Preclinical Safety Evaluation of a Recombinant AAV8 Vector for X-Linked Retinoschisis After Intravitreal Administration in Rabbits

Abstract

X-linked retinoschisis (XLRS) is a retinal disease caused by mutations in the gene encoding the protein retinoschisin (RS1) and one of the most common causes of macular degeneration in young men. Currently, no FDA-approved treatments are available for XLRS and a replacement gene therapy could provide a promising strategy. We have developed a novel gene therapy approach for XLRS, based on the administration of AAV8-scRS/IRBPhRS, an adeno-associated viral vector coding the human RS1 protein, via the intravitreal route. On the basis of our prior study in an Rs1-KO mouse, this construct transduces efficiently all the retinal layers, resulting in an RS1 expression similar to that observed in the wild-type and improving retinal structure and function. In support of a clinical trial, we carried out a study to evaluate the ocular safety of intravitreal administration of AAV8-scRS/IRBPhRS into 39 New Zealand White rabbits. Two dose levels of vector, 2e 10 and 2e 11 vector genomes per eye (vg/eye), were tested and ocular inflammation was monitored over a 12-week period by serial ophthalmological and histopathological analysis. A mild ocular inflammatory reaction, consisting mainly of vitreous infiltrates, was observed within 4 weeks from injection, in both 2e 10 and 2e 11 vg/eye groups and was likely driven by the AAV8 capsid. At 12-week follow-up, ophthalmological examination revealed no clinical signs of vitreitis in either of the dose groups. However, while vitreous inflammatory infiltrate was significantly reduced in the 2e 10 vg/eye group at 12 weeks, some rabbits in the higher dose group still showed persistence of inflammatory cells, histologically. In conclusion, intravitreal administration of AAV8-scRS/IRBPhRS into the rabbit eye produces a mild and transient intraocular inflammation that resolves, at a 2e 10 vg/eye dose, within 3 months, and does not cause irreversible tissue damages. These data support the initiation of a clinical trial of intravitreal administration of AAV8-scRS/IRBPhRS in XLRS patients.

Ocular Inflammatory Response to Intravitreal Injection of Adeno-Associated Virus Vector: Relative Contribution of Genome and Capsid

“…Furthermore, the present study was not designed to differentiate whether the vg content-related responses were due to the mere presence of AAV genome or whether transcriptional and/or translational activities had a role in inflammation. Additional research will be necessary to address these intriguing questions; reports by Marangoni et al 12 and Maclachlan et al, 9 however, indicated minimal impact of gene expression on inflammation. Regardless, the data presented in this study suggest that enrichment for genome containing capsids improves retinal transduction and reduces VC inflammation.…”

“…[4][5][6][7][8] Both SR and IVT ocular AAV vector dosings in higher species induce mild and temporary inflammatory responses, which are stronger when dose levels increase. [9][10][11][12] Foreign protein and foreign DNA are known inducers of inflammation, which is also true in the immune-privileged ocular environment. 13,14 We designed a series of studies to explore which component(s) of AAV vectors, viral capsid, or viral DNA drive inflammatory responses following IVT dosing of AAV vectors.…”

Helper-Dependent Adenovirus Transduces the Human and Rat Retina but Elicits an Inflammatory Reaction When Delivered Subretinally in Rats

“…40 Similarly, Marangoni et al reported inflammatory cell infiltrates in the vitreous of New Zealand White rabbits after intravitreal delivery of AAV8 coding the human retinoschisin protein. 41 Despite these observations, a phase I/IIa clinical dose-escalation trial (NCT02317887) was conducted to evaluate the safety and efficacy of AAV8-RS1 in nine patients with molecularly confirmed RS1 Xlinked retinoschisis. 5 Cukras et al reported that the virus was well tolerated in all but one of the individuals, but they also observed dose-dependent inflammation, including an increase in systemic antibodies raised against the AAV8 capsid.…”

Advancing Therapeutic Strategies for Inherited Retinal Degeneration: Recommendations From the Monaciano Symposium

“…Some level of caution may be warranted in developing this approach, however, as there are reports of viral transduction extending outside the eye to sites including the optic nerve, brain, and other tissues after intravitreal injection, 54,55 and there is also a concern that inflammation may persist in the eye after higher viral doses. 56 The rare nature of most retinal dystrophies, coupled with the genotypic and phenotypic heterogeneity observed in patients, means that only a relatively small number of individuals might benefit from treatments targeting specific gene mutations. This raises issues relative to whether the costs of developing such therapies can be recovered after market authorization, and how to encourage investment in therapies for rare diseases that may involve only a single administration.…”