Heterogeneity of CD5 Membrane Expression on B-Chronic Lymphocytic Leukemia Cells

The CD5 antigen has been used to characterize the typical B-chronic lymphocytic leukemia B cell. CD5 antigen while found on mature T cells is also frequently found on malignant clonal B cells in B-CLL. We have sequentially evaluated the presence of CD5 antigen on a group of B-CLL cells using flow cytometry. Purified peripheral blood B cells from B-CLL patients were studied for the presence of both CD19 and CD5. This approach insured that the presence of CD5 antigen was only assessed on CD19 positive B cells. Our data suggests that there is considerable heterogeneity for presentation of CD5 antigen in clonal B cells in this disease. We define 3 B cell groups based on the presentation of CD5; low CD5, intermediate CD5 and high CD5 antigen positive B cells. In addition sequential analysis over several months of study indicates that the CD5 antigen is consistently present on these clonal B cells. Low CD5 B cells appear to have an excess of kappa phenotype. In conclusion CD5 antigen may be considerably more heterogeneous on clonal CLL B cells than previously thought. This variable presentation of CD5 antigen on CLL B cell clones needs to be considered in the assessment and characterization of B-CLL.