Low level CD20 expression on T cell malignancies

Publisher Website
Google Scholar
Abstract
Although initially thought to be a B lineage restricted antigen, low “density” or antibody binding capacity (ABC) CD20 has recently been detected on subset(s) of normal T lymphocytes (Hultin et al.: Cytometry 14:196–204, 1993). We report low ABC CD20 expression in three (two children, one adult) cases of T‐acute lymphoblastic leukemia (T‐ALL). CD20 and other pertinent antigens were detected using a direct dual color method with a Becton Dickinson FACScan® flow cytometer and Simulset® software. Only one cell population based on light scatter was noted in each case that immunophenotypically represented almost a pure population of malignant cells expressing T lymphocyte antigens (for example, CD7 98%, 92%, and 100%, respectively). A total of 95%, 87%, and 79% of the cells from the three cases expressed CD20 with an unusual low ABC compared to the customary “bright” CD20 expression on normal B lymphocytes. Other B lymphocyte associated antigens, such as CD19, CD22, Dr, and immunoglobulin light chains, were negative. Eleven other T lymphocytic malignancies from 1991 to 1993 were CD20 negative, including three other case of T‐ALL (one adult and two children). One unusual case of intestinal small lymphocytic non‐Hodgkin's lymphoma with a natural killer/T lymphocytic immunophenotype not described in this report appeared to be CD20“dim”+. Low ABC CD20 expression by T lymphocytic malignancies may provide a more unique immunophenotypic “fingerprint” to help support the diagnosis of T cell neoplasia vs. normal/reactive T cells (for example, low ABC CD20 cells represent only 2.4 ± 1.5% of normal peripheral blood lymphocytes). This characteristic might also facilitate monitoring patients for residual or recurrent disease. The prognostic significance of CD20 co‐expression is uncertain and must await further studies.