Enhancement of muscle gene delivery with pseudotyped adeno-associated virus type 5 correlates with myoblast differentiation

Adeno-associated virus (AAV)-based muscle gene therapy has achieved tremend ous success in numerous animal models of human diseases. Recent clinical tr ials with this vector have also demonstrated great promise. However, to ach ieve therapeutic benefit in patients, large inocula of virus will likely be necessary to establish the required level of transgene expression. For the se reasons, efforts aimed at increasing the efficacy of AAV-mediated gene d elivery to muscle have the potential for improving the safety and therapeut ic benefit in clinical trials. In the present study, we compared the effici ency of gene delivery to mouse muscle cells for recombinant AAV type 2 (rAA V-2) and rAAV-2cap5 (AAV-2 genomes pseudo-packaged into AAV-5 capsids). Des pite similar levels of transduction by these two vectors in undifferentiate d myoblasts, pseudotyped rAAV-2cap5 demonstrated dramatically enhanced tran sduction in differentiated myocytes in vitro (> 500-fold) and in skeletal m uscle in vivo (> 200-fold) compared to rAAV-2. Serotype-specific difference s in transduction efficiency did not directly correlate with viral binding to muscle cells but rather appeared to involve endocytic or intracellular b arriers to infection. Furthermore, application of this pseudotyped virus in a mouse model of Duchenne's muscular dystrophy also demonstrated significa ntly improved transduction efficiency. These findings should have a signifi cant impact on improving rAAV-mediated gene therapy in muscle.