scholarly journals The effect of recombinant mast cell growth factor on purified murine hematopoietic stem cells.

1991 ◽  
Vol 173 (5) ◽  
pp. 1205-1211 ◽  
Author(s):  
P de Vries ◽  
K A Brasel ◽  
J R Eisenman ◽  
A R Alpert ◽  
D E Williams
Keyword(s):  
Stem Cells ◽  
Mast Cell ◽  
Growth Factor ◽  
Cell Growth ◽  
Hematopoietic Stem Cells ◽  
Bone Marrow Cells ◽  
Fold Increase ◽  
Hematopoietic Stem ◽  
Mast Cell Growth Factor

Pluripotent hematopoietic stem cells (PHSC) are very rare cells whose functional capabilities can only be analyzed indirectly. For a better understanding and possible manipulation of mechanisms that regulate self-renewal and commitment to differentiation of PHSC, it is necessary to purify these cells and to develop assays for their growth in vitro. In the present study, a rapid and simple, widely applicable procedure to highly purify day 14 spleen colony-forming cells (day 14 CFU-S) is described. Low density bone marrow cells (rho less than or equal to 1.078 g/cm3) were enriched by two successive light-activated cell sorting procedures. In the first sort, cells within a predetermined light scatter (blast cell) window that are wheat germ agglutinin/Texas Red (WGA/TxR) positive and mAb 15-1.4.1/fluorescein isothiocyanate negative (granulocyte-monocyte marker) were selected. In the second sort, cells were selected on the basis of retention of the supravital dye rhodamine 123 (Rh123). Cells that take up little Rh123 (Rh123 dull cells) and those that take up more Rh123 (Rh123 bright cells) were 237-fold and 132-fold enriched, respectively, for day 14 CFU-S. Both Rh123 fractions were cultured for various time periods in vitro in the presence of mast cell growth factor (MGF), with or without interleukin 3 (IL-3) or IL-1 alpha. Both Rh123 fractions proliferated in response to MGF alone as determined by a [3H]TdR assay or by counting nucleated cells present in the cultures over time. MGF also acted synergistically with both IL-3 and IL-1 alpha to promote stem cell proliferation. Stimulation of both Rh123 fractions with MGF alone did not result in a net increase of day 14 CFU-S. Stimulation with MGF + IL-3 or MGF + IL-alpha resulted in a 4.4- or 2.6-fold increase of day 14 CFU-S in the Rh123 dull fraction, and an 11.6-fold or 2.6-fold increase of day 14 CFU-S in the Rh123 bright fraction, respectively. The data presented in this paper indicate that in vitro MGF acts on primitive hematopoietic stem cells by itself and also is a potent synergistic factor in combination with IL-3 or IL-1 alpha.

Reversible Expression of CD34 by Murine Hematopoietic Stem Cells

Blood ◽  
1999 ◽  
Vol 94 (8) ◽  
pp. 2548-2554 ◽  
Author(s):  
Takashi Sato ◽  
Joseph H. Laver ◽  
Makio Ogawa
Keyword(s):  
Stem Cells ◽  
Hematopoietic Stem Cells ◽  
Bone Marrow Cells ◽  
Cell Populations ◽  
Hematopoietic Stem ◽  
Adult Mice ◽  
Cd34 Expression ◽  
Marrow Cells

We used a mouse transplantation model to address the recent controversy about CD34 expression by hematopoietic stem cells. Cells from Ly-5.1 C57BL/6 mice were used as donor cells and Ly-5.2 mice were the recipients. The test cells were transplanted together with compromised marrow cells of Ly-5.2 mice. First, we confirmed that the majority of the stem cells with long-term engraftment capabilities of normal adult mice are CD34−. We then observed that, after the injection of 150 mg/kg 5-fluorouracil (5-FU), stem cells may be found in both CD34− and CD34+ cell populations. These results indicated that activated stem cells express CD34. We tested this hypothesis also by using in vitro expansion with interleukin-11 and steel factor of lineage−c-kit+ Sca-1+ CD34− bone marrow cells of normal mice. When the cells expanded for 1 week were separated into CD34− and CD34+ cell populations and tested for their engraftment capabilities, only CD34+ cells were capable of 2 to 5 months of engraftment. Finally, we tested reversion of CD34+ stem cells to CD34− state. We transplanted Ly-5.1 CD34+post–5-FU marrow cells into Ly-5.2 primary recipients and, after the marrow achieved steady state, tested the Ly-5.1 cells of the primary recipients for their engraftment capabilities in Ly-5.2 secondary recipients. The majority of the Ly-5.1 stem cells with long-term engraftment capability were in the CD34− cell fraction, indicating the reversion of CD34+ to CD34−stem cells. These observations clearly demonstrated that CD34 expression reflects the activation state of hematopoietic stem cells and that this is reversible.

scholarly journals Age-Associated Characteristics of Murine Hematopoietic Stem Cells

2000 ◽  
Vol 192 (9) ◽  
pp. 1273-1280 ◽  
Author(s):  
Kazuhiro Sudo ◽  
Hideo Ema ◽  
Yohei Morita ◽  
Hiromitsu Nakauchi
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Hematopoietic Stem Cells ◽  
Bone Marrow Cells ◽  
Lymphoid Cells ◽  
Differentiation Potential ◽  
Self Renewal ◽  
Hematopoietic Stem ◽  
Functional Changes

Little is known of age-associated functional changes in hematopoietic stem cells (HSCs). We studied aging HSCs at the clonal level by isolating CD34−/lowc-Kit+Sca-1+ lineage marker–negative (CD34−KSL) cells from the bone marrow of C57BL/6 mice. A population of CD34−KSL cells gradually expanded as age increased. Regardless of age, these cells formed in vitro colonies with stem cell factor and interleukin (IL)-3 but not with IL-3 alone. They did not form day 12 colony-forming unit (CFU)-S, indicating that they are primitive cells with myeloid differentiation potential. An in vivo limiting dilution assay revealed that numbers of multilineage repopulating cells increased twofold from 2 to 18 mo of age within a population of CD34−KSL cells as well as among unseparated bone marrow cells. In addition, we detected another compartment of repopulating cells, which differed from HSCs, among CD34−KSL cells of 18-mo-old mice. These repopulating cells showed less differentiation potential toward lymphoid cells but retained self-renewal potential, as suggested by secondary transplantation. We propose that HSCs gradually accumulate with age, accompanied by cells with less lymphoid differentiation potential, as a result of repeated self-renewal of HSCs.

scholarly journals In vivo and in vitro stem cell function of c-kit- and Sca-1-positive murine hematopoietic cells

Blood ◽  
1992 ◽  
Vol 80 (12) ◽  
pp. 3044-3050 ◽  
Author(s):  
S Okada ◽  
H Nakauchi ◽  
K Nagayoshi ◽  
S Nishikawa ◽  
Y Miura ◽  
...  
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Stem Cell ◽  
Hematopoietic Stem Cells ◽  
Cell Function ◽  
Bone Marrow Cells ◽  
Synergistic Effects ◽  
Single Cells ◽  
Hematopoietic Stem

c-kit is expressed on hematopoietic stem cells and progenitor cells, but not on lymphohematopoietic differentiated cells. Lineage marker- negative, c-kit-positive (Lin-c-kit+) bone marrow cells were fractionated by means of Ly6A/E or Sca-1 expression. Lin-c-kit+Sca-1+ cells, which consisted of 0.08% of bone marrow nucleated cells, did not contain day-8 colony-forming units-spleen (CFU-S), but 80% were day-12 CFU-S. One hundred cells rescued the lethally irradiated mice and reconstituted hematopoiesis. On the other hand, 2 x 10(3) of Lin-c- kit+Sca-1- cells formed 20 day-8 and 11 day-12 spleen colonies, but they could not rescue the lethally irradiated mice. These data indicate that Lin-c-kit+Sca-1+ cells are primitive hematopoietic stem cells and that Sca-1-cells do not contain stem cells that reconstitute hematopoiesis. Lin-c-kit+Sca-1+ cells formed no colonies in the presence of stem cell factor (SCF) or interleukin-6 (IL-6), and only 10% of them formed colonies in the presence of IL-3. However, approximately 50% of them formed large colonies in the presence of IL-3, IL-6, and SCF. Moreover, when single cells were deposited into culture medium by fluorescence-activated cell sorter clone sorting system, 40% of them proliferated on a stromal cell line (PA-6) and proliferated for more than 2 weeks. In contrast, 15% of the Lin-c- kit+Sca-1-cells formed colonies in the presence of IL-3, but no synergistic effects were observed in combination with SCF plus IL-6 and/or IL-3. Approximately 10% proliferated on PA-6, but most of them degenerated within 2 weeks. The population ratio of c-kit+Sca-1+ to c-kit+Sca-1- increased 2 and 4 days after exposure to 5-fluorouracil (5-FU). These results are consistent with the relative enrichment of highly proliferative colony-forming cells by 5-FU. These data show that, although c-kit is found both on the primitive hematopoietic stem cells and progenitors, Sca-1+ cells are more primitive and respond better than Sca-1- cells to a combination of hematopoietic factors, including SCF and stromal cells.

In Vitro Myelo-Lymphoid Colony Formation by Mouse Hematopoietic Stem Cells

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 3861-3861
Author(s):  
Jun Ooehara ◽  
Hina Takano ◽  
Shin-ichiro Takayanagi ◽  
Hiromitsu Nakauchi ◽  
Hideo Ema
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Hematopoietic Stem Cells ◽  
Bone Marrow Cells ◽  
Culture Conditions ◽  
Differentiation Potential ◽  
Hematopoietic Stem ◽  
Lymphoid Progenitors ◽  
Marrow Cells

Abstract Hematopoietic stem cells (HSCs) clonally differentiate into all myeloid, B-lymphoid, and T-lymphoid lineages. Mouse HSCs are known to form in vitro colonies comprised of morphologically identifiable myeloid cells such as neutrophils, macrophages, erythroblasts, and megakaryocytes. Whether HSCs are able to differentiate along B-and T-lymphoid lineages in such colonies remains obscure. The co-culture systems with stromal cells such as S17, OP9, OP9/Delta cells have been shown to support B- and T-cell development. These systems have been used to identify subclasses of progenitors with lymphoid potentials. However, neither B cells nor T cells have been successfully generated from HSCs in vitro. This is most likely due to the lack of culture conditions which support HSCs to differentiate into a certain stage of lymphoid progenitors. In this study, we attempted to use serum-free single-cell culture to identify cytokines which fill the developmental gap between HSCs and lymphoid progenitors. Here we show that myelo-lymphoid colonies are formed by HSCs in the presence of thrombopoietin (TPO), interleukin (IL)-11, or IL-12 together with stem cell factor (SCF). CD34-negative/low, c-Kit-positive, Sca-1-positive, lineage marker-negative (CD34-KSL) bone marrow cells were individually cultured with a combination of cytokines for 7 days. All cells in each colony were transplanted into each from a group of lethally irradiated mice, along with compromised bone marrow cells. The recipient mice were periodically analyzed after transplantation to detect transient myeloid and lymphoid reconstitution. All myeloid, B-, and T-lymphoid progenitor activities were detected in single colonies formed in the presence of SCF+TPO, SCF+IL-11, SCF+IL-12. Only myeloid progenitor activity was predominantly detected in single colonies formed in the presence of SCF+IL-3, consistent with previous observations in blast colony assays. All these combinations of cytokines support self-renewal in HSCs to varying degrees. We conclude that TPO, IL-11, and IL-12 directly act on HSCs and support them to differentiate into progenitors with lymphoid differentiation potential. Early differentiation pathways in HSCs are likely to be used in common by myeloid and lymphoid lineages and be supported in common by multiple cytokines.

scholarly journals Stroma-Derived Connective Tissue Growth Factor Maintains Cell Cycle Progression and Repopulation Activity of Hematopoietic Stem Cells In Vitro

2015 ◽  
Vol 5 (5) ◽  
pp. 702-715 ◽  
Author(s):  
Rouzanna Istvánffy ◽  
Baiba Vilne ◽  
Christina Schreck ◽  
Franziska Ruf ◽  
Charlotta Pagel ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Stem Cells ◽  
Growth Factor ◽  
Connective Tissue ◽  
Hematopoietic Stem Cells ◽  
Cell Cycle Progression ◽  
Tissue Growth ◽  
Cycle Progression ◽  
Hematopoietic Stem

scholarly journals A limited role for p16Ink4a and p19Arf in the loss of hematopoietic stem cells during proliferative stress

Blood ◽  
2005 ◽  
Vol 106 (3) ◽  
pp. 827-832 ◽  
Author(s):  
Lilia Stepanova ◽  
Brian P. Sorrentino
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Hematopoietic Stem Cells ◽  
Bone Marrow Cells ◽  
Dominant Role ◽  
Wild Type ◽  
Hematopoietic Stem ◽  
Serial Transplantation ◽  
Marrow Cells

Abstract It has long been known that prolonged culture or serial transplantation leads to the loss of hematopoietic stem cells (HSCs); however, the mechanisms for this loss are not well understood. We hypothesized that expression of p16Ink4a or p19Arf or both may play a role in the loss of HSCs during conditions of enhanced proliferation, either in vitro or in vivo. Arf was not expressed in freshly isolated HSCs from adult mice but was induced in phenotypically primitive cells after 10 to 12 days in culture. When cultured bone marrow cells from either Arf–/– or Ink4a-Arf–/– mice were compared to wild-type cells in a competitive repopulation assay, no significant differences in HSC activity were seen. We then evaluated the role of p19Arf and p16Ink4a in the loss of HSCs during serial transplantation. Bone marrow cells from Ink4a-Arf–/–, but not Arf–/–, mice had a modestly extended life span and, on average, supported reconstitution of one additional recipient compared to wild-type cells. Mice given transplants of Ink4a-Arf–/–cells eventually did die of hematopoietic failure in the next round of transplantation. We conclude that mechanisms independent of the Ink4a-Arf gene locus play a dominant role in HSC loss during conditions of proliferative stress.

scholarly journals The supportive effects of erythropoietin and mast cell growth factor on CD34+/CD36- sorted bone marrow cells of myelodysplasia patients

Blood ◽  
1996 ◽  
Vol 88 (2) ◽  
pp. 505-510 ◽  
Author(s):  
S Brada ◽  
J de Wolf ◽  
D Hendriks ◽  
M Esselink ◽  
M Ruiters ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Mast Cell ◽  
Growth Factor ◽  
Cell Growth ◽  
Bone Marrow Cells ◽  
Early Stage ◽  
Erythroid Differentiation ◽  
Erythroid Development ◽  
Mast Cell Growth Factor ◽  
Marrow Cells

In the present study, we analyzed the capacity of CD34+/CD36- sorted bone marrow cells of myelodysplasia patients (n = 4) to differentiate along the erythroid lineage in the presence of erythropoietin (Epo) and mast cell growth factor (MGF). Two subgroups could be identified. In 6 patients, a normal number of burst-forming units-erythroid (BFU-Es) were cultured from CD34+/CD36- sorted cells. Cells from these patients did have the capacity to differentiate to colony-forming units- erythroid (CFU-Es) progenitors in cell suspension cultures with Epo plus MGF followed by Epo in the culture assay. Moreover, the cells became CD34-/CD36+/gly-cophorin A (GpA)+ after 7 days of culture with Epo plus MGF, a pattern comparable to that of normal progenitors. In contrast, in 8 patients, a different pattern was observed. No BFU-Es or a low number of BFU-Es were cultured from the CD34+/CD36- sorted cell fraction that was, in most of the cases, incapable of differentiating to CFU-E progenitors. Flow cytometry of the sorted population showed that, after 7 days of culture with Epo plus MGF, a high proportion of CD34+/CD36- cells persisted, whereas a low proportion of cells became CD34-/CD36+/GpA+. The unresponsiveness is not caused by the used growth factor combination, because the addition of interleukin-3 did not correct the defect. Evi-1 expression was studied in 9 cases to show whether an aberrant Evi-1 expression correlates with a disturbed erythroid development. Evi-1 expression was shown in 4 of 9 cases, whereas 3 of 9 cases did have a disturbed erythroid differentiation. In summary, the results show that the defects in the erythroid development in a subpopulation of patients with myelodysplasia is localized at an early stage of the erythroid differentiation and is associated with the persistent expression of the CD34 antigen and, in some cases, with the expression of Evi-1.

Hematopoietic Stem Cell Expansion by HOXB4 Is Greatly Enhanced in p21 Deficient Stem Cells.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 1688-1688 ◽  
Author(s):  
Noriko Miyake ◽  
Ann C.M. Brun ◽  
Mattias Magnusson ◽  
David T. Scadden ◽  
Stefan Karlsson
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Stem Cell ◽  
Hematopoietic Stem Cells ◽  
Hematopoietic Stem Cell ◽  
Bone Marrow Cells ◽  
Ex Vivo ◽  
Self Renewal ◽  
Hematopoietic Stem

Abstract Hox transcription factors have emerged as important regulators of hematopoiesis. In particular, enforced expression of HOXB4 is a potent stimulus for murine hematopoietic stem cell (HSC) self-renewal. Murine HSCs engineered to overexpress HoxB4 expand significantly more than control cells in vivo and ex vivo while maintaining a normal differentiation program. HSCs are regulated by the cell proliferation machinery that is intrinsically controlled by cyclin-dependent kinase inhibitors such as p21Cip1/Waf1(p21) and p27Kip1 (p27). The p21 protein restricts cell cycling of the hematopoietic stem cell pool and maintains hematopoietic stem cell quiescence. In order to ask whether enhanced proliferation due to HOXB4 overexpression is mediated through suppression of p21 we overexpressed HOXB4 in hematopoietic cells from p21−/− mice. First, we investigated whether human HOXB4 enhances in vitro expansion of BM cells from p21−/− mice compared to p21+/+ mice. 5FU treated BM cells from p21−/− or p21+/+ mice were pre-stimulated with SCF, IL-6, IL-3 for 2 days followed by transduction using retroviral vector expressing HOXB4 together with GFP (MIGB4) or the control GFP vector (MIG). The cells were maintained in suspension cultures for 13 days and analyzed for GFP positive cells by flow-cytometry. Compared to MIG transduced BM cells from p21+/+ mice (MIG/p21+), the numbers of GFP positive cells were increased 1.1-fold in MIG/p21−, 3.2-fold in MIGB4/p21+ and 10.0-fold in MIGB4/p21− respectively (n=5). CFU assays were performed after 13 days of culture. The numbers of CFU were increased 4.8-fold in MIG/p21−, 19.5-fold in MIG/p21+ and 33.9 -fold in MIGB4/p21− respectively. Next, we evaluated level of HSCs expansion by bone marrow repopulation assays. After 12-days of culture, 1.5 x 105 MIGB4 or MIG-transduced cells (Ly5.2) were transplanted into lethally irradiated mice in combination with 8 x 105 fresh Ly5.1 bone marrow cells. Sixteen weeks after transplantation, no Ly5.2 cells could be detected in MIG/p21+ or MIG/p21− transplanted mice (n=6). In contrast, Ly5.2 positive cells were detected in both MIGB4/p21+/+ and MIGB4/p21−/− cells. The % of Ly5.2 positive cells in MIGB4/p21− transplanted mice was 9.9-fold higher than MIGB4/p21+ transplanted mice. (38.4 % vs 3.9 %, P<0.02, n=5). These Ly5.2 positive cells differentiated into all lineages, as determined by proportions of Mac-1, B-220, CD3 and Ter119 positive populations. Currently, we are enumerating the expansion of HOXB4 transduced HSCs in p21 deficient BM cells using the CRU assay. Our findings suggest that HOXB4 increases the self-renewal of hematopoietic stem cells by a mechanism that is independent of p21. In addition, the findings demonstrate that deficiency of p21 in combination with enforced expression of HOXB4 can be used to rapidly and effectively expand hematopoietic stem cells.

Pleiotrophin Is a Growth Factor for Hematopoietic Stem Cells and Induces Stem Cell Self-Renewal

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 78-78
Author(s):  
Heather A Himburg ◽  
Garrett Muramoto ◽  
Sarah Kristen Meadows ◽  
Alice Bryn Salter ◽  
Nelson J Chao ◽  
...  
Keyword(s):  
Stem Cells ◽  
Growth Factor ◽  
Hematopoietic Stem Cells ◽  
Fold Increase ◽  
Post Transplantation ◽  
Cell Content ◽  
Self Renewal ◽  
Hematopoietic Stem ◽  
A Genome ◽  
Cells Cultured

Abstract The ability to undergo self-renewal is a defining feature of hematopoietic stem cells (HSCs) but the extrinsic signals which regulate HSC self-renewal remain unclear. We performed a genome-wide expression analysis on primary human brain ECs (HUBECs, n=10) which support the ex vivo expansion of HSCs in non-contact culture (Blood100:4433–4439; Blood105:576–583) and non-brain ECs which do not support HSC expansion (n=8) in order to identify soluble proteins overexpressed by the HSC-supportive HUBECs. We identified pleiotrophin (PTN), an 18 kD heparin binding growth factor, to be 32-fold overexpressed in HUBECs as compared to non-supportive EC lines. PTN has established activity in angiogenesis, embryogenesis, neuronal cell growth and tumorigenesis, but has no known function in hematopoiesis. We first tested whether secreted PTN was responsible for the amplification of HSCs that we have observed in co-cultures of HSCs with HUBECs via “loss of function” studies in which a blocking anti-PTN antibody was added to HUBEC cultures and HSC content was measured. Competitive repopulating unit (CRU) assays were performed in which limiting doses of donor CD45.1+ bone marrow (BM) 34−c-kit+sca-1+lin− (34-KSL) HSCs (10, 30 or 100 cells) or their progeny following 7 day non-contact culture with HUBECs + IgG or HUBECs + a blocking anti-PTN were transplanted into lethally irradiated CD45.2+ C57Bl6 mice. Mice transplanted with the progeny of 34-KSL cells cultured with HUBECs demonstrated 4–6 fold increased levels of donor-derived CD45.1+ multilineage repopulation at 8-, 12- and 24-weeks post-transplantation as compared to mice transplanted with input 34-KSL cells. In contrast, mice transplanted with the progeny of 34-KSL cells following culture with HUBECs + anti-PTN demonstrated significant reduction in donor CD45.1+ cell repopulation compared to mice transplanted with the progeny of HUBEC cultures and no difference in donor CD45.1+ cell engraftment compared to mice transplanted with input 34-KSL cells. CRU frequency within day 0 34-KSL cells was estimated to be 1 in 40 cells (95% Confidence Interval [CI]: 1/22-1/72), whereas the CRU estimate within the progeny of 34-KSL cells following HUBEC culture was 1 in 4 cells (CI: 1/2-1/9). The addition of anti-PTN to the HUBEC co-culture decreased the CRU estimate to 1 in 29 cells (CI: 1/16-1/52), suggesting that PTN signaling was responsible for the expansion of HSCs observed in HUBEC co-cultures. In order to confirm whether PTN is indeed a novel growth and self-renewal factor for HSCs, we next performed “gain of function” studies in which 34-KSL cells were placed in liquid suspension cultures with cytokines (thrombopoietin 50 ng/mL, SCF 120 ng/mL, flt-3 ligand 20 ng/mL) with and without the addition of increasing doses of recombinant murine PTN (10, 50 and 100 ng/mL) and total cell expansion and HSC content were compared. The addition of 100 ng/mL PTN to cytokine cultures caused a 20-fold increase in KSL cell content at day 7 compared to input (P<0.001), whereas a decline in KSL cells was observed with cytokine cultures alone (P<0.001), suggesting that PTN caused an expansion of stem/progenitor cells in vitro. Competitive repopulating assays were performed in which CD45.2+ recipient mice were lethally irradiated and transplanted with limiting doses (10, 30 and 100 cells) of CD45.1+ donor BM 34-KSL cells or their progeny following culture with cytokines alone or cytokines + 100 ng/mL PTN. CRU analysis at 4 weeks post-transplantation revealed that the CRU frequency within input 34-KSL cells was was 1 in 32 cells (CI: 1/18-1/57) and the CRU estimate within the progeny of 34-KSL cells cultured with cytokines alone was 1 in 69 (CI: 1/36-1/130). Conversely, the CRU estimate within the progeny of 34-KSL cells cultured with cytokines + PTN was 1 in 4 cells (CI: 1/2-1/10), indicating a 8-fold increase in short term repopulating cell content in response to PTN treatment. Longer term analysis will be performed in these mice to confirm whether PTN treatment induces the self-renewal and amplification of long-term repopulating HSCs in culture. Taken together, these data demonstrate that secreted PTN is primarily responsible for amplification of HSCs that we have observed in cultures of HSCs with ECs and the addition of PTN alone induces the expansion of phenotypic and functional HSCs in culture. PTN is therefore a novel soluble growth factor for HSCs and appears to play an important role in the extrinsic regulation of HSC self-renewal.

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