Chromosome Abnormalities and Karyotype Evolution in the Stem Cell Compartments of AML and MDS

The phenotype of the (pre)leukemic stem cell in AML and MDS has not been identified as yet. We have investigated whether cells with a stem cell-like immunophenotype (CD34+/CD38-) are involved in the leukemogenic process. In 12 patients with AML and in one patient with MDS the identification of (pre)leukemic cells was performed by classical cytogenetics. Highly purified (96-98% purity) cellular subpopulations were generated by fluoresence activated cell sorting according to the expression of CD34 and CD38. Following brief incubation with a cytokine cocktail (EPO, GCSF, GM-CSF, IL-3, SCF) the sorted subpopulations were processed for chromosome analysis. In 9/12 AML patients clonal karyotype abnormalities were observed in the unsorted material. In 7/9 cases the chromosomal changes found in unsorted specimens were also detected in the immature stem cell-like population (CD34+/CD38-). In 9/9 cases the karyotype abnormalities were diagnosed in the population of committed progenitors (CD34+/CD38+). Additional secondary abnormalities were also demonstrable in both subpopulations in a case of M4Eo with inv(16). In a patient with secondary MDS RA, 2 subpopulations, CD34+/CD38- and CD34+/CD38+, were sorted together (CD34+/ 38+ -) because of the rarity of available cells. Cytogenetic analysis revealed a mosaic of normal and abnormal cells with 5 different dependent cell clones. All abnormal cell clones were demonstrable in the CD34+, sorted cell population. The relevance of our findings for pathogenesis, autologous stem cell transplantation and targeted gene therapy are discussed.