Genetic testing helps researchers find markers or variants in your DNA. If you do not have recently confirmed genetic confirmation of the RPGR genetic variant from a sponsor approved lab, during screening for this study, study staff will collect DNA from you through a saliva sample to test for the RPGR gene variant. Eligible participants must have the RPGR variation associated with XLRP to take part in this study. If genetic testing has been completed previously, those results may be used if done by a sponsor-approved laboratory.

Gene therapy delivers a copy of a healthy gene to try to help certain conditions. The investigational gene therapy in the LUMEOS study involves surgery to deliver a healthy RPGR gene in participants with XLRP-RPGR.

The surgery in this study is an outpatient surgery, takes about 1 hour, and is a standard technique for many different conditions. You will have surgery on your worse-seeing eye first, then on your other eye 7 to 21 days later. Study staff will provide instructions before and after surgery. You will not be able to travel home by yourself the day of surgery.

Participants will receive all study-related procedures, assessments, and the investigational gene therapy at no cost. Travel assistance will be available. However, you will not be paid to participate in the study.

There are possible risks involved with any clinical research study. Your study doctor will review the risks with potential participants, and all participants will be closely monitored throughout the study.

• All participants will receive the investigational gene therapy, which is the study treatment given during surgery.
• Following an optional prescreening period up to 12 months before screening and a screening period lasting up to 6 months, eligible participants will be enrolled in the study and randomly assigned (like drawing straws) to dosing assignment and immediate study treatment group or delayed study treatment group.
• Participants in both study treatment groups will undergo two surgeries for the investigational gene therapy: first in their worse-seeing eye, then in their other eye 7 to 21 days later. The surgery is an injection of the investigational gene therapy to the back of the eye (retina).
• Both groups will be monitored during a long-term follow-up phase.
• Lab tests, a physical exam, and other assessments and questionnaires will be conducted at the study visits.
• Not all activities will occur at every visit