Transient Production of Bone Morphogenetic Protein 2 by Allogeneic Transplanted Transduced Cells Induces Bone Formation

The aim of this study was to evaluate the use of transplantation of genetically modified allogeneic cells as a method to induce bone formation. In this study, we infected a murine osteoprogenitor cell line with a retroviral vector containing the human bone morphogenic protein 2 (BMP2) gene. Transduced cells exhibited more alkaline phosphatase activity than cells treated with any of the tested doses of recombinant human BMP2 protein (rhBMP2). The transduced cells were suspended in a collagen solution and injected into the quadriceps muscle in immunocompetent outbred mice. Radiographic and histological examinations demonstrate abundant ectopic bone formation in 85% of the transplanted animals (n=13). PCR and Southern blot analysis for the puromycin resistance gene revealed that the transplanted cells were detectable for up to 1 week, but not at later time points. None of the animals developed tumors. Our results suggest that allogeneic BMP2-expressing transduced cells may have therapeutic potential for enhancing new bone formation. This model also provides a simple, inexpensive, and sensitive assay for evaluating in vivo the osteoinductive potentials of secreted proteins without the requirement of protein purification or the use of immunodeficient animals.