Abstract
Purpose::
To evaluate recombinant adeno-associated virus (rAAV)-mediated gene therapy to restore cone function in a canine model of achromatopsia.
Methods::
rAAV2/5 containing human CNGB3 cDNA under control of the truncated human red cone opsin promoter was injected unilaterally into the subretinal space of dogs affected by either a null or missense mutation (D262N) of CNGB3. The contralateral eyes were treated by subretinal injection of saline. The dogs were between 8 and 28 weeks old at the time of treatment. Three variations of the human red cone opsin promoter were used: PR0.5, a short proximal promoter, 3LCR-PR0.5, PR0.5 plus 3 copies of the 35bp LCR, and PR2.1, PR0.5 plus about 1.5kbp surrounding the LCR. Depending on the size of the dogs, the total injected volume varied between 70 and 180 µl containing between 3.73 and 10.5 x 1012 particles per ml. At least 4 weeks after treatment, cone function was evaluated behaviorally and by electroretinography (ERG) under photopic conditions.
Results::
Successful restoration of cone function, measured by both behavior and ERG, was achieved in both CNGB3 null and missense mutant dogs at all age groups evaluated. While positive results were seen with all 3 promoters, the longest version of the human red cone opsin promoter (PR2.1) lead to the best restoration of cone function as assessed by ERG. These results confirm our previous data evaluating the intensity of GFP expression regulated by the same promoters. No adverse effects of the viral vectors or the expression of the human CNGB3 were noted.
Conclusions::
We achieved successful restoration of cone function in 2 canine models of achromatopsia using rAAV2/5 with human CNGB3 expression regulated by the human red cone opsin promoter. Since CNGB3 mutations account for 50% of all human cases with autosomal recessive achromatopsia, our results augur well for future gene therapy in human patients with homologous disorders and other diseases that affect cones.
Keywords: gene transfer/gene therapy • photoreceptors • ion channels