In Vivo Bone Formation by Human Bone Marrow Stromal Cells: Reconstruction of the mouse calvarium and mandible

¹ Division of Plastic Surgery, Department of Surgery, University of California San Francisco, San Francisco, California
² Craniofacial and Skeletal Diseases Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland
³ Preventive and Restorative Dental Sciences, University of California San Francisco, San Francisco, California

^* To whom correspondence should be addressed. E-mail: mmankani{at}sfghsurg.ucsf.edu.

	Abstract

Bone marrow stromal cells (BMSCs) contain a subset of multi-potent cells with the potential to repair hard tissue defects. Mouse BMSCs, combined with a collagen carrier, can close critical-sized homologous mouse calvarial defects, but this new bone has a poor union with the adjacent calvarium. When human BMSCs are transplanted for the purpose of engineering new bone, best results can be achieved if the cells are combined with hydroxyapatite/ tricalcium phosphate particles (HA/TCP). Here, we demonstrate that transplantation of cultured human BMSCs in conjunction with HA/TCP particles can be used to successfully close mouse craniofacial bone defects, and that removal of the periosteum from the calvarium significantly enhances union with the transplant. Transplants were followed for up to 96 weeks and were found to change in morphology but not bone content after 8 weeks; this constitutes the first description of human BMSCs placed long-term to heal bone defects. New bone formation continued to occur in the oldest transplants, confirmed by tetracycline labeling. Additionally, the elastic modulus of this engineered bone resembled that of the normal mouse calvarium, and our use of atomic force microscopy (AFM)-based nano-indentation offered us the first opportunity to compare these small transplants against equally minute mouse bones. Our results provide insights into the long-term behavior of newly engineered orthotopic bone from human cells, and have powerful implications for therapeutic human BMSC transplantation.