Clonal chromosomal abnormalities in the stem cell compartment of patients with acute myeloid leukemia in morphological complete remission

Acute myeloid leukemia arises from the clonal expansion of a malignant transformed progenitor cell. Despite intensive chemotherapy, final disease eradication is achieved by a small proportion of cases only and 50-70% of adults with AML will ultimately relapse and die from their disease. Hence residual disease below the level of morphological detectability must be assumed in clinical and morphological complete remission. CD34+/CD38- and CD34+/CD38+ subpopulations of seven patients in morphological complete remission were isolated by FACS (purity98%) and were analyzed by conventional cytogenetics or FISH for chromosomal aberrations. In five of seven patients, clonal chromosomal abnormalities were detected in the CD34+/CD38+ subpopulation and in one patient with AML M2 (add (2)(q37)) in the most immature CD34+/CD38- stem cell compartment. One patient with AML M4Eo (inv(16),+8), showed a normal karyotype by conventional cytogenetic analysis, whereas four of 15 metaphases of the sorted CD34+/CD38+ subpopulation revealed the inversion 16. These observations underline that leukemic cells can survive intensive chemotherapy in the niche of the stem cell compartment. In some patients the sensitivity for the detection of persistent leukemic cells seems to be higher in FACS-sorted subpopulations than conventional cytogenetic analysis of the unseparated bone marrow. Immunophenotyping revealed minimal residual disease in four of the patients. Functional analysis has to be performed to investigate the leukemogenic potential of these residual cells.