scholarly journals Dose-dependent effects of the Notch ligand Delta1 on ex vivo differentiation and in vivo marrow repopulating ability of cord blood cells

Blood ◽  
2005 ◽  
Vol 106 (8) ◽  
pp. 2693-2699 ◽  
Author(s):  
Colleen Delaney ◽  
Barbara Varnum-Finney ◽  
Keisuke Aoyama ◽  
Carolyn Brashem-Stein ◽  
Irwin D. Bernstein
Keyword(s):  
Cord Blood ◽  
Notch Signaling ◽  
Cell Fate ◽  
Cell Biology ◽  
Ex Vivo ◽  
Hematopoietic Stem ◽  
Notch Ligand ◽  
Ligand Density ◽  
Organ Systems

AbstractAlthough significant advances have been made over the last decade with respect to our understanding of stem cell biology, progress has been limited in the development of successful techniques for clinically significant ex vivo expansion of hematopoietic stem and progenitor cells. We here describe the effect of Notch ligand density on induction of Notch signaling and subsequent cell fate of human CD34+CD38– cord blood progenitors. Lower densities of Delta1ext-IgG enhanced the generation of CD34+ cells as well as CD14+ and CD7+ cells, consistent with early myeloid and lymphoid differentiation, respectively. However, culture with increased amounts of Delta1ext-IgG induced apoptosis of CD34+ precursors resulting in decreased cell numbers, without affecting generation of CD7+ cells. RNA interference studies revealed that the promotion of lymphoid differentiation was primarily mediated by Delta1 activation of Notch1. Furthermore, enhanced generation of NOD/SCID repopulating cells was seen following culture with lower but not higher densities of ligand. These studies indicate critical, quantitative aspects of Notch signaling in affecting hematopoietic precursor cell-fate outcomes and suggest that density of Notch ligands in different organ systems may be an important determinant in regulating cell-fate outcomes. Moreover, these findings contribute to the development of methodology for manipulation of hematopoietic precursors for therapeutic purposes.

Runx1 Is Required for Notch-Induced Specification of Megakaryocyte Development from Early Hematopoietic Stem and Progenitor Cells

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 1370-1370
Author(s):  
Melanie G Cornejo ◽  
Thomas Mercher ◽  
Joseph D. Growney ◽  
Jonathan Jesneck ◽  
Ivan Maillard ◽  
...  
Keyword(s):  
Notch Signaling ◽  
Cell Fate ◽  
Stromal Cells ◽  
Gfp Expression ◽  
Hematopoietic Stem ◽  
Cell Fate Decisions ◽  
Insight Into ◽  
Megakaryocyte Differentiation

Abstract The Notch signaling pathway is involved in a broad spectrum of cell fate decisions during development, and in the hematopoietic system, it is known to favor T cell- vs B cell lineage commitment. However, its role in myeloid lineage development is less well understood. We have shown, using heterotypic co-cultures of murine primary hematopoietic stem cells (Lin-Sca-1+ckit+ HSCs) and OP9 stromal cells expressing the Notch ligand Delta1 (OP9-DL1), that Notch signaling derived from cell non-autonomous cues acts as a positive regulator of megakaryocyte fate from LSK cells. Bone marrow transplantation experiments with a constitutively active Notch mutant resulted in enhanced megakaryopoiesis in vivo, with increased MEP numbers and megakaryocyte colony formation. In contrast, expression of dnMAML using a conditional ROSA26 knock-in mouse model significantly impaired megakaryopoiesis in vivo, with a marked decrease in megakaryocyte progenitors. In order to understand the cellular differentiation pathways controlled by Notch, we first examined the ability of various purified progenitor populations to differentiate toward megakaryocytes upon Notch stimulation in vitro. We observed that CMP and MEP, but not GMP, can engage megakaryopoiesis upon Notch stimulation. Our results were consistent with expression analysis of Notch signaling genes in these purified progenitors and were supported by the observation that transgenic Notch reporter mice display higher levels of reporter (i.e. GFP) expression in HSC and MEP, vs. CMP and GMP in vivo. Furthermore, purified progenitors with high GFP expression gave rise to increased numbers of megakarocyte-containing colonies when plated in vitro compared to GFP-negative progenitors. In addition, further purification of the HSC population into long-term (LT), short-term (ST), and lymphoid-primed myeloid progenitors (LMPP) before plating on OP9-DL1 stroma showed that LMPP have a reduced ability to give rise to megakaryocytes compared to the other two populations. These data support the hypothesis that there is an early commitment to erythro/megakaryocytic fate from HSC prior to lymphoid commitment. To gain insight into the molecular mechanism underlying Notch-induced megakaryopoiesis, we performed global gene expression analysis that demonstrated the engagement of a megakaryopoietic transcriptional program when HSC were co-cultured with OP9-DL1 vs. OP9 stroma or OP9-DL1 treated with gamma-secretase inhibitor. Of interest, Runx1 was among the most upregulated genes in HSC co-cultured on OP9-DL1 stroma. To assess whether Notch signaling engages megakaryocytic fate through induction of Runx1, we plated HSC from Runx1 −/− mice on OP9-DL1 stroma. Compared to WT cells, Runx1 −/− HSC had a severely reduced ability to develop into CD41+ cells. In contrast, overexpression of Runx1 in WT HSC was sufficient to induce megakaryocyte fate on OP9 stroma without Notch stimulation. Together, our results indicate that Notch pathway activation induced by stromal cells is an important regulator of cell fate decisions in early progenitors. We show that Notch signaling is upstream of Runx1 during Notch-induced megakaryocyte differentiation and that Runx1 is an essential target of Notch signaling. We believe that these results provide important insight into the pathways controlling megakaryocyte differentiation, and may have important therapeutic potential for megakaryocyte lineage-related disorders.

Cytokine Treatment of CD34+ Cord Blood Cells with G-CSF, GM-CSF, or SCF During 48 Hours of Ex Vivo Culture Alters CD26/DPPIV Peptidase Activity and Subsequent Engraftment Into NSG Immunodeficient Mice.

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 1460-1460
Author(s):  
Laura A Paganessi ◽  
Lydia Luy Tan ◽  
Sucheta Jagan ◽  
Robin Frank ◽  
Antonio M. Jimenez ◽  
...  
Keyword(s):  
Cord Blood ◽  
Ex Vivo ◽  
Hematopoietic Stem ◽  
Immunodeficient Mice ◽  
Gm Csf ◽  
Cytokine Treatment ◽  
Ex Vivo Culture ◽  
Inhibitor Treatment

Abstract Abstract 1460 Many patients with hematologic malignancies choose hematopoietic stem cell transplantation (HSCT) as a treatment option. The most common source of Hematopoietic Stem and Progenitor Cells (HSC/HPC) for adult recipients is mobilized Peripheral Blood (mobPB). Limited quantities of HSC/HPC obtainable from an umbilical cord restricts its use for adult recipients. Ex vivo treatment of umbilical cord blood (CB) with cytokines and growth factors is being used to expand the population of cord blood HSC/HPCs in hopes of obtaining higher numbers of transplantable CB cells. In addition, cytokines and growth factors are often utilized post-transplant in an attempt to improve the rate of immune reconstitution. It has been previously reported that granulocyte-colony-stimulating factor (G-CSF), and granulocyte-macrophage-colony-stimulating factor (GM-CSF) up-regulate CD26 (dipeptidyl peptidase IV/DPPIV) activity on freshly isolated CD34+ CB cells within 18 hours of culture [Christopherson, et al. Exp Hematol 2006]. Separate studies have demonstrated that treatment of uncultured CD34+ CB cells with the CD26 inhibitor Diprotin A increases transplant efficiency into immunodeficient mice [Christopherson, et al. Stem Cells Dev. 2007]. We evaluated here the in vitro and in vivo effects of CD26 inhibitor treatment on previously frozen CB CD34+ cells cultured ex vivo with G-CSF, GM-CSF or SCF for 48 hours. We examined CD26 expression by multivariate flow cytometry, CD26 activity using the established chromogenic CD26 substrate, Gly-Pro-p-nitroanilide (Gly-Pro-pNA), and SDF-1α induced migration and adhesion. In vivo, we examined long-term engraftment in NSG (NOD/SCID/IL2Rγnull) immunodeficient mice. After 48 hours of culture with cytokine treatment we observed altered CD26 expression on CD34+ CB cells. There was both an increase in the percentage of CD26+ cells and the mean fluorescence intensity (MFI) of CD26. Additionally, CD26 activity was 1.20, 1.59, 1.58, and 1.65 fold greater after ex vivo culture in untreated, G-CSF, GM-CSF and SCF treated CB CD34+ cells respectively compared to the CD26 activity prior to culture. The increase in CD26 activity as a result of treatment with G-CSF (p≤ 0.01), GM-CSF (p≤ 0.05) or SCF (p≤ 0.01) was significantly higher than the CD26 activity measured in the untreated cells following 48 hours of culture. Post-culture treatment with the CD26 inhibitor, Diprotin A, significantly improved SDF-1α induced migration and adhesion of cultured CD34+ CB cells in vitro, particularly in G-CSF treated cells (p≤ 0.05). Diprotin A treatment of CD34+ CB cells previously treated with G-CSF also significantly increased the long-term in vivo engraftment of stem and progenitor (CD34+CD38-, p=0.032), monocyte (CD14+, p=0.015), and megakaryocyte/platelet (CD61+, p=0.020) cells in the bone marrow of NSG mice. CD26 has been previously shown to cleave SDF-1 (stromal cell-derived factor 1/CXCL12). After cleavage, SDF-1 retains its ability to bind to its receptor (CXCR4) but no longer signals. SDF-1 is a powerful chemoattractant and has been shown to be important in mobilization, homing, and engraftment of HSCs and HPCs. This study demonstrates the influence of ex vivo culture and the effect of cytokine treatment on CD26 activity and subsequent biologic function related to HSCT. All three cytokines studied caused a significant increase in enzymatic activity at 48 hours compared to untreated cells. The up-regulation of CD26 protein expression caused by cytokine treatment for 48 hours, in particular G-CSF, had a significant impact on SDF-1 stimulated migration and adhesion. This was demonstrated in vitro by the improvement in cell function after CD26 inhibitor treatment and in vivo by the improved engraftment seen in the G-CSF treated cells with CD26 inhibitor treatment. These experiments suggest that combining CD26 inhibitor treatment following culture with G-CSF treatment during culture has the greatest overall benefit in engraftment outcome. By increasing our understanding of the effects of exogenous cytokines during culture on trafficking, ex vivo expanded CB has the potential to become a more effective means of not only increasing numbers of CB HSC/HPCs but also engraftment outcomes. This would ultimately allow expanded cord blood to become a more viable option for HSCT. Disclosures: No relevant conflicts of interest to declare.

Activation of Notch Signaling Mediates Ex Vivo Expansion of Multilineage, Engrafting Murine Hematopoietic Progenitors From Embryonic Sources.

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 2321-2321
Author(s):  
Brandon K Hadland ◽  
Barbara Varnum-Finney ◽  
Irwin D. Bernstein
Keyword(s):  
Notch Signaling ◽  
Ex Vivo ◽  
Fetal Liver ◽  
Signal Pathways ◽  
Mouse Bone Marrow ◽  
Human Cord Blood ◽  
Hematopoietic Stem ◽  
Notch Activation

Abstract Abstract 2321 An important goal in the application of pluripotent stem cells (PSC) for therapeutic purposes is the derivation of hematopoietic stem and progenitor cells (HSPC) capable of efficient engraftment in vivo. Fundamental to achieving this goal is improved understanding of key signal pathways required to establish, maintain and expand HSPCs from embryonic sources. Ex vivo activation of Notch signaling in mouse bone marrow and human cord blood-derived HSC can facilitate expansion of rapidly engrafting multilineage progenitors, which has recently been translated for therapeutic purposes. In contrast, similar expansion of engrafting progenitors has not been successful from PSC. This prompted us to evaluate whether embryonic-derived HSPC have capacity to respond to ligand-induced Notch signaling ex vivo, and whether Notch activation could promote expansion of engrafting progenitors from these embryonic sources. We have examined the effects of ex vivo activation of Notch receptors by immobilized, exogenous Notch ligands on highly enriched populations of embryonic HSC and HSC precursors (pre-HSC) at various developmental stages. We find that activation of Notch by the ligand Delta1 within HSC/pre-HSC isolated from embryonic aorta-gonad-mesonephros (AGM) promotes expansion of progenitors with erythromyeloid colony forming potential and T/B-lymphoid potential in vitro, with concurrent expression of surface phenotypes resembling fetal liver-stage HSC. Furthermore, Notch activation in embryonic HSPC also mediates expansion of progenitors with rapidly engrafting myeloid and lymphoid capacity in irradiated mouse models. Our results demonstrate that embryonic stage HSPC have capacity to expand in response to Notch activation, and thus further studies comparing AGM- and PSC-derived hematopoietic precursors are needed to elucidate differences that may account for failure to expand HSPC from PSC. Disclosures: Bernstein: Seattle Genetics, Inc.: Consultancy.

scholarly journals Prolonged Adherence of Human Immunodeficiency Virus-Derived Vector Particles to Hematopoietic Target Cells Leads to Secondary Transduction In Vitro and In Vivo

2006 ◽  
Vol 81 (2) ◽  
pp. 639-649 ◽  
Author(s):  
Yung-Wei Pan ◽  
Jarrad M. Scarlett ◽  
Tammy T. Luoh ◽  
Peter Kurre
Keyword(s):  
Human Immunodeficiency Virus ◽  
Cell Biology ◽  
Germ Line ◽  
Ex Vivo ◽  
Critical Parameters ◽  
Target Cells ◽  
Hematopoietic Stem ◽  
Immunodeficiency Virus ◽  
Vector Particles

ABSTRACT Human immunodeficiency virus type 1-derived lentivirus vectors bearing the vesicular stomatitis virus G (VSV-G) envelope glycoprotein demonstrate a wide host range and can stably transduce quiescent hematopoietic stem cells. In light of concerns about biosafety and potential germ line transmission, they have been used predominantly for ex vivo strategies, thought to ensure the removal of excess surface-bound particles and prevent in vivo dissemination. Studies presented here instead reveal prolonged particle adherence after ex vivo exposure, despite serial wash procedures, with subsequent transduction of secondary target cells in direct and transwell cocultures. We explored the critical parameters affecting particle retention and transfer and show that attachment to the cell surface selectively protects virus particles from serum complement-mediated inactivation. Moreover, studies with nonmyeloablated murine recipients show that transplantation of vector-exposed, washed hematopoietic cells results in systemic dissemination of functional VSV-G/lentivector particles. We demonstrate genetic marking by inadvertent transfer of vector particles and prolonged expression of transgene product in recipient tissues. Our findings have implications for biosafety, vector design, and cell biology research.

Ex Vivo Expansion of Human Umblical Cord Blood Hematopoietic Stem Cells (HSC) with Valproic Acid or Notch-Ligand +/− Fibronectin

Cytotherapy ◽  
2016 ◽  
Vol 18 (6) ◽  
pp. S42
Author(s):  
P. Yurdakul ◽  
E. Gencer ◽  
H. Akin ◽  
K. Dalva ◽  
D. Katlan ◽  
...  
Keyword(s):  
Stem Cells ◽  
Valproic Acid ◽  
Hematopoietic Stem Cells ◽  
Cord Blood ◽  
Ex Vivo ◽  
Ex Vivo Expansion ◽  
Hematopoietic Stem ◽  
Notch Ligand

Notch Signaling Is Necessary and Sufficient for Runx1-Dependent Stem Cell Induction in the Embryonic Aorta-Gonad-Mesonephros (AGM) Region.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 4161-4161
Author(s):  
Caroline Erter Burns ◽  
Leonard I. Zon
Keyword(s):  
Stem Cell ◽  
Notch Signaling ◽  
Cell Fate ◽  
Notch Pathway ◽  
Notch Receptor ◽  
Dorsal Aorta ◽  
Loss Of Function ◽  
Cardinal Vein ◽  
Hematopoietic Stem

Abstract Vertebrate hematopoiesis can be divided into two embryonic phases: a short primitive wave predominantly generating erythrocytes and a definitive (fetal/adult) wave producing long-term hematopoietic stem cells (HSCs). The definitive wave occurs in the embryonic aorta-gonad-mesonephros (AGM) region through the asymmetric induction of HSCs from the ventral, but not dorsal, aortic endothelial wall. Since Notch signaling is critical for orchestrating a variety of developmental cell fate choices from invertebrates to humans and has been implicated in affecting the differentiation of some hematopoietic lineages, we analyzed whether the Notch pathway regulates definitive HSC induction in vivo. The zebrafish mutant mindbomb harbors a mutation in an essential E3 ligase that ubiquitylates Delta, which in turn allows the Notch intercellular domain to be released and activate downstream target gene transcription. Thus, in the absence of Mindbomb function Notch signaling does not occur. We found that although mindbomb mutants show normal primitive hematopoiesis, definitive c-myb and runx1 HSC expression is lacking. Since embryos injected with synthetic morpholinos designed to inhibit proper splicing of runx1 RNA ( runx morphants) show the same hematopoietic phenotype as mindbomb mutants, we next addressed the epistatic relationship between notch and runx1 using classic gain-of-function and loss-of-function analyses. In runx1 morphants expression of a notch receptor, notch3, and a delta ligand, deltaC, in the developing dorsal aorta was normal. Moreover, injection of runx1 RNA rescued HSCs in the AGM of mindbomb mutants. Together, these results suggest that Runx1 functions downstream of Notch in promoting HSC fate. We next analyzed whether a constitutively activated form of Notch (NICD) is sufficient for HSC specification in the AGM using an inducible binary transgenic system. Zebrafish carrying the heat-shock promoter driving the activator gal4 were mated to animals carrying 6 gal4 -responsive tandem upstream activating sequences (UAS) driving NICD. At the 10 somite-stage the embryos were heat-shocked at 37°C for 1 hour to activate NICD throughout the double transgenic animals. Surprisingly, expression of both HSC markers, c-myb and runx1, were expanded from their normal restricted domain in the ventral endothelium to the entire circumference of the dorsal aorta. Most interestingly, the presence of ectopic c-myb and runx1 transcripts were observed in the developing post-cardinal vein, a vessel that normally does not produce HSCs. These data imply that activation of the Notch pathway generates increased numbers of HSCs in vivo. When runx1 RNA is injected into wild-type embryos a similar expansion of c-myb transcripts is seen throughout the entire dorsal aorta and post-cardinal vein, further indicating that Runx1 functions downstream of Notch in HSC induction. In summary, discovery of the molecular programs essential and sufficient for fetal/adult hematopoietic ontogeny will lead to a further understanding of the physiologic and pathologic processes regulating stem cell homeostasis and translate into more effective therapies for blood disorders.

Notch Signaling Induces Megakaryocytic Cell Fate.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 200-200
Author(s):  
Thomas Mercher ◽  
Melanie Cornejo ◽  
Christopher Sears ◽  
Thomas Kindler ◽  
Sandra Moore ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Bone Marrow Transplantation ◽  
Notch Signaling ◽  
Cell Fate ◽  
Marrow Transplantation ◽  
Notch Pathway ◽  
Severe Thrombocytopenia ◽  
Hematopoietic Stem ◽  
Cell Fate Decisions

Abstract The Notch pathway regulates a broad range of biological mechanisms including proliferation, border formation and cell fate decisions. In the hematopoietic system, Notch signaling is generally thought to specify T cell lineage fate at the expense of the B cell whereas its role in the myeloid lineage development is unclear. When using heterotypic co-cultures of murine primary hematopoietic stem cells (HSC: Lin-Sca1+Kit+) with OP9 stromal cells, or OP9 cells expressing the Notch ligand Delta1 (OP9-DL1), we unexpectedly observed the development of large cells with cytoplasmic protrusions reminiscent of proplatelet production by megakaryocytes on OP9-DL1 stroma. These cells stained positive for acetylcholinesterase, specific for megakaryocyte, and displayed large polylobated nuclei. Flow cytometric analysis indicated a 10-fold increase in the number of CD41+ cells in OP9-DL1 co-cultures compared to parental OP9 co-cultures. Expression of a constitutively active intra-cellular Notch (ICN) mutant allowed differentiation of HSC into CD41+ cells in parental OP9 co-cultures without DL1 stimulation, whereas expression of a dominant-negative MAML1 (dnMAML1) mutant abrogated this effect in OP9-DL1 co-cultures. In addition, megakaryocyte differentiation in OP9-DL1 co-cultures was blocked by γ-secretase inhibitors treatment and rescued by ectopic expression of ICN. Global gene expression analysis demonstrated engagement of a megakaryopoietic transcriptional program when HSC were co-cultured with OP9-DL1 vs. OP9 stroma or OP9-DL1 stroma treated with γ-secretase inhibitor. Bone marrow transplantation experiments with ICN, resulted in enhanced megakaryopoiesis in vivo with increased MEP numbers and megakaryocyte colony formation. Furthermore, transplantation of bone marrow cells transduced with dnMAML1 significantly impaired megakaryopoiesis in vivo with a 4- to 7-fold decrease in maturing megakaryocytes. These findings demonstrate a positive regulatory role for Notch signaling in specification of megakaryocyte development, and indicate that Notch plays a complex role in cell fate decisions among myeloid progenitors. They suggest the possibility that inhibition of Notch signaling may have therapeutic potential in malignancies of the megakaryocytic lineage. Furthermore, Notch pathway stimulation could be of value in enhancing megakaryocyte growth in clinical contexts associated with severe thrombocytopenia, such as hematopoietic reconstitution following bone marrow transplantation or chemotherapy.

Functional analysis of the Human Pbx Interacting Protein (HPIP) in Human Hematopoiesis

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 2430-2430
Author(s):  
Pawandeep Kaur ◽  
Christiane Stadler ◽  
Farid Ahmed ◽  
Monica Cusan ◽  
R. Keith Humphries ◽  
...  
Keyword(s):  
Cord Blood ◽  
Cell Fate ◽  
Constitutive Expression ◽  
Homeodomain Protein ◽  
Acute Lymphocytic Leukaemia ◽  
Human Cord Blood ◽  
Interacting Protein ◽  
Hematopoietic Stem

Abstract The recognition of novel proteins that regulate human hematopoietic stem cell and early progenitor cell fate is a prime objective in experimental and clinical hematology. Human hematopoietic PBX interacting protein (HPIP), with no significant homology to known proteins, is a 731 amino acid protein, discovered as a novel interacting partner of the PBX homeodomain protein. HPIP has been implicated as a nuclear-cytoplasmic shuttle molecule and shown to have the capacity to bind to the cytoskeleton. It also inhibits the ability of PBX-HOX heterodimers to bind to target sequences and strongly inhibits the transactivation activity of E2A-PBX1 [t(1;19) translocation, which occurs in 25% of pediatric pre-B cell acute lymphocytic leukaemia] (Abramovich C. et al JBC, 2000; Oncogene, 2002). It is highly expressed in human CD34+ progenitor cells, but is silenced in differentiated cells. To gain further insights into the possible functional role of HPIP and its domains and its possible role in a common pathway with HOX transcription co-factor PBX1, HPIP cDNA was cloned in pMSCV-IRES-YFP cassette. Umbilical cord blood enriched with CD34+ population of stem cells was obtained to perform in vitro and in vivo experiments. Mutants, with deletions of the microtubule binding region (ΔMBR-HPIP), and nuclear receptor and PBX1 interacting motif (ΔNRPID-HPIP) were generated and tested in vitro and in vivo. The constitutive expression of HPIP wt and ΔMBR-HPIP in human cord blood cells (CD34+) enhanced erythroid colony formation in CFC assay (p=0.008, n=6) while the ΔNRPID-HPIP mutant nullified the effect. Both mutants of HPIP augmented significantly, the formation of primitive colonies (GEMM and GM) in methylcellulose assay (p≤0.01, n=6) as compared to YFP control and HPIP wt. In replating CFC assays ΔNRPID-HPIP showed an increased number of myeloid colonies (p≤0.01, n=6) and GM (p=ns) colonies but a decrease in granulocytic colonies (p≤0.05, n=6) compared to YFP control and HPIP wt

Preclinical Development of a Cryopreservable Megakaryocyte Cell Product from Cord Blood Derived Hematopoietic Stem Cells

Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 3859-3859
Author(s):  
Helen Fong ◽  
Goar Mosoyan ◽  
Ami Patel ◽  
Ronald Hoffman ◽  
Jay Tong ◽  
...  
Keyword(s):  
Stem Cells ◽  
Hematopoietic Stem Cells ◽  
Cord Blood ◽  
Shelf Life ◽  
Ex Vivo ◽  
Culture Conditions ◽  
Hematopoietic Stem ◽  
Cell Product ◽  
Cd34 Cells

Abstract Platelet (PTL) transfusions are currently the most effective treatment for patients with thrombocytopenia. Demand for PTL transfusions has steadily increased in recent years, straining a PTL supply that is already limited due to dependency on volunteer donors, short shelf life, risk of infections, and alloimmunization. This dilemma has stimulated the search for alternative approaches for generating PTLs ex vivo from different sources of hematopoietic stem cells (HSCs). Although PTLs have been successfully generated in cultures initiated with primary human CD34+ cells and pluripotent stem cells, the generation of a clinically relevant PTL product ex vivo faces significant obstacles due to scalability, reproducibility and shelf life. We propose an alternative approach to overcome such obstacles by developing a cryopreservable cell product consisting of megakaryocytes (MK) that can produce PTL in vivo after transfusion into patients. Umbilical cord blood units (CBU) are FDA-approved, readily available sources for allogeneic HSC for transplantation in patients with various blood disorders. Our method utilizes a previously developed two-step culture system of megakaryopoiesis from CB CD34+ cells to generate an MK culture composed of defined MK populations: CD34+/CD41+/CD42b- MK precursors (MKP), immature CD34-/CD41+/CD42b- MK (iMK) and mature CD34-/CD41+/CD42b+ MK (mMK). While robust, the yield of MKs obtained in these cultures is restricted due to limited numbers of HSCs in CB. Our group has recently demonstrated that the numbers of CB CD34+ can be significantly expanded by epigenetic reprogramming following treatment with valproic acid (VPA). Here, we report the integration and optimization of HSC expansion with MK differentiation in order to generate a clinically relevant MK cell product. We tested 20 different culture conditions in which CD34+ cells were cultured for 5 to 8 days in the absence or presence of VPA in serum-free media with various cytokines to allow for HSC expansion. The resulting HSC pool is cultured for additional 4 to 7 days in MK differentiation/maturation media. The overall yield of CD41+ MKs obtained ranged from 8 to 33 MK per input CD34+ cell expanded in the presence of cytokines alone (n=10; mean 19.8 MK) and from 9 to 34 MK per input CD34+ cell expanded in the presence of cytokines plus VPA (n=10; mean 20.7 MK). Given that up to 2x106 CD34+ cells can be isolated from one CBU, it is anticipated that a culture yielding 28 or more MK per one CD34+ cell would generate over 56x106 MK or the equivalent of 7x105 CD41+ MK/kg/body weight for infusion into an 80 kg recipient. The culture conditions resulting in a yield of 28 or more MK per one CD34+ cell input are currently optimized to further maximize the fraction of MK generated which currently varies between 15-57% of culture. The predominant sub-population of MK resulted in these conditions consists of mMKs, regardless of VPA treatment. However, in the presence of VPA, the cultures contain a greater number of assayable CFU-MKs as compared to cytokines alone. Furthermore, preliminary studies suggest that transplantation of ex vivo generated MK leads to detectable human CD41+ cells into the BM and human PTL into the PB of NSG recipient mice. These results indicate that a MK cell product derived from CB HSCs expanded by VPA comprises not only mMK and iMK capable of immediate PTL release but also MKP and HPCs which are capable of sustained MK and PTL production. Another major advantage of a transfusion product composed of nucleated MKs is the possibility of storage by cryopreservation. Due to the fragility of mMK, we tested the cryopreservation of heterogeneous and purified MK cultures. Viability of cryopreserved MK cultures post-thaw was between 68.4-70% and no changes in the MK phenotype. Studies are ongoing to test the ex vivo and in vivo functionality of the cryopreserved MKs. In summary, starting with expanded CB HSC we created a cryopreservable cell product composed of different MK sub-populations within the MK hierarchy which is being developed into a clinically relevant therapy for treatment of thrombocytopenia. Disclosures No relevant conflicts of interest to declare.

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