N-cadherin is developmentally regulated and functionally involved in early hematopoietic cell differentiation

2001 ◽  
Vol 114 (8) ◽  
pp. 1567-1577 ◽  
Author(s):  
S. Puch ◽  
S. Armeanu ◽  
C. Kibler ◽  
K.R. Johnson ◽  
C.A. Muller ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Cell Adhesion ◽  
Progenitor Cells ◽  
Mononuclear Cells ◽  
Classical Type ◽  
Type I ◽  
Facs Analysis ◽  
Hematopoietic Progenitors ◽  
Developmentally Regulated ◽  
Adhesive Interactions

The cadherins, an important family of cell adhesion molecules, are known to play major roles during embryonic development and in the maintenance of solid tissue architecture. In the hematopoietic system, however, little is known of the role of this cell adhesion family. By RT-PCR, western blot analysis and immunofluorescence staining we show that N-cadherin, a classical type I cadherin mainly expressed on neuronal, endothelial and muscle cells, is expressed on the cell surface of resident bone marrow stromal cells. FACS analysis of bone marrow mononuclear cells revealed that N-cadherin is also expressed on a subpopulation of early hematopoietic progenitor cells. Triple-color FACS analysis defined a new CD34(+) CD19(+) N-cadherin(+) progenitor cell population. During further differentiation, however, N-cadherin expression is lost. Treatment of CD34(+) progenitor cells with function-perturbing N-cadherin antibodies drastically diminished colony formation, indicating a direct involvement of N-cadherin in the differentiation program of early hematopoietic progenitors. N-cadherin can also mediate adhesive interactions within the bone marrow as demonstrated by inhibition of homotypic interactions of bone-marrow-derived cells with N-cadherin antibodies. Together, these data strongly suggest that N-cadherin is involved in the development and retention of early hematopoietic progenitors within the bone marrow microenvironment.

Laminin isoform–specific promotion of adhesion and migration of human bone marrow progenitor cells

Blood ◽  
2003 ◽  
Vol 101 (3) ◽  
pp. 877-885 ◽  
Author(s):  
Yu-Chen Gu ◽  
Jarkko Kortesmaa ◽  
Karl Tryggvason ◽  
Jenny Persson ◽  
Peter Ekblom ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Progenitor Cells ◽  
Marrow Cell ◽  
Extracellular Proteins ◽  
Human Bone ◽  
Human Bone Marrow ◽  
Hematopoietic Progenitors ◽  
Erythroid Progenitor ◽  
Adhesive Interactions ◽  
Laminin 1

Abstract Laminins are αβγ heterotrimeric extracellular proteins that regulate cellular functions by adhesion to integrin and nonintegrin receptors. Laminins containing α4 and α5 chains are expressed in bone marrow, but their interactions with hematopoietic progenitors are unknown. We studied human bone marrow cell adhesion to laminin-10/11 (α5β1γ1/α5β2γ1), laminin-8 (α4β1γ1), laminin-1 (α1β1γ1), and fibronectin. About 35% to 40% of CD34+ and CD34+CD38− stem and progenitor cells adhered to laminin-10/11, and 45% to 50% adhered to fibronectin, whereas they adhered less to laminin-8 and laminin-1. Adhesion of CD34+CD38− cells to laminin-10/11 was maximal without integrin activation, whereas adhesion to other proteins was dependent on protein kinase C activation by 12-tetradecanoyl phorbol-13-acetate (TPA). Fluorescence-activated cell-sorting (FACS) analysis showed expression of integrin α6 chain on most CD34+ and CD34+CD38−cells. Integrin α6 and β1 chains were involved in binding of both cell fractions to laminin-10/11 and laminin-8. Laminin-10/11 was highly adhesive to lineage-committed myelomonocytic and erythroid progenitor cells and most lymphoid and myeloid cell lines studied, whereas laminin-8 was less adhesive. In functional assays, both laminin-8 and laminin-10/11 facilitated stromal-derived factor-1α (SDF-1α)–stimulated transmigration of CD34+ cells, by an integrin α6 receptor–mediated mechanism. In conclusion, we demonstrate laminin isoform–specific adhesive interactions with human bone marrow stem, progenitor, and more differentiated cells. The cell-adhesive laminins affected migration of hematopoietic progenitors, suggesting a physiologic role for laminins during hematopoiesis.

scholarly journals Changes in the growth properties of CD34+, CD38- bone marrow progenitors during human fetal development

Blood ◽  
1995 ◽  
Vol 86 (2) ◽  
pp. 710-718 ◽  
Author(s):  
EK Waller ◽  
S Huang ◽  
L Terstappen
Keyword(s):  
Bone Marrow ◽  
Single Cell ◽  
Progenitor Cells ◽  
Stromal Cells ◽  
Mononuclear Cells ◽  
Bone Marrow Cells ◽  
Hematopoietic Progenitors ◽  
Fetal Bone ◽  
Hla Dr ◽  
Stromal Progenitor Cells

We have previously described the isolation of separate populations of CD34+, CD38- stromal and hematopoietic progenitors cells within fetal bone marrow. The CD34+, CD38-, CD50+, HLA-DR+ population contained the majority of primitive hematopoietic progenitor cells, whereas stromal progenitors were contained within the CD34+, CD38-, CD50-, HLA-DR- population. In this study, we compared the frequencies and total numbers of clonogenic CD34+, CD38- stromal and hematopoietic cells as a function of fetal gestational age using single-cell fluorescent- activated cell sorting (FACS). At 14 weeks of gestation, 1/500 fetal bone marrow mononuclear cells were primitive hematopoietic CD34+, CD38- , HLA-DR+ progenitor cells, whereas 1/1,000 were stromal progenitors with the CD34+, CD38-, HLA-DR- phenotype. During fetal ontogeny there was a continuous, age-dependent decrease in the frequency of stromal progenitors, such that, at 24 weeks of gestation, only 1/100,000 of bone marrow cells had the CD34+, CD38-, HLA-DR- phenotype and were clonogenic stromal cells when isolated by FACS. In contrast, 1/250 bone marrow cells in a 24-week fetus had the CD34+, CD38-, HLA-DR+ phenotype and were clonogenic hematopoietic progenitors. The decrease in the frequency of stromal progenitors was a function of both a decreased frequency of cells with the CD34+, CD38-, HLA-DR- phenotype and a decrease in the growth potential of individual with this phenotype. The total numbers of mononuclear cells and the total numbers of hematopoietic progenitors in two fetal femurs increased in parallel, 100-fold, between 14 and 24 weeks of gestation. In contrast, the total numbers of clonogenic CD34+, CD38-, HLA-DR- stromal progenitor cells remained constant during this period. Although adult bone marrow samples contained stromal progenitor cells at a frequency of approximately 1/7,000 mononuclear cells, clonogenic stromal cells with the CD34+, CD38-, HLA-DR- phenotype could not be isolated by single- cell FACS from these samples. Thus, there are significant differences between the frequencies and biologic characteristics of stromal and hematopoietic stem cells during fetal and postnatal ontogeny.

scholarly journals Isolation and characterization of human bone marrow microvascular endothelial cells: hematopoietic progenitor cell adhesion

Blood ◽  
1994 ◽  
Vol 84 (1) ◽  
pp. 10-19 ◽  
Author(s):  
S Rafii ◽  
F Shapiro ◽  
J Rimarachin ◽  
RL Nachman ◽  
B Ferris ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Endothelial Cells ◽  
Cell Adhesion ◽  
Progenitor Cells ◽  
Progenitor Cell ◽  
Divalent Cations ◽  
Hematopoietic Cells ◽  
Hematopoietic Progenitor Cell ◽  
Microvascular Endothelial Cells ◽  
Microvascular Endothelial

Abstract To examine potential mechanisms by which hematopoiesis may be regulated by endothelial cells within the bone marrow (BM) microenvironment, we have devised a technique for the in vitro study of the interaction of human BM microvascular endothelial cells (BMEC) with hematopoietic cells. Microvessels isolated by collagenase digestion of spicules obtained from filtered BM aspirate were plated on gelatin-coated plastic dishes, and colonies of endothelial cells grown from microvessel explants were further purified by Ulex europaeus lectin affinity separation. BMEC monolayers isolated by this technique grew in typical cobblestone fashion, stained positively with antibody to factor VIII/von Willebrand factor, and incorporated acetylated LDL. Immunohistochemical studies showed that BM microvessels and BMEC monolayers express CD34, PECAM, and thrombospondin. Incubation of resting BMEC with BM mononuclear hematopoietic cells resulted in the selective adhesion of relatively large numbers of CD34+ progenitor cells and megakaryocytes. The binding of purified BM-derived CD34+ progenitor cells to BMEC was dependent on divalent cations and was partially blocked by antibodies to CD34. IL-1 beta treatment of BMEC monolayers resulted in an increase of CD34+ progenitor cell adhesion by mechanisms independent of CD34 or divalent cations. BMEC exhibit specific affinity for CD34+ progenitor cells and megakaryocytes, suggesting that the BM microvasculature may play a role in regulating the trafficking, proliferation, and differentiation of lineage specific hematopoietic elements, and possibly of pluripotent stem cells within the CD34+ population.

scholarly journals Heparanase regulates retention and proliferation of primitive Sca-1+/c-Kit+/Lin− cells via modulation of the bone marrow microenvironment

Blood ◽  
2008 ◽  
Vol 111 (10) ◽  
pp. 4934-4943 ◽  
Author(s):  
Asaf Spiegel ◽  
Eyal Zcharia ◽  
Yaron Vagima ◽  
Tomer Itkin ◽  
Alexander Kalinkovich ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Stem Cell ◽  
Progenitor Cells ◽  
Progenitor Cell ◽  
Cathepsin K ◽  
Hematopoietic Progenitors ◽  
Hematopoietic Progenitor ◽  
Cell Mobilization ◽  
Tumor Growth And Metastasis

Abstract Heparanase is involved in tumor growth and metastasis. Because of its unique cleavage of heparan sulfate, which binds cytokines, chemokines and proteases, we hypothesized that heparanase is also involved in regulation of early stages of hematopoiesis. We report reduced numbers of maturing leukocytes but elevated levels of undifferentiated Sca-1+/c-Kit+/Lin− cells in the bone marrow (BM) of mice overexpressing heparanase (hpa-Tg). This resulted from increased proliferation and retention of the primitive cells in the BM microenvironment, manifested in increased SDF-1 turnover. Furthermore, heparanase overexpression in mice was accompanied by reduced protease activity of MMP-9, elastase, and cathepsin K, which regulate stem and progenitor cell mobilization. Moreover, increased retention of the progenitor cells also resulted from up-regulated levels of stem cell factor (SCF) in the BM, in particular in the stem cell–rich endosteum and endothelial regions. Increased SCF-induced adhesion of primitive Sca-1+/c-Kit+/Lin− cells to osteoblasts was also the result of elevation of the receptor c-Kit. Regulation of these phenomena is mediated by hyperphosphorylation of c-Myc in hematopoietic progenitors of hpa-Tg mice or after exogenous heparanase addition to wildtype BM cells in vitro. Altogether, our data suggest that heparanase modification of the BM microenvironment regulates the retention and proliferation of hematopoietic progenitor cells.

scholarly journals Effect of oxygenated sterol compounds on human bone marrow granulocytic progenitor cells

Blood ◽  
1981 ◽  
Vol 57 (1) ◽  
pp. 164-169 ◽  
Author(s):  
PC Hoffman ◽  
CM Richman ◽  
RC Hsu ◽  
J Chung ◽  
AM Scanu ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Dna Synthesis ◽  
Progenitor Cells ◽  
Mammalian Cells ◽  
Mononuclear Cells ◽  
Potent Inhibitor ◽  
Mevalonic Acid ◽  
Sterol Synthesis ◽  
Marked Inhibition

Abstract Oxygenated sterol compounds are potent inhibitors of sterol and DNA synthesis in mammalian cells. We studied the effects of oxygenated sterols on human marrow granulocytic progenitor cells in vitro (CFU-C). 25-Hydroxycholesterol was found to be a potent inhibitor of sterol synthesis in marrow mononuclear cells, with 50% inhibition occurring at approximately 10(-7) M. This compound, as well as 6-ketocholestanol, 7- ketocholesterol, and 20 alpha-hydroxycholesterol, also demonstrated marked inhibition of CFU-C proliferation. The latter effect, which was not a result of direct cytoxicity of the compounds, was reversible by cholesterol, but not by mevalonic acid. We conclude that inhibition of sterol synthesis by oxygenated sterol compounds may be insufficient to explain their suppression of CFU-C proliferation.

scholarly journals Cytokines increase human hemopoietic cell adhesiveness by activation of very late antigen (VLA)-4 and VLA-5 integrins.

1995 ◽  
Vol 181 (5) ◽  
pp. 1805-1815 ◽  
Author(s):  
J P Lévesque ◽  
D I Leavesley ◽  
S Niutta ◽  
M Vadas ◽  
P J Simmons
Keyword(s):  
Bone Marrow ◽  
Progenitor Cells ◽  
Normal Bone Marrow ◽  
Gm Csf ◽  
Normal Bone ◽  
Cd34 Cells ◽  
Late Antigen ◽  
Beta 1 Integrin ◽  
Functional States ◽  
Adhesive Interactions

Cytokines are known to be important regulators of normal hemopoiesis, acting in concert with components of the bone marrow microenvironment. Interactions with this microenvironment are known to regulate the proliferation, differentiation, and homing of hemopoietic progenitor (CD34+) cells. Adhesive interactions with the extracellular matrix retain CD34+ cells in close proximity to cytokines, but may also provide important costimulatory signals. Thus, the functional states of adhesion receptors are critical properties of CD34+ cells, but the physiological mechanisms responsible for regulating functional properties of cell adhesion receptors on primitive hemopoietic cells are still unknown. We confirm that the integrins very late antigen (VLA)-4 and VLA-5 are expressed on the CD34+ cell lines MO7e, TF1, and on normal bone marrow CD34+ progenitor cells, but in a low affinity state, conferring on them a weak adhesive phenotype on fibronectin (Fn). Herein, we show that the cytokines interleukin (IL)-3, granulocyte-macrophage CSF (GM-CSF), and KIT ligand (KL) are physiological activators of VLA-4 and VLA-5 expressed by MO7e, TF1, and normal bone marrow CD34+ progenitor cells. Cytokine-stimulated adhesion on Fn is dose dependent and transient, reaching a maximum between 15 and 30 min and returning to basal levels after 2 h. This cytokine-dependent activation is specific for VLA-4 and VLA-5, since activation of other beta 1 integrins was not observed. The addition of second messenger antagonists staurosporine and W7 abolished all cytokine-stimulated adhesion to Fn. In contrast, genistein inhibited KL-stimulated adhesion, but failed to inhibit GM-CSF- and IL-3-stimulated adhesion. Our data suggest that cytokines GM-CSF and IL-3 specifically stimulate beta 1 integrin function via an "inside-out" mechanism involving protein kinase activity, while KL stimulates integrin activity through a similar, but initially distinct, pathway via the KIT tyrosine-kinase. Thus, in addition to promoting the survival, proliferation, and development of hemopoietic progenitors, cytokines also regulate adhesive interactions between progenitor cells and the bone marrow microenvironment by modifying the functional states of specific integrins. These data are of importance in understanding the fundamental processes of beta 1 integrin activation and cellular response to mitogenic cytokines as well as on the clinical setting where cytokines induce therapeutic mobilization of hematopoietic progenitors.

Donor Origin of Multipotent Adult Progenitor Cells in Radiation Chimeras.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 1395-1395
Author(s):  
Morayma Reyes ◽  
Jeffrey S. Chamberlain
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Stem Cell ◽  
Progenitor Cells ◽  
Y Chromosome ◽  
Stromal Cells ◽  
Mononuclear Cells ◽  
Multipotent Adult Progenitor Cells

Abstract Multipotent Adult Progenitor Cells (MAPC) are bone marrow derived stem cells that can be extensively expanded in vitro and can differentiate in vivo and in vitro into cells of all three germinal layers: ectoderm, mesoderm, endoderm. The origin of MAPC within bone marrow (BM) is unknown. MAPC are believed to be derived from the BM stroma compartment as they are isolated within the adherent cell component. Numerous studies of bone marrow chimeras in human and mouse point to a host origin of bone marrow stromal cells, including mesenchymal stem cells. We report here that following syngeneic bone marrow transplants into lethally irradiated C57Bl/6 mice, MAPC are of donor origin. When MAPC were isolated from BM chimeras (n=12, 4–12 weeks post-syngeneic BM transplant from a transgenic mouse ubiquitously expressing GFP), a mixture of large and small GFP-positive and GFP-negative cells were seen early in culture. While the large cells stained positive for stroma cell markers (smooth muscle actin), mesenchymal stem cell makers (CD73, CD105, CD44) or macrophages (CD45, CD14), the small cells were negative for all these markers and after 30 cell doublings, these cells displayed the classical phenotype of MAPC (CD45−,CD105−, CD44−, CD73−, FLK-1+(vascular endothelial growth factor receptor 2, VEGFR2), Sca-1+,CD13+). In a second experiment, BM obtained one month post BM transplant (n=3) was harvested and mononuclear cells were sorted as GFP-positive and GFP-negative cells and were cultured in MAPC expansion medium. MAPC grew from the GFP-positive fraction. These GFP positive cells displayed the typical MAPC-like immunophenotypes, displayed a normal diploid karyotype and were expanded for more than 50 cell doublings and differentiated into endothelial cells, hepatocytes and neurons. To rule out the possibility that MAPC are the product of cell fusion between a host and a donor cell either in vivo or in our in vitro culture conditions, we performed sex mismatched transplants of female GFP donor BM cells into a male host. BM from 5 chimeras were harvested 4 weeks after transplant and MAPC cultures were established. MAPC colonies were then sorted as GFP-positive and GFP- negative and analyzed for the presence of Y-chromosome by FISH analysis. As expected all GFP-negative (host cells) contained the Y-chromosome whereas all GFP-positive cells (donor cells) were negative for the Y-chromosome by FISH. This proves that MAPC are not derived from an in vitro or in vivo fusion event. In a third study, BM mononuclear cells from mice that had been previously BM-transplanted with syngeneic GFP-positive donors (n=3) were transplanted into a second set of syngeneic recipients (n=9). Two months after the second transplant, BM was harvested and mononuclear cells were cultured in MAPC medium. The secondary recipients also contained GFP-positive MAPC. This is the first demonstration that BM transplantation leads to the transfer of cells that upon isolation in vitro generate MAPCs and, whatever the identity of this cell may be, is eliminated by irradiation. We believe this is an important observation as MAPC hold great clinical potential for stem cell and/or gene therapy and, thus, BM transplant may serve as a way to deliver and reconstitute the MAPC population. In addition, this study provides insight into the nature of MAPC. The capacity to be transplantable within unfractionated BM transplant renders a functional and physiological distinction between MAPC and BM stromal cells. This study validates the use of unfractionated BM transplants to study the nature and possible in vivo role of MAPC in the BM.

Enrichment of CD34+ Hematopoietic Stem and Progenitor Cells from Human Bone Marrow Using a P-Selectin-Coated Microtube.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 1219-1219
Author(s):  
Srinivas D. Narasipura ◽  
Jane L. Liesveld ◽  
Joel C. Wojciechowski ◽  
Nichola Charles ◽  
Karen Rosell ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Progenitor Cells ◽  
Adhesion Molecule ◽  
Mononuclear Cells ◽  
Single Cells ◽  
Bone Marrow Mononuclear Cells ◽  
Cell Capture ◽  
Hematopoietic Stem ◽  
Stem And Progenitor Cells ◽  
Coated Surfaces

Abstract Enrichment and purification of hematopoietic stem and progenitor cells (HSPCs) is important in transplantation therapies for hematological disorders and for basic stem cell research. Primitive CD34+ HSPCs have demonstrated stronger rolling adhesion than mature CD34- mononuclear cells on selectins (Blood2000; 95:478–486). We have exploited this differential rolling behavior to capture and purify HSPCs from bone marrow, by perfusing mononuclear cells through selectin-coated microtubes. Bone marrow mononuclear cells were perfused through the cell capture microtubes coated with adhesion molecules. These utilized a parallel plate flow chamber (Glycotech), and the P-selectin was adsorbed with laboratory tubing of appropriate lengths attached to the inlet, outlet, and vacuum ports of the gasket chamber. After perfusion, the device lumen was washed and captured cells were visualized and estimated by video microscopy. “Rolling” cells were defined as cells translating at less than 50% of the calculated hydrodynamic free stress velocity. Velocities of single cells were determined using a MATLAB program designed to measure the change in position of the cell centroid in a given time period. Adherent cells were eluted by high shear, calcium free buffer and air embolism. Immunofluorescence staining followed by flow cytometry was used to analyze CD34+ HSPCs. CD34+ HSPC purity of cells captured in adhesion molecule-coated devices was significantly higher than the fraction of CD34+ cells found in bone marrow- mononuclear cells (2.5 ± 0.8%). P-selectin coated surfaces yielded 16–20% CD34+ cell purity, while antibody coated surfaces yielded 12–18%. Although the CD34+ cell purities were comparable between selectin and antibody surfaces, the total number of CD34+ HSPCs captured was significantly higher in P-selectin devices (∼5.7–7.1 × 104) when compared to the antibody device (∼1.74–2.61 × 104). Furthermore, analysis for cells positive for CD133, a surface marker for more primitive HSPCs, depicted approximately 10–14 fold enrichment in P-selectin samples over control bone marrow mononuclear cells. The captured cells were viable and exhibited in vitro colony forming capabilities. Thus, P-selectin can be used in a compact flow device to capture and enrich HSPCs. This study supports the hypothesis that flow-based adhesion molecule-mediated capture may be a viable physiologic approach to the capture and purification of HSPCs.

ALL Cells Mobilized by AMD3100 Are More Proliferative, and Remain In the Circulation Longer Than Normal HSC, Enhancing the Action of Vincristine

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 2137-2137 ◽  
Author(s):  
Linda J. Bendall ◽  
Robert Welschinger ◽  
Florian Liedtke ◽  
Carole Ford ◽  
Aileen Dela Pena ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Progenitor Cells ◽  
Peripheral Blood ◽  
Bone Marrow Microenvironment ◽  
Hematopoietic Progenitors ◽  
Cxcr4 Antagonist ◽  
Hematopoietic Stem ◽  
Stem And Progenitor Cells ◽  
Cell Mobilization ◽  
Cycle Dependent

Abstract Abstract 2137 The chemokine CXCL12, and its receptor CXCR4, play an essential role in homing and engraftment of normal hematopoietic cells in the bone marrow, with the CXCR4 antagonist AMD3100 inducing the rapid mobilization of hematopoietic stem and progenitor cells into the blood in mice and humans. We have previously demonstrated that AMD3100 similarly induces the mobilization of acute lymphoblastic leukemia (ALL) cells into the peripheral blood. The bone marrow microenvironment is thought to provide a protective niche for ALL cells, contributing to chemo-resistance. As a result, compounds that disrupt leukemic cell interactions with the bone marrow microenvironment are of interest as chemo-sensitizing agents. However, the mobilization of normal hematopoietic stem and progenitor cells may also increase bone marrow toxicity. To better evaluate how such mobilizing agents affect normal hematopoietic progenitors and ALL cells, the temporal response of ALL cells to the CXCR4 antagonist AMD3100 was compared to that of normal hematopoietic progenitor cells using a NOD/SCID xenograft model of ALL and BALB/c mice respectively. ALL cells from all 7 pre-B ALL xenografts were mobilized into the peripheral blood by AMD3100. Mobilization was apparent 1 hour and maximal 3 hours after drug administration, similar to that observed for normal hematopoietic progenitors. However, ALL cells remained in the circulation for longer than normal hematopoietic progenitors. The number of ALL cells in the circulation remained significantly elevated in 6 of 7 xenografts examined, 6 hours post AMD3100 administration, a time point by which circulating normal hematopoietic progenitor levels had returned to baseline. No correlation between the expression of the chemokine receptor CXCR4 or the adhesion molecules VLA-4, VLA-5 or CD44, and the extent or duration of ALL cell mobilization was detected. In contrast, the overall motility of the ALL cells in chemotaxis assays was predictive of the extent of ALL cell mobilization. This was not due to CXCL12-specific chemotaxis because the association was lost when correction for background motility was undertaken. In addition, AMD3100 increased the proportion of actively cells ALL cells in the peripheral blood. This did not appear to be due to selective mobilization of cycling cells but reflected the more proliferative nature of bone marrow as compared to peripheral blood ALL cells. This is in contrast to the selective mobilization of quiescent normal hematopoietic stem and progenitor cells by AMD3100. Consistent with these findings, the addition of AMD3100 to the cell cycle dependent drug vincristine, increased the efficacy of this agent in NOD/SCID mice engrafted with ALL. Overall, this suggests that ALL cells will be more sensitive to effects of agents that disrupt interactions with the bone marrow microenvironment than normal progenitors, and that combining agents that disrupt ALL retention in the bone marrow may increase the therapeutic effect of cell cycle dependent chemotherapeutic agents. Disclosures: Bendall: Genzyme: Honoraria.

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