Assessment of AAV Dual Vector Safety in the Abca4-/- Mouse Model of Stargardt Disease

Purpose: Adeno-associated viral (AAV) gene therapy treatment for Stargardt disease currently requires a dual vector approach owing to the size of the ATP-binding cassette transporter family member gene (ABCA4). The nature of the dual vector system creates the potential for adverse events. Here we have investigated an overlapping adeno-associated viral ABCA4 dual vector system for signs of toxicity in Abca4(-/-) mice as a prelude to dual vector first in human clinical trials. Methods: Abca4(-/-) mice received a subretinal injection of a 1:1 5':3' dual vector mix; 5' vector only; 3' vector only; a GFP reporter vector; or diluent only (sham). All vectors were adeno-associated virus-8 Y733F. Mice were subsequently assessed for signs of toxicity as measured by loss in retinal structure by optical coherence tomography and retinal function by electroretinography up to 6 months after injection. Results: Subretinal delivery of the dual vector system and its comprising parts induced no structural or functional changes relative to paired uninjected eyes beyond those observed in the sham control cohort. Histologic changes were limited to the superior retina where the injection was performed. Electroretinography analysis confirmed the dual vector system inferred no functional changes beyond those observed in the sham control cohort. Conclusions: An optimized overlapping dual vector system for the treatment of Stargardt disease shows no additional signs of toxicity beyond those observed from a sham injection. Translational Relevance: This presentation of safety of a dual vector system for the treatment of Stargardt disease encourages its future use in clinical trial.