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Long-term and age-dependent restoration of visual function in a mouse model of CNGB3-associated achromatopsia following gene therapy.

Carvalho LS, Xu J, Pearson RA, Smith AJ, Bainbridge JW, Morris LM, Fliesler SJ, Ding XQ, Ali RR - Hum. Mol. Genet. (2011)

Bottom Line: Following subretinal delivery of the vector, CNGB3 was detected in both M- and S-cones and resulted in increased levels of CNGA3, increased cone density and survival, improved cone outer segment structure and normal subcellular compartmentalization of cone opsins.Therapy also resulted in long-term improvement of retinal function, with restoration of cone ERG amplitudes of up to 90% of wild-type and a significant improvement in visual acuity.Remarkably, successful restoration of cone function was observed even when treatment was initiated at 6 months of age; however, restoration of normal visual acuity was only possible in younger animals (e.g. 2-4 weeks old).

View Article: PubMed Central - PubMed

Affiliation: The Department of Genetics, UCL Institute of Ophthalmology, London, UK.

ABSTRACT
Mutations in the CNGB3 gene account for >50% of all known cases of achromatopsia. Although of early onset, its stationary character and the potential for rapid assessment of restoration of retinal function following therapy renders achromatopsia a very attractive candidate for gene therapy. Here we tested the efficacy of an rAAV2/8 vector containing a human cone arrestin promoter and a human CNGB3 cDNA in CNGB3 deficient mice. Following subretinal delivery of the vector, CNGB3 was detected in both M- and S-cones and resulted in increased levels of CNGA3, increased cone density and survival, improved cone outer segment structure and normal subcellular compartmentalization of cone opsins. Therapy also resulted in long-term improvement of retinal function, with restoration of cone ERG amplitudes of up to 90% of wild-type and a significant improvement in visual acuity. Remarkably, successful restoration of cone function was observed even when treatment was initiated at 6 months of age; however, restoration of normal visual acuity was only possible in younger animals (e.g. 2-4 weeks old). This study represents achievement of the most substantial restoration of visual function reported to date in an animal model of achromatopsia using a human gene construct, which has the potential to be utilized in clinical trials.

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Related in: MedlinePlus

Representative ERG traces from Cngb3−/− mice following gene therapy. Wild-type and untreated traces are shown in parallel for comparison. Representative traces shown are from the P30 injected group. Scotopic measurements shown here are from 0.007 cd.s/m2 intensity. Photopic flash recordings shown are from 10 cd.s/m2 intensity and flicker recordings are of varying frequencies on a 20 cd.s/m2 background light.
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DDR218F3: Representative ERG traces from Cngb3−/− mice following gene therapy. Wild-type and untreated traces are shown in parallel for comparison. Representative traces shown are from the P30 injected group. Scotopic measurements shown here are from 0.007 cd.s/m2 intensity. Photopic flash recordings shown are from 10 cd.s/m2 intensity and flicker recordings are of varying frequencies on a 20 cd.s/m2 background light.

Mentions: In order to determine whether gene supplementation leads to long-term restoration of cone function and if there was an optimal age window for effective treatment, vector was injected at P6, 15, 30, 90 and 180. ERG recordings were then performed at monthly intervals, starting at 30 days PI. Figure 3 shows a comparison between representative ERG traces from treated, untreated and wild-type recordings in animals treated at P30 and assessed 120 days PI. We observed substantial rescue of photopic flash and flicker responses in treated animals, while scotopic traces remained unchanged. Averaged ERG recordings measured at 3–4 months PI for all age groups are shown in Figure 4. There was significant improvement in function between treated and untreated eyes in all age groups (P< 0.05). However, it is evident from the results that an ideal window for treatment is present around P15–30 and thus the group injected at P30 was selected to evaluate the long-term efficacy of treatment. Figure 5 shows that the photopic ERG response in injected eyes was restored to near wild-type levels in this group and persisted for up to 270 days PI (the longest time point examined here). Moreover, we were able to observe a consistent long-term effect of treatment in all age-treated groups up to 180 days PI (Fig. 6). These experiments show that treatment performed at P15 and P30 achieves a near complete ERG restoration (>90% of wild-type level), while treatment performed at P90 and P180 resulted in functional rescue at 70–80% and 60–70% of wild-type levels, respectively. The group showing the smallest rescue was the group treated at P6, where visual function only reached ∼55% of wild-type levels. This could be explained by the increased amount of retinal damage observed after injection in the P6 animals, most likely caused by the small eye size and increased surgical trauma (data not shown), but the possibility of low vector transduction and, consequently, low CNGB3 expression levels in these younger treated animals can also not be excluded.Figure 3.


Long-term and age-dependent restoration of visual function in a mouse model of CNGB3-associated achromatopsia following gene therapy.

Carvalho LS, Xu J, Pearson RA, Smith AJ, Bainbridge JW, Morris LM, Fliesler SJ, Ding XQ, Ali RR - Hum. Mol. Genet. (2011)

Representative ERG traces from Cngb3−/− mice following gene therapy. Wild-type and untreated traces are shown in parallel for comparison. Representative traces shown are from the P30 injected group. Scotopic measurements shown here are from 0.007 cd.s/m2 intensity. Photopic flash recordings shown are from 10 cd.s/m2 intensity and flicker recordings are of varying frequencies on a 20 cd.s/m2 background light.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3140821&req=5

DDR218F3: Representative ERG traces from Cngb3−/− mice following gene therapy. Wild-type and untreated traces are shown in parallel for comparison. Representative traces shown are from the P30 injected group. Scotopic measurements shown here are from 0.007 cd.s/m2 intensity. Photopic flash recordings shown are from 10 cd.s/m2 intensity and flicker recordings are of varying frequencies on a 20 cd.s/m2 background light.
Mentions: In order to determine whether gene supplementation leads to long-term restoration of cone function and if there was an optimal age window for effective treatment, vector was injected at P6, 15, 30, 90 and 180. ERG recordings were then performed at monthly intervals, starting at 30 days PI. Figure 3 shows a comparison between representative ERG traces from treated, untreated and wild-type recordings in animals treated at P30 and assessed 120 days PI. We observed substantial rescue of photopic flash and flicker responses in treated animals, while scotopic traces remained unchanged. Averaged ERG recordings measured at 3–4 months PI for all age groups are shown in Figure 4. There was significant improvement in function between treated and untreated eyes in all age groups (P< 0.05). However, it is evident from the results that an ideal window for treatment is present around P15–30 and thus the group injected at P30 was selected to evaluate the long-term efficacy of treatment. Figure 5 shows that the photopic ERG response in injected eyes was restored to near wild-type levels in this group and persisted for up to 270 days PI (the longest time point examined here). Moreover, we were able to observe a consistent long-term effect of treatment in all age-treated groups up to 180 days PI (Fig. 6). These experiments show that treatment performed at P15 and P30 achieves a near complete ERG restoration (>90% of wild-type level), while treatment performed at P90 and P180 resulted in functional rescue at 70–80% and 60–70% of wild-type levels, respectively. The group showing the smallest rescue was the group treated at P6, where visual function only reached ∼55% of wild-type levels. This could be explained by the increased amount of retinal damage observed after injection in the P6 animals, most likely caused by the small eye size and increased surgical trauma (data not shown), but the possibility of low vector transduction and, consequently, low CNGB3 expression levels in these younger treated animals can also not be excluded.Figure 3.

Bottom Line: Following subretinal delivery of the vector, CNGB3 was detected in both M- and S-cones and resulted in increased levels of CNGA3, increased cone density and survival, improved cone outer segment structure and normal subcellular compartmentalization of cone opsins.Therapy also resulted in long-term improvement of retinal function, with restoration of cone ERG amplitudes of up to 90% of wild-type and a significant improvement in visual acuity.Remarkably, successful restoration of cone function was observed even when treatment was initiated at 6 months of age; however, restoration of normal visual acuity was only possible in younger animals (e.g. 2-4 weeks old).

View Article: PubMed Central - PubMed

Affiliation: The Department of Genetics, UCL Institute of Ophthalmology, London, UK.

ABSTRACT
Mutations in the CNGB3 gene account for >50% of all known cases of achromatopsia. Although of early onset, its stationary character and the potential for rapid assessment of restoration of retinal function following therapy renders achromatopsia a very attractive candidate for gene therapy. Here we tested the efficacy of an rAAV2/8 vector containing a human cone arrestin promoter and a human CNGB3 cDNA in CNGB3 deficient mice. Following subretinal delivery of the vector, CNGB3 was detected in both M- and S-cones and resulted in increased levels of CNGA3, increased cone density and survival, improved cone outer segment structure and normal subcellular compartmentalization of cone opsins. Therapy also resulted in long-term improvement of retinal function, with restoration of cone ERG amplitudes of up to 90% of wild-type and a significant improvement in visual acuity. Remarkably, successful restoration of cone function was observed even when treatment was initiated at 6 months of age; however, restoration of normal visual acuity was only possible in younger animals (e.g. 2-4 weeks old). This study represents achievement of the most substantial restoration of visual function reported to date in an animal model of achromatopsia using a human gene construct, which has the potential to be utilized in clinical trials.

Show MeSH
Related in: MedlinePlus