HUMAN BLOOD-MOBILIZED HEMATOPOIETIC PRECURSORS DIFFERENTIATE INTO OSTEOCLASTS IN THE ABSENCE OF STROMAL CELLS

Osteoclastogenesis is a complex process that is facilitated by bone ma rrow stromal cells (SCs). To determine if SCs are an absolute requirem ent for the differentiation of human hematopoietic precursors into ful ly mature osteoclasts (OCs), CD34(+) cells were mobilized into the per ipheral circulation with granulocyte colony-stimulating factor, harves ted by leukapheresis, and purified by magnetic-activated cell sorting. This procedure yields a population of CD34(+) cells that does not con tain SC precursors, as assessed by the lack of expression of the SC an tigen Stro-1, and that differentiates only into hematopoietic cells. W e found that CD34(+), Stro-1(-) cells cultured with a combination of g ranulocyte/macrophage colony-stimulating factor, interleukin 1, and in terleukin 3 generated cells that fulfill current criteria for the char acterization of OCs, including multinucleation, presence of tartrate-r esistant acid phosphatase, and expression of the calcitonin and vitron ectin receptors and of pp60(c-src) tyrosine kinase. These OCs also exp ressed mRNA for the noninserted isoform of the calcitonin receptor and excavated characteristic resorption pits in devitalized bone slices. These data demonstrate that accessory SCs are not essential for human osteoclastogenesis and that granulocyte colony-stimulating factor trea tment mobilizes OC precursors into the peripheral circulation.