PHENOTYPIC CHARACTERIZATION OF NORMAL AND CML CD34-POSITIVE CELLS - ONLY THE MOST PRIMITIVE CML PROGENITORS INCLUDE PH-NEG CELLS

We studied the sequence.of acquisition of CD33, CD38 and HLA-DR antige ns on CD34+ cells from marrow and blood of Ph-chromosome positive CML patients and normal marrow. We examined the Ph status of the various C ML cell populations. The mean proportions of normal and CML CD34+ cell s expressing CD33 and CD38 were not significantly different. However, a significantly greater proportion of CML CD34+ cells expressed HLA-DR antigens compared with normal CD34+ cells and the level of HLA-DR exp ression per CML cell was abnormally high. When the sequence of acquisi tion of these antigens on normal and CML CD34+ cells was evaluated usi ng 3-colour fluorescence analysis, the results suggested that HLA-DR w as expressed earlier than CD38 or CD33 and these findings were confirm ed by following the acquisition of CD38 and CD34+/DR+/CD38-subpopulati on during liquid culture. We performed cytogenetic studies on CD34+ su bpopulations in 6 cases. In 4 cases there were some Ph-negative metaph ases detectable in the CD34+/DR-subpopulation (range 12.5 to 60%). In the CD34+/DR+ fractions, however, all 6 patients had only Ph-positive metaphases and only 1/5 patients had detectable Ph-negative metaphases in the CD34+/CD38-subpopulation. We conclude that expression of HLA-D R antigens may precede the expression of CD38 on CD34+ cells during no rmal stem cell differentiation. In CML DR may be expressed aberrantly and Ph-negative cells are found predominantly in the DR negative subpo pulation.