On the maturation order of AML cells: a distinction on the basis of self-renewal properties and immunologic phenotypes

To investigate the heterogeneous cellular structure of human acute myeloid leukemia (AML), subpopulations of cells were distinguished by two combined criteria: proliferation and differentiation. Purified blast cells were fractionated from blood or bone marrow of patients with newly diagnosed AML and colonies and clusters grown in phytohemagglutinin (PHA)-leukocyte feeder cultures. Large colonies, small colonies, macroclusters, and microclusters were recloned separately to assess the replicative capacities as a function of clone size. Large colonies showed higher proliferative capacities than did small ones, etc. Anti-Ia and an antigranulocyte (B4.3) monoclonal antibody (MoAb) were then employed to evaluate the stage of differentiation of AML cells in two patients before and following colony culture. Alterations of the immunologic phenotypes appeared during colony formation. This suggested differentiation of cells to more mature B4.3 granulocyte antigen-positive stages. MoAb-dependent cell lysis with the two antibodies was subsequently performed to assess the phenotypes of the precursors of the colonies and clusters. Leukemic colony-forming cells were Ia-positive and B4.3-negative and different from cluster-forming cells, which were largely Ia-negative and B4.3- negative. These data suggest that the cell organization of AML fits a maturation scheme containing immature cells with relatively high proliferative capacities, intermediate cells with low proliferative capacities, and end cells that are nonreplicative, and each with specific phenotypes.