Intravital Imaging of Young and Aged Stem Cells in the Marrow of Long Bones: Visualizing Mammalian Stem Cell Behavior in Real-Time in Vivo

Abstract Hematopoiesis, the process in which blood cells are generated from hematopoietic stem and progenitor cells (HSPCs) is primarily confined to the bone cavities. The interactions of hematopoietic cells with stroma cells forming niches inside the bone cavities are central to hematopoiesis, as these regulate cell proliferation, self-renewal and differentiation. Hematopoietic cell/stroma interactions have thus been, in analogy to the immunological synapse, named stem/progenitor cell synapses. So far, visualization of the behavior of somatic stem and progenitor cells in an undisturbed in vivo environment has not been reported for the mammalian system and consequently, the cellular dynamics of stem, progenitor and differentiated cells in vivo are only poorly defined. We developed and performed intravital time-lapse 2-photon microscopy in the marrow of the long bones (tibia) of mice to study the behavior and dynamics of differentiated hematopoietic cells as well as HPCs and HSCs in close vicinity to the endosteum in vivo over time. We demonstrate that HPCs as well as HSCs reside in close vicinity to the endosteum, further supporting the notion of an endosteal stem cell niche, and that they are, in contrast to differentiated macrophages and dendritic cells, solitary and immobile. Both HPCs and HSCs occupy distinct positions relative to the endosteum and show cell protrusion movement consistent with an active stem/progenitor cell synapse. Lastly, we report that aged HSCs show increased protrusion movement and localize more distantly to the endosteum compared to young HSCs. In addition, aged HSCs present with reduced adhesion to stroma as well as reduced polarity upon adhesion in vitro, implying a connection between altered stem cell dynamics in vivo and stem cell aging. The intravital imaging technology developed might establish a basis for further delineating additional important questions in stem cell biology like cellular mechanisms of hematopoietic stem cell self-renewal and differentiation in the context of the stroma/niche in vivo.

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Involvement of the Integrin Alpha 6 Receptor in the Homing and Engraftment of Hematopoietic Stem and Progenitor Cells to Bone Marrow.

Blood ◽

10.1182/blood.v104.11.1293.1293 ◽

2004 ◽

Vol 104 (11) ◽

pp. 1293-1293

Author(s):

Hong Qian ◽

Sten Eirik W. Jacobsen ◽

Marja Ekblom

Keyword(s):

Bone Marrow ◽

Stem Cell ◽

Progenitor Cells ◽

Progenitor Cell ◽

Bone Marrow Cells ◽

Hematopoietic Stem ◽

Stem And Progenitor Cells ◽

Functional Blocking

Abstract Within the bone marrow environment, adhesive interactions between stromal cells and extracellular matrix molecules are required for stem and progenitor cell survival, proliferation and differentiation as well as their transmigration between bone marrow (BM) and the circulation. This regulation is mediated by cell surface adhesion receptors. In experimental mouse stem cell transplantation models, several classes of cell adhesion receptors have been shown to be involved in the homing and engraftment of stem and progenitor cells in BM. We have previously found that integrin a6 mediates human hematopoietic stem and progenitor cell adhesion to and migration on its specific ligands, laminin-8 and laminin-10/11 in vitro (Gu et al, Blood, 2003; 101:877). Using FACS analysis, the integrin a6 chain was now found to be ubiquitously (>95%) expressed in mouse hematopoietic stem and progenitor cells (lin−Sca-1+c-Kit+, lin−Sca-1+c-Kit+CD34+) both in adult bone marrow and in fetal liver. In vitro, about 70% of mouse BM lin−Sca-1+c-Kit+ cells adhered to laminin-10/11 and 40% adhered to laminin-8. This adhesion was mediated by integrin a6b1 receptor, as shown by functional blocking monoclonal antibodies. We also used a functional blocking monoclonal antibody (GoH3) against integrin a6 to analyse the role of the integrin a6 receptor for the in vivo homing of hematopoietic stem and progenitor cells. We found that the integrin a6 antibody inhibited the homing of bone marrow progenitors (CFU-C) into BM of lethally irradiated recipients. The number of homed CFU-C was reduced by about 40% as compared to cells incubated with an isotype matched control antibody. To study homing of long-term repopulating stem cells (LTR), antibody treated bone marrow cells were first injected intravenously into lethally irradiated primary recipients. After three hours, bone marrow cells of the primary recipients were analysed by competitive repopulation assay in secondary recipients. Blood analysis 16 weeks after transplantation revealed an 80% reduction of stem cell activity of integrin a6 antibody treated cells as compared to cells treated with control antibody. These results suggest that integrin a6 plays an important role for hematopoietic stem and progenitor cell homing in vivo.

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Integrin alpha 6 Is Essential for Fetal Hematopoietic Progenitor, but Not Fetal Stem Cell Homing to Bone Marrow.

Blood ◽

10.1182/blood.v106.11.1387.1387 ◽

2005 ◽

Vol 106 (11) ◽

pp. 1387-1387

Author(s):

Hong Qian ◽

Sten Eirik W. Jacobsen ◽

Marja Ekblom

Keyword(s):

Bone Marrow ◽

Stem Cell ◽

Progenitor Cells ◽

Progenitor Cell ◽

Fetal Liver ◽

Hematopoietic Stem ◽

Stem And Progenitor Cells ◽

Integrin Alpha 6

Abstract Homing of transplanted hematopoietic stem cells (HSC) in the bone marrow (BM) is a prerequisite for establishment of hematopoiesis following transplantation. However, although multiple adhesive interactions of HSCs with BM microenviroment are thought to critically influence their homing and subsequently their engraftment, the molecular pathways that control the homing of transplanted HSCs, in particular, of fetal HSCs are still not well understood. In experimental mouse stem cell transplantation models, several integrins have been shown to be involved in the homing and engraftment of both adult and fetal stem and progenitor cells in BM. We have previously found that integrin a6 mediates human hematopoietic stem and progenitor cell adhesion to and migration on its specific ligands, laminin-8 and laminin-10/11 in vitro (Gu et al, Blood, 2003; 101:877). Furthermore, integrin a6 is required for adult mouse HSC homing to BM in vivo (Qian et al., Abstract American Society of Hematology, Blood 2004 ). We have now found that the integrin a6 chain like in adult HSC is ubiquitously (>99%) expressed also in fetal liver hematopoietic stem and progenitor cells (lin−Sca-1+c-Kit+, LSK ). In vitro, fetal liver LSK cells adhere to laminin-10/11 and laminin-8 in an integrin a6b1 receptor-dependent manner, as shown by function blocking monoclonal antibodies. We have now used a function blocking monoclonal antibody (GoH3) against integrin a6 to analyse the role of the integrin a6 receptor for the in vivo homing of fetal liver hematopoietic stem and progenitor cells to BM. The integrin a6 antibody inhibited homing of fetal liver progenitors (CFU-C) into BM of lethally irradiated recipients. The number of homed CFU-C in BM was reduced by about 40% as compared to the cells incubated with an isotype matched control antibody. To study homing of long-term repopulating stem cells, BM cells were first incubated with anti-integrin alpha 6 or anti-integrin alpha 4 or control antibody, and then injected intravenously into lethally irradiated primary recipients. After three hours, BM cells of the primary recipients were analysed by competitive repopulation assay in secondary recipients. Blood analysis up to 16 weeks after transplantation showed that no reduction of stem cell reconstitution from integrin a6 antibody treated cells as compared to cells treated with control antibody. In accordance with this, fetal liver HSC from integrin a6 gene deleted embryos did not show any impairment of homing and engraftment in BM as compared to normal littermates. These results suggest that integrin a6 plays an important developmentally regulated role for homing of distinct hematopoietic stem and progenitor cell populations in vivo.

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Ex vivo expansion of human hematopoietic stem and progenitor cells

Blood ◽

10.1182/blood-2011-01-283606 ◽

2011 ◽

Vol 117 (23) ◽

pp. 6083-6090 ◽

Cited By ~ 187

Author(s):

Ann Dahlberg ◽

Colleen Delaney ◽

Irwin D. Bernstein

Keyword(s):

Stem Cell ◽

Growth Factors ◽

Notch Signaling ◽

Progenitor Cells ◽

Ex Vivo ◽

Ex Vivo Expansion ◽

Hematopoietic Growth Factors ◽

Self Renewal ◽

Hematopoietic Stem ◽

Stem And Progenitor Cells

AbstractDespite progress in our understanding of the growth factors that support the progressive maturation of the various cell lineages of the hematopoietic system, less is known about factors that govern the self-renewal of hematopoietic stem and progenitor cells (HSPCs), and our ability to expand human HSPC numbers ex vivo remains limited. Interest in stem cell expansion has been heightened by the increasing importance of HSCs in the treatment of both malignant and nonmalignant diseases, as well as their use in gene therapy. To date, most attempts to ex vivo expand HSPCs have used hematopoietic growth factors but have not achieved clinically relevant effects. More recent approaches, including our studies in which activation of the Notch signaling pathway has enabled a clinically relevant ex vivo expansion of HSPCs, have led to renewed interest in this arena. Here we briefly review early attempts at ex vivo expansion by cytokine stimulation followed by an examination of our studies investigating the role of Notch signaling in HSPC self-renewal. We will also review other recently developed approaches for ex vivo expansion, primarily focused on the more extensively studied cord blood–derived stem cell. Finally, we discuss some of the challenges still facing this field.

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Elevated Mcl-1 perturbs lymphopoiesis, promotes transformation of hematopoietic stem/progenitor cells, and enhances drug resistance

Blood ◽

10.1182/blood-2010-04-281071 ◽

2010 ◽

Vol 116 (17) ◽

pp. 3197-3207 ◽

Cited By ~ 80

Author(s):

Kirsteen J. Campbell ◽

Mary L. Bath ◽

Marian L. Turner ◽

Cassandra J. Vandenberg ◽

Philippe Bouillet ◽

...

Keyword(s):

Progenitor Cells ◽

Progenitor Cell ◽

Fetal Liver ◽

Cytotoxic Agents ◽

Hematopoietic Stem ◽

Stem And Progenitor Cells ◽

Fetal Liver Cells ◽

Follicular Lymphomas ◽

The Impact

Abstract Diverse human cancers with poor prognosis, including many lymphoid and myeloid malignancies, exhibit high levels of Mcl-1. To explore the impact of Mcl-1 overexpression on the hematopoietic compartment, we have generated vavP-Mcl-1 transgenic mice. Their lymphoid and myeloid cells displayed increased resistance to a variety of cytotoxic agents. Myelopoiesis was relatively normal, but lymphopoiesis was clearly perturbed, with excess mature B and T cells accumulating. Rather than the follicular lymphomas typical of vavP-BCL-2 mice, aging vavP-Mcl-1 mice were primarily susceptible to lymphomas having the phenotype of a stem/progenitor cell (11 of 30 tumors) or pre-B cell (12 of 30 tumors). Mcl-1 overexpression dramatically accelerated Myc-driven lymphomagenesis. Most vavP-Mcl-1/ Eμ-Myc mice died around birth, and transplantation of blood from bitransgenic E18 embryos into unirradiated mice resulted in stem/progenitor cell tumors. Furthermore, lethally irradiated mice transplanted with E13 fetal liver cells from Mcl-1/Myc bitransgenic mice uniformly died of stem/progenitor cell tumors. When treated in vivo with cyclophosphamide, tumors coexpressing Mcl-1 and Myc transgenes were significantly more resistant than conventional Eμ-Myc lymphomas. Collectively, these results demonstrate that Mcl-1 overexpression renders hematopoietic cells refractory to many cytotoxic insults, perturbs lymphopoiesis and promotes malignant transformation of hematopoietic stem and progenitor cells.

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The GEF Lsc Regulates Hematopoietic Stem Cell Motility, Mobilization and Recruitment.

Blood ◽

10.1182/blood.v108.11.1346.1346 ◽

2006 ◽

Vol 108 (11) ◽

pp. 1346-1346

Author(s):

Isabelle Petit ◽

Prashant Kaul ◽

Daniel J. Lerner ◽

Shahin Rafii

Keyword(s):

Stem Cell ◽

Cell Migration ◽

Tumor Growth ◽

Cell Motility ◽

Progenitor Cells ◽

Hematopoietic Stem Cell ◽

Tumor Angiogenesis ◽

Progenitor Cell ◽

Hematopoietic Stem ◽

Stem And Progenitor Cells

Abstract Lsc is a Rho GTPase guanine nucleotide exchange factor (RhoGEF) that physically and functionally links G-protein coupled receptors (GPCR) to the monomeric GTPase RhoA in mature hematopoietic and other cells. Lsc−/− (LscKO) mice have a peripheral leukocytosis, abnormal neutrophil and B cell motility, and immune response deficiencies. Although Lsc is required for neutrophil homeostasis, its role in hematopoietic stem and progenitor cells is unknown. In this study, we have used LscKO mice to determine if Lsc is required for normal stem cell motility and mobilization. Initially, we used immunofluorescence labeling to demonstrate that hematopoietic stem and progenitor cells express Lsc. This suggested that Lsc may be required for normal hematopoietic stem and progenitor cell migration. Stromal-cell derived factor-1 (SDF-1) is a potent chemokine for hematopoietic stem cells and activates the CXCR4 GPCR. It has been reported that Lsc is not required for SDF-1-stimulated migration of mature murine T and B cells. However, using a bare-filter transwell assay, we found that while LscKO Sca-1+ cells and Sca-1+Lin- cells have normal spontaneous migration, they have significantly increased SDF-1-stimulated migration compared to their wild-type (WT) counterparts, 1.4 and 2.3 fold, respectively. We then demonstrated that adhesion of LscKO Sca-1+ cells to bone marrow (BM) stromal MS-5 cells was normal, indicating that impaired adhesion was not responsible for the abnormal SDF-1-stimulated migration. Using colony assay, we demonstrated that LscKO mice have a normal number of circulating peripheral stem and progenitor cells. Strikingly, after 5 days of G-CSF administration, LscKO mice have 1.6 fold and 2.3 fold the number of peripheral mature WBC and stem and progenitor cells (colony forming units), respectively, compared to WT mice. Recruitment of BM CXCR4+ pro-angiogenic stem and progenitor cells has been linked to enhanced tumor angiogenesis. Because LscKO BM cells had abnormal SDF-1-stimulated migration and mobilization, we hypothesized that Lsc might regulate tumor angiogenesis as well. To this end, we assessed tumor growth in LscKO mice by injecting congenic Lewis lung carcinoma cells subcutaneously into LscKO mice and WT controls. Preliminary experiments revealed that tumors were 3.3 times larger in the LscKO mice as compared to WT mice. Quantification of the tumor vessels with anti-CD31 staining demonstrated that the tumors in LscKO mice were 1.4 fold more vascularized than controls. In summary, our results demonstrate that the Rho GEF Lsc is essential for normal hematopoietic stem cell migration and mobilization. In addition, we propose that absence of Lsc facilitates tumor growth by promoting BM stem and progenitor cell recruitment to the neo-angiogenic vessels, possibly augmenting tumor vascularization.

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Systemic Administration of Pleiotrophin Induces Hematopoietic Stem Cell Regeneration In Vivo.

Blood ◽

10.1182/blood.v114.22.1498.1498 ◽

2009 ◽

Vol 114 (22) ◽

pp. 1498-1498

Author(s):

Heather A Himburg ◽

Pamela Daher ◽

Sarah Kristen Meadows ◽

J. Lauren Russell ◽

Phuong Doan ◽

...

Keyword(s):

Stem Cell ◽

Growth Factor ◽

Progenitor Cells ◽

Progenitor Cell ◽

Fold Increase ◽

Cell Regeneration ◽

Hematopoietic Stem ◽

Hematopoietic Reconstitution

Abstract Abstract 1498 Poster Board I-521 Significant progress has been made toward delineating the intrinsic and extrinsic signaling pathways that regulate hematopoietic stem cell (HSC) self-renewal. However, much less is known regarding the process of HSC regeneration or the extrinsic signals that regulate hematopoietic reconstitution following stress or injury. Elucidation of the microenvironmental signals which promote HSC regeneration in vivo would have important implications for the treatment of patients undergoing radiation therapy, chemotherapy and stem cell transplantation. We recently reported that pleiotrophin, a soluble heparin-binding growth factor, induced a 10-fold expansion of murine long-term repopulating HSCs in short term culture (Himburg et al. Blood (ASH Annual Meeting Abstracts), Nov 2008; 112: 78). Based on this observation, we hypothesized that PTN might also be a regenerative growth factor for HSCs. Here we tested the effect of systemic administration of PTN to non-irradiated and irradiated C57Bl6 mice to determine if PTN could promote HSC regeneration in vivo. C57Bl6 mice were irradiated with 700 cGy total body irradiation (TBI) followed by intraperitoneal administration of 2 μg PTN or saline x 7 days, followed by analysis of BM stem and progenitor cell content. Saline-treated mice demonstrated significant reductions in total BM cells, BM c-kit+sca-1+lin- (KSL) cells, colony forming cells (CFCs) and long term culture-initiating cells (LTC-ICs) compared to non-irradiated control mice. In contrast, PTN-treated mice demonstrated a 2.3-fold increase in total BM cells (p=0.03), a 5.6-fold increase in BM KSL stem/progenitor cells (p=0.04), a 2.9-fold increase in BM CFCs (p=0.004) and an 11-fold increase in LTC-ICs (p=0.03) compared to saline-treated mice. Moreover, competitive repopulating transplantation assays demonstrated that BM from PTN-treated, irradiated mice contained 5-fold increased competitive repopulating units (CRUs) compared to saline-treated, irradiated mice (p=0.04). Taken together, these data demonstrate that the administration of PTN induces BM HSC and progenitor cell regeneration in vivo following injury. Comparable increases in total BM cells, BM KSL cells and BM CFCs were also observed in PTN-treated mice compared to saline-treated controls following 300 cGy TBI, demonstrating that PTN is a potent growth factor for hematopoietic stem/progenitor cells in vivo at less than ablative doses of TBI. In order to determine whether PTN acted directly on BM HSCs to induce their proliferation and expansion in vivo, we exposed mice to BrDU in their drinking water x 7 days and compared the response to saline treatment versus PTN treatment. PTN-treated mice demonstrated a significant increase in BrDU+ BM KSL cells compared to saline-treated controls (p=0.04) and cell cycle analysis confirmed a significant increase in BM KSL cells in S phase in the PTN-treatment group compared to saline-treated controls (p=0.04). These data indicate that PTN serves as a soluble growth factor for BM HSCs and induces their proliferation and expansion in vivo while preserving their repopulating capacity. These results suggest that PTN has therapeutic potential as a novel growth factor to accelerate hematopoietic reconstitution in patients undergoing myelosuppressive radiotherapy or chemotherapy. Disclosures: No relevant conflicts of interest to declare.

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Identification of a Novel Candidate Regulator of HSC Aging.

Blood ◽

10.1182/blood.v108.11.1345.1345 ◽

2006 ◽

Vol 108 (11) ◽

pp. 1345-1345

Author(s):

Erin J. Oakley ◽

Gary Van Zant

Keyword(s):

Stem Cells ◽

Stem Cell ◽

Progenitor Cells ◽

Secretory Pathway ◽

Cell Function ◽

Mammalian Species ◽

Cell Aging ◽

Self Renewal ◽

Hematopoietic Stem ◽

Stem And Progenitor Cells

Abstract It is well documented that both quantitative and qualitative changes in the murine hematopoietic stem cell (HSC) population occur with age. In mice, the effect of aging on stem cells is highly strain-specific, thus suggesting genetic regulation plays a role in HSC aging. We have previously mapped a quantitative trait locus (QTL) to murine Chr 2 that is associated with the variation in frequency of HSCs between aged B6 and D2 mice. In C57BL/6 (B6) mice the HSC population steadily increases with age, whereas in DBA/2 mice, this population declines. A QTL regulating the natural variation in lifespan between the two strains was mapped to the same location on mouse Chr 2, thus leading to the hypothesis that stem cell function affects longevity. B6 alleles, associated with expansion of the stem cell pool, are also associated with a ~50% increase in lifespan. Using a congenic mouse model, in which D2 alleles in the QTL interval were introgressed onto a B6 background, genome wide gene expression analyses were performed using sorted lineage negative hematopoietic cells, which are enriched for primitive stem and progenitor cells. Three variables were examined using Affymetrix M430 arrays:the effect of strain--congenic versus background;the effect of age--2 months versus 22 months; andthe effects of 2 Gy of radiation because previous studies indicated that congenic animals were highly sensitive to the effects of mild radiation compared to B6 background animals. Extensive analysis of the expression arrays pointed to a single strong candidate, the gene encoding ribosome binding protein 1 (Rrbp1). Real-time PCR was used to validate the differential expression of Rrbp1 in lineage negative, Sca-1+, c-kit+ (LSK) cells, a population highly enriched for stem and progenitor cells. Further analysis revealed the presence eight non-synonymous, coding single nucleotide polymorphisms (SNPs), and at least one of them because of its location and nature may significantly alter protein structure and function. The Rrbp1 gene consists of 23 exons in mouse and is highly conserved among mammalian species including mouse, human, and canine. The Rrbp1 protein is present on the surface of the rough endoplasmic reticulum where it tethers ribosomes to the membrane, stabilizes mRNA transcripts, and mediates translocation of nascent proteins destined for the cell secretory pathway. It is well established that the interaction of HSCs with microenvironmental niches in the bone marrow is crucial for their maintenance and self-renewal, and that this interaction is mediated in part by the molecular repertoires displayed on the cell surfaces of both HSCs and niche stromal cells. Therefore, we hypothesize that age and strain specific variation in Rrbp1, through its role in the secretory pathway, affects the molecular repertoire at the cell surface of the HSC, thus altering the way stem cells interact with their niches. This altered microenvironmental interaction could have profound effects on fundamental properties relevant to stem cell aging such as pluripotency, self-renewal, and senescence.

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Myxoma Virus Targets Primary Human Leukemic Stem and Progenitor Cells While Sparing Normal Hematopoietic Stem and Progenitor Cells.

Blood ◽

10.1182/blood.v114.22.14.14 ◽

2009 ◽

Vol 114 (22) ◽

pp. 14-14 ◽

Cited By ~ 1

Author(s):

Christopher R. Cogle ◽

Manbok Kim ◽

Masmudur Rahman ◽

Edward W Scott ◽

Grant McFadden ◽

...

Keyword(s):

Progenitor Cells ◽

Progenitor Cell ◽

Cell Function ◽

Human Cancer ◽

Myxoma Virus ◽

High Dose ◽

Hematopoietic Stem ◽

Stem And Progenitor Cells

Abstract Abstract 14 High dose chemotherapy followed by autologous blood and marrow transplantation (ABMT) has been used to treat patients with acute myeloid leukemia (AML), but leukemia relapse rates remain high. One reason is the potential contamination of marrow with leukemic stem and progenitor cells (LSPCs). Purging autologous hematopoietic grafts of LSPCs prior to transplant serves as a viable strategy for increasing transplant efficacy in these cases; however, previous attempts using cytotoxic agents and cell culture techniques have generally resulted in loss of normal stem and progenitor cell numbers and/or functionality. Oncolytic poxviruses, such as myxoma virus (MYXV), are promising new instruments in targeting human cancer. MYXV has normal tropism towards European rabbits (Oryctolagus cuniculus) while remaining nonpathogenic for all other vertebrate species tested including humans and mice. Despite this host specificity, we have shown that MYXV is capable of infecting and killing a wide variety of human cancer cell lines. In light of these observations, we investigated whether MYXV could specifically target and eliminate LSPCs from primary AML using an ex vivo purging technique as assessed using both in vitro and in vivo functional analyses. Using a MYXV construct that expresses GFP upon cell infection, we observed GFP+ cells in leukemia exposed to MYXV at a concentration of 10 MOI over a 3-day period. No GFP expression was observed in normal bone marrow (BM) or mock (vehicle only) treated controls. GFP+ AML cells also began to undergo apoptosis shown by positive Annexin V staining. For myxoma to be a viable therapeutic for leukemia, it must not only target primary leukemia but also spare normal hematopoietic stem and progenitor cells (HSPCs). To test normal progenitor cell function following exposure to MYXV, normal BM cells were incubated with and without MYXV and tested for colony forming cell (CFC) content. Following incubation with MYXV, we observed differentiated colonies forming after 14 days indicating that the CFC potential of normal HSPCs was not adversely affected by MYXV. The frequency of the different colonies formed was also similar between mock and MYXV treated groups. When AML cells were mock treated pleomorphic colonies formed consistent with AML-colony forming units (AML-CFUs). Conversely, when exposed to MYXV, AML cells did not form recognizable AML-CFU colonies and instead remained heterodispersed suggesting impairment of progenitor cell function in vitro. To assess functional effects of MYXV on leukemia engraftment, sublethally irradiated NOG mice were transplanted with either mock treated primary AML (n=7) or primary AML pre-treated with MYXV for 3 hours (n=10). After 8 weeks, the percentage of engrafted mice was 100% after mock treated AML transplant but dropped to 10% after MYXV treatment. Significantly lower mean engraftment was observed in the group that received MYXV treated AML in comparison to mock treated samples (4.5% vs. 24% respectively; p < 0.05). Moreover, we show susceptibility of a primary AML specimen harboring an activating internal tandem duplication (ITD) mutation in FLT3, which represents an aggressive malignancy well-known for insensitivity to conventional chemotherapy. In animals showing leukemia engraftment by FACS, PCR was positive for the FLT3 ITD mutation. However, molecular remissions were evident in mice receiving MYXV treated samples. Efficacy against this leukemia signifies opportunity for disease eradication in an otherwise grim clinical setting. Finally, to assess functional effects of MYXV on normal HSPC engraftment, sublethally irradiated NOG mice were transplanted with either mock treated normal BM (n=10) or MYXV treated BM (n=9). After 8 weeks, there was no difference in the numbers of mice that engrafted between mock treated or MYXV treated groups (70% vs. 78% respectively; p = 0.72). There was also no difference in mean levels of engraftment per animal (1% vs. 2%; p = 0.41) suggesting that MYXV does not adversely affect the in vivo engraftment potential of normal HSPCs. In these studies, primary human LSPCs were targeted by MYXV purging, while normal human HSPCs showed no response maintaining both in vitro and in vivo functional potential. Given this demonstrated efficacy and safety, ex vivo purging of autologous hematopoietic grafts with MYXV may be feasible in cancer patients undergoing high dose chemotherapy followed by ABMT. Disclosures: No relevant conflicts of interest to declare.

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Oncogenic Wilms Tumor 1 (WT1) Mutation Augments Hematopoietic Progenitor Cell Clonogenicity and Promotes Expansion Of The Long-Term Hematopoietic Stem Cell (LT-HSC) Compartment: Implications For WT1-Mediated Leukemogenesis

Blood ◽

10.1182/blood.v122.21.1269.1269 ◽

2013 ◽

Vol 122 (21) ◽

pp. 1269-1269

Author(s):

Colleen E. Annesley ◽

Rachel E. Rau ◽

Daniel Magoon ◽

David Loeb ◽

Patrick Brown

Keyword(s):

Progenitor Cells ◽

Progenitor Cell ◽

Wilms Tumor ◽

Wild Type ◽

Hematopoietic Progenitor ◽

Self Renewal ◽

Hematopoietic Stem ◽

Exon 9

Abstract Background The WT1 gene encodes for a zinc finger-containing transcription factor involved in differentiation, cell cycle regulation and apoptosis. WT1 expression is developmentally regulated and tissue-specific, with expression maintained in the kidney and in CD34+ hematopoietic progenitor cells. Inactivating mutations of this tumor suppressor gene are well-described in sporadic Wilms tumor and as germline mutations in Wilms tumor predisposition syndromes. WT1 mutations have been reported in approximately 10% of both adult and pediatric patients with cytogenetically-normal acute myeloid leukemia (CN-AML), and have been associated with treatment failure and a poor prognosis. These reported mutations consist of insertions, deletions or point mutations. Many are frameshift mutations in exon 7, can occur as biallelic double mutations, and result in truncated proteins which may alter DNA-binding ability. Missense mutations in exon 9 have also been identified, and reports suggest that these may act in a dominant-negative manner, resulting in a loss of function. Despite these observations, the functional contribution of WT1 mutations to leukemogenesis is still largely undetermined. Methods/Results We obtained a novel knock-in WT1 mutant mouse model, which is heterozygous for the missense mutation R394W in exon 9, and homologous to exon 9 mutations seen in human AML. We hypothesized that WT1 mutations may have an aberrant effect on hematopoiesis, and specifically, could alter progenitor cell differentiation or proliferation. To investigate this, we collected lineage-negative bone marrow (lin- BM) cells from two-month old WT1 mutant (WT1mut) and wild-type (wt) mice. We performed methylcellulose colony-forming assays, serially replating cells every 10-12 days. Strikingly, WT1mut progenitor cells showed higher in vitro colony-forming capacity and an increased ability to serially replate, suggesting aberrantly enhanced self-renewal capability. Furthermore, WT1mut colonies from secondary and tertiary passages were larger and more cohesive than wild-type colonies, demonstrating increased proliferation and morphology consistent with blast colony-forming units (CFU-blast). Flow cytometric analysis of these WT1mut cells at tertiary replating revealed an immature, largely c-Kit+ population. Next, in order to study the effects of WT1mut on HSCs in vivo, we performed serial competitive transplantation of HSC-enriched, lineage-depleted BM into lethally irradiated mice. At 14 weeks post-transplant, the donor bone marrow cells were harvested and analyzed by flow cytometry. We observed a significant expansion of the LT-HSC compartment in the WT1mut mice compared to wild-type mice. These data provide new insight into the biology and functional role of WT1 mutations in the aberrant regulation of hematopoietic stem and progenitor cell expansion. Conclusion Oncogenic WT1 mutations confer enhanced proliferation and renewal of myeloid progenitor cells in vitro and expansion of LT-HSCs in vivo. Our findings suggest that WT1 mutations enhance stem cell self-renewal, potentially priming these cells for leukemic transformation upon acquisition of cooperative events. Disclosures: No relevant conflicts of interest to declare.

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Murine hematopoietic stem and progenitor cells: I. Enrichment and biologic characterization

Blood ◽

10.1182/blood.v85.6.1472.bloodjournal8561472 ◽

1995 ◽

Vol 85 (6) ◽

pp. 1472-1479 ◽

Cited By ~ 121

Author(s):

CL Li ◽

GR Johnson

Keyword(s):

Stem Cell ◽

Progenitor Cells ◽

Bone Marrow Cells ◽

Cell Populations ◽

Hematopoietic Stem ◽

Murine Bone Marrow ◽

Stem And Progenitor Cells

Murine bone marrow cells were fractionated by fluorescence-activated cell sorting into Rh123lo Lin- c-kit+ Ly6A+, Rh123hi Lin-c-kit+ Ly6A+, and Lin- c-kit+ Ly6A- populations within which most, if not all, of the hematopoietic activities of the marrow resided. The Rh123lo Lin- c- kit+Ly6A+ cells, which consist exclusively of small- or medium-sized lymphocyte-like cells, are highly enriched for long-term hematopoietic in vivo repopulating cells. The enrichment factor for these cells from the marrow was estimated as 2,000-fold. The Rh123hi Lin- c-kit+ Ly6A+ cells, although also highly enriched for day-12 spleen colony-forming units, were relatively depleted of long-term in vivo repopulation capacity. Most, if not all Lin- c-kit+ Ly6A- cells were Rb123hi. In contrast to both Rh123lo and Rh123hi Lin- c-kit+ Ly6A+ stem cell populations, the Lin- c-kit+ Ly6A- cells can be stimulated to proliferate in vitro in the presence of single cytokines, which is a characteristic of committed progenitor cells. No marked synergistic interactions between individual cytokines were observed with this cell population. Both Rh123hi Lin- c-kit+ Ly6A+ mature stem cell and Lin- c- kit+ Ly6A- progenitor cell populations displayed in vivo repopulation kinetics resembling those of the putative short-term hematopoietic repopulating cells.

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