EFFICIENT MUSCLE-SPECIFIC TRANSGENE EXPRESSION AFTER ADENOVIRUS-MEDIATED GENE-TRANSFER IN MICE USING A 1.35 KB MUSCLE CREATINE-KINASE PROMOTER ENHANCER/

Replication-defective (E1+E3 deleted) human adenovirus vectors are a p romising means of therapeutic gene delivery to skeletal muscle cells. Since the tropism of adenovirus is nonselective, muscle-specific expre ssion of systemically administered vectors can only be achieved by the use of a tissue-specific promoter/enhancer that is small enough to fi t the insert capacity of the vector. We have generated two replication -defective adenovirus recombinants (AV) in which the reporter gene (ei ther firefly luciferase or E. coli beta-galactosidase) was driven by a truncated (1.35 kb) muscle creatine kinase (MCK) promoter/enhancer or by the fast troponin I (Tnl) promoter/enhancer. Highly efficient and muscle-specific transgene expression was demonstrated in immunodeficie nt mice after local injection of AV into muscles at an early age. In n onmuscle tissues (brain, liver, kidney, lung), the transgene expressio n was extremely low even though in these tissues in situ polymerase ch ain reaction showed as high an infectivity of the cells by the AV as i n muscle. The relatively small size, the good efficiency and the muscl e specificity of the MCK promoter would make it ideal to drive the 6.3 kb (truncated) dystrophin cDNA in first generation AV (with a limited (8 kb) insert capacity), designed for gene therapy of Duchenne muscul ar dystrophy.