Detection of the proliferated donor cells in bone grafts in rats, using a PCR for a Y-chromosome-specific gene.

Conventional corticocancellous bone grafts are known to revascularize gradually and to become repopulated with osteocytes and other types of cells. This study was conducted to study the origin of the cells found within conventional bone grafts as a function of time, using a new method which accurately identifies donor cells transplanted with the graft. The technique requires the transplantation of a 25-mm tibial diaphyseal bone graft from a male rat to a female isogenous recipient, placed anatomically in the tibia. The presence and relative proportion of cells containing the Y-chromosome (i.e., originating from the bone graft) was determined 4, 8, and 12 weeks after transplantation. At these times, genomic DNA was extracted from the grafted bones and a polymerase chain reaction (PCR) specific for the sex-determining region of the Y-chromosome (Sry) was performed, with appropriate controls. Sry-specific bands were evident in none out of three grafts at 4 weeks, two out of three at 8 weeks, and all grafts at 12 weeks. These data demonstrate that not all cells within a conventional graft result from "creeping substitution" of necrotic bone. Instead, a small number of intrinsic cells from a nonvascularized corticocancellous structural graft survive and proliferate over time.