Ex vivo manipulation of umbilical cord blood-derived hematopoietic stem/progenitor cells with recombinant human stem cell factor can up-regulate levels of homing-essential molecules to increase their transmigratory potential

Role of Neurotransmitters in Steady State Hematopoiesis, Aging, and Leukemia

Haematopoiesis within the bone marrow (BM) represents a complex and dynamic process intricately regulated by neural signaling pathways. This delicate orchestration is susceptible to disruption by factors such as aging, diabetes, and obesity, which can impair the BM niche and consequently affect haematopoiesis. Genetic mutations in Tet2, Dnmt3a, Asxl1, and Jak2 are known to give rise to clonal haematopoiesis of intermediate potential (CHIP), a condition linked to age-related haematological malignancies. Despite these insights, the exact roles of circadian rhythms, sphingosine-1-phosphate (S1P), stromal cell-derived factor-1 (SDF-1), sterile inflammation, and the complement cascade on various BM niche cells remain inadequately understood. Further research is needed to elucidate how BM niche cells contribute to these malignancies through neural regulation and their potential in the development of gene-corrected stem cells. This literature review describes the updated functional aspects of BM niche cells in haematopoiesis within the context of haematological malignancies, with a particular focus on neural signaling and the potential of radiomitigators in acute radiation syndrome. Additionally, it underscores the pressing need for technological advancements in stem cell-based therapies to alleviate the impacts of immunological stressors. Recent studies have illuminated the microheterogeneity and temporal stochasticity of niche cells within the BM during haematopoiesis, emphasizing the updated roles of neural signaling and immunosurveillance. The development of gene-corrected stem cells capable of producing blood, immune cells, and tissue-resident progeny is essential for combating age-related haematological malignancies and overcoming immunological challenges. This review aims to provide a comprehensive overview of these evolving insights and their implications for future therapeutic strategies.

Engineering microenvironments for manufacturing therapeutic cells

There are a growing number of globally approved products and clinical trials utilizing autologous and allogeneic therapeutic cells for applications in regenerative medicine and immunotherapies. However, there is a need to develop rapid and cost-effective methods for manufacturing therapeutically effective cells. Furthermore, the resulting manufactured cells may exhibit heterogeneities that result in mixed therapeutic outcomes. Engineering approaches that can provide distinct microenvironmental cues to these cells may be able to enhance the growth and characterization of these cell products. This mini-review describes strategies to potentially enhance the expansion of therapeutic cells with biomaterials and bioreactors, as well as to characterize the cell products with microphysiological systems. These systems can provide distinct cues to maintain the quality attributes of the cells and evaluate their function in physiologically relevant conditions.

Conditioned Medium from Human Tonsil-Derived Mesenchymal Stem Cells Enhances Bone Marrow Engraftment via Endothelial Cell Restoration by Pleiotrophin

Cotransplantation of mesenchymal stem cells (MSCs) with hematopoietic stem cells (HSCs) has been widely reported to promote HSC engraftment and enhance marrow stromal regeneration. The present study aimed to define whether MSC conditioned medium could recapitulate the effects of MSC cotransplantation. Mouse bone marrow (BM) was partially ablated by the administration of a busulfan and cyclophosphamide (Bu–Cy)-conditioning regimen in BALB/c recipient mice. BM cells (BMCs) isolated from C57BL/6 mice were transplanted via tail vein with or without tonsil-derived MSC conditioned medium (T-MSC CM). Histological analysis of femurs showed increased BM cellularity when T-MSC CM or recombinant human pleiotrophin (rhPTN), a cytokine readily secreted from T-MSCs with a function in hematopoiesis, was injected with BMCs. Microstructural impairment in mesenteric and BM arteriole endothelial cells (ECs) were observed after treatment with Bu–Cy-conditioning regimen; however, T-MSC CM or rhPTN treatment restored the defects. These effects by T-MSC CM were disrupted in the presence of an anti-PTN antibody, indicating that PTN is a key mediator of EC restoration and enhanced BM engraftment. In conclusion, T-MSC CM administration enhances BM engraftment, in part by restoring vasculature via PTN production. These findings highlight the potential therapeutic relevance of T-MSC CM for increasing HSC transplantation efficacy.

Stem cell factor supports migration in canine mesenchymal stem cells

Adult Mesenchymal Stem Cells (MSC) are cells that can be defined as multipotent cells able to differentiate into diverse lineages, under appropriate conditions. These cells have been widely used in regenerative medicine, both in preclinical and clinical settings. Initially discovered in bone marrow, MSC can now be isolated from a wide spectrum of adult and foetal tissues. Studies to evaluate the therapeutic potential of these cells are based on their ability to arrive to damaged tissues. In this paper we have done a comparative study analyzing proliferation, surface markers and OCT4, SOX9, RUNX2, PPARG genes expression in MSC cells from Bone marrow (BMMSC) and Adipose tissue (ASC). We also analyzed the role of Stem Cell Factor (SCF) on MSC proliferation and on ASCs metalloproteinases MMP-2, MMP-9 secretion. Healthy dogs were used as BMMSC donors, and ASC were collected from omentum during elective ovariohysterectomy surgery. Both cell types were cultured in IMDM medium with or without SCF, 10% Dog Serum (DS), and incubated at 38 °C with 5% CO2. Growth of BMMSCs and ASCs was exponential until 25-30 days. Flow citometry of MSCs revealed positive results for CD90 and negative for CD34, CD45 and MCH-II. Genes were evaluated by RT-PCR and metalloproteinases by zymografy. Our findings indicate morphological and immunological similarities as well as expression of genes from both origins on analyzed cells. Furthermore, SCF did not affect proliferation of MSCs, however it up-regulated MMP-2 and MMP-9 secretion in ASCs. These results suggest that metalloproteinases are possibly essential molecules pivoting migration.

Reduced potency of cytotoxic T lymphocytes from patients with high-risk myelodysplastic syndromes

INTRODUCTION

Myelodysplastic syndromes (MDS) are a group of clonal bone marrow disorders, with dysplasia, cytopenias and increased risk of progression to acute myeloid leukemia. A dysregulated immune system precipitates MDS, and to gain insights into the relevance of cytotoxic T lymphocyte (CTL) in this process, we examined the frequency and function of CX3CR1- and CD57-positive T lymphocytes from MDS patients.

MATERIALS AND METHODS

Peripheral blood and/or bone marrow samples from 31 MDS patients and 12 healthy controls were examined by flow cytometry. Expression of cytotoxic granule constituents, immunological co-receptors, adhesion molecules and markers of activation were quantified on unstimulated lymphocytes. Degranulation, cytotoxicity and conjugate formation with target cells following co-culture of CTL with target cell lines or autologous bone marrow-derived CD34(+) cells were quantified by flow cytometry.

RESULTS

CX3CR1 expression was increased in bone marrow from high-risk MDS patients compared to healthy controls. Expression of CD57 and CX3CR1 was closely correlated, identifying a CTL subset with high cytotoxic capacity. In vitro, TCR-induced redirected cytotoxicity was markedly decreased for high-risk MDS patients compared to controls. CTL from MDS patients with the lowest target cell cytotoxicity had reduced expression of adhesion molecules and formed fewer conjugates with target cells.

DISCUSSION

Although phenotypically defined CTL numbers were increased in the bone marrow of MDS patients, we found that CTL from high-risk MDS patients exhibited a lower TCR-induced redirected cytotoxic capacity. Thus, decreased T cell cytotoxicity seems related to reduced adhesion to target cells and may contribute to impaired anti-leukemic immune surveillance in MDS.

Higher Early Monocyte and Total Lymphocyte Counts Are Associated with Better Overall Survival after Standard Total Body Irradiation, Cyclophosphamide, and Fludarabine Reduced-Intensity Conditioning Double Umbilical Cord Blood Allogeneic Stem Cell Transplantation in Adults

This single-center retrospective study aimed to report the impact of early hematopoietic and immune recoveries after a standard total body irradiation, cyclophosphamide, and fludarabine (TCF) reduced-intensity conditioning (RIC) regimen for double umbilical cord blood (dUCB) allogeneic stem cell transplantation (allo-SCT) in adults. We analyzed 47 consecutive patients older than 17 years who engrafted after a dUCB TCF allo-SCT performed between January 2006 and April 2013 in our department. Median times for neutrophil and platelet recoveries were 17 (range, 6 to 59) and 37 days (range, 0 to 164), respectively. The 3-year overall (OS) and disease-free survivals, relapse incidence, and nonrelapse mortality were 65.7%, 57.2%, 27.1%, and 19%, respectively. In multivariate analysis, higher day +30 monocyte (≥615/mm(3); hazard ratio [HR], .04; 95% confidence interval [CI], .004 to .36; P < .01) and day +42 lymphocyte (≥395/mm(3); HR, .16; 95% CI, .03 to .78; P = .02) counts were independently associated with better OS. These results suggest that early higher hematopoietic and immune recovery is predictive of survival after dUCB TCF RIC allo-SCT in adults. Factors other than granulocyte colony-stimulating factor, which was used in all cases, favoring expansion of monocytes or lymphocytes, should be tested in the future as part of the UCB transplantation procedure.

Matrix metalloproteinases in stem cell mobilization

Hematopoietic stem cells (HSCs) have the capability to migrate back and forth between their preferred microenvironment in bone marrow niches and the peripheral blood, but under steady-state conditions only a marginal number of stem cells can be found in the circulation. Different mobilizing agents, however, which create a highly proteolytic milieu in the bone marrow, can drastically increase the number of circulating HSCs. Among other proteases secreted and membrane-bound matrix metalloproteinases (MMPs) are known to be involved in the induced mobilization process and can digest niche-specific extracellular matrix components and cytokines responsible for stem cell retention to the niches. Iatrogenic stem cell mobilization and stem cell homing to their niches are clinically employed on a routine basis, although the exact mechanisms of both processes are still not fully understood. In this review we provide an overview on the various roles of MMPs in the induced release of HSCs from the bone marrow.

Hematopoietic Stem Cell Mobilization and Homing after Transplantation: The Role of MMP-2, MMP-9, and MT1-MMP

Hematopoietic stem/progenitor cells (HSPCs) are used in clinical transplantation to restore hematopoietic function. Here we review the role of the soluble matrix metalloproteinases MMP-2 and MMP-9, and membrane type (MT)1-MMP in modulating processes critical to successful transplantation of HSPC, such as mobilization and homing. Growth factors and cytokines which are employed as mobilizing agents upregulate MMP-2 and MMP-9. Recently we demonstrated that MT1-MMP enhances HSPC migration across reconstituted basement membrane, activates proMMP-2, and contributes to a highly proteolytic bone marrow microenvironment that facilitates egress of HSPC. On the other hand, we reported that molecules secreted during HSPC mobilization and collection, such as hyaluronic acid and thrombin, increase MT1-MMP expression in cord blood HSPC and enhance (prime) their homing-related responses. We suggest that modulation of MMP-2, MMP-9, and MT1-MMP expression has potential for development of new therapies for more efficient mobilization, homing, and engraftment of HSPC, which could lead to improved transplantation outcomes.

Hematopoietic stem and progenitor cell trafficking

Migration of hematopoietic stem cells (HSCs) is essential during embryonic development and throughout adult life. During embryogenesis, trafficking of HSCs is responsible for the sequential colonization of different hematopoietic organs by blood-producing cells. In adulthood, circulation of HSCs maintains homeostasis of the hematopoietic system and participates in innate immune responses. HSC trafficking is also crucial in clinical settings such as bone marrow (BM) and stem cell transplantation. This review provides an overview of the molecular and cellular signals that control and fine-tune trafficking of HSCs and hematopoietic progenitor cells in embryogenesis and during postnatal life. We also discuss the potential clinical utility of therapeutic approaches to modulate HSC trafficking in patients.

Communication of substance P, calcitonin-gene-related neuropeptides and chemokine receptor 4 (CXCR4) in cord blood hematopoietic stem cells

BACKGROUND

Modulation of the expression of CXCR4 as a critical adhesion molecule on cord blood (CB) CD34+ cells could overcome delay following cord blood transplantation. Identification of beneficial effects of growth factors including cytokines and neuropeptides on CXCR4 expression would enable our understanding of this complicated network. Therefore, we aimed to assess the role of substance P (SP) and Calcitonin gene related peptide (CGRP) on CXCR4 levels.

MATERIAL AND METHODS

CD34+cells purified from CB were cultured in a serum-free liquid culture system. Different concentrations of SP and CGRP were used in combination with cytokine cocktail. Expression of CXCR4 at protein and genomic levels was assessed by flow cytometry and real time RT-PCR.

RESULTS

Our results indicate increased CXCR4+ CD34+ cells after 7 days cultivation with SP and/or CGRP. Increased gene expression of the CXCR4 molecule was observed at 10(-9) M either SP or CGRP individually, by day 11 as compared to control group.

CONCLUSIONS

Our study indicates that SP and CGRP induce CXCR4 protein expression in short term culture, and stimulate its expression. Consequently, the increased expression of CXCR4 could improve engraftment of CB CD34+ cells.

Protein kinase B (PKB/c-akt) regulates homing of hematopoietic progenitors through modulation of their adhesive and migratory properties

Limited number of hematopoietic stem cells in umbilical cord blood (UCB) presents a problem when using UCB for stem cell transplantation. Improving their homing capacity could reduce the need for high initial cell numbers during transplantation procedures. Although it is evident that protein kinase B (PKB/c-Akt) plays an important role in regulation of migration of various cell types, a role for PKB in regulation of migration and homing of human hematopoietic stem and progenitor cells remains to be determined. PKB activity was found to be required for induction of adhesion to bone marrow-derived stromal cells and detrimental for migration of UCB-derived CD34(+) hematopoietic progenitors. In addition, PKB activity was found to positively regulate integrin expression. CD34(+) hematopoietic progenitors, and their capacity to form colonies in vitro, were not affected by transient inhibition of PKB. Finally, transplantation of β2-microglobulin(-/-) nonobese diabetic/severe combined immunodeficient mice with CD34(+) cells ectopically expressing constitutively active PKB resulted in reduced migration to the bone marrow, whereas inhibition of PKB activity resulted in an induction in bone marrow homing and engraftment. These results indicate that transient inhibition of PKB activity may provide a means for ex vivo stem cell manipulation to improve bone marrow transplantation regimes.

Effects of neuropeptide substance P on the expression of adhesion molecules in cord blood hematopoietic stem cells

Modulation of adhesion molecules expression on the surface of cord blood (CB) CD34(+) cells may assist in overcoming the delay in cord blood engraftment. Likewise, utilization of diverse growth factors such as neuropeptides could also be helpful. Therefore, we aimed to assess the role of Substance P (SP) along with a cytokine cocktail on CB CD34(+) adhesion molecule expression. CB CD34(+) cells were cultured in a serum-free media containing different concentrations of SP in combination with a cytokine cocktail (SCF, FL, TPO, IL-3, and IL-6). Expression of adhesion molecules CXCR4, CD44, CD49e, and CD62L was analyzed after 7 and/or 11 days of cell cultivation. Additionally, the colonogenic capacity of cells was analyzed by colony formation unit assay. Our results show an enhanced percentage of CD34(+)cells with CXCR4, CD44, and CD62L on day 7, as compared with control. Furthermore, an increase in frequency was observed for CD49e(+) CD34(+)cells by day 7 in both test and control groups compared with day 0. Colonogenic assays show occurrence of more total colony formation and immature progenitor cells in SP-treated cells. Our study indicates that SP could act as an effective modulator for expression of cell adhesion molecules.

Blockade of alpha6-integrin reveals diversity in homing patterns among human, baboon, and murine cells

Our understanding of the mechanisms by which intravenously transplanted hematopoietic stem/progenitor cells (HSPCs) home to and engraft the bone marrow (BM) remains incomplete, but participation of adhesion molecules has been documented. We here demonstrate that blockade of the alpha6-integrin enhanced BM homing of human and nonhuman primate BM-derived HSPCs by >60% in the xenogeneic transplant model and led to significantly improved engraftment. The effect was limited to BM-derived HSPCs, as granulocyte-colony-stimulating factor mobilized peripheral blood or cord blood HSPCs express little or no alpha6 integrin. By contrast, despite high alpha6 integrin expression, no effect of alpha6 blockade on murine BM-HSPCs homing/engraftment was observed.

Human umbilical cord blood stem cells upregulate matrix metalloproteinase-2 in rats after spinal cord injury

Matrix metalloproteinases (MMPs) are a large family of proteolytic enzymes involved in inflammation, wound healing and other pathological processes after neurological disorders. MMP-2 promotes functional recovery after spinal cord injury (SCI) by regulating the formation of a glial scar. In the present study, we aimed to investigate the expression and/or activity of several MMPs, after SCI and human umbilical cord blood mesenchymal stem cell (hUCB) treatment in rats with a special emphasis on MMP-2. Treatment with hUCB after SCI altered the expression of several MMPs in rats. MMP-2 is upregulated after hUCB treatment in spinal cord injured rats and in spinal neurons injured either with staurosporine or hydrogen peroxide. Further, hUCB induced upregulation of MMP-2 reduced formation of the glial scar at the site of injury along with reduced immunoreactivity to chondroitin sulfate proteoglycans. Blockade of MMP-2 activity in hUCB cocultured injured spinal neurons reduced the protection offered by hUCB which indicated the involvement of MMP-2 in the neuroprotection offered by hUCB. Based on these results, we conclude that hUCB treatment after SCI upregulates MMP-2 levels and reduces the formation of the glial scar thereby creating an environment suitable for endogenous repair mechanisms.

CXCR4 induction in hematopoietic progenitor cells from Fanca(-/-), -c(-/-), and -d2(-/-) mice

OBJECTIVE

Bone marrow failure is a near-universal occurrence in patients with Fanconi anemia (FA) and is thought to result from exhaustion of the hematopoietic stem cell (HSC) pool. Retrovirus-mediated expression of the deficient protein corrects this phenotype and makes FA a candidate disease for HSC-directed gene therapy. However, inherent repopulation deficits and stem cell attrition during conventional transduction culture prevent therapeutic chimerism.

MATERIALS AND METHODS

We previously reported rapid transduction protocols to limit stem cell losses after ex vivo culture. Here we describe a complementary strategy intended to improve repopulation through upregulation of chemokine receptor (CXCR) 4, a principal factor in hematopoietic homing.

RESULTS

Using murine models with transgenic disruption of Fanca, -c, and -d2, we found that c-kit(+) and sca-1(+) progenitor cells express levels of CXCR4 comparable with those of wild-type littermates. Lineage-depleted progenitor populations rapidly upregulated CXCR4 transcript and protein in response to cytokine stimulation or hypoxia, regardless of genotype. Hypoxia conditioning of lineage-depleted Fancc(-/-) progenitors also reduced oxidative stress, improved in vitro migration and led to improved chimerism in myeloablated recipients after transplantation.

CONCLUSION

These studies provide evidence that CXCR4 regulation in progenitor cells from transgenic mice representing multiple FA genotypes is intact and that modulation of homing offers a potential strategy to offset the FA HSC repopulation deficiency.

Canine stem cell factor augments expression of matrix metalloproteinase-9 by CD34 cells

BACKGROUND

Canine models have proved to be predictive of clinical findings in human bone marrow (BM) transplantation; consequently, the utilization of dogs is an excellent tool for supporting therapeutic purposes. Considering the role of growth factors in homing and mobilization of hematopoietic progenitors, the aim of this work was to evaluate whether canine stem cell factor (cSCF) contributes to matrix metalloproteinase (MMP)-9 secretion by CD34 cells.

METHODS

The study was carried out in a cell population selected by immunomagnetic techniques using the anti-canine CD34 monoclonal antibody (MAb) 3B4 produced by us. Secretion of MMP-9 was evaluated by zymography.

RESULTS

Analyzes of canine CD34(+) cells guaranteed that the MAb 3B4 was optimum for selecting a subset population with defined characteristics of primitive hematopoietic cells. The isolated cells were able to proliferate onto irradiated pre-established stroma, giving rise to mature neutrophils. There was also a 20-fold enrichment in the long-term culture-initiating cell content when the isolated population was added to irradiated cultures, with respect to the starting mononuclear cell population.

DISCUSSION

We have provided the first evidence that canine BM CD34(+) cells constitutively express MMP-9 and the role of cSCF in up-regulating the secretion of this enzyme. The fact that cSCF augments expression of MMP-9 together with the ability of the isolated CD34(+)cells to proliferate onto irradiated pre-established stroma enables further investigations to determine whether the secretion of MMP-9 mediated by cSCF is one of the factors that enhance migration, homing and repopulation of primitive hemopoietic cells.

Umbilical cord blood transplantation: basic biology and clinical challenges to immune reconstitution

Allogeneic stem cell transplantation has continued to evolve as a common procedure for the treatment of hematological malignancies and bone marrow failure. Donor bone marrow and mobilized peripheral stem cells are routinely employed for the reconstitution of immune function in leukemia and lymphoma patients following radiation and/or chemotherapy. Unfortunately, only 30% of patients have an HLA-identical sibling donor and the identification of matched unrelated donors, particularly for minorities, can present an exceptional challenge. The transplantation of umbilical cord blood (UCB) represents the most recent strategy to expand the potential donor pool while maintaining an acceptable level of treatment-related complications. First utilized in children, UCB transplantation permits a higher degree of HLA disparity while demonstrating a reduction in the incidence and severity of graft-versus-host disease (GvHD) compared to previous transplantation modalities. Despite the apparent decrease in GvHD, relapse rates remain comparable to transplantation with bone marrow or mobilized peripheral blood suggesting a strong graft-versus-leukemia/lymphoma (GvL) effect. However, several issues complicate the use of UCB transplantation and its extension to the treatment of adults. Many infections that afflict transplant patients are particularly frequent and more severe in the context of UCB transplantation. UCB T-cells are naive and therefore display less proliferation and IFN-gamma production in response to cognate antigen and also appear to demonstrate defects in signal transduction mechanisms. In addition, UCB contains T regulatory cells (Treg) with more potent suppressor function than adult Treg. Furthermore, adult patients often require more total cells and CD34+ progenitors for transplantation than a single UCB unit can provide. Thus, strategies to expand selected subpopulations from UCB and the use of multi-unit transplantation are areas of active research. This review will provide a condensed summary of the clinical history of UCB transplantation and emphasize the advantages and disadvantages of this approach to hematological malignancies in comparison to other methods of hematopoietic stem cell transplantation. Subsequently, it will mainly focus on the current challenges to immune reconstitution presented by UCB transplantation, recent research into their cellular and molecular mechanisms, and experimental approaches to overcome them.

Humanized SCID mouse models for biomedical research

There is a growing need for effective animal models to carry out experimental studies on human hematopoietic and immune systems without putting individuals at risk. Progress in development of small animal models for the in vivo investigation of human hematopoiesis and immunity has seen three major breakthroughs over the last three decades. First, CB 17-Prkdc(scid) (abbreviated CB 17-scid) mice were discovered in 1983, and engraftment of these mice with human fetal tissues (SCID-Hu model) and peripheral blood mononuclear cells (Hu-PBL-SCID model) was reported in 1988. Second, NOD-scid mice were developed and their enhanced ability to engraft with human hematolymphoid tissues as compared with CB17-scid mice was reported in 1995. NOD-scid mice have been the "gold standard" for studies of human hematolymphoid engraftment in small animal models over the last 10 years. Third, immunodeficient mice bearing a targeted mutation in the IL-2 receptor common gamma chain (IL2rgamma(null)) were developed independently by four groups between 2002 and 2005, and a major increase in the engraftment and function of human hematolymphoid cells as compared with NOD-scid mice has been reported. These new strains of immunodeficient IL2rgamma(null) mice are now being used for studies in human hematopoiesis, innate and adaptive immunity, autoimmunity, infectious diseases, cancer biology, and regenerative medicine. In this chapter, we discuss the current state of development of these strains of mice, the remaining deficiencies, and how approaches used to increase the engraftment and function of human hematolymphoid cells in CB 17-scid mice and in previous models based on NOD-scid mice may enhance human hematolymphoid engraftment and function in NOD-scid IL2rgamma(null) mice.

Hematopoietic progenitor cells (HPC) from mobilized peripheral blood display enhanced migration and marrow homing compared to steady-state bone marrow HPC

OBJECTIVE

Faster engraftment of G-CSF-mobilized peripheral blood (MPB) transplants compared to steady-state bone marrow (ssBM) is well documented and clinically relevant. A number of different factors likely contribute to this outcome. In the present study we explored whether independent of cell number there are intrinsic differences in the efficiency of progenitor cell homing to marrow between MPB and ssBM.

METHODS

Mobilization was achieved by continuous infusion of G-CSF alone or in combination with other mobilizing agents. In vivo homing assays, in vitro migration assays, gene expression analysis, and flow cytometry were utilized to compare homing-related in vivo and in vitro properties of MPB and ssBM HPC.

RESULTS

Marrow homing of murine MPB HPC, generated by different mobilizing schemes, was reproducibly significantly superior to that of ssBM, in lethally irradiated as well as in nonirradiated hosts. This phenotype was independent of MMP9, selectins, and beta2- and alpha4-integrins. Superior homing was also observed for human MPB HPC transplanted into NOD/SCIDbeta2microglobulin(-/-) recipients. Inhibition of HPC migration abrogated the homing advantage of MPB but did not affect homing of ssBM HPC, whereas enhancement of motility by CD26 inhibition improved marrow homing only of ssBM HPC. Enhanced SDF-1-dependent chemotaxis and low CD26 expression on MPB HPC were identified as potential contributing factors. Significant contributions of the putative alternative SDF-1 receptor, RDC1, were unlikely based on gene expression data.

CONCLUSION

The data suggest increased motility as a converging endpoint of complex changes seen in MPB HPC which is likely responsible for their favorable homing.

Early proliferation of umbilical cord blood cells from premature neonates

BACKGROUND AND OBJECTIVE

Human umbilical cord blood (UCB) is an important source of haematopoietic stem cells; however, the behaviour of progenitor cells obtained from premature and full-term neonates is still a controversy subject. Thus, the aim of this study was to evaluate cell cycle parameters and the proliferative capacity of UCB progenitor cells from premature and full-term neonates.

MATERIAL AND METHODS

Clonogenic assays were performed with methylcellulose, medium supplemented with recombinant stimulating growth factors and the colonies were scored on the seventh day and the 14th day of culture. A cell cycle study was carried out by DNA analysis using flow cytometry and 30 000 events were acquired; p107 and p130 expressions were analysed by Western blotting.

RESULTS

Cultures obtained from UCB of premature neonates showed an early growth of colony-forming unit (CFU)-burst forming unit erythroid/CFU-granulocyte, erythrocyte, macrophage and megakaryocyte (BFU-E/GEMM), and CFU-granulocyte, macrophage (GM) by the seventh day of culture (P < 0.001). Therefore, the number and morphological characteristics of these colonies were comparable with those obtained from full-term neonates, on the 14th day of culture. At the 14th day, a large amount of CFU-GM was detected in the premature group (P < 0.0032). The premature culture on the 14th day showed fibroblasts and was comparable to those of full-term neonates on the 21st day in terms of number and morphology of the colonies. DNA analysis showed that the number of cells in S-phase was also higher in premature samples when compared to full-term neonates, P < 0.0021 (0 h = 12.8 vs. 2.5%; 16 h = 10.5 vs. 5.9%; 20 h = 13.5 vs. 10.3%; 24 h = 13.8 vs. 9.1%; 48 h = 14.0 vs. 5.4%; 72 h = 20.5 vs. 8.9%; 96 h = 13.8 vs. 7.7%). The Western blotting results demonstrated that p107 and p130 cell cycle protein expressions were higher in premature cells than in full-term cells.

CONCLUSION

These results suggest that the higher capacity of proliferation and early differentiation of premature UCB might not be related only to the amount of stem/progenitor cells but also to a different timing of cell cycle entry.

Distinct roles of integrins alpha6 and alpha4 in homing of fetal liver hematopoietic stem and progenitor cells

Homing of hematopoietic stem cells (HSCs) into the bone marrow (BM) is a prerequisite for establishment of hematopoiesis during development and following transplantation. However, the molecular interactions that control homing of HSCs, in particular, of fetal HSCs, are not well understood. Herein, we studied the role of the alpha6 and alpha4 integrin receptors for homing and engraftment of fetal liver (FL) HSCs and hematopoietic progenitor cells (HPCs) to adult BM by using integrin alpha6 gene-deleted mice and function-blocking antibodies. Both integrins were ubiquitously expressed in FL Lin(-)Sca-1(+)Kit(+) (LSK) cells. Deletion of integrin alpha6 receptor or inhibition by a function-blocking antibody inhibited FL LSK cell adhesion to its extracellular ligands, laminins-411 and -511 in vitro, and significantly reduced homing of HPCs to BM. In contrast, the anti-integrin alpha6 antibody did not inhibit BM homing of HSCs. In agreement with this, integrin alpha6 gene-deleted FL HSCs did not display any homing or engraftment defect compared with wild-type littermates. In contrast, inhibition of integrin alpha4 receptor by a function-blocking antibody virtually abrogated homing of both FL HSCs and HPCs to BM, indicating distinct functions for integrin alpha6 and alpha4 receptors during homing of fetal HSCs and HPCs.

Fibronectin and laminin enhance engraftibility of cultured hematopoietic stem cells

To test the hypothesis that extracellular matrix (ECM) components maintain stem cell property, murine bone marrow (BM) cells were expanded in fibronectin and laminin coated plate in the presence of cytokines. We observed significant phenotypic and functional improvement of expanded cells. In 10 days, 800-fold expansion of colony-forming unit-granulocyte erythrocyte monocyte megakaryocyte (CFU-GEMM) was observed in the cultured cells. No apparent activation of cell cycle was observed, but CD29 and very late antigen-4 (VLA-4) expression was increased, as compared to the normal BM cells. A fraction of the expanded cells became verapamil sensitive, suggesting upregulation of multi-drug resistant gene(s), as found in the primitive hematopoietic stem cells (HSCs). Competitive repopulation assay confirmed that HSCs compartment was amplified during culture. Overall, our study clearly demonstrated that ex vivo culture of murine HSCs in the presence of fibronectin and laminin resulted in expansion of primitive stem cells and improvement in the marrow engraftibility.

Apoptotic lymphocytes and CD34+ cells in cryopreserved cord blood detected by the fluorescent vital dye SYTO 16 and correlation with loss of L-selectin (CD62L) expression

Discrimination between live and apoptotic cells is important for accurate determination of viable CD34(+) cells in hematopoietic stem cell transplant products. SYTO16 is a sensitive fluorescent dye for discriminating live from apoptotic leukocytes. The incidence of apoptotic leukocytes in paired samples of fresh and cryopreserved-thawed cord blood (CB) was determined by the SYTO16/7-AAD flow cytometric assay. Cell migration and expression of the cell homing molecule L-selectin (CD62L) was determined in relation to SYTO16 staining. SYTO16 detected significant proportions of apoptotic lymphocytes and CD34(+) cells in fresh and thawed CB buffy-coat samples that were not detected by 7-AAD. Compared to fresh CB, the proportion of apoptotic lymphocytes and CD34(+) cells significantly increased following thawing. Significantly higher proportions of live SYTO16(bright) lymphocytes and CD34(+) cells were found in the migrated cell population compared to the non-migrated population. Significantly fewer lymphocytes and CD34(+) cells expressed CD62L following thawing. Absence of CD62L expression was strongly correlated with apoptotic/SYTO16(dim) lymphocytes and CD34(+) cells. Cryopreserved-thawed CB contains significant proportions of apoptotic lymphocytes and CD34(+) cells that are not detected by 7-AAD. SYTO16 offers a sensitive method for discrimination of live from apoptotic leukocytes and assists in accurate assessment of CB quality and suitability for use in clinical transplantation.

Higher expression of transcription targets and components of the nuclear factor-kappaB pathway is a distinctive feature of umbilical cord blood CD34+ precursors

Delayed engraftment, better reconstitution of progenitors, higher thymic function, and a lower incidence of the graft-versus-host disease are characteristics associated with umbilical cord blood (UCB) transplants, compared with bone marrow (BM). To understand the molecular mechanisms causing these intrinsic differences, we analyzed the differentially expressed genes between BM and UCB hematopoietic stem and progenitor cells (HSPCs). The expressions of approximately 10,000 genes were compared by serial analysis of gene expression of magnetically sorted CD34(+) cells from BM and UCB. Differential expression of selected genes was evaluated by real-time polymerase chain reaction on additional CD34(+) samples from BM (n = 22), UCB (n = 9), and granulocyte colony stimulating factor-mobilized peripheral blood (n = 6). The overrepresentation of nuclear factor-kappaB (NF-kappaB) pathway components and targets was found to be a major characteristic of UCB HSPCs. Additional promoter analysis of 41 UCB-overrepresented genes revealed a significantly higher number of NF-kappaB cis-regulatory elements (present in 22 genes) than would be expected by chance. Our results point to an important role of the NF-kappaB pathway on the molecular and functional differences observed between BM and UCB HSPCs. Our study forms the basis for future studies and potentially for new strategies to stem cell graft manipulation, by specific NF-kappaB pathway modulation on stem cells, prior to transplant.

Cytokine-containing gelfoam implants at a postsurgical tumor excision site to stimulate local immune reactivity

We previously demonstrated increased numbers of CD34(+) progenitor cells in the peripheral blood of tumor bearers. Also demonstrated was the feasibility of chemoattracting these cells by sponge implants containing VEGF. The present study used a murine Lewis lung carcinoma (LLC) model to test if CD34(+) cells that are chemoattracted to a tumor excision site can be differentiated in situ into dendritic cells and whether this leads to increased local immune reactivity. After surgically excising established LLC tumors, mice received at the excision site gelatin sponge implants containing VEGF to chemoattract CD34(+) cells, and/or GM-CSF plus SCF to induce CD34(+) cell differentiation into dendritic cells. In some studies, lysates of GFP-transfected LLC cells (LLC(GFP)) were also included in the implants as a source of tumor antigen. After 2 weeks, implants and local lymph nodes were removed and analyzed. Implants containing VEGF, GM-CSF/SCF or VEGF/GM-CSF/SCF had a higher proportion of CD34(+) cells compared to control implants. However, the number of dendritic cells was higher in implants containing GM-CSF/SCF or VEGF/GM-CSF/SCF than those containing either VEGF or diluent. Regional lymph node from mice containing GM-CSF/SCF or VEGF/GM-CSF/SCF implants showed increased dendritic cell levels. However, when lysates from LLC(GFP) were added to the implants, the highest proportion of dendritic cells associated with GFP was in lymph nodes of mice containing GM-CSF/SCF implants. Lymph node cells from mice with GM-CSF/SCF or VEGF/GM-CSF/SCF had a higher level of proliferation and IFN-gamma secretion in response to in vitro LLC lysate challenge, with the greatest response being from lymph node cells of mice with GM-CSF/SCF implants. These results suggest the feasibility of using GM-CSF/SCF-containing implants to increase dendritic cell levels, uptake of tumor antigens, trafficking to lymph nodes and stimulation of immune reactivity at tumor excision sites with residual tumor.

Ex vivo culture of human CD34+ cord blood cells with thrombopoietin (TPO) accelerates platelet engraftment in a NOD/SCID mouse model

OBJECTIVES

Hematopoietic recovery, in particular platelet reconstitution, can be severely delayed after transplantation with cord blood (CB) stem cells (SC). Expansion of CB SC may be one way to improve the recovery, but there is concern that ex vivo expansion compromises the repopulating ability of SC.

METHODS

We used a short-term expansion protocol with TPO as single growth factor. The expanded cells were tested in the NOD/SCID mouse model and both platelet recovery and repopulation capacity were examined and compared with unexpanded CD34+ CB cells of the same CB donor.

RESULTS

Platelet recovery started 1 week earlier in mice transplanted with TPO-expanded CD34+ cells and at days 5 and 8 after transplantation, 6.2 +/- 2.6 and 13.9 +/- 6.7 plt/microL were observed, respectively. At similar time intervals 0.0 and 1.5 +/- 0.2 plt/microL respectively were detected in mice receiving the unmanipulated CD34+ grafts. This was accompanied by a higher number of CFU-Mk in the bone marrow (BM) 7 days after transplantation. Moreover, the BM engraftment and the lineage differentiation of human cells at 6 weeks after transplantation was similar, suggesting that long-term engraftment was not compromised by the expansion procedure.

CONCLUSION

Ex vivo expansion with TPO as single growth factor results in an accelerated platelet recovery in NOD/SCID mice and appears not to affect the long-term repopulation capacity.

Osteopontin, a key component of the hematopoietic stem cell niche and regulator of primitive hematopoietic progenitor cells

Although recent data suggests that osteoblasts play a key role within the hematopoietic stem cell (HSC) niche, the mechanisms underpinning this remain to be fully defined. The studies described herein examine the role in hematopoiesis of Osteopontin (Opn), a multidomain, phosphorylated glycoprotein, synthesized by osteoblasts, with well-described roles in cell adhesion, inflammatory responses, angiogenesis, and tumor metastasis. We demonstrate a previously unrecognized critical role for Opn in regulation of the physical location and proliferation of HSCs. Within marrow, Opn expression is restricted to the endosteal bone surface and contributes to HSC transmarrow migration toward the endosteal region, as demonstrated by the markedly aberrant distribution of HSCs in Opn-/- mice after transplantation. Primitive hematopoietic cells demonstrate specific adhesion to Opn in vitro via beta1 integrin. Furthermore, exogenous Opn potently suppresses the proliferation of primitive HPCs in vitro, the physiologic relevance of which is demonstrated by the markedly enhanced cycling of HSC in Opn-/- mice. These data therefore provide strong evidence that Opn is an important component of the HSC niche which participates in HSC location and as a physiologic-negative regulator of HSC proliferation.

A combination of catalase and trehalose as additives to conventional freezing medium results in improved cryoprotection of human hematopoietic cells with reference to in vitro migration and adhesion properties

BACKGROUND

Cryopreservation of hematopoietic cells from cord blood is an essential component in unrelated transplant settings. Cell damage during freezing is caused by multiple factors, of which membrane damage and oxygen free radical generation are two major factors. It was reported earlier that a combination of catalase and trehalose as additives in freezing medium affords better cryoprotection in terms of long-term culture assays.

STUDY DESIGN AND METHODS

Mononuclear and CD34+ cells isolated from cord blood were used as a source of hematopoietic cells. KG1a cell line was used as a model system in adhesion assays. The cells were frozen in a programmable freezer and stored at -196 degrees C. Various homing-related assays were carried out on the frozen cells.

RESULTS

Herein it is reported that these two additives afford better preservation of adhesion- and migration-related properties of the frozen cells. The test cells frozen with additives resulted in improved migration toward stromal-derived factor-1alpha and showed higher expression of its receptor CXCR4. Colony-forming unit assay of migrated test cells showed that these cells are early progenitors having capacity to give rise to all types of myeloid colonies. Test cells also show increased expression of FLT3R and improved responsiveness to FLT3 ligand, the homing-related cytokine. Adhesion to stroma and extracellular matrix was better in test cells as compared to control cells.

CONCLUSION

The present data provide evidence that addition of catalase and trehalose to the conventional freezing medium preserves migration- and adhesion-related properties of the hematopoietic graft.

Expression and function of homing-essential molecules and enhanced in vivo homing ability of human peripheral blood-derived hematopoietic progenitor cells after stimulation with stem cell factor

Hematopoietic stem cell (HSC) homing from blood to bone marrow is a multistep process involving rolling, extravasation, migration, and finally adhesion in the correct microenvironment. With view to the hematopoietic recovery after clinical stem cell transplantation, we investigated the effect of stem cell factor (SCF) on the expression and the adhesive function of the alpha4beta1 and alpha5beta1 integrins very-late antigen (VLA)-4 and VLA-5 on peripheral blood-derived hematopoietic progenitor cells. After SCF stimulation, the expression of VLA-4 and VLA-5 on CD34+/c-kit+ cells obtained from healthy donors increased from 54% to 90% and from 3% to 82%, respectively. For patient-derived cells, the increase was 67% to 90% and 12% to 46%. The proportion of mononuclear cells adhering to the fibronectin fragment CH296 increased by stimulation with SCF from 14% to 23%. Accordingly, functional studies showed an approximate 30% increase of adherent long-term culture-initiating cell. The improvement of the homing abilities of SCF-stimulated HSC was confirmed by transplantation into sublethally irradiated nonobese diabetic-scid/scid mice. Six weeks after the transplantation, in eight of eight animals receiving human HSC with the addition of SCF, a profound multilineage hematopoietic engraftment was detected, whereas in the control group receiving only HSC, none of eight animals engrafted. Our data provide the first in vivo evidence that stimulation with cytokines improves the homing ability of transplanted human hematopoietic progenitor cells.

Umbilical Cord Blood Transplantation: A New Alternative Option

Allogeneic hematopoietic stem cell transplantation is a life-saving procedure for hematopoietic malignancies, marrow failure syndromes, and hereditary immunodeficiency disorders. However, wide application of this procedure is limited by availability of suitably HLA-matched adult donors. Umbilical cord blood (UCB) has being increasingly used as an alternative hematopoietic stem cell source for these patients. To date, over 6000 UCB transplant procedures in children and adults have been performed worldwide using UCB donors. Broader use of UCB for adult patients is however limited by the available infused cell dose. This has prompted intensive research on ex vivo expansion of UCB stem cells and UCB graft-engineering including accessory cells able to improve UCB engraftment and reconstitution and for tissue regenerative potential. Recently, two large European and North American retrospective studies demonstrated that UCB is an acceptable alternative source of hematopoietic stem cells for adult recipients who lack HLA-matched adult donors. UCB is anticipated to address needs in both transplantation and regenerative medicine fields. It has advantages of easy procurement, no risk to donors, low risk of transmitting infections, immediate availability and immune tolerance allowing successful transplantation despite HLA disparity.

Stem cell factor improves SCID-repopulating activity of human umbilical cord blood-derived hematopoietic stem/progenitor cells in xenotransplanted NOD/SCID mouse model

Poor in vivo homing capacity of hematopoietic stem/progenitor cells (HS/PCs) from umbilical cord blood (UCB) can be reversed by short-term ex vivo manipulation with recombinant human stem cell factor (rHuSCF). This study was designed to evaluate the effect of ex vivo manipulation of UCB-derived HS/PCs with rHuSCF on human cell engraftment rates in xenotransplanted NOD/SCID mouse model. The human cell engraftment rates in xenotransplanted primary and secondary NOD/SCID mice were characterized using four-color flow cytometric analysis and progenitor assay. Grafts of rHuSCF-treated UCB CD34(+) cells resulted in significantly higher levels of human cell engraftment than that of nontreated ones in both xenotransplanted primary and secondary NOD/SCID recipients. Fresh UCB CD34(+) cells did not express either of the matrix metalloproteinase (MMP) family members MMP-2 or MMP-9. rHuSCF-treated UCB CD34(+) cells expressed significant levels of MMP-2 and MMP-9. Pretreatment of UCB CD34(+) cells with the specific MMP inhibitor completely blocked human cell engraftment in xenotransplanted NOD/SCID recipients. Our results indicate that ex vivo manipulation of human HS/PCs with rHuSCF might provide an optimal approach to develop more effective stem cell-based therapies in situations where engraftment is delayed due to limiting HS/PCs number, for example, UCB transplantation.

Transplantable stem cells: home to specific niches

PURPOSE OF REVIEW

Although the concept of engraftment and clinical reconstitution of the bone marrow was described several decades ago, the analysis of individual steps within this process remains a major focus of much current research in stem cell biology. In particular, this extends to the identification and characterization of the specific stem cell niche first proposed by Schofield in 1978. It is appropriate, therefore, that on the 25th anniversary of this publication, that we review recent progress in our understanding of the location and composition of the bone marrow stem cell niche and of the mechanisms involved in the initial phases of hematopoietic stem cell engraftment.

RECENT FINDINGS

During the past 12 months there have been significant advancements in our understanding of the interplay of molecules involved in the homing of hematopoietic stem cells to the bone marrow. In addition, innovative methodologies have become available for the visualization of hematopoietic stem cells within the bone marrow in situ. In an important development in this area, studies our now focusing on events after transendothelial migration into the marrow cords, including mechanisms involved in hematopoietic stem cell migration to and lodgment within the hematopoietic stem cell niche. Furthermore, there have been numerous new reports analyzing the molecular regulation of hematopoietic stem cells within the bone marrow niche in situ.

SUMMARY

Overall, recent advancements in our understanding of hematopoietic stem cell biology and, in particular, the interaction of hematopoietic stem cells with the hematopoietic microenvironment paves the way for expanded use in regenerative medicine.