Safety and Efficacy Evaluation of rAAV2tYF-PR1.7-hCNGA3 Vector Delivered by Subretinal Injection in CNGA3 Mutant Achromatopsia Sheep

Abstract

{These authors contributed equally to this work.Applied Genetic Technologies Corporation (AGTC) is developing a recombinant adeno-associated virus (rAAV) vector expressing the human CNGA3 gene designated AGTC-402 (rAAV2tYF-PR1.7-hCNGA3) for the treatment of achromatopsia, an inherited retinal disorder characterized by markedly reduced visual acuity, extreme light sensitivity, and absence of color discrimination. The results are herein reported of a study evaluating safety and efficacy of AGTC-402 in CNGA3-deficient sheep. Thirteen day-blind sheep divided into three groups of four or five animals each received a subretinal injection of an AAV vector expressing a CNGA3 gene in a volume of 500 lL in the right eye. Two groups (n = 9) received either a lower or higher dose of the AGTC-402 vector, and one efficacy control group (n = 4) received a vector similar in design to one previously shown to rescue cone photoreceptor responses in the day-blind sheep model (rAAV5-PR2.1-hCNGA3). The left eye of each animal received a subretinal injection of 500 lL of vehicle (n = 4) or was untreated (n = 9). Subretinal injections were generally well tolerated and not associated with systemic toxicity. Most animals had mild to moderate conjunctival hyperemia, chemosis, and subconjunctival hemorrhage immediately after surgery that generally resolved by postoperative day 7. Two animals treated with the higher dose of AGTC-402 and three of the efficacy control group animals had microscopic findings of outer retinal atrophy with or without inflammatory cells in the retina and choroid that were procedural and/or test-article related. All vector-treated eyes showed improved cone-mediated electroretinography responses with no change in rod-mediated electroretinography responses. Behavioral maze testing under photopic conditions showed significantly improved navigation times and reduced numbers of obstacle collisions in all vector-treated eyes compared to their contralateral control eyes or predose results in the treated eyes. These results support the use of AGTC-402 in clinical studies in patients with achromatopsia caused by CNGA3 mutations, with careful evaluation for possible inflammatory and/ or toxic effects.

Safety and Efficacy of AAV5 Vectors Expressing Human or Canine CNGB3 in CNGB3-Mutant Dogs

“…Except for focal retinal atrophy in the right eye of animal M731, who received the lower dose of the vector expressing canine CNGB3, the pathologic changes were minimal or non-existent in the eyes treated with the lower vector dose. The dose-related inflammation seen in these studies is consistent with results seen in other studies of gene therapy vectors delivered by intraocular injection in a variety of species, 17,[21][22][23] but an explanation for the unexpected development of more severe chorioretinitis with the canine CNGB3 vector than with the human CNGB3 vector in study 3 is not apparent. It was not due to a mix-up in labeling of the vectors that were administered, since residual samples of vector collected after subretinal administration were tested by polymerase chain reaction (PCR) and determined to have the correct sequence of the canine or human CNGB3 cDNA specified in the protocol (data not shown).…”

Long-term retinal cone rescue using a capsid mutant AAV8 vector in a mouse model of CNGA3-achromatopsia

“…Recently, successful gene therapies have been reported in CNGA3-deficient sheep, a large-animal model of achromatopsia [ 50 – 52 ]. In these studies, AAV serotype 2 and 5 vectors carry Cnga3 gene under control of a human red/green cone opsin promoter.…”

Large Animal Models of Inherited Retinal Degenerations: A Review

“…The first identified has a nonsense mutation (p.Arg236Ter) and the second a missense mutation (p.Gly540Ser) [84]. Adeno-associated virus gene therapy was able to restore cone function in both models [84,85].…”