Experimental study on bone formation potential of cryopreserved human bone marrow mesenchymal cell/hydroxyapatite complex in the presence of recombinant human bone morphogenetic protein-2.

Secondary bone grafting in the alveolar cleft is one of the most important treatment modalities for patients with a cleft lip and palate. In children, however, harvesting a sufficient amount of bone graft from the donor site is difficult, and the procedure imposes a heavy burden on the patients. This problem may be resolved if autologous transplantation can be performed using a cell-hybrid type of artificial bone prepared with the patient's own bone marrow cells through a tissue engineering technique. In the current study, we examined the possibility of achieving such an autologous transplantation using cryopreserved human bone marrow cells. Human bone marrow cells were grown in culture and cryopreserved, and the cells preserved for 3 years and the cells preserved for 3 months were then thawed and recultivated. In one experiment, the recultivated cells were seeded onto a complex composed of porous hydroxyapatite and bone morphogenetic protein (BMP), and the complex was grafted subcutaneously in nude mice. In another experiment, the cells were seeded onto the porous hydroxyapatite and cultivated for 10 days before grafting in a medium supplemented with BMP. The bone formation potential of the cells was compared between these two experiments. Formation of mature bone was observed 2 weeks after transplantation in the former experiment, whereas only scarce bone formation was evident 4 weeks after transplantation in the latter experiment. It is therefore assumed that exposing the cultured human bone marrow cells to a high concentration of BMP in vivo strongly promotes bone formation.