Bone morphogenetic protein gene therapy for the induction of spinal arthrodesis

Ex vivo bone morphogenetic protein-9 gene therapy using human mesenchymal stem cells induces spinal fusion in rodents

OBJECTIVE

Ex vivo gene therapy with the use of human mesenchymal stem cells (hMSCs) and bone morphogenetic protein (BMP) genes provides a local supply of precursor cells and a supraphysiological dose of osteoinductive molecules that may promote bone formation in patients with inadequate hMSC populations because of age, osteoporosis, metastatic bone disease, iatrogenic depletion, or other metabolic derangements. This study was undertaken to evaluate the efficacy of ex vivo gene therapy with the use of hMSCs and the BMP-9 gene to promote spinal fusion in the rat.

METHODS

Sixteen athymic nude rats were treated with hMSCs transduced with recombinant, replication-defective Type 5 adenovirus containing the cytomegalovirus promoter and either the BMP-9 (Ad-BMP-9) or the beta-galactosidase (Ad-beta-gal) gene. Ad-beta-gal served as the control. Each animal received a percutaneous, paraspinal injection of 10(6) hMSCs transduced with 50 plaque-forming units/cell adenovirus in the lumbar region, with Ad-BMP-9 on the left and Ad-beta-gal on the right. At 8 weeks postinjection, computed tomographic scans of the lumbosacral spine were obtained, and the lumbosacral spine specimens were examined histologically.

RESULTS

Both computed tomographic studies and histological analysis clearly demonstrated large volumes of ectopic bone at the Ad-BMP-9-transduced hMSC injection sites, resulting in successful spinal fusion and no evidence of nerve root compression or local or systemic toxicity. The contralateral regions that were treated with Ad-beta-gal-transduced hMSCs showed no evidence of osteogenesis.

CONCLUSION

The results of this study suggest that hMSC and BMP-9 ex vivo gene therapy may be useful in inducing spinal fusion as well as other related procedures and certainly warrants further clinical development.

In vivo new bone formation by direct transfer of adenoviral-mediated bone morphogenetic protein-4 gene

Previous studies have demonstrated that bone morphogenetic protein-4 (BMP4) could participate in vivo endochondral ossification and is one of the main local contributing factors in the early stage of fracture healing. To investigate the effectiveness of BMP4 gene transfer, we constructed an adenoviral vector, Ad-BMP4, and evaluated its osteoinduction activity both in vitro and in vivo. In vitro study suggested that this vector could efficiently transduce mouse myoblast C2C12 cells and produce osteogenic BMP4 protein, as confirmed by immunofluorescence analysis and alkaline phosphatase activity assay. For in vivo study, Ad-BMP4 was directly injected into the hind limb muscles of male athymic nude rats. Visible new bone formation under X-ray films could be detected as early as three weeks post-injection. The bone tissue was further analyzed by histological staining and revealed a typical remodeled bone structure. In conclusion, this study is the first to establish the feasibility of adenovirus-based BMP4 gene therapy for bone regeneration.

Ectopic osteogenesis using adenoviral bone morphogenetic protein (BMP)-4 and BMP-6 gene transfer

Bone morphogenetic proteins (BMPs) delivered on scaffolds can induce ectopic bone formation after subcutaneous injection. Adenoviral vectors (Ad) carrying BMP2, BMP7, and BMP9 cDNAs have been shown to produce bone through endochondral ossification. The present study was performed to elucidate the histological events leading to ectopic ossification for two novel first-generation adenoviral constructs encoding BMPs, AdBMP4 and AdBMP6. In vitro, the viral constructs produced and secreted the mature BMP4 and BMP6 proteins. In vivo, the calf muscles of athymic nude rats were injected with AdBMP4, AdBMP6, AdBMP2, or AdlacZ. Rats were sacrificed 3, 6, 9, 16, 21, 60, and 90 days postinjection. Whereas AdBMP4 produced ectopic bone through mechanisms similar to endochondral ossification, AdBMP6 seemed to induce bone by way of mechanisms similar to both intramembranous and endochondral ossification pathways. At the relatively low vector dose used in this study, AdBMP2 caused an initial recruitment of primitive mesenchymal cells, without further development to bone. From computed tomographic analysis, AdBMP6 produced the most rapid tissue calcification. The ultimate density of ectopic bone formed by AdBMP4 and AdBMP6 was comparable. The current study demonstrates that AdBMP4 and AdBMP6 are more potent than the prototypical osteogenic adenoviral vector AdBMP2 and seem to induce ectopic bone by different mechanisms.

Orthopedic applications of gene therapy

A literature review of the applications of gene therapy for the treatment of orthopedic disorders was conducted, and showed that gene therapy provides us with new possibilities for the clinical management of orthopedic disorders. Most of these disorders, such as failure to obtain spinal fusion, disc degeneration, fracture and segmental bone defects, bone tumor, articular disorders, soft-tissue injury, genetic disorders, and nerve and muscular disorders, are difficult to treat by traditional surgical or medical means, and are under investigation for gene therapy. Many rapid advances have been made in the field of this novel approach. Although a number of obstacles remain to be solved before gene therapy can be applied for clinical use in humans, it is already apparent that gene therapy has the great potential of becoming a valuable clinical treatment for orthopedic disorders in the twenty-first century. With the development of gene transfer techniques, gene therapy will probably have numerous applications in orthopedic disorders.

Bone morphogenetic proteins and bone morphogenetic protein gene therapy in neurological surgery: a review

OBJECTIVE

To review the uses of bone morphogenetic proteins (BMPs) and BMP gene therapy for the treatment of neurosurgical disorders.

METHODS

Literature review.

RESULTS

BMPs are members of the transforming growth factor beta superfamily, and they play an important role in the growth and development of numerous tissues, including bone, brain, and spinal cord. Although the majority of previous studies have focused on the regulatory functions of BMPs in the normal growth and differentiation of the skeletal system, BMPs also seem to be exquisitely involved in the regulation of cellular proliferation, survival, differentiation, apoptosis, and lineage commitment in the central nervous system. When specific BMPs are delivered on biological matrices, they have the capacity to induce bone, cartilage, ligament, and tendon at both heterotopic and orthotopic sites, suggesting that they may play a major role in the future treatment of spinal and craniofacial pathology. For example, recent studies have clearly demonstrated the usefulness of BMPs and BMP gene therapy for the induction of spinal arthrodesis in several animal models. In addition, several BMPs have been shown to have a neuroprotective effect in animal models of head injury, cerebral ischemia, and Parkinson's disease and may therefore have direct clinical applications for the treatment of central nervous system disorders.

CONCLUSION

As the physiological activity of BMPs in the development and pathology of the central nervous system and spine are more fully elucidated, BMP therapeutics and gene therapy will probably have numerous applications in neurological surgery.