Effective ex vivo generation of megakaryocytic cells from mobilized peripheral blood CD34(+) cells with stem cell factor and promegapoietin

Sars-CoV-2 Virus Infection May Interfere CD34+ Hematopoietic Stem Cells and Megakaryocyte-Erythroid Progenitors Differentiation Contributing to Platelet Defection towards Insurgence of Thrombocytopenia and Thrombophilia

To date, several cases of thrombosis have been confirmed to be related to Sars-CoV-2 infection. Multiple attempts detected the prolonged occurrence of Sars-CoV-2 viral RNA (long COVID) in whole blood suggesting that virus byproducts may remain within cells and tissues well over the disease has finished. Patients may develop severe thrombocytopenia, acute anemia of inflammation and, systemic thrombosis with the fatal course of disease, which is suggestive of further interferences of Sars-CoV-2 on hematopoietic stem cells (HSCs) within the differentiation process towards erythroid and megakaryocytic cells. Therefore, we speculated whether Sars-CoV-2 propagates in or compartmentalizes with hematopoietic progenitor, erythroid, and megakaryocytic cells as the main cause of thrombotic events in either COVID-19 patients or vaccinated individuals. Results: The Sars-CoV-2 RNA replication, protein translation and infectious particle formation as the spike proteins in hematopoietic cell lines take place via the angiotensin-converting enzyme 2 (ACE2) entry pathway within primary CD34⁺ HSCs inducing, ex vivo, the formation of defected erythroid and megakaryocytic cells that eventually become targets of humoral and adaptive immune cells. Conclusions: Viral particles from affected CD34⁺ HSCs or the cellular component of RBC units and eventually platelets, present the greatest risk for sever thrombosis-transmitted Sars-CoV-2 infections.

Zika virus infection studies with CD34+ hematopoietic and megakaryocyte-erythroid progenitors, red blood cells and platelets

BACKGROUND

To date, several cases of transfusion-transmitted ZIKV infections have been confirmed. Multiple studies detected prolonged occurrence of ZIKV viral RNA in whole blood as compared to plasma samples indicating potential ZIKV interaction with hematopoietic cells. Also, infection of cells from the granulocyte/macrophage lineage has been demonstrated. Patients may develop severe thrombocytopenia, microcytic anemia, and a fatal course of disease occurred in a patient with sickle cell anemia suggesting additional interference of ZIKV with erythroid and megakaryocytic cells. Therefore, we analyzed whether ZIKV propagates in or compartmentalizes with hematopoietic progenitor, erythroid, and megakaryocytic cells.

METHODS

ZIKV RNA replication, protein translation and infectious particle formation in hematopoietic cell lines as well as primary CD34⁺ HSPCs and ex vivo differentiated erythroid and megakaryocytic cells was monitored using qRT-PCR, FACS, immunofluorescence analysis and infectivity assays. Distribution of ZIKV RNA and infectious particles in spiked red blood cell (RBC) units or platelet concentrates (PCs) was evaluated.

RESULTS

While subsets of K562 and KU812Ep6^EPO cells supported ZIKV propagation, primary CD34⁺ HSPCs, MEP cells, RBCs, and platelets were non-permissive for ZIKV infection. In spiking studies, ZIKV RNA was detectable for 7 days in all fractions of RBC units and PCs, however, ZIKV infectious particles were not associated with erythrocytes or platelets.

CONCLUSION

Viral particles from plasma or contaminating leukocytes, rather than purified CD34⁺ HSPCs or the cellular component of RBC units or PCs, present the greatest risk for transfusion-transmitted ZIKV infections.

miRNAs can increase the efficiency of ex vivo platelet generation

The process of megakaryopoiesis culminates in the release of platelets, the pivotal cellular component for hemostasis and wound healing. The regulatory architecture including the modulatory role of microRNAs, which underlies megakaryocytic maturation and platelet formation, is incompletely understood, precluding the ex vivo generation of sufficient platelet numbers for transfusion medicine. We derived a highly efficient differentiation protocol to produce mature polyploid megakaryocytes and functional platelets from CD34⁺-hematopoietic stem and progenitor cells by comparing previously published approaches. Our megakaryocytic culture conditions using the cytokines SCF, TPO, IL-9, and IL-6 include nicotinamide and Rho-associated kinase (ROCK) inhibitor Y27632 as contextual additives. The potency of our novel megakaryocytic differentiation protocol was validated using cord blood and peripheral blood human hematopoietic stem and progenitor cells. Using this novel megakaryocytic differentiation protocol, we characterized the modulatory capacity of several miRNAs highly expressed in normal megakaryocytic cells or malignant blasts from patients with megakaryoblastic leukemia. Overexpression of candidate microRNAs was achieved by lentiviral transduction of CD34⁺-hematopoietic stem and progenitor cells prior to differentiation. We revealed miR-125b and miR-660 as enhancers of polyploidization, as well as platelet output of megakaryocytes. The oncogene miR-125b markedly expanded the number of megakaryocytes during in vitro culture. Conversely, the miR-23a/27a/24-2 cluster, which is highly expressed in normal megakaryocytes, blocked maturation and platelet formation. Our study on the utilization of microRNAs in conjunction with a highly efficient differentiation protocol constitutes another step towards ex vivo platelet manufacturing on a clinically relevant scale.

Bone marrow niche-inspired, multiphase expansion of megakaryocytic progenitors with high polyploidization potential

BACKGROUND AIMS

Megakaryopoiesis encompasses hematopoietic stem and progenitor cell (HSPC) commitment to the megakaryocytic cell (Mk) lineage, expansion of Mk progenitors and mature Mks, polyploidization and platelet release. pH and pO2 increase from the endosteum to sinuses, and different cytokines are important for various stages of differentiation. We hypothesized that mimicking the changing conditions during Mk differentiation in the bone marrow would facilitate expansion of progenitors that could generate many high-ploidy Mks.

METHODS

CD34+ HSPCs were cultured at pH 7.2 and 5% O2 with stem cell factor (SCF), thrombopoietin (Tpo) and all combinations of Interleukin (IL)-3, IL-6, IL-11 and Flt-3 ligand to promote Mk progenitor expansion. Cells cultured with selected cytokines were shifted to pH 7.4 and 20% O2 to generate mature Mks, and treated with nicotinamide (NIC) to enhance polyploidization.

RESULTS

Using Tpo + SCF + IL-3 + IL-11, we obtained 3.5 CD34+ CD41+ Mk progenitors per input HSPC, while increasing purity from 1% to 17%. Cytokine cocktails with IL-3 yielded more progenitors and mature Mks, although the purities were lower. Mk production was much greater at higher pH and pO2. Although fewer progenitors were present, shifting to 20% O2 /pH 7.4 at day 5 (versus days 7 or 9) yielded the greatest mature Mk production, 14 per input HSPC. NIC more than doubled the percentage of high-ploidy Mks to 40%.

CONCLUSIONS

We obtained extensive Mk progenitor expansion, while ensuring that the progenitors could produce high-ploidy Mks. We anticipate that subsequent optimization of cytokines for mature Mk production and delayed NIC addition will greatly increase high-ploidy Mk production.

Enhanced generation of megakaryocytes from umbilical cord blood-derived CD34(+) cells expanded in the presence of two nutraceuticals, docosahexanoic acid and arachidonic acid, as supplements to the cytokine-containing medium

BACKGROUND AIMS

Ex vivo generation of megakaryocytes (MK) from hematopoietic stem cells (HSC) is important for both basic research, to understand the mechanism of platelet biogenesis, and clinical infusions, for rapid platelet recovery in thrombocytopenic patients. We investigated the role of two nutraceuticals, docosahexanoic acid (DHA) and arachidonic acid (AA), in the in vitro generation of MK.

METHODS

Umbilical cord blood (UCB)-derived CD34+cells were cultured with stem cell factor (SCF) and thrombopoietin (TPO) in the presence (test) or absence (control) of the two additives. On day 10, MK and platelets generated were quantitated by morphologic, phenotypic and functional assays.

RESULTS

The cell yield of MK and platelet numbers were significantly higher in test compared with control cells. Phenotypic analyzes and gene expression profiles confirmed these findings. Functional properties, such as colony-forming unit (CFU)-MK formation, chemotaxis and platelet activation, were found to be enhanced in cells cultured with nutraceuticals. The engraftment potential of ex vivo-expanded cells was studied in NOD/SCID mice. Mice that received MK cultured in the presence of DHA/AA engrafted better. There was a reduction in apoptosis and total reactive oxygen species (ROS) levels in the CD41(+) compartment of the test compared with control sets. The data suggest that these compounds probably exert their beneficial effect by modulating apoptotic and redox pathways.

CONCLUSIONS

Use of nutraceuticals like DHA and AA may prove to be a useful strategy for efficient generation of MK and platelets from cord blood cells, for future use in clinics and basic research.

A rationally designed agonist antibody fragment that functionally mimics thrombopoietin

By using rational design, antibody fragments (Fabs) that mimic thrombopoietin (TPO) were created. A peptide with cMpl receptor-binding capability was grafted into different complementarity-determining regions of a fully human Fab scaffold. Functional presentation of the peptide was optimized by using phage display and cell-based panning. Select antibodies and fragments containing two grafted peptides were assayed for their ability to stimulate the cMpl receptor in vitro. Several candidates demonstrated agonist activity in an in vitro cMpl receptor signaling reporter assay, including Fab59, which was estimated to be equipotent to TPO. Fab59 additionally was able to effectively stimulate platelet production in normal mice. These rationally designed mimetic Fabs may provide a therapeutic intervention for thrombocytopenia while avoiding the potential generation of neutralizing antibodies to endogenous TPO. Furthermore, this study demonstrates a method by which short-lived linear peptides with binding activity may be converted to more stable and potent agonists capable of activating cell surface receptors.

[Effects of liquid crystal-related compounds on human megakaryocytopoiesis and thrombopoiesis]

In the present study, the effects of liquid crystal-related compounds on the megakaryocytopoiesis and thrombopoiesis were evaluated in vitro using CD34+ cells prepared from human placental and umbilical cord blood (CB). About 20 kinds of compounds were tested for their effects on the clonal growth of CB CD34+ megakaryocytic progenitor cells (CFU-Meg) in plasma clot culture. The compounds, dissolved in DMSO, were added to the cultures within a concentration range of 10-100 nM. When used alone, none of the compounds supported the clonal growth of CFU-Meg. However, when thrombopoietin (TPO) was used as a growth factor, three compounds increased CFU-Meg clonal growth significantly, producing approximately 1.3-1.4 fold increases in the total number of megakaryocyte colonies in comparison with the control. These compounds promoted mainly mature CFU-Meg-derived small colonies, suggesting that their target is relatively mature CFU-Meg. These effective compounds were examined in liquid culture supplemented with TPO alone for 14 days. Although there was no evident promotion of the total number of cells harvested from the culture, two compounds suppressed cell growth significantly. Only one compound enhanced the generation of CFU-Meg in the harvested cells. Although these results do not indicate a strong correlation between the chemical structure of each compound and biological effectiveness, the incorporation of phenylpyridine and phenylpyrimidine and binding of a hydroxyl residue into the structure may play an important role in the activity. Thus, liquid crystal-related compounds whose biological action was previously unknown have been shown to act as regulators of hematopoiesis.

Efficient in vitro megakaryocyte maturation using cytokine cocktails optimized by statistical experimental design

OBJECTIVE

A multi-step statistical strategy was applied to quantify individual and interactive effects of cytokines on megakaryopoiesis and to determine the concentration of the selected cytokines that optimize ex vivo megakaryocyte (MK) expansion, maturation, and platelet production in stromal- and serum-free conditions.

MATERIALS AND METHODS

Immature MK were first generated from human CD34(+)-enriched cord blood cells cultured for 7 days in conditions favoring MK commitment. Then, the effect of different combinations of cytokines at various concentrations on MK differentiation and platelet production was tested on the day-7 MK.

RESULTS

A large-scale screening of 13 cytokines in the presence of thrombopoietin (TPO) using Placket-Burman designs (PBD) was initially performed to identify stimulators of MK maturation. Afterwards, a statistical analysis of the two-level factorial designs revealed that in the presence of TPO, MK maturation was significantly stimulated by stem cell factor (SCF), interleukin (IL)-6, and IL-9, whereas Flt-3 ligand (FL) had a positive effect only on the expansion of MK progenitors. In contrast, erythropoietin (EPO) and IL-8 were inhibitors of MK maturation. A response surface methodology was then used to optimize the concentrations of the selected cytokines (TPO, SCF, IL-6, and IL-9) and defined a new cytokine cocktail that maximized MK expansion and maturation. Importantly, the increased MK output was accompanied by a very high MK purity ( approximately 90%). Another optimum was also found at a higher SCF concentration, which further improved MK expansion and maturation, but reduced MK purity.

CONCLUSION

These statistical methods provide an efficient tool to analyze complex systems of cytokines and to develop promising ex vivo MK culture systems for clinical applications.

Ex Vivo Expansion of Megakaryocyte Progenitor Cells: Cord Blood Versus Mobilized Peripheral Blood

Thrombocytopenia is a problematic and potentially fatal occurrence after transplantation of cord blood stem cells. This problem may be alleviated by infusion of megakaryocyte progenitor cells. Here, we compared the ability of hematopoietic progenitor cells obtained from cord blood and expanded in culture to that of mobilized peripheral blood cells. The CD34(+) cells were plated for 10 days in presence of thrombopoietin (TPO) alone and combined with stem cell factor (SCF), Flt3-ligand (FL), interleukin-3 (IL-3), IL-6, and IL-11. Cells were analyzed for the CD41 and CD42b expression and for their ploidy status. Ex vivo produced platelets were enumerated. We show that (1) TPO alone was able to induce differentiation of CD34(+) cells into CD41(+) cells, with limited total leucocyte expansion; (2) the addition of SCF to TPO decreased significantly CD41(+) cell percentage in CB, but not in MPB; and (3) in CB, the addition of FL, IL-6, and IL-11 to TPO increased the leukocyte expansion with differentiation and terminal maturation into MK lineage. In these conditions, high numbers of immature CD34(+)CD41(+) MK progenitor cells were produced. Our results thereby demonstrate a different sensitivity of CB and MPB cells to SCF, with limited CB MK differentiation. This different sensitivity to SCF (produced constitutively by BM stromal cells) could explain the longer delay of platelet recovery after CB transplant. Nevertheless, in CB, the combination of TPO with FL, IL-6, and IL-11 allows generation of a suitable number of immature MK progenitor cells expressing both CD34 and CD41 antigens, which are supposed to be responsible for the platelet recovery after transplantation.

Generation of functional culture-derived platelets from CD34+ progenitor cells to study transgenes in the platelet environment

The possibility of evaluating the function of transgenes in platelets requires the generation of platelets from nucleated progenitor cells in vitro. In this article, we provide effective culture conditions for generating functional culture-derived (CD) human and mouse platelets from CD34(+) progenitor cells that allow expression of any foreign protein of interest. We have evolved an effective cytokine cocktail (thrombopoietin, stem cell factor, interleukin [IL]-1beta, IL-6) that induces a high yield of CD platelets and optimal shedding from cultivated megakaryocytes generated from CD34(+) progenitor cells. CD platelets showed similar functional and morphological characteristics compared with isolated blood platelets, including surface expression of platelet antigens (CD41, CD42, CD62P), aggregation, release of granule constituents (P-selectin, platelet factor 4, serotonin). Moreover, transmission electron microscopy revealed the presence of typical alpha- and dense granules and dense tubular system in CD platelets. Additionally, we showed that stable transgene expression in CD platelets can be performed through infection of CD34(+) progenitor cells using adenoviral vectors. Thus, we describe a methodology that enables studying functional consequences of transgenes of interest in the natural environment of platelets that may impose substantial impact on potential future platelet research and therapeutic target evaluation. The full text of this article is available online at http://circres.ahajournals.org.

Thrombopoietin as a drug: biologic expectations, clinical realities, and future directions

After the cloning of thrombopoietin (c-mpl ligand, Tpo) in 1994, 2 recombinant thrombopoietic growth factors, full-length glycosylated recombinant human Tpo (reHuTPO) and polyethylene glycol conjugated megakaryocyte growth and development factor (PEG-reHuMGDF), have been studied in humans in a variety of clinical settings. Both thrombopoietins are generally well tolerated if administered intravenously (IV). The c-mpl ligands produce a dose-related enhancement of platelet levels, reduce nonmyeloablative chemotherapy-induced mild thrombocytopenia, and mobilize hematopoietic progenitors. On September 11, 1998, the development of PEG-reHuMGDF was suspended in the U.S., due to formation of the neutralizing anti-Tpo antibody. Those neutralizing antibodies lead to thrombocytopenia and pancytopenia in some patients receiving subcutaneous (SC) PEG-reHuMGDF. Japanese investigators indicate that the probability of antibody formation against PEG-reHuMGDF is low when the drug is administered IV instead of SC. reHuTPO has a more favorable safety profile from the point of antibody production. The c-mpl ligands can improve apheresis yields when administered to normal platelet donors. Preliminary data about the use of PEG-reHuMGDF in myelodysplasia, aplastic anemia, and immune thrombocytopenic purpura are promising. Tpo is usually not effective in myeloablative thrombocytopenia when bone marrow hematopoietic progenitors are not present. The major obstacle for the thrombopoietins is their delayed action for managing clinical thrombocytopenia. This review will focus on the biologic basis, current clinical experience, and future directions for the use of thrombopoietic molecules as drugs. The identification of a safe, effective, and potent pharmacologic platelet growth factor could significantly improve the management of thrombocytopenia-induced bleeding.

Preclinical ex vivo expansion of cord blood hematopoietic stem and progenitor cells: duration of culture; the media, serum supplements, and growth factors used; and engraftment in NOD/SCID mice

BACKGROUND

Ex vivo expansion of cord blood (CB) hematopoietic stem and progenitor cells increases cell dose and may reduce the severity and duration of neutropenia and thrombocytopenia after transplantation. This study's purpose was to establish a clinically applicable culture system by investigating the use of cytokines, serum-free media, and autologous plasma for the expansion of CB cells and the engraftment of expanded product in nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice.

STUDY DESIGN AND METHODS

Enriched CB CD34+ cells were cultured in four media (Iscove's modified Dulbecco's medium with FCS, Gibco; X-Vivo-10, BioWhittaker; QBSF-60, Quality Biological; and StemSpan SFEM, Stem Cell Technologies) with four cytokine combinations (thrombopoietin [TPO], SCF, Flt-3 ligand [FL] with and without G-CSF, and/or IL-6). The effect of autologous CB plasma was also investigated. The read-out measures were evaluated on Days 8 and 12. After expansion at the optimized condition, cultured cells were transplanted into sublethally irradiated NOD/SCID mice. The engraftment of human CD45+ cells and subsets in the bone marrow, spleen, and peripheral blood was determined.

RESULTS

QBSF-60 or StemSpan SFEM supported high yields of early progenitors (CD34+ cells, <or= 64.8-fold; CD34+CD38- cells, 330-fold; CFU-granulocyte erythroid macrophage megakaryocyte [GEMM], 248-fold) and CFUs of the myeloid (CFU-GM, 407-fold) and erythroid (BFU/CFU-E, 144-fold) lineages. The expansion of the megakaryocytic lineage was consistently higher in X-Vivo-10 (CFU-megakaryocyte, 684-fold). Autologous plasma promoted colony formation but reduced CD34+ cells and CFU-GEMM. The addition of G-CSF or IL-6 improved cell yields; G-CSF was more effective for committed progenitors. Expansion products from cultures in QBSF-60 with the cytokines engrafted and differentiated into the myeloid and lymphoid lineages in NOD/SCID mice.

CONCLUSION

The data supported the strategy of expansion. The optimized condition may be applicable to clinical expansion for the abrogation or reduction of posttransplant cytopenia.

Promegapoietin, a family of chimeric growth factors, supports megakaryocyte development through activation of IL-3 and c-Mpl ligand signaling pathways

OBJECTIVE

The signaling pathways induced by promegapoietin (PMP), a family of chimeric growth factors that activate the human IL-3 and c-Mpl receptors, were investigated.

METHODS

The biological activity of PMP was examined by receptor binding, cell proliferation, ex vivo expansion of hematopoietic progenitor cells, and in vivo production of platelets. The activation of signaling pathways was examined by Western blot and Northern blot analyses.

RESULTS

Two PMP molecules, PMP-1 and PMP-1a, induced proliferation of cells expressing the IL-3 receptor, c-Mpl, or both receptors and bound to the IL-3 receptor and c-Mpl with high affinity. Ex vivo expansion assays using human bone marrow CD34(+) cells suggested that PMP-1 induced greater total cellular expansion as well as expansion of CD41(+) megakaryocytic precursor cells than IL-3 or c-Mpl ligand alone. Subcutaneous administration of 50 microg/kg of PMP-1 for 10 days to rhesus monkeys resulted in increased platelet production in vivo from a baseline of 357 +/- 45 x 10(3) cells/mL to 1376 +/- 151 x 10(3) cell/mL. PMP-1 induced phosphorylation of the beta(c) subunit of IL-3 receptor and c-Mpl, JAK2, and STAT5b, but not STAT3. PMP-1 induced greater expression of Pim-1, c-Myc, and cyclin D2 than did either an IL-3 receptor agonist or c-Mpl receptor agonist alone. The magnitude of induction of early response genes was similar for PMP and the coaddition of IL-3 receptor agonist and c-Mpl receptor agonist.

CONCLUSION

PMP combines the biological activities of IL-3 and c-Mpl ligand in a single molecule that can simultaneously activate signaling pathways induced by both these ligands.