Hematopoietic stem/progenitor cell mobilization. A continuing quest for etiologic mechanisms

Stretching the limits: from homeostasis to stem cell plasticity in wound healing and cancer

Stem cells (SCs) govern tissue homeostasis and wound repair. They reside within niches, the special microenvironments within tissues that control SC lineage outputs. Upon injury or stress, new signals emanating from damaged tissue can divert nearby cells into adopting behaviours that are not part of their homeostatic repertoire. This behaviour, known as SC plasticity, typically resolves as wounds heal. However, in cancer, it can endure. Recent studies have yielded insights into the orchestrators of maintenance and lineage commitment for SCs belonging to three mammalian tissues: the haematopoietic system, the skin epithelium and the intestinal epithelium. We delineate the multifactorial determinants and general principles underlying the remarkable facets of SC plasticity, which lend promise for regenerative medicine and cancer therapeutics.

Thymic stromal lymphopoietin-mediated extramedullary hematopoiesis promotes allergic inflammation

Extramedullary hematopoiesis (EMH) refers to the differentiation of hematopoietic stem cells (HSCs) into effector cells that occurs in compartments outside of the bone marrow. Previous studies linked pattern-recognition receptor (PRR)-expressing HSCs, EMH, and immune responses to microbial stimuli. However, whether EMH operates in broader immune contexts remains unknown. Here, we demonstrate a previously unrecognized role for thymic stromal lymphopoietin (TSLP) in promoting the population expansion of progenitor cells in the periphery and identify that TSLP-elicited progenitors differentiated into effector cells including macrophages, dendritic cells, and granulocytes and that these cells contributed to type 2 cytokine responses. The frequency of circulating progenitor cells was also increased in allergic patients with a gain-of-function polymorphism in TSLP, suggesting the TSLP-EMH pathway might operate in human disease. These data identify that TSLP-induced EMH contributes to the development of allergic inflammation and indicate that EMH is a conserved mechanism of innate immunity.

The long road to the thymus: the generation, mobilization, and circulation of T-cell progenitors in mouse and man

The majority of T cells develop in the thymus. T-cell progenitors in the thymus do not self-renew and so progenitor cells must be continuously imported from the blood into the thymus to maintain T-cell production. Recent work has shed light on both the identity of the cells that home to the thymus and the molecular mechanisms involved. This review will discuss the cells in the bone marrow and blood that are involved in early thymopoiesis in mouse and man. Understanding the pre-thymic steps in T-cell development may translate into new therapeutics, especially in the field of hematopoietic stem cell transplantation.

Fms-related tyrosine kinase 3 expression discriminates hematopoietic stem cells subpopulations with differing engraftment-potential: identifying the most potent combination

BACKGROUND

Fms-related tyrosine kinase 3 (Flt3)-ligand (FL) promotes the proliferation, differentiation, development, and mobilization of hematopoietic cells. We previously found that FL-mobilized hematopoietic stem cells (HSC) engraft efficiently, whereas FL-expanded bone marrow HSC do not. The function of FL-mobilized c-Kit(+) Sca-1(+)Lin(-)(KSL) subpopulations has not been systematically evaluated. A precise definition of the repopulating ability is needed to define which HSC subpopulations are critical for long-term chimerism and tolerance induction. FL significantly mobilized c-Kit(hi) and c-Kit(lo) Sca-1(+)Lin(-) cells into peripheral blood (PB). Here, we evaluated the influence of Flt3 expression on long-term repopulating ability of HSC subpopulations.

METHODS

c-Kit(hi) or c-Kit(lo) KSL cells were sorted from PB of FL-treated green fluorescent protein-positive donors. The function of these cells was evaluated using competitive reconstitution assays, colony-forming units spleen, and colony forming cell assays. The function of c-Kit(hi) CD34(-)Flt3(-) KSL, c-Kit CD34(+)Flt3(-) KSL, c-Kit(hi) CD34(+)Flt3(+) KSL were investigated in an in vivo transplantation model.

RESULTS

Only FL-mobilized PB c-Kit(hi) KSL cells exhibited high spleen colony-forming unit activity, generated high numbers of both lymphoid and myeloid colonies in vitro, and rescued ablated recipients. FL-mobilization expanded both c-Kit(hi) CD34(+)Flt3(-) cells (short-term HSC) and c-Kit(hi) CD34(-)Flt3(-) KSL cells (long-term HSC). There was a significant decrease in c-Kit CD34Flt3 KSL late multipotent progenitors in PB. A combination of c-Kit(hi) CD34Flt3 and c-Kit CD34(+)Flt3(-) KSL cells offered the most effective rescue of ablated recipients.

CONCLUSIONS

These data suggest that engraftment of purified HSC is influenced by both short- and long-term repopulating populations and that Flt3 expression may be useful for selecting the most critical HSC subpopulations for transplantation.

Osteolineage niche cells initiate hematopoietic stem cell mobilization

Recent studies have implicated bone-lining osteoblasts as important regulators of hematopoietic stem cell (HSC) self-renewal and differentiation; however, because much of the evidence supporting this notion derives from indirect in vivo experiments, which are unavoidably complicated by the presence of other cell types within the complex bone marrow milieu, the sufficiency of osteoblasts in modulating HSC activity has remained controversial. To address this, we prospectively isolated mouse osteoblasts, using a novel flow cytometry-based approach, and directly tested their activity as HSC niche cells and their role in cyclophosphamide/granulocyte colony-stimulating factor (G-CSF)-induced HSC proliferation and mobilization. We found that osteoblasts expand rapidly after cyclophosphamide/G-CSF treatment and exhibit phenotypic and functional changes that directly influence HSC proliferation and maintenance of reconstituting potential. Effects of mobilization on osteoblast number and function depend on the function of ataxia telangiectasia mutated (ATM), the product of the Atm gene, demonstrating a new role for ATM in stem cell niche activity. These studies demonstrate that signals from osteoblasts can directly initiate and modulate HSC proliferation in the context of mobilization. This work also establishes that direct interaction with osteolineage niche cells, in the absence of additional environmental inputs, is sufficient to modulate stem cell activity.

Stem cell trafficking in tissue development, growth, and disease

Regulated movement of stem cells is critical for organogenesis during development and for homeostasis and repair in adulthood. Here we analyze the biological significance and molecular mechanisms underlying stem cell trafficking in the generation of the germline, and the generation and regeneration of blood and muscle. Comparison across organisms and lineages reveals remarkable conservation as well as specialization in homing and migration mechanisms used by mature leukocytes, adult and fetal stem cells, and cancer stem cells. In vivo trafficking underpins the successful therapeutic application of hematopoietic stem cells for bone-marrow transplant, and further elucidation of homing and migration pathways in other systems will enable broader application of stem cells for targeted cell therapy and drug delivery.

Enhanced functional response of CD133+ circulating progenitor cells in patients early after acute myocardial infarction

AIMS

Circulating progenitor cells (PC) may contribute to myocardial recovery following infarction. Growth factors including VEGF are produced during ischaemia and stimulate PC release and activation. In this study, we focused on the functional chemotactic response of PC to VEGF in subjects early after myocardial ischaemia.

METHODS AND RESULTS

Number and phenotype of PC were characterized using flow-cytometry. CD133(+)PC were isolated from peripheral blood using positive MACS isolation. The chemotactic response towards members of the VEGF family (VEGF-A, PlGF-1, and VEGF-E) was analysed in three groups: (i) early period following acute myocardial infarction (days 2-4) treated with primary PCI (AMI) (n = 35), (ii) stable coronary artery disease (CAD) (n = 35), and (iii) controls (CTR) (n = 20). CD133(+)PC number was 2-fold higher in AMI when compared with CAD and CTR (P = 0.0001), whereas CAD was not different from CTR. The chemotactic response of CD133(+)PC to VEGF-A, PlGF-1, and VEGF-E was significantly enhanced (2-fold) in AMI when compared with CAD (P = 0.0001). While the increase of the VEGFR-1-mediated/PlGF-triggered response was rapid (2 days following infarction), the VEGFR-2-mediated/VEGF-E-triggered response was maximally increased on day 4 post-AMI, thus correlating with the kinetics of maximal inflammatory activation reflected by increased CRP levels (P = 0.019).

CONCLUSION

The enhanced chemotactic response of CD133(+)PC following myocardial infarction represents a novel principle potentially involved in cardiovascular repair early after myocardial infarction. Acute inflammatory processes are closely associated with this increased cellular function.

Trafficking from the bone marrow to the thymus: a prerequisite for thymopoiesis

T-cell development in the thymus requires periodic importation of hematopoietic progenitors from the bone marrow. Such thymus settling progenitors arise from hematopoietic stem cells (HSCs) that are retained in a specific bone marrow microenvironmental niche. Vacation of this niche is required for HSC proliferation and differentiation into downstream progenitors. In order to reach the thymus, progenitors must then be mobilized from bone marrow to blood. Finally, progenitors in blood must settle in the thymus. Here we review signals and molecular interactions that are likely to play a role in trafficking from the bone marrow to the thymus, focusing on how these interactions may regulate which progenitors physiologically contribute to thymopoiesis.

G-CSF increases the expression of VCAM-1 on stromal cells promoting the adhesion of CD34+ hematopoietic cells: studies under flow conditions

OBJECTIVE AND METHODS

The knowledge of the mechanisms underlying the adhesive processes that lead to homing and/or mobilization of hematopoietic progenitor cells, and the influence of blood rheology, is still limited. We analyzed the impact of flow conditions on the adhesion of CD34+ peripheral blood progenitor cell (PBPC) to the adhesive proteins fibronectin, laminin, and collagen, and to stromal cells.

RESULTS

Under static conditions, all the adhesive substrata assayed promoted adhesion of CD34+ PBPC, being higher on the stromal cells. Under flow conditions, adhesion of CD34+ PBPC was remarkable on stromal cells while insignificant onto the purified proteins. Exposure of stromal cell monolayers to granulocyte colony-stimulating factor (G-CSF) further enhanced PBPC adhesion. This effect correlated with the activation of p38 MAPK and with an increase in the expression of VCAM-1 on stromal cells exposed to G-CSF. In inhibitory assays, both an antibody to the G-CSFR and a specific inhibitor of the p38 MAPK blocked the effects induced by the cytokine.

CONCLUSION

Our results provide direct evidence that in stromal cells G-CSF activates the signaling protein p38 MAPK, inducing expression of the adhesion receptor VCAM-1. This mechanism seems to promote adhesion of CD34+ cells on stromal cells and could play a potential role in homing events.

Circulating hematopoietic progenitors with T lineage potential

The thymus is seeded via the blood, but the identity of hematopoietic progenitors with access to the circulation in adult mice is unknown. We report here that the only progenitors in blood with efficient T lineage potential were lineage negative with high expression of stem cell antigen 1 and c-Kit (LSK cells). The blood LSK population, like its counterpart in the bone marrow, contained hematopoietic stem cells and nonrenewing, multipotent progenitors, including early lymphoid progenitors and CD62L(+) cells previously described as efficient T lineage progenitors. Common lymphoid progenitors could not be identified in the circulation, suggesting they are not physiological T lineage precursors. We conclude that blood LSK cells are the principal circulating progenitors with T lineage potential.

Biology of hematopoietic stem cells and progenitors: implications for clinical application

Stem cell biology is scientifically, clinically, and politically a current topic. The hematopoietic stem cell, the common ancestor of all types of blood cells, is one of the best-characterized stem cells in the body and the only stem cell that is clinically applied in the treatment of diseases such as breast cancer, leukemias, and congenital immunodeficiencies. Multicolor cell sorting enables the purification not only of hematopoietic stem cells, but also of their downstream progenitors such as common lymphoid progenitors and common myeloid progenitors. Recent genetic approaches including gene chip technology have been used to elucidate the gene expression profile of hematopoietic stem cells and other progenitors. Although the mechanisms that control self-renewal and lineage commitment of hematopoietic stem cells are still ambiguous, recent rapid advances in understanding the biological nature of hematopoietic stem and progenitor cells have broadened the potential application of these cells in the treatment of diseases.

Chronic myelogenous leukemia as a paradigm of early cancer and possible curative strategies

The chronological history of the important discoveries leading to our present understanding of the essential clinical, biological, biochemical, and molecular features of chronic myelogenous leukemia (CML) are first reviewed, focusing in particular on abnormalities that are responsible for the massive myeloid expansion. CML is an excellent target for the development of selective treatment because of its highly consistent genetic abnormality and qualitatively different fusion gene product, p210(bcr-abl). It is likely that the multiple signaling pathways dysregulated by p210(bcr-abl) are sufficient to explain all the initial manifestations of the chronic phase of the disease, although understanding of the circuitry is still very incomplete. Evidence is presented that the signaling pathways that are constitutively activated in CML stem cells and primitive progenitors cooperate with cytokines to increase the proportion of stem cells that are activated and thereby increase recruitment into the committed progenitor cell pool, and that this increased activation is probably the primary cause of the massive myeloid expansion in CML. The cooperative interactions between Bcr-Abl and cytokine-activated pathways interfere with the synergistic interactions between multiple cytokines that are normally required for the activation of stem cells, while at the same time causing numerous subtle biochemical and functional abnormalities in the later progenitors and precursor cells. The committed CML progenitors have discordant maturation and reduced proliferative capacity compared to normal committed progenitors, and like them, are destined to die after a limited number of divisions. Thus, the primary goal of any curative strategy must be to eliminate all Philadelphia positive (Ph+) primitive cells that are capable of symmetric division and thereby able to expand the Ph+ stem cell pool and recreate the disease. Several highly potent and moderately selective inhibitors of Bcr-Abl kinase have recently been discovered that are capable of killing the majority of actively proliferating early CML progenitors with minimal effects on normal progenitors. However, like their normal counterparts, most of the CML primitive stem cells are quiescent at any given time and are relatively invulnerable to the Bcr-Abl kinase inhibitors as well as other drugs. We propose that survival of dormant Ph+ stem cells may be the most important reason for the inability to cure the disease during initial treatment, while resistance to the inhibitors and other drugs becomes increasingly important later. An outline of a possible curative strategy is presented that attempts to take advantage of the subtle differences in the proliferative behavior of normal and Ph+ stem cells and the newly discovered selective inhibitors of Bcr-Abl. Leukemia (2003) 17, 1211-1262. doi:10.1038/sj.leu.2402912

Cell fate determination from stem cells

In the adult, tissue-specific stem cells are thought to be responsible for the replacement of differentiated cells within continuously regenerating tissues, such as the liver, skin, and blood system. In this review, we will consider the factors that influence stem cell fate, taking as a primary example the cell fate determination of hematopoietic stem cells.

Changes in integrin expression are associated with altered homing properties of Lin(-/lo)Thy1.1(lo)Sca-1(+)c-kit(+) hematopoietic stem cells following mobilization by cyclophosphamide/granulocyte colony-stimulating factor

OBJECTIVE

Although migration of hematopoietic stem cells (HSC) is essential for normal hematopoiesis and successful hematopoietic cell transplantation, little is known about the mechanisms that underlie this movement. We have sought to characterize the factors that regulate HSC migration by analyzing changes in expression of particular adhesion receptors associated with cyclophosphamide/granulocyte colony-stimulating factor (Cy/G-CSF)-induced HSC mobilization.

METHODS

Expression by Lineage(-/lo)Thy1.1(lo)Sca-1(+)c-kit(+) HSC of members of the beta1 integrin family of adhesion molecules was assessed in untreated or Cy/G-CSF-treated mice by multiparameter flow cytometry. In parallel, the in vivo homing properties of normal and mobilized HSC were compared following intravenous transfer of fluorescently marked HSC.

RESULTS

Normal adult HSC express high levels of several beta1 integrin family members. Following Cy/G treatment, bone marrow HSC selectively downregulate alpha 2 integrin expression and upregulate alpha 5 expression. HSC found in the blood following Cy/G-CSF treatment express significantly lower levels of multiple integrins than their bone marrow and/or splenic counterparts. Changes in integrin expression by blood-borne HSC correlate with a 50% decrease in their ability to home to the bone marrow in short-term assays, and with previously observed defects in competitive engraftment by these HSC. Similar reductions in bone marrow (BM) homing are observed for BM HSC treated with alpha 4 integrin function blocking mAb prior to injection. Modulation of integrin expression induced by mobilization was not associated with cell-cycle progression.

CONCLUSION

Changes in integrin expression and function are associated with HSC mobilization and likely significantly affect the engraftment potential of hematopoietic stem cells.

Sulfated polysaccharides increase plasma levels of SDF-1 in monkeys and mice: involvement in mobilization of stem/progenitor cells

It was previously reported that treatment with the sulfated polysaccharide fucoidan or the structurally similar dextran sulfate increased circulating mature white blood cells and hematopoietic progenitor/stem cells (HPCs) in mice and nonhuman primates; however, the mechanism mediating these effects was unclear. It is reported here that plasma concentrations of the highly potent chemoattractant stromal-derived factor 1 (SDF-1) increase rapidly and dramatically after treatment with fucoidan in monkeys and in mice, coinciding with decreased levels in bone marrow. In vitro and in vivo data suggest that the SDF-1 increase is due to its competitive displacement from heparan sulfate proteoglycans that sequester the chemokine on endothelial cell surfaces or extracellular matrix in bone marrow and other tissues. Although moderately increased levels of interleukin-8, MCP1, or MMP9 were also present after fucoidan treatment, studies in gene-ablated mice (GCSFR(-/-), MCP1(-/-), or MMP9(-/-)) and the use of metalloprotease inhibitors do not support their involvement in the concurrent mobilization. Instead, SDF-1 increases, uniquely associated with sulfated glycan-mobilizing treatments and not with several other mobilizing agents tested, are likely responsible. To the authors' knowledge, this is the first published report of disrupting the SDF-1 gradient between bone marrow and peripheral blood through a physiologically relevant mechanism, resulting in mobilization with kinetics similar to other mobilizing CXC chemokines. The study further underscores the importance of the biological roles of carbohydrates.

Quantitative expression of adhesion molecules on granulocyte colony-stimulating factor-mobilized peripheral blood, bone marrow, and cord blood CD34+ cells

The purpose of this study is to investigate the function of the main adhesion receptors on CD34(+) cells during hematopoietic stem cell transplantation. Expression was quantified by flow cytometry using calibration beads. CD34(+) cells were isolated from either bone marrow (BM), cord blood (CB), or peripheral blood (PB) from study patients and a control group after granulocyte colony-stimulating factor (G-CSF) administration. The study of the CD34(+) cell differentiation showed that CD34(+) cells are mainly CD38(+) and HLA-DR(+), whatever the type of harvest. However, quantitative analysis elicited a weaker expression of CD38 on PB and CB CD34(+) cells in comparison to BM CD34(+) cells. The proportions of CD34(+)/CD49d(+) and CD34(+)/CD49e(+) were smaller on PB cells, without quantitative expression variation. This phenotypic variation promotes CD34(+) cells to exit from BM into circulation, inducing the mobilization. The homing of the CD34(+) cells to the BM involves the CD62L receptor. The expression of this receptor was found to be more frequent and stronger on PB cells than on BM or CB cells. The CD11b, CD18, and CD54 receptors are implicated in CD34(+) cell adhesion to BM microenvironment. No significant variation in CD34(+)/CD11b(+) and CD34(+)/CD18(+) cell frequency was noted. Moreover, the CD54 receptor was more frequently expressed on CB and PB cells. Quantitative analysis revealed that CD18 was more strongly expressed on BM than on PB cells to promote progenitors adhesion by interacting with stromal cells. Finally, the quantitative expression of the main receptors on CD34(+) cells explained cellular functions during the different steps of hematopoietic stem cells transplantation.

[Quantitative expression of the adhesion receptors VLA-4, VLA-5, L-selectin, MAC-1, and ICAM-1 on the surface of CD34+ cells]

The aim of this work was to quantify by flow cytometry the main adhesion receptors on CD34+ cells. These cells were isolated from bone marrow (BM) or mobilized peripheral blood (PB). The proportions of CD34+/CD49d+ and CD34+/CD49e+ are weaker on PB cells, without quantitative expression variation. This phenotypic variation may induce CD34+ cells exist from BM into circulation, promoting the mobilization. The homing to the BM implicate the CD62L receptor, which expression was found more frequently and stronger on PB cells than on BM. The CD11b, CD18 and CD54 receptors are implicated in CD34+ cells adhesion to BM micro-environment. No significant variation in CD34+/CD11b+ and CD34+/CD18+ cells frequency was noted. Moreover, CD54 receptor was more frequently expressed on PB cells. Quantitative analysis revealed that CD18 was more strongly expressed on BM than on PB cells. This quantitative variation could promote progenitor adhesion by interacting with stromal cells. Finally, quantitative expression of the main receptors on CD34+ cells provides an original option for studying CD34+ cells during the mobilization, the homing or the adhesion to BM micro-environment.

Collection of hematopoietic stem cells from patients with autoimmune diseases

We reviewed data from 24 transplant centers in Asia, Australia, Europe, and North America to determine the outcomes of stem cell collection including methods used, cell yields, effects on disease activity, and complications in patients with autoimmune diseases. Twenty-one unprimed bone marrow harvests and 174 peripheral blood stem cell mobilizations were performed on 187 patients. Disease indications were multiple sclerosis (76 patients), rheumatoid arthritis (37 patients), scleroderma (26 patients), systemic lupus erythematosus (19 patients), juvenile chronic arthritis (13 patients), idiopathic autoimmune thrombocytopenia (8 patients), Behcet's disease (3 patients), undifferentiated vasculitis (3 patients), polychondritis (1 patient) and polymyositis (1 patient). Bone marrow harvests were used in the Peoples Republic of China and preferred worldwide for children. PBSC mobilization was the preferred technique for adult stem cell collection in America, Australia, and Europe. Methods of PBSC mobilization included G-CSF (5, 10, or 16 microg/kg/day) or cyclophosphamide (2 or 4 g/m2) with either G-CSF (5 or 10 microg/kg/day) or GM-CSF (5 microg/kg/day). Bone marrow harvests were without complications and did not affect disease activity. A combination of cyclophosphamide and G-CSF was more likely to ameliorate disease activity than G-CSF alone (P < 0.001). g-csf alone was more likely to cause disease exacerbation than the combination of cyclophosphamide and g-csf (P = 0.003). Three patients died as a result of cyclophosphamide-based stem cell collection (2.6% of patients mobilized with cyclophosphamide). When corrected for patient weight and apheresis volume, progenitor cell yields tended to vary by underlying disease, prior medication history and mobilization regimen. Trends in the approaches to, and results of, progenitor cell mobilization are suggested by this survey. While cytokine-based mobilization appears less toxic, it is more likely to result in disease reactivation. Optimization with regard to cell yields and safety are likely to be disease-specific and prospective disease-specific studies of mobilization procedures appear warranted.

The CD3- 16+ 56+ NK cell count independently predicts autologous blood stem cell mobilization

Better predictive factors for autologous blood stem cell mobilization (BSCM) are needed. The purpose of this study was to determine if an independent association exists between lymphocyte or NK cell counts and BSCM. Data were analyzed on 141 consecutive patients aged 19-69 years (median 45) who received combined chemotherapy plus G-CSF for BSCM, and who had measurements of immune cells prior to BSCM. Of the 141 patients, 41% had breast cancer, 14% Hodgkin's disease, 34% non-Hodgkin's lymphoma, and 11% other diagnoses. BSCM involved dose-intensive cyclophosphamide, etoposide, cisplatin (DICEP) plus G-CSF 300 microg (<70 kg) or 480 microg (>70 kg) for 45% of patients, while the remaining 55% received other chemotherapy plus similar doses of G-CSF. Only a single apheresis was performed for 94% of patients. The following factors were analyzed for predictors of BSCM: age, gender, prior chemotherapy, prior radiotherapy, diagnosis, disease status, marrow involvement, mobilization regimen, Hb, WBC, platelet count, B cell, T cell, and NK cell counts. The peripheral blood CD34+ counts on the first day of apheresis (PBCD34) were 6-1783 x 10(6)/l (median 150). The PBCD34 count correlated strongly with the number of CD34+ cells collected/l blood apheresed and with the number of CD34+ cells collected/kg. By multivariate analysis using continuous variables, relapsed status (P = 0.0003), not using DICEP mobilization (P = 0.0001), female gender (P = 0.0057), low platelet count (P = 0.051), and low CD3- 16+ 56+ count (P = 0.0158) were associated with low PBCD34 counts. Using categorical variables, the only factors that independently predicted a PBCD34 count <150 x 10(6)/l were: >1 prior chemotherapy regimen (odds ratio = 5.12, P = 0.0003), not using DICEP mobilization (odds ratio = 4.94, P = 0.0001), and CD3- 16+ 56+ count <125 x 10(6)/l (odds ratio= 2.58, P = 0.0157). In conclusion, the CD3- 16+ 56+ count may be a useful additional predictor of BSCM and warrants further study.

Increase in circulating SDF-1 after treatment with sulfated glycans. The role of SDF-1 in mobilization

SDF-1 is a potent chemoattractant for mature white blood cells and hemopoietic stem/progenitor cells (HPCs). An important role for this chemokine in mobilization has been postulated, but in vivo studies directly addressing its effects are lacking. After one injection of fucan sulfate (FucS) or dextran sulfate, plasma levels of SDF-1 are greatly increased in mice or primates. Increases are dose-dependent and correlate with mobilization of HPCs. Elevated levels of circulating SDF-1 appear to be uniquely associated with this treatment, as it was not seen with cytokine or anti-integrin antibody treatments that induce mobilization. In vitro, these sulfated glycans specifically bind to SDF-1 and inhibit SDF-1/heparin binding, suggesting a mechanism of release from sequestration on heparan sulfate proteoglycans in vivo. Although other chemokines including IL8 and cytokines like G-CSF also increase, evidence in GCSFR-deficient mice suggests that at least these two factors are unlikely participants in FucS-induced mobilization. Likewise, although the activity of the metallo-protease MMP9 increases after FucS treatment, experiments in MMP9-/- mice indicate its presence is dispensable for mobilization or SDF-1 release. However, effects of other proteases cannot be ruled out by these experiments. Finally, anti-SDF-1 antibodies partially inhibit FucS-induced mobilization, supporting a causative relationship. Our data offer a unique insight into the mechanism of sulfated glycan-induced mobilization and suggest a novel way of disturbing SDF-1 gradients between bone marrow and peripheral blood.

Differences in cell cycle kinetics of candidate engrafting cells in human bone marrow and mobilized peripheral blood

Patients undergoing hematopoietic stem cell transplantation (HSCT) with mobilized peripheral blood (MPB) engraft quicker than those receiving bone marrow (BM). Our objective was to determine whether candidate engrafting cells--primitive hematopoietic progenitors (PHPs)--from MPB and BM exhibit different responses to cytokines that could explain this observation. We compared the cell cycle kinetics and ex vivo expansion of PHP-enriched cells obtained from MPB (n = 12) and BM (n = 10) by fluorescence-activated sorting of CD90+, AC133+ or CD38(dull) subsets of pre-selected CD34(+) cells. Cell cycle status, before and after 40 hours of serum-free culture with a cytokine cocktail, was assessed by multiparameter flow cytometry following incubation with Hoechst 33342 and pyronin Y. We found that 0.2% +/- 0.3% of MPB CD34(+)CD90(+) cells were in S/G(2)/M phases at hour 0, compared with 5% +/- 2.5% of those from BM (p = 0.0001), and 86.3% +/- 9.7% were in G(0), compared with 65.3% +/- 10% of those in BM (p = 0.0001). After 40 hours of culture, CD34(+)CD90(+) cells from MPB were more mitotically active than those from BM, with 29% +/- 4.9% in S/G(2)/M and 20% +/- 11.4% in G(0), compared to 19% +/- 6.5% (p = 0.001) and 39.2% +/- 22% (p = 0.027) of cells from BM. There was greater expansion of both total CD34(+) cells and the CD90(+) subset from MPB samples (p = 0.001 and 0.0001, respectively). Results from PHPs defined on the basis of AC133 expression correlated well with results obtained in CD90(+) subsets (r(2) = 0.81; p = 0.014).MPB PHPs appear to be primed for a greater acceleration in mitotic activity upon cytokine exposure. This qualitative difference may contribute to the earlier engraftment seen after HSCT using MPB grafts.

Differential MMP and TIMP production by human marrow and peripheral blood CD34(+) cells in response to chemokines

As stromal cell-derived factor-1 (SDF-1), macrophage inflammatory protein-1alpha (MIP-1alpha), and interleukin-8 (IL-8) are implicated in the homing and mobilization of human hematopoietic progenitors (HPC), we hypothesized that these chemokines mediate the migration of HPC across subendothelial basement membranes by regulating production of matrix metalloproteinases (MMPs) and their natural tissue inhibitors (TIMPs). Assays for migration across reconstituted basement membrane (Matrigel) and chemotaxis were carried out using CD34(+) cells derived from normal human bone marrow (BM) and mobilized peripheral blood (PB). Secretion of MMPs and TIMPs was evaluated by zymography and reverse zymography and gene expression by RT-PCR. We found that an SDF-1 gradient increases the chemotaxis of BM and PB CD34(+) cells across Matrigel (BM > PB), which is blocked by inhibitors of MMPs (o-phenanthroline, rhTIMP-1, rhTIMP-2, and anti-MMP-9 and anti-MMP-2 antibodies) but enhanced by tumor necrosis factor-alpha (TNF-alpha), a strong stimulator of MMPs. Preincubation of these cells with SDF-1 stimulated the secretion of MMP-2 and MMP-9 in BM and PB CD34(+) cells but of TIMP-1 and TIMP-2 only in PB CD34(+) cells. Preincubation with MIP-1alpha and IL-8 also stimulated the secretion of MMP-9 and MMP-2 (BM > PB), but with respect to TIMPs, the effect was reversed (PB > BM), resulting in trans-Matrigel migration of BM but not of PB CD34(+) cells. We therefore propose that MMPs and TIMPs are involved in 1) SDF-1-induced chemotaxis of human HPC across subendothelial basement membranes, and 2) MIP-1alpha- and IL-8-stimulated migration of HPC.

Sulfated glycans induce rapid hematopoietic progenitor cell mobilization: evidence for selectin-dependent and independent mechanisms

The adhesive mechanisms leading to the mobilization of hematopoietic progenitor cells (HPCs) from the bone marrow into the blood are poorly understood. We report on a role for selectins and fucoidan in progenitor mobilization. Baseline levels of circulating HPCs are increased in endothelial selectin-deficient (P/E−/−) mice. Similar levels are observed when E-selectin null (E−/−) mice are treated with anti-P-selectin antibody or with fucoidan (which inhibits P- and L-selectin function). In particular, administration of 2 doses of fucoidan (25 mg/kg) over 6 hours produces profound mobilization of progenitors in wild-type mice and the response is greatly enhanced in E−/− and P/E−/− mice. Competitive reconstitution experiments reveal that fucoidan also elicits long-term (more than 6 months) repopulating stem cells. Mobilization assays using chimeric mice harboring L-selectin–deficient progenitors and wild-type progenitors expressing the green fluorescence protein suggest that L-selectin expression is not required but confers an advantage for fucoidan-induced mobilization. Sulfation is critical as desulfated fucoidan is ineffective. In addition, sulphogalactosylceramide (sulfatide) but not heparin can induce HPC mobilization. Our results indicate that administration of sulfated glycans, especially with concurrent inhibition of E-selectin function, represents a powerful novel method for rapid mobilization of long-term–repopulating stem cells. These findings may help elucidate the mechanisms of HPC trafficking during development and adult life.

Sulfated glycans induce rapid hematopoietic progenitor cell mobilization: evidence for selectin-dependent and independent mechanisms

The adhesive mechanisms leading to the mobilization of hematopoietic progenitor cells (HPCs) from the bone marrow into the blood are poorly understood. We report on a role for selectins and fucoidan in progenitor mobilization. Baseline levels of circulating HPCs are increased in endothelial selectin-deficient (P/E−/−) mice. Similar levels are observed when E-selectin null (E−/−) mice are treated with anti-P-selectin antibody or with fucoidan (which inhibits P- and L-selectin function). In particular, administration of 2 doses of fucoidan (25 mg/kg) over 6 hours produces profound mobilization of progenitors in wild-type mice and the response is greatly enhanced in E−/− and P/E−/− mice. Competitive reconstitution experiments reveal that fucoidan also elicits long-term (more than 6 months) repopulating stem cells. Mobilization assays using chimeric mice harboring L-selectin–deficient progenitors and wild-type progenitors expressing the green fluorescence protein suggest that L-selectin expression is not required but confers an advantage for fucoidan-induced mobilization. Sulfation is critical as desulfated fucoidan is ineffective. In addition, sulphogalactosylceramide (sulfatide) but not heparin can induce HPC mobilization. Our results indicate that administration of sulfated glycans, especially with concurrent inhibition of E-selectin function, represents a powerful novel method for rapid mobilization of long-term–repopulating stem cells. These findings may help elucidate the mechanisms of HPC trafficking during development and adult life.

CD44v10 in hematopoiesis and stem cell mobilization

Transplantation of hematopoietic progenitor cells provides in many instances of malignant tumors an ultimate chance of curative therapy, whereby the transfer of peripheral blood stem cells (PBSC) may even be advantageous as compared to bone marrow cells. Yet, the transfer of PBSC requires mobilization of stem cells into the periphery, which is mostly achieved via hematopoietic growth factors like G-CSF. Although G-CSF has been found to efficiently mobilize stem cells in most instances, some patients do not or insufficiently respond to G-CSF treatment In addition, G-CSF treatment may by accompanied by maturation of the most primitive progenitors and this may have an impact on stem cell homing and recovery of hemopoiesis. Therefore, additional approaches for stem cell mobilization have been searched for, in particular mobilization via a blockade of an adhesion molecule expressed by CD34-positive cells, like VLA-4 (CD49d) and the hematopoietic isoform of CD44 (CD44s). We recently described that in the mouse one of the CD44 variant isoforms, CD44v10, is expressed on a subpopulation of bone marrow cells, whereas a CD44v10 receptor-globulin only binds to stromal elements. These features appeared promising for anti-CD44v10 as a means of stem cell mobilization. Indeed, treatment with anti-CD44v10 revealed promising results concerning the recovery of multilineage colony forming units in the spleen and the peripheral blood. We here summarize features of expression and function of CD44 in hematopoiesis an provide further evidence for anti-CD44v10 as a means to mobilize hematopoietic progenitor cells.

Mobilization of stem/progenitor cells by sulfated polysaccharides does not require selectin presence

Employing carbohydrate ligands, which have been extensively used to block selectin function in vitro and in vivo, we have examined the involvement of such ligands in stem/progenitor cell mobilization in mice and monkeys. We found that sulfated fucans, branched and linear, are capable of increasing mature white cells in the periphery and mobilizing stem/progenitor cells of all classes (up to 32-fold) within a few hours posttreatment in a dose-dependent manner. To elicit the effect, the presence of sulfate groups was necessary, yet not sufficient, as certain sulfated hexosamines tested (chondroitin sulfates A or B) were ineffective. Significant mobilization of stem/progenitor cells and leukocytosis was elicited in selectin-deficient mice (L(-/-), PE(-/-), or LPE(-/-)) similar to that of wild-type controls, suggesting that the mode of action of sulfated fucans is not through blockade of known selectins. Other mechanisms have been entertained, in particular, the release of chemokines/cytokines, including some previously implicated in mobilization. Significant increases were documented in the levels of seven circulating chemokines/cytokines within a few hours after fucan sulfate treatment and support such a proposition. Additionally, an increase was noted in plasma metalloproteinase (MMP) 9, which might independently contribute to the mobilization process by enzymatically facilitating chemokine/cytokine release. Mobilization by sulfated polysaccharides provides a distinct paradigm in the mobilization process and uncovers an additional novel in vivo biological role for sulfated glycans. As similarly sulfated compounds were ineffective in vivo, the data also underscore the fact that polysaccharides with similar structures may elicit diverse in vivo effects.