Long-term platelet production assessed in NOD/SCID mice injected with cord blood CD34+ cells, thrombopoietin-amplified in clinical grade serum-free culture

Humanized mouse models for inherited thrombocytopenia studies

Inherited thrombocytopenia (IT) is a group of hereditary disorders characterized by a reduced platelet count as the main clinical manifestation, and often with abnormal platelet function, which can subsequently lead to impaired hemostasis. In the past decades, humanized mouse models (HMMs), that are mice engrafted with human cells or genes, have been widely used in different research areas including immunology, oncology, and virology. With advances of the development of immunodeficient mice, the engraftment, and reconstitution of functional human platelets in HMM permit studies of occurrence and development of platelet disorders including IT and treatment strategies. This article mainly reviews the development of humanized mice models, the construction methods, research status, and problems of using humanized mice for the in vivo study of human thrombopoiesis.

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.

A network-based method using a random walk with restart algorithm and screening tests to identify novel genes associated with Menière's disease

As a chronic illness derived from hair cells of the inner ear, Menière’s disease (MD) negatively influences the quality of life of individuals and leads to a number of symptoms, such as dizziness, temporary hearing loss, and tinnitus. The complete identification of novel genes related to MD would help elucidate its underlying pathological mechanisms and improve its diagnosis and treatment. In this study, a network-based method was developed to identify novel MD-related genes based on known MD-related genes. A human protein-protein interaction (PPI) network was constructed using the PPI information reported in the STRING database. A classic ranking algorithm, the random walk with restart (RWR) algorithm, was employed to search for novel genes using known genes as seed nodes. To make the identified genes more reliable, a series of screening tests, including a permutation test, an interaction test and an enrichment test, were designed to select essential genes from those obtained by the RWR algorithm. As a result, several inferred genes, such as CD4, NOTCH2 and IL6, were discovered. Finally, a detailed biological analysis was performed on fifteen of the important inferred genes, which indicated their strong associations with MD.

Thrombopoietin treatment of one graft in a double cord blood transplant provides early platelet recovery while contributing to long-term engraftment in NSG mice

Human cord blood (CB) hematopoietic stem cell (HSC) transplants demonstrate delayed early neutrophil and platelet recovery and delayed longer term immune reconstitution compared to bone marrow and mobilized peripheral blood transplants. Despite advances in enhancing early neutrophil engraftment, platelet recovery after CB transplantation is not significantly altered when compared to contemporaneous controls. Recent studies have identified a platelet-biased murine HSC subset, maintained by thrombopoietin (TPO), which has enhanced capacity for short- and long-term platelet reconstitution, can self-renew, and can give rise to myeloid- and lymphoid-biased HSCs. In previous studies, we have shown that transplantation of human CB CD34(+) cells precultured in TPO as a single graft accelerates early platelet recovery as well as yielding long-term repopulation in immune-deficient mice. In this study, using a double CB murine transplant model, we investigated whether TPO cultured human CB CD34(+) cells have a competitive advantage or disadvantage over untreated human CB CD34(+) cells in terms of (1) short-term and longer term platelet recovery and (2) longer term hematological recovery. Our studies demonstrate that the TPO treated graft shows accelerated early platelet recovery without impairing the platelet engraftment of untreated CD34(+) cells. Notably, this was followed by a dominant contribution to platelet production through the untreated CD34(+) cell graft over the intermediate to longer term. Furthermore, although the contribution of the TPO treated graft to long-term hematological engraftment was reduced, the TPO treated and untreated grafts both contributed significantly to long-term chimerism in vivo.

No Synergistic Effect of Cotransplantation of MSC and Ex Vivo TPO-Expanded CD34(+) Cord Blood Cells on Platelet Recovery and Bone Marrow Engraftment in NOD SCID Mice

After cord blood (CB) transplantation, early platelet recovery in immune-deficient mice is obtained by expansion of CB CD34(+) cells with thrombopoietin (TPO) as single growth factor. Moreover, improvement of hematopoietic engraftment has been shown by cotransplantation of mesenchymal stem cells (MSC). We investigated whether a combination of both approaches would further enhance the outcome of CB transplantation in NOD SCID mice. NOD SCID mice were transplanted with either CB CD34(+) cells, CD34(+) cells with MSC, TPO-expanded CD34(+) cells or TPO-expanded CD34(+) cells with MSC. We analyzed human platelet recovery in the peripheral blood (PB) from day 4 after transplantation onward and human bone marrow (BM) engraftment at week 6. The different transplants were assessed in vitro for their migration capacity and expression of CXCR4. TPO expansion improved the early platelet recovery in the PB of the mice. Cotransplantation of MSC with CD34(+) cells improved BM engraftment and platelet levels in the PB 6 weeks after transplantation. Combining TPO expansion and MSC cotransplantation, however, neither resulted in a more efficient early platelet recovery, nor in a better BM engraftment, nor even very low or absent BM engraftment occurred. In vitro, MSC boosted the migration of CD34(+) cells, suggesting a possible mechanism for the increase in engraftment. Our results show that cotransplantation of MSC with TPO-expanded CD34(+) cells at most combines, but does not increase the separate advantages of these different strategies. A combination of both strategies even adds a risk of non engraftment.

Cord blood CD34+ cells expanded on Wharton's jelly multipotent mesenchymal stromal cells improve the hematopoietic engraftment in NOD/SCID mice

OBJECTIVE

This study aims to investigate the capability of Wharton's jelly multipotent mesenchymal stromal cells (WJ-MSC) to support the in vitro expansion of hematopoietic stem/progenitor cells (HSPC) derived from cord blood (CB) in the absence of exogenous cytokines, and the effect on engraftment of the expanded cells in a mouse model.

METHODS

CB-CD34+ cells were seeded on WJ-MSC layer and cultured in HP01 serum-free medium. Day-7 and day-13 expanded cells were transplanted in NOD/SCID mice. After 8 wk, engraftment was evaluated in mouse bone marrow as percentage of human CD45+ cells.

RESULTS

CD34+ population was expanded without increasing the differentiation rate. Co-culture increased the expansion of the CD34+ cells by 2.0 and 7.3 times after 7 and 13 d, respectively, and maintained the CD34+ cells up to day 20. In particular, earlier CD34+/CD90+ and CD34+/CD33- subtypes were increased. An advantage of the day-7 co-cultured HSPC in respect of HSPC at day 0 in the engraftment of NOD/SCID mice was obtained both as percentage of mice engrafted (100% vs. 75%) and as percentage of chimerism.

CONCLUSIONS

Although the increase in hematopoietic progenitors is not dramatic as in the presence of added cytokines, this study demonstrates the effectiveness of the WJ-MSC not only to preserve the CD34+ population but also to improve the repopulating efficacy of the amplified HSPC, also in the absence of added cytokines and growth factors.

Functional characterization of TPO-expanded CD34+ cord blood cells identifies CD34- CD61- cells as platelet-producing cells early after transplantation in NOD/SCID mice and rCD34+ cells as CAFC colony-forming cells

Transplantation of thrombopoietin (TPO)-expanded cord blood CD34(+) cells accelerates human platelet recovery in NOD/SCID mice. It is unknown which subpopulations of the TPO-expanded cells mediate accelerated platelet recovery and bone marrow (BM) engraftment. In this study, the contribution of these subpopulations to human platelet appearance in the blood and BM engraftment was studied in NOD/SCID mice. Following transplantation of CD34(-) /CD61(-)/lineage(-) cells (Lin(-)), human platelets were detected in the blood of recipient mice from day 4. Both time to platelet recovery and blood platelet counts at 6 weeks after transplantation showed Lin(-) dose dependence. The Lin(-) population was virtually negative for lineage marker expression and lacked CD42b expression but was heterogeneous with regard to CD36 and CD38 expression, reflecting a population in transit but not fully committed toward the megakaryocyte (MK) lineage. Although no definitive phenotype could be established of the cells generating prompt platelet production and cells generating platelets 6 weeks after transplantation, this relatively heterogeneous Lin(-) population is prerequisite to accelerate platelet recovery in vivo. The interval to platelet recovery after transplantation of the CD34(+) cells remaining after expansion (rCD34(+)) was similar to mice transplanted with nonexpanded CD34(+) cells, although the total platelet counts and the engraftment levels in the BM were lower. Cobblestone area-forming cell colony-forming cells resided mostly in the rCD34(+) population. The pro-MK CD61(+) cells did not contribute to human platelet recovery or engraftment in the BM. Our study shows that not all expanded cells appear critical for transplantation. These data support that functional characterization of the expanded cell populations is warranted to make future expansion protocols suitable for clinical application.

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.

Effects of extracellular matrix proteins on the growth of haematopoietic progenitor cells

Umbilical cord blood (UCB) transplantation and haematological recovery are currently limited by the amount of haematopoietic progenitor cells (HPCs) present in each unit. HPCs and haematopoietic stem cells (HSCs) normally interact with cells and extracellular matrix (ECM) proteins present within the endosteal and vascular niches. Hence, we investigated whether coating of culture surfaces with ECM proteins normally present in the marrow microenvironment could benefit the ex vivo expansion of HPCs. Towards this, collagen types I and IV (COL I and IV), laminin (LN) and fibronectin (FN) were tested individually or as component of two ECM-mix complexes. Individually, ECM proteins had both common and unique properties on the growth and differentiation of UCB CD34+ cells; some ECM proteins favoured the differentiation of some lineages over that of others (e.g. FN for erythroids), some the expansion of HPCs (e.g. LN and megakaryocyte (MK) progenitor) while others had less effects. Next, two ECM-mix complexes were tested; the first one contained all four ECM proteins (4ECMp), while the second 'basement membrane-like structure' was without COL I (3ECMp). Removal of COL I led to strong reductions in cell growth and HPCs expansion. Interestingly, the 4ECMp-mix complex reproducibly increased CD34+ (1.3-fold) and CD41+ (1.2-fold) cell expansions at day 6 (P < 0.05) versus control, and induced greater myeloid progenitor expansion (P < 0.05) than 3ECMp. In conclusion, these results suggest that optimization of BM ECM protein complexes could provide a better environment for the ex vivo expansion of haematopoietic progenitors than individual ECM protein.

Irradiated Mesenchymal Stem Cells improve the ex vivo expansion of Hematopoietic Progenitors by partly mimicking the bone marrow endosteal environment

Mesenchymal Stem Cells (MSCs) regulate the growth and differentiation of Hematopoietic Progenitor cells (HPCs) through the release of soluble factors or through their differentiation into osteoblasts. We recently demonstrated that expansion of megakaryocyte (MK) progenitors ex vivo had reached a plateau when CD34(+) cells were grown with two optimized cytokine cocktails developed for the growth of MK. Hence, we sought to determine whether co-culture of CD34(+) cells with Bone Marrow (BM) MSCs could further increase the expansion of myeloid and MK progenitors. First, we tested the impact of cell-cell contact and pre-irradiation treatment of the MSCs to identify the condition that best supports HPC expansion. This screen revealed that HPC expansions were generally greater in the non-contact conditions, and that pre-irradiation of the MSCs appeared to be of added benefits. Improved expansion of both myeloid and MK progenitors in co-culture with irradiated MSCs without contact was subsequently confirmed. Next, cytokine array profiling was carried out to investigate why irradiation promoted progenitor expansion. This revealed that the levels of as many as 33 factors were potentially altered. ELISA confirmed the significant up regulation of NT-3 and IGFBP-2. Since, these factors are known to be released by and important for osteogenic and endothelial cells, we investigated and confirmed that irradiation of MSCs induced their rapid differentiation into osteogenic-like cells, but not into endothelial-like cells. Supporting this finding, expansions of myeloid and MK progenitors were increased when CD34(+) cells were co-culture with MSCs-derived osteoblasts. Altogether, these results indicate that the improved expansion of HPCs obtained with irradiated MSCs is due in part to their differentiation into osteoblast-like cells, thereby recreating an endosteal-like environment that provides improved support for HPCs expansion.

Generation of hematopoietic humanized mice in the newborn BALB/c-Rag2null Il2rγnull mouse model: a multivariable optimization approach

Hematopoietic humanized mice generated via transplantation of human hematopoietic stem cells (hHSCs) into immunodeficient mice are a valuable tool for studying development and function of the human immune system. This study was performed to generate a protocol that improves development and quality of humanized mice in the BALB/c-Rag2(null)Il2rγ(null) strain, testing route of injection, in vitro culture and freezing of hHSCs, types of cytokines in the culture, and co-injection of lineage-depleted CD34(-) cells. Specific hHSC culturing conditions and the addition of support cells were found to increase the frequency, and human hematopoietic chimerism, of humanized mice. The optimized protocol resulted in BALB/c-Rag2(null)Il2rγ(null) humanized mice displaying more consistent human hematopoietic and lymphoid engraftment. Thus, hematopoietic humanized mice generated on a BALB/c immunodeficient background represent a useful model to study the human immune system.

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.

Mesenchymal stem cells from bone marrow show a stronger stimulating effect on megakaryocyte progenitor expansion than those from non-hematopoietic tissues

In order to evaluate whether mesenchymal stem cells (MSCs) from non-hematopoietic tissues are able to regulate megakaryocytopoiesis, we identified human MSCs from adult bone marrow (ABM), fetal pancreas (FPan) and umbilical cord (UC), and their abilities to support megakaryocyte (MK) differentiation from CD34(+) hematopoietic progenitor cells (HPCs) were comparatively studied. First, MSCs were isolated from ABM, FPan and UC then their growth kinetics, molecular characterization and mesodermal differentiation capacity were determined. ABM-MSCs, FPan-MSCs and UC-MSCs were irradiated and cocultured with human umbilical cord blood (UCB) CD34(+) cells, and the expansion efficiency of MK progenitor cells and MK formation were analysed and compared. Finally, SCF, IL-6 and GM-CSF expression by the three types of MSCs were also examined. Our results showed that FPan-MSCs and UC-MSCs shared most of the characteristic of ABM-MSCs, including morphology, immunophenotype, adipogenic and osteogenic differentiation potentials. Compared with ABM-MSCs, fetal MSCs had higher proliferative capacity. After 7 days' coculture, the maximal production of CD34(+)/CD41a(+) cells was obtained in a group of CD34(+) HPCs + ABM-MSCs. Furthermore, this group produced more MK colonies than other groups (p < 0.05). Surface antigen and ploidy analysis morphological observation demonstrated that a proportion of expanded cells in each group differentiated into mature MKs. ABM-MSCs, FPan-MSCs and UC-MSCs were revealed to express SCF, IL-6 and GM-CSF at mRNA level. We conclude that FPan-MSCs and UC-MSCs have the ability to promote megakaryocytopoiesis, while ABM-MSCs expand more MK progenitor cells from CD34(+) HPCs than MSCs from non-hematopoietic tissues and CD34(+) cells alone.

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.

Expansion of cord blood CD34 cells in presence of zVADfmk and zLLYfmk improved their in vitro functionality and in vivo engraftment in NOD/SCID mouse

Background

Cord blood (CB) is a promising source for hematopoietic stem cell transplantations. The limitation of cell dose associated with this source has prompted the ex vivo expansion of hematopoietic stem and progenitor cells (HSPCs). However, the expansion procedure is known to exhaust the stem cell pool causing cellular defects that promote apoptosis and disrupt homing to the bone marrow. The role of apoptotic machinery in the regulation of stem cell compartment has been speculated in mouse hematopoietic and embryonic systems. We have consistently observed an increase in apoptosis in the cord blood derived CD34⁺ cells cultured with cytokines compared to their freshly isolated counterpart. The present study was undertaken to assess whether pharmacological inhibition of apoptosis could improve the outcome of expansion.

Methodology/Principal Findings

CB CD34⁺ cells were expanded with cytokines in the presence or absence of cell permeable inhibitors of caspases and calpains; zVADfmk and zLLYfmk respectively. A novel role of apoptotic protease inhibitors was observed in increasing the CD34⁺ cell content of the graft during ex vivo expansion. This was further reflected in improved in vitro functional aspects of the HSPCs; a higher clonogenicity and long term culture initiating potential. These cells sustained superior long term engraftment and an efficient regeneration of major lympho-myeloid lineages in the bone marrow of NOD/SCID mouse compared to the cells expanded with growth factors alone.

Conclusion/Significance

Our data show that, use of either zVADfmk or zLLYfmk in the culture medium improves expansion of CD34⁺ cells. The strategy protects stem cell pool and committed progenitors, and improves their in vitro functionality and in vivo engraftment. This observation may complement the existing protocols used in the manipulation of hematopoietic cells for therapeutic purposes. These findings may have an impact in the CB transplant procedures involving a combined infusion of unmanipulated and expanded grafts.

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.

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.

Umbilical cord transplantation: epilogue

The field of cord blood transplantation has come a long way since the first transplant more than 20 years ago. Advancements in the field will require continuing efforts to better understand hematopoietic stem and progenitor cell function and engraftment. Cautious optimism is inherent in the potential relevance and applicability of nonhematopoietic stem and progenitor cell types found in cord blood, and induced pluripotent stem cells generated from cord blood cells. Rigorous investigations and close interactions between scientific and clinical investigators are required to translate human in vitro and animal in vivo findings into clinical utility.

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.