Detection of acute leukemia cells with mixed lineage leukemia (MLL) gene rearrangements by flow cytometry using monoclonal antibody 7.1

Abstract

Translocations involving 11q23 are among the most common genetic abnormalities in hematologic malignancies, occurring in approximately 5-10% of acute lymphoblastic leukemia (ALL) and 5% of acute myeloblastic leukemia (AML). In 11q23 translocations, the mixed lineage leukemia (MLL) gene on chromosome 11, band q23, is usually disrupted. The human homologue of the rat NG2 chondroitin sulfate proteoglycan molecule, as detected by the monoclonal antibody (moab) 7.1, was shown to be expressed on leukemic cells with MLL rearrangements of children with acute leukemia. We further investigated the reactivity of the moab 7.1 on 533 cell samples of adults (n = 215) and children (n = 318) with acute leukemias (271 AML, 217 B-lineage ALL, 37 T-lineage ALL, eight CD7 ؉ CD56 ؉ myeloid/natural killer cell precursor acute leukemias) by flow cytometry. In AML, 38 samples were positive for moab 7.1 ('20%-cut-off-level'). These moab 7.1-positive AML cases revealed a myelomonocytic-differentiated immunophenotype with coexpression of the NK cell marker CD56 in 33 of 38 cases. Two of eight cell samples of the recently described CD7 ؉ CD56 ؉ myeloid/natural killer cell precursor acute leukemia entity reacted with moab 7.1. In ALL, 35 samples mostly of the pro-B-ALL subtype (33 pro-B-ALL, one common-ALL, one pre-B-ALL) were positive for moab 7.1. 58 (81%) of 72 samples with MLL rearrangements were positive for moab 7.1 including 28/31 with a t(4;11), 16/17 with a t(9;11), 3/5 with a t(11;19), and 2/6 with a del(11)(q23). All moab 7.1-positive ALL (n = 34) and childhood AML (n = 17) cases revealed MLL rearrangements as detected by Southern blot analysis and RT-PCR. However, 11 adults with AML, and one adult with moab 7.1-positive CD7 ؉ CD56 ؉ myeloid/natural killer cell precursor acute leukemia were negative for MLL rearrangements as proved by Southern blot analysis. We conclude that moab 7.1 is a sensitive but not entirely specific marker for the identification of 11q23-associated AML and ALL by flow cytometry in children and adults.

Immunophenotyping of acute leukemias and myelodysplastic syndromes

“…As an example, accumulating evidence supports the notion that during B-cell ontogeny, CD10 is expressed at a very early stage even prior to CD19 (36,38). In this case, BI or null ALL, which typically display a cCD79aϩ, CD19ϩ, CD10Ϫ immature (CD34ϩ, IgϪ) phenotype (43,44), would not fit into the normal B-cell maturation scheme (36,38). Also, the absence of reactivity for CD10 would represent an aberrant phenotype.…”

“…The occurence of these aberrant phenotypes can only be explained because of the existence of underlying genetic abnormalities in leukemic blast cells. Accordingly, CD10Ϫ blast cells from pro-B ALL frequently are CD15ϩ, 7.1ϩ, and/or CD65ϩ (43,44), a phenotype which has been shown to be closely related to the presence of t(4;11) and other cytogenetic abnormalities involving chromosome 11q23 (43,44). This concept can also contribute to the understanding of the associations observed between a common-ALL phenotype and hyperdiploidy (49), t(9;22) (18,49), and t(12;21) (17,20), as well as the additional correlations reported in adult and childhood common-ALL between the latter two translocations and a CD34high, CD38dim (18), and a CD20Ϫ/partialϩ, CD9Ϫ /partialϩ, CD34Ϫ/ϩheteroge-neous phenotype (17,20), respectively.…”

Insights into the cellular origin and etiology of the infant pro-B acute lymphoblastic leukemia with MLL-AF4 rearrangement

“…54 In fact, NG2 has gradually been incorporated in diagnostic panels for immunophenotyping of leukemic patients because of its potential predictive value for MLL rearrangements in childhood and adult acute myeloid leukemias. [54][55][56][57][58] Moreover, commonly seen in the clinic are leukemic patients harboring MLL rearrangements but lacking NG2 expression (Table 1). 55,57,59 Conversely, there are a proportion of cases in which expression of NG2 is clearly detected in the absence of MLL rearrangements.…”

“…[54][55][56][57][58] Moreover, commonly seen in the clinic are leukemic patients harboring MLL rearrangements but lacking NG2 expression (Table 1). 55,57,59 Conversely, there are a proportion of cases in which expression of NG2 is clearly detected in the absence of MLL rearrangements. 56,57 More recently, it has been suggested that 7.1 expression could be specifically associated with only two specific subtypes of leukemia harboring either the translocations t(4;11)(q21;q23) or t(9;11)(p13;q23), which encode for the leukemic fusion genes MLL-AF4 and MLL-AF9, respectively, but not for other MLL rearrangements.…”

“…55,57,59 Conversely, there are a proportion of cases in which expression of NG2 is clearly detected in the absence of MLL rearrangements. 56,57 More recently, it has been suggested that 7.1 expression could be specifically associated with only two specific subtypes of leukemia harboring either the translocations t(4;11)(q21;q23) or t(9;11)(p13;q23), which encode for the leukemic fusion genes MLL-AF4 and MLL-AF9, respectively, but not for other MLL rearrangements. 19 Importantly, we and many others have reported the existence of acute leukemias and plasmacytoid dendritic cell (pDC) leukemias (450%) lacking MLL rearrangements but expressing NG2 (Table 1).…”