Muscle-specific promoters may be necessary for adeno-associated virus-mediated gene transfer in the treatment of muscular dystrophies

Recombinant adeno-associated virus (rAAV) vectors allow efficient gene tran sfer and expression in the muscle; therefore, rAAVs represent a potential g ene therapy vector for muscular dystrophies, For further investigations, we used a mouse muscular dystrophy model (gsg(-/-) mice) gamma -sarcoglycan, a subunit of the dystrophin-glycoprotein complex, is missing. gsg(-/-) mice develop progressive dystrophy representative of a severe human phenotype d isease. We previously showed high levels and stable expression of gamma -sa rcoglycan in myofibers after direct muscle injection into gsg(-/-) mice of a recombinant AAV vector (AAV.dMCK.gSG) carrying the gamma -sarcoglycan cDN A driven by a muscle-specific promoter (truncated version of muscle creatin e kinase), Here, we show that when gamma -sarcoglycan expression is driven by the ubiquitous cytomegalovirus (CMV) promoter (AAV.CMV.gSG), lower level s of transgene expression are observed and are associated with a humoral re sponse to gamma -sarcoglycan, When using an rAAV vector, expressing the hig hly immunogenic product gamma -galactosidase under the CMV promoter (AAV.CM V.LacZ), we measured a strong cellular and humoral immune response to the t ransgene after intramuscular injection into gsg(-/-) mice. This study sugge sts that restriction of transgene expression to the muscle is an important criterion for the treatment of muscular dystrophies and will aid in the des ign of protocols for gene therapy.