Phase 2 randomized, active-controlled, double-masked, dose-ranging trial in adults with Diabetic Macular Edema (DME).

This Phase 2 trial is a prospective, multicenter, randomized, active-controlled, double-masked dose-ranging trial to evaluate the safety and efficacy of 4D-150 in adults with DME. The trial will be conducted in two parts: Dose Confirmation and Dose Expansion.

Inclusion Criteria:

• ≥18 years of age
• Type I or Type II diabetes mellitus with macular thickening secondary to DME involving the center of the fovea; diagnosis of DME must be within 2 years of Screening
• CST ≥ 350 μm (Spectralis SD-OCT) in the study eye at Screening, confirmed by the independent reading center
• Demonstrate clinical response to on-study aflibercept injection in the study eye.
• Decreased visual acuity attributable primarily to DME
• BCVA in the study eye between 25 and 83 ETDRS letters, inclusive (~20/320 and 20/25, respectively) at Screening
• Study eye amenable to IVT injection
• Sufficient clear ocular media, pupil dilation and fixation in the study eye to permit adequate imaging; ability to perform tests of visual and retinal function and structure; and ability to comply with other protocol-specified procedures
• Provide written informed consent

Exclusion Criteria:

• Macular edema in the study eye considered to be secondary to a cause other than DME
• Systemic anti-VEGF treatment (e.g. sunitinib, bevacizumab, pazopanib) within 6 months, or anticipated need for systemic anti-VEGF therapy during study participation
• Systemic corticosteroids (oral, intravenous, intramuscular, intra-articular) or other immunosuppressive medications within 3 months
• Received an investigational drug, agent, device, or therapy (ocular or non-ocular) in the 3 months (or at least 5 half-lives, whichever is longer) prior to 4D-150 administration (Day 1)
• Prior gene therapy (ocular or non-ocular) and/or ocular stem cell therapy in either eye
• Any concurrent ocular condition in the study eye that is likely to require surgical intervention (e.g. cataract surgery) during the 2 year (104 week) study duration

Note: Other inclusion/exclusion criteria apply.

No masking in Dose Confirmation (Part 1). In Dose Expansion (Part 2), participants and outcomes assessors will be masked to the treatment arm for the duration of the trial.