The possibility of gene therapy for the treatment of choroidal neovascularization

Purpose: Choroidal neovascularization (CNV) is responsible for most cases o f severe visual loss in age-related macular degeneration. Recently, the pos sibility of gene therapy has been proposed for the treatment of CNV. The pu rpose of this study was to examine the feasibility of ex vivo and in situ g ene therapy approaches for CNV. Design: Experimental study. Methods: Human retinal pigment epithelial (RPE) cells were transduced with a retroviral vector coding for beta-galactosidase. Transduced cells were gr own on type II collagen sheets and transplanted under the retina of 20 rabb its. Animals were observed for 3 to 56 days, and transplanted cells were ex amined histologically and with X-gal staining. Bovine choroidal endothelial cells (CEC) were transduced with retroviral vectors coding for tissue inhi bitor of metalloproteinase-2 (TIMP-2) or control vector. Production of TIMP -2 by transduced cells was determined by immunohistochemical analysis and e nzyme-linked immunosorbent assay. Effect of transduction on in vitro prolif eration, migration, and tube formation was examined in response to vascular endothelial growth factor (VEGF). Four CNV lesions were induced in one cyn omolgus monkey by laser photocoagulation. Two days later, retroviral vector coding for TIMP-2 or control vector was injected into the subretinal space overlying the CNV lesions. The monkey was observed for 12 weeks using fluo rescein angiography. Results: Transplantation of transduced RPE cells was technically achieved i n 10 of 20 animals. In these animals, RPE cells at the site of transplantat ion formed a monolayer and expressed beta-galactosidase for 14 days. beta-G alactosidase-positive cells were not identified at 56 days. Choroidal endot helial cells transduced with TIMP-2 secrete TIMP-2 into the media and show decreased migration and tube formation in vitro. In the in vivo monkey mode l, the control CNV lesions (n = 2) showed prominent leakage, whereas the ex perimental lesions (n = 2) showed minimal hyperfluorescence. Conclusions: Retrovirally transduced RPE cells survive in the subretinal sp ace for at least 14 days and continue to express the gene product coded for by the vector. Choroidal endothelial cells retrovirally transduced for TIM P-2 produce TIMP-2 in vitro and show decreased angiogenic responses in vitr o in response to VEGF. A preliminary study attempting in situ delivery of T IMP-2 vector to CNV lesions in a monkey eye supports the feasibility of thi s approach and encourages further study. (C) 2000 by the American Academy o f Ophthalmology.