Cellular characteristics of acute myeloblastic leukemia associated with t(8;21)(q22;q22). The Japanese Cooperative Group of Leukemia/Lymphoma.

A large number of AML cases is reviewed in order to clarify biological characteristics of t(8;21) AML cells. The incidence of positivities for stem cell antigens, CD34 and HLA-DR, on blasts in t(8;21) AML is higher in comparison with those in other M2 or M3 categories. Frequent expression of CD34 and HLA-DR is indicative of the stem cell derivation of t(8;21) AML cells. The non-blastic leukemic cells in t(8;21) AML tend to lose the immature phenotype with discordant maturation such as low CD33 expression. Further, the blasts show frequent expression of the B-cell antigen, CD19, without other B-cell antigens and immunoglobulin gene rearrangements. AML cells with t(8;21) showed poorer response to granulocyte-macrophage colony-stimulating factor (GM-CSF) due to a decreased number of GM-CSF binding sites. The absence of monocytic differentiation in t(8;21) AML cells might represent the abnormal response to growth factors at the bifurcation stage of granulocyte and monocyte differentiation. Recently, breakpoint region genes for the 8;21 translocation in chromosome 8 and 21 have been isolated, 48-50 and have been named AML1 and ETO, respectively. The AML1 gene showed a strong homology with the Drosophila segmentation gene, runt, which is thought to be necessary for the Sex lethal gene expression. Since the GM-CSF receptor alpha chain gene locates in the pseudoautosomal region of the sex chromosome, the decrease of GM-CSF binding sites might be related to the AML1/ETO fusion gene expression. Further molecular genetic investigations of the breakpoint genes in the future are expected to clarify the unique biological events seen in this type of leukemia.