RAPID COMMUNICATION Dendritic Cells and Macrophages Can Mature Independently From a Human Bone Marrow

CD34' precursors in normal human bone marrow (BM) generate large numbers of dendritic cells alongside macrophages and granulocytic precursors when cultured for 12 to 14 days in c-kit ligand, granulocyte-macrophage colonystimulating factor (GM-CSF), and tumor necrosis factor-a (TNF-a). This study reports an intermediate cell type that develops by day 6, and has the potential to differentiate into either macrophages or dendritic cells. When the d6 progeny are depleted of mature macrophages and residual CD34' precursors, a discrete CD14' HLA-DR' population persists in addition to immunostimulatory CD14HLADR'" dendritic cells. Half of the CD14+ HLA-DR' population is in cell cycle (Ki-67'). but colony-forming units (CFUs) are no longer detectable. The cells are c-fms+. but lack myeloperoxidase and nonspecific esterase. They also possess substantial phagocytic and allostimulatory activity. These post-