Expression of the non-T ALL-associated p24 antigen on leukaemic blasts from patients with ANLL

Leukaemic cells from the peripheral blood of 90 patients with acute leukaemia (54 non-lymphocytic (ANLL) 36 lymphocytic (ALL)) have been examined for the presence of the platelet/ALL-associated p24 membrane antigen by indirect immunofluorescence and flow cytometry using monoclonal antibody FMC8. Cells from 28 of the ANLL patients and 24 of the ALL patients expressed the antigen. In many specimens, both ANLL and ALL, blast cell populations were heterogeneous with respect to FMC8 binding. In ANLL, FMC8-positive cells were observed in specimens from a range of morphological subtypes. Proteolytic stripping/resynthesis experiments demonstrated that the antigen was synthesized by ANLL cells, not passively acquired. Immunoprecipitation and electrophoretic analysis of the antigen from NP40 lysates of 125I surface labelled cells from a patient with acute monoblastic leukaemia confirmed that the epitope identified by FMC8 was present on a peptide of the same molecular weight (p24) as that observed on ALL cells.