Toward Development of Cell Therapies for Human Retinal Disease: Subretinal Delivery of GFP-Labeled Human Forebrain Progenitor Cells to the Primate Eye

Abstract

Purpose: : Cell-based therapies for retinal disease have shown efficacy in rodent models of human disease. However, further knowledge is needed to translate these findings to human therapy. Key questions remain regarding dosage, cell distribution, cell survival, ocular safety and the best delivery method. Primate eyes provide the best preclinical model, as they share close structural similarity to the human eye including the presence of a macula. We investigated the distribution and efficacy of GFP-labelled human cortical neural progenitor cells (hNPC^ctx) grafted into the subretinal space of adult rhesus monkeys. Studies of safety and efficacy of GFP-labelled cells also were carried out in RCS rats, in which native unlabelled hNPC^ctx were previously shown to rescue vision and retinal structure.

Methods: : Neurospheres of GFP-labelled hNPC^ctx were dissociated into single cell suspensions and 100 µl containing 6x10⁵ cells was injected into the subretinal space either within or outside the macula. In some cases, cyclosporin immunosupression was started 2 days prior to injection. Multifocal ERGs were performed before and after surgery. After 1-4 weeks, animals were sacrificed and eyes were processed for histology. Subretinal injections of hNPC^ctx-GFP were also evaluated in RCS rats by optomotor-response acuity and morphology.

Results: : Cell injections were followed by rapid retinal reattachment and no adverse events. Injected cells spread outward to a much broader area than the injection bleb. mfERGs documented intact function within injection sites, and morphology showed excellent preservation of retinal structure and no signs of inflammation or rejection. hNPC^ctx showing robust GFP expression were distributed in the subretinal space in a single layer, with no sign of cells migrating into the inner retina. In RCS rats, hNPC^ctx-GFP showed the same efficacy and safety profile as unlabeled hNPC^ctx .

Conclusions: : hNPC^ctx -GFP injected subretinally in the rhesus monkey eye showed survival up to 4 weeks with minimal side effects and a good safety profile. This study provides a foundation for future studies of cell-based therapy, including evaluation of other potentially therapeutic cell types and tests of efficacy in monkeys with age-related maculopathy.

Keywords: age-related macular degeneration • transplantation • protective mechanisms