An Allele-Independent Gene Therapy Strategy Induces Rod Function in a Transgenic Swine Model of Autosomal Dominant Retinitis Pigmentosa

Abstract

Purpose : Retinitis pigmentosa (RP), is characterized by an initial loss of rod photoreceptors, followed by a subsequent loss of cones. A large percentage of RP results from mutations in the rhodopsin (RHO) gene, although there is significant allelic heterogeneity. We hypothesized that an allele-independent gene therapy targeting rhodopsin mutations could be a broadly applied approach. We tested this hypothesis in a transgenic P23H human RHO (TgP23H) pig model of RP using a AAV viral vector that has been successfull in a dog and mouse RP model. We studied the efficacy and safety of this dual rAAV vector that combines a short hairpin RNA (shRNA), to eliminate expression of both mutant human and WT pig rhodopsin protein, with a shRNA resistant augmentation cassette, to augment human WT rhodopsin.

Methods : The rAAV dual vector, shRNA820/RHO820, was subretinally injected (50µl total volume) at several titers (5 x 10¹¹ to 1 x 10¹³µg/ml). Injections were performed in TgP23H and WT piglets between postnatal day (P) 3 and 7. The structural and functional integrity of the retinas were assessed non-invasively at monthly intervals through ~20 weeks post-injection using sd-optical coherence tomography[B1] , and full-field electroretinogram (ffERG). At the terminal assessment, pigs were euthanized, their eyes enucleated, and retinas processed for morphological analyses.

Results : Through P30 TgP23H pig retinas retain rod photoreceptors. Despite their presence, a rod isolated ffERG retinal response is absent. In contrast, AAV shRNA820/RHO820 injections induced a rod isolated ffERG response that did not diminish through 20 wpi in 8/11 eyes. We found a dose-response curve where ffERG rod-isolated b-wave amplitude scales with viral titer. The retinas retained rod photoreceptors that express normally localized rhodopsin. The photopic ffERG response of treated TgP23H retinas remains undiminished. Scotopic and photopic function are not altered in treated WT piglets (control) and retinal morphology also is unaffected.

Conclusions : Our results show that the AAV shRNA820/RHO820 reduces rod degeneration and induces rod function in the TgP23H swine model of human adRP. Combined with previously published results in a dog and mouse models of adRP, our data show that this allele independent approach should be useful for patients with any RHO-linked RP.

This is a 2020 ARVO Annual Meeting abstract.