Cord blood progenitor cells have greater transendothelial migratory activity and increased responses to SDF-1 and MIP-3beta compared with mobilized adult progenitor cells

Circulating angiogenic cells in glioblastoma: toward defining crucial functional differences in CAC-induced neoplastic versus reactive neovascularization

Background

In order to identify suitable therapeutic targets for glioma anti-angiogenic therapy, the process of neovascularization mediated by circulating angiogenic cells (CACs) needs to be scrutinized.

Methods

In the present study, we compared the expression of neovascularization-related genes by 3 circulating CAC subsets (hematopoietic progenitor cells [HPCs], CD34⁺, and KDR⁺ cells; internal controls: peripheral blood mononuclear cells and circulating endothelial cells) of treatment-naïve patients with glioblastoma (GBM) to those of patients undergoing reactive neovascularization (myocardial infarction (MI). CACs from umbilical cord (representing developmental neovascularization) and healthy subjects served as controls. Fluorescent-activated cell sorting was used to isolate CACs, RT-PCR to determine the expression levels of a panel of 48 neovascularization-related genes, and Luminex assays to measure plasma levels of 21 CAC-related circulating molecules.

Results

We found essential differences in gene expression between GBM and MI CACs. GBM CACs had a higher expression of proangiogenic factors (especially, KITL, CXCL12, and JAG1), growth factor and chemotactic receptors (IGF1R, TGFBR2, CXCR4, and CCR2), adhesion receptor monomers (ITGA5 and ITGA6), and matricellular factor POSTN. In addition, we found major differences in the levels of neovascularization-related plasma factors. A strong positive correlation between plasma MMP9 levels and expression of CXCR4 in the CAC subset of HPCs was found in GBM patients.

Conclusions

Our findings indicate that CAC-mediated neovascularization in GBM is characterized by more efficient CAC homing to target tissue and a more potent proangiogenic response than in physiologic tissue repair in MI. Our findings can aid in selecting targets for therapeutic strategies acting against GBM-specific CACs.

SDF1 gradient associates with the distribution of c-Kit+ cardiac cells in the heart

Identification of the adult cardiac stem cells (CSCs) has offered new therapeutic possibilities for treating ischemic myocardium. CSCs positive for the cell surface antigen c-Kit are known as the primary source for cardiac regeneration. Accumulating evidence shows that chemokines play important roles in stem cell homing. Here we investigated molecular targets to be utilized in modulating the mobility of endogenous CSCs. In a four week follow-up after experimental acute myocardial infarction (AMI) with ligation of the left anterior descending (LAD) coronary artery of Sprague-Dawley rats c-Kit+ CSCs redistributed in the heart. The number of c-Kit+ CSCs in the atrial c-Kit niche was diminished, whereas increased amount was observed in the left ventricle and apex. This was associated with increased expression of stromal cell-derived factor 1 alpha (SDF1α), and a significant positive correlation was found between c-Kit+ CSCs and SDF1α expression in the heart. Moreover, the migratory capacity of isolated c-Kit+ CSCs was induced by SDF1 treatment in vitro. We conclude that upregulation of SDF1α after AMI associates with increased expression of endogenous c-Kit+ CSCs in the injury area, and show induced migration of c-Kit+ cells by SDF1.

Human Cord Blood-Derived Mesenchymal Stem Cells Home and Survive in the Marrow of Immunodeficient Mice after Systemic Infusion

Bone marrow is the residence site of mesenchymal stem cells (MSC), which upon commitment and maturation develop into several mesenchymal phenotypes. Recently, we have described the presence of MSC in human cord blood (cbMSC) and informed that their properties are the same as those for MSC obtained from adult bone marrow. In this study we have investigated the capability of transplanted cbMSC to home and survive in the marrow of unconditioned nude mice. cbMSC utilized for transplantation studies were characterized by morphology, differentiation potential, and immunophenotype. After transplantation by systemic infusion, human DNA (as detected by PCR amplification of human-specific β-globin gene) was detected in the marrow of recipients as well as in ex vivo-expanded stromal cells prepared from the marrow of transplanted animals. These results demonstrate homing and survival of cbMSC into the recipient marrow and also suggest a mesenchymal-orientated fate of engrafted cells, because human DNA was also detected in cells of other recipient tissues, like cardiac muscle, teeth, and spleen.

Cell cycle and tissue of origin contribute to the migratory behaviour of human fetal and adult mesenchymal stromal cells

Mesenchymal stromal cells (MSC) are potential cells for cellular therapies, in which the recruitment and migration of MSC towards injured tissue is crucial. Our data show that culture-expanded MSC from fetal lung and bone marrow, adult bone marrow and adipose tissue contained a small percentage of migrating cells in vitro, but the optimal stimulus was different. Overall, fetal lung-MSC had the highest migratory capacity. As fetal bone marrow-MSC had lower migratory potential than fetal lung-MSC, the tissue of origin may determine the migratory capacity of MSC. No additive effect in migration towards combined stimuli was observed, which suggests only one migratory MSC fraction. Interestingly, actin rearrangement and increased paxillin phosphorylation were observed in most MSC upon stromal cell-derived factor-1alpha or platelet-derived growth factor-BB stimulation, indicating that this mechanism involved in responding to migratory cues is not restricted to migratory MSC. Migratory MSC maintained differentiation and migration potential, and contained significantly less cells in S- and G2/M-phase than their non-migrating counterpart. In conclusion, our results suggest that MSC from various sources have different migratory capacities, depending on the tissue of origin. Similar to haematopoietic stem cells, cell cycle contributes to MSC migration, which offers perspectives for modulation of MSC to enhance efficacy of future cellular therapies.

SDF1-3' G801A polymorphisms in Polish patients with systemic lupus erythematosus

It has been reported that stromal cell-derived factor-1 (SDF1), currently also designated CXCL12, plays a significant role in the development of nephritis and death in the lupus mice model. Using restriction length fragment polymorphism (RFLP) analysis we assessed the frequencies of SDF1-3' G801A (rs 1801157) polymorphic variants between systemic lupus erythematosus (SLE) patients (n = 150) and controls (n = 300). There were no significant differences in the prevalence of SDF1-3' G801A polymorphic variants in SLE patients and healthy individuals. However, we observed that the SDF1-3' A/A and G/A genotypes (recessive model) contributed to renal manifestations of SLE OR = 3.042 (95% CI = 1.527-6.058, P = 0.002), and the p value stayed statistically significant after Bonferroni correction (p(corr) = 0.032) in SLE patients. We also found an association of the SDF1-3' A/A and G/A genotypes (recessive model) with dermal manifestations of SLE OR = 2.510 (95% CI = 1.247-5.052, P = 0.0122), (p(corr) = 0.1952) but this did not remain statistically significant after Bonferroni correction. Our observations suggest that the SDF1-3' G801A genotype may be associated with some clinical manifestations in patients with SLE.

Tamoxifen epigenetically modulates CXCL12 expression in MCF-7 breast cancer cells

The CXCL12 chemokine binds to the CXCR4 receptor and contributes to survival, proliferation, and migration of malignant cells. Recent reports indicate that breast cancer cells lacking expression of CXCL12 but exhibiting CXCR4 can metastasize to target organs that secrete CXCL12. We observed that Tamoxifen (Tam), similarly to 5-dAzaC, results in significantly increased levels of CXCL12 transcript and protein in MCF-7 breast cancer cells. Bisulfite sequencing suggests that Tam, similarly to 5-dAzaC, may increase CXCL12 expression via reduction in methylation of cytosine in the cytosine-guanosine (CpG) dinucleotide island of the CXCL12 promoter of MCF-7 cells. Our results, together with findings of other researches, may suggest that Tam epigenetically activates CXCL12 expression in breast cancer cells and can make these cells less susceptible to attraction by exogenous CXCL12 to metastasis sites.

Adhesion receptor expression by CD34+ cells from peripheral blood or bone marrow grafts: correlation with time to engraftment

OBJECTIVE

This study was undertaken to define the pattern of cell adhesion receptor expression by the CD34+ progenitor cells from mobilized peripheral blood and bone marrow from normal and autologous donors, and to correlate the adhesion receptor profile with time to blood cell recovery for patients undergoing autologous transplant.

METHODS

Blood cell recovery was determined by absolute neutrophil count (> 500/microL), time to last red cell transfusion, and platelet count (> 50,000/microL and > 100,000/microL). The analysis for expression of adhesion receptors alphaL (CD11a), alpha2 (CD49b), alpha3 (CD49c), alpha4 (CD49d), alpha5 (CD49e), alpha6 (CD49f), beta1 (CD29), L-selectin (CD62L), ICAM-1 (CD54), PECAM-1 (CD31), HCAM (CD44), and P-selectin (CD62P) was performed by two-color flow cytometry. The Kruskal-Wallis test and Spearman's rank correlation were used for statistical analysis.

RESULTS

Statistical analysis of adhesion expression by the CD34+ population for patients undergoing autologous transplant demonstrated that the higher percent expression of PECAM-1 correlated with longer time to platelet recovery (> 100,000/microL, p = 0.049). In contrast, the higher the percent expression of alpha6 (p = 0.013) and the increased density of expression of alpha2 (p = 0.035), alpha3 (p = 0.023), alpha4 (p = 0.044), beta1 (p = 0.027), and ICAM-1 (p = 0.010) correlated with shorter time to platelet recovery. Neutrophil recovery time decreased with increased density of expression of alphaL (p = 0.014) and P-selectin (p = 0.007) receptors. Increased density of expression of CD44 (HCAM) was associated with longer time to red blood cell recovery (p = 0.05).

CONCLUSION

These data suggest that upregulation of specific adhesion receptors or selection of certain cell populations could result in earlier blood cell recovery after transplant.

Cytokines produced by cultured human umbilical cord blood (HUCB) cells: Implications for brain repair

The potential therapeutic benefits from human umbilical cord blood (HUCB) cells for the treatment of injuries, diseases, and neurodegeneration are becoming increasingly recognized. The transplantation or infusion of cord blood cells in various animal models, such as ischemia/stroke, traumatic brain injury, myocardial infarction, Parkinson's disease, and amyotropic lateral sclerosis, has resulted in amelioration of behavioral deficits, and with some diseases, a prolonged lifespan decreased neuropathology. Previously, we reported the migration of HUCB cells to ischemic brain supernatant (tissue extracts) is time-dependent, and the expression of specific chemokines responds to this migration pattern. The mechanism(s) responsible for these effects are unknown. The expression of cytokines and chemokines produced by HUCB cells (under various culturing conditions) was investigated in this study. IL-8, MCP-1, and IL-1alpha were consistently expressed by the HUCB mononuclear cells regardless of the culture condition. These results provide insights to factors that may be partially responsible for the functional improvements seen in the animal models of injury investigating the therapeutic use of HUCB cells.

Expression of cardiomyocytic markers on adipose tissue-derived cells in a murine model of acute myocardial injury

Animal and early clinical studies have provided evidence suggesting that intracoronary administration of autologous bone marrow-derived cells results in improved outcome following myocardial infarction. Animal studies with cultured marrow stromal cells (MSC) have provided similar data. Cells with properties that are similar to MSC have been identified in adipose tissue. Other groups have demonstrated in vivo differentiation of adipose tissue-derived cells (ADC) into cells exhibiting biochemical and functional markers of cardiac myocytes, including spontaneous beating. Based on these observations, the objective of the present study was to determine whether ADC might undergo similar differentiation in vivo in the context of myocardial injury.ADC were isolated from subcutaneous adipose tissue of Rosa26 mice (which express the beta-galactosidase transgene in almost every tissue) and injected into the intraventricular chamber of B6129S recipient mice immediately following induction of myocardial cryoinjury. Groups of recipients were euthanized at 24 hours, 7 and 14 days post surgery and examined for the presence of donor-derived cells within the heart.Beta-gal positive cells were identified in the infarcts of ADC-treated animals. No staining was observed in uninjured myocardium or in infarcts of control animals. Immunohistochemical analysis revealed co-expression of beta-gal with Myosin Heavy Chain, Nkx2.5 and with Troponin I. Co-expression of beta-galactosidase with Connexin 43, CD31, von Willebrand factor, MyoD or CD45 was not detected.Thus, these data indicate that adipose tissue contains a population of cells that has the ability to engraft injured myocardium and that this engraftment is associated with expression of cardiomyocytic markers by donor-derived cells.

Stroke-induced Migration of Human Umbilical Cord Blood Cells: Time Course and Cytokines

The therapeutic window for treatment of individuals after stroke is narrow, regardless of the treatment regime; extension of this window would provide a major therapeutic advance. In prior reports, we demonstrated significant improvements in the behavioral defects of rats that received human umbilical cord blood (HUCB) cells 24 h after a middle cerebral arterial occlusion. These effects paralleled the recruitment of these cells to the site of tissue damage. While the administration of HUCB cells 24 h after stroke was effective, the optimal time to administer these cells after stroke has not been established. Here, we investigated the migration of HUCB cells to ischemic tissue extracts. After ischemic assault, brain tissue was homogenized, and the supernatants were assayed for their ability to attract HUCB mononuclear cells as well as for levels of several cytokines. We demonstrate increased migratory activity of HUCB cells toward the extracts harvested at 24-72 h after stroke. The extracts possessed increased levels of certain cytokines and chemokines, suggesting their participation in HUCB cell migration. The results from this study are promising in that the current 3-h therapeutic window for the treatment of stroke victims, using approved anticoagulant treatment, may be extended with the use of HUCB cell therapy 24-72 h post stroke. Last, the chemokines present in the supernatant provide a sound starting point to start examining the mechanisms responsible for the in vivo migration of HUCB cells after the induction of stroke.

Hierarchy of molecular-pathway usage in bone marrow homing and its shift by cytokines

Efficient bone marrow (BM) homing is a prerequisite for successful engraftment of transplanted hematopoietic cells (HPCs). Contradictory conclusions about the contribution of SDF-1/CXCR4 have clouded our understanding of its role within the molecular pathway cooperation needed for BM homing, particularly with the well-defined hierarchic network of adhesion molecules. In the present study we sought to unravel cooperative and compensatory molecular pathways guiding BM homing. Fresh BM-HPCs, rendered either SDF-1 unresponsive or Gi-signaling refractory, homed quite efficiently, because of compensation by alpha4-integrin interacting with VCAM-1. The contribution of SDF-1/CXCR4- or Gi-protein-mediated signals to BM homing became apparent after their blockade was combined with deletion of alpha4-integrin, leading to dramatic reduction in BM homing. Similar conclusions were revealed when VCAM-1-deficient hosts were used. Cytokine incubation changed the functional properties of BM-HPCs and hierarchy of molecular pathway usage in homing, by shifting the dominance among the homing mediators: loss of CXCR4 or Gi-signaling now significantly reduced BM homing, with only partial compensation through alpha4/VCAM-1 and endothelial selectins. These studies depict a flexible hierarchy of cooperating homing pathways, in which dominant players are repositioned with changing cytokine milieu, and possibly source of HPCs.

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

OBJECTIVE

The cause of delayed hematopoietic reconstitution after umbilical cord blood transplantation (UCBT) remains controversial. We hypothesized that hematopoietic stem/progenitor cells (HS/PCs) from UCB have some defects of the homing-related molecules responsible for their slow engraftment.

MATERIALS AND METHODS

A homing-related molecule repertoire expressed on HS/PCs from fresh and cryopreserved UCB, mobilized peripheral blood (mPB), and bone marrow (BM) were compared using sensitive, four-color fluorescence-activated cell sorting analysis. Purified CD34+ cells were subjected to ex vivo transmigration through double-coated transwell filter inserts, and an in vivo homing assay was performed in xenotransplanted NOD/SCID mice.

RESULTS

UCB-derived CD34(bright) cells expressed significantly lower levels of CD49e, CD49f, and CXCR-4 than their mPB and BM counterparts. CD34+ cells from UCB (and BM) exhibited significantly lower ex vivo transmigration than those from mPB, which were largely blocked by neutralizing antibodies to CD49e or CD49f. Recombinant human tumor necrosis factor-alpha treatment enhanced ex vivo transmigration of CD34+ cells from UCB and BM by inducing expression of the matrix metalloproteinases MMP-2/MMP-9. Short-term treatment of UCB-derived CD34+ cells with rHu-stem cell factor (rHuSCF) up-regulated levels of the homing-related molecules with their increased ex vivo transmigratory and in vivo homing potential.

CONCLUSION

Our results indicate that disadvantageous transmigratory behavior of HS/PCs from UCB, which might partly explain the delayed reconstitution after UCBT, can be reversed by ex vivo manipulation with rHuSCF.

Effect of stromal-cell-derived factor 1 on stem-cell homing and tissue regeneration in ischaemic cardiomyopathy

BACKGROUND

Myocardial regeneration via stem-cell mobilisation at the time of myocardial infarction is known to occur, although the mechanism for stem-cell homing to infarcted tissue subsequently and whether this approach can be used for treatment of ischaemic cardiomyopathy are unknown. We investigated these issues in a Lewis rat model (ligation of the left anterior descending artery) of ischaemic cardiomyopathy.

METHODS

We studied the effects of stem-cell mobilisation by use of granulocyte colony-stimulating factor (filgrastim) with or without transplantation of syngeneic cells. Shortening fraction and myocardial strain by tissue doppler imaging were quantified by echocardiography.

FINDINGS

Stem-cell mobilisation with filgrastim alone did not lead to engraftment of bone-marrow-derived cells. Stromal-cell-derived factor 1 (SDF-1), required for stem-cell homing to bone marrow, was upregulated immediately after myocardial infarction and downregulated within 7 days. 8 weeks after myocardial infarction, transplantation into the peri-infarct zone of syngeneic cardiac fibroblasts stably transfected to express SDF-1 induced homing of CD117-positive stem cells to injured myocardium after filgrastim administration (control vs SDF-1-expressing cardiac fibroblasts mean 7.2 [SD 3.4] vs 33.2 [6.0] cells/mm2, n=4 per group, p<0.02) resulting in greater left-ventricular mass (1.24 [0.29] vs 1.57 [0.27] g) and better cardiac function (shortening fraction 9.2 [4.9] vs 17.2 [4.2]%, n=8 per group, p<0.05).

INTERPRETATION

These findings show that SDF-1 is sufficient to induce therapeutic stem-cell homing to injured myocardium and suggest a strategy for directed stem-cell engraftment into injured tissues. Our findings also indicate that therapeutic strategies focused on stem-cell mobilisation for regeneration of myocardial tissue must be initiated within days of myocardial infarction unless signalling for stem-cell homing is re-established.

Effect of recombinant human deoxyribonuclease on the expression of cell adhesion molecules of thawed and processed cord blood hematopoietic progenitors

BACKGROUND AND OBJECTIVES

The integrity of granulocytic cells and platelets is compromised within cryopreserved stem cell transplants, and consequent DNA release during the thawing procedure can therefore lead to clotting phenomena or microaggregate formation and that in turn may cause loss of progenitor cells. To circumvent this problem a new processing protocol was introduced using recombinant human deoxyribonuclease (rhDNase) to prevent cell aggregate formation. In addition, the impact of this new processing protocol on CD34+ umbilical cord blood (UCB) cells was assessed.

MATERIALS AND METHODS

Fifty samples derived from 7 buffy coat (BC) volume reduced UCB units were cryopreserved, thawed, and processed with washing solutions that were supplemented with rhDNase in various concentrations. Thereafter, clotting and microaggregate formation was scored microscopically. In addition, expression of the adhesion molecules leukocyte function-associated antigen 1 (LFA-1, n = 6), intercellular adhesion molecule-1 (ICAM-1, n = 11), and L-selectin (n = 11) on CD34+ UCB cells was analyzed by flow cytometry after incubating the samples with either dimethyl sulfoxide (DMSO) 5.5%, rhDNase 10 or 50 U/mL, or a combination of DMSO 5.5% and rhDNase 50 U/mL.

RESULTS

At a minimal concentration of 10 U rhDNase/mL, clotting or microaggregate formation could be prevented for all tested samples, whereas cell clots could be observed for concentrations up to 8 U/mL. The expression of adhesion molecules on untreated CD34+ UCB cells (L-selectin: 64.6 +/- 18.8%; LFA-1: 62.6 +/- 7.5%; ICAM-1: 14.8 +/- 4.1%) did not show any significant difference compared with cells that were incubated with up to 50 U/mL rhDNase (L-selectin: 62.2 +/- 19.3%; LFA-1: 63.1 +/- 5.9%; ICAM-1: 17.5 +/- 6.7%). However, after a combined treatment with DMSO 5.5% and rhDNase 50 U/mL, a slight but significant decrease in L-selectin expression could be observed (P < 0.03).

CONCLUSION

The supplementation of rhDNase to a final concentration of 10 U/mL cell suspension proved to be effective in preventing clot formation under the conditions examined and did not lead to decreased expression levels of adhesion molecules. We therefore recommend the use of rhDNase for the prevention of clot formation and cell loss during the processing of thawed UCB transplants.

Influence of cell cycling and cell division on transendothelial migration of CD34+ cells

The migration of haemopoietic stem and progenitor cells across endothelium lining bone marrow sinuses is a critical first step in the homing and successful engraftment of these cells. We have previously shown that freshly isolated mobilized peripheral blood CD34+ cells adhere to the endothelial surface but do not transmigrate unless activated by growth factors. The aim of this work was to examine the relationship between cell cycle progression, cell division and migration across endothelium. We now show that the enhanced migration of cytokine-activated cells is selective for cells which are in G0G1 phase of the cell cycle. Thus, the transmigrated population of CD34+ cells was enriched for cells in G0G1 phase, and sorted cells in G0G1 migrated more efficiently than those in S+G2M. Conversely, cells in S+G2M were more adherent to endothelium, a finding that may explain their reduced migration. Using the cytoplasmic dye, carboxyfluorescein diacetate succinimidyl ester, to track the divisional kinetics of CD34+ cells, we found that migration occurred preferentially in non-divided cells. Thus, although CD34+ cells require cytokine activation in order to migrate, cell division is not required for transmigration, which occurs optimally before cells enter S phase. The superior migratory ability of CD34+ cells in G0G1 phase of the cell cycle may have important implications for the homing and engraftment of ex vivo expanded cells.

Treatment of circulating CD34(+) cells with SDF-1alpha or anti-CXCR4 antibody enhances migration and NOD/SCID repopulating potential

OBJECTIVE

Stromal cell-derived factor-1alpha (SDF-1alpha) has been implicated in homing and engraftment of primitive hematopoietic progenitor cells (HPC) in studies demonstrating reduced NOD/SCID repopulating potential of HPC exposed to supra-physiologic concentrations of SDF-1alpha or anti-CXCR4. Outcome of CXCR4 signaling in some cells has been shown to be dependent on the concentration of SDF-1alpha. We aimed to determine whether similar concentration-dependent responses to CXCR4 signaling are present in CD34(+)cells.

MATERIALS AND METHODS

Human peripheral blood (PB), mobilized PB (MPB), or bone marrow (BM) CD34(+) cells were incubated for 30 minutes with different concentrations of SDF-1alpha or anti-CXCR4, washed, then assessed for in vitro hematopoietic potential, migration, and NOD/SCID repopulating potential.

RESULTS

Exposure of MPB or PB CD34(+) cells to 100 ng/mL SDF-1alpha increased tyrosine phosphorylation without subsequent proliferation or apoptosis. Spontaneous and SDF-1alpha-directed migration also increased in pretreated cells, despite previous exposure to SDF-1alpha. Cells exposed to 1 microg anti-CXCR4/10(6) cells displayed similar increases in activation and migration as cells exposed to SDF-1alpha, demonstrating the ability of anti-CXCR4 to activate the CXCR4 receptor. Interestingly, chimerism in NOD/SCID mice transplanted with MPB CD34(+) cells pretreated with SDF-1alpha or anti-CXCR4 was increased, while exposure of these cells to 10- to 100-fold higher concentrations of these proteins inhibited in vitro migration and NOD/SCID repopulating potential. Migration and NOD/SCID repopulating potential of BM CD34(+) cells remained unchanged after treatment with either protein.

CONCLUSIONS

These results illustrate the ability of SDF-1alpha and anti-CXCR4 to augment repopulating potential of CD34(+) cells, and suggest that HPC function can be favorably modulated through specific CXCR4 signaling.

Increased binding and defective migration across fibronectin of cycling hematopoietic progenitor cells

Engraftment of hematopoietic progenitor cells has been shown to decrease during cell cycle transit. We studied cell cycle-associated changes in adhesion and migration of mitotically activated cord blood CD34+ cells. Migration toward medium conditioned by the stromal-derived factor-1-producing cell line MS-5 was studied in bovine serum albumin- and fibronectin (Fn)-coated transwells. Migration was reduced in cycling CD34+ cells and long-term culture-initiating cells (LTC-ICs) compared with their noncycling counterparts across Fn but not across bovine serum albumin. Conversely, Fn binding was higher in cycling CD34+ cells and LTC-ICs compared with noncycling progenitor cells, while adhesion of both subsets to bovine serum albumin was undetectable. The contribution of alpha4 and alpha5 integrins in mediating adhesion and migration of activated CD34+ cells onto Fn was analyzed by neutralization experiments. While alpha4-mediated Fn binding decreased during G(2)/M, alpha5 integrin-mediated adhesion increased during transit from G(0)/G(1) to S and G(2)/M phases. As for migration, the contribution of alpha4 integrin was similar in all phases, whereas alpha5-directed migration was lower in G(2)/M compared with G(0)/G(1) and S phases. Defective migration of cycling CD34+ cells was not due to differences in alpha5 integrin expression. In conclusion, chemotaxis across Fn is less efficient in cycling progenitor cells in correlation with an increased Fn binding capacity. In addition, alpha4 and alpha5 integrin functions are independently modulated during cell cycle transit.

Fetal haemopoietic cells display enhanced migration across endothelium

Fetal haemopoietic cells continually circulate and migrate into tissues, and thus may have specialized homing capabilities. In this study we investigated the in vitro features of haemopoietic cells in fetal blood and liver which are relevant to homing and engraftment. Fetal cells were examined for long-term culture-initiating cell (LTC-IC) and progenitor content, adhesion molecule expression, cell cycle behaviour and transendothelial migratory activity. The LTC-IC content of fetal CD34+ cells is similar to that of CD34+ cells from cord and adult mobilized blood. In contrast to adult and cord blood CD34+ cells, fetal CD34+ cells were actively cycling (11.0 +/- 1.7% and 28 +/- 1.1% of fetal blood and liver CD34+ cells, respectively, in S+G2M, P < 0.001, compared with cord and adult cells). The striking finding was that fetal haemopoietic cells (both LTC-ICs and committed progenitors) displayed significantly higher levels of migration across endothelium (P < 0.05 compared with cord, P < 0.01 compared with adult blood and bone marrow CD34+ cells), which were further increased by chemokines and growth factors. The superior migratory activity of fetal haemopoietic cells may underlie a more efficient homing ability, in keeping with their physiological role.

Homing of human hematopoietic stem and progenitor cells: new insights, new challenges?

In healthy adults, hematopoiesis takes place in the bone marrow, where the majority of hematopoietic progenitor cells (HPC) reside. In patients undergoing chemo- and/or radiotherapy, hematopoiesis is seriously disturbed. Reconstitution of bone-marrow function can be achieved by bone marrow transplantation or peripheral blood stem cell transplantation. The success of stem cell transplantation depends on the ability of intravenously infused stem cells to lodge in the bone marrow, a process referred to as homing. However, the molecular mechanisms that govern this process are poorly understood. It is hypothesized that homing is a multistep process, consisting of adhesion of the HPC to endothelial cells of the marrow sinusoids, followed by transendothelial migration directed by chemoattractants, and finally anchoring within the extravascular bone marrow spaces where proliferation and differentiation will occur. In this review, we discuss the factors that determine the engraftment potential of stem cells, and focus on various aspects of migration and homing of HPC, i.e., the role of the chemokine stromal cell-derived factor-1 (SDF-1) and its receptor CXCR-4, the involvement of adhesion molecules, and the induction of actin polymerization in the HPC. Defining the role of chemokines and adhesion molecules in human stem cell migration and engraftment will help us uncover the underlying mechanisms that regulate stem cell homing and will eventually advance clinical stem cell transplantation.

SDF-1-induced actin polymerization and migration in human hematopoietic progenitor cells

OBJECTIVE

The capacity of hematopoietic progenitor cells (HPCs; CD34(+) cells) to respond to chemotactic stimulation is essential for their homing efficiency, e.g., during stem cell transplantation. Previous studies established that stromal cell-derived factor-1 (SDF-1) and its receptor CXCR-4 play an important role in the homing of HPCs. The aim of the present study was to analyze SDF-1-induced actin polymerization and migration of HL-60 cells and primary human CD34(+) cells.

MATERIALS AND METHODS

SDF-1-induced migration of CD34(+) cells from cord blood (CB) and peripheral blood (PB) across fibronectin-coated filters was measured in a Transwell assay. Actin polymerization was detected using fluorescent phalloidin and analyzed by confocal microscopy and FACS analysis.

RESULTS

SDF-1 induced a rapid and transient increase in actin polymerization and in polarization of the actin cytoskeleton in primary CD34(+) cells and HL-60 cells. SDF-1 was found to induce significantly more actin polymerization in CB CD34(+) cells that show fast migration in vitro compared to slow migrating PB CD34(+) cells. Moreover, CB CD34(+) cells that had migrated toward SDF-1 showed an elevated and prolonged rise in F-actin upon second exposure to SDF-1 compared to nonmigrated cells, although both cell types expressed equal levels of the SDF-1 receptor CXCR-4.

CONCLUSIONS

The relatively high migratory capacity of CB-derived human HPCs is not related to cellular polarization or high expression of the SDF-1 receptor but is largely determined by their capacity to efficiently polymerize F-actin in response to SDF-1.

Enumeration of bone marrow 'homing' haemopoietic stem cells from G-CSF-mobilised normal donors and influence on engraftment following allogeneic transplantation

Expression of the chemokine receptor CXCR4 on human haemopoietic stem cells (HSC) may play a crucial role in localising these cells to the bone marrow. To evaluate whether CXCR4 expression is clinically relevant we have enumerated CXCR4-positive HSC used for allogeneic transplantation and sought any relationship with the rate of subsequent haemopoietic reconstitution. CD34-positive progenitor cells were isolated from peripheral blood stem cell (PBSC) collections from 16 normal donors. The proportion of cells co-expressing CXCR4 was enumerated and the times to recipient haemopoietic reconstitution measured. The median frequency of CD34-positive cells co-expressing CXCR4 was 41% (range 16% to 76%) and the median number of CXCR4 CD34 double-positive cells infused at transplantation was 2.5 x 10(6) cells/kg (range 0.8-10.3). Patients receiving >2.5 x 10(6) CXCR4 CD34 double-positive cells/kg demonstrated a significant shortening of time to platelet engraftment compared to the recipients of the lower cell doses (10 days vs 14.5 days, respectively, P = 0.02) with all but one of the recipients of the higher cell doses achieving platelet engraftment by day 11. Co-expression of CXCR4 on CD34-positive progenitor cells may be an important determinant of post-transplant engraftment and in our hands transplantation of a minimum of 2.5 x 10(6) CXCR4 CD34 double-positive cells/kg ensured rapid post-transplant platelet recovery.

Both CD34+38+ and CD34+38- cells home specifically to the bone marrow of NOD/LtSZ scid/scid mice but show different kinetics in expansion

Human hemopoietic stem cells (HSC) have been shown to engraft, differentiate, and proliferate in the hemopoietic tissues of sublethally irradiated NOD/LtSZ scid/scid (NOD/SCID) mice. We used this model to study homing, survival, and expansion of human HSC populations from different sources or phenotype. We observed that CD34+ cells homed specifically to bone marrow (BM) and spleen, but by 3 days after injection, survived only in the BM. These BM-homed CD34+ cells proliferated intensively and gave rise to a 12-fold, 5.5-fold, and 4-fold expansion in 3 days for umbilical cord blood, adult mobilized peripheral blood, and adult BM-derived cells, respectively. By injection of purified subpopulations, it was demonstrated that both CD34+38+ and CD34+38- umbilical cord blood HSC homed to the BM and expanded. Importantly, kinetics of expansion were different: CD34+38+ cells started to increase in cell number from day 3 onwards, and by 4 wk after injection, virtually all CD34+ cells had disappeared. In contrast, CD34+38- cells remained quiescent during the first week and started to expand intensively from the third week on. In this paper, we have shown that homing, survival, and expansion of stem cells are three independent phenomena important in the early phase of BM engraftment and that kinetics of engraftment differ between CD34+38+ and CD34+38- cells.

Similar myeloid recovery despite superior overall engraftment in NOD/SCID mice after transplantation of human CD34(+) cells from umbilical cord blood as compared to adult sources

Umbilical cord blood (UCB), bone marrow (BM) and mobilized peripheral blood (mPB) are used as sources of hematopoietic stem cells for transplantation. The NOD/SCID mouse model was used to compare the lineage-specific repopulating potential of CD34(+) cells derived from these sources. Six to 8 weeks after transplantation, blood, BM, spleen, liver and thymus, were harvested, and analyzed by flow cytometry using CD34, CD45, myeloid, and lymphoid lineage-specific antibodies. Fifty percent engraftment of human cells in bone marrow of mice was estimated to be reached with 0.55 x 10(6) CD34(+) UCB cells or with 7.9 x 10(6) CD34(+) cells from adult sources, illustrating a 10-fold superiority of UCB CD34(+) cells to engraft NOD/SCID mice. Lineage-specific characterization of engrafted human cells showed that the high engraftment potential of CD34(+) cells from UCB was due to a preferential B cell development (2-81%). In contrast, comparable percentages of myeloid cells were found following transplantation of CD34(+) cells from UCB, BM and mPB (1-38%), and occurred at significant levels only at relatively high doses. Since the CD34 content of UCB transplants is usually at least one log lower than of transplant from adult sources, these results correspond to the clinical findings with UCB transplantation showing a relatively high overall engraftment, but delayed myeloid recovery.

Umbilical cord blood transplants

With the establishment of cord blood banks, the number of related and unrelated umbilical cord blood transplants is increasing worldwide. Close links have been established with the cord blood banks. Available data showed that umbilical cord blood transplants offer overall results comparable to those obtained with related or unrelated bone marrow transplants. Several differences were found: engraftment with cord blood was delayed, resulting in an increased incidence of early transplant complications, and the incidence of acute and chronic graft-versus-host disease was significantly reduced with cord blood grafts, even in HLA-mismatched transplants and in adults. In patients with leukemia, the rate of relapse appeared to be similar to that documented in bone marrow transplant recipients. These data confirm the potential benefit of using umbilical cord blood hematopoietic stem cells for allogeneic transplants.