Restoration of retinal function and structure in an Rpe65-deficient murine model via AAV9-mediated gene replacement therapy

Abstract

Purpose : Mutations in RPE65 block the visual cycle, resulting in a congenitally inadequate supply of chromophore to both rod- and cone-photoreceptors. HG004 is a recombinant adeno-associated virus serotype 9 (rAAV9)-based gene therapy vector containing human RPE65 gene expression cassette. This study aimed to evaluate the efficacy of HG004 in a Rpe65-deficient murine model after a single subretinal injection.

Methods : To select AAV serotype, either AAV9-orAAV2-hRPE65 was administrated in 1-month-old Rpe65^-/- mice and the restoration of retinal function was detected by electroretinography (ERG). To evaluate the efficacy of HG004, 6-week-old Rpe65^-/- mice and Rpe65^+/+ control mice (n≥5 per group) underwent unilateral subretinal injection of either HG004 (AAV9-mediated hRPE65 expression) or vehicle control. Scotopic ERG was conducted to identify any improvement in retinal function from week 3 to 34 after injection followed by retinal optical coherence tomography (OCT) imaging that measured retinal sublayer thickness. Retinal structure was assessed by histological analysis at week 35 post-injection.

Results : In Rpe65^-/- mice, AAV9-hRPE65 showed higher efficacy than AAV2-hRPE65 expression (Fig. 1). Therefore, AAV9 has been chosen to further development of HG004. After HG004 administration, scotopic b-wave responses in all treated groups were recovered at all time points, compared with vehicle-injected control eyes of Rpe65^-/- mice (p<0.01) (Fig. 2). At 8.5-months post-injection, HG004 not only significantly preserved photoreceptor layer thickness in the treated retina compared with that in untreated eyes in Rpe65^-/- mice (p<0.01), but also prevented the photoreceptor outer segments discs structure from disorganizing (Fig. 2).

Conclusions : These data provide proof-of-principle of the efficacy of HG004 in a murine model of RPE65-associated retinal degeneration. HG004 significantly restored the function of RPE cells and photoreceptor cells and maintained the integrity of retinal structure. Furthermore, the durability of the therapeutic effect maintains for at least 34 weeks in Rpe65^-/- mice. These results strongly support the hypothesis that HG004 may provide benefits to RPE65 mutated patients. A follow-on clinical trial is warranted.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.

 

Scotopic ERG responses of Rpe65^-/- mice after injection of AAV9- or AAV2-hRPE65

 

The restoration of retina function and structure after HG004 treatment