Toleration of SubRetinal Delivered EIAV-Based RetinoStat® in the Rodent, Rabbit and Nonhuman Primate

Abstract

Purpose: : We are currently developing a range of novel equine infectious anemia virus (EIAV)-based lentiviral vectors, for the treatment of a number of retinal disorders including age-related macular degeneration. One of these vector therapies, called RetinoStat^®, expresses the potent angiostatic proteins endostatin and angiostatin via the retinal pigment epithelial (RPE) specific VMD2 promoter thereby limiting expression to the RPE following subretinal delivery. Key to success of these vector-based therapies is the successful delivery of therapeutic genes to target cells with acceptable ocular tolerance. We have examined vector delivery and ocular tolerance in a number of species to help predict effects that may be observed in human patients in clinical trials.

Methods: : EIAV VMD2 LacZ vector was examined in mice, rabbits or cynomolgus macaques following subretinal delivery. The region of gene transfer and expression was determined by X-Gal staining of whole eyes at the end of the study. Slit-lamp biomicroscopic and indirect ophthalmoscopic examinations were used to examine ocular tolerance in rabbits and non-human primates (NHP), and multi-focal electroretinography (mfERG) and optical coherence tomography (OCT) were evaluated as potential techniques to assess impact on retinal function and structure.

Results: : Using a vector with the VMD2 promoter demonstrated that LacZ staining was confined to RPE cells and long term studies in mice demonstrated gene persistence for up to 1 yr. Ocular examinations in NHP and rabbits demonstrated dose-dependent transient ocular inflammation that resolved in subsequent weeks. mfERG and OCT measurements in the NHP indicated that there were no significant pathophysiological changes associated with subretinal injections on the retinal function or structure up to 2 months post injection.

Conclusions: : Subretinal delivery of EIAV VMD2 LacZ vector in mice, rabbits and in NHPs leads to predominant expression of the reporter gene in RPE cells. Ocular tolerance to the vector is dose- and time-dependent with modest dilutions of the maximal feasible manufactured doses being well tolerated in all species. mfERG and OCT may be informative techniques to incorporate in future studies.

Keywords: drug toxicity/drug effects • gene transfer/gene therapy • age-related macular degeneration