Enhancement of spine fusion using combined gene therapy and tissue engineering BMP-7-expressing bone marrow cells and allograft bone

Study Design. Prospective study to assess the enhancement of spine fusion using a tissue engineering construct consisting of bone marrow cells genetically modified by adenovirus (Ad) vector-encoding bone morphogenetic protein-7 (BMP-7) seeded onto an allograft scaffold in a rat model. Objectives. To evaluate Ad transgene expression at the fusion site and the effect of AdBMP-7 treatment on fusion rates, mechanical stability, microscopic anatomy, and bone formation rates. Summary of Background Data. Nonunion is a major complication of spine fusion. Gene transfer may be an effective method for locally overexpressing BMP-7, a gene important for bone formation and regeneration to enhance allograft spine fusion. Materials and methods. Bone marrow cells were treated with AdBMP-7 or Adbetagal (encoding the marker gene beta-galactosidase), AdNull (with no gene), or no vector and implanted with allograft in a site of posterior spine fusion. Marker gene expression was assessed up to 14 days after administration. Fusions were evaluated at 8 weeks. Results. Ad gene expression was maximal on day 3, waning to background levels by 14 days. With AdBMP-7 treatment, radiographic fusion rate was 70% and mechanical fusion rate was 80% versus 0% by either parameter in control groups. Fused AdBMP-7-treated spines had a 2.5-fold to 3.0-fold lower range of motion and 1.7-fold to 1.9-fold lower hysteresis than controls. Fusion masses of AdBMP-7-treated spines had the microscopic appearance of normal trabecular bone and showed a 23-fold higher uptake of fluorochrome indicating increased bone formation. Conclusions. Addition of AdBMP-7-modified marrow cells can enhance allograft spine fusion.