EVIDENCE FOR MALIGNANT TRANSFORMATION IN ACUTE MYELOID-LEUKEMIA AT THE LEVEL OF EARLY HEMATOPOIETIC STEM-CELLS BY CYTOGENETIC ANALYSIS OF CD34(+) SUBPOPULATIONS

Acute myeloid leukemia (AML) is a heterogenous disease according to mo rphology, immunophenotype, and genetics. The retained capacity of diff erentiation is the basis for the phenotypic classification of the bulk population of leukemic blasts and the identification of distinct subp opulations. Within the hierarchy of hematopoietic development and diff erentiation it is still unknown at which stage the malignant transform ation occurs. It was our aim to analyze the potential involvement of c ells with the immunophenotype of pluripotent stem cells in the leukemi c process by the use of cytogenetic and cell sorting techniques. Cytog enetic analyses of bone marrow aspirates were performed in 13 patients with AML (11 de novo and 2 secondary) and showed karyotype abnormalit ies in 10 cases [2q+, +4, 6p ,t(6;9), 7, +8 in 1 patient each and inv( 16) in 4 patients each]. Aliquots of the samples were fractionated by fluorescence-activated cell sorting of CD34(+) cells. Two subpopulatio ns, CD34(+)/CD38(-) (early hematopoietic stem cells) and CD34(+)/CD38( +) (more mature progenitor cells), were screened for karyotype aberati ons as a marker for leukemic cells. Clonal abnormalities and evaluable metaphases were found in 8 highly purified CD34(+)/CD38(-) population s and in 9 of the CD34(+)/CD38(-) specimens, respectively. In the majo rity of cases (CD34(+)/CD38(-), 6 of 8 informative samples; CD34(+)/CD 38(+), 5 of 9 informative samples), the highly purified CD34(+) specim ens also contained cytogenetically normal cells. Secondary, progressio n-associated chromosomal changes (+8, 12) were identified in the CD34( +)/CD38(-) cells of 2 patients. We conclude that clonal karyotypic abn ormalities are frequently found in the stem cell-like (CD34(+)/CD38(-) ) and more mature (CD34(+)/CD38(+)) populations of patients with AML, irrespective of the phenotype of the bulk population of leukemic blast s and of the primary or secondary character of the leukemia. Our data suggest that, in AML, malignant transformation as well as disease prog ression may occur at the level of CD34(+)/CD38(-) cells with multiline age potential. (C) 1995 by The American Society of Hematology.