Reversibility of CD34 expression on human hematopoietic stem cells that retain the capacity for secondary reconstitution

Abstract The cell surface protein CD34 is frequently used as a marker for positive selection of human hematopoietic stem/progenitor cells in research and in transplantation. However, populations of reconstituting human and murine stem cells that lack cell surface CD34 protein have been identified. In the current studies, we demonstrate that CD34 expression is reversible on human hematopoietic stem/progenitor cells. We identified and functionally characterized a population of human CD45+/CD34− cells that was recovered from the bone marrow of immunodeficient beige/nude/xid (bnx) mice 8 to 12 months after transplantation of highly purified human bone marrow–derived CD34+/CD38− stem/progenitor cells. The human CD45+ cells were devoid of CD34 protein and mRNA when isolated from the mice. However, significantly higher numbers of human colony-forming units and long-term culture-initiating cells per engrafted human CD45+ cell were recovered from the marrow of bnx mice than from the marrow of human stem cell–engrafted nonobese diabetic/severe combined immunodeficient mice, where 24% of the human graft maintained CD34 expression. In addition to their capacity for extensive in vitro generative capacity, the human CD45+/CD34− cells recovered from thebnx bone marrow were determined to have secondary reconstitution capacity and to produce CD34+ progeny following retransplantation. These studies demonstrate that the human CD34+ population can act as a reservoir for generation of CD34− cells. In the current studies we demonstrate that human CD34+/CD38− cells can generate CD45+/CD34− progeny in a long-term xenograft model and that those CD45+/CD34− cells can regenerate CD34+ progeny following secondary transplantation. Therefore, expression of CD34 can be reversible on reconstituting human hematopoietic stem cells.

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Robo4/Magic Roundabout Is a Novel Surface Marker for Murine and Human Hematopoietic Stem Cells.

Blood ◽

10.1182/blood.v108.11.682.682 ◽

2006 ◽

Vol 108 (11) ◽

pp. 682-682

Author(s):

Fumi Shibata ◽

Yuko Goto-Koshino ◽

Miyuki Ito ◽

Yumi Fukuchi ◽

Yoshihiro Morikawa ◽

...

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Cell Surface ◽

Hematopoietic Stem Cells ◽

Surface Markers ◽

Hematopoietic Stem ◽

Hematopoietic System ◽

Cd34 Cells ◽

Human Hscs

Abstract A variety of cell surface markers such as c-Kit, Sca-1, CD34 and Flt-3 have been utilized to prospectively isolate murine or human hematopoietic stem cells (HSCs). While murine HSCs were shown to be highly enriched in CD34−c-Kit+Sca-1+Lineage- (CD34−KSL) fraction, this population is still not homogeneous for long-term HSCs. In human, CD34+ cells are regarded as crude HSC fraction and used for clinical applications. However, quiescent human HSCs are also found in CD34− fraction, indicating that CD34 is not a bona fide marker for human HSC. Thus, novel surface markers that can be used to purify human or murine HSCs to homogeneity need to be identified. Roundabout (Robo) family proteins are immunoglobulin-type cell surface receptors that are predominantly expressed in nervous system. Slit2, a ligand for Robo, is a large leucine-rich repeat-containing secreted protein that is also expressed in brain. By binding with Robo, Slit2 acts as a repellant for axon guidance of developing neurons and they are critical for correct wiring of neuronal network. Robo family comprises four family members, Robo1 – Robo4, and Robo4 is distinct in that it is expressed specifically in endothelial cells, but not in brain. In this study, we investigated Robo4 for its possible application for HSC identification in murine and human hematopoietic system. By RT-PCR, Robo4 was specifically expressed in murine KSL fraction, and was not expressed in lineage positive cells and various progenitors such as common myeloid progenitor (CMP), granulocyte-monocyte progenitor (GMP), megakaryocyte/erythroid progenitor (MEP) and common lymphoid progenitor (CLP). Moreover, the expression of Robo4 was highest in side population of KSL cells (KSL-SP), and moderate in KSL-main population (KSL-MP) cells. Monoclonal antibody raised against Robo4 identified its high expression in KSL cells by FACS. FACS analysis of human cord blood cells revealed that Robo4 is highly expressed in CD34+ cells, and CD34+Robo4high population fell into CD38− fraction, which enriches human HSCs. Bone marrow transplantation experiments revealed that Robo4+ fraction of murine KSL cells had long-term repopulating activity, while Robo4−KSL cells not. Although both Robo4+ and Robo4− CD34−KSL cells repopulated murine hematopoietic system for long-term, Robo4+CD34−KSL cells achieved higher chimerism after repopulation compared with Robo4−CD34−KSL. To investigate the physiological role of Robo4 in HSC homeostasis, we next examined the expression of Slit2 in hematopoietic system. Interestingly, Slit2 is specifically expressed in bone marrow stromal cells, but not in hematopoietic cells. Moreover, Slit2 is induced in osteoblasts, a critical cellular component composing HSC niche, in response to myelosuppressive stress such as 5FU treatment. These results indicate that Robo4 is expressed in murine and human hematopoietic HSCs and useful for HSC purification, and Robo4 - Slit2 system may play a role in HSC physiology in niche environment under hematopoietic stress.

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BCR-ABL enhances differentiation of long-term repopulating hematopoietic stem cells

Blood ◽

10.1182/blood-2009-04-215376 ◽

2010 ◽

Vol 115 (16) ◽

pp. 3185-3195 ◽

Cited By ~ 64

Author(s):

Mirle Schemionek ◽

Christian Elling ◽

Ulrich Steidl ◽

Nicole Bäumer ◽

Ashley Hamilton ◽

...

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Chronic Myeloid Leukemia ◽

Hematopoietic Stem Cells ◽

Progenitor Cells ◽

Myeloid Leukemia ◽

Bone Marrow Cells ◽

Hematopoietic Stem ◽

Multipotent Progenitor Cells

Abstract In a previously developed inducible transgenic mouse model of chronic myeloid leukemia, we now demonstrate that the disease is transplantable using BCR-ABL+ Lin−Sca-1+c-kit+ (LSK) cells. Interestingly, the phenotype is more severe when unfractionated bone marrow cells are transplanted, yet neither progenitor cells (Lin−Sca-1−c-kit+), nor mature granulocytes (CD11b+Gr-1+), nor potential stem cell niche cells (CD45−Ter119−) are able to transmit the disease or alter the phenotype. The phenotype is largely independent of BCR-ABL priming before transplantation. However, prolonged BCR-ABL expression abrogates the potential of LSK cells to induce full-blown disease in secondary recipients and increases the fraction of multipotent progenitor cells at the expense of long-term hematopoietic stem cells (LT-HSCs) in the bone marrow. BCR-ABL alters the expression of genes involved in proliferation, survival, and hematopoietic development, probably contributing to the reduced LT-HSC frequency within BCR-ABL+ LSK cells. Reversion of BCR-ABL, or treatment with imatinib, eradicates mature cells, whereas leukemic stem cells persist, giving rise to relapsed chronic myeloid leukemia on reinduction of BCR-ABL, or imatinib withdrawal. Our results suggest that BCR-ABL induces differentiation of LT-HSCs and decreases their self-renewal capacity.

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Generation of Dyskeratosis Congenita-like Hematopoietic Stem Cells through the Stable Inhibition of DKC1

10.21203/rs.3.rs-26927/v3 ◽

2021 ◽

Author(s):

Carlos Carrascoso-Rubio ◽

Hidde A. Zittersteijn ◽

Laura Pintado-Berninches ◽

Beatriz Fernández-Varas ◽

M. Luz Lozano ◽

...

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Hematopoietic Stem Cells ◽

Bone Marrow Failure ◽

Clinical Manifestations ◽

Dyskeratosis Congenita ◽

Bone Marrow Failure Syndrome ◽

Hematopoietic Stem ◽

Human Cd34 ◽

Cd34 Cells

Abstract Dyskeratosis congenita (DC) is a rare telomere biology disorder, which results in different clinical manifestations, including severe bone marrow failure. To date, the only curative treatment for bone marrow failure in DC patients is allogeneic hematopoietic stem cell transplantation. However due to the toxicity associated to this treatment, improved therapies are recommended for DC patients. Here we aimed at generating DC-like human hematopoietic stem cells in which the efficacy of innovative therapies could be investigated. Because X-linked DC is the most frequent form of the disease and is associated with an impaired expression of DKC1, we have generated DC-like hematopoietic stem cells based on the stable knock-down of DKC1 in human CD34 + cells with lentiviral vectors encoding for DKC1 short hairpin RNAs. At a molecular level, DKC1 -interfered CD34 + cells showed a decreased expression of TERC, as well as a diminished telomerase activity and increased DNA damage, cell senescence and apoptosis. Moreover, DKC1 -interfered human CD34 + cells showed defective clonogenic ability and were incapable of repopulating the hematopoiesis of immunodeficient NSG mice. The development of DC-like hematopoietic stem cells will facilitate the understanding of the molecular and cellular basis of this inherited bone marrow failure syndrome, and will serve as a platform to evaluate the efficacy of new hematopoietic therapies for DC.

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Expression of Endomucin, a CD34-Like Sialomucin, Marks Definitive Hematopoietic Stem Cells throughout Development.

Blood ◽

10.1182/blood.v104.11.563.563 ◽

2004 ◽

Vol 104 (11) ◽

pp. 563-563

Author(s):

Azusa Maeda ◽

Atsushi Iwama ◽

Koji Eto ◽

Hideo Ema ◽

Toshio Kitamura ◽

...

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Cell Surface ◽

Hematopoietic Stem Cells ◽

Signal Sequence ◽

High Yield ◽

Specific Gene ◽

Mouse Bone Marrow ◽

Hematopoietic Stem ◽

Cd34 Cells

Abstract In order to identify cell surface molecules specific to hematopoietic stem cells (HSCs), a modified signal sequence trap was applied to mouse bone marrow (BM) CD34− c-Kit+ sca-1+ lineage− (CD34−KSL) cells which is highly enriched for HSCs. Among the identified genes, mRNA expression of Endomucin, an endothelium-specific gene encoding a CD34-like sialomucin, appeared highly specific to CD34-KSL HSCs. To further investigate the expression of Endomucin, we generated two rat anti-mouse Endomucin monoclonal antibodies that recognize different epitopes (AE2D4, AE7F2). Taking advantage of these and another monoclonal antibody, V7c7 (1999, Blood, 93; 1; 165), detailed expression analysis was performed. Endomucin expression was largely confined to lineage markers-negative (Lin−) cells. Approximately 7 % of Lin− cells were Endomucin-positive. Cells strongly expressing Endomucin represented 30% of c-kit+ sca-1+ cells. Gating out CD34+ cells from Lin− Endomucin+ population resulted in high yield of KSL cells. High correlation between Lin− Endomucin+CD34− cells and KSL cells was confirmed by in vivo bone marrow transplantation. When Lin− cells were fractionated by their expression of CD34 and Endomucin, only Lin− Endomucin+CD34− cells contributed to long-term repopulation (LTR), and as few as 100 cells were enough to obtain engraftment. Furthermore, the majority of CD34−KSL cells were Endomucin+, and again, only CD34−KSL-Endomucin+ cells had LTR activity. These data indicate two facts: 1) A single positive marker, Endomucin can substitute for c-kit+ sca-1+, 2) All LTR -HSCs express Endomucin. We then analyzed the expression of Endomucin during embryonic development of the hematopoietic system. Definitive HSCs arise from the hemogenic endothelium lining the wall of the dorsal aorta in embryonic aorta-gonads-mesonephros (AGM) region, then seed to the fetal liver. E10.5 AGM CD45− cells were segregated into subpopulations by their expression of Endomucin and CD41, an early marker of embryonic hematopoiesis. In vitro coculture system with a stromal cell line, OP9, was applied to detect the ability of hematopoietic potential. Hematopoietic activity was exclusively found in the CD41+Endomucin+ population, that represents 24% of CD41+ cells. Taken together, these data indicate that Endomucin marks both embryonic and adult HSCs, providing a novel useful cell surface marker for definitive HSCs throughout development. Figure Figure

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Plxdc2 Marks Hematopoietic Stem Cells and Th2 Cytokine-Producing Innate Lymphocytes in Adult Bone Marrow

Blood ◽

10.1182/blood.v118.21.1278.1278 ◽

2011 ◽

Vol 118 (21) ◽

pp. 1278-1278

Author(s):

Yasushi Kubota ◽

Ivo Lieberam ◽

Shinya Kimura ◽

Thomas M Jessell ◽

Shin-Ichi Nishikawa

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

T Cell ◽

Cell Surface ◽

Hematopoietic Stem Cells ◽

Cell Population ◽

Specific Marker ◽

Simple Method ◽

Hematopoietic Stem

Abstract Abstract 1278 Hematopoietic stem cells (HSCs) have been highly enriched using combinations of more than 10 surface markers. However the simple method using a few positive markers is preferable to identify HSCs location in tissue section. We performed a stringent comparative gene expression profiling analysis to find genes preferentially expressed in the HSC population, and identified a total of 63 genes that are highly expressed in HSC among various hematopoietic cell population. In order to find HSC-specific marker we focused on genes encoding cell surface protein, and found that plexin domain containing 2 (Plxdc2) is highly expressed in CD34—c-Kit+Sca-1+Lineage−(CD34−KSL) HSC population using Plxdc2::GFP knock-in mice. Only 0.2% of whole bone marrow cells were Plxdc2+, and competitive repopulation assay clearly showed that all HSCs are included in the Plxdc2+ fraction. These results identify Plxdc2 as a new marker of HSCs. Plxdc2+ population contain not only HSCs but uncharacterized c-Kitlow/−Sca-1+Lineage−cells. To further purify HSCs, we investigated the additional positive marker. Throughout the screening of various known HSC-related marker, CD150 was selected. CD150 is already recognized as a positive HSC marker (Kiel, et al. Cell 2005). The Plxdc2+CD150+ fraction represented only 0.1%±0.002% in whole bone marrow, and 6% in c-Kit+Sca-1+Lineage− cells, respectively. To test whether the combination of Plxdc2 and CD150 with or without other markers can highly enrich long-term HSCs, we competitively reconstituted irradiated mice with single Plxdc2+CD150+ cells or single Plxdc2+CD150+c-Kit+Sca-1+Lineage− cells. One out of every 4.6 Plxdc2+CD150+ cells (22%), and one out of 2.2 Plxdc2+CD150+c-Kit+Sca-1+Lineage− cells (44%) engrafted and gave long-term multi-lineage reconstitution. The simple combination of Plxdc2 and CD150 significantly increased HSC purity. In addition, we found robust levels of PLXDC2 transcripts in purified human cord blood CD34+ HSCs. Next, we attempted to characterize the another Plxdc2+ fraction which is c-Kitlow/−Sca-1+Lineage−. Multicolor flowcytometric analysis revealed that Plxdc2+c-Kitlow/−Sca-1+Lineage− cells uniformly express CD45, IL7Rα, Thy-1.2, CD27, T1/ST2 (IL1RL1, a subunit of IL33R) and CD25. These cell surface phenotype indicated that this population is probably of lymphoid lineage. However, culturing Plxdc2+ c-Kit low/−Sca-1+Lineage− cells on OP9-DL1, which supports the development of T-cell progenitors to mature T-cells, did not induce T-cell differentiation. Plxdc2+c-Kitlow/−Sca-1+Lineage−cells also did not differentiate into B cells when co-cultured with OP9 stroma cell line. Furthermore Plxdc2+c-Kitlow/−Sca-1+Lineage− cells produce IL-5 and IL-13 in response to IL-33 or a combination of IL-2 and IL-25. These characteristics resemble that of “natural helper (NH) cells”, a recently identified cell population capable of producing large amounts of Th2 cytokines in fat-associated lymphoid clusters (Moro, et al. Nature 2010). Immunohistochemical staining of bone section to detect HSCs, and functional analyses to clarify why Plxdc2 specifically express in HSCs and bone marrow “NH cells” using Plxdc2-deficient mice are our ongoing tasks. Disclosures: No relevant conflicts of interest to declare.

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STS1 and STS2 Are Important Regulators Of Hematopoietic Stem Cells

Blood ◽

10.1182/blood.v122.21.1186.1186 ◽

2013 ◽

Vol 122 (21) ◽

pp. 1186-1186

Author(s):

Jing Zhang ◽

Hubert Serve ◽

Christian H. Brandts

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Cell Surface ◽

Hematopoietic Stem Cells ◽

Progenitor Cells ◽

Wild Type ◽

Short Term ◽

Double Knockout ◽

Hematopoietic Stem ◽

Stem And Progenitor Cells

Abstract The receptor tyrosine kinases FLT3 and KIT are highly expressed on the surface of leukemic blasts in most patients with acute myeloid leukemia. Although about one third of patients display activating mutations in FLT3 (and more rarely in KIT), the majority of patients have no mutations in FLT3 or KIT. Previously, we demonstrated that Cbl functions as the E3 ligase for both FLT3 and KIT, and that ligase-inactivating mutations of Cbl stabilize FLT3 and KIT on the cell surface by preventing endocytosis and degradation (Sargin et al, Blood 2007). Furthermore, we demonstrated that expression of E3-ligase deficient Cbl mutants led to the development of a myeloproliferative disease in a murine bone marrow transplantation model (Bandi et al, Blood 2009). However, Cbl mutations are rarely found in AML. Here, we investigated the role of the Cbl regulators suppressors of T-cell signaling 1 and 2(STS1 and STS2) in stabilizing wild-type FLT3 and KIT on the cell surface of hematopoietic stem and progenitor cells (HSPCs). STS1 is ubiquitously expressed, while STS2 expression is restricted to the hematopoietic tissue. STS1 and STS2 constitutively bind to Cbl, while their binding to FLT3 and KIT is dependent on ligand-activation by FL and SCF, respectively. Interestingly, STS1 (but not STS2) functions as a tyrosine phosphatase for both ligand-activated FLT3 and KIT. This required the PGM domain of STS1, as PGM point mutant of STS1 did not dephosphorylate FLT3 or KIT. In line with this, knockdown of STS1 using stably expressing shRNA constructs showed a significant hyperphosphorylation of FLT3 and KIT. By using STS1/STS2 single and double knockout mice, we analyzed the effects of STS1 and STS2 on hematopoietic stem and progenitor cells in vivo. We found that deficiency of STS1 causes an increase of both absolute number and frequency of LSK (lineage marker-, KIT+, Sca1+) cells, which contain HSPCs. This phenotype was even more pronounced in STS1 and STS2 double knockout (dKO) mice, and is mainly attributable to the short term hematopoietic stem cell (ST-HSC) and multipotent progenitor (MPP) cell population, as defined by both standard and SLAM markers. Colony assays using primary bone marrow cells revealed a significantly higher colony forming ability in STS1-KO and dKO cells compared to wild type (wt) cells, particularly after serial replating. A careful analysis of the cells derived from methylcellulose culture revealed an increased proportion of immature (Mac1- CD48+ CD16/32-) cells in STS1-KO and dKO cells. Competitive repopulation assays showed an advantage for dKO cells when compared to wt, suggesting that the LT-HSC compartment is also affected. Even more pronounced were the differences in CFU-S assays (colony forming units spleen), displaying significantly more colonies of dKO compared to wt donor cells, functionally demonstrating a significantly increased ST-HSC / MPP population in dKO donors. A detailed analysis of the downstream signaling events demonstrated that loss of STS1 specifically causes an activated PI3-Kinase / AKT pathway. In summary, our data demonstrates that STS1 functions as a phosphatase of FLT3 and KIT and, using genetic mouse models, indicates a critical role in the maintenance and proliferation of long-term and short-term hematopoietic stem cells. This may also affect sensitivity to kinase inhibitors. Disclosures: No relevant conflicts of interest to declare.

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Ex Vivo Expansion and Transplantation of Hematopoietic Stem/Progenitor Cells Supported by Mesenchymal Stem Cells from Human Umbilical Cord Blood

Cell Transplantation ◽

10.3727/000000007783465073 ◽

2007 ◽

Vol 16 (6) ◽

pp. 579-585 ◽

Cited By ~ 48

Author(s):

Guo-Ping Huang ◽

Zhi-Jun Pan ◽

Bing-Bing Jia ◽

Qiang Zheng ◽

Chun-Gang Xie ◽

...

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Mesenchymal Stem Cells ◽

Cord Blood ◽

Progenitor Cells ◽

Umbilical Cord Blood ◽

Ex Vivo ◽

Hematopoietic Stem ◽

Cd34 Cells

Human mesenchymal stem cells (MSCs) are multipotential and are detected in bone marrow (BM), adipose tissue, placenta, and umbilical cord blood (UCB). In this study, we examined the ability of UCB-derived MSCs (UCB-MSCs) to support ex vivo expansion of hematopoietic stem/progenitor cells (HSPCs) from UCB and the engraftment of expanded HSPCs in NOD/SCID mice. The result showed that UCB-MSCs supported the proliferation and differentiation of CD34+ cells in vitro. The number of expanded total nucleated cells (TNCs) in MSC-based culture was twofold higher than cultures without MSC (control cultures). UCB-MSCs increased the expansion capabilities of CD34+ cells, long-term culture-initiating cells (LTC-ICs), granulocyte-macrophage colony-forming cells (GM-CFCs), and high proliferative potential colony-forming cells (HPP-CFCs) compared to control cultures. The expanded HSPCs were transplanted into lethally irradiated NOD/SCID mice to assess the effects of expanded cells on hematopoietic recovery. The number of white blood cells (WBCs) in the peripheral blood of mice transplanted with expanded cells from both the MSC-based and control cultures returned to pretreatment levels at day 25 posttransplant and then decreased. The WBC levels returned to pretreatment levels again at days 45–55 posttransplant. The level of human CD45+ cell engraftment in primary recipients transplanted with expanded cells from the MSC-based cultures was significantly higher than recipients transplanted with cells from the control cultures. Serial transplantation demonstrated that the expanded cells could establish long-term engraftment of hematopoietic cells. UCB-MSCs similar to those derived from adult bone marrow may provide novel targets for cellular and gene therapy.

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Long-term repopulation of irradiated mice with limiting numbers of purified hematopoietic stem cells: in vivo expansion of stem cell phenotype but not function

Blood ◽

10.1182/blood.v85.4.1006.bloodjournal8541006 ◽

1995 ◽

Vol 85 (4) ◽

pp. 1006-1016 ◽

Cited By ~ 245

Author(s):

GJ Spangrude ◽

DM Brooks ◽

DB Tumas

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Stem Cell ◽

Cell Surface ◽

Hematopoietic Stem Cells ◽

Peripheral Blood ◽

Antigen Expression ◽

Hematopoietic Stem ◽

Surface Antigen Expression

Hematopoietic stem cells were isolated from normal adult mouse bone marrow based on surface antigen expression (Thy-1.1(low)Lin(neg)Ly- 6A/E+) and further selected for low retention of rhodamine 123. This population of cells (Rh-123low) could mediate radioprotection and long- term (greater than 12 months) repopulation after transplantation of as few as 25 cells. Transfer of five genetically marked Rh-123low cells in the presence of 10(5) normal bone marrow cells resulted in reconstitution of peripheral blood by greater than 10% donor cells in 64% (30 of 47) of recipient mice. Of 46 animals surviving after 24 weeks, 10 had over 50% donor-derived cells in peripheral blood. Two general patterns of long-term reconstitution were observed: one in which many donor-derived cells were observed 5 to 6 weeks after reconstitution and another in which donor-derived cells were rare initially but expanded with time. This result suggests that two classes of long-term repopulating hematopoietic stem cells exist, differing in their ability to function early in the course of transplantation. Alternatively, distinct anatomic sites of engraftment may dictate these two outcomes from a single type of cell. As an approach to measure the extent of self-renewal by the injected cells, recipients of five or 200 stem cells were killed 8 to 13 months after the transplants, and Thy- 1.1(low)Lin(neg)Ly-6A/E+ progeny of the original injected cells were isolated for a second transplant. While a numerical expansion of cells expressing the cell surface phenotype of stem cells was observed, along with activity in the colony-forming unit-spleen assay, the expanded cells were vastly inferior in radioprotection and long-term reconstitution assays when compared with cells freshly isolated from normal animals. This result demonstrates that in stem cell expansion experiments, cell surface antigen expression is not an appropriate indicator of stem cell function.

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Etoposide-Initiated MLL Rearrangements Detected at High Frequency in Human Primitive Hematopoietic Stem Cells with In Vitro and In Vivo Long-Term Repopulating Potential.

Blood ◽

10.1182/blood.v106.11.98.98 ◽

2005 ◽

Vol 106 (11) ◽

pp. 98-98 ◽

Cited By ~ 1

Author(s):

Jolanta Libura ◽

Marueen Ward ◽

Grzegorz Przybylski ◽

Christine Richardson

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Hematopoietic Stem Cells ◽

Scid Mouse ◽

P Value ◽

Hematopoietic Stem ◽

Cd34 Cells

Abstract Rearrangements involving the MLL gene locus at chromosome band 11q23 are observed in therapy-related acute myeloid leukemia and myelodysplastic syndromes following treatment with topoisomerase II (topoII) inhibitors including etoposide. We have shown that one hour of etoposide exposure (20–50 μM) stimulates stable MLL rearrangements in primary human CD34+ cells and that the spectrum of repair products within MLL gene is broader than so far described (Libura et al, Blood, 2005). Clinical data suggest that MLL-associated malignant leukemias originate within primitive hematopietic stem cells capable of differentiation into all hematopoietic lineages and repopulation of myelo-ablated hosts. These cells can be analyzed using the in vivo NOD-SCID mouse model as well as the in vitro long-term culture initiating cell (LTC-IC) assay. We adopted our in vitro CD34+ cell culture model to investigate the impact of etoposide exposure on the most primitive hematopoietic stem cells using parallel assays for LTC-IC and NOD-SCID Repopulating Cells (SRC). Following etoposide exposure (20–50 μM for 1 hour), and 48–96 hours recovery in vitro, untreated control and etoposide-treated CD34+ cells were either seeded in LTC-IC with a supportive feeder layer (Stem Cell Technologies, Inc.), or injected into NOD-SCID mice (0.1–1.5x106 cells per mouse). After 12 weeks, both LTC-IC cultures and bone marrow cells from NOD-SCID mice were seeded in methylcellulose media supplemented with growth factors that promote only human cell colony formation. An increased number of colonies in etoposide-treated samples was obtained from LTC-IC cultures in 3 out of 5 experiments (p value<0.05). This increase in colony number was more dramatic in etoposide-treated samples from NOD-SCID bone marrow (57 versus 0, 8 versus 0). These data demonstrate that etoposide exposure can significantly alter the potential of early hematopoietic stem cells to survive and proliferate both in vitro and in vivo. Injection of as few as 3x105 CD34+ cells into a NOD-SCID mouse was sufficient to obtain methylcellulose colonies, suggesting that this method can be used for the analysis of cells obtained from a single patient sample. Mutation analysis of human methylcellulose colonies derived from both LTC-IC and NOD-SCID was performed by inverse PCR and ligation-mediated PCR followed by sequencing. This analysis revealed that rearrangements originating within the MLL breakpoint cluster region (bcr) were present in 12 out of 29 colonies from etoposide-treated samples versus 5 out of 39 colonies from control samples (p value <0.01), demonstrating that etoposide exposure promotes stable rearrangements within a hematopoietic stem cell compartment with significant proliferative potential. Eight of the 17 events were sequenced, and showed 6 MLL tandem duplications within intron 8, one complex translocation between MLL and chr.15 and tandem duplication, and one event with foreign sequence of unknown origin. Our data are the first report of the spectrum and frequency of MLL rearrangements following topo II inhibitor exposure in a cell population thought to be the target for recombinogenic events leading to therapy-related leukemias.

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Mobilization of Hematopoitic Stem/Progenitor Cells by a Cdc42 Activity-Specific Inhibitor

Blood ◽

10.1182/blood.v112.11.68.68 ◽

2008 ◽

Vol 112 (11) ◽

pp. 68-68 ◽

Cited By ~ 1

Author(s):

Wei Liu ◽

Lei Wang ◽

Xun Shang ◽

Fukun Guo ◽

Marnie A. Ryan ◽

...

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Hematopoietic Stem Cells ◽

Progenitor Cells ◽

Peripheral Blood ◽

Actin Polymerization ◽

Specific Inhibitor ◽

Hematopoietic Stem

Abstract Hematopoietic stem cell transplantation has become a standard of care for the treatment of many hematological diseases. Transplantation of mobilized peripheral blood stem cells has replaced bone marrow (BM) transplantation as the preferred method for hematopoietic recovery. To date, G-CSF mobilized hematopoietic stem/progenitor cell (HSPC) harvest is the main FDA-approved preparative regiment for transplantation protocols, but this application has several limitations in utilities including diverse individual variability and potential side effects in several patient populations. Although AMD3100, a chemical CXCR4-blocker, has been found effective for HSPC mobilization, the development of additional HSPC mobilization agents that work through well defined molecular mechanisms remains in need. Previously our laboratory has shown in a conditional knockout mouse model that deficiency of the Rho GTPase Cdc42 in the BM causes impaired adhesion, homing, lodging and retention of HSPCs, leading to massive egress of HSPCs from BM to the peripheral blood without compromising their proliferative potential. From an array of small molecule inhibitors of PIP2-induced actin-polymerization discovered in a high throughput screening, we identified CASIN, a novel Cdc42 Activity-Specific Inhibitor, that is effective in suppressing Cdc42 activity in a dose-dependent manner in murine fibroblasts and low density bone marrow (LDBM) cells and human CD34+ umbilical cord blood (HCB) cells in vitro, and in murine LDBM cells in vivo. The inhibitory effect by CASIN appears to be specific to Cdc42 and is reversible. We subsequently tested the hypothesis that pharmacological targeting Cdc42 by CASIN may transiently mimic the Cdc42 knockout phenotype leading to HSPC mobilization. In the dose range of 5–10 uM, CASIN does not show detectable toxicity in wild type or Cdc42 knockout HSPCs in cell survival and colony-forming unit activity assays. CASIN treatment of 32D murine myeloid progenitor cells or freshly isolated progenitor cells results in a reversible inhibition of F-actin polymerization induced by SDF-1α and blockade of α5β1 integrin mediated adhesion to fibronectin fragment CH296. Its effects on actin organization and adhesion are associated with an inhibition of directional migration of the colony-forming cells toward SDF-1α. In contrast, CASIN does not show a detectable effect on the adhesion and migration activities of Cdc42 knockout HSPCs, suggesting that it works specifically through Cdc42 to affect cell actin structure and adhesion. Upon injection into mice (5mg/Kg, intraperitoneally), CASIN is effective in stimulating mobilization of progenitor activity into the peripheral blood (~ 6-fold increase compared to control at 40 hrs post injection). Subsequent serial transplantation experiments show that the PB harvested from CASIN treated mice could reconstitute various lineages of blood cells in primary, secondary, and tertiary recipients, indicating that long-term hematopoietic stem cells were mobilized from the BM of CASIN-treated donor mice. Consistent with the mobilization phenotype, FACS analysis shows that intravenous injection of CASIN can cause transient reduction of long-term hematopoietic stem cells (IL7Ra−Lin−Sca-1+c-Kit+CD34−) and short-term hematopoietic stem cells (IL7Ra−Lin−Sca-1+c-Kit+CD34+) from BM. Similar to the effects on murine HSPCs, CASIN is active on CD34+ HCB cells in transiently suppressing F-actin assembly, adhesion to fibronectin, and SDF-1α induced migration without detectable toxicity in vitro. Whether CASIN is effective in mobilizing HCB-engrafted NOD/SCID mice is currently under investigation. Our studies suggest that the novel concept of pharmacological targeting of Cdc42, that transiently and reversibly mimics the effect of Cdc42 knockout, may be developed into a mobilization regiment with a well defined molecular and cellular mechanism.

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