Atsena Therapeutics Completes Phase I/II Dosing for XLRS Gene Therapy, Advances to Pivotal Trial
Key Insights
Atsena Therapeutics (search) has completed dosing in Part B of the LIGHTHOUSE trial for ATSN-201, a gene therapy treating X-linked retinoschisis (search), with no serious adverse events reported.
The company plans to initiate enrollment of the pivotal Part C cohort in Q1 2026, which will evaluate 56 adult and pediatric patients across treatment and control groups.
ATSN-201 represents the first XLRS (search) gene therapy to demonstrate efficacy in clinical trials, with patients showing improvements in retinal structure and visual function.
Atsena Therapeutics (search) announced the completion of dosing across all adult and pediatric cohorts in Part B of its Phase I/II/III LIGHTHOUSE trial evaluating ATSN-201, an investigational gene therapy for X-linked retinoschisis (search) (XLRS (search)). The clinical-stage gene therapy company plans to begin enrollment of the pivotal Part C cohort in the first quarter of 2026, with a Biologics License Application (BLA) submission targeted for early 2028.
Favorable Safety Profile Maintained Across Patient Populations
Part B of the multicenter study evaluated nine adults and three pediatric patients with XLRS (search). All three pediatric patients were successfully dosed with ATSN-201 with no surgical complications reported. According to Dr. Kenji Fujita, Chief Medical Officer of Atsena Therapeutics (search), "Preliminary safety data remain favorable, and no serious adverse events related to treatment have been reported."
The adult cohorts were divided into three groups: low volume, high volume, and control. Patients in the control group are observed off therapy for one year before having the option to receive treatment. Pediatric patients received the low-volume dosing regimen.
Pivotal Phase III Trial Design Approved by FDA
The FDA agreed in July 2025 to expand the study to serve as a pivotal trial. Part C will function as the Phase III portion, evaluating 56 adult and pediatric patients with XLRS (search) at leading U.S. and international clinical sites. Patients will be randomized into treatment and control groups, with the treatment group receiving bilateral or unilateral ATSN-201 administration. Control group patients will be observed for 12 months before having the option to receive treatment.
"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," said Patrick Ritschel, CEO of Atsena Therapeutics (search). "Results from this cohort will support a potential regulatory submission, bringing us one step closer to delivering the first ever approved therapy for XLRS (search)."
First-in-Class Therapy for Rare Genetic Condition
XLRS (search) is a monogenic X-linked disease caused by mutations in the RS1 (search) gene, which encodes retinoschisin (search), a protein secreted primarily by photoreceptors. The condition is characterized by schisis, or abnormal splitting of retinal layers, causing impaired visual acuity that cannot be corrected with glasses and leads to progressive vision loss and ultimately blindness. XLRS primarily affects males and is typically diagnosed in early childhood, with approximately 30,000 males in the U.S. and EU affected by the condition. Currently, no approved treatments exist for XLRS.
Novel AAV Technology Shows Clinical Promise
ATSN-201 leverages AAV.SPR (search), a novel, laterally spreading capsid designed to efficiently target photoreceptors in the central retina while avoiding surgical risks of foveal detachment. The therapy represents the first XLRS (search) gene therapy to demonstrate efficacy and positive safety data in a Phase I/II trial.
Clinical results show that the majority of patients demonstrated improvements in retinal structure, specifically foveal schisis closure, and meaningful improvements in retinal and visual function as assessed by microperimetry, best-corrected visual acuity, and low-luminance visual acuity. The therapy has maintained a favorable safety profile and has been well-tolerated for at least one year post-treatment with no serious adverse events reported to date.
Regulatory Recognition and Market Position
ATSN-201 has received multiple FDA designations, including Regenerative Medicine Advanced Therapy, Fast Track, Rare Pediatric Disease, and Orphan Drug Designations. If approved, ATSN-201 would become the first gene therapy approved for XLRS (search) treatment.
The AAV.SPR (search) capsid technology differentiates ATSN-201 from other approaches by spreading laterally beyond the subretinal injection site. Preclinical studies in non-human primates demonstrated that AAV.SPR promotes transgene expression well beyond subretinal injection bleb margins, contrasting with benchmark AAV vectors that remain confined to original bleb margins. At clinically relevant doses, AAV.SPR efficiently transduces foveal cones without requiring surgical detachment and demonstrates a favorable safety profile relative to benchmark capsids.