The development of tissue-engineered bone of different origin through endochondral and intramembranous ossification following the implantation of mesenchymal stem cells and osteoblasts in a murine model.

The study of host cell recruitment by implanted exogenous cells is one of the novel challenges in tissue engineering. We previously reported the development of tissue-engineered bone deposited by host cells in porous ceramic scaffolds seeded with murine mesenchymal stem cells (MSC) and implanted in immunocompromised mice. To better highlight the contribution of host cells to the development of the engineered tissue and to investigate whether the capacity to recruit host cells was dependent on the donor cell commitment, we implanted ceramic scaffolds seeded with either murine GFP labeled MSC or GFP labeled osteoblasts (OB) into immunocompromised mice. Although we observed formation of bone in all scaffolds, the origin of bone cells and the ossification type were strictly dependent on the nature and commitment of the seeded cells. MSC implants led to formation of bone of host origin through the activation of an endochondral ossification process while an intramembranous ossification directly performed by the seeded cells was observed in OB implants. Moreover, we observed an increased vascularization in MSC implants due to the higher capacity of MSC to recruit host CD31+ endothelial cells. The relationship between this enhanced vascularization and the type of ossification is discussed.