Expansion Of Hematopoietic Stem And Progenitor Cells Research Articles

Differentiation of hematopoietic stem and progenitor cells to NK cells in a stroma-free, serum-free culture system

Abstract Natural Killer (NK) cells play an important role in innate immunity by secreting proinflammatory cytokines and killing tumor cells and virus-infected cells. Human NK cells can be generated by culturing CD34+ hematopoietic stem and progenitor cells (HSPCs) with stromal cells and cytokines. The use of stroma (and serum) is, however, not desirable in clinical applications. We developed a culture method for generating large numbers of NK cells from purified CD34+ cord blood (CB) HSPCs in the absence of serum and stromal cells. CD34+ CB cells were isolated by EasySep magnetic separation, seeded into culture plates coated with a Notch ligand and cultured for two weeks in StemSpan Serum-Free Expansion Medium (SFEM II) supplemented with SCF, TPO, Flt3L and IL-7. These conditions promote expansion of HSPCs and their differentiation into CD7+CD5+ lymphoid progenitors. Cells were then transferred to non-coated plates and cultured for two more weeks in StemSpan SFEM II supplemented with SCF, Flt3L, IL-7, IL-15 and a small molecule, UM729, to promote differentiation into NK cells. After culture, on average 76% (range: 54–90%, n=12) of cells expressed the NK cell marker CD56 and 58% (range: 25–80%) coexpressed CD56 and NKp46 (a NK cell activating receptor). A more mature CD56+CD16+ NK cell subset also emerged in these cultures (5%, range: 1–11%). The yield of CD56+ NK cells was ~13,000 (600–41,000) per initial CD34+ cell. The NK cells were functional and able to kill K562 target cells. These results show that HSPCs can expand and differentiate into NK cells under stroma- and serum-free culture conditions. This novel culture system will be useful for studies directed toward the development of cancer immunotherapies where large numbers of NK cells are needed.

365 - Enabling efficient ex vivo expansion of long-term human hematopoietic stem and progenitor cells for cell therapy

Umbilical-cord blood (UCB) is an important source of hematopoietic stem and progenitor cells (HSPC) for transplantation into patients lacking a suitable HLA-matched donor. However, due to the limited cell dose in each cord blood unit, individuals >60 kg are restricted from the use of UCB-based therapy. Ex vivo expansion of UCB CD34+ cells is one strategy employed to increase the hematopoietic cell dosage. A major limitation of current systems used for the expansion of HSPC is that ex vivo culture leads to expansion and differentiation at the expense of the most primitive pluripotent long-term stem cells. This has limited the clinical application of ex vivo expanded HSPC, since short-term progenitor cells only provide transient protection, ultimately reducing the long-term positive health outcomes, increasing the duration of hospitalizations, and health care costs per patient. Development of a culture system that expands both short-term and long-term HSPC would facilitate immune protection during the early phase of recovery, and provides a suitable solution for transfusion-independent hematopoiesis. Therefore, we sought to develop a HSPC culture medium that enables the expansion of both long-term and short-term HSPC, while maintaining their functional properties. To this end, we conducted several iterative rounds of Design of Experiments (DOE) involving multifactorial analysis, and mathematical modeling methods. Definitive Screening DOEs allowed us to identify optimal combinations and concentrations of essential media components, small molecules, and growth factors. The performance of candidate HSPC expansion media were evaluated after 7 days of culture, with the following attributes assessed: (1) viability of cells; (2) numbers of total nucleated cells; (3) percentages and numbers of CD34+ cells; (4) percentages and numbers of CD34+CD90+CD45RA- cells; (5) expression of aldehyde dehydrogenase by expanded CD34+ cells; and (6) colony-forming unit (CFU) assays. As the transplantation of HSPC in immuno-deficient mice is the gold standard in determining whether the expanded cells are engraftable, we plan to conduct these studies with the lead candidate HSPC expansion medium. Taken together, we seek to highlight our design philosophy in HSPC culture media development. We believe that our efforts are critical for the successful utilization of hematopoietic stem cell transplants in translational cell therapies.

PLAG1 and USF2 Co-regulate Expression of Musashi-2 in Human Hematopoietic Stem and Progenitor Cells.

SummaryMSI2, which is expressed predominantly in hematopoietic stem and progenitor cells (HSPCs), enforces HSPC expansion when overexpressed and is upregulated in myeloid leukemias, indicating its regulated transcription is critical to balanced self-renewal and leukemia restraint. Despite this, little is understood of the factors that enforce appropriate physiological levels of MSI2 in the blood system. Here, we define a promoter region that reports on endogenous expression of MSI2 and identify USF2 and PLAG1 as transcription factors whose promoter binding drives reporter activity. We show that these factors co-regulate, and are required for, efficient transactivation of endogenous MSI2. Coincident overexpression of USF2 and PLAG1 in primitive cord blood cells enhanced MSI2 transcription and yielded cellular phenotypes, including expansion of CD34+ cells in vitro, consistent with that achieved by direct MSI2 overexpression. Global chromatin immunoprecipitation sequencing analyses confirm a preferential co-binding of PLAG1 and USF2 at the promoter of MSI2, as well as regulatory regions corresponding to genes with roles in HSPC homeostasis. PLAG1 and USF2 cooperation is thus an important contributor to stem cell-specific expression of MSI2 and HSPC-specific transcriptional circuitry.

Defective cholesterol metabolism in haematopoietic stem cells promotes monocyte-driven atherosclerosis in rheumatoid arthritis.

Rheumatoid arthritis (RA) is associated with an approximately two-fold elevated risk of cardiovascular (CV)-related mortality. Patients with RA present with systemic inflammation including raised circulating myeloid cells, but fail to display traditional CV risk-factors, particularly dyslipidaemia. We aimed to explore if increased circulating myeloid cells is associated with impaired atherosclerotic lesion regression or altered progression in RA. Using flow cytometry, we noted prominent monocytosis, neutrophilia, and thrombocytosis in two mouse models of RA. This was due to enhanced proliferation of the haematopoietic stem and progenitor cells (HSPCs) in the bone marrow and the spleen. HSPCs expansion was associated with an increase in the cholesterol content, due to a down-regulation of cholesterol efflux genes, Apoe, Abca1, and Abcg1. The HSPCs also had enhanced expression of key myeloid promoting growth factor receptors. Systemic inflammation was found to cause defective cellular cholesterol metabolism. Increased myeloid cells in mice with RA were associated with a significant impairment in lesion regression, even though cholesterol levels were equivalent to non-arthritic mice. Lesions from arthritic mice exhibited a less stable phenotype as demonstrated by increased immune cell infiltration, lipid accumulation, and decreased collagen formation. In a progression model, we noted monocytosis, enhanced monocytes recruitment to lesions, and increased plaque macrophages. This was reversed with administration of reconstituted high-density lipoprotein (rHDL). Furthermore, RA patients have expanded CD16+ monocyte subsets and a down-regulation of ABCA1 and ABCG1. Rheumatoid arthritis impairs atherosclerotic regression and alters progression, which is associated with an expansion of myeloid cells and disturbed cellular cholesterol handling, independent of plasma cholesterol levels. Infusion of rHDL prevented enhanced myelopoiesis and monocyte entry into lesions. Targeting cellular cholesterol defects in people with RA, even if plasma cholesterol is within the normal range, may limit vascular disease.

Ex Vivo Expansion of CD34+ CD90+ CD49f+ Hematopoietic Stem and Progenitor Cells from Non-Enriched Umbilical Cord Blood with Azole Compounds.

Umbilical cord blood (UCB) transplants in adults have slower hematopoietic recovery compared to bone marrow (BM) or peripheral blood (PB) stem cells mainly due to low number of total nucleated cells and hematopoietic stem and progenitor cells (HSPC). As such in this study, we aimed to perform ex vivo expansion of UCB HSPC from non‐enriched mononucleated cells (MNC) using novel azole‐based small molecules. Freshly‐thawed UCB–MNC were cultured in expansion medium supplemented with small molecules and basal cytokine cocktail. The effects of the expansion protocol were measured based on in vitro and in vivo assays. The proprietary library of >50 small molecules were developed using structure‐activity‐relationship studies of SB203580, a known p38‐MAPK inhibitor. A particular analog, C7, resulted in 1,554.1 ± 27.8‐fold increase of absolute viable CD45+CD34+CD38–CD45RA– progenitors which was at least 3.7‐fold higher than control cultures (p < .001). In depth phenotypic analysis revealed >600‐fold expansion of CD34+/CD90+/CD49f+ rare HSPCs coupled with significant (p < .01) increase of functional colonies from C7 treated cells. Transplantation of C7 expanded UCB grafts to immunodeficient mice resulted in significantly (p < .001) higher engraftment of human CD45+ and CD45+CD34+ cells in the PB and BM by day 21 compared to non‐expanded and cytokine expanded grafts. The C7 expanded grafts maintained long‐term human multilineage chimerism in the BM of primary recipients with sustained human CD45 cell engraftment in secondary recipients. In conclusion, a small molecule, C7, could allow for clinical development of expanded UCB grafts without pre‐culture stem cell enrichment that maintains in vitro and in vivo functionality. Stem Cells Translational Medicine 2018;7:376–393

Stromalized microreactor supports murine hematopoietic progenitor enrichment.

There is an emerging need to process, expand, and even genetically engineer hematopoietic stem and progenitor cells (HSPCs) prior to administration for blood reconstitution therapy. A closed-system and automated solution for ex vivo HSC processing can improve adoption and standardize processing techniques. Here, we report a recirculating flow bioreactor where HSCs are stabilized and enriched for short-term processing by indirect fibroblast feeder coculture. Mouse 3T3 fibroblasts were seeded on the extraluminal membrane surface of a hollow fiber micro-bioreactor and were found to support HSPC cell number compared to unsupported BMCs. CFSE analysis indicates that 3T3-support was essential for the enhanced intrinsic cell cycling of HSPCs. This enhanced support was specific to the HSPC population with little to no effect seen with the Lineagepositive and Lineagenegative cells. Together, these data suggest that stromal-seeded hollow fiber micro-reactors represent a platform to screening various conditions that support the expansion and bioprocessing of HSPCs ex vivo.

Megakaryocytic TGFβ1 Partitions Hematopoiesis into Amplifying Stem and Progenitor Cells and Maturing Effector Cells

Background: Chronic anemia is a significant problem affecting over 3 million Americans annually. Therapies are restricted to transfusion and Erythropoietin Stimulating Agents (ESA). There is a need for new approaches to treat chronic anemia. Immature erythroid progenitors are thought to be continuously produced and then permitted to survive and mature if there is sufficient erythropoietin (Epo) available. This model is elegant in that oxygen sensing within the kidney triggers Epo production so anemia can increase Epo and promote erythroid output. However, during homeostasis this model suggests that considerable energy is used to produce unneeded erythroid progenitors. We searched for independent control and compartmentalization of erythropoiesis that could couple early hematopoiesis to terminal erythroid commitment and maturation.Methods: We previously found the proportion of bone marrow megakaryocytes (MKs) staining for active, signaling-competent TGFβ transiently increases during bone marrow regeneration after chemotherapy. To assess the functional role of Mk-TGFβ, we crossed murine strains harboring a floxed allele of TGFβ1 (TGFβ1Flox/Flox) littermate with a Mk-specific Cre deleter to generate mice with Mk-specific deletion of TGFβ1 (TGFβ1ΔMk/ΔMk). We analyzed hematopoiesis of these mice using high-dimensional flow cytometry, confocal immunofluorescent microscopy and in vitro and in vivo assays of hematopoietic function (Colony forming assays, and in vivo transplantation).Results: Using validated, 9-color flow cytometry panels capable of quantifying hematopoietic stem cells (HSCs) and six other hematopoietic progenitor populations, we found that Mk-specific deletion of TGFβ1 leads to expansion of immature hematopoietic stem and progenitor cells (HSPCs) (Fig1A&B). Functional assays confirmed a more than three-fold increase in hematopoietic stem cells (HSCs) capable of serially-transplanting syngeneic recipients in the bone marrow (BM) of TGFβ1ΔMk/ΔMk mice compared to their TGFβ1Flox/Flox littermates. Expansion was associated with less quiescent (Go) HSCs implicating Mk-TGFβ in the control of HSC cell cycle entry. Similarly, in vitro colony forming cell assays and in vivo spleen colony forming assays confirmed expansion of functional progenitor cells in TGFβ1ΔMk/ΔMk mice. These results place Mk-TGFβ as a critical regulator of the size of the pool of immature HSPCs.We found that the blood counts and total BM cellularity of TGFβ1ΔMk/ΔMk mice was normal despite the dramatic expansion of immature HSPCs. Using a combination of confocal immunofluorescence microscopy (cleaved caspase 3) (Fig1C) and flow cytometry (Annexin V and cleaved caspase 3) (Fig1D), we found ~10-fold greater apoptosis of mature precursor cells in TGFβ1ΔMk/ΔMk BM and spleens. Coincident with this, we found the number of Epo receptor (EpoR) expressing erythroid precursors to be dramatically increased. Indeed, apoptosis of erythroid precursors peaked as they transitioned from dual positive Kit+EpoR+ precursors to single positive cells expressing EpoR alone. Epo levels were normal in the serum of these mice. We reasoned that the excess, unneeded EpoR+ cells were not supported physiologic Epo levels but might respond to even small doses of exogenous Epo. Indeed, we found that the excess erythroid apoptosis could be rescued by administration of very low doses of Epo (Fig1E). Whereas TGFβ1Flox/Flox mice showed minimal reticulocytosis and no change in blood counts, TGFβ1ΔMk/ΔMk mice responded with exuberant reticulocytosis and raised RBC counts almost 10% within 6 days (Fig. 1F). Low dose Epo also rescued survival of Epo receptor positive erythroid precursors in the bone marrow, spleen and blood of TGFβ1ΔMk/ΔMk mice. TGFβ1ΔMk/ΔMk mice showed a similarly brisk and robust erythropoietic response during recovery from phenylhydrazine-induced hemolysis (Fig.1G). Exogenous TGFβ worsened BM apoptosis and caused anemia in treated mice. Pre-treatment of wild-type mice with a TGFβ signaling inhibitor sensitized mice to low dose Epo.Conclusion: These results place megakaryocytic TGFβ1 as a gate-keeper that restricts the pool of immature HSPCs and couples immature hematopoiesis to the production of mature effector cells. This work promises new therapies for chronic anemias by combining TGFβ inhibitors to increase the outflow of immature progenitors with ESAs to support erythroid maturation. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

EBF1 As a Novel Regulator of Bone Marrow Mesenchymal Stromal Progenitors

Hematopoietic stem and progenitor cells (HSPC) are in daily demand worldwide because of their ability to replenish entire blood system. However, the in vitro expansion of HSPC is still a major challenge since the cues from bone marrow microenvironment remain largely elusive. Signals coming from the bone marrow niche, and specifically mesenchymal stem and progenitor cells (MSPC), orchestrate maintenance, trafficking and stage specific differentiation of HSPCs. Although, it is generally accepted that MSPCs are essential for hematopoietic homeostasis and generating multiple types of stromal cells, the exact transcriptional networks regulating MSPCs are not well established. Early B-cell factor 1 (Ebf1) has been discovered as lineage-specific transcription factor governing B lymphopoiesis. Additionally, it has been shown to play important role in differentiation of adipocytes, which are a niche component supporting hematopoietic regeneration. Thus, in this study we seek to examine if Ebf1 has an alternative function in non-hematopoietic compartment of bone marrow, specifically in mesenchymal stromal cells that maintain proper hematopoiesis.Here, we identified Ebf1 as new transcription regulator of MSPCs activity. Mesenchymal progenitors isolated from Ebf1-/- mice show diminished capacity to form fibroblasticcolonies (CFU-F) indicating reduced self-renewal. Moreover, cells expanded from these colonies display impaired in vitro differentiation towards osteoblasts, chondrocytes and adipocytes. In order to test how this defective MSPCs influence maintenance of HSPCs, we performed long-term culture-initiating cell assay (LTC-IC). After 5 weeks of co-culture of Ebf1-deficient stromal cells with wild type HSPCs we could observe significantly decreased number of cobblestone and CFU colonies formed by primitive HSPCs, in comparison to co-cultures with control stromal cells. Furthermore, in vivo adoptive transfers of wild type HSPCs to Ebf1+/- recipient mice showed a decrease in the absolute numbers of HSPCs in primary recipients and reduced donor chimerism within the HSCP compartment in competitive secondary transplant experiments. Additionally, Prx1-Cre-mediated deletion of Ebf1 specifically in MSPCs of mice leads to reduced frequency and numbers of HSPCs and myeloid cells in the bone marrow. These results confirm that mesenchymal stromal cells lacking Ebf1 render insufficient support for HSPCs to sustain proper hematopoiesis. Interestingly, we also observed a reduced ability of HSPCs sorted from Prx1CreEbf1fl/fl mice to form colonies in methylcellulose, suggesting not only impaired maintenance but also hindered function of these cells. Moreover, HSPCs exposed to Ebf1-deficient niche exhibit changes in chromatin accessibility with reduced occupancy of AP-1, ETS, Runx and IRF motifs, which is consistent with decreased myeloid output seen in Prx1CreEbf1fl/fl mice. These results support the hypothesis that defective niche can cause epigenetic reprograming of HSPCs. Finally, single cell and bulk transcriptome analysis of MSPCs lacking Ebf1 revealed differences in the niche composition and decreased expression of lineage-instructive signals for myeloid cells. Thus, our study establishes Ebf1 as a novel regulator of MSPCs playing a crucial role in the maintenance and differentiation of HSPCs. DisclosuresNo relevant conflicts of interest to declare.

Endothelial jagged-2 sustains hematopoietic stem and progenitor reconstitution after myelosuppression.

Angiocrine factors, such as Notch ligands, supplied by the specialized endothelial cells (ECs) within the bone marrow and splenic vascular niche play an essential role in modulating the physiology of adult hematopoietic stem and progenitor cells (HSPCs). However, the relative contribution of various Notch ligands, specifically jagged-2, to the homeostasis of HSPCs is unknown. Here, we show that under steady state, jagged-2 is differentially expressed in tissue-specific vascular beds, but its expression is induced in hematopoietic vascular niches after myelosuppressive injury. We used mice with EC-specific deletion of the gene encoding jagged-2 (Jag2) to demonstrate that while EC-derived jagged-2 was dispensable for maintaining the capacity of HSPCs to repopulate under steady-state conditions, by activating Notch2 it did contribute to the recovery of HSPCs in response to myelosuppressive conditions. Engraftment and/or expansion of HSPCs was dependent on the expression of endothelial-derived jagged-2 following myeloablation. Additionally, jagged-2 expressed in bone marrow ECs regulated HSPC cell cycle and quiescence during regeneration. Endothelial-deployed jagged-2 triggered Notch2/Hey1, while tempering Notch2/Hes1 signaling in HSPCs. Collectively, these data demonstrate that EC-derived jagged-2 activates Notch2 signaling in HSPCs to promote hematopoietic recovery and has potential as a therapeutic target to accelerate balanced hematopoietic reconstitution after myelosuppression.

The Vascular Niche Regulates Hematopoietic Stem and Progenitor Cell Lodgment and Expansion via klf6a-ccl25b

In mammals, hematopoietic stem and progenitor cells (HSPCs) rapidly expand in the fetal liver (FL), but the underlying mechanism remains unclear. Here, we characterize zebrafish caudal hematopoietic tissue (CHT) and identify an important cellular and molecular mechanism of HSPC expansion. Time-lapse imaging showed that HSPCs localize adjacent to vascular endothelial cells (ECs), and their migration and expansion display caudal vein-specific orientation in the CHT. RNA sequencing and functional analysis identified that an EC-expressed transcription factor, Krüppel-like factor 6a (Klf6a), is essential for the CHT niche. We further demonstrated that Klf6a directly regulates the expression of thechemokine (C-C motif) ligand 25b to modulate HSPC lodgment and proliferation. Exvivo culture results support the conserved role of Ccl21/Ccr7 signaling in promoting HSPC expansion in mammals. Together, we identify the Klf6a-Ccl25b/Ccr7 axis in controlling the complex HSPC-CHT niche interaction, which may be applicable to invitro expansion or engraftment of HSPCs after transplantation.

Continuous blockade of CXCR4 results in dramatic mobilization and expansion of hematopoietic stem and progenitor cells

AbstractInteraction between the chemokine receptor CXCR4 and its chief ligand CXCL12 plays a critical role in the retention and migration of hematopoietic stem and progenitor cells (HSPCs) in the bone marrow (BM) microenvironment. In this study, qualitative and quantitative effects of long-term pharmacologic inhibition of the CXCR4/CXCL12 axis on the HSPC compartment were investigated by using 3 structurally unrelated small molecule CXCR4 antagonists. A >10-fold increase in mobilization efficiency was achieved by administering the antagonists as a subcutaneous continuous infusion for 2 weeks compared to a single bolus injection. A concurrent increase in self-renewing proliferation leading to a twofold to fourfold expansion of the HSPC pool in the BM was observed. The expanded BM showed a distinct repopulating advantage when tested in serial competitive transplantation experiments. Furthermore, major changes within the HSPC niche associated with previously described HSPC expansion strategies were not detected in bones treated with a CXCR4 antagonist infusion. Our data suggest that prolonged but reversible pharmacologic blockade of the CXCR4/CXCL12 axis represents an approach that releases HSPC with efficiency superior to any other known mobilization strategy and may also serve as an effective method to expand the BM HSPC pool.

Bordetella pertussis vaccine composition drives hematopoietic stem and progenitor cell expansion and immune response during vaccination and subsequent challenge.

Abstract Pertussis is a re-emerging infectious disease world-wide. It is hypothesized that current acellular vaccines (ACVs) wane in efficacy each year after immunization. We hypothesized that whole cell vaccines (WCVs) induce hematopoietic stem and progenitor cell (HSPC) expansion and differentiation processes necessary for life-long protection. While HSPC innate immune signaling and expansion play a critical role in directing immune response to infection, their role in vaccine efficacy is unclear. To test our hypothesis, we assessed bone marrow (BM) HSPC frequency, peripheral blood composition, and immune cell proportions in the spleen and thymus upon vaccination. We find that the BM Lineage-Sca1+cKit+ (LSK) cell population undergoes progressive expansion in WCV mice when compared to ACV and PBS-injected control mice. Additionally, peripheral white blood cells and spleen size increase in WCV mice, suggesting that BM cells mobilize to the blood and spleen, where extramedullary hematopoiesis can occur. Upon infection, myeloid cells have been demonstrated to leave the spleen, enter infected tissues, and produce cytokines that favor the generation of Th1 cells. Occurring more rapidly in WCV mice, LSK cell frequency increases and spleen size decreases upon B. pertussis challenge in both WCV and PBS-injected mice when compared to ACV mice. WCV mice exhibit increased peripheral blood monocytes, neutrophils, and lymphocytes when compared to other groups. Taken together, our data suggest that HSPC expansion, differentiation, and mobilization upon WCV immunization may prime the host to better respond to pathogen, and that ACVs formulated with adjuvants that stimulate HSPC expansion, such as TLR4 agonists, may enhance vaccine efficacy.

ETV2/ER71 regulates hematopoietic regeneration by promoting hematopoietic stem cell proliferation.

Recent studies have established that hematopoietic stem cells (HSCs) are quiescent in homeostatic conditions but undergo extensive cell cycle and expansion upon bone marrow (BM) transplantation or hematopoietic injury. The molecular basis for HSC activation and expansion is not completely understood. In this study, we found that key developmentally critical genes controlling hematopoietic stem and progenitor cell (HSPC) generation were up-regulated in HSPCs upon hematopoietic injury. In particular, we found that the ETS transcription factor Ets variant 2 (Etv2; also known as Er71) was up-regulated by reactive oxygen species in HSPCs and was necessary in a cell-autonomous manner for HSPC expansion and regeneration after BM transplantation and hematopoietic injury. We found c-Kit to be downstream of ETV2. As such, lentiviral c-Kit expression rescued Etv2-deficient HSPC proliferation defects in vitro and in short-term BM transplantation in vivo. These findings demonstrate that Etv2 is an important regulator of hematopoietic regeneration.

Glucose-Dependent Insulinotropic Polypeptide Receptor Deficiency Leads to Impaired Bone Marrow Hematopoiesis.

The bone marrow (BM) contains controlled specialized microenvironments, or niches, that regulate the quiescence, proliferation, and differentiation of hematopoietic stem and progenitor cells (HSPC). The glucose-dependent insulinotropic polypeptide (GIP) is a gut-derived incretin hormone that mediates postprandial insulin secretion and has anabolic effects on adipose tissue. Previous studies demonstrated altered bone microarchitecture in mice deficient for GIP receptor (Gipr-/- ), as well as the expression of high-affinity GIP receptor by distinct cells constructing the BM HSPC niche. Nevertheless, the involvement of GIP in the process of BM hematopoiesis remains elusive. In this article, we show significantly reduced representation and proliferation of HSPC and myeloid progenitors in the BM of Gipr-/- mice. This was further manifested by reduced levels of BM and circulating differentiated immune cells in young and old adult mice. Moreover, GIP signaling was required for the establishment of supportive BM HSPC niches during HSPC repopulation in radioablated BM chimera mice. Finally, molecular profiling of various factors involved in retention, survival, and expansion of HSPC revealed significantly lower expression of the Notch-receptor ligands Jagged 1 and Jagged 2 in osteoblast-enriched bone extracts from Gipr-/- mice, which are important for HSPC expansion. In addition, there was increased expression of CXCL12, a factor important for HSPC retention and quiescence, in whole-BM extracts from Gipr-/- mice. Collectively, our data suggest that the metabolic hormone GIP plays an important role in BM hematopoiesis.

Zebrafish Caudal Haematopoietic Embryonic Stromal Tissue (CHEST) Cells Support Haematopoiesis

Haematopoiesis is an essential process in early vertebrate development that occurs in different distinct spatial locations in the embryo that shift over time. These different sites have distinct functions: in some anatomical locations specific hematopoietic stem and progenitor cells (HSPCs) are generated de novo. In others, HSPCs expand. HSPCs differentiate and renew in other locations, ensuring homeostatic maintenance. These niches primarily control haematopoiesis through a combination of cell-to-cell signalling and cytokine secretion that elicit unique biological effects in progenitors. To understand the molecular signals generated by these niches, we report the generation of caudal hematopoietic embryonic stromal tissue (CHEST) cells from 72-hours post fertilization (hpf) caudal hematopoietic tissue (CHT), the site of embryonic HSPC expansion in fish. CHEST cells are a primary cell line with perivascular endothelial properties that expand hematopoietic cells in vitro. Morphological and transcript analysis of these cultures indicates lymphoid, myeloid, and erythroid differentiation, indicating that CHEST cells are a useful tool for identifying molecular signals critical for HSPC proliferation and differentiation in the zebrafish. These findings permit comparison with other temporally and spatially distinct haematopoietic-supportive zebrafish niches, as well as with mammalian haematopoietic-supportive cells to further the understanding of the evolution of the vertebrate hematopoietic system.

Suitability of small diagnostic peripheral-blood samples for cell-therapy studies

Background aimsPrimary hematopoietic stem and progenitor cells (HSPCs) are key components of cell-based therapies for blood disorders and are thus the authentic substrate for related research. We propose that ubiquitous small-volume diagnostic samples represent a readily available and as yet untapped resource of primary patient-derived cells for cell- and gene-therapy studies. MethodsIn the present study we compare isolation and storage methods for HSPCs from normal and thalassemic small-volume blood samples, considering genotype, density-gradient versus lysis-based cell isolation and cryostorage media with different serum contents. Downstream analyses include viability, recovery, differentiation in semi-solid media and performance in liquid cultures and viral transductions. ResultsWe demonstrate that HSPCs isolated either by ammonium-chloride potassium (ACK)-based lysis or by gradient isolation are suitable for functional analyses in clonogenic assays, high-level HSPC expansion and efficient lentiviral transduction. For cryostorage of cells, gradient isolation is superior to ACK lysis, and cryostorage in freezing media containing 50% fetal bovine serum demonstrated good results across all tested criteria. For assays on freshly isolated cells, ACK lysis performed similar to, and for thalassemic samples better than, gradient isolation, at a fraction of the cost and hands-on time. All isolation and storage methods show considerable variation within sample groups, but this is particularly acute for density gradient isolation of thalassemic samples. DiscussionThis study demonstrates the suitability of small-volume blood samples for storage and preclinical studies, opening up the research field of HSPC and gene therapy to any blood diagnostic laboratory with corresponding bioethics approval for experimental use of surplus material.

Study of stem cell homing & self-renewal marker gene profile of ex vivo expanded human CD34+ cells manipulated with a mixture of cytokines & stromal cell-derived factor 1.

Background & objectives:Next generation transplantation medicine aims to develop stimulating cocktail for increased ex vivo expansion of primitive hematopoietic stem and progenitor cells (HSPC). The present study was done to evaluate the cocktail GF (Thrombopoietin + Stem Cell factor + Flt3-ligand) and homing-defining molecule Stromal cell-derived factor 1 (SDF1) for HSPC ex vivo expansion.Methods:Peripheral blood stem cell (n=74) harvests were analysed for CD34hi CD45lo HSPC. Immunomagnetically enriched HSPC were cultured for eight days and assessed for increase in HSPC, colony forming potential in vitro and in vivo engrafting potential by analyzing human CD45+ cells. Expression profile of genes for homing and stemness were studied using microarray analysis. Expression of adhesion/homing markers were validated by flow cytometry/ confocal microscopy.Results:CD34hi CD45lo HSPC expansion cultures with GF+SDF1 demonstrated increased nucleated cells (n=28, P< 0.001), absolute CD34+ cells (n=8, P=0.021) and increased colony forming units (cfu) compared to unstimulated and GF-stimulated HSPC. NOD-SCID mice transplanted with GF+SDF1-HSPC exhibited successful homing/engraftment (n=24, P< 0.001). Microarray analysis of expanded HSPC demonstrated increased telomerase activity and many homing-associated genes (35/49) and transcription factors for stemness/self-renewal (49/56) were significantly upregulated in GF+SDF1 stimulated HSPC when compared to GF-stimulated HSPC. Expression of CD44, CXCR4, CD26, CD14, CD45 and soluble IL-6 in expanded cultures were validated by flow cytometry and confocal microscopy.Interpretation & conclusions:Cocktail of cytokines and SDF1 showed good potential to successfully expand HSPC which exhibited enhanced ability to generate multilineage cells in short-term and long-term repopulation assay. This cocktail-mediated stem cell expansion has potential to obviate the need for longer and large volume apheresis procedure making it convenient for donors.

A Zebrafish Model of Fetal Bone Marrow Provides a Dynamic View of Hematopoietic Stem Cell Niche Colonization

The entire blood system is supported throughout life by a small number of hematopoietic stem and progenitor cells (HSPCs) that are produced exclusively during embryonic development. These stem cells are generated from the hemogenic endothelium of the dorsal aorta, then migrate to the fetal liver where they expand, before making a final migration to the fetal bone marrow. After seeding the bone marrow, the stem cell pool stabilizes and the total number of HSPCs remains relatively constant. Very little is known about this early stage of bone marrow niche colonization. A better understanding of native stem cell pool establishment will likely lead to improved clinical HSPC transplantation that depends on repopulation of the bone marrow niche. Currently, imaging technology does not allow direct visualization of the bone marrow niche during colonization because it occurs in utero in the long bones of the fetus. The zebrafish is an advantageous model because the embryos develop externally and are transparent. To quantify the early stem cell pool, we employed long term fate mapping with clonal analysis using the multicolor Zebrabow system, which imparts a unique fluorescent hue to stem cells and their progeny. Our findings reveal that 21 HSPC clones exist prior to HSPC emergence (24 hours post fertilization) and 30 clones are present during peak production from the aorta (48 hours post fertilization). Seeding of the presumptive adult marrow niche in zebrafish begins 4-5 days post fertilization, versus 16.5 days in the mouse. We previously described a transgenic zebrafish line (Runx:mCherry) that marks long term repopulating HSPCs throughout development and into adulthood. HSPC-specific expression is driven by the well-characterized Runx1 +23 kb mouse enhancer element. We used this line to directly observe the earliest immigration events of HSPCs as they arrive in the marrow. To achieve this, we immobilized the zebrafish by injection of the snake venom protein alpha-bungarotoxin directly into circulation. This allowed long term live imaging of the niche (~16 hours) so we could quantify the dynamics of HSPC colonization and expansion. To rapidly acquire high resolution imaging data for this deep tissue we applied lightsheet microscopy. By simultaneously illuminating the sample in the X plane, while taking images in the Z plane, hundreds of optical sections can be captured in seconds. The high pixel and temporal resolution of lightsheet microscopy in a large volume of tissue provides a highly dynamic view of the entire marrow niche. We could assess the localization of HSPCs in relation to other cell types within the niche. For example, HSPCs were closely associated with endothelial cells in a perivascular niche, similar to what has been described in mammalian bone marrow. Furthermore, we could quantify single Runx+ nuclei over time on one side of the bilateral kidney marrow. During this early stage of niche colonization, we found the number of HSPCs per side was ~50 (so ~100 total) and that remained relatively constant. This was in fact a dynamic equilibrium achieved by ingress and egress of cells, as well as occasional cell divisions. This cell number was independently validated using another transgenic zebrafish line, cd41:GFP, that also marks HSPCs. This quantification, combined with our data from earlier development, suggests that HSPCs undergo around two population doublings between emergence from the aorta and engraftment in the marrow. This unique platform for the quantification of a total stem cell pool will allow further functional and mechanistic studies using both genetics and chemical biology. Our goal is to gain insights into the establishment of the stem cell pool within the niche microenvironment and how this could improve clinical transplantation outcomes. DisclosuresZon:Marauder Therapeutics: Equity Ownership, Other: Founder; Scholar Rock: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Other: Founder; Fate, Inc.: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Other: Founder.

Histone Deacetylase Inhibitors As Enhancers of Human Hematopoietic Stem Cell Activity

IntroductionThe identification of compounds which increase the number but also keep or enhance the activity of hematopoietic stem and progenitor cells (HSPCs) could improve the clinical outcome after autologous and allogeneic hematopoietic stem cell transplantation (HSCT). So far, most attempts to increase HSPC numbers ex vivo have been unsuccessful because of either inadequate cell numbers and/or loss of engraftment capacity and HSPC quality during expansion. Executing drug discovery screens in vertebrate systems is generally expensive, technically challenging and time consuming. Therefore, the zebrafish represents a versatile vertebrate model allowing HSPC regulation and development studies during embryogenesis and adulthood.MethodsWe used a semi-automated chemical screen to identify modulators of HSPC activity by transgenic (cmyb:EGFP) zebrafish embryos. Verification of identified histone deacetylase (HDAC) inhibitor candidates was carried out in vitro using human CD34+ HSPCs which were isolated from apharesis samples of healthy donors after mobilization with G-CSF by anti-CD34 coupled magnetic beads. The influence of HDAC inhibitors on HSPC phenotype, gene expression pattern as well as adhesion and migration capacity was analyzed after 5 days of treatment either in single or in co-culture with bone marrow-derived mesenchymal stromal cells (MSCs).ResultsThe HDAC inhibitors valproic acid (VPA), resminostat and entinostat were shown to significantly amplify the number of hematopoietic precursors in a chemical in vivo zebrafish embryo screen (Arulmozhivarman et al. 2016). Treatment of human CD34+ HSPCs with these compounds in vitro resulted in a significantly increased percentage of CD34+CD90+ cells up to 60% compared to controls which showed only 2% of double positive cells as well as in 3-fold higher CD34+ and about 12-fold higher CD34+CD90+ absolute cell numbers. CD34 is a well-known surface marker for human immature HSPCs and in combination with CD90 it defines a potentially pluripotent subpopulation. In a co-culture setting, we found that VPA treated cells showed 2 to 3-fold higher attachment capacity on MSCs compared to the control cells. This finding led us to quantify the adhesive capacity of cells using static adhesion assay and atomic force microscopy based single-cell force spectroscopy (AFM-SCFS). Interestingly, detachment forces of VPA treated HSPCs were 3 times increased on MSCs compared to control cells and a similar phenotype was observed by static adhesion assay. Accordingly, the chemokine-mediated migration of VPA treated HSPCs towards SDF-1/CXCL12 was inhibited. To reveal underlying downstream molecules and mechanisms mediating the modified cellular characteristics, a whole genome expression array was carried out for HSPCs treated with VPA in comparison to untreated controls. Amongst a panel of regulated genes, the melanoma cell adhesion molecule (MCAM/CD146), Notch 3 and its downstream effector Hes-1 as well as the SDF-1 receptor CXCR-4 were found to be significantly changed. Whereas the decreased expression of CXCR4 correlates with the inhibited migration potential of VPA-treated HSPCs and Notch-3/Hes-1 have a known role in normal and malignant hematopoiesis (Gu et al. 2016), the induced expression of MCAM on HSPCs was not described so far. The result was confirmed by flow cytometry which revealed a 40% MCAM-positive cell population when treated with VPA, whereas the control showed only negative cells. Additionally, significant higher transcript levels were detected for MCAM by quantitative real-time PCR in VPA expanded cells. Recently, we described a role of MCAM in MSCs for the hematopoietic support (Stopp et al. 2013). The inducible expression in HSPCs may reflect homotypic interactions which preserve a more immature subpopulation with high stem cell activity.ConclusionWe describe for the first time the ability of the HDAC inhibitors VPA, resminostat and entinostat to efficiently expand CD34+ HSPCs ex vivo especially supporting a CD34+CD90+ subpopulation with potentially high stem cell activity. Moreover, a potential role of MCAM in this context may offer new perspectives of the HSPC expansion ex vivo for the improvement of HSCT. DisclosuresNo relevant conflicts of interest to declare.

Mesenchymal Stromal Cell-derived Extracellular Vesicles Promote Myeloid-biased Multipotent Hematopoietic Progenitor Expansion via Toll-Like Receptor Engagement

Mesenchymal stromal cells (MSCs) present in the bone marrow microenvironment secrete cytokines and angiogenic factors that support the maintenance and regenerative expansion of hematopoietic stem and progenitor cells (HSPCs). Here, we tested the hypothesis that extracellular vesicles (EVs) released by MSCs contribute to the paracrine crosstalk that shapes hematopoietic function. We systematically characterized EV release by murine stromal cells and demonstrate that MSC-derived EVs prompt a loss of HSPC quiescence with concomitant expansion of murine myeloid progenitors. Our studies reveal that HSPC expansion by MSC EVs is mediated via the MyD88 adapter protein and is partially blocked by treatment with a TLR4 inhibitor. Imaging of fluorescence protein-tagged MSC EVs corroborated their cellular co-localization with TLR4 and endosomal Rab5 compartments in HSPCs. The dissection of downstream responses to TLR4 activation reveals that the mechanism by which MSC EVs impact HSPCs involves canonical NF-κB signaling and downstream activation of Hif-1α and CCL2 target genes. Our aggregate data identify a previously unknown role for MSC-derived EVs in the regulation of hematopoiesis through innate immune mechanisms and illustrate the expansive cell-cell crosstalk in the bone marrow microenvironment.