Purpose: The transfer of exogenous genes to the entire retina and other ocular structures is possible with a vascular route of gene delivery using a non-viral gene transfer method. The present studies examine the extent to which either beta-galactosidase or luciferase expression plasmids are targeted to the retina in the adult rhesus monkey following intravenous administration. In addition, these studies examine the pattern of organ expression of the transgene in the rhesus monkey depending on whether the plasmid is under the influence of a widely expressed promoter, the SV40 promoter, or an ocular-specific promoter, the opsin promoter.
Methods: The plasmid DNA with either the SV40 or opsin promoter is encapsulated in the interior of 85 nm pegylated immunoliposomes (PILs), which are targeted across the blood-retinal barrier and into ocular cells with a monoclonal antibody to the human insulin receptor. Following a single intravenous injection of the PIL carrying the transgene, the animals were sacrificed 2, 7, or 14 days later for the measurement of beta-galactosidase or luciferase gene expression in the monkey eye and peripheral organs.
Results: Histochemistry showed expression of the beta-galactosidase gene throughout the entire primate retina including the photoreceptor cells with either an SV40 or a bovine opsin promoter. Whereas the SV40 promoter enables gene expression in other organs of the primate (brain, liver, spleen), the opsin promoter restricted trans-gene expression to the primate eye, as there was no gene expressed in other organs. The retinal luciferase activity at 2 days after administration was 9.6+/-0.4 pg luciferase/mg protein, and at 14 days after administration was still comparable to maximal levels of luciferase gene expression in the mouse or rat. Confocal microscopy with antibodies to the insulin receptor and to beta-galactosidase demonstrated co-localization in the retina, with high expression of the trans-gene and the insulin receptor in the inner segments of the photoreceptor cells.
Conclusions: The PIL non-viral gene transfer technology makes possible adult transgenics in 24 h. Ectopic expression of exogenous genes in organs other than the target organ is made possible with the use of organ specific promoters, and gene expression in the primate is restricted to the eye when the trans-gene is under the influence of the opsin promoter. Plasmid-based gene expression is still in the therapeutic range for 2-3 weeks after a single intravenous administration. Exogenous genes are expressed throughout the entire primate retina following the delivery of the gene to the eye via a trans-vascular route.