Antibodies directed against CD20 (L26, Leu 16, and Bl) are frequently used to determine the presence of B lymphocytes. However, recent publications describe the unexpected presence of CD20-positive T cells in the 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 myelogenous leukemia |AML|, 4 HIV positive, 2 myelodysplastic/myeloproliferative, 2 chronic myelogenous leukemia |CML|, 1 chronic lymphocytic lymphoma |CLL], 1 multiple myeloma). A small population of cells coexpressing CD3 (Leu 4) and CD20 dim (Leu 16) was identified in 94% of the specimens, representing 0% to 11%Phenotyping of human lymphoid proliferations is of value in determining cell lineage. Immunophenotyping uses monoclonal antibodies directed against B-or T-cell specific antigens. B lymphocytes are identified by the presence of the antigens CD 19, CD20, CD21, and CD22. CD20 is a 33-kDa membrane phosphoprotein' with three hydrophobic regions that traverse the cell membrane, creating a structure similar to an ion channel. 2This protein is expressed on the majority of B cells, appearing early in B-cell development (following CD 19 and CD 10, but preceding CD21, cell surface expression of CD22, and surface immunoglobulin). "5 CD20 is retained on mature B cells until plasma cell development. 34 The CD20 antigen can be identified by immunohistochemistry or flow cytometry using several commercially available monoclonal antibodies: Leu 16, Bl, and L26 (Leu 16

Leukemias are characterized by an idiopathic proliferation of a progenitor cell that is committed to a single cell lineage. However, leukemias with dual-lineage differentiation are being described, especially within the pediatric age group. The authors reviewed 118 cases of adult acute leukemia phenotyped by immunofluorescent flow cytometry; 7 cases demonstrated mixed cell lineage. Immunophenotypically these cases were defined by early B-lymphocyte differentiation (TdT, HLA-DR, and CD19) coexpressed with a myeloid receptor (CD13, CD15, or CD33) on the same leukemic cell. Routine cytochemical evaluation demonstrated punctate positivity of the blasts with naphthol AS-D chloroacetate esterase stain in five of seven cases. Cytogenetic analysis revealed structural abnormalities of chromosome 11 in four of the seven cases. Three of these studies showed a break at 11q23-24, the location of the human proto-oncogene ets-1. Clinically, two of these leukemias represented chronic myelogenous leukemia in blast crisis, and all cases behaved aggressively. The authors' data suggest that mixed lineage leukemias are an identifiable subset of adult acute leukemias and are associated with a poor prognosis.

The Southwest Oncology Group analyzed outcome with cytotoxic chemotherapy for previously untreated acute myeloblastic leukemia (AML) from 1982 through 1986. Results with acute promyelocytic leukemia (APL) prompted comparison with patients from 1986 through 1991 and analysis of factors contributing to APL results. Patient and disease characteristics and treatment outcome were compared for all evaluable patients, with more detailed analysis of factors affecting APL treatment outcome. From 1982 through 1986, median survival and disease- free survival in 45 APL patients were 106 months and greater than 105 months, respectively, versus 6 and 14 months for 417 other AML patients. Such differences were not seen from 1986 through 1991. In the 141 APL patients from 1982 through 1991, after adjusting for significant patient and disease characteristics, higher daunomycin (DNR) doses during induction were significantly associated with higher complete remission rates (P < .0001), longer survival (P < .0001), and longer DFS (P < .0001). Cytosine arabinoside (Ara-C) induction dose, the inclusion of other chemotherapy agents in induction, postremission therapy (consolidation, maintenance, or bone marrow transplantation) other than DNR, APL subtype, and patient age did not appear to significantly affect outcome of APL, except for a significant detrimental effect of high-dose Ara-C in consolidation (P = .0042). Morphologic AML subtypes other than APL did not affect outcome. We conclude that high-dose DNR selectively increases survival in APL. This good survival is important for evaluation of combined all-trans retinoic acid (ATRA)/chemotherapy protocols and for planning future combinations of chemotherapy and ATRA. These results illustrate the need to individualize chemotherapy for subtypes of AML. Therapeutic response of APL is independent of age. Except for APL, morphologic subclassification of AML contributed little prognostic information.

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