Delineation of cell cycle state and correlation to adhesion molecule expression of human CD34+ cells from steady-state bone marrow and peripheral blood mobilized following G-CSF-supported chemotherapy

The Low Toxicity of Graphene Quantum Dots is Reflected by Marginal Gene Expression Changes of Primary Human Hematopoietic Stem Cells

Graphene quantum dots (GQDs) are a promising next generation nanomaterial with manifold biomedical applications. For real world applications, comprehensive studies on their influence on the functionality of primary human cells are mandatory. Here, we report the effects of GQDs on the transcriptome of CD34+ hematopoietic stem cells after an incubation time of 36 hours. Of the 20 800 recorded gene expressions, only one, namely the selenoprotein W, 1, is changed by the GQDs in direct comparison to CD34+ hematopoietic stem cells cultivated without GQDs. Only a meta analysis reveals that the expression of 1171 genes is weakly affected, taking into account the more prominent changes just by the cell culture. Eight corresponding, weakly affected signaling pathways are identified, which include, but are not limited to, the triggering of apoptosis. These results suggest that GQDs with sizes in the range of a few nanometers hardly influence the CD34+ cells on the transcriptome level after 36 h of incubation, thereby demonstrating their high usability for in vivo studies, such as fluorescence labeling or delivery protocols, without strong effects on the functional status of the cells.

Chemical and biological properties of a supramolecular complex of tuftsin and cucurbit[7]uril

Cucurbit[7]uril (CB7) is an uncharged and water-soluble macrocyclic host. CB7 binds to doubly protonated tuftsin, which is the tetrapeptide Thr-Lys-Pro-Arg, with moderate affinity (K_a=2.1×10³M^-1). In this study, the host-guest complexation was confirmed by fluorescence titration. This affinity would allow for easy release of the peptide under physiological conditions. According to density functional theory calculations, the structural binding motif involves hydrogen bonding. The most energetically stable form had the Arg side chain inside the CB7 cavity. The effects of the tuftsin-CB7 complex on the proliferation and cytokine activity of immune cells were studied. The complex had broader spectrum immunomodulation than free peptides, and caused statistically significant (p<0,05) changes in cytokine production (tumor necrosis factor-α, interleukin-2, interferon-γ, and interleukin-10) by mononuclear cells. By contrast, the free peptide only activated tumor necrosis factor-α production.

[Hematopoietic stem cells mobilization: state of the art in 2011 and perspectives]

High-dose chemotherapy with stem cells support has largely improved in terms of hematopoietic stem and progenitor cells harvest procedures as well as in those, which target or manipulate the cellular composition of autologous graft. Optimal preparative regimens and supportive care had lead to better use of autologous transplantation procedure. For other patients assigned to hematopoietic transplantation, availability of allogeneic donors appears to be an interesting alternative source of hematopoietic stem cells. Since three decades, hematopoietic growth factors development has allowed mobilization optimization and collection of peripheral hematopoietic stem cells leading to reduced days of hospitalization and less blood products requirements, being more cost-effective for patients in autologous transplantation settings and for stem cell collection facilities in allogeneic ones. New perspectives include, besides ex vivo manipulation of graft, development of mobilizing drugs in order to perform transplantation even in poor mobilizers patients. An important goal is achieved with the description of genetic polymorphisms related to optimal mobilization of stem cells. New approach using more promising and selective agents called chemokines, such as plerixafor the main leader among these agents are now available and appear complementary for alternative approach using cytokines alone (G-CSF, GM-CSF, SCF). The aim of this review is to assess the evolution of theses biotechnologies and their role in different steps of autologous transplantation and allogeneic stem cells collection.

Rb and nucleolin antagonize in controlling human CD34 gene expression

Retinoblastoma protein (Rb) controls cell proliferation, differentiation, survival and gene expression and it has a central role in the signaling network that provides a cell cycle checkpoint in the G1 phase of the cell cycle. Studies in mice have shown that Rb regulates interactions between hematopoietic stem cells and their bone marrow microenvironment and it acts as a critical regulator of hematopoietic stem and progenitor cells under stress. In human hematopoiesis, the CD34 protein is expressed on a subset of progenitor cells capable of self-renewal, multilineage differentiation, and hematopoietic reconstitution, and CD34 has a role in the differentiation of hematopoietic cells. Here we find that, in CD34-positive hematopoietic cells, Rb controls the human CD34 promoter region by antagonizing the CD34 promoter factor nucleolin to provide a mechanism that links expression of endogenous CD34 to cell cycle progression. Our study suggests a direct involvement of Rb in the transcriptional program of human CD34-positive hematopoietic stem/progenitor cells, thus providing further insights into the molecular network relevant to the features of these cells.

Pseudotyped recombinant adeno-associated viral vectors mediate efficient gene transfer into primary human CD34(+) peripheral blood progenitor cells

BACKGROUND AND AIMS

Because of their pluripotency, human CD34(+) peripheral blood progenitor cells (PBPC) are targets of interest for the treatment of many acquired and inherited disorders using gene therapeutic approaches. Unfortunately, most current vector systems lack either sufficient transduction efficiency or an appropriate safety profile. Standard single-stranded recombinant adeno-associated virus 2 (AAV2)-based vectors offer an advantageous safety profile, yet lack the required efficiency in human PBPC.

METHODS

A panel of pseudotyped AAV vectors (designated AAV2/x, containing the vector genome of serotype 2 and capsid of serotype x, AAV2/1-AAV2/6) was screened on primary human granulocyte-colony-stimulating factor (G-CSF)-mobilized CD34(+) PBPC to determine their gene transfer efficacy. Additionally, double-stranded self-complementary AAV (dsAAV) were used to determine possible second-strand synthesis limitations.

RESULTS

AAV2/6 vectors proved to be the most efficient [12.8% (1.8-25.4%) transgene-expressing PBPC after a single transduction], being significantly more efficient (all P<0.005) than the other vectors [AAV2/2, 2.0% (0.2-7.3%); AAV2/1, 1.3% (0.1-2.9%); others, <; 1% transgene-expressing PBPC]. In addition, the relevance of the single-to-double-strand conversion block in transduction of human PBPC could be shown using pseudotyped dsAAV vectors: for dsAAV2/2 [9.3% (8.3-20.3%); P<0.001] and dsAAV2/6 [37.7% (23.6-61.0%); P<0.001) significantly more PBPC expressed the transgene compared with their single-stranded counterparts; for dsAAV2/1, no significant increase could be observed.

CONCLUSIONS

We have shown that clinically relevant transduction efficiency levels using AAV-based vectors in human CD34(+) PBPC are feasible, thereby offering an efficient alternative vector system for gene transfer into this important target cell population.

Comparison of unmobilized and mobilized graft characteristics and the implications of cell subsets on autologous and allogeneic transplantation outcomes

Autologous and allogeneic hematopoietic stem cell transplantation (HSCT) are considered the standard of care for many malignancies, including lymphoma, myeloma, and some leukemias. In many cases, mobilized peripheral blood has become the preferred source of hematopoietic stem cells. The efficacy of different mobilization regimens and transplantation outcomes based on cell doses has been well studied; however, the characteristics of the stem cell graft may be of equal importance with respect to patient outcomes following autologous or allogeneic HSCT. This review summarizes available preclinical and clinical data for bone marrow and mobilized peripheral blood HSCT characteristics, defined as the cell types found in the graft as well as their gene expression profiles. It also explores how graft characteristics can affect bone marrow homing, engraftment, immune reconstitution, and other posttransplantation outcomes in both the allogeneic and autologous HSCT settings.

CD34+ cells obtained from "good mobilizers" are more activated and exhibit lower ex vivo expansion efficiency than their counterparts from "poor mobilizers"

BACKGROUND

The classification of patients into "good" or "poor" mobilizers is based on CD34+ cell count in their peripheral blood (PB) after granulocyte-colony-stimulating factor (G-CSF) injection. We hypothesized that, apart from their mobilization from marrow to the blood, the response to G-CSF of CD34+ cells also includes activation of proliferation, metabolic activity, and proliferative capacity.

STUDY DESIGN AND METHODS

Mobilized PB CD34+ cells purified from samples obtained by cytapheresis of multiple myeloma or non-Hodgkin's lymphoma patients of both good (>50 CD34+ cells/microL) and poor (< or =50 CD34+ cells/microL) mobilizers were studied. The initial cell cycle state of CD34+ cells after selection and their kinetics of activation (exit from G(0) phase) during ex vivo culture were analyzed. Their proliferative capacity was estimated on the basis of ex vivo generation of total cells, CD34+ cells, and colony-forming cells (CFCs), in a standardized expansion culture. Indirect insight in metabolic activity was obtained on the basis of their survival (viability and apoptosis follow-up) during the 7-day-long conservation in hypothermia (4 degrees C) in the air or in atmosphere containing 3% O(2)/6% CO(2).

RESULTS

CD34+ cells obtained from good mobilizers were in lower proportion in the G(0) phase, their activation in a cytokine-stimulated culture was accelerated, and they exhibited a lower ex vivo expansion efficiency than those from poor mobilizers. The resistance to hypothermia of good immobilizers' CD34+ cells is impaired.

CONCLUSION

A good response to G-CSF mobilization treatment is associated with a higher degree of proliferative and metabolic activation of mobilized CD34+ cells with a decrease in their expansion capacity.

Differences in functional activity and antigen expression of granulocytes primed in vivo with filgrastim, lenograstim, or pegfilgrastim

BACKGROUND

Granulocyte-colony-stimulating factor (G-CSF) is known to affect functional activity and antigen expression of neutrophil granulocytes. Beside nonglycosylated filgrastim and glycosylated lenograstim, pegylated filgrastim (pegfilgrastim) has recently been introduced for single administration into clinical use.

STUDY DESIGN AND METHODS

Here, granulocytes from 27 patients with nonmyeloid malignancies were compared functionally (migration, reactive oxygen species production, and G-CSF serum levels) and phenotypically (cell surface antigen expression) before and after G-CSF administration.

RESULTS

After exposure to G-CSF, chemotaxis was reduced significantly in the filgrastim group. Immunophenotypically, in vivo G-CSF-primed granulocytes were more mature in the lenograstim than in the filgrastim and to lesser extent in the pegfilgrastim groups as shown by the expression profile for CD11b, CD14, and CD16. Of note, G-CSF serum levels were similar among the groups.

CONCLUSION

Our data suggest that granulocytes exposed to glycosylated G-CSF in vivo seem to resemble more closely their steady-state phenotype than after treatment with nonglycosylated and to lesser extent pegylated G-CSF.

Ex vivo expansion of G-CSF-mobilized peripheral blood CD133+ progenitor cells on coculture with human stromal cells

OBJECTIVE

The pentaspan molecule CD133 has been shown to be a marker of more primitive hematopoietic progenitors in mobilized peripheral blood (PB). Our objective was to assess the efficacy of PB CD133(+) cells in our coculture system using human telomerized stromal (HTS) cells.

METHODS

Five thousand PB CD133(+) cells or conventional cord blood (CB) CD34(+) cells were expanded with or without HTS cells in the presence or absence of stem cell factor, thrombopoietin, and Flk-2/Flt-3 ligand.

RESULTS

The coculture was significantly superior in expanding PB clonogenic cells as compared with the stroma-free culture (CFU-C, 2 +/- 0 vs 111 +/- 15-fold of initial cell number, p < 0.01), and the fold increase of PB clonogenic cells was comparable to that for CB cells after two weeks of coculture (BFU-E, 54 +/- 3 vs 56 +/- 4-fold; CFU-GM, 156 +/- 26 vs 83 +/- 9-fold; CFU-Mix, 30 +/- 11 vs 80 +/- 36-fold). However, proliferation of CFU-Mk from PB on coculture with HTS cells was modest as compared with stroma-free culture. Concomitantly, multiple hematopoietic cells transmigrated below the stromal layer and formed cobblestone areas (CAs). The production of hematopoietic progenitor cells from CAs after coculture with PB was significantly lower than that seen in cells cocultured with CB for four weeks (CFU-Mix, 0 +/- 0 vs 9 +/- 5-fold on day 28, p < 0.01), although a similar number of CAs derived from PB and CB were observed.

CONCLUSION

PB CD133(+) cells proliferated efficiently above the stromal layer, while the characteristics of PB CD133(+) cells underneath the human stromal layer were likely to be maintained, even after long-term hematopoietic-stromal interaction.

Catalytic Activities of G1Cyclin-Dependent Kinases and Phosphorylation of Retinoblastoma Protein in Mobilized Peripheral Blood CD34+Hematopoietic Progenitor Cells

Depending on the source of cells, the cell cycle status of hematopoietic stem and progenitor cells capable of repopulating the marrow of transplant recipients is controversial. In this study, using biochemical methods, the cell cycle status of mobilized CD34+ cells was analyzed. It was demonstrated in CD34+ cell extracts that there was high catalytic activity of G(1) cyclin-dependent kinases 4 and 6 (CDK4 and CDK6) but low activity of CDK2. This was in contrast to the resting reference cells that showed only minimal or no activity of these CDKs. Since at the G0-->G1-->S transition CDK4/6 and CDK2 sequentially phosphorylate the retinoblastoma protein (pRB), its phosphorylation status was analyzed. Previously, we showed that p110RB was unphosphorylated at serine (Ser)-608 in CD34+ cells, consistent with the ability to suppress cell growth. Here, it was established that this form of pRB was phosphorylated at Ser-780, Ser-795, and Ser-807/811 in CD34+ but not in resting reference cells. This result was therefore consistent with the presence of high CDK4/6 activities in CD34+ cells. Conversely, CDK2 activity was low and the pRB residues Ser-612 and threonine (Thr)-821, which are exclusively phosphorylated by CDK2 in conjunction with either cyclin E or A, were unphosphorylated in >90% of CD34+ cells. We therefore show for the first time the exact position of mobilized CD34+ cells within the cell cycle; that is, they do not reside in G0 but in early G1 phase and did not cross the restriction point into late G1 phase.

Clonal analysis of individual marrow-repopulating cells after experimental peripheral blood progenitor cell transplantation

Methods to analyze the clonality of an adverse event in preclinical or clinical retroviral stem cell gene therapy protocols are needed. We analyzed the progeny of retrovirally transduced human peripheral blood progenitor cells (PBPCs) after transplantation and engraftment in immune-deficient mice. The integration site of the provirus serves as a unique tag of the individual transduced PBPC. A plasmid library of junctions between proviral and human genomic DNA was generated. We were able to detect individual transduced cell clones that amounted to 0.14%-0.0001% of chimeric bone marrow cells. This is the first report in which the contribution of individual marrow-repopulating cells to human hematopoiesis is directly quantified.

Homing and mobilization of hematopoietic stem cells and hematopoietic cancer cells are mirror image processes, utilizing similar signaling pathways and occurring concurrently: circulating cancer cells constitute an ideal target for concurrent treatment with chemotherapy and antilineage-specific antibodies

Adhesion molecules and stromal cell-derived factor-1 (SDF-1)/CXCR4 signaling play key role in homing and mobilization of hematopoietic progenitor (HPC) and hematopoietic cancer clonogenic cells (HCC). High expression of VLA-4 is required for homing of HPC and HCC, whereas downregulation of these molecules is required for successful mobilization of HPC and HCC. Upregulation and activation of the SDF-1/CXCR4 signaling is required for homing of HPC and HCC, whereas disruption of the SDF-1 signaling is required for mobilization of HPC and HCC. Hence, mobilizations of HPC and HCC occur concurrently. It is proposed that drug resistance evolves as a result of repeated cycles of chemotherapy. Following each cycle of chemotherapy, HCC lose adhesion molecules and SDF-1 signaling. Surviving cells, released from tumor sites, circulate until re-expression of adhesion molecules and CXCR4 occurs, then homing to stroma of distal tissues occurs. Cytokines secreted by cells in the new microenvironment induce proliferation and drug resistance of HCC. This process is amplified in each cycle of chemotherapy resulting in disease progression. A novel model for treatment is proposed in which circulating HCC are the target for clinical intervention, and concurrent treatment with chemotherapy and antilineage-specific antibodies will result in abrogation of the 'vicious cycle' of conventional anticancer therapy.

Molecular biology of hematopoietic stem cells

Human CD34+ hematopoietic stem and progenitor cells are capable of maintaining a life-long supply of the entire spectrum of blood cells dependent on systemic needs. Recent studies suggest that hematopoietic stem cells are, beyond their hematopoietic potential, able to differentiate into nonhematopoietic cell types, which could open novel avenues in the field of cellular therapy. Here, we concentrate on the molecular biology underlying basic features of hematopoietic stem cells. Immunofluorescence analyses, culture assays, and transplantation models permit an extensive immunological as well as functional characterization of human hematopoietic stem and progenitor cells. New methods such as cDNA array technology have demonstrated that distinct gene expression patterns of transcription factors and cell cycle genes molecularly control self-renewal, differentiation, and proliferation. Furthermore, several adhesion molecules have been shown to play an important role in the regulation of hematopoiesis and stem cell trafficking. Progress has also been made in elucidating molecular mechanisms of stem cell aging that limit replicative potential. Finally, more recent data provide the first molecular basis for a better understanding of transdifferentiation and developmental plasticity of hematopoietic stem cells. These findings could be helpful for non-hematopoietic cell therapeutic approaches.

Imatinib restores expression of CD62L in BCR-ABL-positive cells

Chronic myelogenous leukemia (CML) is characterized by aberrant trafficking of malignant hematopoietic progenitor cells in the peripheral blood. Expression of the cell adhesion molecule CD62L was reported to be significantly lower in CML patients than in normal controls. We studied whether the transcription of CD62L in CML cells is dependent on the activity of the BCR-ABL tyrosine kinase. Following addition of the Abelson (ABL) tyrosine kinase inhibitor imatinib (formerly STI571) to two BCR-ABL-positive cell lines (BV173, SD-1), we observed a dose-dependent increase in CD62L RNA levels of up to 45-fold by a quantitative, real-time polymerase chain reaction and an increase in the amount of cell surface-bound CD62L of up to 18-fold by quantitative flow cytometry, respectively. These data are validated by an increased CD62L expression in the bone marrow of patients (n=6) with advanced CML who received imatinib. Restoration of defective cell adhesion mediated via the CD62L pathway may be one mechanism of action of imatinib in BCR-ABL-positive leukemias.

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.

Decreased stroma adhesion capacity of CD34+ progenitor cells from mobilized peripheral blood is not lineage- or stage-specific and is associated with low beta 1 and beta 2 integrin expression

Molecular mechanisms leading to mobilization of hematopoietic cells from bone marrow (BM) to peripheral blood (PB) involve modulation of adhesion molecule expression on these cells that probably result in changes in adhesion capacity to the microenvironment. However, it is not clear whether these changes involve different stages or lineages of progenitor cells. In this study, we compared the capacity of mature and immature clonogenic progenitor cells from granulocyte colony-stimulating factor (G-CSF)-mobilized PB and normal BM CD34+ cells to adhere to complete marrow stroma. This functional capacity was assessed concurrently with molecular expression on CD34+ cells of integrins VLA-4 (alpha 4/beta 1), VLA-5 (alpha 5/beta 1), and LFA-1 (alpha L/beta 2) by interindividual (between mobilized PB and normal BM) and intraindividual (between mobilized PB and steady-state BM and PB in the same patient) analysis. The proportion of adherent clonogenic progenitor cells was significantly lower in PB than in BM, not only for total progenitor cells but also for mature and immature progenitor cells, and the difference was found for granulocytic and particularly for erythroid lineages. The lower adhesion capacity of PB CD34+ cells to stroma was associated with decreased expression (signal/noise MFI ratio) of integrin alpha 4, beta 1, alpha L, and beta 2 chains whereas that of alpha 5 chain did not differ from BM cells with the lowest expression level. Similar differences in integrin expression levels were also found between mobilized PB and steady-state BM CD34+ cells in the same patient except for the alpha L chain. Moreover, we demonstrated for the first time a strong positive correlation between mobilizing capacity and expression levels on mobilized CD34+ cells for the LFA-1 alpha L chain but not for VLA-4 or VLA-5. In conclusion, the decreased adhesion capacity of mobilized PB progenitor cells to stroma involves different maturation stages and different lineages. This is associated with down-regulation of integrins VLA-4 and LFA-1, but mobilizing capacity appears positively correlated with LFA-1 levels.

Comparison between granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor in the mobilization of peripheral blood stem cells

Peripheral blood stem cells (PBSC) have become the preferred source of stem cells for autologous transplantation because of the technical advantage and the shorter time to engraftment. Mobilization of CD34+ into the peripheral blood can be achieved by the administration of granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), or both, either alone or in combination with chemotherapy. G-CSF and GM-CSF differ somewhat in the number and composition of PBSCs and effector cells mobilized to the peripheral blood. The purpose of this review is to give a recent update on the type and immunologic properties of CD34+ cells and CD34+ cell subsets mobilized by G-CSF or GM-CSF with emphasis on (1) relative efficacy of CD34+ cell mobilization; (2) relative toxicities of G-CSF and GM-CSF as mobilizing agents; (3) mobilization of dendritic cells and their subsets; (4) delineation of the role of adhesion molecules, CXC receptor 4, and stromal cell-derived factor-1 signaling pathway in the release of CD34+ cell to the peripheral blood after treatment with G-CSF or GM-CSF.

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.

Ultrastructural features of CD34+ hematopoietic progenitor cells from bone marrow, peripheral blood and umbilical cord blood

Hematopoietic progenitor cells from different sources have been widely characterized, but their ultrastructural morphology has never been described in detail. In this study, imunomagnetically separated CD34+ cells from normal bone marrow (BM), mobilized peripheral blood (PBSC) and human umbilical cord blood (CB) were studied by transmission electron microscopy (TEM) using a cytochemical method which reveals endogenous myelo-peroxidase (MPO) activity. This technique is particularly suited for detecting early signs of the myeloid commitment. The CD34+ cells from PBSC were morphologically very homogeneous and 94.7+/-4.5% of these cells were MPO-: these ultrastructural features are generally considered typical of immature cells. The CD34+ BM cells were instead more heterogeneous, with 24.6+/-7.4% showing intense MPO activity. The ultrastructural characteristics of CB cells fell between those observed in PBSC and BM, but there was a high percentage of morphologically immature cells with no evidence of MPO activity (about 83%). The number of apoptotic cells within samples from different sources was also examined both by TEM and flow cytometry. The percentage of apoptotic cells was 0.7% in PBSC, 2.3% in BM, 2.9% in CB from vaginal delivery and 11.6% in CB from cesarean section. These observations confirm the relative phenotypic immaturity of CB in comparison with BM cells; they also suggest that CB collected after cesarean section may be associated with reduced stem cells viability.

Recent Developments in the Regulation of Peripheral Blood Stem Cell Mobilization and Engraftment by Cytokines, Chemokines, and Adhesion Molecules

Peripheral blood stem cells (PBSC) have become the preferred source of stem cells for autologous transplantation because of the technical advantage and the shorter time to engraftment. Administration of hematopoietic growth factors such as granulocyte colony-stimulating factor (G-CSF) or granulocyte-macrophage colony-stimulating factor (GM-CSF) results in mobilization of PBSCs into the peripheral blood. G-CSF and GM-CSF differ somewhat in the number and composition of CD34(+) cells and effector cells mobilized to the peripheral blood; however, the molecular mechanism underlying the release and engraftment of CD34(+) cells by these growth factors is poorly understood. This review provides a recent update on the involvement of hematopoietic growth factors, chemokines, adhesion molecules, and chemokine receptors in the regulation of stem cell release and engraftment. The involvement of very late antigen-4 (VLA-4), VLA-5, leukocyte function associated-1 molecule (LFA-1), and L-selectin and their receptors CXCR4 and its ligand SDF-1 will be discussed, and cross talk between these factors will also be reviewed in the context of stem cell release and engraftment. Finally, PBSC mobilization by chemokines will be reviewed in relation to hematopoietic growth factors.

Proliferating status of peripheral blood progenitor cells from patients with BCR/ABL-positive chronic myelogenous leukemia

To investigate the mechanisms behind the leukemic expansion of BCR/ABL-positive chronic myelogenous leukemia (CML), we examined the cell cycle status of hematopoietic progenitor cells from peripheral blood (PB) and bone marrow (BM) of 37 patients with newly diagnosed BCR/ABL-positive CML. We found a high proportion of 12.51 +/- 1.19% of CD34+ peripheral blood progenitor cells (PBPC) in S/G2M phase. Comparison of PB and BM from 19 cases revealed similar proliferation rates (10.74 +/- 1.41% vs 15.97 +/- 1.95%). Furthermore, even primitive CD34+/CD38- PBPC displayed high proliferation rates (17.45 +/- 2.98%) in 10 cases examined. In contrast, PBPC from 11 patients with BCR/ABL-negative myeloproliferative disorders were almost noncycling (S/G2M 1.46 +/- 0.47%). When matched pairs of PB and BM from six patients with BCR/ABL-negative myeloproliferative disorders were examined, only 0.89 +/- 0.41% of the CD34+ PBPC, but 8.29 +/- 3.13% CD34+ cells from BM were in S/G2M phase. Consistently, as compared to 19 patients with newly diagnosed BCR/ABL-positive CML, a significantly lower PB/BM ratio of CD34+ cells in S/G2M phase was found in these six patients with BCR/ABL-negative myeloprolifrative disorders. Administration of the tyrosine kinase inhibitor STI571 to 13 patients with CML in chronic phase, accelerated phase, or blast crisis lead to an inhibition of PBPC proliferation within a few days. Interestingly, CD34+ hematopoietic progenitor cells from BM remained proliferating in five cases examined, indicating that CML PBPC are more easily inhibited by STI571 as compared to CD34+ CML hematopoietic progenitor cells from BM. These data suggest that BCR/ABL leads to an enhanced cell cycle activation of CD34+ cells, which seems to be, at least in part, independent of additional factors provided by the bone marrow microenvironment.

Growth factor mobilization and modulation of progenitor cell adhesion to stromal cells: role of VLA-4

Cellular interactions between hematopoietic progenitor cells and bone marrow (BM) stromal cells are mediated by cell adhesion molecules (CAM). In agreement with previous studies, our flow cytometric analysis of isolated CD34+ cells showed that VLA-4 expression was significantly (p < 0.001) higher on steady-state BM than on CD34+ cells from growth factor-mobilized peripheral stem cell (PSC) products. To determine whether the expression of VLA-4 on progenitor cells plays a role in their adhesion to stromal cells, we examined the binding of isolated CD34+ progenitor cells from BM (n = 14) and PSC (n = 10) products to BM stromal cells in the presence or absence of a neutralizing antibody to VLA-4. In these studies, similar kinetics of BM and PSC CD34+ cell adhesion to BM stromal cells were observed. However, neutralizing antibody to VLA-4 significantly inhibited BM CD34+ but not PSC CD34+ cell adherence to stromal cells, suggesting a role for alternative CAM in cell binding. Further, in long-term co-cultures of BM CD34+ cells with BM stroma, we observed a significantly higher number of colony-forming units granulocyte-macrophage (CFU-GM) released into the media following treatment with neutralizing antibody to VLA-4 than in untreated control cultures. In contrast, no difference in the frequency of nonadherent CFU-GM between antibody-treated and control long-term co-cultures of PSC CD34+ cells with BM stromal cells was observed. This suggests that VLA-4 expression on mobilized PSC versus BM CD34+ cells has biologic relevance for at least 2 weeks based on the long-term BM culture results. In summary, these data suggest that the decreased expression of VLA-4 may have a role in the mobilization of progenitor cells, in part, by regulating their adherence to stromal cells, although additional mediators of adhesion are also involved.

Mobilization of CD34+ haematopoietic stem cells is associated with a functional inactivation of the integrin very late antigen 4

The beta1 integrin very late antigen 4 (VLA-4) plays a central role in mobilization and homing of CD34+ cells. In this study, we examined the activation state of VLA-4 on CD34+ cells from bone marrow (BM) and peripheral blood (PB) by flow cytometry using a vascular cell adhesion molecule I-immunoglobulin (VCAM-I/IgG) fusion protein as soluble ligand. In an intraindividual analysis, we found a significantly reduced affinity and avidity of the VLA-4 receptor on CD34+ cells from PB during granulocyte colony-stimulating factor (G-CSF)-enhanced marrow recovery in comparison with steady-state BM. Moreover, the amount of circulating CD34+ cells during marrow recovery was inversely related to the activation state but not to the expression level of VLA-4, suggesting that a modulation of the functional state of VLA-4 is involved in the mobilization of CD34+ cells. Moreover, VLA-4 function on CD34+ cells from BM was associated with the maturation state of CD34+ cells as high-affinity VLA-4 receptors were observed on the vast majority of more primitive CD34+ cells. In addition, we found that Mg2+ ions as well as co-incubation of CD34+ cells with endothelial cells resulted in an activation of the VLA-4 receptor. In conclusion, modulation of the functional state of VLA-4 appears to be of relevance for the mobilization and homing of CD34+ haematopoietic stem cells.

Soluble bone marrow stroma factors improve the efficiency of retroviral transfer of the human multidrug resistance 1 gene to human mobilized peripheral blood progenitor cells

Hematopoietic stem cells (HSCs) are a potential target for the retrovirus-mediated transfer of chemotherapeutic drug resistance genes. For integration of the proviral DNA in the HSC genome cell division is required. In the bone marrow (BM) hematopoiesis occurs in the vicinity of stroma cells. Soluble stroma components were shown to play a permissive role for the proliferation of lineage-committed and primitive hematopoietic progenitors in conjunction with cytokines. We investigated the effect of stroma-conditioned medium (SCM) of the FBMD1 cell line on the gene transfer rate of the human multidrug resistance 1 (MDR1) gene contained in the retroviral SF-MDR vector into human mobilized peripheral blood progenitor cells (PBPCs) from tumor patients (n = 14) during transwell transduction in the presence of the recombinant fibronectin fragment CH-296. Addition of SCM during transduction increased the gene transfer efficiency into myeloid lineage-committed colony-forming cells by an average of 1.5-fold (p = 0.02) as detected by an SF-MDR provirus-specific polymerase chain reaction (PCR). These data were paralleled by significantly (p = 0.04 to p = 0.007) higher proportions of MDR1-expressing myelo-monocytic progeny after transduction in SCM plus interleukin 3 (IL-3), IL-3/Flt3 ligand (FL), IL-3/IL-6/FL, or IL-3/IL-6/stem cell factor (SCF) when compared with transductions without SCM as measured by rhodamine-123 exclusion. A similar trend was observed for SCM employed in combination with IL-3/IL-6/SCF/FL or FL/thrombopoietin (TPO)/SCF during transduction. The latter combination plus SCM yielded the highest proportion, 19.16 +/- 3.10% Rh-123dull cells. The beneficial effect of SCM on transduction efficiency was confirmed in additional four patients' samples, using a serum-free viral supernatant transduction protocol. As soluble BM stroma factors are able to increase the efficiency of retrovirus-mediated gene transfer into committed progenitor cells, beyond that achieved with fibronectin fragment CH-296, their effect on gene transfer into primitive repopulating hematopoietic cells may also prove beneficial.

Peripheral blood progenitor cell (PBPC) counts during steady-state haemopoiesis enable the estimation of the yield of mobilized PBPC after granulocyte colony-stimulating factor supported cytotoxic chemotherapy: an update on 100 patients

Peripheral blood progenitor cells (PBPC) can be mobilized using chemotherapy and granulocyte colony-stimulating factor (G-CSF). We and others previously reported a correlation of steady-state PBPC counts and the PBPC yield during mobilization in a small group of patients. Here we present data on 100 patients (patients: 25 non-Hodgkin's lymphoma (NHL), five Hodgkin's disease, 35 multiple myeloma (MM), 35 solid tumour) which enabled a detailed analysis of determinants of steady-state PBPC levels and of mobilization efficiency in patient subgroups. Previous irradiation (P = 0.0034) or previous chemotherapy in patients with haematological malignancies (P = 0.0062) led to a depletion of steady-state PB CD34+ cells. A correlation analysis showed steady-state PB CD34+ cells (all patients: r = 0.52, P < 0.0001; NHL patients, r = 0.69, P = 0.0003; MM patients: r = 0.66, P = 0.0001) and PB colony-forming cells can reliably assess the CD34+ cell yield in mobilized PB. In patients with solid tumour a similar trend was observed in mobilization after the first chemotherapy cycle (r = 0.51, P = 0.05) but not if mobilization occurred after the second or further cycle of a sequential dose-intensified G-CSF-supported chemotherapy regimen, when premobilization CD34+ counts were 18-fold elevated (P = 0.004). When the patients with MM (r = 0.63, P = 0.0008) or with NHL (r = 0.65, P = 0.006) were analysed separately, a highly significant correlation of the steady-state PB CD34+ cell count to the mean leukapheresis CD34+ cell yield was found, whereas no correlation was observed for patients with a solid tumour. For patients with haematological malignancies estimates could be calculated which, at a specific steady-state PB CD34+ cell count, could predict with a 95% probability a defined minimum progenitor cell yield. These results enable recognition of patients who mobilize PBPC poorly and may assist selection of patients for novel mobilization regimens.

Ex vivo expansion of hematopoietic stem and progenitor cells: are we there yet?

Ex vivo expansion of hematopoietic stem and progenitor cells is a very ambitious idea that would have major implications in the areas of stem cell transplantation and somatic gene therapy. However, successful ex vivo expansion has evaded and frustrated scientists for a number of years. The goal of ex vivo expansion is to induce cell division and proliferation of stem cells while maintaining their primary functional characteristic, namely, their ability to engraft and sustain long-term hematopoiesis. Only when a balance between these two requirements is reached can ex vivo expansion of stem cells be considered successful. Establishing such a balance has not been easy. However, many lessons have been learned along the way, and today we have a more profound understanding of the potential obstacles facing ex vivo expansion than we did only a few years ago. In this review, we discuss these obstacles and evaluate the current status of ex vivo expansion of stem and progenitor cells both from the perspective of basic stem cell biology and from the viewpoint of clinical utility of these cells in transplantation.

Adhesion to fibronectin stimulates proliferation of wild-type and bcr/abl-transfected murine hematopoietic cells

Cells of most tissues require adhesion to a surface to grow. However, for hematopoietic cells, both stimulation and inhibition of proliferation by adhesion to extracellular matrix components have been described. Furthermore, it has been suggested that progenitor cells from chronic myelogenous leukemia show decreased beta1 integrin-mediated adhesion to fibronectin, resulting in increased proliferation and abnormal trafficking. However, we show here that the chronic myelogenous leukemia-specific fusion protein p210bcr/abl stimulates the expression of alpha5beta1 integrins and induces adhesion to fibronectin when expressed in the myeloid cell line 32D. Moreover, proliferation of both p210bcr/abl-transfected 32D (32Dp210) cells and untransfected 32D cells is stimulated by immobilized fibronectin. Cell cycle analysis revealed that nonadherent 32D and 32Dp210 cells are arrested in late G1 or early S phase, whereas the adherent fractions continue cycling. Although both adherent and nonadherent p210bcr/abl-transfected and parental 32D cells express equal amounts of cyclin A, a protein necessary for cell cycle progression at the G1/S boundary, cyclin A complexes immunoprecipitated from 32D cells cultured on immobilized fibronectin were found to be catalytically inactive in nonadherent but not in adherent cells. In addition, as compared with untransfected 32D cells, cyclin A immunoprecipitates from 32Dp210 cells exhibited a greatly elevated kinase activity and remained partially active irrespective of the adhesion status. The lack of cyclin A/cyclin-dependent kinase (CDK) 2 activity in nonadherent 32D cells appeared to result from increased expression and cyclin A complex formation of the CDK inhibitor p27(Kip1). Taken together, our results indicate that adhesion stimulates cell cycle progression of hematopoietic cells by down-regulation of p27(Kip1), resulting in activation of cyclin A/CDK2 complexes and subsequent transition through the G1/S adhesion checkpoint.