Tetracycline-controlled transgenic targeting from the SCL locus directs conditional expression to erythrocytes, megakaryocytes, granulocytes, and c-kit-expressing lineage-negative hematopoietic cells

Blood ◽  
2006 ◽  
Vol 108 (5) ◽  
pp. 1533-1541 ◽  
Author(s):  
Ernesto Bockamp ◽  
Cecilia Antunes ◽  
Marko Maringer ◽  
Rosario Heck ◽  
Katrin Presser ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Expression Pattern ◽  
Bone Marrow Cells ◽  
Regulatory Elements ◽  
Hematopoietic Stem ◽  
Tetracycline Transactivator ◽  
Adult Mice ◽  
Endogenous Expression ◽  
Conditional Expression

The stem cell leukemia gene SCL, also known as TAL-1, encodes a basic helix-loop-helix transcription factor expressed in erythroid, myeloid, megakaryocytic, and hematopoietic stem cells. To be able to make use of the unique tissue-restricted and spatio-temporal expression pattern of the SCL gene, we have generated a knock-in mouse line containing the tTA-2S tetracycline transactivator under the control of SCL regulatory elements. Analysis of this mouse using different tetracycline-dependent reporter strains demonstrated that switchable transgene expression was restricted to erythrocytes, megakaryocytes, granulocytes, and, importantly, to the c-kit-expressing and lineage-negative cell fraction of the bone marrow. In addition, conditional transgene activation also was detected in a very minor population of endothelial cells and in the kidney. However, no activation of the reporter transgene was found in the brain of adult mice. These findings suggested that the expression of tetracycline-responsive reporter genes recapitulated the known endogenous expression pattern of SCL. Our data therefore demonstrate that exogenously inducible and reversible expression of selected transgenes in myeloid, megakaryocytic, erythroid, and c-kit-expressing lineage-negative bone marrow cells can be directed through SCL regulatory elements. The SCL knock-in mouse presented here represents a powerful tool for studying normal and malignant hematopoiesis in vivo.

JAK2V617F Promotes Stem Cell Amplification Driving MPN Clonal Dominance in Mice and Treatment by IFNa Prevents This Effect

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 616-616 ◽  
Author(s):  
Caroline Marty ◽  
Catherine Lacout ◽  
Marie Cuingnet ◽  
Salma Hasan ◽  
Eric Solary ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Bone Marrow Cells ◽  
Conflicts Of Interest ◽  
Myeloproliferative Neoplasm ◽  
Jak2 V617f ◽  
Lymphoid Cells ◽  
Hematopoietic Stem ◽  
Endogenous Expression ◽  
Long Term Treatment

Abstract Abstract 616 JAK2V617F is the major mutation involved in classic myeloproliferative neoplasm (MPN). It promotes growth factor independent cell growth and is able to recapitulate MPN features in retroviral, transgenic (TG) or knock-in (KI) mouse models. Several mutations implicated in epigenetic modifications or leukemic transformations have been also identified in MPN and several reports have questioned the particular role of JAK2V617F on hematopoietic stem cells (HSC) proliferation thus as a driver of MPN emergence. Therefore, we investigated the in vivo effect of an endogenous expression of JAK2V617F on early stages of differentiation and their ability to compete for normal cells in a repopulation assay. For this study, we develop a novel mouse conditional JAK2V617F KI model based on the “FLEX switch” strategy. These KI mice were crossed with TG mice expressing the Cre recombinase under the control of the vav promoter in order to restrict JAK2V617F expression to hematopoietic and some endothelial tissues. VavCre/JAK2+/V617F KI mice developed high hematocrit (70 ± 2 %, control values 49 ± 1 % n=13), platelet (2.3 ± 0.1 × 109 / mL, control values 0.84 ± 0.04 × 109 / mL n=20) and white blood cell (20-40 × 106/mL, control values between 6–10 × 106 / mL) values and a splenomegaly at 2–3 months of age but after 6 months of age an anemia and a thrombocytopenia appeared. This model mimics human polycythemia vera with secondary myelofibrosis. At 2–3 months of age, cumulative numbers in bone marrow (BM) and spleen of CFU-E, BFU-E and GM-CFC were increased 15-, 3-, 1.2–fold, respectively, compared to control. Most CFU-E grew without the addition of erythropoietin. A 6-fold amplification of total early progenitors LSK and a tendency toward SLAM (LSK/CD48−/CD150+) cell amplification, mainly due to a significant 9-fold increase in the spleen, were also observed. Competitive repopulation assays using 30% KI and 70% WT bone marrow cells demonstrated 17 weeks after BM transplantation (BMT) a rapid and strong amplification, from 30% to > 80%, of blood myeloid cells (Gr-1+/Mac1+) from KI origin. Late after transplantation (35 weeks), Lin-, LSK and SLAM cell compartments from KI origin raised from the initial 30% to almost 100% in the BM and even KI blood lymphoid cells (B220+ and CD3+) demonstrated a significant amplification compared to control. This shows that endogenous expression of JAK2V617F gives an advantage to HSC, promoting clonal dominance in mice. Then, we analyzed at which levels of differentiation acts IFNα, a drug promoting cycling of dormant cells and proven efficacious in PV treatment in human. In a chimeric model, we demonstrated that IFNα could prevent the development of MPN induced in vavCre/JAK2+/V617F KI recipient mice by inhibiting the amplification of KI cells. Secondary BMT from treated animals demonstrated the eradication of disease-initiating cells after long-term treatment. This study shows that IFNα acts at the level of the disease-initating cell by reverting the HSC promoting clonal dominance induced by JAK2V617F. Disclosures: No relevant conflicts of interest to declare.

High Levels of HoxA10 Severely Impair Erythoid Development In Vivo and Cause Lethal Anemia.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 2773-2773 ◽  
Author(s):  
Mattias Magnusson ◽  
Ann C.M. Brun ◽  
Noriko Miyake ◽  
Mats Ehinger ◽  
Eva Nilsson ◽  
...  
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
Bone Marrow Cells ◽  
Hematopoietic Cells ◽  
Hemoglobin Level ◽  
Separate Experiment ◽  
Severe Anemia ◽  
Hematopoietic Stem ◽  
Tetracycline Transactivator

Abstract Several Homeobox transcription factors (Hox) have been shown to be highly involved in the complex regulation of hematopoiesis, controlling proliferation, differentiation and self-renewal capacity of hematopoietic stem cells (HSC). One of these genes, HOXA10, has been shown to be expressed in primitive hematopoietic cells and meyolid progenitors, but is downregulated as the cells mature. The expression of HOXA10 is found in almost all types of human acute myeloid leukemia (AML) and overexpression of HOXA10 in mice by a retroviral vector induces proliferation of myeloid progenitors, that eventual leads to AML. In order to further study the role of HOXA10 in hematopoiesis and to ask whether the effect of HOXA10 is dose dependent, we generated an inducible system based on the tetracycline transactivator system, by mating our previously published transgenic HOXA10 mouse model with the Rosa26rtTA mouse. The Rosa locus is transcriptionally active in many organs including all hematopoietic tissues. Here we show that we can induce the expression of HOXA10 in the bone marrow of inducible mice in vivo by administrating doxycycline and no leakiness was detected in uninduced bone marrow. Double transgenic mice were born at normal ratios and hematopoiesis was normal prior to induction. When the gene was systemically induced by administration of doxycycline (2 mg/ml) in the drinking water the mice died within one to two weeks. Analysis showed small hemorrhages (intestine, skin), low hemoglobin level (HOXA10: 82±21 g/L, wt: 130±4 g/L), low RBC (HOXA10: 5.9±1.7x1012/L, wt: 8.67±0.4x1012/L) and the platelet count was severely reduced (A10: 33±26x109/L, wt: 845±121x109/L, data from three experiments n=6, p<0.002). In order to further study the effect of HoxA10 in hematopoietic cells we transplanted inducible HOXA10 bone marrow cells to lethally irradiated wild type recipients. The expression of HOXA10 was induced as above and analysis revealed severe anemia 3–4 weeks after induction with reduced hemoglobin level (HOXA10: 71±18 g/L wt: 124±6 g/L), and low RBC count (HOXA10: 4.8±1.3x1012/L, wt: 8.1±0.7x1012/L, data from three experiments, n=8, p<0.001). When the mice became terminally ill, they were sacrificed, displaying splenomegaly with immature erythrocytes at different stages of development indicating a block in erythroid maturation. In a separate experiment a lower dose (1.5x106) of inducible HOXA10 BM was transplanted. Most of these mice survived but displayed a reduction in hemoglobin levels at three weeks post BMT. Linage analysis showed that high HOXA10 expression caused a block in CD3+ T-cells (HOXA10: 2.88±1.59%, uninduced: 17±1%, wt: 19±1% p<0.0001) and an increase in the proportion of Gr1/Mac1+ positive cells (HOXA10: 45±5%, uninduced: 18±4%, wt: 18±5% p<0.0001). In summary, we present a new model system for studying the effect of a transcription factor in vivo and demonstrate that high levels of HOXA10 cause a block in erythroid development and a severe anemia. Furthermore, high levels of HOXA10 cause reduced numbers of T-cells and increased myelopoiesis, while B cell development is unaffected.

scholarly journals CD34+ human marrow cells that express low levels of Kit protein are enriched for long-term marrow-engrafting cells

Blood ◽  
1996 ◽  
Vol 87 (10) ◽  
pp. 4136-4142 ◽  
Author(s):  
I Kawashima ◽  
ED Zanjani ◽  
G Almaida-Porada ◽  
AW Flake ◽  
H Zeng ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Bone Marrow Cells ◽  
Marrow Cell ◽  
In Utero ◽  
Fetal Sheep ◽  
Hematopoietic Stem ◽  
Show Evidence ◽  
Marrow Cells

Using in utero transplantation into fetal sheep, we examined the capability of human bone marrow CD34+ cells fractionated based on Kit protein expression to provide long-term in vivo engraftment. Twelve hundred to 5,000 CD34+ Kit-, CD34+ Kit(low), and CD34+ Kit(high) cells were injected into a total of 14 preimmune fetal sheep recipients using the amniotic bubble technique. Six fetuses were killed in utero 1.5 months after bone marrow cell transplantation. Two fetuses receiving CD34+ Kit(low) cells showed signs of engraftment according to analysis of CD45+ cells in their bone marrow cells and karyotype studies of the colonies grown in methylcellulose culture. In contrast, two fetuses receiving CD34+ Kit(high) cells and two fetuses receiving CD34+ Kit- cells failed to show evidence of significant engraftment. Two fetuses were absorbed. A total of six fetuses receiving different cell populations were allowed to proceed to term, and the newborn sheep were serially examined for the presence of chimerism. Again, only the two sheep receiving CD34+ Kit(low) cells exhibited signs of engraftment upon serial examination. Earlier in studies of murine hematopoiesis, we have shown stage-specific changes in Kit expression by the progenitors. The studies of human cells reported here are in agreement with observations in mice, and indicate that human hematopoietic stem cells are enriched in the Kit(low) population.

scholarly journals CXCL12-CXCR4 chemokine signaling is essential for NK-cell development in adult mice

Blood ◽  
2011 ◽  
Vol 117 (2) ◽  
pp. 451-458 ◽  
Author(s):  
Mamiko Noda ◽  
Yoshiki Omatsu ◽  
Tatsuki Sugiyama ◽  
Shinya Oishi ◽  
Nobutaka Fujii ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Nk Cells ◽  
Nk Cell ◽  
Cell Development ◽  
Hematopoietic Stem ◽  
Adult Mice ◽  
Multipotent Progenitors ◽  
Chemokine Signaling ◽  
Chemokine Ligand

Abstract Natural killer (NK) cells are granular lymphocytes that are generated from hematopoietic stem cells and play vital roles in the innate immune response against tumors and viral infection. Generation of NK cells is known to require several cytokines, including interleukin-15 (IL-15) and Fms-like tyrosine kinase 3 ligand, but not IL-2 or IL-7. Here we investigated the in vivo role of CXC chemokine ligand-12 (CXCL12) and its primary receptor CXCR4 in NK-cell development. The numbers of NK cells appeared normal in embryos lacking CXCL12 or CXCR4; however, the numbers of functional NK cells were severely reduced in the bone marrow, spleen, and peripheral blood from adult CXCR4 conditionally deficient mice compared with control animals, probably resulting from cell-intrinsic CXCR4 deficiency. In culture, CXCL12 enhanced the generation of NK cells from lymphoid-primed multipotent progenitors and immature NK cells. In the bone marrow, expression of IL-15 mRNA was considerably higher in CXCL12-abundant reticular (CAR) cells than in other marrow cells, and most NK cells were in contact with the processes of CAR cells. Thus, CXCL12-CXCR4 chemokine signaling is essential for NK-cell development in adults, and CAR cells might function as a niche for NK cells in bone marrow.

scholarly journals Normal cycling patterns of hematopoietic stem cell subpopulations: an assay using long-term in vivo BrdU infusion

Blood ◽  
1985 ◽  
Vol 66 (6) ◽  
pp. 1460-1462 ◽  
Author(s):  
ME Pietrzyk ◽  
GV Priestley ◽  
NS Wolf
Keyword(s):  
Bone Marrow ◽  
Bone Marrow Cells ◽  
Improved Method ◽  
Hematopoietic Stem ◽  
Infusion Study ◽  
A Cell ◽  
Cell Subpopulations ◽  
Over Time

It was found in a long-term bromodeoxyuridine (BrdU) infusion study that two or more different subpopulations of bone marrow stem cells exist in mice. One of these subpopulations appears to be noncycling and forms approximately 10% of eight-day CFU-S. Another one, a subpopulation of slowly cycling bone marrow cells, is represented as 14- day CFU-S. The 14-day CFU-S have a regular increment in the percentage of the subpopulation entering the cycle over time, with a cell generation half-time of 21 days. The cycling status in these experiments was ascertained by in vivo continuous long-term BrdU infusion. An improved method is presented for long-term BrdU infusion with UV killing of cycled cells.

Phenotypic correction of Fanconi anemia group C knockout mice

Blood ◽  
2000 ◽  
Vol 95 (2) ◽  
pp. 700-704 ◽  
Author(s):  
Kimberly A. Gush ◽  
Kai-Ling Fu ◽  
Markus Grompe ◽  
Christopher E. Walsh
Keyword(s):  
Bone Marrow ◽  
Progenitor Cells ◽  
Mitomycin C ◽  
Fanconi Anemia ◽  
Bone Marrow Cells ◽  
Bone Marrow Failure ◽  
Genetic Disorder ◽  
Hematopoietic Stem ◽  
Marrow Cells

Fanconi anemia (FA) is a genetic disorder characterized by bone marrow failure, congenital anomalies, and a predisposition to malignancy. FA cells demonstrate hypersensitivity to DNA cross-linking agents, such as mitomycin C (MMC). Mice with a targeted disruption of the FANCC gene (fancc −/− nullizygous mice) exhibit many of the characteristic features of FA and provide a valuable tool for testing novel therapeutic strategies. We have exploited the inherent hypersensitivity offancc −/− hematopoietic cells to assay for phenotypic correction following transfer of the FANCC complementary DNA (cDNA) into bone marrow cells. Murine fancc −/− bone marrow cells were transduced with the use of retrovirus carrying the humanfancc cDNA and injected into lethally irradiated recipients. Mitomycin C (MMC) dosing, known to induce pancytopenia, was used to challenge the transplanted animals. Phenotypic correction was determined by assessment of peripheral blood counts. Mice that received cells transduced with virus carrying the wild-type gene maintained normal blood counts following MMC administration. All nullizygous control animals receiving MMC exhibited pancytopenia shortly before death. Clonogenic assay and polymerase chain reaction analysis confirmed gene transfer of progenitor cells. These results indicate that selective pressure promotes in vivo enrichment offancc-transduced hematopoietic stem/progenitor cells. In addition, MMC resistance coupled with detection of the transgene in secondary recipients suggests transduction and phenotypic correction of long-term repopulating stem cells.

Lentiviral gene transfer regenerates hematopoietic stem cells in a mouse model for Mpl-deficient aplastic anemia

Blood ◽  
2011 ◽  
Vol 117 (14) ◽  
pp. 3737-3747 ◽  
Author(s):  
Dirk Heckl ◽  
Daniel C. Wicke ◽  
Martijn H. Brugman ◽  
Johann Meyer ◽  
Axel Schambach ◽  
...  
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Mouse Model ◽  
Hematopoietic Stem Cells ◽  
Aplastic Anemia ◽  
Bone Marrow Cells ◽  
Specific Expression ◽  
Hematopoietic Stem ◽  
Egfp Reporter

AbstractThpo/Mpl signaling plays an important role in the maintenance of hematopoietic stem cells (HSCs) in addition to its role in megakaryopoiesis. Patients with inactivating mutations in Mpl develop thrombocytopenia and aplastic anemia because of progressive loss of HSCs. Yet, it is unknown whether this loss of HSCs is an irreversible process. In this study, we used the Mpl knockout (Mpl−/−) mouse model and expressed Mpl from newly developed lentiviral vectors specifically in the physiologic Mpl target populations, namely, HSCs and megakaryocytes. After validating lineage-specific expression in vivo using lentiviral eGFP reporter vectors, we performed bone marrow transplantation of transduced Mpl−/− bone marrow cells into Mpl−/− mice. We show that restoration of Mpl expression from transcriptionally targeted vectors prevents lethal adverse reactions of ectopic Mpl expression, replenishes the HSC pool, restores stem cell properties, and corrects platelet production. In some mice, megakaryocyte counts were atypically high, accompanied by bone neo-formation and marrow fibrosis. Gene-corrected Mpl−/− cells had increased long-term repopulating potential, with a marked increase in lineage−Sca1+cKit+ cells and early progenitor populations in reconstituted mice. Transcriptome analysis of lineage−Sca1+cKit+ cells in Mpl-corrected mice showed functional adjustment of genes involved in HSC self-renewal.

STAT5 promotes multilineage hematolymphoid development in vivo through effects on early hematopoietic progenitor cells

Blood ◽  
2002 ◽  
Vol 99 (1) ◽  
pp. 95-101 ◽  
Author(s):  
Jonathan W. Snow ◽  
Ninan Abraham ◽  
Melissa C. Ma ◽  
Nancy W. Abbey ◽  
Brian Herndier ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Blood Cell ◽  
Progenitor Cells ◽  
Cell Types ◽  
Hematopoietic Stem ◽  
Signal Transducers ◽  
Adult Mice ◽  
Colony Forming Units ◽  
Proliferation Activity

The transcription factor signal transducers and activators of transcription 5 (STAT5) is activated by numerous cytokines that orchestrate blood cell development. Multilineage peripheral blood cytopenias were observed in adult mice lacking both isoforms of STAT5 (STAT5A and STAT5B) as well as accelerated rates of apoptosis in the bone marrow. Although the hematopoietic stem cell (HSC) population was preserved in a number of these mice, the post-HSC progenitor populations were diminished and a marked reduction in functional progenitors (spleen colony-forming units) was detected. Competitive bone marrow transplantation studies in vivo revealed a profound impairment of repopulation potential of STAT5-null HSCs, leading to complete lack of contribution to the myeloid, erythroid, and lymphoid lineages. These abnormalities were associated with heightened proliferation activity in the HSC fraction, suggesting the action of homeostatic mechanisms to maintain sufficient levels of diverse blood cell types for viability. Thus, STAT5 normally sustains the robust hematopoietic reserve that contributes to host viability through crucial survival effects on early progenitor cells.

Dynamic Patterns of Migration and Expansion of Hematopoiesis during MGMT Mediated Drug Selection.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 156-156 ◽  
Author(s):  
Yuan Lin ◽  
Perrin Cheung ◽  
David L. Wilson ◽  
Stanton L. Gerson
Keyword(s):  
Bone Marrow ◽  
In Vivo Imaging ◽  
Bone Marrow Cells ◽  
Clonal Expansion ◽  
Dependent Manner ◽  
Drug Selection ◽  
Hematopoietic Stem ◽  
Mouth Disease Virus ◽  
Marrow Cells

Abstract While hematopoietic engraftment kinetics are well appreciated after lethal irradiation in the mouse, most observations have been limited to blood samples or terminal examination of marrow or spleen. The development of non-invasive bioluminescence in vivo imaging technology allows a dynamic picture of engraftment and clonal expansion to be defined. We have extended this technology to the process of drug resistance gene therapy. We hypothesized that drug selection would profoundly affect the extent and dynamics of hematopoietic stem cells (HSC) engraftment and clonal expansion after lentiviral mediated gene transfer of the P140KMGMT gene into murine HSC. In previous studies, we have shown that P140KMGMT gene containing retroviral and lentiviral transduced bone marrow cells provided significant protection against chemotherapeutic drugs BCNU and TMZ given with BG (O6-Benzylguanine), in vitro and in vivo. We generated a bicistronic lentiviral vector containing P140KMGMT gene and firefly luciferase gene linked by 2A sequence of FMDV(Foot-and-Mouth Disease Virus), which will cleave itself during ribosomal translation. Whole bone marrow cells was collected from BALB/c mice 4 days after 5-FU treatment and transduced with P140KMGMT-luc lentiviruses at MOI of 1.4. Transduced bone marrow cells were transplanted into lethally irradiated or non-myeloablated syngeneic recipient mice at different cell numbers. Initial bioluminescent signal emerged 6–8 days after transplantation in both lethally irradiated and non-myeloablated recipients. The onset of bioluminescent foci after transplantation occurred in a cell dose dependent manner. The initial signal emitted predominantly from bone marrow, especially femurs, humeri and vertebrae during the early stage of clonal expansion. Intense signal appeared in spleen at days 12–14 and became weaker or even disappeared by days 20–28. Clonal expansion and engraftment greatly increased after a single course of BG+TMZ treatment and initiated strong hematopoiesis in non-myeloablated recipients. Total body bioluminescence intensity of drug treated mice increased 24 fold and 7 fold compared to non-treated mice in both non-myeloablated and lethally irradiated recipients, respectively. A transient phase suggesting migration through the lymphatic system and in the spleen occurred in most mice and was exacerbated by drug selection, but this was less clear in lethally irradiated mice, where engraftment was more confined to the marrow spaces. Bioluminescence in vivo imaging reveals active migration between the bone marrow and the spleen during hematopoiesis. Drug selection has a significant impact on the patterns of engraftment and clonal expansion of HSC and progenitor cells after transplantation.

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

Blood ◽  
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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