations , we have inserted an L1 retrotransposon/transgene element into a helper-de pendent adenovirus to create a novel chimeric gene delivery vector. Efficie nt adenovirus-mediated delivery of the L1 element into cultured human cells results in subsequent retrotransposition and stable integration of the tra nsgene. L1 retrotransposition frequency was found to correlate with increas ing multiplicity of infection by the chimeric vector, and further retrotran sposition from newly integrated elements was not observed on prolonged cult ure. Therefore, this vector, which utilizes components of low immunogenic p otential, represents a novel two-stage gene delivery system capable of achi eving high titers via the initial helper-dependent adenovirus stage and per manent transgene integration via the retrotransposition stage.