85. AAV9-Utrophin Prevents Myonecrosis in Dystrophic Mice and Dogs without Immunosuppression

The majority of mutations causing Duchenne muscular dystrophy (DMD) are multi-exon, frameshifting deletions, complicating therapy with recombinant dystrophin because of the potential for chronic immune recognition of the “non-self” protein. The paralogous protein utrophin is ubiquitously expressed at levels insufficient to prevent myonecrosis in animal models for DMD, but may confer central immunological tolerance through early developmental expression in the thymus. Here we show for a first time histological evidence for the complete prevention of myonecrosis in dystrophin-deficient striated muscles following systemic administration of an AAV9 vector carrying a 3.5 kb synthetic utrophin transgene (AAVµU). The cDNA was miniaturized by removal of domains least conserved in a comprehensive evolutionary comparison, and further optimized for maximal expression in striated muscle by using the codon bias of mammalian genes encoding contractile proteins. Administration of 1015 AAVµU vector genomes (vg) per kg to neonatal mice prevented centronucleation and saturated global recovery of the sarcoglycan complex, despite a subsequent tenfold increase in striated muscle mass with growth. In neonatal dystrophic dogs, intravenous injection of 1013.5 AAVµU vg/kg without immunosuppression restored sarcoglycan levels and normalized the myofiber size-distribution following a fourfold increase in muscle mass. Interferon-gamma ELISpot assays using utrophin-derived peptides revealed no reactivity in injected dogs, consistent with central immunological tolerance. These findings provide a rationale for high dose, neonatal gene therapy using utrophin as a “self” protein to forestall disability and mortality in DMD, while minimizing the risk of chronic immunotoxicity.