IND-enabling studies of non-immunogenic gene therapy for ultra-rare DMD patients excluded from dystrophin trials

About This Grant

Abstract Duchenne muscular dystrophy (DMD) is a rare childhood onset neuromuscular disease caused by genetic deficiency of the protein dystrophin. DMD is an incurable disease with a devastating impact on patients as a result of progressive weakness, wheelchair confinement, loss of independence/activities of daily living, and ultimately premature death from combined cardiorespiratory insufficiency. The majority of dystrophin gene mutations worldwide are multi-exon, frameshifting deletions that eliminate expression of variable portions of the 79 exon gene into the 427 Kd full length protein isoform Dp427. Dp427 is a cytoskeletal protein primarily composed of three protein folding domains, the largest of which is the rodlike mid-section composed of 24 spectrin-like triple helical repeats. Dp427 is thought to transmit muscle contractile force between the outermost sacomeres and the membrane-spanning proteins of the dystrophin-glycoprotein complex (DGC). Recently, an ultra-rare subset of DMD patients has been found to develop T cell-mediated, treatment-emergent serious adverse events (TESAEs) following systemic gene therapy using AAV vectors encoding miniaturized, ~ 140 Kd recombinant proteins derived from Dp427 by internal deletion. Our preclinical studies, as published in 2019 by Song, et al, Nature Medicine, predicted these TESAEs by virtue of our use of an informative animal model, the German Shorthaired Pointer Muscular Dystrophy (GSHPMD) in which a naturally occurring deletions eliminates peptide epitopes corresponding to the miniaturized versions of Dp427. In this study we also showed that a non- immunogenic alternative AAV vector encoding a miniaturized version of the dystrophin-related protein utrophin was protected from T cell destruction of transduced myofibers by central immunological tolerance towards this “self” protein. In this U01 proposal, we provide a milestone-driven, comprehensive translational and clinical research program to set the stage for a safe and effective alternative for the ultra-rare subset of DMD patients excluded from dystrophin gene therapy trials. We propose innovative, non-invasive physiological and biochemical outcome measures precisely targeted to the underlying pathophysiology of the disease, segmental myonecrosis incited by forceful muscle contraction. The four Specific Aims are structured to yield the highest probability of a successful IND application as the final deliverable, while providing ample information generalizable to therapeutics development for other genetic diseases under the NINDS mission. The proposed IND application will set the stage for a phase 1/2a clinical trial of AAV-microutrophin gene therapy in the ultra- rare subset of DMD patients with N-terminal dystrophin deletions, with results of the trial anticipated to apply broadly to the entire DMD patient population.