ABBV-RGX-314 is being developed as a novel, potential one-time gene therapy treatment for the treatment of Diabetic Retinopathy (DR) with and without Center-Involved Diabetic Macular Edema (CI-DME). DR is a chronic and progressive complication of diabetes mellitus. It is a sight-threatening disease characterized in the early stages by neuronal and vascular dysfunction in the retina, and later by neovascularization that leads to further deterioration of functional vision. Despite the availability of current treatments, diabetic retinopathy remains the leading cause of vision loss in working-age adults, those between the ages of 20 and 74. Existing treatment with anti-VEGF agents, although shown to be effective, are limited by short therapeutic half-lives, which then require frequent intravitreal injections over the patient's lifetime, resulting in increased risk of associated adverse events and significant treatment burden. Due to the burden of treatment, patients often do not closely adhere to treatment regimens and experience sub-optimal outcomes and a decline in vision.

This phase 2, randomized, dose-escalation study is designed to evaluate the efficacy, safety and tolerability of ABBV-RGX-314 gene therapy in subjects with DR with and without center-involved diabetic macular edema (CI-DME).

Part 1: For subjects with DR without CI-DME, approximately 100 participants who meet the inclusion/exclusion criteria will be enrolled into one of 5 cohorts. Participants will be randomized in Cohorts 1, 2, 4 and 5 to receive ABBV-RGX-314 or to be observed, and participants enrolled in Cohort 3 will receive ABBV-RGX-314. Cohort 1 will evaluate ABBV-RGX-314 Dose 1, Cohorts 2 and 3 will evaluate ABBV-RGX-314 Dose 2, and Cohorts 4 and 5 will evaluate ABBV-RGX-314 Dose 3. Following SCS ABBV-RGX-314 administration, participants in Cohorts 4 and 5 will receive a protocol-mandated post-procedure steroid regimen for 7 weeks. Participants who are randomized to be observed in Cohorts 1, 2, 4 and 5 will be offered ABBV-RGX-314 after completing the study.

Part 2: For subjects with DR with CI-DME, approximately 30 participants who meet the inclusion/exclusion criteria will be enrolled into one cohort (Cohort A). Participants will be randomized to receive ABBV-RGX-314 or Aflibercept Control. Cohort A will evaluate ABBV-RGX-314 Dose 4. Participants randomized to receive SCS ABBV-RGX-314 will receive a protocol-mandated course of steroid. Participants who are randomized to the Aflibercept Control arm will be offered ABBV-RGX-314 after completing the study.

Part 1 (DR without CI-DME):

Inclusion Criteria:

• Patients 25-89 years of age with a diabetic retinopathy (DR) diagnosis of nonproliferative diabetic retinopathy (NPDR) and proliferative diabetic retinopathy (PDR) secondary to diabetes mellitus Type 1 or 2 for which PRP or anti-VEGF injections can be safely deferred for at least 6 months
• HbA1c < 12%.
• Best corrected visual acuity (BCVA) Early Treatment Diabetic Retinopathy Study (ETDRS) letter score in the study eye of ≥69 letters (approximate Snellen equivalent of 20/40 or better).
• Prior history of CI-DME in the study eye is acceptable.
• Must be willing and able to provide written, signed informed consent.

Exclusion Criteria:

• Neovascularization in the study eye from a cause other than DR.
• Presence of any active CI-DME.
• Active or history of retinal detachment in the study eye.
• Any evidence or documented history of PRP or retinal laser in the study eye.
• Patients who had a prior vitrectomy surgery.
• Women of childbearing potential.

Part 2 (DR with CI-DME):

Inclusion Criteria:

• Patients 25-89 years of age with diabetic retinopathy secondary to diabetes mellitus Type 1 or 2.
• HbA1c < 12%
• Macular thickening secondary to DME involving the center of the fovea, CST on SD-OCT (≥ 325 μm)
• Best corrected visual acuity (BCVA) Early Treatment Diabetic Retinopathy Study (ETDRS) letter score in the study eye of 78-25 letters (approximate Snellen equivalent of 20/32 to 20/320)
• Participants must have demonstrated a meaningful response to anti-VEGF therapy.
• Must be willing and able to provide written, signed informed consent

Exclusion Criteria:

• Neovascularization in the study eye from a cause other than DR.
• Active or history of retinal detachment in the study eye.
• Any evidence or documented history of PRP or retinal laser in the study eye.
• Patients who had a prior vitrectomy surgery.
• Women of childbearing potential.

Note: Other inclusions/exclusions criteria apply.