RECOMBINANT ADENO-ASSOCIATED VIRUS VECTORS
Recombinant vectors based on the AAV are limited in that only 4.5 kb of DNA can be effectively packaged into the capsid. Despite this drawback, its lack of pathogenicity has meant that this virus has been extensively used as a gene transfer agent. Typically, the rep and cap genes are replaced with an expression cassette encoding the therapeutic gene and the vector is propagated in HEK 293 cells by co-transfection with two extra plasmids; one expressing rep, cap and the second expressing adenoviral E1, E2, E4-orf6 and VA RNA (see diagram two).
Diagram Two: AAV Vectors
Recombinant AAV vectors are unable to site-specifically integrate into the host genome, due to the absence of the Rep protein, however, the vector genome forms head-to-tail concatamers that persist in infected cells for many months. AAV vectors can be repeatedly administered without a severe immune response and as such represent the safest viral-based gene transfer vector evaluated to date.
