Kasun Kodippili

Safe and bodywide muscle transduction in young adult Duchenne muscular dystrophy dogs with adeno-associated virus

The ultimate goal of muscular dystrophy gene therapy is to treat all muscles in the body. Global gene delivery was demonstrated in dystrophic mice more than a decade ago using adeno-associated virus (AAV). However, translation to affected large mammals has been challenging. The only reported attempt was performed in newborn Duchenne muscular dystrophy (DMD) dogs. Unfortunately, AAV injection resulted in growth delay, muscle atrophy and contracture. Here we report safe and bodywide AAV delivery in juvenile DMD dogs. Three ∼2-m-old affected dogs received intravenous injection of a tyrosine-engineered AAV-9 reporter or micro-dystrophin (μDys) vector at the doses of 1.92-6.24 × 10(14) viral genome particles/kg under transient or sustained immune suppression. DMD dogs tolerated injection well and their growth was not altered. Hematology and blood biochemistry were unremarkable. No adverse reactions were observed. Widespread muscle transduction was seen in skeletal muscle, the diaphragm and heart for at least 4 months (the end of the study). Nominal expression was detected in internal organs. Improvement in muscle histology was observed in μDys-treated dogs. In summary, systemic AAV gene transfer is safe and efficient in young adult dystrophic large mammals. This may translate to bodywide gene therapy in pediatric patients in the future.

Full-Length Dystrophin Reconstitution with Adeno-Associated Viral Vectors

Duchenne muscular dystrophy (DMD) is the most common lethal muscle disorder in children. It is caused by mutations of the dystrophin gene. Adeno-associated virus (AAV)-mediated gene replacement therapy has been actively pursued to treat DMD. However, this promising therapeutic modality has been challenged by the small packaging capacity of the AAV vector. The size of the full-length dystrophin cDNA is >11 kb, while an AAV virus can carry only a 5 kb genome. Innovative high-capacity AAV vectors may offer an opportunity to express the full-length dystrophin coding sequence. Here we describe several sets of tri-AAV vectors for full-length human dystrophin delivery. In each set, the full-length human dystrophin cDNA was split into three fragments and independently packaged into separate recombinant AAV vectors. Each vector was engineered with unique recombination signals for directional recombination. Tri-AAV vectors were coinjected into the tibialis anterior muscle of dystrophin-deficient mdx4cv mice. Thirty-five days after injection, dystrophin expression was examined by immunofluorescence staining. Despite low reconstitution efficiency, full-length human dystrophin was successfully expressed from the tri-AAV vectors. Our results suggest that AAV can be engineered to express an extra-large (up to 15 kb) gene that is approximately three times the size of the wild-type AAV genome. Further optimization of the trivector strategy may expand the utility of AAV for human gene therapy.

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.

Characterization of 65 epitope-specific dystrophin monoclonal antibodies in canine and murine models of duchenne muscular dystrophy by immunostaining and western blot.

Epitope-specific monoclonal antibodies can provide unique insights for studying cellular proteins. Dystrophin is one of the largest cytoskeleton proteins encoded by 79 exons. The absence of dystrophin results in Duchenne muscular dystrophy (DMD). Over the last two decades, dozens of exon-specific human dystrophin monoclonal antibodies have been developed and successfully used for DMD diagnosis. Unfortunately, the majority of these antibodies have not been thoroughly characterized in dystrophin-deficient dogs, an outstanding large animal model for translational research. To fill the gap, we performed a comprehensive study on 65 dystrophin monoclonal antibodies in normal and dystrophic dogs (heart and skeletal muscle) by immunofluorescence staining and western blot. For comparison, we also included striated muscles from normal BL10 and dystrophin-null mdx mice. Our analysis revealed distinctive species, tissue and assay-dependent recognition patterns of different antibodies. Importantly, we identified 15 antibodies that can consistently detect full-length canine dystrophin in both immunostaining and western blot. Our results will serve as an important reference for studying DMD in the canine model.

Dystrophin contains multiple independent membrane-binding domains

Dystrophin is a large sub-sarcolemmal protein. Its absence leads to Duchenne muscular dystrophy (DMD). Binding to the sarcolemma is essential for dystrophin to protect muscle from contraction-induced injury. It has long been thought that membrane binding of dystrophin depends on its cysteine-rich (CR) domain. Here, we provide in vivo evidence suggesting that dystrophin contains three additional membrane-binding domains including spectrin-like repeats (R)1-3, R10-12 and C-terminus (CT). To systematically study dystrophin membrane binding, we split full-length dystrophin into ten fragments and examined subcellular localizations of each fragment by adeno-associated virus-mediated gene transfer. In skeletal muscle, R1-3, CR domain and CT were exclusively localized at the sarcolemma. R10-12 showed both cytosolic and sarcolemmal localization. Importantly, the CR-independent membrane binding was conserved in murine and canine muscles. A critical function of the CR-mediated membrane interaction is the assembly of the dystrophin-associated glycoprotein complex (DGC). While R1-3 and R10-12 did not restore the DGC, surprisingly, CT alone was sufficient to establish the DGC at the sarcolemma. Additional studies suggest that R1-3 and CT also bind to the sarcolemma in the heart, though relatively weak. Taken together, our study provides the first conclusive in vivo evidence that dystrophin contains multiple independent membrane-binding domains. These structurally and functionally distinctive membrane-binding domains provide a molecular framework for dystrophin to function as a shock absorber and signaling hub. Our results not only shed critical light on dystrophin biology and DMD pathogenesis, but also provide a foundation for rationally engineering minimized dystrophins for DMD gene therapy.

A Five-Repeat Micro-Dystrophin Gene Ameliorated Dystrophic Phenotype in the Severe DBA/2J-mdx Model of Duchenne Muscular Dystrophy

Micro-dystrophins are highly promising candidates for treating Duchenne muscular dystrophy, a lethal muscle disease caused by dystrophin deficiency. Here, we report robust disease rescue in the severe DBA/2J-mdx model with a neuronal nitric oxide synthase (nNOS)-binding micro-dystrophin vector. 2 × 1013 vector genome particles/mouse of the vector were delivered intravenously to 10-week-old mice and were evaluated at 6 months of age. Saturated micro-dystrophin expression was detected in all skeletal muscles and the heart and restored the dystrophin-associated glycoprotein complex and nNOS. In skeletal muscle, therapy substantially reduced fibrosis and calcification and significantly attenuated inflammation. Centronucleation was significantly decreased in the tibialis anterior (TA) and extensor digitorum longus (EDL) muscles but not in the quadriceps. Muscle function was normalized in the TA and significantly improved in the EDL muscle. Heart histology and function were also evaluated. Consistent with the literature, DBA/2J-mdx mice showed myocardial calcification and fibrosis and cardiac hemodynamics was compromised. Surprisingly, similar myocardial pathology and hemodynamic defects were detected in control DBA/2J mice. As a result, interpretation of the cardiac data proved difficult due to the confounding phenotype in control DBA/2J mice. Our results support further development of this microgene vector for clinical translation. Further, DBA/2J-mdx mice are not good models for Duchenne cardiomyopathy.

499. Intravenous Delivery of a Novel Micro-Dystrophin Vector Prevented Muscle Deterioration in Young Adult Canine Duchenne Muscular Dystrophy Dogs

Duchenne muscular dystrophy (DMD) is a progressive, muscle wasting disorder that affects all muscles in the body. An effective gene therapy for DMD will require efficient whole body muscle transduction. It was recently demonstrated that a single intravenous injection of adeno-associated virus (AAV) can lead to safe, bodywide muscle gene transfer in adolescent dogs affected by the canine model of DMD (cDMD) (Yue et al. 2015 Hum Mol Genet). Here we evaluated systemic gene therapy in three 3.5-m-old cDMD dogs using a novel canine codon-optimized micro-dystrophin vector. Transcriptional regulation is controlled by the muscle-specific CK8 promoter and a synthetic polyadenylation signal. All experimental subjects received transient immune suppression. One dog was administrated with 5×1013 viral genome (vg) particles/kg of the vector. Two dogs received 1×1014 vg particles/kg of the vector. All dogs tolerated injection well. Blood biochemistry (weekly in the first four weeks and biweekly thereafter) was unremarkable. Growth curve was nominally disturbed during the immunosuppression regimen, but recovered thereafter. Biopsy at 1,3 and 6 months after injection revealed widespread micro-dystrophin expression in 50-80% myofibers. The dystrophin-associated glycoprotein complex, including neuronal nitric oxide synthase (nNOS), was restored. While limited in sample size, muscle damage usually seen in young adult untreated dogs (inflammation, fibrosis, calcification) were rarely observed. CD4+, CD8+, and regulatory T cells were minimally detected. Night activity monitoring showed a trend of improvement. Limb muscle force (both forelimb and hind limb) was significantly enhanced compared to that of pre-injection. Our data suggest that systemic AAV micro-dystrophin therapy may translate to large mammals afflicted by DMD (Supported by Solid GT, NIH, DOD, Jesses Journey).

Nitric oxide‐dependent attenuation of noradrenaline‐induced vasoconstriction is impaired in the canine model of Duchenne muscular dystrophy

We developed a novel method to study sympatholysis in dogs. We showed abolishment of sarcolemmal nNOS, and reduction of total nNOS and total eNOS in the canine Duchenne muscular dystrophy (DMD) model. We showed sympatholysis in dogs involving both nNOS‐derived NO‐dependent and NO‐independent mechanisms. We showed that the loss of sarcolemmal nNOS compromised sympatholysis in the canine DMD model. We showed that NO‐independent sympatholysis was not affected in the canine DMD model.

679. Efficient Reconstitution of a 7kb Therapeutic Mini-Dystrophin Gene in Duchenne Muscular Dystrophy Dog Muscle

Duchenne muscular dystrophy (DMD) is a devastating muscle wasting disease caused by mutations in the dystrophin gene. Restoring dystrophin expression by adeno-associated virus mediated gene therapy holds great promise as a mutation-independent therapy for all DMD patients. The full-length dystrophin cDNA (≈11 kb) is far beyond the 5 kb packaging capacity of a single AAV vector. Consequently, truncated micro- and mini-dystrophin genes have been used. The micro- and mini-dystrophin genes encode ≈30% and ≈50% of the full-length dystrophin coding sequence, respectively. Mini-dystrophin is expected to provide better protection than micro-dystrophin. We have previously shown that dual AAV vectors can efficiently express a 6 to 8-kb mini-dystrophin in mdx mice. Dual AAV-mediated mini-dystrophin gene therapy significantly ameliorated histopathology and improved muscle function in mdx mice, a mouse model of DMD. To translate this promising therapy to large mammals, here we evaluated the reconstitution of a 7-kb minigene in the canine model of DMD by local injection. We engineered a pair of dual-AAV vectors to express a 7-kb canine codon-optimized ΔH2-R15 mini-dystrophin gene. For easy detection, a flag-tag and a GFP gene were fused to the N-terminal and C-terminal ends, respectively. To determine whether dual AAV vectors can lead to efficient mini-dystrophin expression, we co-delivered both vectors to the extensor carpi ulnaris muscle in the forelimb of DMD dogs at a dose of 2×013 vg particles/vector/muscle. Two months after gene transfer we evaluated transduction efficiency and observed successful expression of mini-dystrophin from the dual-AAV vectors. All flag-tag positive myofibers were also positive for minidystrophin, GFP and dystrophin-associated glycoprotein complex proteins. Importantly, mini-dystrophin gene therapy also reduced muscle force loss under the stress of repeated cycles of eccentric contraction. These results establish the proof-of-concept for mini-dystrophin gene therapy in dystrophic muscles of large mammals.