OBJECTIVETo evaluate the cartilage formation ability of allogeneic mesenchymal stem cells implanted into sheep joint cavity without the use of immunosuppressive therapy.

METHODSAllogeneic mesenchymal stem cells (MSCs) loaded onto porous beta-tricalcium phosphate ceramic (beta-TCP) were implanted into normal sheep joint cavity. A complete mismatch between donor stem cells and recipient sheep was confirmed by mixed lymphocyte reaction assays prior to implantation. Eight weeks after implantation, the implants were taken out for histological and immunohistochemical analysis. The histological results were compared with data derived from joint cavity implantation of autologous MSCs-ceramic composites and cell-free ceramics. The systemic immune response was evaluated by the analysis of recipient serum for production of antibodies against allogeneic cells.

RESULTSFor implantation with allogeneic MSCs, no sign of adverse immune response was detected. Histologically, few inflammation cells infiltration occurred and no antibodies against allogeneic cells were detected. Neocartilage formation in implants loaded with either allogeneic or autologous mesenchymal stem cells was revealed by histochemical and immunohistochemical analysis. In implants without stem cells, no cartilage formation was detected.

CONCLUSIONSAllogeneic mesenchymal stem cells are capable of forming cartilage under the effect of joint cavity environment. Without the use of immunosuppressive therapy, allogeneic MSCs do not provoke an adverse immune response in vivo.