Different clones of mAbs, directed against the same cluster of differentiation, may vary in their ability to detect the corresponding antigen on leukemic cells. For example, the expression of CD34, a membrane-associated glycoprotein found on pluripotential stem cells, lineage-committed hematopoietic progenitors, and some mature populations of both endothelial and stromal lineage (44-46), may be dependent on the choice of reagent. It has been found that CD34 mAbs react with different sites on the CD34 antigen (at least three as defined by their sensitivity to neurominidase) and, as a result, have different binding properties (44-48). The epitope recognized by B13C5 is sialic acid-dependent, in contrast to that recognized by ICH3. Therefore, it is not surprising that different antibodies can produce variation both in CD34 estimation and sensitivity in identifying circulating hematopoietic progenitors (20,49).
The use of different panels and even clones of mAbs may account for the wide variation in incidence reported for myeloid antigen expression in acute and chronic lymphoproliferative disorders. The coexpression of myeloid- and lymphoid-associated antigens in childhood acute lymphoblastic leukemia is well described, although the incidence of aberrant expression ranges from less than 5% to more than 30% (50,51). This discrepancy can be partly explained by the use of different panels of mAbs, but significant differences still occur when comparing antibodies with the same CD antigen. Thus, in two studies, the incidence of cases expressing CD13 and/or CD33 was 4% and 16%, respectively (52,53). In addition, the expression of myeloid antigens has been reported to be of prognostic importance by some (50), but not by all (54), groups. Interestingly, a further study (55) noted that the detection of myeloid antigens in childhood acute lymphoblastic leukemia is dependent, in part, on the commercial source of antibody. Similar conflicting data have been reported for CD13 and CD33 expression in B-cell chronic lymphocytic leukemia (56,57). Furthermore, CD14 was not detected by Polliack and colleagues (57), whereas others have described between 29% and 84% of cases that were positive for this antigen (56,58). Interestingly, Pinto and colleagues (59) demonstrated that the CD14 epitope is detected only with the My-4 antibody and not by other CD14 antibodies. We have reported similar findings in chronic lymphatic leukemia, in which CD13 and CD33 were detected using only a particular reagent (60).
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