Safety of intravitreally delivered AAV2 vector‐mediated multi‐characteristic opsin genetic construct in wild type beagle dogs

Abstract Background A novel adeno‐associated virus 2 (AAV2)‐carried multi‐characteristic opsin (MCO) (MCO‐010) is undergoing several clinical trials as a novel therapeutic modality for the treatment of degenerative retinal diseases including retinitis pigmentosa and Stargardt disease. The present study aimed to determine the ocular and systemic safety of MCO‐010 and the AAV2 vehicle in adult Beagle dogs following intravitreal (IVT) injection. Methods The current safety/toxicology studies spanning 13 weeks described here utilized well‐documented techniques to assess the effects of IVT injection of MCO‐010 up to 2.2 × 10 11 genome copies (gc) per eye, or the AAV2 capsid (vehicle control) on gross behavioral and immunogenic changes, alterations in body weights, blood biochemistry, hematology, blood coagulation, gross necropsy lesions, organ weight changes and histopathology in the dogs (n = 4 per group; two males and two females per group). Immunohistochemical and functional electroretinogram studies were also conducted to determine MCO expression in the retina and determine any retinal toxicity associated with MCO‐010. Results There were no significant deleterious effects of the MCO‐010 (or the AAV2 at the tested doses) on any of the examined parameters, including the absence of any severe ocular or systemic adverse events. However, as expected, inflammation after IVT delivery of AAV2 and MCO‐010 was observed in the conjunctivae of all groups of animals, although this self‐resolved within 1 week post‐injection. Quantitative immunohistochemical analyses of MCO‐010‐associated mCherry revealed successful delivery of the gene therapy within the inner retina. Conclusions In summary, MCO‐010 demonstrated a favorable safety profile when administered to the eyes of adult Beagle dogs of both sexes at dose levels up to 2.2 × 10 11 gc per eye, with no adverse effects observed. This dose was identified as the No Observed Adverse Effect Level (i.e. NOAEL) and guided selection of safe doses for human clinical trials.