Tolerability and Potency of Sequential and Repeated AAV Corneal Gene Therapy

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Abstract Mucopolysaccharidosis I (MPS I) is an autosomal recessive monogenetic disorder caused by mutations in the gene encoding alpha-L-iduronidase (IDUA), a ubiquitous enzyme that breaks down large sugar molecules called glycosaminoglycans (GAGs). In the absence of IDUA, intra- and extra-cellular GAG accumulation results in enlarged cells/organs resulting in a multifactorial and potentially lethal disease depending upon the nature of the mutation and the correlative severity [1, 2]. MPS I afflicts approximately 3,000-8,000 patients worldwide, and symptoms include clouding of the cornea occurring in 70% of MPS I patients which is the leading cause of blindness. Currently, no therapeutics exist to address MPS I corneal clouding and penetrating keratoplasty is not a current standard of care due to transplant rejection (>70%) in this high-risk patient population. To address this blinding disorder, over the past 5 years we have optimized adeno-associated virus (AAV) gene delivery to the cornea, including the engineering and validation of RainBIO-1 (RBIO-1), an optimized IDUA cDNA genetic cassette amenable to AAV gene therapy. In several reports, RBIO-1 has demonstrated the ability to restore IDUA activity to MPS I patient cells, elevate IDUA activity in WT human corneas >10-fold, and most remarkably, prevent and reverse MPS I corneal opacity in a canine model following a single corneal intrastromal injection. Rigorous safety studies of RBIO-1 in WT rabbit corneas (n=20), demonstrate complete tolerability, even at doses 10-fold higher than the lowest effective dose, and strict vector genome containment to the injected cornea and retina was observed. These optimistic safety and efficacy data have positioned RBIO-1 as the likely first-in-class AAV therapeutic for any anterior ocular disease. Regarding a clinical protocol for RBIO-1, administration to a single cornea, initially, is most prudent to evaluate safety and efficacy in MPS I patients. If RBIO-1 alleviates MPS I corneal storage disease similar to results obtained from MPS I canines, sequential administration to the contralateral cornea would be desired for bilateral vision. This clinically relevant question of sequential AAV gene delivery to the cornea will be answered by the execution of the experiments proposed in Aim 1 using a rabbit model. Although, we have reported strong IDUA production and therapeutic success out nearly 1 year in MPS I canines (n=10) and 6 months in rabbits, the durability of AAV transgene expression in the cornea remains unknown, and perhaps redosing of RBIO-1 to a single cornea may be required for long-term sustained efficacy. The experiments in Aim 2 will determine the extent of AAV vector transduction following re-administration to a previously dosed rabbit cornea. The work herein will employ RBIO-1 to determine the feasibility of sequential AAV vector injections and repeat administration in the cornea and thereby provide critical data for Phase I protocol design to treat MPS I corneal clouding. More broadly, the relevance of the critical data obtained herein extends beyond MPS I to all corneal, and perhaps ocular surface, disorders which also may benefit from an AAV gene therapy approach.