Prolonged survival of B-lineage acute lymphoblastic leukemia cells is accompanied by overexpression of bcl-2 protein.
Overexpression of bcl-2 delays the onset of apoptosis in lymphohematopoietic cells. We measured levels of bcl-2 protein in normal and leukemic human B-cell progenitors with a specific monoclonal antibody and flow cytometry. Normal immature B cells had low levels of bcl-2 protein; the intensity of fluorescence, expressed as molecules of soluble fluorochrome per cell, within CD10+ cells was 3,460 +/- 1,050 (mean +/- SD; 5 samples). In 16 cases of B-lineage acute lymphoblastic leukemia (ALL), cells had levels of bcl-2 that were strikingly higher than those of their normal counterparts (33,560 +/- 14,570; P < .001 by t-test analysis). We next investigated whether the intensity of bcl-2 expression correlated with the resistance of immature B cells to in vitro culture. In 12 cases of B-lineage ALL, the cells recovered after 7 days of culture on allogeneic bone marrow stromal layers were 69% to 178% (median, 95.5%) of those originally seeded. Prolonged survival of leukemic cells in vitro was observed even in the absence of stromal layers in 6 of these 12 cases; the intensity of bcl-2 protein expression in these cases was 45,000 +/- 13,270, compared with 21,500 +/- 7,260 in the 6 cases in which greater than 99.5% of cells rapidly died by apoptosis under the same culture conditions (P = .003). Five immature B-cell lines, continuously growing in the absence of stroma, had the highest bcl-2 expression (79,400 +/- 20,330). By contrast, most normal CD19+, sIg-immature B cells died despite the presence of bone marrow stromal layers; 9.7% to 28.2% were recovered after 7 days of culture in three experiments. We conclude that abnormal bcl-2 gene expression influences the survival ability of B-cell progenitors. This may contribute to leukemogenesis and explain the aptitude of leukemic lymphoblasts to expand outside the bone marrow microenvironment.
Campana
D
D
Department of Hematology-Oncology, St Jude Children's Research Hospital, Memphis, TN 38101.
Coustan-Smith
E
E
Manabe
A
A
Buschle
M
M
Raimondi
S C
SC
Behm
F G
FG
Ashmun
R
R
Aricò
M
M
Biondi
A
A
Pui
C H
CH
D000293:Adolescent; D000328:Adult; D000595:Amino Acid Sequence; D017209:Apoptosis; D001402:B-Lymphocytes / Q000378:metabolism / Q000473:pathology*; D001854:Bone Marrow Cells; D002051:Burkitt Lymphoma / Q000378:metabolism / Q000473:pathology*; D002454:Cell Differentiation; D002470:Cell Survival; D002648:Child; D002675:Child, Preschool; D006412:Hematopoietic Stem Cells / Q000378:metabolism / Q000473:pathology; D006801:Humans; D007223:Infant; D008969:Molecular Sequence Data; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2; D014407:Tumor Cells, Cultured
D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2