Gene therapy in the second eye of RPE65-deficient dogs improves retinal function

Abstract

The purpose of this study was to evaluate whether immune responses interfered with gene therapy rescue using subretinally delivered recombinant adeno-associated viral vector serotype 2 carrying the RPE65 cDNA gene driven by the human RPE65 promoter (rAAV2.hRPE65p.hRPE65) in the second eye of RPE65À/À dogs that had previously been treated in a similar manner in the other eye. Bilateral subretinal injection was performed in nine dogs with the second eye treated 85-180 days after the first. Electroretinography (ERG) and vision testing showed rescue in 16 of 18 treated eyes, with no significant difference between first and second treated eyes. A serum neutralizing antibody (NAb) response to rAAV2 was detected in all treated animals, but this did not prevent or reduce the effectiveness of rescue in the second treated eye. We conclude that successful rescue using subretinal rAAV2.hRPE65p.hRPE65 gene therapy in the second eye is not precluded by prior gene therapy in the contralateral eye of the RPE65À/À dog. This finding has important implications for the treatment of human LCA type II patients. Gene Therapy (2011) The condition is characterized by severe visual impairment in dim light, typically progressing to complete blindness in the second decade of life. LCA type II results from mutations in the RPE65 gene, and accounts for 10-15% of LCA cases. 2,3 RPE65 encodes a protein that forms an essential component of the visual cycle and is expressed within the retinal pigment epithelium. 3 The visual cycle is responsible for the supply of the chromophore, 11-cis-retinal, to the photoreceptor cells for combination with the rod and cone opsins to form the visual pigments. RPE65 is an isomerohydrolase that converts esters of vitamin A to 11-cis-retinol for subsequent oxidation to 11-cis-retinal prior to transport to the photoreceptors. A spontaneous 4 basepair deletion in RPE65 in the Briard breed of dog results in a premature stop codon and an absence of RPE65 gene product, resulting in a very similar phenotype to LCA type II. 4 Affected dogs have markedly reduced vision and an abnormal electroretinogram with greatly elevated threshold of responses. 4,5 The similarities between the human and canine disease resulting from RPE65 mutations, make the RPE65À/À Briard a valuable large animal model for LCA type II.Dramatic restoration of vision with gene therapy was first reported in the canine RPE65À/À model of LCA. 6 A number of studies have shown rod and cone photoreceptor rescue using rAAV vectors to deliver a normal copy of the RPE65 gene via a subretinal injection in the RPE65 mutant Briard. [6][7][8][9][10][11][12][13] On the basis of the great success of the canine trials, phase I/II clinical trials of rAAV-RPE65 gene replacement therapy in human LCA patients have started with the first reported results showing great promise. 14-16 Thus far in all human patients only one eye has been treated. A critical aspect of the management of LCA

Gene Therapy of Inherited Retinopathies: A Long and Successful Road from Viral Vectors to Patients

“…However, unlike what was observed in the preclinical studies (Acland et al, 2001;Narfstrom et al, 2003;Le Meur et al, 2007;Annear et al, 2011), full-field Ganzfeld ERGs remained negligible in all treated LCA2 eyes. In two cases, the reduced nystagmus allowed the measurement of electrical responses from the treated area by the sensitive multifocal ERG technique (Maguire et al, 2009) (Table 1).…”

“…This can be attributed to the features of the RPE (i.e., transducibility), the need for fine-regulated transgene expression in PRs, or the different rates of retinal degeneration, which is usually faster in PR-than RPE-specific diseases . To date, the most successful preclinical gene therapy study for a recessive RPE defect is represented by the AAV-mediated delivery of the 65-kDa RPE-specific isomerase (RPE65) in a dog model of LCA2 (Acland et al, 2001;Narfstrom et al, 2003;Le Meur et al, 2007;Annear et al, 2011), which has led to three independent human clinical trials in LCA2 patients, as discussed later. Gene replacement has been successfully evaluated in additional rodent models of IR caused by mutations in genes expressed in the RPE, such as MER tyrosine kinase (Mertk) (Vollrath et al, 2001;Smith et al, 2003;Tschernutter et al, 2005) and lecithin-retinol acyltransferase (LRAT) (Batten et al, 2005).…”

Retinal-chitosan Conjugates Effectively Deliver Active Chromophores to Retinal Photoreceptor Cells in Blind Mice and Dogs

“…Dogs were maintained initially in the dark for 3 days and then under a very dim light. ERGs were performed as previously described (Annear et al, 2011) except that an Espion e 2 visual electrophysiology system with ColorDome Ganzfeld (Diagnosys, Lowell, MA) was used and only a limited number of stimuli were tested following International Society for Clinical…”

Gene Therapy of Inherited Retinal Degenerations: Prospects and Challenges

“…In addition, in one trial, despite observed visual improvement, the rate of progression of retinal degeneration in the vector-treated retina was reported to be similar to that in the contralateral untreated eye, 33 raising concerns about the longevity of the effects. Finally, unlike what was observed in LCA2 dogs, 25,[34][35][36] no improvement in the full-field electroretinogram has thus far been reported in LCA2 patients treated with AAV. Interspecies differences in either levels of RPE65 expression or AAV retinal transduction efficiency may explain this and suggest that there is room for improvement in LCA2 retinal gene therapy.…”