Expansion of mouse hematopoietic stem/progenitor cells in three-dimensional cocultures on growth-suppressed stromal cell layer

2019 ◽  
Vol 42 (7) ◽  
pp. 374-379 ◽  
Author(s):  
Hirotoshi Miyoshi ◽  
Chiaki Sato ◽  
Yuichiro Shimizu ◽  
Misa Morita
Keyword(s):  
Progenitor Cells ◽  
Mitomycin C ◽  
Stromal Cells ◽  
Fetal Liver ◽  
Three Dimensional ◽  
Hematopoietic Cells ◽  
Liver Cells ◽  
Hematopoietic Progenitor ◽  
Hematopoietic Stem ◽  
Fetal Liver Cells

With the aim of establishing an effective method to expand hematopoietic stem/progenitor cells for application in hematopoietic stem cell transplantation, we performed ex vivo expansion of hematopoietic stem/progenitor cells derived from mouse fetal liver cells in three-dimensional cocultures with stromal cells. In these cocultures, stromal cells were first cultured within three-dimensional scaffolds to form stromal layers and then fetal liver cells containing hematopoietic cells were seeded on these scaffolds to expand the hematopoietic cells over the 2 weeks of coculture in a serum-containing medium without the addition of cytokines. Prior to coculture, stromal cell growth was suppressed by treatment with the DNA synthesis inhibitor mitomycin C, and its effect on hematopoietic stem/progenitor cell expansion was compared with that in control cocultures in which fetal liver cells were cocultured with three-dimensional freeze-thawed stromal cells. After coculture with mitomycin C-treated stromal cells, we achieved a several-fold expansion of the primitive hematopoietic cells (c-kit+hematopoietic progenitor cells >7.8-fold, and CD34+hematopoietic stem/progenitor cells >3.5-fold). Compared with control cocultures, expansion of hematopoietic stem/progenitor cells tended to be lower, although that of hematopoietic progenitor cells was comparable. Thus, our results suggest that three-dimensional freeze-thawed stromal cells have higher potential to expand hematopoietic stem/progenitor cells compared with mitomycin C-treated stromal cells.

Long-Term Cell Autonomous Effect of Tet2 Loss in Hematopoietic Cells in Mice.

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 2416-2416
Author(s):  
Tomoya Muto ◽  
Goro Sashida ◽  
Motohiko Oshima ◽  
Chiaki Nakaseko ◽  
Kotaro Yokote ◽  
...  
Keyword(s):  
Fetal Liver ◽  
Hematopoietic Cells ◽  
Extramedullary Hematopoiesis ◽  
Liver Cells ◽  
Severe Anemia ◽  
Wild Type ◽  
Hematopoietic Stem ◽  
Myeloid Malignancies ◽  
Fetal Liver Cells

Abstract Abstract 2416 TET2 mutations are frequently observed in myeloid malignancies including myelodysplastic syndrome (MDS), myeloproliferative neoplasm (MPN) and MDS/MPN. Several groups have already reported that deletion of Tet2 in mice leads to dysregulated hematopoietic stem cell self-renewal and subsequent development of myeloid malignancies. Of note, mice hypomorphic or heterozygous for the Tet2 allele have been reported to show similar phenotypes as those of Tet2-null mice, suggesting that haploinsufficiency of Tet2 plays a role in the development of myeloid malignancies. However, little is known about long-term cell autonomous effects of Tet2 loss in hematopoietic cells: most of the reports were based on relatively short-term observations or did not exclude the influence of Tet2 loss in the niche cells. To study long-term cell autonomous effect of Tet2 loss in hematopoietic cells, we analyzed the hematopoiesis of wild-type recipient mice reconstituted with fetal liver cells from Tet2 hypomorphic mice for a longer period up to 1 year. Tet2 gene trap mice (Tet2trap/trap), in which the gene trap vector was inserted into the exon 2 of Tet2 just before the first coding exon, express Tet2 mRNA at the level approximately 20% of that of the wild-type (WT) mice (Shide et al. Leukemia 2012). We transplanted fetal liver cells from E14.5 WT or Tet2trap/trap mice into lethally irradiated recipient mice. At 4 months after transplantation, the recipient mice reconstituted with Tet2trap/trap cells showed a significantly increased proportion of monocytes in peripheral blood (PB) compared with those with WT cells (WT=5.59±2.57%, Tet2trap/trap=12.67±7.45%, p=0.01). While there were no significant differences between the two groups in the bone marrow (BM) compartments including the numbers of Lineage−Sca-1+c-Kit+ (LSK) hematopoietic stem/progenitor cells, extramedullary hematopoiesis in the spleen was markedly enhanced in the recipients with Tet2trap/trap cells. The proportion of LSK, granulocyte/macrophage progenitors (GMPs) and megakaryocyte/erythroid progenitors (MEPs) in the spleen of recipient mice reconstituted with WT and Tet2trap/trap cells were 0.002±0.001% vs 0.006±0.001% (p<0.01), 0.007±0.004% vs 0.029±0.01% (p=0.026) and 0.084±0.024% vs 0.25±0.044% (p<0.01), respectively. These findings were compatible with those reported previously and indicated that recipient mice reconstituted with Tet2trap/trapcells induce chronic myelomonocytic leukemia (CMML)-like disease. Of note, after a long observation period, particularly after 9 months post-transplantation, mice reconstituted with Tet2trap/trap cells developed advanced hematological disease and 53.3% (8 of 15) died or were killed because of their moribund condition by 11 months after transplantation. Detailed analysis on moribund as well as surviving mice reconstituted with Tet2trap/trap cells (n=3 each) revealed that the 2/3 of the mice developed CMML-like disease with monocytosis in PB and evident extramedullary hematopoiesis harboring increased number of LSK and GMPs in spleen, whereas the remaining 1/3 of mice developed MDS/MPN-like disease with severe anemia. The latter mice did not show monocytosis in PB and BM, but displayed dyserythropoiesis accompanied by massive extramedullary erythropoiesis, as we saw increased number of LSK and MEPs, but not GMPs, in spleen. The proportion of Annexin V+ cells in Ter119highCD71higherythroblasts in the BM of WT mice, CMML-like disease-carrying mice and MDS/MPN-like disease-carrying mice were 9.46±0.53%, 10.71±0.36%, and 19.04±0%, respectively, suggesting that the enhanced apoptosis led to the severe anemia seen in the MDS/MPN-like disease-carrying mice. Thus, decreased expression of Tet2 is sufficient to promote not only CMML-like disease, but also an MDS/MPN-like disease as well. Our findings confirmed a long-term cell autonomous effect from insufficient function of Tet2 in the development of hematological diseases. Interested in the molecular mechanism of disease progression, we have identified 1,642 differentially methylated regions (DMRs) in Tet2trap/trap GMPs compared with WT GMPs by ChIP-sequencing. We are now working to understand how these DMRs are involved in the development of the two distinct diseases associated with hypomorphic Tet2. Disclosures: No relevant conflicts of interest to declare.

Inhibitory Receptor, gp49B1, Is Co-Expressed with c-Kit and Regulates Hematopoiesis during Development

Blood ◽  
2015 ◽  
Vol 126 (23) ◽  
pp. 4751-4751
Author(s):  
Mi Deng ◽  
Zhigang Lu ◽  
Jaehyup Kim ◽  
Chengcheng Zhang
Keyword(s):  
Bone Marrow ◽  
Progenitor Cells ◽  
Bone Marrow Cells ◽  
Conflicts Of Interest ◽  
Fetal Liver ◽  
Hematopoietic Cells ◽  
Deficient Mouse ◽  
Hematopoietic Progenitor ◽  
Post Transplantation ◽  
Hematopoietic Stem

Abstract During development, hematopoietic stem cells (HSCs) undergo dramatic expansion in fetal liver, and then migrate to spleen and bone marrow afterwards. Mouse HSCs are enriched in lineage- Sca-1+ c-Kit+ (LSK) cells and defined by their ability to reconstitute the hematopoietic system of lethally irradiated recipients. Although c-Kit is required for HSCs function, heterogeneous c-Kit expression represents functionally distinct subsets of HSCs and progenitor cells. Recently, we demonstrated the one of inhibitory leukocyte immunoglobulin-like receptors, LILRB2, and its mouse homolog, PIRB, are expressed in HSCs. Besides PIRB, the gp49B1 is the only other member of mouse LILRB family. The function of gp49B1 in hematopoiesis is not known. Here we demonstrated that gp49B1 is not expressed by LSK cells of adult mice but is expressed on neonatal bone marrow and spleen LSK cells. Two distinct populations of neonatal LSK cells can be identified based on c-Kit expression. In neonatal bone marrow, 96% of c-Kithi LSK cells are gp49B1+ whereas only 3% of c-Kitlo LSK cells express gp49B1. Similarly, 99% of c-Kithi but only 9% of c-Kitlo LSK cells are gp49B1+ in neonatal spleen. The gp49B1+ LSK cells showed 4.2-folds higher expression level of c-Kit than that of the gp49B1- LSK cells. Because c-Kit is required for hematopoietic progenitor or HSC (HSPC) function, we sought to test whether gp49B1 has regulatory effects on HSC activity. Neonatal splenic gp49B1- LSK cells produced 26-folds more colonies than gp49+ LSK cells after 7 day in methylcellulose media. To compare their reconstitution abilities, we injected 1,000 sorted neonatal splenic gp49B1+ or gp49B1- LSK cells into lethally irradiated 8 weeks-old C57BL6 mice. All mice transplanted by gp49B1+ LSK cells died within 2 weeks post-transplantation, whereas all gp49B1- LSK cells transplanted survived. These results suggest gp49B1- LSK cells, which have less c-Kit expression, are enriched for HSC activity. To further confirm it, 500 sorted gp49B1+ or gp49B1- LSK cells (CD45.2+) were transplanted with 100,000 competitor bone marrow cells (CD45.1+) into lethally irradiated congenic recipients (CD45.1+). Mice transplanted with gp49B1- LSK cells exhibited increasing peripheral blood donor CD45 chimerism levels from 3 to 18 weeks after transplant (14.7%~68.2%); but gp49B1+ LSK cells transplanted mice only have modest chimerism levels (<2%; exception of 1 out of 7 mice has 13% at 18 weeks). Interestingly, neonatal splenic gp49B1+ LSK cells exhibited a lineage bias compared to gp49B1- LSK cells after transplantation (B cell: 2% vs. 30.1%, p<0.01; T cell: 61.3% vs. 17.4%, p<0.05; and Myeloid cell: 42.8% vs. 60.2%, p=0.32). Consistently, c-Kithi LSK cells of which over 96% are gp49B1+ showed much less HSPC activities comparing with c-Kitlo LSK cells in colony formation (40-folds less), non-competitive transplantation (all died in 2 weeks vs. all survived after transplantation), and competitive transplantation (donor CD45 chimerism: 0.04~0.34% vs. 5.8~33.6%, from 6 to 20 weeks). We continued to study the function of gp49B1's function using gp49b1 deficient mice. We found that c-Kithi LSK cells were increased in gp49B1-deficient mouse (0.18% vs. 0.14%), whereas KO c-Kithi LSK% decreased (0.09% vs. 0.14%). The c-Kithi LSK cells of gp49B1-deficient mouse also exhibited low repopulation potential. While the same number of WT and KO LSK cells had comparable repopulation abilities, five hundred gp49b1-deficient c-Kitlo LSK cells exhibited a greater reconstitution capacity (65.3% vs. 33.6%) than wild-type c-Kitlo LSK cells. These results suggest that gp49B1 may regulate the repopulation of primitive neonatal hematopoietic cells. Together, our results demonstrate that the gp49B1 is co-expressed with high level of c-Kit in hematopoietic progenitor cells of neonatal mouse, and it regulates maturation, repopulation, and differentiation of hematopoietic cells during development. Disclosures No relevant conflicts of interest to declare.

Use of human fetal liver cells for treatment of patients with lower limb peripheral artery disease

2014 ◽  
Vol 2 (1) ◽  
pp. 10-13
Author(s):  
R. Salyutin ◽  
D. Dombrowski ◽  
M. Komarov ◽  
N. Sokolov ◽  
S. Palyanitsya ◽  
...  
Keyword(s):  
Progenitor Cells ◽  
Lower Limb ◽  
Fetal Liver ◽  
Life Quality ◽  
Liver Cells ◽  
Surgical Reconstruction ◽  
Clinical Effects ◽  
Doppler Flowmetry ◽  
Human Fetal Liver ◽  
Fetal Liver Cells

In the group of patients (n = 21, mean age 54 ± 5.8 years) with chronic lower limb ischemia stage IIB who were non-liable for reconstructiverestoration surgery, we have established positive clinical effects of local transplantation of human fetal liver progenitor cells. Complex examination following 1, 3, 6 and 12 months after transplantation included duplex scanning of limb arteries, x-ray contrast arteriography and laser Doppler flowmetry as well as measuring pain-free walking and evaluating life quality based on individual questionnaire data.Owing to the transplant “Cryopreserved human fetal liver progenitor cells” the patients demonstrated stable increase of life quality index and pain-free walking as well as improvement of general health allowing assign them to the group of patients with lower ischemia stage,  quicker social rehabilitation and lesser risk of disabling surgery (р < 0.05). Also, there were observations of improved microcirculation in the ischemic extremities owing to activation of endothelium-independent mechanisms of vasodilatation, reduced myotonus and neurotonus of the pre-capillaries and improved endothelium-dependent influence on the microhaemodynamic and, hence, an increased reserve capillary blood flow (p < 0.05).Analysis of the obtained results indicates prospects and effectiveness of using fetal liver cells transplantation in the patients who are not liable for surgical reconstruction of the vascular bed.

Novel three-dimensional long-term bone marrow culture system using polymer particles with grafted epoxy-polymer-chains supports the proliferation and differentiation of hematopoietic stem cells

2011 ◽  
Vol 236 (11) ◽  
pp. 1342-1350 ◽  
Author(s):  
Yukio Hirabayashi ◽  
Yoshihiro Hatta ◽  
Jin Takeuchi ◽  
Isao Tsuboi ◽  
Tomonori Harada ◽  
...  
Keyword(s):  
Stromal Cells ◽  
Culture System ◽  
3D Structure ◽  
Three Dimensional ◽  
Hematopoietic Cells ◽  
3D Culture ◽  
Polymer Chains ◽  
Polymer Particles ◽  
Hematopoietic Stem ◽  
3D Culture System

Hematopoiesis occurs in the bone marrow, where primitive hematopoietic cells proliferate and differentiate in close association with a three-dimensional (3D) hematopoietic microenvironment composed of stromal cells. We examined the hematopoietic supportive ability of stromal cells in a 3D culture system using polymer particles with grafted epoxy polymer chains. Umbilical cord blood-derived CD34+ cells were co-cultivated with MS-5 stromal cells. They formed a 3D structure in the culture dish in the presence of particles, and the total numbers of cells and the numbers of hematopoietic progenitor cells, including colony-forming unit (CFU)-Mix, CFU-granulocyte-macrophage, CFU-megakaryocyte and burst-forming unit-erythroid, were measured every seven days. The hematopoietic supportive activity of the 3D culture containing polymer particles and stromal cells was superior to that of 2D culture, and allowed the expansion and maintenance of hematopoietic progenitor cells for more than 12 weeks. Various types of hematopoietic cells, including granulocytes, macrophages and megakaryocytes at different maturation stages, appeared in the 3D culture, suggesting that the CD34+ cells were able to differentiate into a range of blood cell types. Morphological examination showed that MS-5 stromal cells grew on the surface of the particles and bridged the gaps between them to form a 3D structure. Hematopoietic cells slipped into the 3D layer and proliferated within it, relying on the presence of the MS-5 cells. These results suggest that this 3D culture system using polymer particles reproduced the hematopoietic phenomenon in vitro, and might thus provide a new tool for investigating hematopoietic stem cell–stromal cell interactions.

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

Blood ◽  
2010 ◽  
Vol 116 (17) ◽  
pp. 3197-3207 ◽  
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.

scholarly journals A novel 37-Kd adhesive membrane protein from cloned murine bone marrow stromal cells and cloned murine hematopoietic progenitor cells

Blood ◽  
1993 ◽  
Vol 82 (5) ◽  
pp. 1436-1444 ◽  
Author(s):  
Y Shiota ◽  
JG Wilson ◽  
K Harjes ◽  
ED Zanjani ◽  
M Tavassoli
Keyword(s):  
Bone Marrow ◽  
Progenitor Cells ◽  
Stromal Cells ◽  
Bone Marrow Stromal Cells ◽  
Stromal Cell ◽  
Hematopoietic Cells ◽  
Marrow Stromal Cells ◽  
Hematopoietic Progenitor Cells ◽  
Single Chain ◽  
Hematopoietic Progenitor

Abstract The adhesion of hematopoietic progenitor cells to bone marrow stromal cells is critical to hematopoiesis and involves multiple effector molecules. Stromal cell molecules that participate in this interaction were sought by analyzing the detergent-soluble membrane proteins of GBI/6 stromal cells that could be adsorbed by intact FDCP-1 progenitor cells. A single-chain protein from GBI/6 cells having an apparent molecular weight of 37 Kd was selectively adsorbed by FDCP-1 cells. This protein, designated p37, could be surface-radiolabeled and thus appeared to be exposed on the cell membrane. An apparently identical 37- Kd protein was expressed by three stromal cell lines, by Swiss 3T3 fibroblastic cells, and by FDCP-1 and FDCP-2 progenitor cells. p37 was selectively adsorbed from membrane lysates by a variety of murine hematopoietic cells, including erythrocytes, but not by human erythrocytes. Binding of p37 to cells was calcium-dependent, and was not affected by inhibitors of the hematopoietic homing receptor or the cell-binding or heparin-binding functions of fibronectin. It is proposed that p37 may be a novel adhesive molecule expressed on the surface of a variety of hematopoietic cells that could participate in both homotypic and heterotypic interactions of stromal and progenitor cells.

scholarly journals Expansion of hematopoietic stem cells in the developing liver of a mouse embryo

Blood ◽  
2000 ◽  
Vol 95 (7) ◽  
pp. 2284-2288 ◽  
Author(s):  
Hideo Ema ◽  
Hiromitsu Nakauchi
Keyword(s):  
Stem Cells ◽  
Hematopoietic Stem Cells ◽  
Mouse Embryo ◽  
Bone Marrow Cells ◽  
Fetal Liver ◽  
Cell Number ◽  
Liver Cells ◽  
Single Wave ◽  
Hematopoietic Stem ◽  
Fetal Liver Cells

Abstract The activity of hematopoietic stem cells in the developing liver of a C57BL/6 mouse embryo was quantified by a competitive repopulation assay. Different doses of fetal liver cells at days 11 to 18 of gestation were transplanted into irradiated mice together with 2 × 105 adult bone marrow cells. A long-term repopulation in myeloid-, B-cell, and T-cell lineage by fetal liver cells was evaluated at 20 weeks after transplantation. At day 12 of gestation multilineage repopulating activity was first detected in the liver as 50 repopulating units (RU) per liver. The number of RU per liver increased 10-fold and 33-fold by day 14 and day 16 of gestation, and decreased thereafter, suggesting a single wave of stem cell development in the fetal liver. A limiting dilution analysis revealed that the frequency of competitive repopulating units (CRU) in fetal liver cells at day 12 of gestation was similar to that at day 16 of gestation. Because of an increase of total fetal liver cell number, the absolute number of CRU per liver from days 12 to 16 of gestation increased 38-fold. Hence, the mean activity of stem cells (MAS) that is given by RU per CRU remained constant from days 12 to 16 of gestation. From these data we conclude that hematopoietic stem cells expand in the fetal liver maintaining their level of repopulating potential.

Mesenchymal Stem and Progenitor Cells In the Mouse Bone Marrow Lack Expression of CD44.

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 2581-2581
Author(s):  
Hong Qian ◽  
Mikael Sigvardsson
Keyword(s):  
Bone Marrow ◽  
Progenitor Cells ◽  
Stromal Cells ◽  
Stromal Cell ◽  
Hematopoietic Cells ◽  
Hematopoietic Stem ◽  
Colony Forming Unit ◽  
Stem And Progenitor Cells ◽  
Cell Fractions

Abstract Abstract 2581 The bone marrow (BM) microenvironment consists of a heterogeneous population including mesenchymal stem cells and as well as more differentiated cells like osteoblast and adipocytes. These cells are believed to be crucial regulators of hematopoetic cell development, however, so far, their identity and specific functions has not been well defined. We have by using Ebf2 reporter transgenic Tg(Ebf2-Gfp) mice found that CD45−TER119−EBF2+ cells are selectively expressed in non-hematopoietic cells in mouse BM and highly enriched with MSCs whereas the EBF2− stromal cells are very heterogenous (Qian, et al., manuscript, 2010). In the present study, we have subfractionated the EBF2− stromal cells by fluorescent activated cell sorter (FACS) using CD44. On contrary to previous findings on cultured MSCs, we found that the freshly isolated CD45−TER119−EBF2+ MSCs were absent for CD44 whereas around 40% of the CD45−TER119−EBF2− cells express CD44. Colony forming unit-fibroblast (CFU-F) assay revealed that among the CD45−LIN−EBF2− cells, CD44− cells contained generated 20-fold more CFU-Fs (1/140) than the CD44+ cells. The EBF2−CD44− cells could be grown sustainably in vitro while the CD44+ cells could not, suggesting that Cd44− cells represents a more primitive cell population. In agreement with this, global gene expression analysis revealed that the CD44− cells, but not in the CD44+ cells expressed a set of genes including connective tissue growth factor (Ctgf), collagen type I (Col1a1), NOV and Runx2 and Necdin(Ndn) known to mark MSCs (Djouad et al., 2007) (Tanabe et al., 2008). Furthermore, microarray data and Q-PCR analysis from two independent experiments revealed a dramatic downregulation of cell cycle genes including Cdc6, Cdca7,-8 and Ki67, Cdk4-6) and up-regulation of Cdkis such as p57 and p21 in the EBF2−CD44− cells, compared to the CD44+ cells indicating a relatively quiescent state of the CD44− cells ex vivo. This was confirmed by FACS analysis of KI67 staining. Furthermore, our microarray analysis suggested high expression of a set of hematopoietic growth factors and cytokines genes including Angiopoietin like 1, Kit ligand, Cxcl12 and Jag-1 in the EBF2−CD44− stromal cells in comparison with that in the EBF2+ or EBF2−CD44+ cell fractions, indicating a potential role of the EBF2− cells in hematopoiesis. The hematopoiesis supporting activity of the different stromal cell fractions were tested by in vitro hematopoietic stem and progenitor assays- cobblestone area forming cells (CAFC) and colony forming unit in culture (CFU-C). We found an increased numbers of CAFCs and CFU-Cs from hematopoietic stem and progenitor cells (Lineage−SCA1+KIT+) in culture with feeder layer of the EBF2−CD44− cells, compared to that in culture with previously defined EBF2+ MSCs (Qian, et al., manuscript, 2010), confirming a high capacity of the EBF2−CD44− cells to support hematopoietic stem and progenitor cell activities. Since the EBF2+ cells display a much higher CFU-F cloning frequency (1/6) than the CD44−EBF2− cells, this would also indicate that MSCs might not be the most critical regulators of HSC activity. Taken together, we have identified three functionally and molecularly distinct cell populations by using CD44 and transgenic EBF2 expression and provided clear evidence of that primary mesenchymal stem and progenitor cells reside in the CD44− cell fraction in mouse BM. The findings provide new evidence for biological and molecular features of primary stromal cell subsets and important basis for future identification of stage-specific cellular and molecular interaction pathways between hematopoietic cells and their cellular niche components. Disclosures: No relevant conflicts of interest to declare.

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