Blood
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The t(4;11)(q21;q23) is the most common translocation involving band 11q23 and is found predominantly in acute lymphoblastic leukemias (ALLs) of infants. Recent studies have shown that this translocation involves the MLL gene on chromosome 11 and the AF-4 gene on chromosome 4. Using oligonucleotide primers derived from these genes, we established reverse transcription-polymerase chain reaction (RT-PCR) assays for the detection of the fusion transcripts from both the der(11) and der(4) chromosomes. ⋯ In contrast, analysis for the der(4)-derived transcript resulted in the detection of this chimeric mRNA in only 84% of the cases analyzed. These data suggest that the critical chimeric gene product involved in the establishment of the leukemic clone is derived from the der(11) chromosome. Moreover, these data demonstrate the utility of the RT-PCR assay for the der(11)-encoded message both for diagnosing t(4;11)-containing leukemia and for monitoring patients for minimal residual disease.
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The cell-surface expression of the MIC2 antigen defined by the monoclonal antibody 12E7 was investigated on human leukocytes in bone marrow (BM), thymus, and peripheral blood (PB) using multiparameter flow cytometry and cell sorting. In contrast to preceding reports, we found that the MIC2 antigen is not restricted to T cells and monocytes. We show that it is also expressed in the B cell and in the granulocytic lineage, the levels of expression being related to distinct maturational stages. ⋯ Similarly high MIC2 densities were found on CD16+ natural killer cells and on CD14+ monocytes, whereas mature peripheral B cells exhibited low or intermediate expression, and granulocytes exhibited no or only dim expression. These results document that the MIC2 antigen (1) is expressed on all leukocyte lineages; (2) is differentially expressed during T- and B-lymphoid, as well as granulocytic maturation; (3) shows highest expression in the most immature lymphocytic and granulocytic developmental stages; and (4) is also differentially expressed on functional T-cell subsets. We speculate that these observations imply a functional significance of MIC2 in the network of hematopoietic adhesion pathways.