Mesenchymal Stem Cell (MSC) Aggregate Formation in vivo.

Human mesenchymal stem/progenitor cells (MSCs) isolated from various adult tissues show remarkable therapeutic potential and are being employed in clinical trials for the treatment of numerous diseases (Prockop et al., 2010). While routes of cell administration vary, profound beneficial effects of MSCs in animal models have been observed following intraperitoneal injections of the cells (Roddy et al., 2011). Similar to MSC spheres formed in culture under conditions where attachment to plastic is not permitted (Bartosh et al., 2010), MSCs injected into the peritoneum of mice spontaneously aggregate into 3D sphere-like structures (Bartosh et al., 2013). During the process of sphere assembly and compaction, MSCs upregulate expression of numerous therapeutic anti-inflammatory and immune modulatory factors. Here we describe the method we previously used for the generation of human bone marrow-derived MSC aggregates/spheres in vivo (Bartosh et al., 2013). By tagging the MSCs with green fluorescent protein (GFP), the aggregates formed can be easily visualized, collected and analyzed for changes in cellular properties and interactions with host immune cells.