Scientific Resources

The HOX family of homeobox genes plays an important role in normal and malignant hematopoiesis. Dysregulated HOX gene expression profoundly effects the proliferation and differentiation of hematopoietic stem cells (HSCs) and committed progenitors,and aberrant activation of HOX genes is a common event in human myeloid leukemia. HOXB6 is frequently overexpressed in human acute myeloid leukemia (AML). To gain further insight into the role of HOXB6 in hematopoiesis,we overexpressed HOXB6 in murine bone marrow using retrovirus-mediated gene transfer. We also explored structure-function relationships using mutant HOXB6 proteins unable to bind to DNA or a key HOX-binding partner,pre-B-cell leukemia transcription factor-1 (PBX1). Additionally,we investigated the potential cooperative interaction with myeloid ecotropic viral integration site 1 homolog (MEIS1). In vivo,HOXB6 expanded HSCs and myeloid precursors while inhibiting erythropoiesis and lymphopoiesis. Overexpression of HOXB6 resulted in AML with a median latency of 223 days. Coexpression of MEIS1 dramatically shortened the onset of AML. Cytogenetic analysis of a subset of HOXB6-induced AMLs revealed recurrent deletions of chromosome bands 2D-E4,a region frequently deleted in HOXA9-induced AMLs. In vitro,HOXB6 immortalized a factor-dependent myelomonocytic precursor capable of granulocytic and monocytic differentiation. These biologic effects of HOXB6 were largely dependent on DNA binding but independent of direct interaction with PBX1. View Publication

Bacterial magnetic particles (BacMPs) are efficient platforms of proteins for surface display systems. In this study,mononuclear cells from peripheral blood were separated using BacMPs expressing protein A on the BacMP membrane surface (protein A-BacMPs),which were complexed with the Fc fragment of anti-mouse IgG antibody. The procedure of positive selection involves incubation of mononuclear cells and mouse monoclonal antibodies against different cell surface antigens (CD8,CD14,CD19,CD20) prior to treatment with protein A-BacMP binding with rabbit anti-mouse IgG secondary antibodies. Flow cytometric analysis showed that approximately 97.5 +/- 1.7% of CD19(+) and CD20(+) cells were involved in the positive fraction after magnetic separation. The ratio of the negative cells in the negative fraction was approximately 97.6 +/-1.4%. This indicates that CD19(+) and CD20(+) cells can be efficiently separated from mononuclear cells. Stem cell marker (CD34) positive cells were also separated using protein A-BacMP binding with antibody. May-Grunwald Giemsa stain showed a high nuclear/cytoplasm ratio,which indicates a typical staining pattern of stem cells. The separated cells had the capability of colony formation as hematopoietic stem cells. Furthermore,the inhibitory effect of magnetic cell separation on CD14(+) cells was evaluated by measurement of cytokine in the culture supernatant by ELISA when the cells were cultured with or without lipopolysaccharide (LPS). The induction of IL1-beta,TNFalpha,and IL6 was observed in the presence of 1 ng/mL LPS in all fractions. On the other hand,in the absence of LPS,BacMPs had little immunopotentiation to CD14(+) cells as well as that of artificial magnetic particles,although TNFalpha and IL6 were slightly induced in the absence of LPS in the positive fraction. View Publication

We investigated the involvement of the urokinase-type plasminogen-activator receptor (uPAR) in granulocyte-colony-stimulating factor (G-CSF)-induced mobilization of CD34+ hematopoietic stem cells (HSCs) from 16 healthy donors. Analysis of peripheral blood mononuclear cells (PBMNCs) showed an increased uPAR expression after G-CSF treatment in CD33+ myeloid and CD14+ monocytic cells,whereas mobilized CD34+ HSCs remained uPAR negative. G-CSF treatment also induced an increase in serum levels of soluble uPAR (suPAR). Cleaved forms of suPAR (c-suPAR) were released in vitro by PBMNCs and were also detected in the serum of G-CSF-treated donors. c-suPAR was able to chemoattract CD34+ KG1 leukemia cells and CD34+ HSCs,as documented by their in vitro migratory response to a chemotactic suPAR-derived peptide (uPAR84-95). uPAR84-95 induced CD34+ KG1 and CD34+ HSC migration by activating the high-affinity fMet-Leu-Phe (fMLP) receptor (FPR). In addition,uPAR84-95 inhibited CD34+ KG1 and CD34+ HSC in vitro migration toward the stromal-derived factor 1 (SDF1),thus suggesting the heterologous desensitization of its receptor,CXCR4. Finally,uPAR84-95 treatment significantly increased the output of clonogenic progenitors from long-term cultures of CD34+ HSCs. Our findings demonstrate that G-CSF-induced upregulation of uPAR on circulating CD33+ and CD14+ cells is associated with increased uPAR shedding,which leads to the appearance of serum c-suPAR. c-suPAR could contribute to the mobilization of HSCs by promoting their FPR-mediated migration and by inducing CXCR4 desensitization. View Publication

Transplantation of genetically corrected autologous hematopoietic stem cells is an attractive approach for the cure of sickle-cell disease and beta-thalassemia. Here,we infected human cord blood cells with a self-inactivating lentiviral vector encoding an anti-sickling betaA-T87Q-globin transgene and analyzed the transduced progeny produced over a 6-month period after transplantation of the infected cells directly into sublethally irradiated NOD/LtSz-scid/scid mice. Approximately half of the human erythroid and myeloid progenitors regenerated in the mice containing the transgene,and erythroid cells derived in vitro from these in vivo-regenerated cells produced high levels of betaA-T87Q-globin protein. Linker-mediated PCR analysis identified multiple transgene-positive clones in all mice analyzed with 2.1 +/- 0.1 integrated proviral copies per cell. Genomic sequencing of vector-containing fragments showed that 86% of the proviral inserts had occurred within genes,including several genes implicated in human leukemia. These findings indicate effective transduction of very primitive human cord blood cells with a candidate therapeutic lentiviral vector resulting in the long-term and robust,erythroid-specific production of therapeutically relevant levels of beta-globin protein. However,the frequency of proviral integration within genes that regulate hematopoiesis points to a need for additional safety modifications. View Publication

GATA-2 is an essential transcription factor in the hematopoietic system that is expressed in hematopoietic stem cells (HSCs) and progenitors. Complete deficiency of GATA-2 in the mouse leads to severe anemia and embryonic lethality. The role of GATA-2 and dosage effects of this transcription factor in HSC development within the embryo and adult are largely unexplored. Here we examined the effects of GATA-2 gene dosage on the generation and expansion of HSCs in several hematopoietic sites throughout mouse development. We show that a haploid dose of GATA-2 severely reduces production and expansion of HSCs specifically in the aorta-gonad-mesonephros region (which autonomously generates the first HSCs),whereas quantitative reduction of HSCs is minimal or unchanged in yolk sac,fetal liver,and adult bone marrow. However,HSCs in all these ontogenically distinct anatomical sites are qualitatively defective in serial or competitive transplantation assays. Also,cytotoxic drug-induced regeneration studies show a clear GATA-2 dose-related proliferation defect in adult bone marrow. Thus,GATA-2 plays at least two functionally distinct roles during ontogeny of HSCs: the production and expansion of HSCs in the aorta-gonad-mesonephros and the proliferation of HSCs in the adult bone marrow. View Publication

Embryonic stem (ES) cells have the potential to serve as an alternative source of hematopoietic precursors for transplantation and for the study of hematopoietic cell development. Using coculture of human ES (hES) cells with OP9 bone marrow stromal cells,we were able to obtain up to 20% of CD34+ cells and isolate up to 10(7) CD34+ cells with more than 95% purity from a similar number of initially plated hES cells after 8 to 9 days of culture. The hES cell-derived CD34+ cells were highly enriched in colony-forming cells,cells expressing hematopoiesis-associated genes GATA-1,GATA-2,SCL/TAL1,and Flk-1,and retained clonogenic potential after in vitro expansion. CD34+ cells displayed the phenotype of primitive hematopoietic progenitors as defined by co-expression of CD90,CD117,and CD164,along with a lack of CD38 expression and contained aldehyde dehydrogenase-positive cells as well as cells with verapamil-sensitive ability to efflux rhodamine 123. When cultured on MS-5 stromal cells in the presence of stem cell factor,Flt3-L,interleukin 7 (IL-7),and IL-3,isolated CD34+ cells differentiated into lymphoid (B and natural killer cells) as well as myeloid (macrophages and granulocytes) lineages. These data indicate that CD34+ cells generated through hES/OP9 coculture display several features of definitive hematopoietic stem cells. View Publication

Hematopoietic progenitor/stem cell homing to the bone marrow requires the concerted action of several adhesion molecules. Endothelial P- and E-selectins play an important role in this process,but their ligands on a large subset of neonate-derived human CD34+ cells are absent,leading to a reduced ability to interact with the bone marrow (BM) microvasculature. We report here that this deficiency results from reduced alpha1,3-fucosyltransferase (FucT) expression and activity in these CD34+ cells. Incubation of CD34+ cells with recombinant human FucTVI rapidly corrected the deficiency in nonbinding CD34+ cells and further increased the density of ligands for both P- and E-selectins on all cord blood-derived CD34+ cells. Intravital microscopy studies revealed that these FucTVI-treated CD34+ cells displayed a marked enhancement in their initial interactions with the BM microvasculature,but unexpectedly,homing into the BM was not improved by FucTVI treatment. These data indicate that,although exogenous FucT enzyme activity can rapidly modulate selectin binding avidity of cord blood CD34+ cells,further studies are needed to understand how to translate a positive effect on progenitor cell adhesion in bone marrow microvessels into one that significantly influences migration and lodgement into the parenchyma. View Publication

Outgrowth,long-term self-renewal,and terminal maturation of human erythroid progenitors derived from umbilical cord blood in serum-free medium can be modulated by steroid hormones. Homogeneous erythroid cultures,as characterized by flow cytometry and dependence on a specific mixture of physiologic proliferation factors,were obtained within 8 days from a starting population of mature and immature mononuclear cells. Due to previous results in mouse and chicken erythroblasts,the proliferation-promoting effect of glucocorticoids was not unexpected. Surprisingly,however,androgen had a positive effect on the sustained expansion of human female but not male erythroid progenitors. Under optimal conditions,sustained proliferation of erythroid progenitors resulted in a more than 10(9)-fold expansion within 60 days. Terminal erythroid maturation was significantly improved by adding human serum and thyroid hormone (3,5,3'-triiodothyronine [T3]) to the differentiation medium. This resulted in highly synchronous differentiation of the cells toward enucleated erythrocytes within 6 days,accompanied by massive size decrease and hemoglobin accumulation to levels comparable to those in peripheral blood erythrocytes. Thus,obviously,different ligand-activated nuclear hormone receptors massively influence the decision between self-renewal and terminal maturation in the human erythroid compartment. View Publication

Adult bone marrow-derived cells can participate in muscle regeneration after bone marrow transplantation. In recent studies a single hematopoietic stem cell (HSC) was shown to give rise to cells that not only reconstituted all of the lineages of the blood,but also contributed to mature muscle fibers. However,the relevant HSC derivative with this potential has not yet been definitively identified. Here we use fluorescence-activated cell sorter-based protocols to test distinct hematopoietic fractions and show that only fractions containing c-kit(+) immature myelomonocytic precursors are capable of contributing to muscle fibers after i.m. injection. Although these cells belong to the myeloid lineage,they do not include mature CD11b(+) myelomonocytic cells,such as macrophages. Of the four sources of mature macrophages tested that were derived either from monocytic culture,bone marrow,peripheral blood after granulocyte colony-stimulating factor mobilization,or injured muscle,none contributed to muscle. In addition,after transplantation of bone marrow isolated from CD11b-Cre-transgenic mice into the Cre-reporter strain (Z/EG),no GFP myofibers were detected,demonstrating that macrophages expressing CD11b do not fuse with myofibers. Irrespective of the underlying mechanisms,these data suggest that the HSC derivatives that integrate into regenerating muscle fibers exist in the pool of hematopoietic cells known as myelomonocytic progenitors. View Publication

Mixed chimaerism and graft rejection are higher after reduced-intensity allogeneic stem cell transplantation (RIST) with T-cell depleted (TCD) allografts. As host immune status before RIST affects engraftment,we hypothesized that targeted depletion of host lymphocytes prior to RIST would abrogate graft rejection and promote donor chimaerism. Lymphocyte-depleting chemotherapy was administered at conventional doses to subjects prior to RIST with the intent of decreasing CD4(+) counts to textless0.05 x 10(9)cells/l. Subjects (n = 18) then received reduced-intensity conditioning followed by ex vivo TCD human leucocyte antigen-matched sibling allografts. All evaluable patients (n = 17) were engrafted; there were no late graft failures. At day +28 post-RIST,12 patients showed complete donor chimaerism. Mixed chimaerism in the remaining five patients was associated with higher numbers of circulating host CD3(+) cells (P = 0.0032) after lymphocyte-depleting chemotherapy and was preferentially observed in T lymphoid rather than myeloid cells. Full donor chimaerism was achieved in all patients after planned donor lymphocyte infusions. These data reflect the importance of host immune status prior to RIST and suggest that targeted host lymphocyte depletion facilitates the engraftment of TCD allografts. Targeted lymphocyte depletion may permit an individualized approach to conditioning based on host immune status prior to RIST. View Publication

The Lyn tyrosine kinase plays essential inhibitory signaling roles within hematopoietic cells by recruiting inhibitory phosphatases such as SH2-domain containing phosphatase-1 (SHP-1),SHP-2,and SH2-domain containing 5'-inositol phosphatase (SHIP-1) to the plasma membrane in response to specific stimuli. Lyn-deficient mice display a collection of hematopoietic defects,including autoimmune disease as a result of autoantibody production,and perturbations in myelopoiesis that ultimately lead to splenomegaly and myeloid neoplasia. In this study,we demonstrate that loss of Lyn results in a stem/progenitor cell-intrinsic defect leading to an age-dependent increase in myeloid,erythroid,and primitive hematopoietic progenitor numbers that is independent of autoimmune disease. Despite possessing increased numbers of erythroid progenitors,and a more robust expansion of these cells following phenylhydrazine challenge,Lyn-deficient mice are more severely affected by the chemotherapeutic drug 5-fluorouracil,revealing a greater proportion of cycling progenitors. We also show that mice lacking SHIP-1 have defects in the erythroid and myeloid compartments similar to those in mice lacking Lyn or SHP-1,suggesting an intimate relationship between Lyn,SHP-1,and SHIP-1 in regulating hematopoiesis. View Publication

Bone marrow-derived endothelial precursor cells incorporate into neovasculature and have been successfully used as vehicles for gene delivery to brain tumors. To determine whether systemically administered Sca1+ bone marrow cells labeled with superparamagnetic iron oxide nanoparticles can be detected by in vivo magnetic resonance imaging in a mouse brain tumor model,mouse Sca1+ cells were labeled in vitro with ferumoxides-poly-L-lysine complexes. Labeled or control cells were administered intravenously to glioma-bearing severe combined immunodeficient (SCID) mice. Magnetic resonance imaging (MRI) was performed during tumor growth. Mice that received labeled cells demonstrated hypointense regions within the tumor that evolved over time and developed a continuous dark hypointense ring at a consistent time point. This effect was not cleared by administration of a gadolinium contrast agent. Histology showed iron-labeled cells around the tumor rim in labeled mice,which expressed CD31 and von Willebrand factor,indicating the transplanted cells detected in the tumor have differentiated into endothelial-like cells. These results demonstrate that MRI can detect the incorporation of magnetically labeled bone marrow-derived precursor cells into tumor vasculature as part of ongoing angiogenesis and neovascularization. This technique can be used to directly identify neovasculature in vivo and to facilitate gene therapy by noninvasively monitoring these cells as gene delivery vectors. View Publication