CD20 (PAN-B CELL ANTIGEN) EXPRESSION ON BONE-MARROW-DERIVED T-CELLS

Antibodies directed against CD20 (L26, Leu 16, and B1) are frequently used to determine the presence of B lymphocytes. However, recent publi cations describe the unexpected presence of CD20-positive T cells in t he peripheral blood of normal subjects and occasional T-cell neoplasms that express CD20. To determine the presence of CD20-positive T cells in bone marrow, flow cytometric analysis was performed on 34 aspirate specimens (14 normal, 5 acute lymphoblastic lymphoma [ALL], 5 acute m yelogenous leukemia [AML], 4 HIV positive, 2 myelodysplastic/myeloprol iferative, 2 chronic myelogenous leukemia [CML], 1 chronic lymphocytic lymphoma [CLL], 1 multiple myeloma). A small population of cells coex pressing CD3 (Leu 4) and CD20(dlm) (Leu 16) was identified in 94% of t he specimens, representing 0% to 11% (mean 1.77%) of marrow mononuclea r cells and 0% to 22.2% (mean 6.54%) of marrow lymphoid cells. There w as no correlation between the percentage of CD20-positive T cells and the CD4:CD8 ratio, patient age, gender, or diagnosis. CD20(dlm) positi ve cells included immature B cells and CD20-positive T cells, Although evaluation of CD20 expression is useful in delineating B-cell process es, caution should be exercised in interpreting its expression on bone marrow T-lymphoid cells. CD20 expression on T cells may be seen in ei ther normal, reactive, or neoplastic processes.