A New Cytokine-Dependent Monoblastic Cell Line With t(9;11)(p22;q23) Differentiates to Macrophages With Macrophage Colony-Stimulating Factor (M-CSF) and to Osteoclast-Like Cells With M-CSF and Interleukin-4

Malignant hematopoietic cell lines: in vitro models for the study of MLL gene alterations

Human tumor cell lines are powerful tools for investigating basic and applied aspects of cell biology. Leukemia-lymphoma cell lines have been instrumental in the cytogenetic and molecular analysis of recurring chromosome rearrangements, notably translocations and inversions, thus illuminating the pathogenesis of hematological malignancy. Chromosomal translocations targeting the MLL gene at 11q23 have come to represent a paradigm in acute leukemias. These translocations result in the in-frame joining of the MLL gene with a partner gene to generate unique fusion proteins of putatively novel function. More than 30 partner genes that participate with MLL in the more than 60 known 11q23 translocations have been reported. Cell lines provide territory to both explore the detailed structures of 11q23 translocations and investigate the leukemogenic activities of MLL fusion proteins. We review here the leukemia cell lines that have been described to carry 11q23 translocations and MLL fusion genes. Except for the t(10;11)(p12;q23), each of the following relatively frequent 11q23/MLL translocations is represented by one or more cell lines: 16 cell lines with t(4;11)(q21;q23), two cell lines with t(6;11)(q27;q23), seven cell lines with t(9;11)(p22;q23), and eight cell lines with t(11;19)(q23;p13). For each of three rare translocations, one cell line has been reported: t(5;11)(q15;q23), t(11;16)(q23;p13), and t(X;11)(q13;q23). Of these 36 cell lines with 11q23 translocations, 17 have been made available to us; we confirmed the occurrence of the alterations reported in these cell lines at the chromosomal and/or gene level. A second type of MLL gene alteration is the partial tandem duplication (PTD), which occurs in acute myeloid leukemia (AML). We found four AML cell lines with an MLL PTD; one acute lymphoblastic leukemia-derived cell line was reported to show a partial nontandem duplication. Finally, a third rearrangement involves intrachromosomal amplification of the unrearranged MLL gene leading to multiple copies of the gene and (presumably) increased expression. Three cell lines carrying such MLL amplifications have been described. The availability of these cell lines as model systems provides the opportunity to explore the altered expression or functions of MLL genes and their partners in oncogenesis.

MLL-AF9 oncogene expression affects cell growth but not terminal differentiation and is downregulated during monocyte–macrophage maturation in AML-M5 THP-1 cells

The MLL-AF9 oncogene - one of the most frequent MLL/HRX/ALL-1 rearrangements found in infantile and therapy-related leukaemias - originates from t(9;11)(p22;q23) and is mainly associated with monocytic acute myeloid leukaemia (AML-M5; FAB-classification). Here, we investigated the MLL-AF9 function by means of an antisense phosphorothioate-oligodeoxyribonucleotide (MLL-AF9-PS-ODNas) using the THP-1 AML-M5 cell line carrying t(9;11). Having confirmed that MLL-AF9-PS-ODNas induces strong inhibition of THP-1 cell growth, but only a moderate increase in apoptosis, we found that MLL-AF9-PS-ODNas did not induce morpho-functional terminal differentiation or restore M-CSF-, G-CSF- or GM-CSF-induced differentiation. Moreover, THP-1 cells showed the same phenotype with/without MLL-AF9-PS-ODNas. In THP-1 cells differentiated to mature macrophage-like cells by PMA/TPA or ATRA, MLL-AF9 expression was downregulated. Thus, in the monocytic lineage, MLL-AF9 may be expressed only in early phases and can induce deregulated amplification in both nonmalignant and malignant cells, maintaining the monocytic phenotype without blocking final maturation. Our findings suggest that: (1) as well as directly promoting cell growth, MLL-AF9 may also indirectly determine phenotype; (2) other leukaemogenic mutations associated with MLL-AF9-related leukaemias should be searched for mainly in processes of resistance to apoptosis (where MLL-AF9 may play only a limited role) and differentiation blockage (where MLL-AF9 may play no role).

Human cell line that differentiates to all myeloid lineages and expresses neutrophil secondary granule genes

The aim of this study was to characterize a human leukemic cell line that appears capable of spontaneous differentiation to all myeloid lineages. The MPD cell line was derived using standard tissue culture techniques from the peripheral blood of a patient with an aggressive nonchronic myelogenous leukemia myeloproliferative disorder. Immunophenotyping, cytogenetic analysis, reverse transcriptase polymerase chain reaction, Northern blotting, immunoblotting, and colony assays were used to characterize the line and to assess its ability to express lineage-specific genes representative of advanced differentiation.Light microscopic morphologic analysis of the MPD cell line suggests that it has the unique property of spontaneous differentiation to mature-appearing neutrophils, macrophages, eosinophils, and basophils in proportions that approximate those found in normal bone marrow or peripheral blood. It was demonstrated that this cell line is capable of producing lineage-specific mRNA and granule proteins of at least two myeloid lineages, neutrophil and eosinophil, including neutrophil secondary granule proteins, which are not expressed in other available human cell lines. MPD cells were found to be capable of producing differentiated myeloid colonies (neutrophil, eosinophil, macrophge, mixed) in semisolid medium. The ability of MPD cells to express genetic programs associated with advanced differentiation of multiple myeloid lineages will make it a valuable tool for the study of the processes underlying lineage commitment and the regulation of expression of lineage-specific genes.

Circulating CD2+ Monocytes Are Dendritic Cells

Low levels of CD2 have been described on subsets of monocytes, macrophages, and dendritic cells. CD2 is expressed on about one-third of circulating monocytes, at levels one-half log lower than on T or NK cells, representing 2–4% of PBMC. FACS analysis of CD2+ and CD2− monocytes revealed no significant difference in the expression of adhesion molecules (CD11a/b/c), class II Ags (HLA-DR, -DQ, -DP), myeloid Ags (CD13, CD14, CD33), or costimulatory molecules (CD80, CD86). Freshly isolated CD2+ and CD2− monocytes were morphologically indistinguishable by phase contrast microscopy. However, scanning electron microscopy revealed large prominent ruffles on CD2+ monocytes in contrast to small knob-like projections on CD2− monocytes. After 2 days of culture, the CD2+ monocytes largely lost CD14 expression and developed distinct dendrites, whereas the CD2− monocytes retained surface CD14 and remained round or oval. Freshly isolated CD2+ monocytes were more potent inducers of the allogeneic MLR and more efficiently induced proliferation of naive T cells in the presence of HIV-1 gp120 than did CD2− monocytes. After culture in the presence of GM/CSF and IL-4, CD2+ monocytes were up to 40-fold more potent than monocyte-derived dendritic cells or CD2− monocytes at inducing allogeneic T cell proliferation. These findings suggest that circulating CD2+ and CD2− monocytes are dendritic cells and the precursors of macrophages, respectively. Thus, dendritic cells are far more abundant in the blood than previously thought, and they and precursors of macrophages exist in the circulation as phenotypically, morphologically, and functionally distinct monocyte populations.