Assessment of Visual Function With Cotoretigene Toliparvovec in X-Linked Retinitis Pigmentosa in the Randomized XIRIUS Phase 2/3 Study.

PURPOSE: Cotoretigene toliparvovec (BIIB112/AAV8-RPGR) is an investigational vector-based gene therapy designed to provide a full-length, codon-optimized, retinitis pigmentosa GTPase regulator (RPGR) protein to individuals with RPGR-associated X-linked retinitis pigmentosa (XLRP). We assessed efficacy and safety of cotoretigene toliparvovec subretinal gene therapy. DESIGN: Part 2 of the XIRIUS trial (NCT03116113) was a Phase 2/3, 12-month, randomized (1:1:1), dose-expansion study. PARTICIPANTS: Males aged ≥10 years with RPGR-associated XLRP were included. METHODS: Participants were randomized 1:1:1 to subretinal cotoretigene toliparvovec low dose (5 × 1010 vector genomes [vg]/eye), cotoretigene toliparvovec high dose (2.5 × 1011 vg/eye), or untreated control. MAIN OUTCOME MEASURES: The primary endpoint was the percentage of participants meeting microperimetry responder criteria (≥7 dB improvement at ≥5 of 16 central loci). Secondary endpoints included change from baseline in retinal sensitivity at the central 16 loci and the entire 68 loci at 12 months and change from baseline in low-luminance visual acuity (LLVA) at 12 months; and the proportion of eyes with a ≥15 and ≥10 LLVA ETDRS letter change from baseline at month 12. RESULTS: Because of the impact of COVID-19, enrollment ended before reaching the initial target, leaving the trial underpowered. Twenty-nine participants were included (low dose n=10, high dose n=10, control n=9). At month 12, the percentage of participants meeting microperimetry responder criteria was not significantly different between cotoretigene toliparvovec (low dose, 37.5%, P=0.3181; high dose, 25.0%, P=0.5177) and control (22.2%). Mean change from baseline in microperimetry sensitivity, however, significantly improved with the low dose versus control at month 12 (P=0.0350). Significant improvement in LLVA occurred with low dose versus control at month 12 (33.3% difference [80% CI, 14.7-55.2]; P=0.0498). Three ocular-related serious adverse events occurred in the low-dose group versus 7 in the high-dose group. CONCLUSIONS: The primary microperimetry endpoint was not met. Significant improvements in LLVA and mean microperimetry and fewer serious adverse events were observed with low-dose cotoretigene toliparvovec.