Intrinsic system for viral vector transgene regulation

A method for the regulated removal of heterologous genetic material from disseminating DNA viral vaccine vectors, comprising:

• providing a wild-type or parental DNA viral vector which includes a wild-type or parental genomic sequence and a recombinantly engineered duplication of the said wild-type or parental genomic sequence;
• providing a transgene expression cassette which comprises a transgene and the necessary regulatory genetic elements for control of transgene expression;
• and
• inserting the transgene expression cassette into the DNA viral vector so that the transgene is flanked by the wild-type or parental genomic sequence and the recombinantly engineered duplication of wild-type or parental genomic sequence;
• whereby homologous recombination between the flanking wild-type or parental genomic sequences subsequently results in removal of the transgene and restoration of only a single copy of the wild-type or parental genomic sequence as is normally found within a wild type or parental DNA virus, thereby regenerating the wild-type or parental DNA virus genome with an absence of any non-parental virus genetic sequence;
• wherein the method comprises a step of selecting a length for the wild-type or parental genomic sequence to be duplicated;
• and
• in which the rate of transgene removal from the viral genome, and hence reversion of recombinant virus genome to wild-type or parental, is a function of the length of the selected duplicated wild-type or parental genomic sequence.