Introduction: Spinal fusion has become a popular surgical technique. Problems of fusion failure or pseudo-arthrosis as well as bone graft donor site complications are common. Ex vivo gene therapy using mesenchymal stem cells (MSCs) and bone morphogenetic protein (BMP) genes can provide a local supply of precursor cells and a supra-physiological dose of osteoinductive molecules that may promote bone formation and lead to spinal fusion.
Methods: Thirty 6–7 weeks old C3H/HeN immune-competent female mice received an injection of 2x106 genetically engineered MSCs to the para-vertebral muscle of the lumbar spine (L2-L6) under manual palpation. Ten animals served as negative control group and 20 animals constituted the experimental group.
Bone formation in the para spinal region of the injected animals was evaluated by histology staining. Quantitative analysis of the fusion mass was monitored by micro computerized tomography (μCT).
Results: At 1, 2, 4 and 8 weeks post injection. Bone formation was extensive, as soon as the 1st week post injection, in the area adjacent to and adhering to the posterior elements of the spine in all the study animals. None of the control animals, in which hBMP-2 was inhibited, showed any new bone formation.
Discussion: Exogenously regulated expression of the hBMP-2 enabled us to regulate bone formation in vivo, using genetically engineered MSC system. The effect of hBMP-2 in inducing bone formation was monitored in real time, non-invasive and quantitative system that enabled us to better understand the biological process during bone regeneration and repair. Our data demonstrate a regulated and monitored system for inducing bone for spinal fusion. We conclude that controlled gene therapy for spinal fusion can be achieved using Tet-regulated hBMP-2 gene and MCSs.
