HEART MUSCLE-SPECIFIC GENE-EXPRESSION USING REPLICATION-DEFECTIVE RECOMBINANT ADENOVIRUS

Adenoviruses are a promising vector system for future gene therapy of heart muscle diseases. The promiscuous tissue tropism of adenoviruses, however, may lead to the undesirable expression of putative therapeut ic genes in nontarget cells and hence to considerable safety limitatio ns for this vector system. To restrict gene expression to cardiomyocyt es we constructed an adenoviral vector (Ad-mlcLuc) in. which the lucif erase gene is under the control of the ventricle-specific myosin light chain-2 (mlc-2v) promoter. For controls, we constructed a recombinant adenovirus without promoter (Ad-Luc) and one with the Rous sarcoma vi rus (RSV) promoter (Ad-rsvLuc). Our data demonstrate that the newly es tablished viral vector Ad-mlcLuc was specifically active in rat neonat al cardiomyocytes in vitro but not in three established cell lines. In jections of the recombinant adenoviruses into the cardiac cavity of ne onatal rats resulted in myocardial specific gene expression of Ad-mlcL uc in vivo, despite the fact that viral DNA was detected by PCR at dif ferent levels in ail tissues investigated In vitro and in vivo, Ad-mlc Luc was exclusively active in cardiac muscle cells, reaching 8-9% of t he RSV-induced luciferase activity. Direct injection of Ad-mlcLuc into thigh muscle gave only background luciferase activity (0.05% of Ad-rs vLuc). Therefore, in the adenoviral system, the mlc-2v promoter allows heart-specific expression of a foreign gene thus providing a promisin g tool for gene transfer targeted to the myocardium.