Identification of committed mononuclear precursors for osteoclast-like cells formed in long term human marrow cultures

Nonadherent marrow mononuclear cells enriched for hematopoietic progenitor cells were cultured in semisolid medium with recombinant human granulocyte-macrophage colony-stimulating factor for 9 days to form colony forming unitgranulocyte macrophage (CFU-GM) colonies. 1,25-Dihydroxyvitamin D was then gently layered over the cultures. After 2 weeks, approximately 30% of the colonies that formed were composed of cells with a unique polygonal morphology. One hundred percent of the polygonal cells in these colonies cross-reacted with the monoclonal antibody 23c6, which preferentially recognizes osteoclasts. Homogenous populations of these polygonal cells formed multinucleated cells (MNC) in suspension culture, 100% of which cross-reacted with the 23c6 monoclonal antibody, and greater than 90% of the MNC contracted in response to calcitonin. Approximately 20% of these MNC formed resorption lacunae on calcified matrices. These results suggest that 1) early osteoclast precursors are derived from CFU-GM, the committed granulocyte-macrophage progenitor; 2) committed mononuclear osteoclast precursors have a distinct polygonal morphology and cross-react with monoclonal antibodies that recognize mature osteoclasts; and 3) these mononuclear precursors are capable of forming multinucleated cells which fulfill the functional criteria for osteoclasts.