Abstract
Purpose: :
To compare the transduction efficiency or a self-complimentary AAV (scAAV) vector with a single-stranded AAV (ssAAV) vector at transducing retinal cells of the dog when delivered by subretinal injection.
Methods: :
ScAAV 2/5 and ssAAV 2/5 both delivering the green fluorescent protein driven by the chicken beta actin promoter were prepared. Two normal dogs were used. In each dog one eye was given a subretinal injection in the dorsal tapetal fundus of 250 µl of 0.5x1012 vgp/ml of scAAV and the other eye given a subretinal injection of 250 µl of 0.5x1012 vgp/ml of ssAAV. The eyes were monitored for GFP expression using a RetCam II fundus camera equipped for fluorescein angiography. One dog was euthanized 6 months after injection and the eyes processed for immunohistochemistry.
Results: :
The results of fundus examinations from both dogs were very similar. In the scAAV injected eye very faint GFP expression could be seen on fundus examination at 6 days post-injection, this was stronger by day 11 and increased in intensity to day 32 and remained stable for the duration of the study. With the ssAAV injected eyes faint fluorescence due to GFP expression was visible by day 32. By day 54 it had reached its maximum intensity and remained at a similar level for the duration of the study. The fluorescence induced by the ssAAV was much less intense than that from the scAAV. On histological examination GFP expression was present in the retinal pigment epithelium (rpe) and the photoreceptors over the injected area for both eyes. As had been seen in vivo the strength of the fluorescence was greater for the scAAV injected eye compared to the ssAAV injected eye.
Conclusions: :
The scAAV construct use transduced canine rpe and photoreceptors when delivered by subretinal injection. The ssAAV construct had previously been shown to transduce rpe and photoreceptors. The scAAV construct resulted in a much more rapid onset of expression of the reporter gene than the ssAAV construct and also a stronger level of expression when given at the same titer. ScAAV may be useful for the treatment of rapidly progressive conditions where speed of transgene expression may be an important factor.
Keywords: gene transfer/gene therapy • photoreceptors • immunohistochemistry