Antigenic phenotype of chronic granulocytic leukaemia progenitor cells in chronic phase and in blastic transformation characterized by means of monoclonal antibodies.

We studied the surface antigens of "early" and "late" granulocyte-macrophage progenitor cells (CFU-GM) from bone marrow and peripheral blood of 18 patients with chronic granulocytic leukaemia in chronic phase (CGL-CP) using 14 selected murine monoclonal antibodies (McAbs) in complement dependent cytotoxicity assay followed by culture in methyl cellulose. The same panel of McAbs was used to determine the antigens on leukaemic blast cells from peripheral blood of 15 patients with CGL in blastic transformation (BT) by complement mediated lysis and in vitro culture technique for clonogenic blasts (CFU-L) and immunofluorescence assay for total blast population. McAb for HLA-DR antigens (L243) and McAbs MY9, S3-13, S17-25 and 53/6 reacted with CFV-GM and CFU-L. In contrast, McAbs PM81 and AML-2-23 recognizing antigens on more mature myeloid cells did not react with these progenitor cells. McAb S4-7 reacted with the majority of CFU-L and a small proportion of "early" and "late" CFU-GM. This McAb may be useful for the prediction of blastic transformation in CGL patients. Generally, the reactivity of most McAbs was more heterogeneous with CFU-L than with CFU-GM in individual patients. The majority of McAbs included in our study reacted with a higher percentage of CFU-L and CFU-GM than predominant blast cell population in individual patients perhaps because the detected antigens are expressed more strongly on dividing progenitors than on relatively nonproliferative progeny. Thus we interpret the results of these studies showing that the antigenic phenotypes of the blast colony progenitor cells in CGL-BT are very similar to but not identical with those of CFU-GM from CGL-CP patients.