Predifferentiation of human MSCs in vitro leads to osteogenesis in vivo

Mesenchymal stem cell (MSC)-loaded matrices were subjected to various in vitro differentiation regimes, followed by ectopic implantation in SCID mice. Sacrefices were performed at 2, 4, and 6 weeks and samples were processed for standard decalcified paraffin histology. Histologic analysis was performed in a blinded manner on samples explanted after six weeks. Gelfoam-MSC matrices that had been precultured for 8 to 14 days prior to implantation had more bony material than other constructs, although bone formation also occurred in these matrices under Dex culture conditions. Furthermore, the de novo bone formation was a result of the implanted cells.