Ex vivo expansion of umbilical cord blood stem cells for transplantation: growing knowledge from the hematopoietic niche

Cord blood transplantation and stem cell regenerative potential

The past 20 years of experience with umbilical cord blood transplantation have demonstrated that cord blood is effective in the treatment of a spectrum of diseases, including hematological malignancies, bone marrow failure, hemoglobinopathies, and inborn errors of metabolism. Cord blood can be obtained with ease and then safely cryopreserved for either public or private use without loss of viability. As compared to other unrelated donor cell sources, cord blood transplantation allows for greater human leukocyte antigen disparity without a corresponding increase in graft-vs.-host disease. Moreover, cord blood has a lower risk of transmitting infections by latent viruses and is less likely to carry somatic mutations than other adult cells. Recently, multiple populations of stem cells with primitive stem cell properties have been identified from cord blood. Meanwhile, there is an increasing interest in applying cord blood mononuclear cells or enriched stem cell populations to regenerative therapies. Accumulating evidence has suggested functional improvements after cord blood transplantation in various animal models for treatments of cardiac infarction, diabetes, neurological diseases, etc. In this review, we will summarize the most recent updates on clinical applications of cord blood transplantation and the promises and limitations of cell-based therapies for tissue repair and regeneration.

Primary cells as feeder cells for coculture expansion of human hematopoietic stem cells from umbilical cord blood--a comparative study

Although umbilical cord blood (UCB) has been widely accepted as an alternative source of hematopoietic stem cells (HSC) for transplantation, its use in adults is restricted because of low absolute HSC numbers. To overcome this obstacle, expansion of HSC in coculture with feeder cells is a promising possibility. In this study, we compared the potential of three human primary cell types, namely, mesenchymal stem cells (MSC), human umbilical cord vein endothelial cells (HUVEC), and Wharton's jelly cells (WJC), for use as feeder cells in a potentially clinically applicable coculture system. In first experiments, we evaluated procedures needed to obtain feeder cells, the possibility to separate them from cells derived from CD34(+) cells after coculture, their ability to activate allogeneic T cells, and their survival in CD34(+)-adapted medium. Finally, we compared their support for UCB-derived CD34(+) expansion. MSC and WJC were superior to HUVEC in terms of ease and reliability of isolation procedures needed. None of the potential feeder cells expressed CD34 or CD45, thus providing markers for cell sorting after coculture. Other markers (CD31, CD90, CD105, CD166) were expressed differently on feeder cell types. While MSC in higher concentrations did not activate allogeneic T cells, those were stimulated by lower concentrations of MSC as shown by CD25, CD69, and CD71 expression. In contrast, HUVEC and WJC were proven to activate T cells at all ratios tested. Feeder cells survived a 7-day culture in CD34(+)-adapted medium. In cocultures of UCB CD34(+)cells with primary feeder cells, mononuclear cell expansion was 30- to 60-fold, colony-forming cell expansion 20- to 40-fold, and cobblestone area-forming cell expansion 10- to 50-fold. We conclude that after a careful further evaluation especially of their immunological properties, all three primary cell types might possibly be suitable for use in a potentially clinically applicable system for expansion from UCB CD34(+)cells, with WJC being best choice and MSC still superior to HUVEC.

Cardiac cell therapies: the next generation

Although significant advances have been made in terms of pharmacological, catheter-based, and surgical palliation, heart failure remains a fatal disease. As a curative concept, regenerative medicine aims at the restoration of the physiologic cellular composition of diseased organs. So far, clinical cardiac regeneration attempts have only been moderately successful, but a better understanding of myocardial cell homeostasis and somatic as well as embryonic stem cell biology has opened the door for the development of more potent therapeutic cardiac regeneration strategies. Accumulating evidence indicates that the postnatal mammalian heart retains a pool of tissue-specific progenitor cells and is also repopulated by cells from extracardiac sources. However, this intrinsic myocardial regeneration potential clearly needs to be augmented by either manipulation of the cell cycle of differentiated cells, activation of resident cardiac progenitor cells, and/or the transplantation of exogenous cells. This review summarizes the recent developments in cardiac regenerative medicine, many of which may find their way into the clinical setting in the foreseeable future.

Aryl hydrocarbon receptor antagonists promote the expansion of human hematopoietic stem cells

Although practiced clinically for more than 40 years, the use of hematopoietic stem cell (HSC) transplants remains limited by the ability to expand these cells ex vivo. An unbiased screen with primary human HSCs identified a purine derivative, StemRegenin 1 (SR1), that promotes the ex vivo expansion of CD34+ cells. Culture of HSCs with SR1 led to a 50-fold increase in cells expressing CD34 and a 17-fold increase in cells that retain the ability to engraft immunodeficient mice. Mechanistic studies show that SR1 acts by antagonizing the aryl hydrocarbon receptor (AHR). The identification of SR1 and AHR modulation as a means to induce ex vivo HSC expansion should facilitate the clinical use of HSC therapy.

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.

Microliter-bioreactor array with buoyancy-driven stirring for human hematopoietic stem cell culture

This work presents the development of an array of bioreactors where finely controlled stirring is provided at the microliter scale (100-300 mul). The microliter-bioreactor array is useful for performing protocol optimization in up to 96 parallel experiments of hematopoietic stem cell (HSC) cultures. Exploring a wide range of experimental conditions at the microliter scale minimizes cost and labor. Once the cell culture protocol is optimized, it can be applied to large-scale bioreactors for stem cell production at the clinical level. The controlled stirring inside the wells of a standard 96-well plate is provided by buoyancy-driven thermoconvection. The temperature and velocity fields within the culture volume are determined with numerical simulations. The numerical results are verified with experimental velocity measurements using microparticle image velocimetry (muPIV) and are used to define feasible experimental conditions for stem cell cultures. To test the bioreactor array's functionality, human umbilical cord blood-derived CD34(+) cells were cultured for 7 days at five different stirring conditions (0.24-0.58 mums) in six repeated experiments. Cells were characterized in terms of proliferation, and flow cytometry measurements of viability and CD34 expression. The microliter-bioreactor array demonstrates its ability to support HSC cultures under stirred conditions without adversely affecting the cell behavior. Because of the highly controlled operative conditions, it can be used to explore culture conditions where the mass transport of endogenous and exogenous growth factors is selectively enhanced, and cell suspension provided. While the bioreactor array was developed for culturing HSCs, its application can be extended to other cell types.

Challenges in umbilical cord blood stem cell banking for stem cell reviews and reports

Twenty years has passed since the first report of a successful cord blood transplant was reported in 1989 in a child with Fanconi's anemia. During these 20 years, the cord blood field has had dramatic growth, with over 400,000 cord blood units donated and stored worldwide for unrelated use. Approximately, 14,000 unrelated cord blood transplants have been performed to date for patients with hematologic malignancies and bone marrow disorders, and who do not have matched family or unrelated donors. In contrast, about 900,000 cord blood units have been stored privately for personal use, with about 100 autologous transplants performed. Twenty years ago, due to the low cell dose, cord blood transplants were only performed in children. Today, with the use of better banking techniques, reduced intensity transplants, and double cord blood transplantation, the majority of cord blood transplants are being performed in adults. In this chapter, we review the scientific basis for cord blood transplantation, and outcome data in both pediatric and adult transplantation. We will then focus on the recent concerns regarding private and public cord blood banking. Finally, we discuss the future of cord blood transplantation, and the exciting work beginning outside of oncology.

Systematic delineation of optimal cytokine concentrations to expand hematopoietic stem/progenitor cells in co-culture with mesenchymal stem cells

The major obstacle to the widespread use of umbilical cord blood (UCB) in hematopoietic stem/progenitor (HSC) cell therapy is the low cell dose available. A cytokine cocktail for the ex vivo expansion of UCB HSC, in co-culture with a bone marrow (BM) mesenchymal stem cells (MSC)-derived stromal layer was optimized using an experimental design approach. Proliferation of total cells (TNC), stem/progenitor cells (CD34(+)) and colony-forming units (CFU) was assessed after 7 days in culture, while sole and interactive effects of each cytokine on HSC expansion were statistically determined using a two-level Face-Centered Cube Design. The optimal cytokine cocktail obtained for HSC-MSC co-cultures was composed by SCF, Flt-3L and TPO (60, 55 and 50 ng mL(-1), respectively), resulting in 33-fold expansion in TNC, 17-fold in CD34(+) cells, 3-fold in CD34(+)CD90(+) cells and 21-fold in CFU-MIX. More importantly, these short-term expanded cells preserved their telomere length and extensively generated cobblestone area-forming cells (CAFCs) in vitro. The statistical tools used herein contributed for the rational delineation of the cytokine concentration range, in a cost-effective way, while systematically addressing complex cytokine-to-cytokine interactions, for the efficient HSC expansion towards the generation of clinically significant cell numbers for transplantation.

Immobilization, stabilization, and activation of human stem cell factor (SCF) on fragmin/protamine microparticle (F/P MP)-coated plates

Fragmin (low-molecular-weight heparin)/protamine microparticles (F/P MPs) immobilize to culture plates, thereby retaining the binding of heparin-binding cytokines such as human stem cell factor (SCF). The purpose of this study was to evaluate the ability of F/P MP-coating to immobilize, stabilize, and enhance SCF-activity. Cell assays showed that SCF and preimmobilized SCF on F/P MP-coated plates significantly stimulated the proliferation of human erythroleukemia cell line TF-1 in a concentration-dependent manner. Heparin and fragmin enhanced SCF-induced proliferation of chlorate-treated TF-1 cells, in which the biosynthesis of endogenous sulfated polysaccharides was blocked, on noncoated plates at a range of concentrations (2-8 microg/mL). However, heparin and fragmin had no effect on SCF-induced proliferation of chlorate-treated TF-1 cells on F/P MP-coated plates. The interaction of SCF with fragmin and F/P MPs prolonged the half-life of SCF bioactivity, and immobilized and protected SCF from inactivation, such as from heat and proteolysis. These results suggest that F/P MP-coated plates protect SCF and enhance its activity, and F/P MP-coating provides an excellent biomaterial to immobilize and retain heparin-binding cytokines, including SCF, in bioactive form for optimal expansion of hematopoietic cells.

Mimicking the haematopoietic niche microenvironment provides a novel strategy for expansion of haematopoietic and megakaryocyte-progenitor cells from cord blood

Severe neutropenia and protracted thrombocytopenia remain serious clinical problems following cord blood transplantation (CBT) due to the paucity of stem and progenitor cells in the grafts. Administration of ex-vivo expanded megakaryocyte progenitor cells may facilitate platelet production. We propose a novel strategy to expand these rare cells ex-vivo, from a small portion of the cord blood (CB) unit, using fibronectin (FN), a major component of hematopoietic niches, combined with cytokines, including thrombopoietin and the hematopoietic stress-associated acetylcholinesterase readthrough peptide (ARP). Application of multiple gates and high definition flow cytometry enabled clear resolution of expanded hematopoietic stem/precursor cells (HSPC) and megakaryocyte progenitors (Mk-p) and their early subsets while eliminating positively stained non-relevant cells. FN increased viability, expansion of all CD34(+) HSPC populations and Mk-p. The combination of FN + thrombopoietin + ARP maintained and expanded very early myeloid and thrombopoietic precursors, increased the proliferation of megakaryocyte, granulocyte-macrophage and multilineage colony-forming progenitors and supported Mk maturation as measured by ploidy and glycoprotein IIb/IIIa expression by quantiative reverse transcription polymerase chain reaction. This approach, which involves expanding HSPC and Mk precursors from a small portion of the CB unit, without sacrificing the coveted stem cells, may lead to improved cell therapy modalities to facilitate earlier myelopoiesis and platelet production post-CBT.

Clinical application of stem cells in the cardiovascular system

Regenerative medicine encompasses "tissue engineering" - the in vitro fabrication of tissues and/or organs using scaffold material and viable cells - and "cell therapy" - the transplantation or manipulation of cells in diseased tissue in vivo. In the cardiovascular system, tissue engineering strategies are being pursued for the development of viable replacement blood vessels, heart valves, patch material, cardiac pacemakers and contractile myocardium. Anecdotal clinical applications of such vessels, valves and patches have been described, but information on systematic studies of the performance of such implants is not available, yet. Cell therapy for cardiovascular regeneration, however, has been performed in large series of patients, and numerous clinical studies have produced sometimes conflicting results. The purpose of this chapter is to summarize the clinical experience with cell therapy for diseases of the cardiovascular system, and to analyse possible factors that may influence its outcome.

Induction of notch signaling by immobilization of jagged-1 on self-assembled monolayers

Notch signaling is a key mechanism during mammal development and stem cell regulation. This study aims to target and control Notch signaling by ligands immobilization using self-assembled monolayers (SAMs) as model surfaces. Non-fouling substrates were prepared by immersion of gold substrates in (1-Mercapto-11-undecyl)tetra(ethylene glycol) thiol solutions. These surfaces were activated with N,N'-carbonyldiimidazole (CDI) at different concentrations (0, 0.03, 0.3, 3 and 30 mg/ml) and an anti-human IgG, Fc specific fragment antibody (Ab) was covalently bound to EG4-SAMs to guarantee the correct exposure of the Notch ligand Jagged-1/Fc chimera (Jag-1). The presence of Ab and Jag-1 was confirmed by radiolabeling, X-ray photoelectron spectroscopy (XPS), ellipsometry and ELISA. The biological activity of Jag-1-Ab-SAMs was assessed by real-time PCR for Hes-1 family gene expression, a Notch pathway target gene, in HL-60 cell line. Results have shown an increase of the amount of immobilized Ab with increasing surface activator concentrations. Jag-1 concentration also increases with Ab concentration. Interestingly, a higher Jagged-1 exposure and fold increase in Hes-1 expression were obtained for surfaces activated with the lowest concentration of CDI (0.03 mg/ml). These results illustrate the great importance of ligands orientation and exposure, when compared with density. This investigation brings new insights into Notch signaling mechanisms. In particular, Jag-1-Ab-SAMs have shown to be adequate model surfaces to study Notch pathway activation and may provide a basis to develop new interfaces in biomaterials to control Notch mechanism in different cell systems.

Molecular profiling of conjunctival epithelial side-population stem cells: atypical cell surface markers and sources of a slow-cycling phenotype

PURPOSE

Side-population (SP) cells isolated from limbal and conjunctival epithelia derive from cells that are slow cycling in vivo, a known feature of tissue stem cells. The purpose of this study was to define the molecular signature of the conjunctival SP cells and identify markers and signaling pathways associated with the phenotype of these cells.

METHODS

Overnight cultures of freshly isolated human conjunctival epithelial cells stained with Hoechst 33342 were sorted by flow cytometry into SP and non-SP cohorts. Isolated RNA was processed for microarray analysis using a commercial oligonucleotide spotted array. Results were validated at the gene and protein levels by quantitative PCR and immunologic methods. Data mining methods were used to identify cellular processes relevant for stem cell function.

RESULTS

Comparative analyses of transcripts expression based on present and absent software calls across four replicate experiments identified 16,993 conjunctival epithelial transcripts including 10,266 unique known genes of approximately 24,000 represented in the array. Of those genes, 1254 and 363 were overexpressed (>2-fold) or underexpressed (<0.5-fold), respectively, in the SP. The overexpressed set included genes coding for proteins that have been associated with (1) embryonic development and/or stem cell self renewal (MSX, MEIS, ID, Hes1, and SIX homeodomain genes); (2) cell survival (e.g., CYP1A1 to degrade aromatic genotoxic compounds); (3) cycling rate (e.g., DUSPs and Pax6 to foster slow cycling); and (4) genes whose expression is not typical in epithelia (e.g., CD62E).

CONCLUSIONS

The molecular signature of conjunctival SP cells is consistent with a stem cell phenotype. Their gene expression patterns underpin slow cycling and plasticity, features associated with tissue stem cells. The results provide valuable insights for the preservation and/or expansion of epithelial stem cells.

Modeling of asymmetric cell division in hematopoietic stem cells--regulation of self-renewal is essential for efficient repopulation

Hematopoietic stem cells (HSCs) are characterized by their ability of self-renewal to replenish the stem cell pool and differentiation to more mature cells. The subsequent stages of progenitor cells also share some of this dual ability. It is yet unknown whether external signals modulate proliferation rate or rather the fraction of self-renewal. We propose three multicompartment models, which rely on a single external feedback mechanism. In Model 1 the signal enhances proliferation, whereas the self-renewal rates in all compartments are fixed. In Model 2 the signal regulates the rate of self-renewal, whereas the proliferation rate is unchanged. In Model 3, the signal regulates both proliferation and self-renewal rates. This study demonstrates that a unique strictly positive stable steady state can only be achieved by regulation of the rate of self-renewal. Furthermore, it requires a lower number of effective cell doublings. In order to maintain the stem cell pool, the self-renewal ratio of the HSC has to be > or =50% and it has to be higher than the self-renewal ratios of all downstream compartments. Interestingly, the equilibrium level of mature cells depends only on the parameters of self-renewal of HSC and it is independent of the parameters of dynamics of all upstream compartments. The model is compatible with the increase of leukocyte numbers following HSC transplantation. This study demonstrates that extrinsic regulation of the self-renewal rate of HSC is most essential in the process of hematopoiesis.

Co-culture with mesenchymal stromal cells increases proliferation and maintenance of haematopoietic progenitor cells

Mesenchymal stromal cells (MSC) have been suggested to provide a suitable cellular environment for in vitro expansion of haematopoietic stem and progenitor cells (HPC) from umbilical cord blood. In this study, we have simultaneously analysed the cell division history and immunophenotypic differentiation of HPC by using cell division tracking with carboxyfluorescein diacetate N-succinimidyl ester (CFSE). Co-culture with MSC greatly enhanced proliferation of human HPC, especially of the more primitive CD34(+)CD38(-) fraction. Without co-culture CD34 and CD133 expressions decreased after several cell divisions, whereas CD38 expression was up-regulated after some cell divisions and then diminished in fast proliferating cells. Co-culture with MSC maintained a primitive immunophenotype (CD34(+), CD133(+) and CD38(-)) for more population doublings, whereas up-regulation of differentiation markers (CD13, CD45 and CD56) in HPC was delayed to higher numbers of cell divisions. Especially MSC of early cell passages maintained CD34 expression in HPC over more cell divisions, whereas MSC of higher passages further enhanced their proliferation rate. Inhibition of mitogen-activated protein kinase 1 (MAPK1) impaired proliferation and differentiation of HPC, but not maintenance of long-term culture initiating cells. siRNA knockdown of N-cadherin and VCAM1 in feeder layer cells increased the fraction of slow dividing HPC, whereas knockdown of integrin beta 1 (ITGB1) and CD44 impaired their differentiation. In conclusion, MSC support proliferation as well as self-renewal of HPC with primitive immunophenotype. The use of early passages of MSC and genetic manipulation of proteins involved in HPC-MSC interaction might further enhance cord blood expansion on MSC.

Protocols for hematopoietic stem cell expansion from umbilical cord blood

The reconstitution of adult stem cells may be a promising source for the regeneration of damaged tissues and for the reconstitution of organ dysfunction. However, there are two major limitations to the use of such cells: they are rare, and only a few types exist that can easily be isolated without harming the patient. The best studied and most widely used stem cells are of the hematopoietic lineage. Pioneering work on hematopoietic stem cell (HSC) transplantation was done in the early 1970s by ED. Thomas and colleagues. Since then HSCs have been used in allogenic and autologous transplantation settings to reconstitute blood formation after high-dose chemotherapy for various blood disorders. The cells can be easily harvested from donors, but the cell number is limited, especially when the HSCs originate from umbilical cord blood (UCB). It would be desirable to set up an ex vivo strategy to expand HSCs in order to overcome the cell dose limit, whereby the expansion would favor cell proliferation over cell differentiation. This review provides an overview of the various existing HSC expansion strategies-focusing particularly on stem cells derived from UCB-of the parameters that might affect the outcome, and of the difficulties that may occur when trying to expand such cells.

Role of interleukin-15 in umbilical cord blood transplantation

Owing to its easier accessibility and less severe graft-versus-host disease, umbilical cord blood (UCB) has been increasingly used as an alternative to bone marrow for hematopoietic stem-cell transplantation. Naiveté of UCB lymphocytes, however, results in delayed immune reconstitution and infection-related mortality in transplant recipients. This article reviews UCB immunology and addresses the potential therapeutic role of interleukin (IL)-15, a pleiotropic gamma chain signaling cytokine, in modulating immune reconstitution, graft-versus-host disease (GVHD), graft-versus-leukemia effect, and infection susceptibility during the post-UCB transplant period. Cytokine immunotherapy using IL-15 simultaneously modulates several immune compartments, thus holds promise for facilitating post-transplant recovery and augmenting antitumor effect without aggravating GVHD in the setting of UCB transplantation.

Haploidentical SCT in children: an update and future perspectives

Transplantation of haploidentical stem cells has become a well-established approach, which makes a potential donor available for almost all patients. This review focuses on current results and new strategies, especially in pediatric patients with malignant diseases. CD34(+) positive selection was the most common procedure for graft manipulation in the past years, whereas T and B cell depletion is a promising new method. GVHD could herewith be effectively reduced and primary engraftment was reported in 83-100% of patients after transplantation of high stem cell doses. For patients with ALL in remission, disease-free survival at 3 years ranged between 22 and 48%. TRM, mainly because of viral infections, was improved by the use of reduced-intensity conditioning (which helped to speed up T cell recovery) and by close monitoring of viral loads and prophylactic/preemptive therapy. The role of donor-derived Ag-specific T cells against viral and fungal antigens is currently under investigation. Patients with active disease at the time of transplantation had a poor outcome and several attempts to improve these results are currently evaluated, such as co-infusion of natural killer cells, co-transplantation of MSC, use of new antileukemic drugs and post-transplant immunotherapy.

Placental/umbilical cord blood-derived mesenchymal stem cell-like stromal cells support hematopoietic recovery of X-irradiated human CD34+ cells

AIMS

The potential of human mesenchymal stem cell-like stroma prepared from placental/umbilical cord blood for hematopoietic regeneration by X-irradiated hematopoietic stem cells is herein assessed.

MAIN METHODS

Placental/umbilical cord blood-derived mesenchymal stem cell-like stromal cells were applied to a regenerative ex vivo expansion of X-irradiated human CD34(+) cells in a serum-free liquid culture supplemented with a combination of interleukine-3 plus stem cell factor plus thrombopoietin.

KEY FINDINGS

The total number of cells and of lineage-committed myeloid hematopoietic progenitor cells generated in the co-culture of both non-irradiated and X-irradiated cells with stromal cells was significantly higher than those in the stroma-free culture. In addition, the number of CD34(+) cells and CD34(+)/CD38(-) cells, immature hematopoietic stem/progenitor cells also increased more than the stroma-free culture. The stromal cells produced various types of cytokines, although there was little difference between the co-cultures of non-irradiated and X-irradiated cells with stromal cells. Furthermore, when X-irradiated cells came in contact with stromal cells for 16 h before cytokine stimulation, a similar degree of hematopoiesis was observed, thus suggesting the critical role of cell-to-cell interaction.

SIGNIFICANCE

The present results showed the potential efficacy of human mesenchymal stem cell-like stroma for hematopoietic regeneration from irradiated hematopoietic stem/progenitor cells.

Reconstitution activity of hypoxic cultured human cord blood CD34-positive cells in NOG mice

Hematopoietic stem cells (HSCs) reside in hypoxic areas of the bone marrow. However, the role of hypoxia in the maintenance of HSCs has not been fully characterized. We performed xenotransplantation of human cord blood cells cultured in hypoxic or normoxic conditions into adult NOD/SCID/IL-2Rgamma(null) (NOG) mice. Hypoxic culture (1% O(2)) for 6 days efficiently supported the maintenance of HSCs, although cell proliferation was suppressed compared to the normoxic culture. In contrast, hypoxia did not affect in vitro colony-forming ability. Upregulation of a cell cycle inhibitor, p21, was observed in hypoxic culture. Immunohistochemical analysis of recipient bone marrow revealed that engrafted CD34(+)CD38(-) cord blood HSCs were hypoxic. Taken together, these results demonstrate the significance of hypoxia in the maintenance of quiescent human cord blood HSCs.

Valproic acid enhances the engraftability of human umbilical cord blood hematopoietic stem cells expanded under serum-free conditions

Valproic acid (VPA) is a histone deacetylase inhibitor previously shown to promote the proliferation and self-renewal of CD34(+) hematopoietic cells. We tested the effect of VPA in conjunction with the selective amplification technology developed by Viacell Inc. Stem cells enriched from frozen cord blood were cultured for 7 d, subjected to reselection and grown in fresh medium for a further 7 d. Treatment with VPA resulted in an average two-fold higher expansion of CD45(+)34(+) cells compared with control. Furthermore, VPA-treatment induced higher numbers of CD45(+)34(+) cells to reside in the S phase than control cultured cells and resulted in a 2.5-fold upregulation in HOXB4 expression. Importantly, VPA-treated cells reconstituted hematopoiesis in non-obese diabetic/severe combined immunodeficient mice with a six-fold higher efficiency than control cells. Collectively, our results indicate that VPA, already used clinically for neurologic disorder treatment, is a useful additive for the ex vivo culture of hematopoietic stem/progenitor cells to enhance engraftment efficiency.

Effect of anti-CD52 antibody alemtuzumab on ex-vivo culture of umbilical cord blood stem cells

Background

Excessive maturation of hematopoietic cells leads to a reduction of long-term proliferative capability during cord blood (CB) expansion. In this study, we report the effects of anit-CD52 (Alemtuzumab, Campath) on both short- and long-term ex vivo expansion of CB hematopoietic stem cells (HSC) by evaluating the potential role of Alemtuzumab in preserving the repopulating capability in CB HSC and nonlymphoid progenitors.

Methods

Ex vivo expansion experiments were carried out using freshly purified CB CD34⁺ cells in StemSpan™ SFEM medium in the presence of stem cell factor, Flt3-Ligand and thrombopoietin at 50 ng/ml. Alemtuzumab (10 μg/ml) was used to deplete CD52⁺ cells during the cultures. Flow cytometry was used to monitor CB HSC and their differentiation. Colony forming unit (CFU) assays and long term culture-initiating cell (LTC-IC) assays were performed on cells obtained from day 0 (before culture) and day 14 after cultures. Secondary cultures was performed using CD34⁺ cells isolated at 35 days from primary cultures and further cultured in StemSpan™ SFEM medium for another 14 days to confirm the long term effect of alemtuzumab in liquid cultures.

Results

Compared to cytokines alone, addition of alemtuzumab resulted in a significant increase in total nucleated cells, absolute CD34⁺ cells, myeloid and megakaryocytic progenitors, multi-lineage and myeloid CFU and LTC-IC.

Conclusion

The results from current study suggested that the use of alemtuzumab for ex vivo expansion of CBHSC maybe advantageous. Our findings may improve current technologies for CBHSC expansion and increase the availability of CB units for transplantation. However, in vivo studies using animal models are likely needed in further studies to test the hematopoietic effects using such expanded CB products.

Cytokine-immobilized microparticle-coated plates for culturing hematopoietic progenitor cells

The purpose of this study was to provide a culture method for an effective expansion of human CD 34 positive hematopoietic progenitor cells (CD 34 (+) HCs) utilizing low molecular weight heparin/protamine microparticles (LH/P MPs) which can be stably coated onto plastic surfaces and cytokines. CD 34 (+) HCs optimally proliferated on LH/P MP-coated plates in the presence of stem cell factor (SCF; 5 ng/ml), thrombopoietin (Tpo; 10 ng/ml), and Flt-3 ligand (Flt-3; 10 ng/ml) in hematopoietic progenitor growth medium (HPGM). After 6 days, the total cells expanded 16.5-fold. Those cytokines were shown to be partially immobilized on the LH/P MP-coated plates, and the immobilized cytokines were gradually released into the medium with half releasing time of 3-4 days. Since flow cytometry analyses revealed that 90% of initial cells and 44.5% of expanded cells were CD 34 positive, CD 34 (+) HCs were estimated to have increased 8.0-fold after 6 days, and to have increased to over 31.9-fold after 12 days. In contrast, cultured CD 34 (+) HCs on non-coated tissue culture plates increased only 2.9-fold in the identical medium after 6 days, and only 5.2-fold after 12 days.

Clonal Analysis of Hematopoiesis-Supporting Activity of Human Mesenchymal Stem Cells in Association with Jagged1 Expression and Osteogenic Potential

Human mesenchymal stem cells (hMSCs) are promising feeder cells for expanding hematopoietic stem cells (HSCs), but their potential is heterogeneous. We examined the hematopoiesis-supporting activity of hMSC at the clonal level in relation to the osteogenic potential and gene expression. Hematopoiesis-supporting activities of stably immortalized clonal hMSC lines were evaluated by the expansion of CD34+CD38- cells after 7-day coculture with human cord blood-derived CD34+ cells. Six of 16 clones expanded the numbers of CD34+CD38- cells >500-fold. These hematopoiesis-supportive clones also showed high gene expression of Jagged1, a Notch ligand, as well as high potential to deposit calcium after osteogenic induction. Thus, osteogenic hMSC clones may provide proper microenvironments for HSC expansion, ultimately conveying self-renewal signals to HSCs via the Notch pathway. However, they lost hematopoiesis-supporting activity after osteogenic differentiation. The hematopoiesis-supportive clones are potentially useful for hematopoietic microenvironment studies and as components of a coculture system for expansion of HSCs, free from contamination by xenogeneic pathogens.

Notch induces cell cycle arrest and apoptosis in human erythroleukaemic TF-1 cells

OBJECTIVE

Notch signalling is known to promote hematopoietic stem cell self-renewal and to influence the lineage commitment decisions of progenitor cells. The purpose of this study was to investigate the mechanism of Notch-induced apoptosis in the erythroleukaemic cell line TF-1, and in primary cord blood CD34+ cells.

METHODS

Retroviral constructs containing constitutively active forms of Notch as well as components of the Notch signalling pathway were used to transduce cells and their effect on cell cycle kinetics and apoptosis assayed by immunostaining for the S-phase marker Ki67 and Annexin V.

RESULTS

We found that TF-1 cells undergo cell cycle arrest followed by apoptosis in a cytokine-independent manner in response to active Notch. Transduction of TF-1 cells with known targets of Notch signalling, Deltex1, HES1 and HERP2, showed that Notch-induced cell cycle arrest was not mediated by these proteins. However, analysis of cell cycle gene expression revealed that Notch signalling was associated with an up-regulation of IFI16 expression in TF-1 cells and in primary cord blood CD34+ cells.

CONCLUSION

These data demonstrate that, in the context of TF-1 cells, Notch signalling can induce cell cycle arrest and apoptosis.

Expanded CD34+ human umbilical cord blood cells generate multiple lymphohematopoietic lineages in NOD-scid IL2rgamma(null) mice

Umbilical cord blood (UCB) is increasingly being used for human hematopoietic stem cell (HSC) transplantation in children but often requires pooling multiple cords to obtain sufficient numbers for transplantation in adults. To overcome this limitation, we have used an ex vivo two-week culture system to expand the number of hematopoietic CD34(+) cells in cord blood. To assess the in vivo function of these expanded CD34(+) cells, cultured human UCB containing 1 x 10(6) CD34(+) cells were transplanted into conditioned NOD-scid IL2rgamma(null) mice. The expanded CD34(+) cells displayed short- and long-term repopulating cell activity. The cultured human cells differentiated into myeloid, B-lymphoid, and erythroid lineages, but not T lymphocytes. Administration of human recombinant TNFalpha to recipient mice immediately prior to transplantation promoted human thymocyte and T-cell development. These T cells proliferated vigorously in response to TCR cross-linking by anti-CD3 antibody. Engrafted TNFalpha-treated mice generated antibodies in response to T-dependent and T-independent immunization, which was enhanced when mice were co-treated with the B cell cytokine BLyS. Ex vivo expanded CD34(+) human UCB cells have the capacity to generate multiple hematopoietic lineages and a functional human immune system upon transplantation into TNFalpha-treated NOD-scid IL2rgamma(null) mice.

The Stromal Activity of Mesenchymal Stromal Cells

SUMMARY: The mechanism that regulates self-renewal and differentiation of hematopoietic stem cells (HSC) is a central question in stem cell biology that might ultimately lead to reliable protocols for in vitro expansion of HSC. Cellular fate is governed by cell-cell interaction with the microenvironment in the bone marrow, the stem cell niche. Mesenchymal stromal cells (MSC) are precursors of the cellular components, and they secrete extracellular matrix proteins of the bone marrow stroma. Therefore, MSC feeder layer might provide a suitable in vitro model system for the stem cell niche. In vitro assays demonstrate that MSC maintain the stem cell function of HSC and that MSC from bone marrow have a higher hematopoiesis supportive activity than MSC from adipose tissue. Co-cultivation with MSC might pave the way for expansion of long-term repopulating HSC, and various clinical trials indicate that co-transplantation of HSC and MSC might enhance engraftment. Thus, MSC are promising tools to elucidate the underlying mechanism of the cellular microenvironment. The large variety of preparative protocols for isolation and cultivation of MSC affects their stromal activity. Standardized isolation methods and molecular characterization of MSC are of utmost importance for reproducible isolation of hematopoiesis supportive stromal cells and for their potential clinical application.

Human CD34+ stem cells produce bone nodules in vivo

OBJECTIVES

The aim of this study was to select and provide enough stem cells for quick transplantation in bone engineering procedures, avoiding any in vitro expansion step.

MATERIALS AND METHODS

Dental germ pulp, collected from 25 healthy subjects aged 13-20 years, were subjected to magnetic-activated cell sorting to select a CD34(+) stem cell population capable of differentiating into pre-osteoblasts. These cells were allowed to adhere to an absorbable polylactic-coglycolic acid scaffold for 30 min, without any prior expansion, and the CD34(+) cell-colonized scaffolds were then transplanted into immunocompromised rats, subcutaneously.

RESULTS

After 60 days, analysis of recovered transplants revealed that they were formed of nodules of bone, of the same dimensions as the original scaffold. Bone-specific proteins were detected by immunofluorescence, within the nodules, and X-ray diffraction patterns revealed characteristic features of bone. In addition, presence of platelet endothelial cell adhesion molecule and von Willebrand factor immunoreactivity were suggestive of neo-angiogenesis and neovasculogenesis taking place within nodules. Importantly, these vessels were HLA-1(+) and, thus, clearly human in origin.

CONCLUSIONS

This study indicates that CD34(+) cells obtained from dental pulp can be used for engineering bone, without the need for prior culture expanding procedures. Using autologous stem cells, this schedule could be used to provide the basis for bone regenerative surgery, with limited sacrifice of tissue, low morbidity at the collection site, and significant reduction in time needed for clinical recovery.

Expansion of human hematopoietic stem cells for transplantation: trends and perspectives

Umbilical cord blood transplantation is clinically limited by its low progenitor cell content. Ex vivo expansion has become an alternative to increase the cell dose available for transplants. Expansion has been evaluated in several ways such as static cultures combining growth factors or mimicking the natural microenvironment using co-culture systems. However, static cultures have a small volume capacity and therefore large-scale expansion has been addressed using bioreactors. These and other biotechnological approaches for the expansion of hematopoietic progenitors and their utility to study several aspects of hematopoietic stem cell biology are discussed here.

Glycogen synthase kinase-3beta inhibition preserves hematopoietic stem cell activity and inhibits leukemic cell growth

Ex vivo expansion of cord blood cells generally results in reduced stem cell activity in vivo. Glycogen synthase kinase-3beta (GSK-3beta) regulates the degradation of beta-catenin, a critical regulator of hematopoietic stem cells (HSCs). Here we show that GSK-3beta inhibition activates beta-catenin in cord blood CD34(+) cells and upregulates beta-catenin transcriptional targets c-myc and HoxB4, both known to regulate HSC self-renewal. GSK-3beta inhibition resulted in delayed ex vivo expansion of CD34(+) cells, yet enhanced the preservation of stem cell activity as tested in long-term culture with bone marrow stroma. Delayed cell cycling, reduced apoptosis, and increased adherence of hematopoietic progenitor cells to bone marrow stroma were observed in these long-term cultures treated with GSK-3beta inhibitor. This improved adherence to stroma was mediated via upregulation of CXCR4. In addition, GSK-3beta inhibition preserved severe combined immunodeficiency (SCID) repopulating cells as tested in the nonobese diabetic/SCID mouse model. Our data suggest the involvement of GSK-3beta inhibition in the preservation of HSC and their interaction with the bone marrow environment. Methods for the inhibition of GSK-3beta may be developed for clinical ex vivo expansion of HSC for transplantation. In addition, GSK-3beta inhibition suppressed leukemic cell growth via the induction of apoptosis mediated by the downregulation of survivin. Modulators of GSK-3beta may increase the range of novel drugs that specifically kill leukemic cells while sparing normal stem cells.

Angiopoietin-like 5 and IGFBP2 stimulate ex vivo expansion of human cord blood hematopoietic stem cells as assayed by NOD/SCID transplantation

Hematopoietic stem cells (HSCs) are the basis of bone marrow transplantation and are attractive target cells for hematopoietic gene therapy, but these important clinical applications have been severely hampered by difficulties in ex vivo expansion of HSCs. In particular, the use of cord blood for adult transplantation is greatly limited by the number of HSCs. Previously we identified angiopoietin-like proteins and IGF-binding protein 2 (IGFBP2) as new hormones that, together with other factors, can expand mouse bone marrow HSCs in culture. Here, we measure the activity of multipotent human severe combined immunodeficient (SCID)-repopulating cells (SRCs) by transplantation into the nonobese diabetic SCID (NOD/SCID) mice; secondary transplantation was performed to evaluate the self-renewal potential of SRCs. A serum-free medium containing SCF, TPO, and FGF-1 or Flt3-L cannot significantly support expansion of the SRCs present in human cord blood CD133+ cells. Addition of either angiopoietin-like 5 or IGF-binding protein 2 to the cultures led to a sizable expansion of HSC numbers, as assayed by NOD/SCID transplantation. A serum-free culture containing SCF, TPO, FGF-1, angiopoietin-like 5, and IGFBP2 supports an approximately 20-fold net expansion of repopulating human cord blood HSCs, a number potentially applicable to several clinical processes including HSC transplantation.

Generation of functional natural killer and dendritic cells in a human stromal-based serum-free culture system designed for cord blood expansion

OBJECTIVE

We have previously reported on the ability of a mesenchymal stem cell-based serum-free culture system to expand human cord blood (CB) hematopoietic stem cells along the myeloid pathway and simultaneously generate a CD7(+)CD34(-) population. In this study, we investigated the ability of the CD7(+)CD34(-) population to differentiate into natural killer and dendritic cells (DCs).

MATERIALS AND METHODS

CB CD34(+) cells were expanded over a mesenchymal stem cell layer in serum-free medium supplemented with stem cell factor, basic fibroblast growth factor, leukemia inhibitor factor, and Flt-3 ligand for 2 weeks. Cultured cells were harvested and CD7(+)CD34(-)Lin(-) cells sorted and plated for 2 additional weeks in either natural killer- or DC-inductive medium.

RESULTS

Culture of CD34(+) cells for the first 2 weeks in this system resulted in expansion of the stem cell pool and the myeloid component of the graft, and also produced a 58-fold increase in the CD7(+)CD34(-) cell population. When sorted CD7(+)CD34(-)Lin(-) cells were induced toward a natural killer cell phenotype, further expansion was observed during this time in culture, and differentiation was confirmed by cytotoxic activity and by flow cytometry, with cells displaying CD16 and CD56 in the absence of CD3. Generation of DC cells in culture was also verified by observing both the characteristic dendritic morphology and the dendritic phenotypes HLA-DR(bright)CD123(bright)CD11c(-) and HLA-DR(bright)CD11c(+).

CONCLUSION

These results demonstrate the ability of an ex vivo culture system to drive expansion of human CB hematopoietic stem cells, while promoting the immune maturation of the graft and generation of DC and natural killer cells that could then be utilized for adoptive cancer cellular immunotherapy.

Ex vivo expansion of umbilical cord blood stem cells using different combinations of cytokines and stromal cells

Umbilical cord blood is a promising source of hematopoietic stem cells (HSC) for allogeneic transplantation. However, graft rejection and delayed engraftment remain major limitations, both of which are related to a limited number of stem cells in the cord blood graft. Ex vivo expansion of HSC has been suggested as one of the ways of overcoming the challenges caused by a limited hematopoietic cell number from cord blood stem cell transplantation. In this study, we quantified and characterized an ex vivo expansion capacity of cord blood-derived HSC in a liquid culture system under different conditions. These conditions included: the combinations and concentrations of hematopoietic growth factors [stem cell factor (SCF), granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin (IL)-3, IL-6 and erythropoietin (EPO)], placental conditioning medium (PCM), and stromal cell support. During culture, the mean nucleated cell count, the mean CD34+ cell count, fold expansion, viability, clonogenic assays and immunophenotypic characterization were performed on day 0, day 7, day 12 and day 14 on the expanded cellular product. The maximum expansion was achieved using GF2 (SCF + IL-3 + GM-CSF) with stromal cell support. The mean CD34+ cell expansion on days 7 and 12 was 16.25- and 21.4-fold (5.2-32), respectively, and the mean nucleated cell expansion was 15.1- and 21-fold (18.1-23.2). The mean nucleated cell viability on day 12 was 87.9% (85.6-92.5). After 12 days, granulocyte-macrophage colony-forming units CFU-GEMM showed a 20.4-fold increase. A 21.4-fold increase in the CD34+ cells and a 20-fold increase in the CFU-GEMM should provide enough cells from a single cord blood unit to reduce the period of cytopenia after single unit cord blood transplantation. Even if there was some doubt about the long-term repopulating capacity of the expanded cells part of the collected umbilical cord cells (25%) could be expanded till day 12 after transplanting the major part (75%) of the collection.

Delayed immune reconstitution after cord blood transplantation is characterized by impaired thymopoiesis and late memory T-cell skewing

Advances in immune assessment, including the development of T-cell receptor excision circle (TREC) assays of thymopoiesis, cytokine-flow cytometry assays of T-cell function, and higher-order phenotyping of T-cell maturation subsets have improved our understanding of T-cell homeostasis. Limited data exist using these methods to characterize immune recovery in adult cord blood (CB) transplant recipients, in whom infection is a leading cause of mortality. We now report the results of a single-center prospective study of T-cell immune recovery after cord blood transplantation (CBT) in a predominantly adult population. Our primary findings include the following: (1) Prolonged T lymphopenia and compensatory expansion of B and natural killer (NK) cells was evident; (2) CB transplant recipients had impaired functional recovery, although we did observe posttransplantation de novo T-cell responses to cytomegalovirus (CMV) in a subset of patients; (3) Thymopoietic failure characterized post-CBT immune reconstitution, in marked contrast to results in other transplant recipients; and (4) Thymopoietic failure was associated with late memory T-cell skewing. Our data suggest that efforts to improve outcomes in adult CB transplant recipients should be aimed at optimizing T-cell immune recovery. Strategies that improve the engraftment of lymphoid precursors, protect the thymus during pretransplant conditioning, and/or augment the recovery of thymopoiesis may improve outcomes after CBT.

Feasibility and outcome of reduced-intensity conditioning in haploidentical transplantation

Allogeneic stem cell transplantation is for a number of patients with malignant and nonmalignant diseases the only curative approach. For those patients who do not have an HLA-identical-related or -unrelated stem cell donor, a related three-loci mismatch haploidentical stem cell transplantation with T cell-depleted stem cells is a viable option. T cell depletion either by CD34(+) positive selection or by CD3-negative depletion strategies is available and has been investigated. We have shown that reduced-intensity conditioning haploidentical transplantation using mobilized peripheral stem cells negatively depleted from T and B lymphocytes is associated with a rapid immune reconstitution, a low transplant-related mortality rate, and a favorable outcome in patients in remission at the time of transplant. For chemorefractory patients, additional posttransplant cellular and humoral immunotherapeutic strategies are needed for prevention of relapse after transplantation.