GATA1s induces hyperproliferation of eosinophil precursors in Down syndrome transient leukemia.

Transient leukemia (TL) is evident in 5-10% of all neonates with Down syndrome (DS) and associated with N-terminal truncating GATA1 mutations (GATA1s). Here we report that TL-cell clones generate abundant eosinophils in a substantial fraction of patients. Sorted eosinophils from patients with TL and eosinophilia carried the same GATA1s mutations as sorted TL blasts, consistent with their clonal origin. TL blasts exhibited a genetic program characteristic of eosinophils and differentiated along the eosinophil lineage in vitro. Similarly, ectopic expression of Gata1s, but not Gata1, in wild-type CD34(+)-hematopoietic stem and progenitor cells induced hyperproliferation of eosinophil promyelocytes in vitro. Although GATA1s retained the function of GATA1 to induce eosinophil genes by occupying their promoter regions, GATA1s was impaired in its ability to repress oncogenic MYC and the pro-proliferative E2F transcription network. Chromatin Immunoprecipitation Sequencing (ChIP-seq) indicated reduced GATA1s occupancy at the MYC promoter. Knockdown of MYC, or the obligate E2F-cooperation partner DP1, rescued the GATA1s-induced hyperproliferative phenotype. In agreement, terminal eosinophil maturation was blocked in Gata1(Δe2) knockin mice, exclusively expressing Gata1s, leading to accumulation of eosinophil precursors in blood and bone marrow. These data suggest a direct relationship between the N-terminal truncating mutations of GATA1 and clonal eosinophilia in DS patients.

Dexamethasone versus prednisone for induction therapy in childhood acute lymphoblastic leukemia: a systematic review and meta-analysis.

This systematic review and meta-analysis compared the efficacy and toxicity of dexamethasone (DEX) versus prednisone (PRED) for induction therapy in childhood acute lymphoblastic leukemia (ALL). We searched biomedical literature databases and conference proceedings for randomized controlled trials comparing DEX and PRED during induction therapy for childhood ALL. A total of eight studies were eligible for inclusion in this meta-analysis. DEX, in comparison with PRED, reduced events (that is, death from any cause, refractory or relapsed leukemia, or second malignancy; risk ratio (RR) 0.80; 95% confidence interval (CI), 0.68-0.94) and central nervous system relapse (RR 0.53; 95% CI, 0.44-0.65), but did not alter bone marrow relapse (RR 0.90; 95% CI, 0.69-1.18) or overall mortality (RR 0.91; 95% CI, 0.76-1.09). Patients receiving DEX had a higher risk of mortality during induction (RR 2.31; 95% CI, 1.46-3.66), neuro-psychiatric adverse events (RR 4.55; 95% CI, 2.45-8.46) and myopathy (RR 7.05; 95% CI, 3.00-16.58). There was no statistically significant difference in the risk of osteonecrosis, sepsis, fungal infection, diabetes or pancreatitis. DEX in induction therapy for children with ALL is more efficacious than PRED. However, DEX is also associated with more toxicity, and currently it remains unclear whether short-term superiority of DEX will also result in better overall survival.

Functional differences between myeloid leukemia-initiating and transient leukemia cells in Down's syndrome.

Children with constitutional trisomy 21 or Down's syndrome (DS) are predisposed to develop myeloid leukemia (ML) at a young age. DS-ML is frequently preceded by transient leukemia (TL), a spontaneously resolving accumulation of blasts during the newborn period. Somatic mutations of GATA1 in the blasts of TL and DS-ML likely function as an initiating event. We hypothesized that the phenotypic difference between TL and DS-ML is due to a divergent functional repertoire of the leukemia-initiating cells. Using an NOD/SCID model, we found that cells initiating DS-ML engrafted, disseminated to distant bone marrow sites, and propagated the leukemic clone in secondary recipients. In contrast, TL cells lacked the ability to expand and to migrate, but were able to persist in the recipient bone marrow. We found some evidence of genomic progression with 1 of 9 DS-ML samples and none of 11 TL samples harboring a mutation of N-RAS. The findings of this pilot study provide evidence for the functional impact of second events underlying the transformation of TL into DS-ML and a needed experimental tool for the functional testing of these promoting events.

Distinct gene signatures of transient and acute megakaryoblastic leukemia in Down syndrome.

Approximately 10% of newborns with Down syndrome develop Transient Leukemia (TL), a disorder that is unique to infants with constitutional trisomy 21 (or trisomy 21 mosaicism). TL blasts disappear spontaneously within the first 3 months of life in the majority of cases. Despite the resolution of TL, 20-30% of these newborns will go on to develop acute megakaryoblastic leukemia (AMKL) later in life. In this study, samples from both TL and AMKL patients were examined using cDNA microarrays to study the pathogenic progression from TL to AMKL. TL and AMKL samples partition separately by cluster analysis, and AMKL samples had substantial increases in apolipoprotein C-I, transporter 1, myosin alkali light chain 4, and spermidine/spermine N-acetyltransferase, compared to TL samples. Although these findings will require validation in an independent series of TL and AMKL samples, they indicate that TL and AMKL have distinct gene signatures, and provide a basis for studies of the different mechanisms underlying either the resolution of TL or its progression to AMKL.

Fusion of two novel genes, RBM15 and MKL1, in the t(1;22)(p13;q13) of acute megakaryoblastic leukemia.

t(1;22) is the principal translocation of acute megakaryoblastic leukemias. Here we show this chromosomal rearrangement to result in the fusion of two novel genes, RNA-binding motif protein-15 (RBM15), an RNA recognition motif-encoding gene with homology to Drosophila spen, and Megakaryoblastic Leukemia-1 (MKL1), a gene encoding an SAP (SAF-A/B, Acinus and PIAS) DNA-binding domain.

cDNA cloning, expression pattern, and chromosomal localization of Mlf1, murine homologue of a gene involved in myelodysplasia and acute myeloid leukemia.

The NPM-MLF1 fusion protein is expressed in blasts from patients with myelodysplasia/acute myeloid leukemia (MDS/AML) containing the t(3;5) chromosomal rearrangement. Nucleophosmin (NPM), a previously characterized nucleolar phosphoprotein, contributes to two other fusion proteins found in lympho-hematopoietic malignancies, anaplastic large cell lymphoma (NPM-ALK) and acute promyelocytic leukemia (NPM-RARalpha). By contrast, the function of the carboxy-terminal fusion partner, myelodysplasia/myeloid leukemia factor 1 (MLF1), is unknown. To aid in understanding normal MLF1 function, we isolated the murine cDNA, determined the chromosomal localization of Mlf1, and defined its tissue expression by in situ hybridization. Mlf1 was highly similar to its human homologue (86% and 84% identical nucleotide and amino acid sequence, respectively) and mapped to the central region of chromosome 3, within a segment lacking known mouse mutations. Mlf1 tissue distribution was restricted during both development and postnatal life, with high levels present only in skeletal, cardiac, and selected smooth muscle, gonadal tissues, and rare epithelial tissues including the nasal mucosa and the ependyma/choroid plexus in the brain. Mlf1 transcripts were undetectable in the lympho-hematopoietic organs of both the embryonic and adult mouse, suggesting that NPM-MLF1 contributes to the genesis of MDS/AML in part by enforcing the ectopic overexpression of MLF1 within hematopoietic tissues.

Expression patterns of the hepatic leukemia factor gene in the nervous system of developing and adult mice.

Hepatic leukemia factor (HLF) is a bZIP transcription factor related to the CES-2 protein, which controls apoptosis of the NSM serotoninergic neurons in Caenorhabditis elegans. Ectopic expression of HLF as an E2A-HLF fusion protein in t(17;19)-positive human pro-B cell acute lymphoblastic leukemias is believed to promote malignancy by interfering with apoptosis. While HLF has been linked to malignancies of the lymphoid system, it is not normally expressed in these cells. Rather, HLF transcripts are detected in the liver, kidney, lung and adult nervous system by Northern blotting. Despite the links to cell death, little is known of the distribution or function of HLF in the adult and developing mammalian nervous system. Therefore, we cloned mouse Hlf and studied its expression by in situ hybridization. During embryonic brain development, Hlf expression was restricted to the anterior pituitary and meninges. By early postnatal life, Hlf was highly expressed in somatosensory cortex, thalamic nuclei, and structures arising from ectodermal placodes. Subsequently, Hlf expression increased in the central nervous system and was found throughout the brain by adulthood. In the developing pituitary gland, Hlf was highly expressed in the rostral tip of the anterior lobe. This pattern is similar to that of Tef, an Hlf-related bZIP protein. However, while Tef is expressed in the anterior pituitary of the adult mouse, Hlf was detected in both the anterior and posterior pituitary. Hlf expression was not associated with cells undergoing programmed cell death in the nervous system. Hlf expression increased markedly with synaptogenesis and was coincident with barrel formation revealed by cytochrome oxidase staining. Together, these data suggest that Hlf plays a role in the function of differentiated neurons in the adult nervous system rather than programmed cell death.

Juvenile chronic myelogenous leukemia multilineage CD34+ cells: aberrant growth and differentiation properties.

Juvenile chronic myelogenous leukemia (JCML) is a hematologic malignancy of monocyte-macrophage lineage in which leukemic progression is mediated in an autocrine manner by tumor necrosis factor (TNF-alpha), GM-CSF and possibly other growth factors. Cytogenetic data showing involvement of both erythroid and monocyte-macrophage lineages in the JCML leukemic clone, as well as an observed episode of B-lineage lymphoid blast crisis in JCML, has strengthened the thesis for a lympho-hematopoietic pluripotent stem cell origin for the disorder. To study this further, JCML CD34+ cells from bone marrow (BM) or spleen from six newly diagnosed patients were isolated and cultured in clonogenic assays with combinations of recombinant cytokines. Compared to control CD34+ cells, JCML cells from all patients showed an aberrant growth pattern restricted almost exclusively to the monocyte-macrophage lineage. Most of the clonogenic activity was seen in a subsorted population of CD34+, HLA-Dr- cells. Additionally, an exaggerated growth response to minute doses of GM-CSF that had no effect on control cells was observed with JCML CD34+ cells. Recloning ("self-renewal") of JCML CD34+ cells was also strongly promoted by GM-CSF. JCML colonies also formed spontaneously in the absence of exogenous cytokines but were augmented by GM-CSF, interleukin 1 and TNF-alpha, the latter feature not seen with control CD34+ cells from normal BM. The abnormal spontaneous growth pattern of CD34+ JCML cells could be suppressed directly in vitro by anti-TNF-alpha antibodies and anti-GM-CSF antibodies alone or in combination, and by soluble TNF-alpha receptors (sTNF-R:Fc), consistent with the notion that JCML CD34+ cells are stimulated by both cytokines in an autocrine manner. In malignant CD34+ cells from one patient, the cytogenetic marker monosomy 7 proved leukemic involvement of monocyte-macrophage, erythroid and B-lymphoid lineages. We conclude that CD34+ JCML cells of multilineage potential exhibit excessive and aberrant monocyte-macrophage colony formation, a property that was previously observed in JCML progenitors found in light density cell fractions. Thus, within the CD34+ cellular compartment is a subpopulation of JCML "stem" cells that accounts for the abnormal leukemic proliferative activity in this disease.

Administration of recombinant human granulocyte-macrophage colony-stimulating factor after autologous bone marrow transplantation in children with acute myelogenous leukemia: a note of caution.

A series of 22 consecutive pediatric patients undergoing ABMT for treatment of primary AML was reviewed in an efficacy analysis of recombinant human granulocytemacrophage colony-stimulating factor (rhGM-CSF). Treatment with at least two cycles of chemotherapy and a standard conditioning regimen of busulfan and cyclophosphamide preceded the marrow infusion. Twelve patients who underwent transplants between 1992 and 1994 received 5.5 micrograms/kg/day rhGM-CSF as part of their transplant protocol. They were compared with 10 patients who underwent transplants between 1989 and 1991 but did not receive rhGM-CSF. Despite containing a significantly higher proportion of patients in first clinical remission at the time of the transplant, the rhGM-CSF-treated group had a significantly higher relapse and poorer overall survival rate after ABMT than the untreated group (36 vs 90%). The rhGM-CSF-treated group tended to have more rapid neutrophil engraftment and shorter hospital stays; however, neither of these trends was statistically significant. To properly determine the role of rhGM-CSF in the survival of pediatric patients undergoing ABMT for treatment of AML, a prospective randomized trial is desirable. Until these data are available, the current analysis suggests that particular caution is indicated with the use of this drug in this group of patients.

Role of interleukin-6 in the proliferation of human multiple myeloma cell lines OCI-My 1 to 7 established from patients with advanced stage of the disease.

Interleukin-6 (IL-6) has been shown to stimulate the proliferation of multiple myeloma cells purified to a high degree from human bone marrow. IL-6 production in multiple myeloma has been attributed to cells belonging to the myeloma clone, thus supporting a mechanism of autostimulation. In addition, it has been shown that IL-6 may be produced by auxiliary cell populations of the bone marrow that are not part of the myeloma clone. A definitive separation of both putative sources for IL-6 may be difficult to achieve in fresh patient IL-6 growth requirement and production by pure myeloma cell populations using seven human myeloma cell lines (OCI-My 1 to 7) that were established from patients with advanced disease. The proliferative response of each line to recombinant IL-6 was measured in a clonogenic assay providing human plasma and methylcellulose as a viscous support and by 3H-thymidine uptake in liquid suspension culture. We observed marked heterogeneity, ranging from IL-6-dependent colony formation by OCI-My 4, to IL-6-independent growth. All lines expressed mRNA for the IL-6 receptor. Expression of IL-6 mRNA was analyzed after amplification by polymerase chain reaction and was present in five of seven lines. IL-6 protein was detected by enzyme-linked immunosorbent assay (ELISA) in the culture supernatants of two lines (OCI-My 3 and 2). Its functional activity was confirmed in a bioassay using the IL-6-dependent murine hybridoma line B 13.29. This activity was neutralized by anti-IL-6 antibody. Two lines did not express mRNA for IL-6. The remaining three lines expressed mRNA for IL-6, but did not secrete IL-6 protein. Immunoprecipitation experiments with lysates of one of these three lines did not detect the presence of IL-6 protein. These results suggest that autocrine stimulation by IL-6 may occur in some cell lines derived from patients with multiple myeloma. However, it does not represent a universal mechanism in myeloma cell growth.

Human B-lymphopoiesis is supported by bone marrow-derived stromal cells.

We have recently reported an in vitro culture system that allows the clonal growth and differentiation of normal human bone marrow B-lineage cells. In the report presented here, we have used this B-cell colony assay to study the influence of cellular components of the human bone marrow microenvironment on B-lymphopoiesis. It is demonstrated that bone marrow stromal cells were able to provide all the necessary requirements for the growth and differentiation of B-lineage cells under the conditions of the B-cell colony assay. These stromal cells were obtained from long-term bone marrow cultures (LTBMC) that had been established from the spicules in human bone marrow. When these stromal cells were plated as an adherent underlayer in the double-agar B-cell colony assay, both immature and mature B-lineage cells were induced to differentiate into colonies containing cells that secreted immunoglobulin. The stromal cells from these spicule-derived LTBMCs maintained the capacity to support B-cell colony formation for up to 9 months.