In vivo survival and osteogenic differentiation of allogeneic rat bone marrow mesenchymal stem cells (MSCs)

Marrow mesenchymal stem cells (MSCs) are multipotent progenitor cells and reported to be immunoprivileged as well as immunosuppressive. Hence, MSCs might be ideal candidates for allogeneic transplantation to induce regeneration of damaged tissues/organs. To confirm the differentiation capability of allogeneic MSCs in vivo is important for the acceleration of regenerative medicine. Consequently, we have established an in vivo rat model using subcutaneous implantation of a hydroxyapatite (HA) ceramic/MSCs composite. Osteogenic differentiation was used as an indicator of differentiation. When syngeneic MSCs were implanted, MSCs showed osteogenic differentiation as evidenced by new bone formation as well as high alkaline phosphatase (ALP) activity. When allogeneic MSCs were implanted, none of the allografts survived or showed osteogenic differentiation. However, when the recipient rats were treated with FK506 immunosuppressant, allogeneic MSCs showed osteogenic differentiation. Although this finding might not be adequate for the acceleration of regenerative medicine, these results did confirm that MSCs are not intrinsically immunoprivileged but that under appropriate immunosuppressant treatment, allogeneic MSCs can survive and show differentiation capability in vivo.