Study design: Disc degeneration and osteoarthritis are diseases of the matrix. Chondrocytes that have been removed from damaged cartilaginous tissues maintain a capacity to proliferate, produce, and secrete matrix components, and respond to physical stimuli such as dynamic loading. A dog model was used to investigate the hypothesis that autologous disc chondrocytes can be used to repair damaged intervertebral disc.
Objectives: Given the capacity for the cells in vitro to produce matrix molecules that would be appropriate for disc chondrocytes, the focus of the experiment was to investigate whether the cells would continue to sustain metabolic function after transplantation.
Summary of the background data: No evidence for long-term integration exists for cell transplantation in species other than rats and rabbits. Furthermore, no controlled studies of 1-year duration have been published.
Materials and methods: Disc chondrocytes were harvested and expanded in culture under controlled and defined conditions, returned to the same animals from which they had been sampled (autologous transplantation) via percutaneous delivery. The animals were analyzed at specific times after transplantation by several methods to examine whether disc chondrocytes integrated with the surrounding tissue, produced the appropriate intervertebral disc extracellular matrix, and might provide a formative solution to disc repair.
Results: In the context of degenerative changes in an injury model: (1) autologous disc chondrocytes were expanded in culture and returned to the disc by a minimally invasive procedure after 12 weeks; (2) disc chondrocytes remained viable after transplantation as shown by Bromodeoxyuridine incorporation and maintained a capacity for proliferation after transplantation as depicted by histology; (3) transplanted disc chondrocytes produced an extracellular matrix that displayed composition similar to normal intervertebral disc tissue. Positive evidence of proteoglycan content was supported by accepted histochemical staining techniques such as Safranin O-Fast Green; (4) both type II and type I collagens were demonstrated in the regenerated intervertebral disc matrix by immunohistochemistry after chondrocyte transplantation; and (5) when the disc heights were analyzed for variance according to treatment, a statistically significantcorrelation between transplanting cells and retention of disc height was achieved.
Conclusions: Autologous chondrocyte transplantation is technically feasible and biologically relevant to repairing disc damage and retarding disc degeneration.