Sequential expression of CD34 and CD33 antigens on myeloid colony-forming cells

The expression of CD33 and CD34 antigens on human bone marrow cells was examined by fluorescence-activated cell sorting and colony assays. A marked difference of antigen expression was observed on sorted progenitors of the granulocyte/macrophage lineage (CFU-GM) with respect to enrichment and maturation status. Single-color cell sorting revealed no difference of enrichment by anti-CD33 antibody between day-7 and d-14 progenitors, while anti-CD34 antibody preferentially enriched d-14 colony-forming units (CFU). By two-color cell sorting it could be shown that enrichment of d-14 CFU-GM occurred mostly in the CD34+CD33- and to a lesser extent in the double-positive fraction. In contrast, there was no difference in degree of enrichment between d-7 and d-14 CD34-CD33+ CFU-GM. From these data we conclude that, during early myelopoiesis, CD34 antigens are gradually lost while CD33 antigens are acquired.