Transplantation of Human Mesenchymal Stems Cells Into Intervertebral Discs in a Xenogeneic Porcine Model

Study Design. Experimental and descriptive study of a xenotransplantation model in minipigs. Objective. To study survival and function of human mesenchymal stem cells (hMSCs) after transplantation into injured porcine spinal discs, as a model for cell therapy. Summary of Background Data. Biologic treatment options of the intervertebral disc are suggested for patients with chronic low back pain caused by disc degeneration. Methods. Three lumbar discs in each of 9 minipigs were injured by aspiration of the nucleus pulposus (NP), 2 weeks later hMSCs were injected in F12 media suspension (cell/med) or with a hydrogel carrier (Puramatrix) (cell/gel). The animals were sacrificed after 1, 3, or 6 months. Disc appearance was visualized by magnetic resonance imaging. Immunohistochemistry methods were used to detect hMSCs by antihuman nuclear antibody staining, and further performed for Collagen II, Aggrecan, and Collagen I. SOX 9, Aggrecan, Versican, Collagen IA, and Collagen IIA and Collagen IIB human mRNA expression was analyzed by real-time PCR. Results. At magnetic resonance imaging all injured discs demonstrated degenerative signs. Cell/gel discs showed fewer changes compared with cell/med discs and only injured discs at later time points. hMSCs were detected in 9 of 10 of the cell/gel discs and in 8 of 9 of the cell/med discs. Immunostaining for Aggrecan and Collagen type II expression were observed in NP after 3 and 6 months in gel/cell discs and colocalized with the antihuman nuclear antibody. mRNA expression of Collagen IIA, Collagen IIB, Versican, Collagen 1A, Aggrecan, and SOX9 were detected in both cell/med and cell/gel discs at the time points 3 and 6 months by real-time PCR. Conclusion. hMSCs survive in the porcine disc for at least 6 months and express typical chondrocyte markers suggesting differentiation toward disc-like cells. As in autologous animal models the combination with a three-dimensional-hydrogel carrier seems to facilitate differentiation and survival of MSCs in the disc. Xenotransplantation seems to be valuable in evaluating the possibility for human cell therapy treatment for intervertebral discs.