398. Sustained Expression of a Canine Micro-Dystrophin Lead To Improvement of Limb Muscle Function in Dystrophic Dogs Following Large Scale AAV-Mediated Treatment

Abstract

Adeno-associated viral (AAV) vectors as gene delivery vehicles have shown promise both in preclinical studies and clinical trials for a number of acquired and inherited diseases, including Duchenne Muscular Dystrophy (DMD). Studies have shown that host immune responses against AAV can compromise vector delivery and prevent sustained therapeutic gene expression in animal models and humans. We developed and demonstrated a novel AAV production system that prevents aberrant packaging of the AAV capsid (cap) genes. Compared to conventional AAV production methods, our new approach eliminates unwanted in vivo expression of AAV capsid proteins and significantly reduces host immune responses. Here, we demonstrated in a pilot study that we were able to reduce a tripledrug immunosuppressive regimen to a mild 2-drug regimen while retaining sustained canine micro-dystrophin expression in CXMD dogs following large scale delivery of an AAV vector carrying the canine micro-dystrophin to a group of muscles in the hind limb.Amelioration of muscle pathology as a result of sustained expression of the therapeutic gene was demonstrated by histological analysis of muscle tissues and by non-invasive magnetic resonance imaging (MRI). Further, we determined functional benefit of micro-dystrophin expression by muscle force measurement and gait analysis. Significant improvement in muscle force, as indicated by more than 100% increase in strength (torque), was observed in the treated limb compared to that in the untreated limb. In conclusion, by combining newly improved AAV production and mild clinically applicable immunosuppression, the finding of long term robust dystrophin expression in CXMD dogs’ limb with significant functional improvement opens the possibility of translating these strategies to a human DMD trial, which can improve patients’ immediate quality of life.