Monoclonal antibodies raised against K562 cells reacted with human haematopoietic pluripotent stem cells.

We describe the properties of three monoclonal antibodies (McAbs) (21H73, 37G7 and 49C12) against K562 cell surface antigens correlated with differentiation induced by 12-O-tetradecanoyl phorbol-13-acetate (TPA). Each of the McAbs immunoprecipitated K562 cell surface antigen with molecular weight (MW) of approximately 51 kD, 82 kD or 92 kD, respectively. The antigens detected by McAbs 21H73 and 37G7 were not immunoprecipitated from K562 cells differentiated into monocyte-macrophages by TPA (K562-TPA). On the other hand, 49C12 immunoprecipitated an antigen with MW of 92 kD from K562-TPA cells, but not from undifferentiated K562 cells. To examine the distribution of these antigens among human haematopoietic stem cells, bone marrow cells were separated by the panning method using these McAbs and subjected to colony-forming assays. The McAb 21H73 reacted with CFU-mix and BFU-E but with neither CFU-E nor CFU-GM. CFU-mix and BFU-E were enriched approximately 6.2-14.7-fold and 2-fold by the panning procedure using 21H73, respectively. On the other hand, 37G7 reacted only with BFU-E, and 49C12 reacted with CFU-GM but not with any other haematopoietic progenitor cells. We also examined the reactivity of these McAbs with leukaemia cells freshly isolated from 26 patients. The antigen defined by 21H73 was not expressed on any leukaemia cells from patients except for cells from an acute lymphocytic leukaemia (ALL, L3) and a CML in blastic crisis. The McAb 37G7 reacted with several types of leukaemia cells. The antigen defined by 49C12 was expressed on almost all leukaemia cells isolated from patients. These results suggest that 21H73 allows purification and enrichment of normal haematopoietic pluripotent stem cells from both normal and leukaemia patients' bone marrow specimens, especially following the step to remove leukaemia cells and haematopoietic progenitor cells other than CFU-mix by using 37G7 and/or 49C12.