Figure 2. The LV-RPE65 Vector Restores the ERG Response of the Rpe65 ^−/− Mice.

Rpe65 ^−/− mice were treated P5 by an intravitreal injection of 20 ng of lentiviral vector.

(A) ERG response to single flashes was recorded in scotopic condition at 2 mo of age. After LV-GFP treatment, the mice showed a response typical for Rpe65 ^−/− mice, with the a-wave absent and the b-wave elicited only for the highest stimuli (i.e., 10 and 25 cd s/m²; left tracings). After LV-RPE65 treatment, a stimulus of 10^{− 2} cd s/m² was sufficient to trigger the b-wave, and the a-wave appeared for a stimulus of 0.3 cd s/m² (right tracings). Vertical bars indicate occurrence of the stimuli; x-axis: 40 ms/div; y-axis: 100 μV/div.

(B) Summary of the ERG recordings performed 2 mo after vector delivery at P5 in Rpe65 ^−/− mice. Amplitude of b-wave (expressed in μV) is represented for each stimulus intensity. In the LV-RPE65-treated group (squares), the b-wave rose with a stimulus as low as 10^{− 2} cd s/m², whereas in the LV-GFP-treated group (triangles) 3 cd s/m² were necessary to elicit the b-wave. ANOVA for repeated measures showed significant stimulus intensity effect (p < 0.0001), group effect (p = 0.023), and group versus stimulus intensity interaction (p = 0.002). Data are presented as mean ± standard error of the mean (SEM).

(C) Improvement of the ERG response after LV-RPE65 treatment is correlated with the level of RPE65 expression. The area of the retina expressing GFP (triangles) or RPE65 (squares) was quantified for each eye at age 4 mo after gene transfer at P5, and plotted against the b-wave threshold (defined as the intensity of the lowest stimulus capable of eliciting the b-wave, expressed in log mcd s/m²).