Cytogenetically aberrant cells are present in the CD34⁺CD33⁻38⁻19⁻ marrow compartment in children with acute lymphoblastic leukemia

Abstract

Acute lymphoblastic leukemia (ALL), the most common cancer in childhood, is characterized by clonal proliferation of transformed lymphoblasts that comprise the majority of marrow and/or blood specimens. Although the leukemic cells typically express antigens associated with lymphoid maturation or activation (ie CD19, CD38, etc), it has been suggested that ALL blasts may evolve from a more primitive precursor. Increased understanding of the phenotypic and molecular heterogeneity of cells in ALL may provide clues to leukemogenesis and/ or impact prognostication or treatment. We utilized a phenotype/genotype approach to measure the prevalence and frequency of cytogenetically aberrant cells in a phenotypically defined primitive compartment (CD34⁺33⁻19⁻38⁻; CD34⁺Lin⁻). Bone marrow cells were flow cytometrically sorted into CD34⁻Lin⁺, CD34⁺Lin⁺ and CD34⁺Lin⁻ subpopulations. Fluorescence in situ hybridization (FISH) was used to quantify the frequency of cells with aneusomies in the sorted populations. Approximately 26% (5/19) of ALL cases at diagnosis contain cytogenetically aberrant CD34⁺Lin⁻ cells. The frequency of cytogenetically aberrant cells in the CD34⁺Lin⁻ compartment is independent of FAB, WBC and blast counts. These data indicate that cytogenetically aberrant cells may reside in a phenotypically defined primitive subpopulation and suggest that ALL blasts in some patients may evolve from a precursor compartment.