ABERRANT PROGENITORS COMMON TO MEGAKARYOCYTIC AND MYELOID CELLS IN A DOWNS INFANT WITH TRANSIENT ABNORMAL MYELOPOIESIS

Phenotypic characteristics of blasts were studied in a Down's infant w ith transient abnormal myelopoiesis (TAM). Two major subpopulations we re identified: (1) CD33+CD42b+ cells with platelet peroxidase activity , the commitment of which to megakaryocytic lineage was supported by a n increased expression of GATA-1 mRNA; (2) CD33+CD34+CD7+CD4+ cells wi th immature ultrastructure, which could be either im mature megakaryoc ytic or myeloid cells with aberrant differentiation. Mixed colonies co ntaining megakaryocytes and monocyte/macrophages in the peripheral blo od suggested the presence of progenitors common to these subpopulation s. These results may indicate that subpopulations of blasts with pheno typic diversity could be derived from aberrant common progenitors to m egakaryocytic and myeloid lineages in this patient.