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[1070] CD33 Antigen Detection with a New Monoclonal Antibody PWS44 Reactive in Paraffin Tissue Sections: Pattern of Reactivity and Potential Diagnostic Utility

I Bansal, EL Flintoft, NH Piggott, M Rees, E Udale, V Reid, J Doherty, PW Scorer, GG McIntosh, A Chadburn, DM Knowles, E Hyjek. Weill Cornell Medical College, New York, NY; Newcastle upon Tyne, United Kingdom

Background: CD33, a siglec family member, is only expressed by hematopoietic cells. It is expressed by the earliest myeloid progenitors, but not hematopoietic stem cells, is present during myelomonocytic differentiation, and is expressed at low levels on granulocytes and resident histiocytes (HC). It is retained on monocytes and expressed on dendritic cells (DC). Anti-CD33 antibodies are used for phenotyping acute myelogenous leukemia (AML) and therapeutic purging of CD33+ AML. So far CD33 can only be detected in viable cell suspensions (flow cytometry; FC) and/or frozen sections (immunohistochemistry; FS IHC) due to a lack of reagents reactive in fixed tissues. We have developed a paraffin reactive monoclonal antibody (Mab), PWS44, recognizing the extracellular domain of CD33 and have characterized its pattern of reactivity.
Design: IHC with PWS44 was done on paraffin sections from 5 normal bone marrows (nl BM), 6 reactive lymph nodes (RLN)/spleen, 2 Kikuchi lymphadenitis (KL), 3 non-caseating granulomas (NCG), 5 MPDs (3 spleens, 2 BMs), 2 cell blocks of CD33+ cell lines (K562 and HL60), 12 BM with AML (6 CD33+, 6 CD33- by FC using MY9 or P67.6 clones), 4 B ALL (3 CD33+, 1 CD33-), 6 granulocytic sarcoma (GS) and 3 NK/T cell NHL mimicking GS on Bond-Max autostainer using Define Polymer HRP Detection System (Vision-BioSystems).
Results: PWS44 was reactive with nl MPD and MDS granulocytic and monocytic lineage cells but not erythroid precursors or megakaryocytes. In RLN/spleen PWS44 was reactive with sinus, germinal center, epitheliod and splenic sinus HC; DC; and plasmacytoid monocytes but not nl B or T cells. PWS44 was reactive with CD33+ cell lines, 6/6 CD33+ AML, 4/6 CD33- AML, 6/6 GS, 3/3 CD33+ B ALL but was negative in 1/1 CD33- B ALL and 3/3 T/NK NHL.
Conclusions: PWS44 identifies normal/neoplastic granulocytic and monocytic lineage cells in fixed tissues; the pattern of PWS44 reactivity parallels that of anti-CD33 Mabs used in FC/FS. It may identify CD33 expression in some AMLs not detected by other Mabs and in conjunction with other markers can be helpful in the differential diagnosis of myeloid tumors from their morphologic lymphoid mimics. Thus, PWS44 is diagnostically useful and, with the development of monoclonal anti-CD33 therapy, may have therapeutic implications.
Category: Hematopathology

Tuesday, March 27, 2007

Poster # 159, Tuesday Morning