Thoracoscopic intradiscal spine fusion using a minimally invasive gene-therapy technique.
BACKGROUND
Gene therapy has been utilized to achieve posterior intertransverse process fusion in rodents. To our knowledge, however, no one has previously reported on the use of this technique to achieve anterior spinal fusion in mammals. The purpose of the present study was to determine if a gene-therapy technique can be utilized to achieve anterior intradiscal fusion in pigs with use of minimally invasive techniques.


METHODS
Mesenchymal stem cells were isolated from each of three pigs, expanded in culture, and transduced with an adenovirus carrying either the gene for bone morphogenetic protein-2 (Adv-BMP2) or the control gene, beta-galactosidase (Adv-betagal). In vitro, assays were performed to detect BMP-2 expression as well as protein markers of bone formation. In vivo, four thoracic disc spaces in each of three pigs were injected thoracoscopically with cells after 1 cm (3) of the disc had been removed. In each of the three pigs, two discs were injected with autologous mesenchymal stem cells transduced with Adv-BMP2, the third disc was injected with cells transduced with Adv-betagal (control 1), and the fourth disc served as the sham-operated control (control 2). The three animals were killed six weeks after the implantation. Computerized tomographic scanning was performed on two of the specimens, and histological examination was performed on all specimens. The computerized tomographic scans and histological examinations were then interpreted in a blinded fashion.


RESULTS
In the in vitro study, a human BMP-2 protein band was detected in the medium of Adv-BMP2-transduced stem cells but not in that of the control cells. The Adv-BMP2-transduced stem cells were associated with a fivefold increase in alkaline phosphatase activity compared with the controls as well as with matrix mineralization and increased protein expression of type-I collagen, osteopontin, and bone sialoprotein. In the in vivo study, radiographic examination demonstrated anterior spinal fusion in all six disc spaces that had been treated with implantation of Adv-BMP2-transduced stem cells. In contrast, the six control disc spaces had little or no intervening bone. Histological examination demonstrated bridging bone from end plate to end plate in all six disc spaces that had been treated with implantation of Adv-BMP2-transduced stem cells. The six control disc spaces had no bridging bone.


CONCLUSIONS
The Adv-BMP2-transduced mesenchymal stem cells produced BMP-2 protein. Further, the cells differentiated into osteoblasts and induced anterior spinal fusion in six of six disc spaces in this pig model. Although many technical and practical challenges remain, the results of the present study suggest that it may eventually be possible to use similar techniques to achieve anterior spinal fusion in humans.
Department of Orthopaedic Surgery, Barnes-Jewish Hospital, and Washington University School of Medicine, St. Louis, Missouri 63110, USA. riewd@msnotes.wustl.edu
K Daniel
KD
Riew
Jueren
J
Lou
Neill M
NM
Wright
Su-Li
SL
Cheng
Kyongtae T
KT
Bae
Louis V
LV
Avioli
D000818:Animals; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000235:genetics* / Q000378:metabolism; D002478:Cells, Cultured; D015870:Gene Expression; D015316:Genetic Therapy / Q000379:methods*; D007150:Immunohistochemistry; D007278:Injections, Spinal; D007403:Intervertebral Disc / Q000000981:diagnostic imaging; D008297:Male; D008648:Mesoderm / Q000166:cytology; D019060:Minimally Invasive Surgical Procedures; D013123:Spinal Fusion / Q000379:methods*; D033581:Stem Cell Transplantation; D013552:Swine; D014057:Tomography, X-Ray Computed; D014161:Transduction, Genetic; D016212:Transforming Growth Factor beta
C525718:BMP2 protein, human; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D016212:Transforming Growth Factor beta