Pattern of Cytoplasmic IgM Expression in Hematogones: A Flow Cytometric Study
DW Sevilla, A Colovai, FN Emmons, MB Levin, G Bhagat, B Alobeid. Columbia University, New York, NY
Background: Hematogones are physiologic B-cell precursors in the marrow. Despite their well-characterized phenotype and maturation patterns, problems persist in differentiating hematogones from the lymphoblasts of precursor B-cell acute lymphoblastic leukemia (B-ALL). The pattern of cytoplasmic IgM (cyt IgM) expression in the context of the three recognized maturational stages of hematogones has not been characterized. This expression is particularly relevant as a proportion of B-ALL demonstrate cyt IgM expression. In this study, we investigated the pattern and maturational sequence of cyt IgM expression in hematogones to provide an additional resource in differentiating hematogones from lymphoblasts.
Design: We prospectively analyzed 12 bone marrow aspirate samples by 3-4 color flow cytometry obtained between February and August 2008. In addition to our standard comprehensive antibody panel, we included additional antibody combinations: CD34/cyt IgM, TdT/cyt IgM and CD10/cyt IgM to further characterize the patterns of cyt IgM expression. Populations were considered negative if <10% of gated cells expressed the antigen.
Results: Using CD10/CD19 in combination the percentage of double positive cells representing the entire hematogone population ranged from 2.1 to 23.1% (median 3.7%). Expression of cyt IgM by hematogones varied depending on the level of maturation, however, two clear populations were identified in all bone marrow aspirate samples: cyt IgM negative early hematogones (TdT+/CD34+/CD10+bright/CD19+dim) ranged from 0.1% to 7.5% (median 0.9%) and cyt IgM positive more mature hematogones (TdT-/CD34-/CD10+dim, CD19+bright) ranged from 0.6% to 20.2% (median 3.1%).
Cytoplasmic IgM Expression
|Early Hematogones||Intermediate Hematogones|
Conclusions: Our findings document a biphenotypic pattern of cyt IgM expression that closely correlates with the stage of hematogone maturation, and indicate that the acquisition of cyt IgM occurs early in transition to the intermediate stage. In contrast to cyt IgM+ B-ALL, there is a spectrum of cyt IgM expression in normal precursor B-cells without aberrant or asynchronous expression. In conjunction with the previously described maturation patterns of B-cell antigens, this highly reproducible pattern of cyt IgM expression should aid in differentiating hematogones from residual or recurrent leukemic lymphoblasts.
Wednesday, March 11, 2009 1:00 PM
Poster Session VI # 171, Wednesday Afternoon