A Preclinical Safety Study of Simian Immunodeficiency Virus (SIV)–Based Lentivirus Vector for Retinal Gene Transfer in Non–Human Primates

Abstract

Abstract: : Purpose: Recently, we have demonstrated the efficient and stable retinal gene transfer mediated by the non–pathogenic simian immunodeficiency virus (SIV)–based lentivirus vector as well as the therapeutic outcome in some animal models of retinal degeneration using recombinant SIV vectors carrying neurotrophic factors, such as pigment epithelium–derived factor (PEDF) and fibroblast growth factor–2 (FGF–2). Here, we report the acute ophthalmic toxicity following intraocular administration of SIV–PEDF in Macaca fascicularis, as a preclinical safety study. Methods: Eleven Macaca fascicularis (body weight=2.35–5.63 kg) were enrolled in this study. Approximately 20 µl of SIV–PEDF (low titer: 2.5x10⁷ transducing units [TU]/ml, equal to clinically available titer, high titer: 2.5x10⁸ TU/ml, and max titer: 1.0x10⁹ TU/ml, n=3, respectively) or control (balanced salt solution: BSS, n=2) were injected into subretinal space via a glass capillary tube. We undertook an ophthalmic examination including slitlamp biomicroscopy, intraocular pressure (IOP) measurement, fundoscopic examination, and fluorescein anigiography, and assessed transgene expression, retinal function with electroretinogram (ERG) and histology for 3 months. Results: SIV vector was efficiently transferred mainly to the retinal pigment epithelium and transgene expression was detected within 3 months. Transient inflammatory cell infiltration to anterior ocular segment and elevation of IOP were observed in some animals, but not dose–dependent. ERGs including multi–focal ERGs revealed no remarkable change of the retinal functions. Retinas treated with both SIV–PEDF and BSS histologically showed no significant inflammatory infiltration and retinal structural destruction. Conclusions: The current study indicated the acute local safety of intraocular administration of SIV–PEDF, even if it was used at 40–times higher titer than clinical available titer. We are now conducting the long–term safety study in non–human primates.

Keywords: gene transfer/gene therapy • retinal degenerations: cell biology • neuroprotection