Retinal AAV8-RS1 Gene Therapy for X-Linked Retinoschisis: Initial Findings from a Phase I/IIa Trial by Intravitreal Delivery

Abstract

This study evaluated the safety and tolerability of ocular RS1 adeno-associated virus (AAV8-RS1) gene augmentation therapy to the retina of participants with X-linked retinoschisis (XLRS). XLRS is a monogenic trait affecting only males, caused by mutations in the RS1 gene. Retinoschisin protein is secreted principally in the outer retina, and its absence results in retinal cavities, synaptic dysfunction, reduced visual acuity, and susceptibility to retinal detachment. This phase I/IIa single-center, prospective, open-label, three-dose-escalation clinical trial administered vector to nine participants with pathogenic RS1 mutations. The eye of each participant with worse acuity (≤63 letters; Snellen 20/63) received the AAV8-RS1 gene vector by intravitreal injection. Three participants were assigned to each of three dosage groups: 1e9 vector genomes (vg)/eye, 1e10 vg/eye, and 1e11 vg/eye. The investigational product was generally well tolerated in all but one individual. Ocular events included dose-related inflammation that resolved with topical and oral corticosteroids. Systemic antibodies against AAV8 increased in a dose-related fashion, but no antibodies against RS1 were observed. Retinal cavities closed transiently in one participant. Additional doses and immunosuppressive regimens are being explored to pursue evidence of safety and efficacy (ClinicalTrials.gov: NCT02317887).

Keywords: AAV vector; X-linked retinoschisis; clinical trial; gene therapy; ocular disease; retinal disease.

Figure 1

Ocular Inflammation and AAV-Neutralizing Antibodies over 18 Months Figure shows level of inflammatory cells within the anterior chamber (AC, blue) or vitreous (orange) for each participant from baseline (time = 0) to 18 months. Cells were determined per the Standardization of Uveitis Nomenclature (SUN) criteria system. Neutralizing antibody titers to AAV8 are shown in gray. Only participant 4 had pre-existing NAb titer (1:160), whereas the remaining were <1:10. Bars at top show use and timing of systemic (yellow) or topical (light blue) immunosuppression (IS) for each participant. Asterisk indicates unable to take a reading from participant 9 at this time due to vitreous hemorrhage.

Figure 2

Change in Study Eye Acuity The change in best corrected visual acuity from the baseline value is shown for each participant over 18 months from baseline (time = 0). Participant 9 had decreased visual acuity at days 14 and 15 with onset of inflammation and subsequent recovery by months 3–6; just prior to the month 9 visit, his visual acuity dropped to −54 letters (data not shown on chart) due to vitreous hemorrhage, with subsequent recovery to baseline at 12 months.

Figure 3

Mean Retinal Sensitivities The change in mean sensitivities of MP1 testing, for the responding points (RPs) and the extra-scotomatous (ES) and para-scotomatous (PS) points from study eyes (upper panels) and fellow eyes (lower panels), are plotted as a function of time relative to baseline 2 (time = 0). For reference in interpreting the data, the dashed lines indicate the calculated limits of repeatability expected for XLRS subjects (see the Materials and Methods). The 2-dB change is cautionary for being a meaningful deviation from normal, based on our data (Jeffrey et al.¹³) and previous papers (Chen et al., Dimopoulos et al., Palkovits et al., Wong et al., Wong et al., and Wu et al.,⁴⁷) Raw data for all five MP1 sensitivity parameters are shown for both eyes of all participants in Figures S3–S5. See also Figure S1, which shows the variability of mean sensitivity of RPs relative to both baseline values.

Figure 4

ERGs over 18 Months for Participants Dark-adapted scotopic ERG amplitudes. Plots of changes in log ERG amplitudes over 18 months relative to the mean of the two baseline values (time = 0) for the study and the fellow eyes. Scotopic a-wave amplitudes were measured from the a-wave trough to b-wave peak for flash stimulus of 3 cd/m² (DA3). The dashed lines indicate the calculated limits of repeatability expected for XLRS subjects (see the Materials and Methods). The solid black line represents participant 9 ERG amplitudes. Scotopic ERG (b-wave:a-wave) amplitude ratios. Plots show change in ERG (b-wave:a-wave) ratio relative to the mean of two baseline (time = 0) values. ERG b-wave amplitude was measured from the a-wave trough to the response amplitude at 47 ms (see the Materials and Methods). The solid black line represents participant 9 ERG (b-wave:a-wave) ratios.

Figure 5

Change in OCT CMT Relative to Baseline Quantitative analysis of retinal thickness was evaluated in the central macula using the ETDRS 1-mm circle, and the percent change in CMT was calculated from the mean baseline values, for examinations over 18 months from dosing, as described in the Materials and Methods. The dashed lines represent the expected repeatability for XLRS subjects (see the Materials and Methods). Data from participants 1–3 varied minimally (range 0%–6.5%) and are not depicted so as not to obscure the remaining data points.

Figure 6

OCT Image of Retinal Macular Schisis Cavities in Participant 9 at Baseline and 2 Weeks after Vector Administration Macular OCT image of participant 9 through center of fovea at pre-vector baseline shows parafoveal scarring and shallow honeycomb distribution of schisis cavities, which extended for 360 degrees across the macula and were localized to the inner nuclear layer of both eyes. 2 weeks after dosing with AAV8-RS1 at 1e11 vg/eye, the injected eye showed complete closure of the schisis cavities, whereas the cavities persisted in the untreated fellow eye.