Characterization of the human burst-forming unit-megakaryocyte

Two classes of human marrow megakaryocyte progenitor cells are described. Colony-forming unit-megakaryocyte (CFU-MK)-derived colonies appeared in vitro after 12-day incubation; burst-forming unit-megakaryocyte (BFU-MK)-derived colonies appeared after 21 days. CFU-MK-derived colonies were primarily unifocal and composed of 11.6 ± 1.2 cells/colony; BFU-MK-derived colonies were composed of 2.3 ± 0.4 foci and 108.6 ± 4.4 cells/colony. CFU-MK and BFU-MK were separable by counterflow centrifugal elutriation. CFU-MK colony formation was diminished by exposure to 5-fluorouracil (5-FU); BFU-MK colony formation was unaffected. CFU-MK and BFU-MK were immunologically phenotyped. CFU-MK expressed the human progenitor cell antigen-1 (HPCA-1, CD34, clone My10) and a major histocompatibility class II locus, HLA-DR, and BFU-MK expressed only detectable amounts of CD34. BFU-MK colony formation was entirely dependent on addition of exogeneous hematopoietic growth factors. Recombinant granulocyte macrophage colony-stimulating factor (GM-CSF) and interleukin-3 (IL-3) possessed such colony-stimulating activity, whereas recombinant erythropoietin (Epo), G-CSF, IL-1a, IL-4, and purified thrombocytopoiesis-stimulating factor did not. These studies indicate the existence of a human megakaryocyte progenitor cell, the BFU-MK, which has unique properties allowing it to be distinguished from the CFU-MK.