Prolonged Gene Expression in Non–Human Primate Retina Using Recombinant Sivagm–Based Lentiviral Vectors

Abstract

Purpose: : Previously, we reported the simian immunodeficiency virus from African green monkey (SIVagm)–mediated efficient gene transfer and therapeutic effects for retinal degeneration in rodents. We now make arrangements for a clinical application to treat retinitis pigmentosa. Thus, it is important to evaluate exactly the efficiency and safety issues for a gene transfer vector itself using large animals. In this study, we have evaluated the ability of our 3rd generation SIVagm vectors to transfer genes into non–human primate retinas as a preclinical study.

Methods: : Five Macaca fascicularis were enrolled in this study. Approximately 20 µl of SIV–GFP (green fluorescent protein) (low titer: 2.5x10⁷ transducing units [TU]/ml, equal to clinically available titer, n=2) or SIV–hPEDF (human pigment epithelium–derived factor) (low titer, high titer: 2.5x10⁸ TU/ml, and max titer: 1.0x10⁹ TU/ml, n=1, respectively) were injected into subretinal space via a glass capillary tube. To detect GFP expression in the retina, we used a fluorescence fundus camera at various time–points after gene transfer (days 14, 28, 90, 180, 270, 360, and 540). Human PEDF expression was assessed with the immunohistochemical analysis for the retinal tissue treated with SIV–hPEDF on day 50.

Results: : The retinas demonstrated a frequent GFP expression that preserved at least for 540 days without significant decline. In all SIV–hPEDF treated eyes, human PEDF expression was detected in retinal pigment epithelium and the layer of rods and cones of retina. There was no remarkable inflammatory cell infiltration in retinal tissue treated with a max titer of SIV–hPEDF on day 50.

Conclusions: : We thus propose that SIVagm–mediated stable gene transfer might be useful for ocular gene transfer in a clinical setting. We are now conducting the safety study in non–human primates.

Keywords: gene transfer/gene therapy • retinal degenerations: cell biology • retinal pigment epithelium