Successful Delivery and Monitoring of CellBeads® in the Subretinal Space and Vitreous of Mice

Abstract

Purpose: : To study the impact of implanted microencapsulated human mesenchymal stem cells (CellBeads^®) on retinal integrity and monitor viability of the xenogenic cells in the mouse eye.

Methods: : CellBeads^® (alginate spheres with a diameter about 160 µm containing eGFP expressing mesenchymal stem cells) were implanted into the subretinal space or vitreous (n=6 each) of SV126 wild type mice using an ab externo approach. Retinal integrity and viability of microencapsulated cells was monitored by non invasive retinal imaging (Spectralis^TM HRA+OCT) and confirmed by correlative light- and electron microscopy, using marker for retinal degeneration. The resolution of the OCT permitted to visualize internal structures (i.e. single cells) within implanted beads, and eGFP fluorescence was used to assess protein production capacity of encapsulated cells.

Results: : Both implantation strategies (subretinal/intravitreal) yielded comparable results in terms of retinal integrity and viability of encapsulated cells. Subsequent in situ analyses corresponded accurately with in vivo imaging results. Focal damage due to the surgical implantation was accompanied by local GFAP upregulation and opsin mislocalization. While all encapsulated cells remained viable over a period of up to 10 weeks, intravitreal CellBeads^® showed a high mobility and subretinal CellBeads^® remained at the site of implantation.

Conclusions: : The accessibility for routine surgery and its immune privileged state make the eye an ideal target for release system implants for e.g. neuroprotective substances. Microencapsulated human mesenchymal stem cells (CellBeads^®) show promise to overcome limitations inherent with single factor release systems as they are capable of producing more physiologic combinations of neurotrophic factors. Here, we show that such approaches appear feasible based on intermediate-term survival of encapsulated protein-producing cells in vivo.

Keywords: neuroprotection • retina • vitreoretinal surgery