Scientific Resources

Myelodysplastic syndromes (MDSs) are a group of hematopoietic stem cell disorders characterized by ineffective hematopoiesis and peripheral blood cytopenias. Lenalidomide has dramatic therapeutic effects in patients with low-risk MDS and a chromosome 5q31 deletion,resulting in complete cytogenetic remission in textgreater60% of patients. The molecular basis of this remarkable drug response is unknown. To gain insight into the molecular targets of lenalidomide we investigated its in vitro effects on growth,maturation,and global gene expression in isolated erythroblast cultures from MDS patients with del(5)(q31). Lenalidomide inhibited growth of differentiating del(5q) erythroblasts but did not affect cytogenetically normal cells. Moreover,lenalidomide significantly influenced the pattern of gene expression in del(5q) intermediate erythroblasts,with the VSIG4,PPIC,TPBG,activin A,and SPARC genes up-regulated by textgreater2-fold in all samples and many genes involved in erythropoiesis,including HBA2,GYPA,and KLF1,down-regulated in most samples. Activin A,one of the most significant differentially expressed genes between lenalidomide-treated cells from MDS patients and healthy controls,has pleiotropic functions,including apoptosis of hematopoietic cells. Up-regulation and increased protein expression of the tumor suppressor gene SPARC is of particular interest because it is antiproliferative,antiadhesive,and antiangiogenic and is located at 5q31-q32,within the commonly deleted region in MDS 5q- syndrome. We conclude that lenalidomide inhibits growth of del(5q) erythroid progenitors and that the up-regulation of SPARC and activin A may underlie the potent effects of lenalidomide in MDS with del(5)(q31). SPARC may play a role in the pathogenesis of the 5q- syndrome. View Publication

Survivin,which is the smallest member of the inhibitor of apoptosis protein (IAP) family,is a chromosomal passenger protein that mediates the spindle assembly checkpoint and cytokinesis,and also functions as an inhibitor of apoptosis. Frequently overexpressed in human cancers and not expressed in most adult tissues,survivin has been proposed as an attractive target for anticancer therapies and,in some cases,has even been touted as a cancer-specific gene. Survivin is,however,expressed in proliferating adult cells,including human hematopoietic stem cells,T-lymphocytes,and erythroid cells throughout their maturation. Therefore,it is unclear how survivin-targeted anticancer therapies would impact steady-state blood development. To address this question,we used a conditional gene-targeting strategy and abolished survivin expression from the hematopoietic compartment of mice. We show that inducible deletion of survivin leads to ablation of the bone marrow,with widespread loss of hematopoietic progenitors and rapid mortality. Surprisingly,heterozygous deletion of survivin causes defects in erythropoiesis in a subset of the animals,with a dramatic reduction in enucleated erythrocytes and the presence of immature megaloblastic erythroblasts. Our studies demonstrate that survivin is essential for steady-state hematopoiesis and survival of the adult,and further,that a high level of survivin expression is critical for proper erythroid differentiation. View Publication

Definitive erythropoiesis occurs in islands composed of a central macrophage in contact with differentiating erythroblasts. Erythroid maturation including enucleation can also occur in the absence of macrophages both in vivo and in vitro. We reported previously that loss of Rb induces cell-autonomous defects in red cell maturation under stress conditions,while other reports have suggested that the failure of Rb-null erythroblasts to enucleate is due to defects in associated macrophages. Here we show that erythropoietic islands are disrupted by hypoxic stress,such as occurs in the Rb-null fetal liver,that Rb(-/-) macrophages are competent for erythropoietic island formation in the absence of exogenous stress and that enucleation defects persist in Rb-null erythroblasts irrespective of macrophage function. View Publication

A first step in hematopoiesis is the specification of the lymphoid and myeloid lineages from multipotent progenitor cells in the bone marrow. Using a conditional ablation strategy in adult mice,we show that this differentiation step requires Patched (Ptch),the cell surface-bound receptor for Hedgehog (Hh). In the absence of Ptch,the development of T- and B-lymphoid lineages is blocked at the level of the common lymphoid progenitor in the bone marrow. Consequently,the generation of peripheral T and B cells is abrogated. Cells of the myeloid lineage develop normally in Ptch mutant mice. Finally,adoptive transfer experiments identified the stromal cell compartment as a critical Ptch-dependent inducer of lymphoid versus myeloid lineage commitment. Our data show that Ptch acts as a master switch for proper diversification of hematopoietic stem cells in the adult organism. View Publication

Efficient in vivo selection increases survival of gene-corrected hematopoietic stem cells (HSCs) and protects hematopoiesis,even if initial gene transfer efficiency is low. Moreover,selection of a limited number of transduced HSCs lowers the number of cell clones at risk of gene activation by insertional mutagenesis. However,a limited clonal repertoire greatly increases the proliferation stress of each individual clone. Therefore,understanding the impact of in vivo selection on proliferation and lineage differentiation of stem-cell clones is essential for its clinical use. We established minimal cell and drug dosage requirements for selection of P140K mutant O6-methylguanine-DNA-methyltransferase (MGMT P140K)-expressing HSCs and monitored their differentiation potential and clonality under long-term selective stress. Up to 17 administrations of O6-benzylguanine (O6-BG) and 1,3-bis(2-chloroethyl)-1-nitroso-urea (BCNU) did not impair long-term differentiation and proliferation of MGMT P140K-expressing stem-cell clones in mice that underwent serial transplantation and did not lead to clonal exhaustion. Interestingly,not all gene-modified hematopoietic repopulating cell clones were efficiently selectable. Our studies demonstrate that the normal function of murine hematopoietic stem and progenitor cells is not compromised by reduced-intensity long-term in vivo selection,thus underscoring the potential value of MGMT P140K selection for clinical gene therapy. View Publication

Fetuses with homozygous alpha-thalassemia usually die at the third trimester of pregnancy or soon after birth. Hence,the disease could potentially be a target for fetal gene therapy. We have previously established a mouse model of alpha-thalassemia. These mice mimic the human alpha-thalassemic conditions and can be used as preclinical models for fetal gene therapy. We tested a lentiviral vector containing the HS 2,3,and 4 of the beta-LCR,a central polypurine tract element,and the beta-globin gene promoter directing either the EGFP or the human alpha-globin gene. We showed that the GFP expression was erythroid-specific and detected in BFU-E colonies and the erythroid progenies of CFU-GEMM. For in utero gene delivery,we did yolk sac vessel injection at midgestation of mouse embryos. The recipient mice were analyzed after birth for human alpha-globin gene expression. In the newborn,human alpha-globin gene expression was detected in the liver,spleen,and peripheral blood. The human alpha-globin gene expression was at the peak at 3-4 months,when it reached 20% in some recipients. However,the expression declined at 7 months. Colony-forming assays in these mice showed low abundance of the transduced human alpha-globin gene in their BFU-E and CFU-GEMM and the lack of its transcript. Thus,lentiviral vectors can be an effective vehicle for delivering the human alpha-globin gene into erythroid cells in utero,but,in the mouse model,delivery at late midgestation could not transduce hematopoietic stem cells adequately to sustain gene expression. View Publication

Aurora kinases play an important role in chromosome alignment,segregation,and cytokinesis during mitosis. We have recently shown that hematopoietic malignant cells including those from acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) aberrantly expressed Aurora A and B kinases,and ZM447439,a potent inhibitor of Aurora kinases,effectively induced growth arrest and apoptosis of a variety of leukemia cells. The present study explored the effect of AZD1152,a highly selective inhibitor of Aurora B kinase,on various types of human leukemia cells. AZD1152 inhibited the proliferation of AML lines (HL-60,NB4,MOLM13),ALL line (PALL-2),biphenotypic leukemia (MV4-11),acute eosinophilic leukemia (EOL-1),and the blast crisis of chronic myeloid leukemia K562 cells with an IC50 ranging from 3 nM to 40 nM,as measured by thymidine uptake on day 2 of culture. These cells had 4N/8N DNA content followed by apoptosis,as measured by cell-cycle analysis and annexin V staining,respectively. Of note,AZD1152 synergistically enhanced the antiproliferative activity of vincristine,a tubulin depolymerizing agent,and daunorubicin,a topoisomerase II inhibitor,against the MOLM13 and PALL-2 cells in vitro. Furthermore,AZD1152 potentiated the action of vincristine and daunorubicin in a MOLM13 murine xenograft model. Taken together,AZD1152 is a promising new agent for treatment of individuals with leukemia. The combined administration of AZD1152 and conventional chemotherapeutic agent to patients with leukemia warrants further investigation. View Publication

Overexpression of wild-type MN1 is a negative prognostic factor in patients with acute myeloid leukemia (AML) with normal cytogenetics. We evaluated whether MN1 plays a functional role in leukemogenesis. We demonstrate using retroviral gene transfer and bone marrow (BM) transplantation that MN1 overexpression rapidly induces lethal AML in mice. Insertional mutagenesis and chromosomal instability were ruled out as secondary aberrations. MN1 increased resistance to all-trans retinoic acid (ATRA)-induced cell-cycle arrest and differentiation by more than 3000-fold in vitro. The differentiation block could be released by fusion of a transcriptional activator (VP16) to MN1 without affecting the ability to immortalize BM cells,suggesting that MN1 blocks differentiation by transcriptional repression. We then evaluated whether MN1 expression levels in patients with AML (excluding M3-AML) correlated with resistance to ATRA treatment in elderly patients uniformly treated within treatment protocol AMLHD98-B. Strikingly,patients with low MN1 expression who received ATRA had a significantly prolonged event-free (P = .008) and overall (P = .04) survival compared with patients with either low MN1 expression and no ATRA,or high MN1 expression with or without ATRA. MN1 is a unique oncogene in hematopoiesis that both promotes proliferation/self-renewal and blocks differentiation,and may become useful as a predictive marker in AML treatment. View Publication

Protein geranylgeranyltransferase type I (GGTase-I) is responsible for the posttranslational lipidation of CAAX proteins such as RHOA,RAC1,and cell division cycle 42 (CDC42). Inhibition of GGTase-I has been suggested as a strategy to treat cancer and a host of other diseases. Although several GGTase-I inhibitors (GGTIs) have been synthesized,they have very different properties,and the effects of GGTIs and GGTase-I deficiency are unclear. One concern is that inhibiting GGTase-I might lead to severe toxicity. In this study,we determined the effects of GGTase-I deficiency on cell viability and K-RAS-induced cancer development in mice. Inactivating the gene for the critical beta subunit of GGTase-I eliminated GGTase-I activity,disrupted the actin cytoskeleton,reduced cell migration,and blocked the proliferation of fibroblasts expressing oncogenic K-RAS. Moreover,the absence of GGTase-I activity reduced lung tumor formation,eliminated myeloproliferative phenotypes,and increased survival of mice in which expression of oncogenic K-RAS was switched on in lung cells and myeloid cells. Interestingly,several cell types remained viable in the absence of GGTase-I,and myelopoiesis appeared to function normally. These findings suggest that inhibiting GGTase-I may be a useful strategy to treat K-RAS-induced malignancies. View Publication

In order to investigate the biologic processes underlying and resulting from the megakaryocytic hyperplasia that characterizes idiopathic myelofibrosis (IMF),peripheral blood CD34+ cells isolated from patients with IMF,polycythemia vera (PV),and G-CSF-mobilized healthy volunteers were cultured in the presence of stem cell factor and thrombopoietin. IMF CD34+ cells generated 24-fold greater numbers of megakaryocytes (MKs) than normal CD34+ cells. IMF MKs were also shown to have a delayed pattern of apoptosis and to overexpress the antiapoptotic protein bcl-xL. MK hyperplasia in IMF is,therefore,likely a consequence of both the increased ability of IMF progenitor cells to generate MKs and a decreased rate of MK apoptosis. Media conditioned (CM) by CD61+ cells generated in vitro from CD34+ cells were then assayed for the levels of growth factors and proteases. Higher levels of transforming growth factor-beta (TGF-beta) and active matrix metalloproteinase-9 (MMP9) were observed in media conditioned with IMF CD61+ cells than normal or PV CD61+ cells. Both normal and IMF CD61+ cells produced similar levels of VEGF. MK-derived TGF-B and MMP-9,therefore,likely contribute to the development of many pathological epiphenomena associated with IMF. View Publication

BACKGROUND: ALDH(br) cells express high aldehyde dehydrogenase (ALDH) activity and have progenitor cell activity in several contexts. We characterized human BM ALDH(br) cells to determine whether cell sorting based on ALDH activity isolates potentially useful populations for cell therapy. METHOD: We measured the expression of ALDH and cell-surface Ag by flow cytometry and compared the ability of sorted ALDH(br),and BM populations remaining after ALDH(br) cells were removed (ALDH(dim) populations),to develop into several cell lineages in culture. RESULTS: The ALDH(br) population comprised 1.2+/-0.8% (mean+/-SD,n=30) nucleated cells and was enriched in cells expressing CD34,CD117,CD105,CD127,CD133 and CD166,and in primitive CD34(+) CD38(-) and CD34(+) CD133(+) progenitors. Most of the CD34(+) and CD133(+) cells were ALDH(dim). ALDH(br) populations had 144-fold more hematopoietic colony-forming activity than ALDH(dim) cells and included all megakaryocyte progenitors. ALDH(br) populations readily established endothelial cell monolayers in cultures. Cells generating endothelial colonies in 7 days were 435-fold more frequent in ALDH(br) than ALDH(dim) populations. CFU-F were 9.5-fold more frequent in ALDH(br) than ALDH(dim) cells,and ALDH(br) cells gave rise to multipotential mesenchymal cell cultures that could be driven to develop into adipocytes,osteoblasts and chondrocytes. DISCUSSION: Hematopoietic,endothelial and mesenchymal progenitor cells can be isolated simultaneously from human BM by cell sorting based on ALDH activity. BM ALDH(br) populations may be useful in several cell therapy applications. View Publication

Ubiquitously acting chromatin opening elements (UCOEs) consist of methylation-free CpG islands encompassing dual divergently transcribed promoters of housekeeping genes that have been shown to confer resistance to transcriptional silencing and to produce consistent and stable transgene expression in tissue culture systems. To develop improved strategies for hematopoietic cell gene therapy,we have assessed the potential of the novel human HNRPA2B1-CBX3 UCOE (A2UCOE) within the context of a self-inactivating (SIN) lentiviral vector. Unlike viral promoters,the enhancer-less A2UCOE gave rise to populations of cells that expressed a reporter transgene at a highly reproducible level. The efficiency of expression per vector genome was also markedly increased in vivo compared with vectors incorporating either spleen focus-forming virus (SFFV) or cytomegalovirus (CMV) promoters,suggesting a relative resistance to silencing. Furthermore,an A2UCOE-IL2RG vector fully restored the IL-2 signaling pathway within IL2RG-deficient human cells in vitro and successfully rescued the X-linked severe combined immunodeficiency (SCID-X1) phenotype in a mouse model of this disease. These data indicate that the A2UCOE displays highly reliable transcriptional activity within a lentiviral vector,largely overcoming insertion-site position effects and giving rise to therapeutically relevant levels of gene expression. These properties are achieved in the absence of classic enhancer activity and therefore may confer a high safety profile. View Publication