Tissue-engineered bone formation with gene transfer and mesenchymal stem cells in a minimally invasive technique

Background: The objective of this study was to use a chitosan-alginate gel to implant bone marrow-derived mesenchymal stem cells subcutaneously in a minimally invasive manner and promote bone formation by the simultaneously transferred osteogenic protein (OP)-1 (bone morphogenic protein-7) gene. Method and Results: The complex of polyethylenimine/luciferase plasmid DNA embedded in the gel was able to transfect HEK 293 cells on a culture dish or co-encapsulated in the gel. When injected into the subcutaneous space of mice, luciferase expression was two to three orders of magnitude increased above the background. To examine the efficacy of gene-, cell-, and combined gene- and cell-encapsulated gels in tissue generation, samples were injected into the subcutaneous space of 6-week-old athymic nude mice, and the OP-1 plasmid was studied. At 8 weeks after the injection, the gels only maintained their volumetric shape when human mesenchymal stem cells (hMSCs)were encapsulated, but otherwise the gels were partially dissolved. Transgene expression of OP-1 was clearly detected in the samples after 4 weeks but not after 8 weeks. Type II collagen was detected in all of the gels containing the OP-1 plasmid, with or without hMSCs. The samples with the combination of OP-1 DNA and hMSCs revealed strong type II collagen expression as well as osteoid foci. Conclusion: These results suggest that combined gene and hMSC delivery within a chitosan-alginate gel could be an interesting approach for tissue engineering.