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 b-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.