Aberrant expression of CD7, CD56, and CD79a antigens in acute myeloid leukemias
Introduction
Aberrant antigen expression in acute myeloid leukemia (AML) is recognized to be a poor prognostic indicator. The European Group for the Immunological Characterization of Acute Leukemia (EGIL) developed a scoring system that ranges from 0.5 to 2.0 for the relative significance of cluster of differentation (CD) antigens in determining the immunophenotype of leukemias (Muller-Hermelink et al., 2001). Use of this scoring system has been used mainly for the identification of leukemias of ambiguous lineage (Cruse et al., 2005).
Flow cytometric immunophenotyping has become an important diagnostic tool for the classification of acute leukemias. The aberrant expression of selected markers in acute myeloid leukemic cells has been associated with relapse and biological aggressiveness (Head, 1996). Recently, there has been an increasing number of reports on the existence of unusual immunophenotypic expression in AML with the prediction of impending relapses prior to clinical manifestations (Campana et al., 1990, Coustan-Smith et al., 1993, Drach et al., 1991, Reading et al., 1993, Terstappen et al., 1991, Wörman et al., 1992). Our study was designed to analyze by flow cytometry the leukemic cells from 46 AML patients, looking for aberrant antigen expression and asynchronous antigen modulation, as well as aberrant light scatter patterns of leukemic cells. In the current study, the primary goals were to (1) determine frequency of lymphoid antigen expression in adult AML, (2) correlate the immunophenotype with FAB subtypes of AML, (3) investigate the role of cytoplasmic CD79a, a B cell marker that is assigned a high score of 2.0 in the WHO classification, and (4) to demonstrate the aberrant expression of CD7, CD56, and CD79a, representing the capacity of these leukemias for trilineal expression of leukocyte differentiation antigens, which portends a poor prognosis.
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Materials and methods
Forty-six recent cases of acute myeloid leukemia diagnosed in the Department of Pathology, University of Mississippi Medical Center, Jackson were classified according to morphology, immunophenotype, and clinical assessment. Immunophenotyping was performed by flow cytometric analysis of bone marrow aspirates, peripheral blood samples collected in EDTA, or lymph node cell preparations, using a flow cytometer (EpicsXL and FC500, Beckman and Coulter, Miami, FL), under standard techniques (Jackson
Results
Among the 46 patients with acute myeloid leukemia, CD7 was expressed in 15 cases (32.6%), and CD56 positivity was found in 10 patients (21.7%). Six (13%) AML cases showed dual expression of both CD7 and CD56. CD79a was expressed in 4 cases (8.7%). Among the 10 cases that were acute myeloblastic leukemia (FAB subtypes M0, M1, M2), 8 expressed CD7, 4 expressed CD56, and 4 were positive for CD79a. In acute myelomonocytic leukemia (FAB M4 subtype), CD7 and CD56 were each positive in 4 cases. There
Discussion
A diagnosis of AML requires the use of an antibody panel specific for AML markers. However, we added some markers not known to be specific to AML diagnosis, such as the T cell specific marker CD7, the B cell marker CD79a, and the natural killer cell marker CD56.
Bahia et al. (2001) analyzed 35 cases of AML for nonmyeloid phenotypes by flow cytometry. In their study, these aberrant phenotypes were found in 88.6% of the cases. Cross lineage antigen expression was present in 34.3%. CD7 was the most
Conclusion
The EGIL scoring system, which assigns relative levels of significance to CD antigens, may be of prognostic importance in the evaluation of aberrant antigen expression in AML. AML with aberrant antigen expression is to be distinguished from biphenotypic leukemia, which may manifest both a myeloid and a lymphoid phenotype. The aberrant expression of CD7, CD56, and CD79a represents the capacity of acute myeloid leukemia for trilineal expression of leukocyte differentiation antigens and portends a
Acknowledgments
The authors express genuine appreciation to Mr. Kevin Beason, B.S., MT (ASCP), CHT (ABHI), Mrs. Patsy Foley, B.S., MT (ASCP) CHT, CHS (ABHF), and Ms. Susan Touchstone, B.S., MT (ASCP), SBB (AABB), CHT CHS (ABHI) for their skilled technical expertise in flow cytometric analysis.
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