Expression of BCL-2 proto-oncogene in adult acute lymphoblastic leukemia.

The products of the BCL-2 gene prolong survival of lymphohematopoietic cells by inhibition of programmed cell death. We studied bcl-2 protein expression in a series of 43 adult acute lymphoblastic leukemia (ALL) at diagnosis, using a specific monoclonal antibody and flow cytometry. All samples expressed bcl-2 with a mean percentage of positive cells of 77.9. The level of bcl-2 in positive cells expressed as mean equivalent of soluble fluorescence (MESF) was highly variable ranging from 5 x 10(3) to 552 x 10(3) (mean +/- s.d.: 96.5 +/- 109 x 10(3)). Neither the percentage of positive cells nor bcl-2 MESF levels were correlated with initial characteristics including blood counts, immunological phenotype, or cytogenetics. The survival of leukemic cells maintained in cytokine-free liquid culture was not correlated with bcl-2 expression. However, cells from ALL with higher white blood cell (WBC) counts, with t(9;22) translocation, or expressing myeloid surface antigens exhibited significantly longer survival in this culture system. The outcome after intensive chemotherapy did not differ according to bcl-2 expression. Factors associated with poor outcome included WBC counts, presence of t(9;22) translocation, presence of myeloid antigens and prolonged survival of cultured cells. These results indicate that high levels of bcl-2 are not associated with distinct clinical or biological characteristics in ALL.