Atsena Therapeutics announced the completion of dosing across all adult and pediatric cohorts in Part B of its phase 1/2/3 LIGHTHOUSE clinical trial evaluating ATSN-201 for the treatment of X-linked retinoschisis (XLRS). The company expects to initiate enrollment of the pivotal phase 3 Part C cohort in the first quarter of 2026.

Part B of the multicenter study enrolled a total of 12 patients, including nine adults and three pediatric patients with XLRS. Adult participants were divided into low-volume, high-volume and control groups, while pediatric patients received the low-volume dose. Patients in the control arm will be observed for 1 year before having the option to receive treatment. In July 2025, the FDA agreed that the expanded study could serve as a pivotal trial.

“Given the significant unmet needs of patients of all ages with XLRS, we are proud to complete dosing in Part B of the LIGHTHOUSE trial, which includes pediatric and adult cohorts,” said Kenji Fujita, MD, chief medical officer of Atsena Therapeutics. “All three pediatric patients have been successfully dosed with ATSN-201 with no surgical complications. Preliminary safety data remain favorable, and no serious adverse events related to treatment have been reported. We look forward to building upon the encouraging structural and functional benefits reported in Part A of the study as we conduct follow-up for Part B and look ahead to the enrollment of Part C, the study’s pivotal cohort.”

Patrick Ritschel, MBA, CEO of Atsena Therapeutics, said the milestone brings the company closer to delivering the first approved therapy for XLRS. “We have alignment with the FDA on the design of the pivotal Part C cohort, and we look forward to beginning enrollment in the first quarter of 2026,” he said. “Results from this cohort will support a potential regulatory submission, bringing us one step closer to delivering the first ever approved therapy for XLRS.”

Part C of the LIGHTHOUSE trial will serve as the phase 3 pivotal portion of the study and is expected to enroll 56 adult and pediatric patients at US and international clinical sites. Participants will be randomized to either a treatment or control group. Patients receiving treatment will undergo unilateral or bilateral subretinal injection of ATSN-201, while those in the control group will be observed for 12 months before having the option to receive therapy. Data from Part C are intended to support a planned Biologics License Application (BLA), anticipated in early 2028.

XLRS is a rare, inherited retinal disease caused by mutations in the RS1 gene, leading to abnormal splitting of the retinal layers, impaired visual acuity and progressive vision loss. The condition primarily affects males and is typically diagnosed in early childhood. An estimated 30,000 males in the United States and European Union are affected, and there are currently no approved treatments.

ATSN-201 is an investigational gene therapy delivered via subretinal injection and utilizes AAV.SPR, a novel laterally spreading capsid designed to efficiently target photoreceptors in the central retina while reducing surgical risks. In earlier phases of the LIGHTHOUSE study, ATSN-201 demonstrated improvements in retinal structure and visual function, along with a favorable safety profile. The therapy has received Regenerative Medicine Advanced Therapy, Fast Track, Rare Pediatric Disease and Orphan Drug designations from the FDA.