Abstract
Abstract: :
Purpose: Subretinal injection of a recombinant adeno–associated virus (rAAV) vectored gene has been shown to restore useful vision in RPE65 null mutation dogs with retinal dystrophy similar to human Leber’s congenital amaurosis. This report concerns the assessment of photoreceptor long–term function. Methods: Five dogs treated with rAAV.RPE65 construct in the subretinal space of the right eye and with rAAV.GFP in the left eye (n=4), or the left eye untouched (n=1), underwent standardized ERG studies every 3rd month up to more than 24 months post–operatively. Scotopic recordings were performed, either using a low and a high light intensity; –2.0 log cd s/m2 and 0.6 log cd s/m2, or a full light intensity series from –4.0 to 0.6 log cd s/m2. The dogs were then light adapted (10 min of 30 cd /m2) and photopic recordings performed at –1.0 and 0.0 log cd s/m2 at 5.1 Hz and 30.1 Hz at 0.0 log cd s/m2. Results: At 10–12 weeks after gene transfer there was a significant increase in all calculated scotopic and photopic b–wave amplitudes, including 30 Hz flicker recordings, in the right eye compared to pre–operatively. The effect on the scotopic amplitudes of the rAAV.RPE65 treated right eyes was then seen to slowly decline but was still highly significant 18–21 months after surgery. Approximately 6–9 months following treatment there was a positive qualitative and quantitative effect on ERG amplitudes also in the fellow eye. Thus, 15–18 months post–op. the scotopic high intensity stimuli and photopic amplitudes were significantly increased in both eyes. Finally, at 21–24 months further reduction of the scotopic responses were seen, while the photopic 30 Hz flicker responses were still significantly increased in both eyes. Intensity response studies showed that there was a 2.5 log unit increase in retinal sensitivity sustained 2 years post–operatively in the treated eye. Conclusions: Long term follow–up shows stable elevation of the photopic b–wave amplitudes and 30Hz flicker amplitudes in the eyes treated with rAAV vectored gene transfer up two years. The dramatic effect on the scotopic b–wave responses on the treated eye, however, observed 10–12 weeks after treatment, declines gradually over time. Further, there is a sustained increase in retinal sensitivity up to 2 years in the treated eye. The qualitative functional improvement of photopic responses observed also in the fellow–eye, observed at long–term follow–up, needs further investigation.
Keywords: gene transfer/gene therapy • retinal degenerations: hereditary • electroretinography: clinical