AAV-8 is more efficient than AAV-9 in transducing neonatal dog heart

Adeno-associated virus serotype-8 and 9 (AAV-8 and 9) are the leading candidate vectors to test bodywide neonatal muscle gene therapy in large mammals. We have previously shown that systemic injection of 2-2.5×10(14) viral genome (vg) particles/kg of AAV-9 resulted in widespread skeletal muscle gene transfer in newborn dogs. However, nominal transduction was observed in the heart. In contrast, robust expression was achieved in both skeletal muscle and heart in neonatal dogs with 7.14-9.06×10(14) vg particles/kg of AAV-8. To determine whether superior cardiac transduction of AAV-8 is because of the higher vector dose, we delivered 6.14×10(14) and 9.65×10(14) vg particles/kg of AAV-9 to newborn puppies via the jugular vein. Transduction was examined 2.5 months later. Consistent with our previous reports, we observed robust bodywide transduction in skeletal muscle. However, increased AAV dose only moderately improved heart transduction. It never reached the level achieved by AAV-8. Our results suggest that differential cardiac transduction by AAV-8 and AAV-9 is likely because of the intrinsic property of the viral capsid rather than the vector dose.