Long-Term Protection of Retinal Structure but Not Function Using RAAV.CNTF in Animal Models of Retinitis Pigmentosa

Abstract

The present study aimed to determine whether intravitreal administration of an adeno-associated virus (AAV) carrying ciliary neurotrophic factor (CNTF) can achieve long-term morphological and physiological rescue of photoreceptors in animal models of retinitis pigmentosa, and whether injection of this virus after degeneration begins is effective in protecting the remaining photoreceptors. We injected rAAV.CNTF.GFP intravitreally in early postnatal Prph2(Rd2/Rd2) (formerly rds/rds) mice and in adult P23H and S334ter rhodopsin transgenic rats. Contralateral eyes received an intravitreal injection of rAAV.GFP or a sham injection. We evaluated the eyes at 6 months (rats) and 8.5 to 9 months (mice) postinfection and looked for histological and electoretinographic (ERG) evidence of photoreceptor rescue and CNTF-GFP expression. Intravitreal administration of rAAV resulted in efficient transduction of retinal ganglion cells in the Prph2(Rd2/Rd2) retina, and ganglion, Muller, and horizontal/amacrine cells in the mutant rat retinas. Transgene expression localized to the retinal region closest to the injection site. We observed prominent morphological protection of photoreceptors in the eyes of all animals receiving rAAV.CNTF.GFP. We found the greatest protection in regions most distant from the CNTF-GFP-expressing cells. The Prph2(Rd2/Rd2) ERGs did not exhibit interocular differences. Eyes of the rat models administered rAAV.CNTF.GFP had lower ERG amplitudes than those receiving rAAV.GFP. The discordance of functional and structural results, especially in the rat models, points to the need for a greater understanding of the mechanism of action of CNTF before human application can be considered.

Immune response following intraocular delivery of recombinant viral vectors

“…AAV serotype 2 (AAV2) has been used successfully and efficiently through subretinal injection to transduce photoreceptors and RPE in a number of gene therapy paradigms. [12][13][14][15][16][17][18][19][20][21][22][23][24][25] This virus also targets ganglion cells efficiently if it is injected intravitreally 26,27 (Figure 1). AAV2 has not been found, as yet, to target structures in the anterior chamber of the eye.…”

Recombinant AAV-mediated gene transfer to the retina: gene therapy perspectives

“…[17][18][19] Intravitreal injection of rAAV-2 leads to efficient ganglion cell transduction. [20][21][22][23] We and others have studied rAAV chimeric serotypes in which the vector is flanked by AAV-2 ITRs, but encapsidated in an AAV-1, -2, -3, -4 or -5 shell generating rAAV-2/1,-2/2, -2/3, -2/4 and -2/5, respectively. In the mouse, subretinal injection of rAAV-2/1egfp shows early onset of EGFP expression (3-4 days) with transgene expression restricted to the RPE.…”

“…rAAV-mediated gene transfer using neurotrophic factors, such as ciliary neurotrophic factor (CNTF), fibroblast growth factors (FGF) and glial cell line-derived neurotrophic factors (GDNF), have increased photoreceptors survival in different rodent models of retinal degeneration. 21,[37][38][39] However, a key issue for successful ocular gene therapy using such neurotrophic factors is the ability to regulate expression for pharmacological and safety reasons. Many proteins have more narrow therapeutic windows, and overproduction could result in toxicity.…”

“…In these two cases, retinas receiving rAAV-2/2cntf showed prominent morphological protection of photoreceptors, but with no improved ERG in the Prph2 Rd2/Rd2 mice and with lower ERG amplitudes in rAAV-2/2cntf-injected rat models compared with rAAV-2/2gfp-injected ones. 21 This discordance of functional and morphological results suggested a deleterious effect of intraocular CNTF gene delivery on the retina. Two recent reports clearly demonstrated that intraocular CNTF expression using rAAV-2/2-mediated gene delivery, in wild-type mice, in Prph2 Rd2/Rd2 mice and in mice with a P216L rds/peripherin mutation, resulted in a significant decrease of function, as assessed by ERG.…”

Gene therapy for optic nerve disease

“…Correction of a specific ocular genetic defect requires gene delivery directly to the defective cells and has been successfully used to slow photoreceptor loss in rodent models of primary photoreceptor disease. 12,[23][24][25] As an example, AAV vectors have recently been used to restore photoreceptor structure and function in retinal degeneration slow (rds) mice. 26 These mice have a mutation in the Prph2 gene and mutations in this gene have also been demonstrated in human retinitis pigmentosa.…”