Evaluation of EIAV Based Lentiviral Vectors Following Ocular Delivery in the Nonhuman Primate Model: Development of RetinoStat®

Abstract

Purpose: : RetinoStat® is a novel EIAV-based lentiviral vector under development for the treatment of neovascular AMD. This vector expresses the potent angiostatic proteins endostatin and angiostatin via the retinal pigment epithelial (RPE) specific VMD2 promoter which limits expression to the RPE cells following subretinal delivery. This approach has been previously shown to inhibit neovascularisation in rodent models of AMD and here we present preliminary work in the more clinically relevant non-human primate.

Methods: : Either an EIAV-CMVLacZ or an EIAV-VMD2LacZ vector was delivered as a single subretinal injection to the macula in the cynomolgus macaque. Control formulation buffer was delivered to the contralateral eye. Slit-lamp biomicroscopic and indirect ophthalmoscopic examinations were made regularly for 3 months. Additionally, multifocal electroretinography (mfERG) and optical coherence tomography (OCT) were evaluated at 2 months to assess retinal function and structure. X-Gal staining of whole eyes at the end of the study was used to determine the region of gene transfer and expression.

Results: : Treatment with both vectors and to a lesser extent the formulation buffer resulted in transient ocular inflammation that subsided over several weeks. mfERG indicated some depression of function and OCT showed some structural changes within the subretinal bleb sites of control and vector-treated eyes. Function and structure were preserved in extra-bleb retinal areas. X-Gal staining revealed widespread LacZ expression across the region of the bleb which persisted for the duration of the 3-month study and appeared restricted to the RPE cells using the EIAV-VMD2LacZ vector.

Conclusions: : Subretinal delivery of an EIAV vector in cynomolgus macaques resulted in expression in predominately RPE cells for at least 3 months. The inflammatory response tended to resolve over time. Delivery did not appear to impact on retinal integrity or function outside the bleb area and there were no mfERG or OCT findings within the bleb area that could clearly be attributed to the vectors in this preliminary study. mfERG and OCT may be informative techniques to incorporate in future toxicological studies. Further studies are in progress to support the transition to a human clinical study.

Keywords: gene transfer/gene therapy • age-related macular degeneration • retinal pigment epithelium