Efficacy of anti-VEGF single-chain variable fragment AAV-based gene therapy in a laser-induced choroidal neovascularisation mouse model

Age-related macular degeneration (AMD) is a leading cause of vision loss in the elderly. Neovascular AMD (nAMD) is characterized by abnormal growth of new blood vessels from the choroid (choroidal neovascularization, CNV), with retinal pigment epithelium dysfunction leading to fluid leakage, bleeding, and central vision loss. nAMD is primarily driven by vascular endothelial growth factor (VEGF). Anti-VEGF therapies are widely used, with brolucizumab, a humanized monoclonal single-chain variable fragment (scFv) that inhibits VEGF, showing promise due to its high molar concentration and superior ability to dry the retina. However, concerns over retinal vasculitis have limited its clinical use. In this proof-of-principle study, we evaluated an AAV-delivered anti-VEGF scFv transgene derived from the brolucizumab sequence, packaged into two recombinant adeno-associated virus serotypes (rAAV6 and rAAV8), and delivered via subretinal injections in a laser-induced CNV mouse model. Leakage in 79 mice across seven groups was assessed by fundus fluorescein angiography. Compared with controls, AAV-treatment showed reduced leakage, particularly at week 9 (3.1% for rAAV6 and ∼10% for rAAV8 high doses), compared with controls (71.9%). Vector genomes were detectable by qPCR at 12 weeks, and electroretinography showed no obvious functional deficit. These findings support further evaluation of sustained AAV-mediated anti-VEGF delivery for nAMD.