In vivo myocardial gene transfer: optimization, evaluation and direct comparison of gene transfer vectors

The purpose was to determine the relative efficiency, toxicity and duration of expression following gene delivery by intramyocardial injection of naked DNA, naked DNA complexed to cationic liposomes, naked DNA complexed to cationic liposomes with integrin-targetting peptide, recombinant (E1-/E3-) adenovirus, recombinant adeno-associated virus and recombinant (ICP27-) herpes simplex virus. All vectors incorporated a LacZ reporter driven by a promoter containing the hCMV-IE promoter/enhancer. Efficiency was scored by counting positive cells in five standard microscopic sections harvested from the left ventricular apex. Rabbit hearts (n = 100) were examined from 2 to 56 days after injection. Uncomplexed and complexed naked DNA were very inefficient with less than one positive cell visible per heart. The viral vectors all resulted in robust gene expression with adenovirus being the most efficient by at least one order of magnitude before 21 days. However, despite disparate titres, the efficiency beyond 21 days of adenovirus and adeno-associated virus were comparable. In contrast to adeno-associated virus, both adenovirus and herpes-simplex virus were associated with a marked inflammatory response. Despite reporter gene activity appearing only after 21 days, adeno-associated virus shows comparative promise as a myocardial gene delivery vector.