Adenoviral delivery of LIM mineralization protein-1 induces new-bone formation in vitro and in vivo

Background: The LIM mineralization protein-1 (LMP-1) gene encodes for an intracellular protein that induces the expression of several bone growth factors. The purpose of the present study was to determine the feasibility and the optimal dose of adenoviral delivery of the LMP-1 cDNA to promote spinal fusion. Methods: A replication-deficient human recombinant adenovirus was constructed with the LMP-1 cDNA driven by a cytomegalovirus promoter. In phase 1, an in vitro dose-response experiment was performed to determine the optimal adenovirus-LMP-1 (AdLMP-1) concentration and infection time. In phase 2, nine rabbits had a single-level posterolateral arthrodesis of the lumbar spine with implantation of a carrier matrix loaded with bone-marrow-derived buffy-coat cells that had been infected for ten minutes with adenovirus containing the cDNA for LMP-1 (AdLMP-1) or beta -galactosidase (AdBgal). In phase 3, posterolateral arthrodesis of the spine was performed with implantation of cells infected with AdLMP-1 (ten rabbits) or cells infected with an empty adenovirus that did not contain LMP-1 cDNA (ten rabbits) and the results were compared. In this phase, peripheral-blood-derived buffy-coat cells were used instead of bone-marrow-derived cells and a collagen-ceramic-composite sponge was used as the carrier. Results: In phase 1, the in vitro dose-response experiment showed that a multiplicity of infection of 0.25 plaque-forming units per cell was the most efficient dose. In phase 2, the implants that had received cells infected with AdLMP-1 induced a solid, continuous spinal fusion mass at five weeks. In contrast, the implants that had received cells infected with AdBgal or a lower dose of AdLMP-1 induced little or no bone formation. In phase 3, a solid spinal fusion was observed at four weeks in all ten rabbits that had received cells infected with AdLMP-1 and in none of the ten rabbits that had received cells infected with the empty adenovirus. Biomechanical and histological testing of the AdLMP-1-treated specimens revealed findings that were consistent with a high-quality spinal fusion. Conclusions: Adenoviral delivery of LMP-1 cDNA promotes spinal fusion in immune-competent rabbits. Clinical Relevance: The use of delivery cells that are readily available from peripheral blood and the short infection time should allow this technique to be performed in any operating room. The use of an ex vivo gene-transfer protocol with a very low dose of virus should minimize the immune response and toxicity seen in association with other adenoviral applications.