Origins of hemopoietic and stromal cells in subcutaneous femur implants.

The origin of spleen colony-forming units (CFUs) and fibroblastoid colony-forming cells (CFUF) repopulating the marrow of femurs subcutaneously implanted in syngeneic and semi-syngeneic mice was studied by making use of a chromosome marker for CFUs and a cytotoxicity test for CFUF. The CFUs present in implants during first 4 weeks were of a mixture of those from the donor and the host, and thereafter, were exclusively of host origin. On the other hand, the colony growth of CFUF from the marrow of C57BL/6 femurs grafted in B6CBAF1 mice remained almost totally unaffected by treatment with C57BL/6 anti-B6CBAF1 serum as late as 40 weeks after implantation. Quite similar results were obtained from the marrow-depleted femur implants. It is concluded from the present studies that chimeric marrow consisting of hemopoietic cells of host origin and stromal cells of donor origin can repopulate the femurs within a matter of several weeks after subcutaneous implantation.