The new analysis, led by Kai-Yang Chen of Chang Gung Memorial Hospital in Taiwan, together with Hoi-Chun Chan of China Medical University and Chi-Ming Chan of Cardinal Tien Hospital and Fu Jen Catholic University, was prospectively registered with PROSPERO and conducted according to the PRISMA 2020 reporting guidelines. The team searched PubMed, Scopus, Web of Science, ScienceDirect, and the Cochrane Library from inception through April 21, 2026, screening more than 1,200 records to identify 25 eligible studies spanning in vitro experiments, animal models, and early- to late-phase human trials.

The biological rationale is compelling. Diabetic retinopathy alone affects approximately 22 percent of people with diabetes, roughly 103 million adults as of 2020, and is projected to reach 160 million by 2045. Neovascular age-related macular degeneration shares a common final pathway: VEGF-driven pathological angiogenesis and breakdown of the blood-retinal barrier, producing macular edema, capillary nonperfusion, and progressive retinal damage. Current anti-VEGF injections suppress these processes only transiently, requiring repeated administration and carrying procedural risks including endophthalmitis, elevated intraocular pressure, and cataract. Gene therapy, typically delivered via adeno-associated viral (AAV) vectors, aims to turn the eye itself into a factory for therapeutic proteins, achieving sustained pathway-level disease control after a single procedure.

The preclinical results are striking. Across eight animal and in vitro studies, gene therapy significantly reduced pathological neovascularization, with a pooled standardized mean difference of −1.16 (95 percent confidence interval, −1.48 to −0.84; p < 0.001), meaning the reduction exceeded one full standard deviation compared with controls. Remarkably, heterogeneity was negligible, with an I² of 0 percent, indicating extraordinary consistency despite differences in vector platforms, transgenes, and disease models. Within the oxygen-induced retinopathy subgroup, the effect was even larger, with a standardized mean difference of approximately −1.29, reflecting robust suppression of ischemia-driven retinal angiogenesis by constructs including soluble VEGF receptor sFLT-1, pigment epithelium-derived factor (PEDF), angiostatin, and the antioxidant enzyme MnSOD.

Vascular leakage, the other hallmark of these diseases, was also significantly reduced. Three preclinical experimental studies using AAV- and adenovirus-mediated gene transfer showed a pooled mean difference of 0.215 on a directionally harmonized scale (95 percent CI, 0.178 to 0.251; p < 0.001), again with zero heterogeneity. Complementary mechanistic work showed that sFLT-1 expression reduced VEGF-induced endothelial permeability by roughly 40 to 60 percent while preserving tight junction proteins, and antioxidant gene transfer reduced oxidative stress-driven barrier breakdown. In vivo, fluorescein leakage scores fell by 30 to 70 percent following anti-VEGF or PEDF gene delivery, while antioxidant therapy reduced acellular capillaries by approximately 40 to 60 percent, indicating preservation of the retinal microvasculature beyond angiogenesis alone.

The clinical evidence, though still early-stage, points in the same direction. Across eight clinical cohorts, ocular gene therapy produced a statistically significant reduction in central subfield thickness of −55.30 micrometers (95 percent CI, −72.58 to −38.03; p < 0.001), a meaningful anatomical improvement reflecting reduced macular edema and fluid accumulation. In the phase 1 trial of intravitreal AAV2-sFLT01 reported by Heier and colleagues, individual eyes showed central thickness reductions of up to roughly 600 micrometers at week 18 and 860 micrometers by week 52, while the phase 2a trial of subretinal rAAV.sFLT-1 by Constable and colleagues demonstrated stabilization of retinal thickness over 52 weeks.

Perhaps the most clinically consequential finding concerns treatment burden. Across seven clinical cohorts, the pooled logit event rate of 0.62 (95 percent CI, 0.20 to 1.04; p = 0.0039) corresponds to approximately 65 percent of participants meeting study-specific criteria for reduced supplemental anti-VEGF injections after gene therapy. Heterogeneity was low, at roughly 11 percent, despite differences between AAV and lentiviral platforms, delivery routes, and dosing regimens. This outcome directly addresses the central weakness of current standard care: the cumulative burden and adherence challenges of repeated intravitreal injections.

The analysis also situates these findings within a rapidly advancing clinical pipeline. Next-generation programs including ABBV-RGX-314, ADVM-022 (ixo-vec), and 4D-150 have progressed into phase II/III trials for neovascular retinal diseases, with early data showing reductions in anti-VEGF injection burden of up to 80 to 97 percent alongside stable visual and anatomical outcomes. Notably, 4D-150 employs dual inhibition of VEGF-A and VEGF-C, an evolution beyond earlier single-target constructs, while ADVM-022 offers intravitreal delivery that avoids surgery, and RGX-314 has shown durability across both subretinal and suprachoroidal routes. The concordance between these emerging results and the meta-analysis findings reinforces the biological validity of sustained intraocular VEGF suppression.

The authors are careful to acknowledge limitations. Some functional outcomes were drawn from trials of non-angiogenic inherited retinal disorders, including Leber hereditary optic neuropathy, RPE65-associated Leber congenital amaurosis, and X-linked retinitis pigmentosa, and were interpreted as proof of concept for gene delivery and durability rather than anti-angiogenic efficacy. The XIRIUS phase 2/3 trial of cotoretigene toliparvovec in X-linked retinitis pigmentosa, for example, missed its primary endpoint, underscoring the importance of disease context, dose selection, and intervention timing. Animal models, meanwhile, do not fully reproduce the chronic metabolic milieu of human diabetic retinopathy. Publication bias analyses were largely reassuring, though small-study effects were flagged for central subfield thickness and injection burden outcomes, and trim-and-fill sensitivity analyses supported the robustness of the primary estimates.

Safety data across translational stages suggest an acceptable early profile, with adverse events largely procedure-related or reflecting transient ocular inflammation. However, the authors caution that limited sample sizes, heterogeneous reporting, and incomplete long-term follow-up constrain safety conclusions, particularly given the potential irreversibility of ocular gene transfer. The path forward, they argue, requires adequately powered, disease-specific randomized trials, standardized outcome definitions, harmonized optical coherence tomography metrics, and long-term surveillance of transgene durability and immunogenicity. If those trials confirm the signals synthesized here, ocular gene therapy could shift the treatment of neovascular retinal disease from a lifetime of monthly injections toward long-acting or single-administration therapy, fundamentally changing the outlook for the hundreds of millions at risk of preventable vision loss worldwide.

Subject of Research: Ocular gene therapy targeting retinal angiogenesis and vascular leakage in neovascular retinal diseases

Article Title: Ocular gene therapy targeting retinal angiogenesis and vascular leakage: translational and clinical evidence from a systematic review and meta-analysis

Article References: Ocular gene therapy targeting retinal angiogenesis and vascular leakage: translational and clinical evidence from a systematic review and meta-analysis. (n.d.). https://doi.org/10.1007/s10456-026-10050-y

Image Credits: AI Generated

DOI: 10.1007/s10456-026-10050-y

Keywords: ocular gene therapy, retinal angiogenesis, vascular leakage, anti-VEGF, adeno-associated virus, neovascular age-related macular degeneration, diabetic retinopathy, systematic review, meta-analysis, sFLT-1, central subfield thickness, retinal disease