[1193] Significant CD5 Expression on Normal Stage III Hematogones and Mature B-Lymphocytes in Bone Marrow

FS Fuda, NJ Karandikar, W Chen. UT Southwestern Medical Center, Dallas, TX

Background: Hematogones (HG) are normal maturing B-lineage precursors that reside in bone marrow (BM) and exhibit a typical consistent, reproducible, complex spectrum of sequential antigen expression. This defines HG into three stages of maturation. We had observed CD5 expression on a subset of HG and mature B cells, particularly in cases with HG hyperplasia. The expression pattern of CD5 on B-cell subsets at different stages of maturation has not yet been systematically evaluated and is the focus of this study.
Design: Twenty-one BM specimens with HG hyperplasia (>3.5% of total events) were prospectively studied by 4-color flow cytometry for 25 lymphoid and myeloid antigens. Cluster analysis was performed using BD Paint-a-Gate software. HG were divided into 3 stages of maturation: Stage 1 HG (CD10+^bright/CD45+^dim/CD20-/CD22+/CD34+), Stage 2 (CD10+/CD45+^moderately/CD20+^variably/CD22+/CD34-) and Stage 3 (CD10+/CD45+^{moderately bright}/CD20+^bright/CD22+^bright). The proportion of cells with CD5 expression was determined for total B-lineage cells, mature B cells and each stage of HG.
Results: Patients ranged in age from 9 months to 63 years; 15 were male and 6 were female. Submitted clinical histories included 17 hematolymphoid neoplasia and 4 cytopenias. Flow cytometric findings were unremarkable in 14 of 21 cases. The remaining specimens showed residual previously diagnosed neoplasia in 6 cases and acute myeloid leukemia in 1 case. Of total events, the percentage (%) of mature B cells ranged form 0 to 6.1 (mean +/- SD: 1.6 +/- 1.9) and HG from 3.7 to 17.0 (7.4 +/- 3.8). Within the HG population, the % of stage 1 HG ranged from 1.2 to 70.0 (14.2 +/- 15.8), stage 2 from 22.0 to 87.0 (66.0 +/- 17.0), and stage 3 from 0 to 45.0 (19.6 +/- 12.0). The % of CD5 expression by entire B-lineage cells ranged from 6.7 to 66 (25.4 +/- 16.0), by mature B cells from 16.0 to 83.0 (53.6 +/- 20.2), and by stage 3 HG from 31.0 to 91.0 (69.7 +/- 14.4). Virtually all CD5(+) B cells expressed polytypic surface light chain. Interestingly, expression of CD5 was not observed on stage 1 and stage 2 HG.
Conclusions: CD5 is expressed on normal subsets of B cells in BM at different stages of maturation, specifically on stage 3 HG and mature B cells. Awareness of this normal pattern of expression would have clinical implications in the differential diagnosis of HG and CD5(+) neoplastic processes. Furthermore, exploration on the mechanism of this highly regulated CD5 expression may shed light on the pathogenesis of CD5(+) B-cell lymphoma.
Category: Hematopathology

Tuesday, March 10, 2009 9:30 AM

Poster Session III # 125, Tuesday Morning