Scientific Resources

There is potential interest for combining allogeneic hematopoietic cell transplantation (HCT),and particularly allogeneic HCT with a nonmyeloablative regimen,to the tyrosine kinase inhibitor imatinib (Glivec; Novartis,Basel,Switzerland,http://www.novartis.com) in order to maximize anti-leukemic activity against Philadelphia chromosome-positive leukemias. However,because imatinib inhibits c-kit,the stem cell factor receptor,it could interfere with bone marrow engraftment. In this study,we examined the impact of imatinib on normal progenitor cell function. Imatinib decreased the colony-forming capacity of mobilized peripheral blood human CD133(+) cells but not that of long-term culture-initiating cells. Imatinib also decreased the proliferation of cytokine-stimulated CD133(+) cells but did not induce apoptosis of these cells. Expression of very late antigen (VLA)-4,VLA-5,and CXCR4 of CD133(+) cells was not modified by imatinib,but imatinib decreased the ability of CD133(+) cells to migrate. Finally,imatinib did not decrease engraftment of CD133(+) cells into irradiated nonobese diabetic/severe combined immunodeficient/beta2m(null) mice conditioned with 3 or 1 Gy total body irradiation. In summary,our results suggest that,despite inhibition of hematopoietic progenitor cell growth in vitro,imatinib does not interfere with hematopoietic stem cell engraftment. View Publication

Although a large proportion of patients with polycythemia vera (PV) harbor a valine-to-phenylalanine mutation at amino acid 617 (V617F) in the JAK2 signaling molecule,the stage of hematopoiesis at which the mutation arises is unknown. Here we isolated and characterized hematopoietic stem cells (HSC) and myeloid progenitors from 16 PV patient samples and 14 normal individuals,testing whether the JAK2 mutation could be found at the level of stem or progenitor cells and whether the JAK2 V617F-positive cells had altered differentiation potential. In all PV samples analyzed,there were increased numbers of cells with a HSC phenotype (CD34+CD38-CD90+Lin-) compared with normal samples. Hematopoietic progenitor assays demonstrated that the differentiation potential of PV was already skewed toward the erythroid lineage at the HSC level. The JAK2 V617F mutation was detectable within HSC and their progeny in PV. Moreover,the aberrant erythroid potential of PV HSC was potently inhibited with a JAK2 inhibitor,AG490. View Publication

Recombinant human erythropoietin (rhEPO) is receiving increasing attention as a potential therapy for prevention of injury and restoration of function in nonhematopoietic tissues. However,the minimum effective dose required to mimic and augment these normal paracrine functions of erythropoietin (EPO) in some organs (e.g.,the brain) is higher than for treatment of anemia. Notably,a dose-dependent risk of adverse effects has been associated with rhEPO administration,especially in high-risk groups,including polycythemia-hyperviscosity syndrome,hypertension,and vascular thrombosis. Of note,several clinical trials employing relatively high dosages of rhEPO in oncology patients were recently halted after an increase in mortality and morbidity,primarily because of thrombotic events. We recently identified a heteromeric EPO receptor complex that mediates tissue protection and is distinct from the homodimeric receptor responsible for the support of erythropoiesis. Moreover,we developed receptor-selective ligands that provide tools to assess which receptor isoform mediates which biological consequence of rhEPO therapy. Here,we demonstrate that rhEPO administration in the rat increases systemic blood pressure,reduces regional renal blood flow,and increases platelet counts and procoagulant activities. In contrast,carbamylated rhEPO,a heteromeric receptor-specific ligand that is fully tissue protective,increases renal blood flow,promotes sodium excretion,reduces injury-induced elevation in procoagulant activity,and does not effect platelet production. These preclinical findings suggest that nonerythropoietic tissue-protective ligands,which appear to elicit fewer adverse effects,may be especially useful in clinical settings for tissue protection. View Publication

The 2 most frequent human MLL hematopoietic malignancies involve either AF4 or AF9 as fusion partners; each has distinct biology but the role of the fusion partner is not clear. We produced Mll-AF4 knock-in (KI) mice by homologous recombination in embryonic stem cells and compared them with Mll-AF9 KI mice. Young Mll-AF4 mice had lymphoid and myeloid deregulation manifest by increased lymphoid and myeloid cells in hematopoietic organs. In vitro,bone marrow cells from young mice formed unique mixed pro-B lymphoid (B220(+)CD19(+)CD43(+)sIgM(-),PAX5(+),TdT(+),IgH rearranged)/myeloid (CD11b/Mac1(+),c-fms(+),lysozyme(+)) colonies when grown in IL-7- and Flt3 ligand-containing media. Mixed lymphoid/myeloid hyperplasia and hematologic malignancies (most frequently B-cell lymphomas) developed in Mll-AF4 mice after prolonged latency; long latency to malignancy indicates that Mll-AF4-induced lymphoid/myeloid deregulation alone is insufficient to produce malignancy. In contrast,young Mll-AF9 mice had predominately myeloid deregulation in vivo and in vitro and developed myeloid malignancies. The early onset of distinct mixed lymphoid/myeloid lineage deregulation in Mll-AF4 mice shows evidence for both instructive" and "noninstructive" roles for AF4 and AF9 as partners in MLL fusion genes. The molecular basis for "instruction" and secondary cooperating mutations can now be studied in our Mll-AF4 model." View Publication

The cellular reservoir for Kaposi sarcoma-associated herpesvirus (KSHV) infection in the hematopoietic compartment and mechanisms governing latent infection and reactivation remain undefined. To determine susceptibility of human CD34+ hematopoietic progenitor cells (HPCs) to infection with KSHV,purified HPCs were exposed to KSHV,and cells were differentiated in vitro and in vivo. Clonogenic colony-forming activity was significantly suppressed in KSHV-infected CD34+ cells,and viral DNA was predominantly localized to granulocyte-macrophage colonies differentiated in vitro. rKSHV.219 is a recombinant KSHV construct that expresses green fluorescent protein from a cellular promoter active during latency and red fluorescent protein from a viral lytic promoter. Infection of CD34+ HPCs with rKSHV.219 showed similar patterns of infection,persistence,and hematopoietic suppression in vitro in comparison with KSHV. rKSHV.219 infection was detected in human CD14+ and CD19+ cells recovered from NOD/SCID mouse bone marrow and spleen following reconstitution with rKSHV.219-infected CD34+ HPCs. These results suggest that rKSHV.219 establishes persistent infection in NOD/SCID mice and that virus may be disseminated following differentiation of infected HPCs into the B-cell and monocyte lineages. CD34+ HPCs may be a reservoir for KSHV infection and may provide a continuous source of virally infected cells in vivo. View Publication

In this study,we demonstrate that extended culture of unfractionated mouse bone marrow (BM) cells,in serum-free medium,supplemented only with fibroblast growth factor (FGF)-1,FGF-2,or FGF-1 +2 preserves long-term repopulating hematopoietic stem cells (HSCs). Using competitive repopulation assays,high levels of stem cell activity were detectable at 1,3,and 5 weeks after initiation of culture. FGFs as single growth factors failed to support cultures of highly purified Lin(-)Sca-1(+)c-Kit(+)(LSK) cells. However,cocultures of purified CD45.1 LSK cells with whole BM CD45.2 cells provided high levels of CD45.1 chimerism after transplant,showing that HSC activity originated from LSK cells. Subsequently,we tested the reconstituting potential of cells cultured in FGF-1 + 2 with the addition of early acting stimulatory molecules,stem cell factor +interleukin-11 + Flt3 ligand. The addition of these growth factors resulted in a strong mitogenic response,inducing rapid differentiation and thereby completely overriding FGF-dependent stem cell conservation. Importantly,although HSC activity is typically rapidly lost after short-term culture in vitro,our current protocol allows us to sustain stem cell repopulation potential for periods up to 5 weeks. View Publication

Several hematopoietic growth factors,including interleukin-10 (IL-10) and transforming growth factor-beta1 (TGF-beta1),promote the differentiation of tolerogenic dendritic cells (DCs). Hepatocyte growth factor (HGF) is a pleiotropic cytokine whose effects on human DC differentiation and function have not been investigated. Monocytes cultured with HGF (HGFMo) differentiated into accessory cells with DC-like morphology,released low amounts of IL-12p70 and up-regulated IL-10 both at the mRNA and at the protein level. Upon activation with HGFMo,allogeneic CD4+CD25- T cells expressed the T regulatory (Treg)-associated transcription factor FoxP3,proliferated poorly,and released high levels of IL-10. Interestingly,blockade of surface immunoglobulin-like transcript 3 (ILT3) on HGFMo or neutralization of secreted IL-10 translated into partial restoration of T-cell proliferation. Secondary stimulation of HGFMo-primed CD4+ T cells with immunogenic DCs differentiated with granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-4 from monocytes of the same donor resulted in measurable T-cell proliferation. HGFMo-primed CD4+ T cells significantly inhibited the proliferation of naive CD4+CD25- T cells in a cell-contact-dependent manner. Finally,DNA microarray analysis revealed a unique gene-expression profile of HGF-activated monocytes. Collectively,our findings point to a novel role for HGF in the regulation of monocyte/DC functions that might be exploited therapeutically. View Publication

Ikaros is expressed in early hematopoietic progenitors and is required for lymphoid differentiation. In the absence of Ikaros,there is a lack of markers defining fate restriction along lympho-myeloid pathways,but it is unclear whether formation of specific progenitors or expression of their markers is affected. Here we use a reporter based on Ikaros regulatory elements to separate early progenitors in wild-type and Ikaros-null mice. We found previously undetected Ikaros-null lympho-myeloid progenitors lacking the receptor tyrosine kinase Flt3 that were capable of myeloid but not lymphoid differentiation. In contrast,lack of Ikaros in the common myeloid progenitor resulted in increased formation of erythro-megakaryocytes at the expense of myeloid progenitors. Using this approach,we identify previously unknown pivotal functions for Ikaros in distinct fate 'decisions' in the early hematopoietic hierarchy. View Publication

Anemia due to chronic disease or chemotherapy often is ameliorated by erythropoietin (Epo). Present studies reveal that,unlike steady-state erythropoiesis,erythropoiesis during anemia depends sharply on an Epo receptor-phosphotyrosine-343-Stat5 signaling axis. In mice expressing a phosphotyrosine-null (PY-null) Epo receptor allele (EpoR-HM),severe and persistent anemia was induced by hemolysis or 5-fluorouracil. In short-term transplantation experiments,donor EpoR-HM bone marrow cells also failed to efficiently repopulate the erythroid compartment. In each context,stress erythropoiesis was rescued to WT levels upon the selective restoration of an EpoR PY343 Stat5-binding site (EpoR-H allele). As studied using a unique primary culture system,EpoR-HM erythroblasts exhibited marked stage-specific losses in Epo-dependent growth and survival. EpoR-H PY343 signals restored efficient erythroblast expansion,and the selective Epo induction of the Stat5 target genes proviral integration site-1 (Pim-1) and oncostatin-M. Bcl2-like 1 (Bcl-x),in contrast,was not significantly induced via WT-EpoR,EpoR-HM,or EpoR-H alleles. In Kit+ CD71+ erythroblasts,EpoR-PY343 signals furthermore enhanced SCF growth effects,and SCF modulation of Pim-1 kinase and oncostatin-M expression. In maturing Kit- CD71+ erythroblasts,oncostatin-M exerted antiapoptotic effects that likewise depended on EpoR PY343-mediated events. Stress erythropoiesis,therefore,requires stage-specific EpoR-PY343-Stat5 signals,some of which selectively bolster SCF and oncostatin-M action. View Publication

Niemann-Pick type C2 (NPC2) protein has been characterized as a cholesterol-binding protein. Its loss leads to NPC2 disease,an inherited neurodegenerative disorder. When analyzing gene expression profile,we noticed high expression of both NPC2 and its receptor,mannose 6-phosphate receptor (MPR),in murine hematopoietic stem cells. NPC2 protein,in the presence of thrombopoietin (TPO),causes an increase in CFU-GEMM (colony-forming unit-granulocyte-erythroid-macrophage-megakaryocyte) and a decrease in CFU-GM (colony-forming unit-granulocyte-macrophage) colony number in colony-forming cell (CFC) assays. This effect is independent of cholesterol binding but does require the presence of MPR. With M07e cells,a TPO-dependent hematopoietic leukemia cell line,NPC2 can inhibit TPO-induced differentiation and enhance TPO-mediated anti-apoptosis effects. Strikingly,these results are not observed under the standard 20% O(2) level of the standard incubator,but rather at 7% O(2),the physiological oxygen level of bone marrow. Furthermore,NPC2 protein upregulates hypoxia inducible factor 1-alpha protein level at 7% O(2),but not at 20% O(2). Our results demonstrate that NPC2 protein plays a role in hematopoiesis at the physiologic bone marrow level of O(2). View Publication

An acquired somatic mutation,Jak2V617F,was recently discovered in most patients with polycythemia vera (PV),chronic idiopathic myelofibrosis (CIMF),and essential thrombocythemia (ET). To investigate the role of this mutation in vivo,we transplanted bone marrow (BM) transduced with a retrovirus expressing either Jak2 wild-type (wt) or Jak2V617F into lethally irradiated syngeneic recipient mice. Expression of Jak2V617F,but not Jak2wt,resulted in clinicopathologic features that closely resembled PV in humans. These included striking elevation in hemoglobin level/hematocrit,leukocytosis,megakaryocyte hyperplasia,extramedullary hematopoiesis resulting in splenomegaly,and reticulin fibrosis in the bone marrow. Histopathologic and flow cytometric analyses showed an increase in maturing myeloid lineage progenitors,although megakaryocytes showed decreased polyploidization and staining for acetylcholinesterase. In vitro analysis of primary cells showed constitutive activation of Stat5 and cytokine-independent growth of erythroid colony-forming unit (CFU-E) and erythropoietin hypersensitivity,and Southern blot analysis for retroviral integration indicated that the disease was oligoclonal. Furthermore,we observed strain-specific differences in phenotype,with Balb/c mice demonstrating markedly elevated leukocyte counts,splenomegaly,and reticulin fibrosis compared with C57Bl/6 mice. We conclude that Jak2V617F expression in bone marrow progenitors results in a PV-like syndrome with myelofibrosis and that there are strain-specific modifiers that may in part explain phenotypic pleiotropy of Jak2V617F-associated myeloproliferative disease in humans. View Publication

Protein tyrosine phosphatase 1B (PTP-1B) is a ubiquitously expressed cytosolic phosphatase with the ability to dephosphorylate JAK2 and TYK2,and thereby down-regulate cytokine receptor signaling. Furthermore,PTP-1B levels are up-regulated in certain chronic myelogenous leukemia patients,which points to a potential role for PTP-1B in myeloid development. The results presented here show that the absence of PTP-1B affects murine myelopoiesis by modifying the ratio of monocytes to granulocytes in vivo. This bias toward monocytic development is at least in part due to a decreased threshold of response to CSF-1,because the PTP-1B -/- bone marrow presents no abnormalities at the granulocyte-monocyte progenitor level but produces significantly more monocytic colonies in the presence of CSF-1. This phenomenon is not due to an increase in receptor levels but rather to enhanced phosphorylation of the activation loop tyrosine. PTP-1B -/- cells display increased inflammatory activity in vitro and in vivo through the constitutive up-regulation of activation markers as well as increased sensitivity to endotoxin. Collectively,our data indicate that PTP-1B is an important modulator of myeloid differentiation and macrophage activation in vivo and provide a demonstration of a physiological role for PTP-1B in immune regulation. View Publication