Transplantation of human peripheral blood CD34-positive cells in combination with ex vivo generated megakaryocytes results in fast platelet formation in NOD/SCID mice

Pre-clinical development of a cryopreservable megakaryocytic cell product capable of sustained platelet production in mice

BACKGROUND

Platelet (PLT) transfusions are the most effective treatments for patients with thrombocytopenia. The growing demand for PLT transfusion products is compounded by a limited supply due to dependency on volunteer donors, a short shelf-life, risk of contaminating pathogens, and alloimmunization. This study provides preclinical evidence that a third-party, cryopreservable source of PLT-generating cells has the potential to complement presently available PLT transfusion products.

STUDY DESIGN AND METHODS

CD34+ hematopoietic stem/progenitor cells derived from umbilical cord blood (UCB) units were used in a simple and efficient culture system to generate a cell product consisting of megakaryocytes (MKs) at different stages of development. The cultures thus generated were evaluated ex vivo and in vivo before and after cryopreservation.

RESULTS

We generated a megakaryocytic cell product that can be cryopreserved without altering its phenotypical and functional capabilities. The infusion of such a product, either fresh or cryopreserved, into immune-deficient mice led to production of functional human PLTs which were observed within a week after infusion and persisted for 8 weeks, orders of magnitude longer than that observed after the infusion of traditional PLT transfusion products. The sustained human PLT engraftment was accompanied by a robust presence of human cells in the bone marrow (BM), spleen, and lungs of recipient mice.

CONCLUSION

This is a proof-of-principle study demonstrating the creation of a cryopreservable megakaryocytic cell product which releases functional PLTs in vivo. Clinical development of such a product is currently being pursued for the treatment of thrombocytopenia in patients with hematological malignancies.

Arachidonic acid and Docosahexanoic acid enhance platelet formation from human apheresis-derived CD34+ cells

An Aberration in megakaryopoiesis and thrombopoiesis, 2 important processes that maintain hemostasis, leads to thrombocytopenia. Though platelet transfusions are used to treat this condition, blood banks frequently face a shortage of platelets. Therefore, methods to generate platelets on a large scale are strongly desirable. However, to generate megakaryocytes (MKs) and platelets (PLTs) in numbers sufficient for clinical application, it is essential to understand the mechanism of platelet production and explore efficient strategies accordingly. We have earlier reported that the N-6 and N-3 poly-unsaturated fatty acids (PUFAs), Arachidonic acid (AA)/Docosahexanoic acid (DHA) have beneficial effect on the generation of MKs and PLTs from umbilical cord blood derived CD34⁺ cells. Here we tested if a similar effect is observed with peripheral blood derived CD34⁺ cells, which are more commonly used in transplantation settings. We found a significant enhancement in cell numbers, surface marker expression, cellular ploidy and expression of cytoskeletal components during PLT biogenesis in cultures exposed to media containing AA/DHA than control cultures that were not exposed to these PUFAs. The test cells engrafted more efficiently in NOD/SCID mice than control cells. AA/DHA appears to have enhanced MK/PLT generation through upregulation of the NOTCH and AKT pathways. Our data show that PUFAs could be valuable additives in the culture system for large scale production of platelets for clinical applications.

Safety and Efficacy of Megakaryocytes Induced from Hematopoietic Stem Cells in Murine and Nonhuman Primate Models

Because of a lack of platelet supply and a U.S. Food and Drug Administration‐approved platelet growth factor, megakaryocytes have emerged as an effective substitute for alleviating thrombocytopenia. Here, we report the development of an efficient two‐stage culture system that is free of stroma, animal components, and genetic manipulations for the production of functional megakaryocytes from hematopoietic stem cells. Safety and functional studies were performed in murine and nonhuman primate models. One human cryopreserved cord blood CD34⁺ cell could be induced ex vivo to produce up to 1.0 × 10⁴ megakaryocytes that included CD41a⁺ and CD42b⁺ cells at 82.4% ± 6.1% and 73.3% ± 8.5% (mean ± SD), respectively, yielding approximately 650‐fold higher cell numbers than reported previously. Induced human megakaryocytic cells were capable of engrafting and producing functional platelets in the murine xenotransplantation model. In the nonhuman primate model, transplantation of primate megakaryocytic progenitors increased platelet count nadir and enhanced hemostatic function with no adverse effects. In addition, primate platelets were released in vivo as early as 3 hours after transplantation with autologous or allogeneic mature megakaryocytes and lasted for more than 48 hours. These results strongly suggest that large‐scale induction of functional megakaryocytic cells is applicable for treating thrombocytopenic blood diseases in the clinic. Stem Cells Translational Medicine2017;6:897–909

Polyunsaturated fatty acids confer cryoresistance on megakaryocytes generated from cord blood and also enhance megakaryocyte production from cryopreserved cord blood cells

BACKGROUND AIMS

Previous data have shown that the addition of docosahexanoic acid (DHA)/arachidonic acid (AA) has a beneficial effect on cytokine-mediated in vitro generation of megakaryocytes (MK) from umbilical cord blood (UCB).Cryopreservation forms an inherent part of UCB banking and MK progenitors are known to be very sensitive to the stresses of freezing. It is therefore imperative to generate functional cells from cryopreserved cells, and the generated cells need to be cryopreserved until used. In the present study, cryopreservation of ex vivo-expanded MK as well as MK generation from cryopreserved UCB samples was investigated.

METHODS

MK generated with or without DHA/AA were cryopreserved in freezing medium containing 10% dimethyl sulfoxide (DMSO). Freezing efficacy was tested by quantitating MK after revival. Cryopreserved CD34(+) cells were cultured with stem cell factor (SCF) and thrombopoietin (TPO), in the presence and absence of DHA/AA for 10 days, and then quantitated for MK. Results. We observed a 1.5-3-fold increase in MK numbers, their progenitor content and their expression of phenotypic markers and MK-related transcription factors. DHA/AA sets showed a 2-5-fold improved engraftment in NOD/SCID mice. These data showed that the beneficial effect of DHA/AA obtained during MK expansion was not altered after freezing stress. The enhancement in MK generation obtained from fresh cord blood (CB) cells was reproduced with comparable efficiency when we used cryopreserved CB samples.

CONCLUSIONS

Taken together, our data suggest that in vitro-generated DHA/AA MK survive cryoinjuries in a functionally better state. DHA/AA support a more efficient generation of MK from cryopreserved UCB.

Model systems of genetically modified platelets

Although platelets are the smallest cells in the blood, they are implied in various processes ranging from immunology and oncology to thrombosis and hemostasis. Many large-scale screening programs, genome-wide association, and "omics" studies have generated lists of genes and loci that are probably involved in the formation or physiology of platelets under normal and pathologic conditions. This creates an increasing demand for new and improved model systems that allow functional assessment of the corresponding gene products in vivo. Such animal models not only render invaluable insight in the platelet biology, but in addition, provide improved test systems for the validation of newly developed anti-thrombotics. This review summarizes the most important models to generate transgenic platelets and to study their influence on platelet physiology in vivo. Here we focus on the zebrafish morpholino oligonucleotide technology, the (platelet-specific) knockout mouse, and the transplantation of genetically modified human or murine platelet progenitor cells in myelo-conditioned mice. The various strengths and pitfalls of these animal models are illustrated by recent examples from the platelet field. Finally, we highlight the latest developments in genetic engineering techniques and their possible application in platelet research.

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.

A defined, feeder-free, serum-free system to generate in vitro hematopoietic progenitors and differentiated blood cells from hESCs and hiPSCs

Human ESC and iPSC are an attractive source of cells of high quantity and purity to be used to elucidate early human development processes, for drug discovery, and in clinical cell therapy applications. To efficiently differentiate pluripotent cells into a pure population of hematopoietic progenitors we have developed a new 2-dimensional, defined and highly efficient protocol that avoids the use of feeder cells, serum or embryoid body formation. Here we showed that a single matrix protein in combination with growth factors and a hypoxic environment is sufficient to generate from pluripotent cells hematopoietic progenitors capable of differentiating further in mature cell types of different lineages of the blood system. We tested the differentiation method using hESCs and 9 iPSC lines generated from different tissues. These data indicate the robustness of the protocol providing a valuable tool for the generation of clinical-grade hematopoietic cells from pluripotent cells.

Individual and synergistic cytokine effects controlling the expansion of cord blood CD34(+) cells and megakaryocyte progenitors in culture

BACKGROUND AIMS

Expansion of hematopoietic progenitors ex vivo is currently investigated as a means of reducing cytopenia following stem cell transplantation. The principal objective of this study was to develop a new cytokine cocktail that would maximize the expansion of megakaryocyte (Mk) progenitors that could be used to reduce periods of thrombocytopenia.

METHODS

We measured the individual and synergistic effects of six cytokines [stem cell factor (SCF), FLT-3 ligand (FL), interleukin (IL)-3, IL-6, IL-9 and IL-11] commonly used to expand cord blood (CB) CD34(+) cells on the expansion of CB Mk progenitors and major myeloid populations by factorial design.

RESULTS

These results revealed an elaborate array of cytokine individual effects complemented by a large number of synergistic and antagonistic interaction effects. Notably, strong interactions with SCF were observed with most cytokines and its concentration level was the most influential factor for the expansion and differentiation kinetics of CB CD34(+) cells. A response surface methodology was then applied to optimize the concentrations of the selected cytokines. The newly developed cocktail composed of SCF, thrombopoietin (TPO) and FL increased the expansion of Mk progenitors and maintained efficient expansion of clonogenic progenitors and CD34(+) cells. CB cells expanded with the new cocktail were shown to provide good short- and long-term human platelet recovery and lymphomyeloid reconstitution in NOD/SCID mice.

CONCLUSIONS

Collectively, these results define a complex cytokine network that regulates the growth and differentiation of immature and committed hematopoietic cells in culture, and confirm that cytokine interactions have major influences on the fate of hematopoietic cells.

Platelet Precursor Cells Can Be Generated from Cultured Human CD34+ Progenitor Cells But Display Recirculation into Hematopoietic Tissue upon Transfusion in Mice

BACKGROUND: Whereas ex vivo expanded megakaryocytic progenitor cells have been investigated for their ability to support platelet regeneration, the question whether more mature platelet-like particles expanded from hematopoietic progenitor cells may be useful for transfusion purposes remains largely elusive. METHODS: Human peripheral blood progenitor cells (PBPCs) were enriched using surface expression of CD34 by immunoselection. CD34+ enriched PBPCs were expanded ex vivo in serum-free medium supplemented with cytokines. As a proof-of-principle, distribution of expanded CD61+ particles was analyzed after transfusion into Non-Obese Diabetic/ Severe Combined Immunodeficiency (NOD/SCID) mice. RESULTS: Highest ex vivo expansion for CD41+/CD61 + cells was achieved when medium was supplemented with SCF, TPO and IL-3. During expansion culture, CD34 marker expression decreased from 85 to 2-8%, while megakaryocytic cells appeared and CD41 and CD61 expression increased from 3 to about 30%. After transfusion of the expanded cells in NOD/SCID mice, CD61 + cells located mainly to bone marrow and to a lesser degree to spleen, but also circulated in blood. CONCLUSIONS: Platelet-like particles using cytokine-substituted serumfree medium can be generated efficiently from CD34+ expansion cultures, but mainly home to hematopoietic tissue.

Human platelets produced in nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice upon transplantation of human cord blood CD34(+) cells are functionally active in an ex vivo flow model of thrombosis

Xenotransplantation systems have been used with increasing success to better understand human hematopoiesis and thrombopoiesis. In this study, we demonstrate that production of human platelets in nonobese diabetic/severe combined immunodeficient mice after transplantation of unexpanded cord-blood CD34(+) cells was detected within 10 days after transplantation, with the number of circulating human platelets peaking at 2 weeks (up to 87 x 10(3)/microL). This rapid human platelet production was followed by a second wave of platelet formation 5 weeks after transplantation, with a population of 5% still detected after 8 weeks, attesting for long-term engraftment. Platelets issued from human hematopoietic stem cell progenitors are functional, as assessed by increased CD62P expression and PAC1 binding in response to collagen-related peptide and thrombin receptor-activating peptide activation and their ability to incorporate into thrombi formed on a collagen-coated surface in an ex vivo flow model of thrombosis. This interaction was abrogated by addition of inhibitory monoclonal antibodies against human glycoprotein Ibalpha (GPIbalpha) and GPIIb/IIIa. Thus, our mouse model with production of human platelets may be further explored to study the function of genetically modified platelets, but also to investigate the effect of stimulators or inhibitors of human thrombopoiesis in vivo.

Characterization and transplantation of induced megakaryocytes from hematopoietic stem cells for rapid platelet recovery by a two-step serum-free procedure

OBJECTIVE

A complete process for mass generation of megakaryocytes from hematopoietic stem cells under serum-free conditions has great clinical potential for rapid platelet reconstruction in thrombocytopenia patients. We have previously reported on the generation of an optimized serum-free medium (serum-free hematopoietic stem cell medium) for ex vivo expansion of CD34(+) cells. Here, we further generated large amounts of functional megakaryocytes from serum-free expanded CD34(+) cells under a complete and optimal serum-free condition for complying with clinical regulations.

MATERIALS AND METHODS

Serum substitutes and cytokines were screened and optimized for their concentration for megakaryocyte generation by systemically methods. Serum-free induced megakaryocytes were characterized by surface antigens, gene expression, ex vivo megakaryocyte activation ability, and ability of megakaryocyte and platelet recovery in nonobese diabetic/severe combined immunodeficient mice.

RESULTS

The optimal serum-free megakaryocyte induction medium was Iscove's modified Dulbecco's medium containing serum substitutes (i.e., human serum albumin, human insulin, and human transferrin) and a cytokine cocktail (i.e., thrombopoietin, stem cell factor, Fms-like tyrosine kinase 3 ligand, interleukin-3, interleukin-6, interleukin-9, and granulocyte-macrophage colony-stimulating factor). After induction, induced megakaryocytes expressed CD41a and CD61 surface antigens, nuclear factor erythroid-derived 2 and GATA-1 transcription factors and megakaryocyte activation ability. Importantly, transplantation of induced megakaryocytes could accelerate megakaryocyte and platelet recovery in irradiated nonobese diabetic/severe combined immunodeficient mice.

CONCLUSION

In conclusion, we have developed a serum-free megakaryocyte induction medium, and the combination of serum-free megakaryocyte and serum-free hematopoietic stem cell media can generate a large amount of functional megakaryocytes efficiently. Our method represents a promising source of megakaryocytes and platelets for future cell therapy.

Detecting minimal residual disease in neuroblastoma: the superiority of a panel of real-time quantitative PCR markers

BACKGROUND

PCR-based detection of minimal residual disease (MRD) in neuroblastoma (NB) patients can be used for initial staging and monitoring therapy response in bone marrow (BM) and peripheral blood (PB). PHOX2B has been identified as a sensitive and specific MRD marker; however, its expression varies between tumors. Therefore, a panel of markers could increase sensitivity.

METHODS

To identify additional MRD markers for NB, we selected genes by comparing SAGE (serial analysis of gene expression) libraries of healthy and NB tissues followed by extensive real-time quantitative PCR (RQ-PCR) testing in samples of tumors (n = 56), control BM (n = 51), PB (n = 37), and cell subsets. The additional value of a panel was determined in 222 NB samples from 82 Dutch stage 4 NB patients (54 diagnosis BM samples, 143 BM samples during/after treatment, and 25 PB samples).

RESULTS

We identified 2 panels of specific RQ-PCR markers for MRD detection in NB patients: 1 for analysis of BM samples (PHOX2B, TH, DDC, CHRNA3, and GAP43) and 1 for analysis of PB samples (PHOX2B, TH, DDC, DBH, and CHRNA3). These markers all showed high expression in NB tumors and no or low expression in control BM or PB samples. In patients' samples, the PHOX2B marker detected most positive samples. In PB samples, however, 3 of 7 PHOX2B-negative samples were positive for 1 or more markers, and in BM examinations during treatment, 7% (6 of 86) of the PHOX2B-negative samples were positive for another marker.

CONCLUSIONS

Because of differences in the sensitivities of the markers in BM and PB, we advise the use of 2 different panels to detect MRD in these compartments.