First patient dosed in phase 3 pivotal cohort of LIGHTHOUSE trial evaluating ATSN-201 for X-linked retinoschisis

Atsena Therapeutics has dosed the first patient in the Phase 3 pivotal cohort of the LIGHTHOUSE trial, advancing ATSN-201 into the registrational stage of development for X-linked retinoschisis (XLRS) and moving the program closer to what would be the first approved therapy for the disease.

The milestone follows the company's initiation of phase 3 enrollment, which was itself built on interim 6-month data from Part B of the study showing structural and functional improvements broadly consistent with earlier adult cohorts.¹ Atsena reported that, since enrollment opened in May 2026, it has already accrued approximately 10% of the pivotal cohort and expects the pace to accelerate as additional sites across North America and Europe are activated. The company is targeting completion of enrollment by the end of the first quarter of 2027, topline results in the first half of 2028, and a Biologics License Application (BLA) filing in the second half of 2028.

"Brisk enrollment of the study reflects the significant unmet need in XLRS, a disease for which no approved treatments exist, and strong interest from leading clinicians and patients who have been following ATSN-201's clinical progress," Kenji Fujita, MD, chief medical officer of Atsena, said in a press release. He added that the majority of treated patients in the Phase 1/2 portion of LIGHTHOUSE demonstrated closure of schisis cavities and improvements in retinal and visual function "at levels consistent with FDA approvability," with effects that have remained durable through at least one year of follow-up.

Patrick Ritschel, CEO of Atsena, framed the dosing as a defining moment for the company and the patient community, citing Phase 1/2 evidence that ATSN-201 can reverse structural retinal damage and meaningfully improve vision.

Trial design and current status

The pivotal portion of LIGHTHOUSE (NCT05878860) is enrolling 76 patients with XLRS, including adults and children as young as 6 years, across leading medical centers in North America and Europe. Participants are randomized approximately 1:1 to a treatment arm receiving ATSN-201 or a control arm that is observed for 12 months and then offered the option to receive treatment. The primary endpoint is change in microperimetry at 52 weeks—a measure the FDA has increasingly accepted for inherited retinal disease programs in which foveal function is at risk—aligned with both the FDA and the European Medicines Agency (EMA). Key secondary endpoints include visual acuity and optical coherence tomography (OCT)-based measures of retinal structure.

The pivotal cohort caps a development path that the FDA agreed in 2025 to compress into a single continuous phase 1/2/3 trial, allowing LIGHTHOUSE itself to serve as the registrational study supporting a BLA rather than requiring a separate phase 3 program.² ATSN-201 has received Regenerative Medicine Advanced Therapy, Fast Track, Rare Pediatric Disease, and Orphan Drug designations from the FDA, along with orphan designation from the EMA.^3,4

Disease background and unmet need

XLRS is a monogenic X-linked disease caused by mutations in the RS1 gene, which encodes retinoschisin, a protein secreted primarily by photoreceptors and localized to the extracellular surface of rods, cones, and bipolar cells. The disease is characterized by schisis—abnormal splitting of the retinal layers—that produces visual acuity loss uncorrectable with glasses and leads to progressive vision decline and, ultimately, blindness. XLRS primarily affects males, is typically diagnosed in early childhood, and affects an estimated 30,000 males in the United States and the European Union combined, with no approved treatments currently available.⁵

ATSN-201 leverages AAV.SPR, a novel laterally spreading capsid engineered to transduce photoreceptors in the central retina when injected outside the macula, thereby avoiding the surgical risks of foveal detachment. In non-human primate studies, the capsid promoted transgene expression well beyond subretinal injection bleb margins, in contrast to benchmark vectors that remain confined to the original bleb.

References

1. Filkins K. ATSN-201 advances to registrational trial for X-linked retinoschisis. Ophthalmology Times. May 6, 2026. https://www.ophthalmologytimes.com/view/atsn-201-advances-to-registrational-trial-for-x-linked-retinoschisis

2. Filkins K. LIGHTHOUSE study of ATSN-201 expanded to continuous phase 1/2/3 trial following FDA feedback. Ophthalmology Times. November 2025. https://www.ophthalmologytimes.com/view/lighthouse-study-of-atsn-201-expanded-to-continuous-phase-1-2-3-trial-following-fda-feedback

3. Hutton D. Atsena Therapeutics receives Orphan Drug Designation from FDA for ATSN-201 gene therapy to treat X-linked retinoschisis. Ophthalmology Times. May 2026. https://www.ophthalmologytimes.com/view/atsena-therapeutics-receives-orphan-drug-designation-from-fda-for-atsn-201-gene-therapy-to-treat-x-linked-retinoschisis

4. Hutton D. Atsena Therapeutics receives Pediatric Disease Designation from the FDA for ATSN-201 gene therapy to treat X-linked retinoschisis. Ophthalmology Times. April 2026. https://www.ophthalmologytimes.com/view/atsena-therapeutics-receives-pediatric-disease-designation-from-the-fda-for-atsn-201-gene-therapy-to-treat-x-linked-retinoschisis

5. Hutton D. Atsena Therapeutics doses first patient in Phase I/II clinical trial of ATSN-201 for treatment of X-linked retinoschisis. Ophthalmology Times. May 18, 2026. https://www.ophthalmologytimes.com/view/atsena-therapeutics-doses-first-patient-in-phase-i-ii-clinical-trial-of-atsn-201-for-treatment-of-x-linked-retinoschisis