Ectopic Osteogenesis of Allogeneic Bone Mesenchymal Stem Cells Loading on β-Tricalcium Phosphate in Canines

Abstract

Bone mesenchymal stem cells are progenitor cells for mesenchymal tissues. The objective of this study was to evaluate the subcutaneous ectopic osteogenesis of allogeneic bone mesenchymal stem cells, which were loaded on β-tricalcium phosphate in canines without immunosuppressive therapy. Osteoinduced allogeneic bone mesenchymal stem cells were seeded onto a β-tricalcium phosphate scaffold to construct tissue-engineered bone. Four dogs (recipients) in the allogeneic group were subcutaneously implanted with the allogeneic bone mesenchymal stem cells/scaffold; four dogs (donors) in the autogeneic group were implanted with the autogeneic bone mesenchymal stem cells/scaffold complex; and four dogs in the control group were implanted with scaffold alone. Systemic immune responses were evaluated by measuring the T-lymphocyte CD4, CD8, and CD4/CD8 subsets of each group. Subcutaneous osteogenesis was compared between the three groups by histologic analysis at week 24 after implantation. Flow cytometry showed no significant differences in the number of CD4 and CD8 T cells and the CD4/CD8 T-cell ratios among the three groups. Histologically, at week 24, both the autogeneic and allogeneic complexes led to subcutaneous osteogenesis, whereas the control group alone did not. There were no significant differences in the percentage of osteogenic area between the allogeneic and the autogeneic complexes on histomorphometric analysis (p > 0.05), which was significantly higher than that produced by the control group alone (p < 0.001). The results demonstrate that osteoinduced, allogeneic bone mesenchymal stem cells loaded on β-tricalcium phosphate enhanced ectopic bone formation in canines without immunosuppressive therapy.