Clonal nature of pluripotent hemopoietic precursors in vitro (CFU-mix).

Direct evidence is presented for the clonal nature of the mixed colonies from pluripotent hemopoietic precursors in vitro in adult murine marrow cells. Bone marrow cells from BDF1 mice were fractionated using the technique of velocity sedimentation according to Miller and Phillips to enrich the concentration of the mixed colony-forming units. After 3 h sedimentation, marrow cells in the 15th fraction were harvested and cultured using a methylcellulose culture assay. After 2 days of culture, dividing single cells were individually aspirated and transferred to fresh culture medium for mixed colonies using a Leitz micromanipulator. 92 macrophage-granulocyte colonies, 11 erythropoietic bursts, and 4 mixed colonies were detected in 358 single-cell culture experiments. The present results indicate that mixed colonies are clonal, and the mixed colony-forming units are pluripotent.