Gene transfer by viral vectors into blood vessels in a rat model of retinopathy of prematurity

Aims - To test the feasibility of gene transfer into hyaloid blood vessels and into preretinal neovascularisation in a rat model of retinopathy of prematurity (ROP), using different viral vectors. Methods - Newborn rats were exposed to alternating hypoxic and hyperoxic conditions in order to induce ocular neovascularisation (ROP rats). Adenovirus, herpes simplex, vaccinia, and retroviral (MuLV based) vectors, all carrying the beta galactosidase (beta -gal) gene, were injected intravitreally on postnatal day IS (PIS). Two sets of controls were also examined: P18 ROP rats injected with saline and P18 rats that were raised in room air before the viral vectors or saline were injected. Two days after injection, the rats were killed, eyes enucleated, and beta -gal expression was examined by X-gal staining in whole mounts and in histological sections. Results - Intravitreal injection of the adenovirus and vaccinia vectors yielded marked beta -gal expression in hyaloid blood vessels in the rat ROP model. Retinal expression of beta -gal with these vectors was limited almost exclusively to the vicinity of the injection site. Injection of herpes simplex yielded a punctuate pattern of beta -gal expression in the retina but not in blood vessels. No significant beta -gal expression occurred in rat eyes injected with the retroviral vector. Conclusions - Adenovirus is an efficient vector for gene transfer into blood vessels in an animal model of ROP. This may be a first step towards utilising gene transfer as a tool for modulating ocular neovascularisation for experimental and therapeutic purposes.