Ex vivo expansion of rat bone marrow mesenchymal stromal cells on microcarrier beads in spin culture

Bone marrow mesenchymal stromal cells (BM-MSC) are attractive candidates for connective tissue regeneration. Currently, their use is limited by poor overall cell survival and high apoptosis rates upon transplantation in vivo. We hypothesized that disruption of cell–extracellular matrix contact either during cell expansion or immediately prior to cell transplantation may impair cell viability and facilitate apoptosis. We therefore investigated whether BM-MSC can be expanded on microcarrier beads in spin culture and directly transplanted. This novel approach removes the need for the repeated trypsinizations that are usually required for expansion and transplantation. CultiSpher-S gelatin microcarrier beads supported Fisher and transgenic green fluorescent protein (GFP)+ Sprague Dawley rat BM-MSC expansion. Bead-expanded BM-MSC could still be differentiated along the chondrogenic, osteogenic and adipogenic lineages. In the short term, direct subcutaneous transplantation of cells expanded on microcarriers was associated with significantly less apoptosis than trypsinized control cells. In the long term, BM-MSC expanded on microcarrier beads induced de novo trabecular bone formation in vivo. This novel approach present several advantages over current expansion–transplantation protocols for mesenchymal tissue regeneration.