Académie royale de Médecine de Belgique

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Résumé de Fabienne Rolling (Séance du 21 octobre 2006)

RESTORATION OF VISION IN RPE65 NULL MUTATION DOGS USING AN AAV  SEROTYPE 4 VECTOR THAT SPECIFICALLY TARGETS THE RETINAL PIGMENTED EPITHELIUM

par Mme F. ROLLING (Université de Nantes), invitée, et coll.

Purpose: The purpose of our study was to evaluate rAAV2 pseudotyped with serotype 4, a serotype which specifically targets the retinal pigmented epithelium, for ability to restore vision in RPE65-/- purebred Briard dogs and to assess the safety of gene transfer with respect to retinal morphology and function.

Methods: Recombinant rAAV2/4 and rAAV2/2 vectors containing the human specific RPE65 promoter and cDNA were generated and administered subretinally in 8 affected dogs, ages 8 to 30 months (n=6 with rAAV2/4, n=2 with rAAV2/2).

Results: Electrophysiological results demonstrated that restoration of rod and cone photoreceptor function started as soon as 15 days post-injection, reaching maximal function at 3 months post-injection, and remaining stable thereafter in all animals treated at 8 to 11 months of age. As assessed by the ability of these animals to avoid obstacles in dim light, functional vision was restored in the treated eye, while the untreated contralateral eye served as an internal control. The dog treated at a later age (30 months) did not recover retinal function or vision, suggesting the existence of a therapeutic window for the successful treatment of RPE65 -/- dogs by gene replacement.

Conclusion: We have demonstrated herein that specific gene transfer to the RPE using a rAAV2/4 vector can be used to correct the RPE65 defect in RPE65-/- purebreed Briard dogs, leading to the stable restoration of normal retinal function and vision dependent behavior. The relative contributions of dysfunction or cell death to the extreme visual loss in human RPE65 deficiency are unknown.  However analysis of our results in dogs suggests that for successful gene therapy to occur in humans, patients should be treated at a young age.

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