Origin of Repopulating Cells in a Mechanically Depleted Medullary Cavity as Determined by Studies With Marrow Transplants

The restoration of marrow in a mechanically depleted segment of rabbit femur has been reported to be a local phenomenon initiated by cells normally resident in bone. That marrow regeneration in an evacuated femur is independent of circulating stem cells has been confirmed in mice bearing a heterologous marrow transplant. Mice were given 800 R of whole-body X-radiation with experimental femur shielded. Rat marrow cells, histochemically distinguishable from those of the mouse by alkaline phosphatase staining, were then transplanted to the irradiated animals. The shielded femur diaphysis was evacuated by dextran perfusion, and 2 weeks later the animal was sacrificed. Imprints were made of the spleen and of the marrow in the contralateral limb, the epiphyseal ends of the depopulated femur, and the depopulated section of the femur. Alkaline phosphatase staining showed that all of the areas involved except the evacuated femur section had an abundance of alkaline-positive rat cells. The depopulated femur diaphysis showed a typical regenerating marrow tissue at 14 days and the cell constituents were of mouse cell origin.