Insulation of a conditionally expressed transgene in an adenoviral vector

Replication-defective recombinant adenoviruses provide an efficient system for in vivo gene transfer and numerous studies have demonstrated that this vector can accommodate tissue-specific promoters to restrict the expression of a transgene to a particular subset of cells. However, in some cases the selectivity of expression is lost when the tissue-specific promoter is placed in an adenoviral environment. In an attempt to restore the conditionality of expression of the transgene driven by the human ERBB2 promoter, we have flanked the expression cassette in 5' and 3' orientations with a 250 bp sequence containing the bovine growth hormone transcriptional stop signal for cloning into a recombinant adenovirus. The data presented here clearly demonstrate that these 'insulator' elements are able to restrict the expression of the transgene (herpes simplex thymidine kinase) to ERBB2-expressing cells and therefore to restore the selectivity mediated by the ERBB2 promoter. This approach could be generally useful to insulate expression cassettes in adenoviral vectors.