Modelling RPE65 and RPGR retinal gene therapy in non-human primates: (I) RPE changes following subretinal viral vector administration

Abstract

Purpose : Dose-related retinal inflammation has been observed in patients receiving voretigene neparvovec (Luxturna) for RPE65 Leber congenital amaurosis and cotoretigene toliparvovec for RPGR X-linked retinitis pigmentosa. We model retinal gene therapy in non-human primates (NHPs) to investigate the mechanism of retinal inflammation and its prevention.

Methods : 25G vitrectomy and OCT-guided subretinal injection of AAV vectors were performed in four eyes of two NHPs as per human gene therapy. NHP1 received 1.5x10¹¹ vg Luxturna (AAV2-CAG-RPE65) in two blebs in each eye. NHP2 received 1.25x10¹¹ gp AAV8-GRK1-RPGR and 2.5x10¹⁰ gp of a ‘shadow’ reporter vector, AAV8-GRK1-mScarlet, in two separate blebs. Thus, all eyes received equivalent to the recommended therapeutic dose as Luxturna. At the end of surgery, subtenon injection of 1mg triamcinolone was given to each eye. Left eyes also received intravitreal anti-TNFα (1.5mg adalimumab) at time of surgery and 4 weekly thereafter. No systemic immunosuppression was given. Serial multimodal retinal imaging, ERG, ophthalmoscopy, blood sampling and vitreous biopsies were performed over 3 months.

Results : Vision recovery following gene therapy was uneventful except for transient photophobia in NHP2. Subretinal blebs resolved by 2 weeks. No clinical uveitis or changes in retinal function were detectable by latest follow-up (6 weeks). Small areas of hypo-autofluorescence (AF) appear around the retinotomy sites and perimeter of blebs at 2 weeks, which became more diffuse at 6 weeks. In one Luxturna treated eye where a superior bleb fused with a temporal bleb, marked hypo-AF changes developed in the area of overlap correlating with outer retinal hyperreflective foci on OCT. In one shadow vector-treated bleb area, concentric crescentic hypo-AF areas could be seen inferior to the retinotomy.

Conclusions : Subretinal injection of AAV2 or AAV8 with ubiquitous or photoreceptor-specific promoter at current recommended clinical dose in NHPs can cause RPE changes and subretinal infiltration within bleb areas. Their distribution is suggestive of localised retinal inflammation at sites of maximal vector particle deposition related to the retinotomy, gravity and pattern of subretinal fluid resorption by RPE pump. Further investigation will explore the mechanism of retinal inflammation and effects of anti-TNFα treatment.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.