Background-The delivery of recombinant genes to cardiomyocytes holds promise for the treatment of a variety of cardiovascular diseases. Previous gene transfer approaches that used direct injection of plasmid DNA or replicationdefective adenovirus vectors have been limited by low transduction frequencies and transient transgene expression due to immune responses, respectively. In this report, we have tested the feasibility of using intramyocardial injection or intracoronary infusions of

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... nt adeno-associated virus (rAAV) vectors to program transgene expression in murine cardiomyocytes in vivo. Methods and Results-We constructed an rAAV containing the LacZ gene under the transcriptional control of the cytomegalovirus (CMV) promoter (AAV CMV-LacZ ). We then injected 1ϫ10 8 infectious units (IU) of this virus into the left ventricular myocardium of adult CD-1 mice. Control hearts were injected with the Ad CMV-LacZ adenovirus vector. Hearts harvested 2, 4, and 8 weeks after AAV CMV-LacZ injection demonstrated stable ␤-galactosidase (␤-gal) expression in large numbers of cardiomyocytes without evidence of myocardial inflammation or myocyte necrosis. In contrast, the Ad CMV-LacZ -injected hearts displayed transient ␤-gal expression, which was undetectable by 4 weeks after injection. Explanted C57BL/6 mouse hearts were also perfused via the coronary arteries with 1.5ϫ10 9 IU of AAV CMV-LacZ and assayed 2, 4, and 8 weeks later for ␤-gal expression. ␤-Gal expression was detected in Ͻ1% of cardiomyocytes at 2 weeks after perfusion but was detected in up to 50% of cardiomyocytes 4 to 8 weeks after perfusion. Conclusions-Direct intramyocardial injection or coronary artery perfusion with rAAV vectors can be used to program stable transgene expression in cardiomyocytes in vivo. rAAV appears to represent a useful vector for the delivery of therapeutic genes to the myocardium. (Circulation. 1999;99:201-205.)