PROJECT SUMMARY The objective of the proposed research is to evaluate the safety and efficacy of a novel method of delivering therapeutics to the central nervous system (CNS) and the retina to treat diseases associated with visual impairment. The hypothesis tested will be that autologous genetically modified mesenchymal stem cells (MSCs) can serve as effective vehicles for sustained delivery of therapeutics to visual centers in the brain and to the retina for the treatment of blinding diseases that result from pathology in one or more parts of the visual system. Proof of concept studies will be performed using a well-characterized and validated canine model of CLN2 neuronal ceroid lipofuscinosis, a disease with pediatric onset characterized by widespread neurodegeneration resulting in progressive loss of vision due to degeneration of both the retina and visual processing centers in the brain, cognitive and motor decline, and seizures. CLN2 disease is caused by mutations in TPP1, which result in deficiencies of the soluble lysosomal enzyme tripeptidyl peptidase-1 (TPP1). It is hypothesized that providing TPP1 to the CNS using implantation of autologous MSCs that have been genetically modified to produce and secrete the protein will ameliorate disease-related vision loss in the canine model. To test this hypothesis, TPP1-producing MSCs will be injected into the vitreous of the eye and into the cerebrospinal fluid (CSF) of dogs affected by CLN2 disease. Based on previous studies, significant transfer of TPP1 from cells implanted in these locations to the retina and brain are anticipated, respectively. Functional vision will be evaluated in treated dogs using a novel iPad tablet based test that requires a choice between a screen displaying solid grey and a screen displaying a black and white stripe / grating pattern. Retinal function will be assessed with electroretinography, and retina-CNS interactions will be assessed with quantitative pupillometry. Dogs will also be monitored with established biomarkers of disease progression to determine if implantation of TPP1-producing MSCs results in amelioration of the neurological disease signs not directly associated with vision, preserves cognitive function, inhibits brain atrophy, and extends healthy lifespan when compared with control dogs. In addition, assessed will be the safety, persistence, and distribution of the implanted MSCs and the TPP1 enzyme they produce through histopathologic and immunohistochemical analysis of CNS tissues. Successful accomplishment of these aims will set the groundwork for testing this approach to therapy in children suffering from CLN2 disease and similar lysosomal storage disorders. It will also serve as the prototype for adopting this approach to treat many other diseases affecting the CNS and retina.