Flow cytometric expression of Bcl-2 protein was analyzed in 67 newly diagnosed acute myeloblastic leukemia (AML) patients using an anti-Bcl-2 monoclonal antibody by direct immunofluorescence technique and result were correlated with FAB subtype, CD34 expression and clinical outcome. The number of Bcl-2+ cells in each sample was heterogenous (range, 19 % to 96 %), with mean of 81 %. The percentage of Bcl-2+ cells was higher in M0 and M1 types according French- American-British classification. The mean fluorescence index (MFI), expressed as the ratio of sample channel: control mean channel was significantly higher (p < 0.01) in M0 (19,0) and M1 (17,6) than M4 (11,7) and M5 (8,9) cytotypes. In addition, Bcl-2 MFI significantly correlated both with CD34 positivity and with CD34 MFI. High percentage expression of Bcl-2 and MFI index of Bcl 2 was associated with a low complete remission rate after intensive chemotherapy (40,4 % in cases with 20 % and more positive cells vs 72 % in cases with less than 20 % positive cells). By statistical analysis we also demonstrated that both Bcl-2 high MFI (> 16) and CD34 expression are independent prognostic factors for achieving CR in AML.

        Key words: Acute myeloid leukemia - Bcl-2 protein - CD34 antigen expression - Complete hematologic remission