Fate of transplanted bone-marrow-derived mesenchymal cells during osteochondral repair using transgenic rats to simulate autologous transplantation.

OBJECTIVE The fate of transplanted cells used in tissue engineering strategies should be followed. With this aim in view, the survival of transplanted bone-marrow-derived mesenchymal cells within osteochondral defects was determined using transgenic rats to simulate autologous transplantation. DESIGN An autologous transplantation model was simulated using transgenic rats - whose transgenes produce no foreign proteins - as donors, and wild-type rats as recipients. Dense masses of mesenchymal cells were prepared from the transgenic rats using the hanging-drop culture technique. These cell masses were then transplanted into osteochondral defects created within the medial femoral condyle of wild-type rats, wherein they are affixed with fibrin glue. The course of repair was assessed histologically. The survival of the transplanted cells was ascertained by in situ hybridization of the transgenes. RESULTS Twenty-four weeks after transplantation, the defects were repaired with hyaline-like cartilage, which was thicker than normal, and with subchondral bone. Using the in situ hybridization technique, cells derived from the transplanted ones were detected within both the cartilaginous and the subchondral bone layers. CONCLUSION Using this simulated autologous transplantation model, the survival of transplanted mesenchymal cells was monitored in vivo. The findings indicate that the transplanted mesenchymal cells contributed to the repair of the osteochondral defects.