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AMA Bashar, Andrew Metcalfe, Ishaq Ahmed viringipurampeer, Cheryl Gregory-Evans, Orson Moritz, Kevin Gregory-Evans; Mesenchymal stem cell based ex vivo gene therapy provides enhanced neuroprotection in X-linked retinoschisis mouse model. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1408.
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X-linked retinoschisis (XLRS) is a juvenile-onset macular degeneration caused by haplo-insufficiency of a cell adhesion protein retinoschisin (RS1), secreted by photoreceptors and bipolar cells. RS1 mutations can lead to secretion of non-functional proteins, thus, as loss-of-function mutations are more amenable to gene therapy, XLRS is an excellent candidate for ex vivo gene therapy. Here, we report the structural and functional benefits observed after intravitreous delivery of MSCs genetically modified to secrete retinoschisin in the retina of our XLRS mouse model.
MSCs were harvested from syngeneic RS1KO mouse adipose tissue and transfected via electroporation with a plasmid containing human RS1 cDNA under a CMV promoter. Transfected cells were selected using geneticin for two weeks and then assayed by ELISA for retinoschisin synthesis. 200,000 genetically modified MSCs, secreting 8 ng/million cells/day, were injected into the vitreous cavity of the RS1KO mice at the age of post natal day 21. The control groups received either unmodified MSCs or sham injection. Electroretinogram (ERG), optokinetic tracking response (OKT) and histology data were recorded for all cohorts at 2, 4 and 8 weeks post injection time points.
Enhanced neuroprotection and inner nuclear layer tissue integrity were observed in retinas which received modified MSCs injection compare to the sham injection at all three time points. Lower a/b wave ratio in dark-adapted maximal ERG response and increased spatial frequency thresholds in OKT highlighted improvement in preserving vision in this group compared to others. These functional benefits were correlated with increased structural preservation of the inner nuclear layer.
Intravitreal delivery of genetically modified MSCs secreting retinoschisin showed promising results in our XLRS mouse model. Our previously reported magnetic targeting of systemically delivered cells would reduce the collateral damage caused by the intraocular injection of these cells, making this ex vivo approach safer, less-invasive, and repeatable; future investigation will focus on this delivery approach.
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