RUNX1C-Mediated Reprogramming Of Human Bone Marrow Stromal Cells into Early Blood Progenitors

Abstract Somatic cell reprogramming to the hematopoietic lineage, either through a pluripotent state or directly, opens the possibility of production of a ready source of autologous hematopoietic stem cells (HSC) that can be used to treat/cure a wide variety of blood disorders. While it has previously been shown that dermal fibroblasts (HFF) can be directly reprogrammed to the hematopoietic lineage, the efficiency was relatively low and the resultant hematopoietic cells lacked multilineage differentiative potential. Stro1(+) isolated stromal progenitors (SIPs) can easily be isolated from the bone marrow (BM) and expanded ex-vivo to obtain clinically significant numbers of cells. In similarity to HSC, SIPs are derived from the mesoderm, and are intimately linked with HSC specification during ontogeny. As such, they are likely to be epigenetically closer to HSC than HFF, and therefore good candidates for reprogramming into hematopoietic cells. To verify the uniqueness of SIPs for reprogramming, we transduced SIPs and HFF with OCT4 and/or RUNX1C, a master transcription factor (TF) that triggers the developmental onset of definitive hematopoiesis, in the following combinations: 1) OCT4 alone; 2) RUNX1C alone; or 3) OCT4+RUNX1C. We then performed a timeline of gene/cell surface marker expression (using microarray, qRT-PCR, and flow cytometry) from day 3-16 post-transduction. Visual inspection of the cultures showed that, while reprogrammed colonies began to appear in SIPs cultures at day 9, no colonies were seen during this time period in HFF cultures. Flow cytometry and molecular analyses of colonies obtained from OCT4+RUNX1C combination demonstrated that expression of CD41, the earliest marker of commitment to the hematopoietic lineage, commenced within only 3-4 days and peaked at day 5-6, by which time ∼20% of SIPs expressed this marker. This peak in CD41 expression coincided with commencement of expression of CD34 and CD45, and maximal induction of several hematopoiesis-specific TFs and phenotypic markers such as PU.1, HOXB4, GATA2, MIXL, WNT3, KDR, CDX4, which occurred at 1-3 logs higher levels in SIPs than HFF. Further studies demonstrated that the chromatin remodeling function of OCT4 could be replaced with the histone methyltransferase inhibitor Bix-01294, with the combination of RUNX1C and Bix-01294 inducing levels of CD34 and CD41 expression by day 5 that were similar to those achieved with RUNX1C plus OCT4. The present studies thus take several important steps towards making the promise of producing autologous hematopoietic cells for transplantation via direct reprogramming a reality. Disclosures: No relevant conflicts of interest to declare.

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CongenitalSTAT3mutation Mediates Primary Persistent Polymorphic Inflammatory Activation and T Cell Leukemogenesis

Blood ◽

10.1182/blood-2019-132138 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 1054-1054 ◽

Cited By ~ 1

Author(s):

Hongxing Liu

Keyword(s):

Bone Marrow ◽

Flow Cytometry ◽

T Cell ◽

Lymph Nodes ◽

Conflicts Of Interest ◽

Sh2 Domain ◽

Janus Kinase ◽

Gingival Hyperplasia ◽

Hematopoietic Stem ◽

T Cell Leukemogenesis

Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathways play a pivotal role in inflammation and immunity, among which, JAK/STAT3 pathway is the most potent and leads the crosstalk of immunity and oncogenesis. Somatic STAT3 activatingmutations have been found in about 40% of T cell large granular lymphocytic leukemia (T-LGLL) patients, most of which are located in exon 21 which encodes Src homology 2 (SH2) domain leading to the increased activity of aberrant STAT3 protein and the upregulation of its transcriptional targets. While germline STAT3activatingmutations represent a newly defined entity of immune dysregulations named infantile-onset multisystem autoimmune disease-1 (ADMIO1, #MIM 615952). Both the two diseases are rare and poorly understood. Here, we report a pedigree including a proband, a six-year-old girl, primarily manifesting as thrombocytopenia and lymphadenopathy and her father diagnosed as T-LGLL with pure red cell aplastic anemia without autoimmune disorders preceding or during his disease course. Morphology of the bone marrow smears of the proband indicated normal hyperplasia without evident dyspepsia or increased blast cells. However, the vacuoles in monocytes and the density and size of granules in neutrophils increased, and megaloblast transformation was observed in some neutrophils. (Fig. 1A, 1B) Biopsy of an enlarged lymph node showed the reactive follicular hyperplasia. (Fig. 1C) Whole exon sequencing and pedigree analysis of the family revealed the germline STAT3 c.833G>A/p.R278Hmutation harbored by the proband which originated de novo from her father who additionally carried a germline TAL1G62Rmutation and somatically accumulated an FLT3-ITD mutation. (Fig. 2) Through single-cell RNA sequencing, we also found the increase of circulating CD8+ T cells and the decrease of NK cells of the proband. (Fig. 3) The STAT3 target genes were generally overactivated, and the expression of cytokines decreased in transcription level. In the genes participating in JAK/STATs pathways, the expression of JAK3, STAT1, and STAT3was up-regulated significantly. (data not shown) Immunophenotype of the proband by flow cytometry confirmed change in immunocyte compartments, (Fig. 4) but the serum cytokine concentrations measured by flow cytometry yielded controversial results, that most of cytokines were moderately elevated, and IL-1β, IL-5, TNF-α, and IFN-γ were of the most evident. (data not shown) During the treatment and follow-up, Cyclosporin A (CsA) was efficient in maintaining her circulating platelets in the range of 166×109/L to 302×109/L, but the enlarged lymph nodes and hepatosplenomegaly had no response. Eleven months later, CsA was replaced by tacrolimusfor the severe gingival hyperplasia, which has efficiently stabilized her platelets count and normalized the enlarged lymph nodes, liver, and spleen. On the contrary, in the three and a half years' span of illness, the father was refractory to CsA and methotrexate (MTX), moreover, lethal bone marrow suppression was induced by one course of fludarabine. For the high level of HLA-I and HLA-II antibodies in the circulation, plantlets transfusions were only efficient after plasmapheresis. The father eventually died from pulmonary and gastrointestinal infection due to the failure of maternal HLA-haploidentical hematopoietic stem cell transplantation (HSCT). We comprehensively elaborated the immunophenotype of the proband and thoroughly elucidated the genetic alternations of the father which led to the T cell leukemogenesis, which brought new insight on these two rare diseases and highlighted a more scrupulous therapeutic strategy in T-LGLL with congenital mutations. Figure 1 Disclosures No relevant conflicts of interest to declare.

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Poly I:C Stimulates Sca-1 Expression in Murine Bone Marrow and Increases the Number of Phenotypic Hematopoietic Stem Cells.

Blood ◽

10.1182/blood.v114.22.2504.2504 ◽

2009 ◽

Vol 114 (22) ◽

pp. 2504-2504

Author(s):

Russell Garrett ◽

Gerd Bungartz ◽

Alevtina Domashenko ◽

Stephen G. Emerson

Keyword(s):

Cell Cycle ◽

Stem Cells ◽

Bone Marrow ◽

Hematopoietic Stem Cells ◽

Conflicts Of Interest ◽

Hematopoietic Cells ◽

Poly I:C ◽

Hematopoietic Stem ◽

Marrow Cells ◽

Myeloid Progenitors

Abstract Abstract 2504 Poster Board II-481 Polyinosinic:polycytidlyic acid (poly I:C) is a synthetic double-stranded RNA used to mimic viral infections in order to study immune responses and to activate gene deletion in lox-p systems employing a Cre gene responsive to an Mx-1 promoter. Recent observations made by us and others have suggested hematopoietic stem cells, responding to either poly I:C administration or interferon directly, enter cell cycle. Twenty-two hours following a single 100mg intraperitoneal injection of poly I:C into 10-12 week old male C57Bl/6 mice, the mice were injected with a single pulse of BrdU. Two hours later, bone marrow was harvested from legs and stained for Lineage, Sca-1, ckit, CD48, IL7R, and BrdU. In two independent experiments, each with n = 4, 41 and 33% of Lin- Sca-1+ cKit+ (LSK) IL-7R- CD48- cells from poly I:C-treated mice had incorporated BrdU, compared to 7 and 10% in cells from PBS-treated mice. These data support recently published reports. Total bone marrow cellularity was reduced to 45 and 57% in the two experiments, indicating either a rapid death and/or mobilization of marrow cells. Despite this dramatic loss of hematopoietic cells from the bone marrow of poly I:C treated mice, the number of IL-7R- CD48- LSK cells increased 145 and 308% in the two independent experiments. Importantly, the level of Sca-1 expression increased dramatically in the bone marrow of poly I:C-treated mice. Both the percent of Sca-1+ cells and the expression level of Sca-1 on a per cell basis increased after twenty-four hours of poly I:C, with some cells acquiring levels of Sca-1 that are missing from control bone marrow. These data were duplicated in vitro. When total marrow cells were cultured overnight in media containing either PBS or 25mg/mL poly I:C, percent of Sca-1+ cells increased from 23.6 to 43.7%. Within the Sca-1+ fraction of poly I:C-treated cultures, 16.7% had acquired very high levels of Sca-1, compared to only 1.75% in control cultures. Quantitative RT-PCR was employed to measure a greater than 2-fold increase in the amount of Sca-1 mRNA in poly I:C-treated cultures. Whereas the numbers of LSK cells increased in vivo, CD150+/− CD48- IL-7R- Lin- Sca-1- cKit+ myeloid progenitors almost completely disappeared following poly I:C treatment, dropping to 18.59% of control marrow, a reduction that is disproportionately large compared to the overall loss of hematopoietic cells in the marrow. These cells are normally proliferative, with 77.1 and 70.53% accumulating BrdU during the 2-hour pulse in PBS and poly I:C-treated mice, respectively. Interestingly, when Sca-1 is excluded from the analysis, the percent of Lin- IL7R- CD48- cKit+ cells incorporating BrdU decreases following poly I:C treatment, in keeping with interferon's published role as a cell cycle repressor. One possible interpretation of these data is that the increased proliferation of LSK cells noted by us and others is actually the result of Sca-1 acquisition by normally proliferating Sca-1- myeloid progenitors. This new hypothesis is currently being investigated. Disclosures: No relevant conflicts of interest to declare.

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Application of Mesenchymal Stem Cells Derived From the Umbilical Cord Instead of Bone Marrow In Hematopoietic Stem Cells Transplantation.

Blood ◽

10.1182/blood.v116.21.4544.4544 ◽

2010 ◽

Vol 116 (21) ◽

pp. 4544-4544

Author(s):

Ching-Tien Peng

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Mesenchymal Stem Cells ◽

Umbilical Cord ◽

Acute Gvhd ◽

Conflicts Of Interest ◽

Ex Vivo ◽

Proliferative Potential ◽

Hematopoietic Stem ◽

Cell Based Therapy

Abstract Abstract 4544 Bone marrow-derived mesenchymal stem cells (BMMSCs) have been found to enhance engraftment of hematopoietic stem cell transplantation (HSCT), plus show effect against graft-versus host disease (GVHD) because of their immunosuppressive properties. However, harvesting these cells is an invasive and painful procedure. To substitute BMMSCs from alternative sources is necessary. We intravenously infused ex vivo-expanded third-party umbilical cord-derived mesenchymal stem cells (UCMSCs) obtained from a bank 8 times in 3 patients who developed severe, steroid-resistant acute GVHD after allogeneic HSCT. The acute GVHD improved with each infusion of UCMSCs. Besides, after cotransplantation of cord blood and UCMSCs in 5 patients, we found UCMSCs enhanced absolute neutrophil counts and platelet counts recovery. No adverse effects after UCMSCs infusions were noted. We also found that UCMSCs had superior proliferative potential and greater immunosuppressive effects than BMMSCs in vitro. This is the first report of UCMSCs in human clinical application. These findings suggest UCMSCs are effective in treating aGVHD and can enhance hematopoiesis after HSCT. Considering that they are not only easy to obtain but also proliferate rapidly, UCMSCs would be the ideal candidate for cell-based therapy, especially for diseases associated with immune responses because of their immunosuppressive effects. Disclosures: No relevant conflicts of interest to declare.

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Role of PDGF/PDGFR in Regulation of Thrombopoiesis: A Possible Explanation for Imatinib Mesylate-Induced Thrombocytopenia in the Treatment of CML

Blood ◽

10.1182/blood.v120.21.3348.3348 ◽

2012 ◽

Vol 120 (21) ◽

pp. 3348-3348

Author(s):

Mo Yang ◽

Fanyi Meng ◽

Jie yu Ye ◽

Yue Xu ◽

Bin Xiao ◽

...

Keyword(s):

Bone Marrow ◽

Imatinib Mesylate ◽

Conflicts Of Interest ◽

Ex Vivo ◽

Potential Effect ◽

Mice Model ◽

Hematopoietic Stem ◽

Platelet Recovery ◽

Bone Marrow Histology

Abstract Abstract 3348 Platelet-derived growth factor (PDGF), a platelet alpha-granule molecule, imply their potential effect in the regulation of megakaryocytopoiesis and thrombopoiesis, which also intimates the existence of an autocrine and/or paracrine loop constructed by megakaryocytes/platelets and their granular constituents. Our previous studies demonstrated the presence of functional PDGF receptors (PDGFR) on human megakaryocytes and platelets (Yang et al, Thromb Haemastasis, 1997) and CD34+ cells, and their ability to mediate a mitogenic response. PDGF promoted the ex vivo expansion of human hematopoietic stem (CD34+) and progenitor (CD41+ CD61+) cells. More significantly, PDGF enhanced the engraftment of human CD45+ cells and their myeloid subsets (CD33+, CD14+ cells) in NOD/SCID mice. PDGF stimulated in vitro megakaryocytopoiesis via PDGFR and/or the indirect effect on bone marrow microenvironment to produce TPO and other cytokines. It also showed a direct stimulatory effect of PDGF on c-Fos, GATA-1 and NF-E2 expressions in megakaryocytes. We speculate that these transcription factors might be involved in the signal transduction of PDGF on the regulation of megakaryocytopoiesis. PDGF also enhanced platelet recovery in mice model with radiation-induced thrombocytopenia. Studies showed that PDGF, like thrombopoietin (TPO), significantly promoted platelet recovery and the formation of bone marrow colony-forming unit-megakaryocyte (CFU-MK) in this irradiated-mouse. An increased number of hematopoietic stem/progenitor cells and a reduction of apoptosis were found in the bone marrow histology sections. In the M-07e apoptotic model, PDGF had a similar anti-apoptotic effect as TPO on megakaryocytes. We also demonstrated that PDGF activated the PI3k/Akt signaling pathway, while addition of imatinib mesylate reduced p-Akt expression. Our findings suggested that the PDGF-initiated radioprotective effect is likely to be mediated via PDGF receptors with subsequent activation of the PI3k/Akt pathway. The study provides a possible explanation that blockage of PDGFR may reduce thrombopoiesis and play a role in imatinib mesylate-induced thrombocytopenia in the treatment of CML. Disclosures: No relevant conflicts of interest to declare.

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Importance of Matrix-dimensionality in Regulating the Bone Marrow Hematopoietic Cells Pool

10.1101/720359 ◽

2019 ◽

Author(s):

P. Zhang ◽

C. Zhang ◽

J. Han ◽

J. Gao ◽

W. Zhao ◽

...

Keyword(s):

Bone Marrow ◽

Progenitor Cells ◽

Ex Vivo ◽

Hematopoietic Cells ◽

Bone Marrow Niche ◽

Hematopoietic Stem ◽

Factors Affecting ◽

Lymphoid Lineage ◽

3D Matrix

AbstractIn bone marrow, hematopoietic stem cells (HSCs) and multiple hematopoietic progenitor cells (HPCs) cooperate to differentiate and replenish blood and immune cells. It has long been recognized bone marrow niche parameters interact with hematopoietic stem and progenitor cells (HSPCs) and additional work is required to study niche physical signals controlling cell behavior. Here we presented that important biophysical signals, stiffness and dimensionality, regulating expansion of bone marrow HSPCs. Mice bone marrow derived progenitor cells were cultured in collagen I hydrogel in vitro. We found stiffer 3D matrix promoted the expansion of lineage negative (Lin−) progenitor cells and Lin−Sca-1+c-kit+ (LSK) HSPCs compared to softer hydrogel. Compared with cells cultured in 2D environment, 3D embedded construct had significant advantage on HSPCs expansion, accompanied by increases on myeloid and lymphoid lineage fractions. Bright changes on gene expression were subsequently discovered. According to these data, we concluded that culture matrix dimensionality is an important factor to regulate the behavior of subpopulations in hematopoietic cell pool, which should be considered in attempts to illuminate HSCs fate decision in vitro.Statement of SignificanceWe would like to submit the enclosed manuscript entitled "Importance of Niche-dimensionality in Regulating the Bone Marrow Hematopoietic Cells Pool", which we wish to be considered for publication in Biophysical Journal. Studies about the interaction between HSCs and factors provided by their microenvironment is largely focus on pure perspective of biology. But biophysical factors affecting HSC fate and behavior needs to be further explore. Herein we found ex vivo culture dimensionality affected HSPC expansion. Cell surface marker detection and mRNA expression analysis predicted the changes on myeloid and lymphoid lineage fractions. We hope niche physical signals which we identified will be considered to design HSC biomimetic niches in clinical applications. And we believe that our study will make it interesting to general readers. We deeply appreciate your consideration of our manuscript, and we look forward to receiving comments from the reviewers.

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An Ex Vivo Bioengineered Human Liver Microenvironment to Support Hematopoietic Stem Cell Maintenance and Expansion

Blood ◽

10.1182/blood-2020-141437 ◽

2020 ◽

Vol 136 (Supplement 1) ◽

pp. 9-10

Author(s):

Na Yoon Paik ◽

Grace E. Brown ◽

Lijian Shao ◽

Kilian Sottoriva ◽

James Hyun ◽

...

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Stem Cell ◽

Conflicts Of Interest ◽

Ex Vivo ◽

Fetal Liver ◽

Human Umbilical Cord ◽

Hematopoietic Stem ◽

Main Site

Over 17,000 people require bone marrow transplants annually, based on the US department of Health and Human Services (https://bloodcell.transplant.hrsa.gov). Despite its high therapeutic value in treatment of cancer and autoimmune disorders, transplant of hematopoietic stem cells (HSC) is limited by the lack of sufficient source material due primarily inadequate expansion of functional HSCs ex vivo. Hence, establishing a system to readily expand human umbilical cord blood or bone marrow HSCs in vitro would greatly support clinical efforts, and provide a readily available source of functional stem cells for transplantation. While the bone marrow is the main site of adult hematopoiesis, the fetal liver is the primary organ of hematopoiesis during embryonic development. The fetal liver is the main site of HSC expansion during hematopoietic development, furthermore the adult liver can also become a temporary extra-medullary site of hematopoiesis when the bone marrow is damaged. We have created a bioengineered micropatterned coculture (MPCC) system that consists of primary human hepatocytes (PHHs) islands surrounded and supported by 3T3-J2 mouse embryonic fibroblasts. Long-term establishment of stable PHH-MPCC allows us to culture and expand HSC in serum-free medium supplemented with pro-hematopoietic cytokines such as stem cell factor (SCF) and thrombopoietin (TPO). HSCs cultured on this PHH-MPCC microenvironment for two weeks expanded over 200-fold and formed tight clusters around the periphery of the PHH islands. These expanded cells also retained the expression of progenitor markers of Lin-, Sca1+, cKit+, as well as the long-term HSC phenotypic markers of CD48- and CD150+. In addition to the phenotypic analysis, the expanded cells were transplanted into lethally irradiated recipient mice to determine HSC functionality. The expanded cells from the PHH-MPCC microenvironment were able to provide multi-lineage reconstitution potential in primary and secondary transplants. With our bioengineered MPCC system, we further plan to scale up functional expansion of human HSC ex vivo and to better understand the mechanistic, cell-based niche factors that lead to maintenance and expansion HSC. Disclosures No relevant conflicts of interest to declare.

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Chromosomal Instability in Cultured Mouse Hematopoietic Cells Associated with Oxidative Stress

Blood ◽

10.1182/blood.v118.21.4819.4819 ◽

2011 ◽

Vol 118 (21) ◽

pp. 4819-4819

Author(s):

Alice M. Liu ◽

William W. Qu ◽

Xia Liu

Keyword(s):

Oxidative Stress ◽

Bone Marrow ◽

Genomic Instability ◽

Chromosomal Instability ◽

Conflicts Of Interest ◽

Hematopoietic Cells ◽

Genetic Alterations ◽

In Vitro Test ◽

Hematopoietic Stem

Abstract Abstract 4819 Hematopoietic stem cells (HSCs) that give rise to all blood cell types are important vehicles for cell-based and gene therapies. After isolation from the bone marrow, HSCs are often cultured in laboratory settings for purposes of ex vivo expansion, gene transduction, and bone marrow transplantation for the treatment of various disorders of the blood and immune systems. While undergoing proliferation and differentiation in vitro, test tube and dish culturing can potentially induce genomic instability in HSCs due to prolonged culturing periods or the exposure to increased levels of oxygen. Here we demonstrate that in vitro culturing outside their bone marrow niches, HSCs may change even under very short durations of time. Lineage− Scal-1+ c-Kit+ (LSK) cells that are enriched with HSCs revealed significant levels of genomic instability in culture, as evidenced by the emergence of aneuploidy cells. To further determine the effects of in vitro culturing conditions, whole bone marrow cells were cultured in a hypoxic environment of 2–3% oxygen, mimicking conditions inside the body's bone marrow. In this case, cells proved to undergo less genetic alterations. Proper dosages of the antioxidant N-Acetyl-Cysteine (NAC) similarly decreased occurrences of chromosomal changes. Furthermore, in vitro normoxic culture-induced chromosomal instability was enhanced in aged hematopoietic cells compared to that in young hematopoietic cells due to noted increased oxidative stress in aged cells. These results reveal that in vitro cell culturing does indeed cause genomic instability in hematopoietic cells. Reduced oxygen levels and additions of antioxidants can be employed as a possible agent to lower oxidative stress and decrease chances of transformation. Additionally, since hematopoietic cells are commonly developed in laboratory settings before transplantation for patient treatment, our findings raise a concern for using cultured hematopoietic cells for therapeutic purposes. Note: Alice Liu and William Qu contributed equally to this work. Disclosures: No relevant conflicts of interest to declare.

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Osteogenic- and Adipogenic- Differentiated Bone Marrow-Derived Mesenchymal Stem Cells Fail to Support Expansion of Adult Hematopoietic Stem Cells

Blood ◽

10.1182/blood.v118.21.4810.4810 ◽

2011 ◽

Vol 118 (21) ◽

pp. 4810-4810

Author(s):

Olga Kulemina ◽

Izida Minullina ◽

Sergey Anisimov ◽

Renata Dmitrieva ◽

Andrey Zaritskey

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Mesenchymal Stem Cells ◽

Cord Blood ◽

Conflicts Of Interest ◽

Ex Vivo ◽

Ex Vivo Expansion ◽

Hematopoietic Stem ◽

Cd34 Cells ◽

Feeder Layers

Abstract Abstract 4810 Ex vivo expansion and manipulation of primitive hematopoietic cells has become a major goal in the experimental hematology, because of its potential relevance in the development of therapeutic strategies aimed at treating a diverse group of hematologic disorders. Osteoblasts, mesenchymal stem/progenitor cells (MSC/MPC), adipocytes, reticular cells, endothelial cells and other stromal cells, have been implicated in regulation of HSC maintenance in endosteal and perivascular niches. These niches facilitate the signaling networks that control the balance between self-renewal and differentiation. In the present study, we evaluated and compared the effects of three different stromal feeder layers on expansion of HSPC derived from BM and cord blood (CB): BM mesenchymal stem cells (MSC), osteoblast-differentiated BM mesenchymal stem cells (Ost-MSC) and adipocyte-differentiated BM mesenchymal stem cells (Ad-MSC). BM-MSC cultures were established from plastic adherent BM cell fractions and analyzed for immunophenotype, frequency of colony forming units (CFU-F), frequency of osteo- (CFU-Ost) and adipo- (CFU-Ad) lineage progenitors. Cultures with similar clonogenity (CFU-F: 26,4 ± 4,5%) and progenitors frequency (CFU-Ost: 14,7 ± 4,5%; CFU-Ad: 13,3 ± 4,5%) were selected for co-culture experiments. All MSC were positive for stromal cell-associated markers (CD105, CD90, CD166, CD73) and negative for hematopoietic lineage cells markers (CD34, CD19, CD14, CD45). CD34+ cells were separared from BM and CB samples by magnetic cell sorting (MACS) and analyzed for CD34, CD38 and CD45 expression. Feeder layers (MSC, Ost-MSC, Ad-MSC) were prepared in 24-well plates prior to co-culture experiments: MSCs (4×104 cells/well) were cultured for 24 h and either used for following experiments or stimulated to differentiate into either osteoblasts or adipoctes according to standard protocols. CD34+ cells (3500-10000 cells per well) were co-cultured in Stem Span media with or without a feeder layers and in the presence of cytokines (10 ng/mL Flt3-L, 10 ng/mL SCF, 10ng/mL IL-7) for 7 days. Expanded cells were analyzed for CD34, CD38 and CD45 expression. Results are shown on figures 1 and 2. As expected, CB-derived HSPC expanded much more effectively than BM-derived HSPC. The similar levels of expansion were observed for both, the total number of HSPC, and more primitive CD34+CD38- fraction in the presence of all three feeder layers. Ost-MSC supported CB-derived HSPC slightly better than MSC and Ad-MSC which is in a good agreement with data from literature (Mishima et.al., European Journal of Haematology, 2010), but difference was not statistically significant. In contrast, whereas BM-MSC feeder facilitated CD34+CD38- fraction in BM-derived HSPC, Adipocyte-differentiated MSC and osteoblast-differentiated MSC failed to support BM-derived CD34+CD38- expansion (11,4 ±.4 folds for MSC vs 0,9 ±.0,14 for Ad-MSC, n=5, p<0,01 and 0,92 ±.0,1 for Ost-MSC, n=5, p<0,01).Figure 1.Cord Blood HSPC ex vivo expansionFigure 1. Cord Blood HSPC ex vivo expansionFigure 2.Bone Marrow HSPC ex vivo expansionFigure 2. Bone Marrow HSPC ex vivo expansion Conclusion: BM- and CB-derived CD34+CD38- cells differ in their dependence of bone marrow stroma. Coctail of growth factors facilitate CB HSPC expansion irrespective of lineage differentiation of supporting MSC feeder layer. In contrast, primitive BM CD34+CD38- HSPC were able to expand only on not differentiated MSC. Disclosures: No relevant conflicts of interest to declare.

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Ontogeny of Hematopoiesis

Blood ◽

10.1182/blood.v122.21.sci-4.sci-4 ◽

2013 ◽

Vol 122 (21) ◽

pp. SCI-4-SCI-4

Author(s):

Elaine Dzierzak

Keyword(s):

Bone Marrow ◽

Endothelial Cells ◽

Transcription Factors ◽

Conflicts Of Interest ◽

Ex Vivo ◽

Developmental Time ◽

Hematopoietic Cell ◽

Conditional Knockout ◽

Hematopoietic Stem ◽

And Function

Abstract The current challenge in hematopoietic transplantation and regeneration therapies is acquiring and/or producing a reliable and plentiful source of hematopoietic stem cells (HSCs). Given that HSCs from bone marrow, peripheral, or umbilical cord blood undergo only limited/no expansion ex vivo, there is a high interest in understanding how the adult cohort of multipotent self-renewing HSCs are generated and expanded during embryonic development. The development of HSCs in vertebrate embryos begins in the major vasculature. HSCs are generated in a short window of developmental time starting at embryonic day E10.5 until E12 in the mouse embryo, and from gestational weeks four to six in the human embryo. The first HSCs, which are as potent as bone marrow HSCs in transplantation procedures, are generated in the aorta-gonad-mesonephros (AGM) region. HSCs are found in the major vasculature – aorta, vitelline artery, and umbilical artery – subsequent to the appearance of hematopoietic cell clusters closely associated with the lumenal walls of these vessels. The relationship of HSCs to these clusters and the identification of the precursors to HSCs have been recently established through genetic, phenotypic, and real-time imaging studies. Remarkably, HSCs and hematopoietic progenitors arise directly from a subset of endothelial cells (hemogenic endothelial cells) in a natural transdifferentiation event. They are made through a process called endothelial to hematopoietic cell transition (EHT). EHT and HSC generation is in part regulated through ventral-derived developmental signals and a group of pivotal (core) transcription factors, including Runx1 and Gata2. Conditional knockout strategies show that these transcription factors are required for the generation of vascular hematopoietic clusters and HSCs, suggesting a role in hematopoietic fate induction and/or cell expansion. Interestingly, whereas both Runx1 and Gata2 are required for HSC generation, only Gata2 remains essential in HSCs after their production. We are profiling hemogenic endothelial and HSCs by RNA sequencing so as to understand the complete genetic program that leads to generation of HSCs. These results will be discussed in the context of developmental signaling pathways (BMP4, Hedgehog, etc.) that appear to impact HSC generation and expansion, and the localized dynamic expression and function of Gata2 and Runx1 in vascular endothelial and hematopoietic cluster cells. Disclosures: No relevant conflicts of interest to declare.

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Deletion of Pleiotrophin in LepR+ Perivascular Cells Depletes Hematopoietic Stem Cells

Blood ◽

10.1182/blood.v128.22.1491.1491 ◽

2016 ◽

Vol 128 (22) ◽

pp. 1491-1491

Author(s):

Heather A Himburg ◽

Vivian Y. Chang ◽

Joshua Sasine ◽

Jenny Kan ◽

Liman Zhao ◽

...

Keyword(s):

Steady State ◽

Stromal Cells ◽

Leptin Receptor ◽

Conflicts Of Interest ◽

Ex Vivo ◽

Hematopoietic Cells ◽

Heparin Binding ◽

Perivascular Cells ◽

Hematopoietic Stem

Abstract Pleiotrophin (PTN) is a heparin binding growth factor which is expressed by bone marrow vascular endothelial cells (BM ECs) and perivascular stromal cells. Treatment of murine or human HSCs ex vivo promotes HSC expansion (Nat Med. 2010 Apr;16(4):475-82) and constitutive deletion of PTN depletes LT-HSCs in steady state and markedly impairs HSC regeneration following myeloablation (Cell Rep. 2012 Oct 25;2(4):964-75; JCI. 2014;18(7):1123-1129). Here, we sought to determine which BM microenvironment cell is responsible for PTN-mediated maintenance of the HSC pool. Utilizing the Cre-loxP system, we deleted PTN from VE-cadherin+ ECs, leptin receptor+ (lepR+) perivascular stromal cells, osteocalcin+ osteoblasts, and vav1+ hematopoietic cells and examined the effects on hematopoiesis. We observed no differences in steady state hematopoiesis or HSC content as measured by long-term competitive repopulation assays in mice lacking PTN expression in osteocalcin+ cells, vav1+ hematopoietic cells or VE-cadherin+ BM ECs. However, deletion of PTN from lepR+ BM perivascular cells caused a significant decrease in BM c-kit+sca-1+lin- cells (KSL cells) and BM SLAM+KSL HSCs, and colony forming cell (CFC) content compared to PTN+/+ controls (*p = 0.04, 0.04, and 0.001, respectively). Importantly, deletion of PTN in lepR+ cells, caused a significant reduction in long-term HSC content as measured by primary and secondary competitive repopulation assays (*P<0.01 for all time points through 20 weeks). These data suggest that LepR+ BM perivascular cells, rather than VE-cadherin+ ECs are the primary source of PTN in the BM niche which contributes to the maintenance of the HSC pool. Figure 1 Figure 1. Figure 2 Figure 2. Disclosures No relevant conflicts of interest to declare.

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