COMPARATIVE QUANTITATIVE EXPRESSION OF BCL-2 BY NORMAL AND LEUKEMIC MYELOID CELLS

Expression of the bcl-2 oncoprotein by AML blasts has previously been demonstrated to be heterogenous with high levels of bcl-2 expression being associated with a low complete remission rate and poor survival. We have quantified bcl-2 expression in AML blasts in relation to expression of the CD34 antigen and in comparison to CD34-positive cells from normal bone marrow. When expressed as molecules of equivalent soluble fluorochrome (MESF) per cell, AML blast cell bcl-2 expression varied from 11.1 to 99.9 x 10(3) (median 39.4 x 10(3), n=56) with 28.5% of patients expressing high MESF values (>50 x 10(3)) and 16% of patients expressing low MESF values (<20 x 10(3)), the remainder expressing intermediate values. There was no significant difference between intensity of bcl-2 expression and FAB classification in the de novo AML cases, and there was no significant differences between de novo and secondary AML cases. Blasts from CD34(+) AML patients expressed significantly higher levels of bcl-2 (mean MESF 43.6 x 10(3) n=36) than CD34(-) AML patients (mean MESE 31.7 x 10(3) n=19). In five cases of CD34(+) AML, bcl-2 expression was determined on purified CD34(+) and CD34(-) blast cell populations, In all cases CD34(+) blasts were found to express significantly higher bcl-2 MESF values compared to the CD34(-) fraction. Purified CD34(+) cells from normal bone marrow consistently expressed high levels of bcl-2 (MESE >75 x 10(3), n=4), which was comparable to that found on CD34(+) AML cells. Our results suggest that the poor prognosis previously associated with AMT, blasts expressing the CD34 antigen may in part be related to high expression of bcl-2. Also the ability to measure bcl-2 in AML blasts quantitatively by now cytometry and to categorize patients into discrete groups may be of value as a prognostic indicator in AML.