Stromal-derived factor 1 inhibits the cycling of very primitive human hematopoietic cells in vitro and in NOD/SCID mice

Effects of protein malnutrition on hematopoietic regulatory activity of bone marrow mesenchymal stem cells

Protein malnutrition causes anemia and leukopenia as it reduces hematopoietic precursors and impairs the production of mediators that regulate hematopoiesis. Hematopoiesis occurs in distinct bone marrow niches that modulate the processes of differentiation, proliferation and self-renewal of hematopoietic stem cells (HSCs). Mesenchymal stem cells (MSCs) contribute to the biochemical composition of bone marrow niches by the secretion of several growth factors and cytokines, and they play an important role in the regulation of HSCs and hematopoietic progenitors. In this study, we investigated the effect of protein malnutrition on the hematopoietic regulatory function of MSCs. C57BL/6NTaq mice were divided into control and protein malnutrition groups, which received, respectively, a normal protein diet (12% casein) and a low protein diet (2% casein). The results showed that protein malnutrition altered the synthesis of SCF, TFG-β, Angpt-1, CXCL-12, and G-CSF by MSCs. Additionally, MSCs from the protein malnutrition group were not able to maintain the lymphoid, granulocytic and megakaryocytic-erythroid differentiation capacity compared to the MSCs of the control group. In this way, the comprehension of the role of MSCs on the regulation of the hematopoietic cells, in protein malnutrition states, is for the first time showed. Therefore, we infer that hematopoietic alterations caused by protein malnutrition are due to multifactorial alterations and, at least in part, the MSCs' contribution to hematological impairment.

How Prostate Cancer Cells Use Strategy Instead of Brute Force to Achieve Metastasis

Akin to many other cancers, metastasis is the predominant cause of lethality in prostate cancer (PCa). Research in the past decade or so has revealed that although metastatic manifestation is a multi-step and complex process that is orchestrated by distinct cellular and molecular mechanisms, the process in itself is an extremely inefficient one. It is now becoming increasingly evident that PCa cells employ a plethora of strategies to make the most of this inefficient process. These strategies include priming the metastatic sites ahead of colonization, devising ways to metastasize to specific organs, outsmarting the host defense surveillance, lying in a dormant state at the metastatic site for prolonged periods, and widespread reprogramming of the gene expression to suit their needs. Based on established, recent, and evolving lines of research, this review is an attempt to understand PCa metastasis from the perspective of military combat, wherein strategic maneuvering instead of brute force often plays a decisive role in the outcome.

Potential Role of CXCR4 Targeting in the Context of Radiotherapy and Immunotherapy of Cancer

Cancer immunotherapy has been established as standard of care in different tumor entities. After the first reports on synergistic effects with radiotherapy and the induction of abscopal effects-tumor shrinkage outside the irradiated volume attributed to immunological effects of radiotherapy-several treatment combinations have been evaluated. Different immunotherapy strategies (e.g., immune checkpoint inhibition, vaccination, cytokine based therapies) have been combined with local tumor irradiation in preclinical models. Clinical trials are ongoing in different cancer entities with a broad range of immunotherapeutics and radiation schedules. SDF-1 (CXCL12)/CXCR4 signaling has been described to play a major role in tumor biology, especially in hypoxia adaptation, metastasis and migration. Local tumor irradiation is a known inducer of SDF-1 expression and release. CXCR4 also plays a major role in immunological processes. CXCR4 antagonists have been approved for the use of hematopoietic stem cell mobilization from the bone marrow. In addition, several groups reported an influence of the SDF-1/CXCR4 axis on intratumoral immune cell subsets and anti-tumor immune response. The aim of this review is to merge the knowledge on the role of SDF-1/CXCR4 in tumor biology, radiotherapy and immunotherapy of cancer and in combinatorial approaches.

Dual Targeting of Acute Leukemia and Supporting Niche by CXCR4-Directed Theranostics

C-X-C chemokine receptor 4 (CXCR4) is a transmembrane receptor with pivotal roles in cell homing and hematopoiesis. CXCR4 is also involved in survival, proliferation and dissemination of cancer, including acute lymphoblastic and myeloid leukemia (ALL, AML). Relapsed/refractory ALL and AML are frequently resistant to conventional therapy and novel highly active strategies are urgently needed to overcome resistance. Methods: We used patient-derived (PDX) and cell line-based xenograft mouse models of ALL and AML to evaluate the efficacy and toxicity of a CXCR4-targeted endoradiotherapy (ERT) theranostic approach. Results: The positron emission tomography (PET) tracer 68Ga-Pentixafor enabled visualization of CXCR4 positive leukemic burden. In xenografts, CXCR4-directed ERT with 177Lu-Pentixather distributed to leukemia harboring organs and resulted in efficient reduction of leukemia. Despite a substantial in vivo cross-fire effect to the leukemia microenvironment, mesenchymal stem cells (MSCs) subjected to ERT were viable and capable of supporting the growth and differentiation of non-targeted normal hematopoietic cells ex vivo. Finally, three patients with refractory AML after first allogeneic hematopoietic stem cell transplantation (alloSCT) underwent CXCR4-directed ERT resulting in leukemia clearance, second alloSCT, and successful hematopoietic engraftment. Conclusion: Targeting CXCR4 with ERT is feasible and provides a highly efficient means to reduce refractory acute leukemia for subsequent cellular therapies. Prospective clinical trials testing the incorporation of CXCR4 targeting into conditioning regimens for alloSCT are highly warranted.

Continuous blockade of CXCR4 results in dramatic mobilization and expansion of hematopoietic stem and progenitor cells

Interaction between the chemokine receptor CXCR4 and its chief ligand CXCL12 plays a critical role in the retention and migration of hematopoietic stem and progenitor cells (HSPCs) in the bone marrow (BM) microenvironment. In this study, qualitative and quantitative effects of long-term pharmacologic inhibition of the CXCR4/CXCL12 axis on the HSPC compartment were investigated by using 3 structurally unrelated small molecule CXCR4 antagonists. A >10-fold increase in mobilization efficiency was achieved by administering the antagonists as a subcutaneous continuous infusion for 2 weeks compared to a single bolus injection. A concurrent increase in self-renewing proliferation leading to a twofold to fourfold expansion of the HSPC pool in the BM was observed. The expanded BM showed a distinct repopulating advantage when tested in serial competitive transplantation experiments. Furthermore, major changes within the HSPC niche associated with previously described HSPC expansion strategies were not detected in bones treated with a CXCR4 antagonist infusion. Our data suggest that prolonged but reversible pharmacologic blockade of the CXCR4/CXCL12 axis represents an approach that releases HSPC with efficiency superior to any other known mobilization strategy and may also serve as an effective method to expand the BM HSPC pool.

Phenotypic and Functional Alterations of Hematopoietic Stem and Progenitor Cells in an In Vitro Leukemia-Induced Microenvironment

An understanding of the cell interactions occurring in the leukemic microenvironment and their functional consequences for the different cell players has therapeutic relevance. By co-culturing mesenchymal stem cells (MSC) with the REH acute lymphocytic leukemia (ALL) cell line, we have established an in vitro leukemic niche for the functional evaluation of hematopoietic stem/progenitor cells (HSPC, CD34+ cells). We showed that the normal homeostatic control exerted by the MSC over the HSPC is considerably lost in this leukemic microenvironment: HSPC increased their proliferation rate and adhesion to MSC. The adhesion molecules CD54 and CD44 were consequently upregulated in HSPC from the leukemic niche. Consequently, with this adhesive phenotype, HSPC showed less Stromal derived factor-1 (SDF-1)-directed migration. Interestingly, multipotency was severely affected with an important reduction in the absolute count and the percentage of primitive progenitor colonies. It was possible to simulate most of these HSPC alterations by incubation of MSC with a REH-conditioned medium, suggesting that REH soluble factors and their effect on MSC are important for the observed changes. Of note, these HSPC alterations were reproduced when primary leukemic cells from an ALL type B (ALL-B) patient were used to set up the leukemic niche. These results suggest that a general response is induced in the leukemic niche to the detriment of HSPC function and in favor of leukemic cell support. This in vitro leukemic niche could be a valuable tool for the understanding of the molecular events responsible for HSPC functional failure and a useful scenario for therapeutic evaluation.

Loss of quiescence and self-renewal capacity of hematopoietic stem cell in an in vitro leukemic niche

Background

Leukemic and mesenchymal stem cells interact in the leukemic microenvironment and affect each other differently. This interplay has also important implications for the hematopoietic stem cell (HSC) biology and function. This study evaluated human HSC self-renewal potential and quiescence in an in vitro leukemic niche without leukemic cells.

Methods

A leukemic niche was established by co-culturing mesenchymal stem cells with a fresh conditioned medium obtained from a leukemic (REH) cell line. After 3 days, the REH-conditioned medium was removed and freshly isolated CD34+ at a density of up to 100,000 cells/ml were added to the leukemic niche. CD34+ cell evaluations (cell cycle, self-renewal gene expression and migration capacity) were performed after 3 further days of co-culture. Additionally, we preliminary investigated the soluble factors present in the leukemic niche and their effect on the mesenchymal stem cells. Statistical significance was assessed by Student’s t test or the nonparametric test Kolmogorov–Smirnov.

Results

By co-culturing normal mesenchymal stem cells with the REH-conditioned medium we showed that hematopoietic stem cells, normally in a quiescent state, enter cell cycle and proliferate. This loss of quiescence was accompanied by an increased expression of Ki-67 and c-Myc, two well-known cell proliferation-associated markers. Two central regulators of quiescence GATA2 and p53 were also down regulated. Importantly, two genes involved in HSC self-renewal, Klf4 and the histone–lysine N-methyltransferase enzyme Ezh2, were severely affected. On the contrary, c-Kit expression, the stem cell factor receptor, was upregulated in hematopoietic stem cells when compared to the normal niche. Interestingly, mesenchymal stem cells incubated with the REH-conditioned medium stopped growing, showed a flattened morphology with the appearance of small vacuoles, and importantly, became positive for the senescence-associated beta-galactosidase activity. Evaluation of the leukemic-conditioned medium showed increased IL-6 and IL-8, suggesting that these cytokines could be responsible for the observed changes.

Conclusions

Our results showed that quiescence and self-renewal are severely affected in this leukemic niche. This in vitro leukemic niche, established without leukemic cells, will facilitate HSC gene expression evaluation and the development of therapeutic agents aimed to neutralize soluble factors and the cell signaling pathways involved in HSC alterations.

Electronic supplementary material

The online version of this article (doi:10.1186/s40164-016-0062-1) contains supplementary material, which is available to authorized users.

Extracellular molecules in hematopoietic stem cell mobilisation

Hematopoietic stem cells are a remarkable resource currently used for the life saving treatment, hematopoietic stem cell transplantation. Today, hematopoietic stem cells are primarily obtained from mobilized peripheral blood following treatment of the donor with the cytokine G-CSF, and in some settings, chemotherapy and/or the CXCR4 antagonist plerixafor. The collection of hematopoietic stem cells is contingent on adequate and timely mobilization of these cells into the peripheral blood. The use of healthy donors, particularly when unrelated to the patient, requires mobilization strategies be safe for the donor. While current mobilization strategies are largely successful, adequate mobilization fails to occur in a significant portion of donors. Understanding the mechanisms involved in the egress of stem cells from the bone marrow provides opportunities to further improve the process of collecting hematopoietic stem cells. Here, the role extracellular components of the blood and bone marrow in the mobilization process are discussed.

Autophagy-dependent regulatory T cells are critical for the control of graft-versus-host disease

Regulatory T cells (Tregs) play a crucial role in the maintenance of peripheral tolerance. Quantitative and/or qualitative defects in Tregs result in diseases such as autoimmunity, allergy, malignancy, and graft-versus-host disease (GVHD), a serious complication of allogeneic stem cell transplantation (SCT). We recently reported increased expression of autophagy-related genes (Atg) in association with enhanced survival of Tregs after SCT. Autophagy is a self-degradative process for cytosolic components that promotes cell homeostasis and survival. Here, we demonstrate that the disruption of autophagy within FoxP3⁺ Tregs (B6.Atg7^fl/fl-FoxP3cre⁺ ) resulted in a profound loss of Tregs, particularly within the bone marrow (BM). This resulted in dysregulated effector T cell activation and expansion, and the development of enterocolitis and scleroderma in aged mice. We show that the BM compartment is highly enriched in TIGIT⁺ Tregs and that this subset is differentially depleted in the absence of autophagy. Moreover, following allogeneic SCT, recipients of grafts from B6.Atg7^fl/fl-FoxP3cre⁺ donors exhibited reduced Treg reconstitution, exacerbated GVHD, and reduced survival compared with recipients of B6.WT-FoxP3cre⁺ grafts. Collectively, these data indicate that autophagy-dependent Tregs are critical for the maintenance of tolerance after SCT and that the promotion of autophagy represents an attractive immune-restorative therapeutic strategy after allogeneic SCT.

Plerixafor (a CXCR4 antagonist) following myeloablative allogeneic hematopoietic stem cell transplantation enhances hematopoietic recovery

Background

The binding of CXCR4 with its ligand (stromal-derived factor-1) maintains hematopoietic stem/progenitor cells (HSPCs) in a quiescent state. We hypothesized that blocking CXCR4/SDF-1 interaction after hematopoietic stem cell transplantation (HSCT) promotes hematopoiesis by inducing HSC proliferation.

Methods

We conducted a phase I/II trial of plerixafor on hematopoietic cell recovery following myeloablative allogeneic HSCT. Patients with hematologic malignancies receiving myeloablative conditioning were enrolled. Plerixafor 240 μg/kg was administered subcutaneously every other day beginning day +2 until day +21 or until neutrophil recovery. The primary efficacy endpoints of the study were time to absolute neutrophil count >500/μl and platelet count >20,000/μl. The cumulative incidence of neutrophil and platelet engraftment of the study cohort was compared to that of a cohort of 95 allogeneic peripheral blood stem cell transplant recipients treated during the same period of time and who received similar conditioning and graft-versus-host disease prophylaxis.

Results

Thirty patients received plerixafor following peripheral blood stem cell (n = 28) (PBSC) or bone marrow (n = 2) transplantation. Adverse events attributable to plerixafor were mild and indistinguishable from effects of conditioning. The kinetics of neutrophil and platelet engraftment, as demonstrated by cumulative incidence, from the 28 study subjects receiving PBSC showed faster neutrophil (p = 0.04) and platelet recovery >20 K (p = 0.04) compared to the controls.

Conclusions

Our study demonstrated that plerixafor can be given safely following myeloablative HSCT. It provides proof of principle that blocking CXCR4 after HSCT enhances hematopoietic recovery. Larger, confirmatory studies in other settings are warranted.

Trial registration

ClinicalTrials.gov NCT01280955

BMP2 Regulation of CXCL12 Cellular, Temporal, and Spatial Expression is Essential During Fracture Repair

The cellular and humoral responses that orchestrate fracture healing are still elusive. Here we report that bone morphogenic protein 2 (BMP2)-dependent fracture healing occurs through a tight control of chemokine C-X-C motif-ligand-12 (CXCL12) cellular, spatial, and temporal expression. We found that the fracture repair process elicited an early site-specific response of CXCL12(+)-BMP2(+) endosteal cells and osteocytes that was not present in unfractured bones and gradually decreased as healing progressed. Absence of a full complement of BMP2 in mesenchyme osteoprogenitors (BMP2(cKO/+)) prevented healing and led to a dysregulated temporal and cellular upregulation of CXCL12 expression associated with a deranged angiogenic response. Healing was rescued when BMP2(cKO/+) mice were systemically treated with AMD3100, an antagonist of CXCR4 and agonist for CXCR7 both receptors for CXCL12. We further found that mesenchymal stromal cells (MSCs), capable of delivering BMP2 at the endosteal site, restored fracture healing when transplanted into BMP2(cKO/+) mice by rectifying the CXCL12 expression pattern. Our in vitro studies showed that in isolated endosteal cells, BMP2, while inducing osteoblastic differentiation, stimulated expression of pericyte markers that was coupled with a decrease in CXCL12. Furthermore, in isolated BMP2(cKO/cKO) endosteal cells, high expression levels of CXCL12 inhibited osteoblastic differentiation that was restored by AMD3100 treatment or coculture with BMP2-expressing MSCs that led to an upregulation of pericyte markers while decreasing platelet endothelial cell adhesion molecule (PECAM). Taken together, our studies show that following fracture, a CXCL12(+)-BMP2(+) perivascular cell population is recruited along the endosteum, then a timely increase of BMP2 leads to downregulation of CXCL12 that is essential to determine the fate of the CXCL12(+)-BMP2(+) to osteogenesis while departing their supportive role to angiogenesis. Our findings have far-reaching implications for understanding mechanisms regulating the selective recruitment of distinct cells into the repairing niches and the development of novel pharmacological (by targeting BMP2/CXCL12) and cellular (MSCs, endosteal cells) interventions to promote fracture healing.

Expression of multidrug resistance 1 gene in association with CXCL12 in chronic myelogenous leukaemia

Even though the BCR-ABL tyrosine kinase inhibitor imatinib significantly improves the prognosis of chronic myelogenous leukaemia (CML) patients, drug resistance is a major obstacle to better management. We examined the interaction of recently defined bone marrow microenvironment factors CXCL12 and ATP-binding cassette (ABC) transporters in the bone marrow of CML patients in the chronic phase and blast crisis.Expression levels of mRNA extracted from frozen specimens of CML patients were measured by real-time polymerase chain reaction. The expression of the ABC transporters MDR1, ABCC1, ABCG2, and CXCL12 was significantly higher in the bone marrow samples of CML blast crisis than in those of CML chronic phase. Immunohistochemical staining for CXCL12 revealed that the proportion of CXCL12 positive reticular cell areas correlated well with the mRNA levels of CXCL12 in CML bone marrow. Finally, co-culture experiments of K562 CML cells with CXCL12 expressing mesenchymal cells (OP9 cells or human CXCL12 transfected 3T3 cells) revealed enhanced mRNA levels for MDR1 in a CXCL12 rich environment.These results suggest that imatinib treatment restores the bone marrow microenvironment in CML with the presence of CXCL12 expressing reticular cells but in turn induces the overexpression of MDR1 in haematopoietic cells due to up-regulated expression of CXCL12.

Leukemia stem cells: the root of chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a clonal myeloproliferative disorder characterized by a chromosome translocation that generates the Bcr-Abl oncogene encoding a constitutive kinase activity. Despite remarkable success in controlling CML at chronic phase by Bcr-Abl tyrosine kinase inhibitors (TKIs), a significant proportion of CML patients treated with TKIs develop drug resistance due to the inability of TKIs to kill leukemia stem cells (LSCs) that are responsible for initiation, drug resistance, and relapse of CML. Therefore, there is an urgent need for more potent and safer therapies against leukemia stem cells for curing CML. A number of LSC-associated targets and corresponding signaling pathways, including CaMKII-γ, a critical molecular switch for co-activating multiple LSC-associated signaling pathways, have been identified over the past decades and various small inhibitors targeting LSC are also under development. Increasing evidence shows that leukemia stem cells are the root of CML and targeting LSC may offer a curable treatment option for CML patients. This review summarizes the molecular biology of LSC and its-associated targets, and the potential clinical application in chronic myeloid leukemia.

Leukemia stem cells: the root of chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a clonal myeloproliferative disorder characterized by a chromosome translocation that generates the Bcr-Abl oncogene encoding a constitutive kinase activity. Despite remarkable success in controlling CML at chronic phase by Bcr-Abl tyrosine kinase inhibitors (TKIs), a significant proportion of CML patients treated with TKIs develop drug resistance due to the inability of TKIs to kill leukemia stem cells (LSCs) that are responsible for initiation, drug resistance, and relapse of CML. Therefore, there is an urgent need for more potent and safer therapies against leukemia stem cells for curing CML. A number of LSC-associated targets and corresponding signaling pathways, including CaMKII-γ, a critical molecular switch for co-activating multiple LSC-associated signaling pathways, have been identified over the past decades and various small inhibitors targeting LSC are also under development. Increasing evidence shows that leukemia stem cells are the root of CML and targeting LSC may offer a curable treatment option for CML patients. This review summarizes the molecular biology of LSC and its-associated targets, and the potential clinical application in chronic myeloid leukemia.

Stromal cell derived factor-1α promotes C-Kit+ cardiac stem/progenitor cell quiescence through casein kinase 1α and GSK3β

A population of c-kit(+) cardiac stem/progenitor cells (CSPC) has been identified in the heart and shown to contribute to myocardial regeneration after infarction. Previously, we have shown the chemokine, stromal cell derived factor 1α (SDF1) is necessary for the myocardial response to infarction where chronic infusion of the CXCR4 antagonist, AMD3100, exacerbated MI. Notably, AMD3100 increased CSPC proliferation. The effect of SDF1 on CSPC proliferation was further investigated in primary cultures of magnetically sorted c-kit(+) CSPCs. SDF1 facilitated CSPC quiescence by blocking cell cycle progression at the G0 to G1 transition. SDF1 decreased casein kinase 1α (CK1α) consequently attenuating β-catenin phosphorylation, destabilization, and degradation. Increased levels of β-catenin with SDF1 were effective, increasing TCF/LEF reporter activity. SDF downregulation of CK1α was dependent on proteasomal degradation and decreased mRNA expression. CK1α siRNA knockdown verified SDF1-dependent CSPC quiescence requires CK1α downregulation and stablilization of β-catenin. Conversely, β-catenin knockdown increased CSPC proliferation. SDF1 also increased GSK3β Y216 phosphorylation responsible for increased activity. SDF1 mediated CK1α downregulation and increase in GSK3β activity affected cell cycle through Bmi-1 downregulation, increased cyclin D1 phosphorylation, and decreased cyclin D1 levels. In conclusion, SDF1 exerts a quiescent effect on resident c-kit(+) CSPCs by decreasing CK1α levels, increasing GSK3β activity, stabilizing β-catenin, and affecting regulation of the cell cycle through Bmi-1 and cyclin D1. SDF1-dependent quiescence is an important factor in stem and progenitor cell preservation under basal conditions, however, with stress or injury in which SDF1 is elevated, quiescence may limit expansion and contribution to myocardial regeneration.

Administration of a plasmid that expresses SDF-1α affects the oncogenic potential of mouse bcr-abl-transformed cells

Stromal-derived factor 1α (SDF‑1α, also known as CXCL12) is a chemokine that exerts its effects through the G-protein coupled receptors, C-X-C chemokine receptor type 4 (CXCR4) and 7 (CXCR7). There is marked evidence that the SDF-1/CXCR4 axis is involved in the pathogenesis of leukemia and therapies that target this axis are under development. The present study aimed to increase the efficacy of a DNA-based bcr-abl vaccine by simultaneously immunizing mice with a plasmid carrying the whole SDF-1α gene. Bcr-abl‑transformed 12B1 cells were used to challenge the mice. These cells have the oncogenic potential to induce both leukemia following intravenous inoculation and lymphoma-type solid tumors after subcutaneous inoculation. Administering an SDF‑1 carrying plasmid together with the bcr-abl vaccine resulted in increased survival following a challenge with subcutaneously administered 12B1 cells, although the difference was not statistically significant. However, there was a difference when the animals that developed subcutaneous tumors were only taken into consideration. In doubly-treated mice, significantly more mice failed to develop solid tumors than mice that had only received the bcr-abl vaccine. By contrast, the occurrence of fatal leukemia was significantly higher in the mice that were treated with the SDF-1 plasmid, regardless of whether they were immunized with the bcr-abl-vaccine. No humoral or cellular immune responses against SDF‑1 were detected in the treated mice, which suggested that the changes in oncogenic potential of 12B1 cells were due to the activity of SDF-1 itself.

The role of CXCL12 and CCL7 chemokines in immune regulation, embryonic development, and tissue regeneration

Chemotactic factors direct the migration of immune cells, multipotent stem cells, and progenitor cells under physiologic and pathologic conditions. Chemokine ligand 12 and chemokine ligand 7 have been identified and investigated in multiple studies for their role in cellular trafficking in the setting of tissue regeneration. Recent early phase clinical trials have suggested that these molecules may lead to clinical benefit in patients with chronic disease. Importantly, these two proteins may play additional significant roles in directing the migration of multipotent cells, such as mesenchymal stem cells and hematopoietic progenitor cells. This article reviews the functions of these two chemokines, focusing on recruitment to sites of injury, immune function modulation, and contributions to embryonic development. Additional research would provide valuable insight into the potential clinical application of these two proteins in stem cell therapy.

CXCR7 participates in CXCL12-induced CD34+ cell cycling through β-arrestin-dependent Akt activation

In addition to its well-known effect on migration and homing of hematopoietic stem/progenitor cells (HSPCs), CXCL12 chemokine also exhibits a cell cycle and survival-promoting factor for human CD34(+) HSPCs. CXCR4 was suggested to be responsible for CXCL12-induced biological effects until the recent discovery of its second receptor, CXCR7. Until now, the participation of CXCR7 in CXCL12-induced HSPC cycling and survival is unknown. We show here that CXCL12 was capable of binding CXCR7 despite its scarce expression at CD34(+) cell surface. Blocking CXCR7 inhibited CXCL12-induced Akt activation as well as the percentage of CD34(+) cells in cycle, colony formation, and survival, demonstrating its participation in CXCL12-induced functional effects in HSPCs. At steady state, CXCR7 and β-arrestin2 co-localized near the plasma membrane of CD34(+) cells. After CXCL12 treatment, β-arrestin2 translocated to the nucleus, and this required both CXCR7 and CXCR4. Silencing β-arrestin expression decreased CXCL12-induced Akt activation in CD34(+) cells. Our results demonstrate for the first time the role of CXCR7, complementary to that played by CXCR4, in the control of HSPC cycling, survival, and colony formation induced by CXCL12. We also provide evidence for the involvement of β-arrestins as signaling hubs downstream of both CXCL12 receptors in primary human HSPCs.

Proteomic analysis of murine bone marrow niche microenvironment identifies thioredoxin as a novel agent for radioprotection and for enhancing donor cell reconstitution

Hematopoiesis is regulated by the bone marrow (BM) niche microenvironment. We recently found that posttransplant administration of AMD3100 (a specific and reversible CXCR4 antagonist) enhanced donor cell engraftment and promoted recovery of all donor cell lineages in a congeneic mouse transplant model. We hypothesized that AMD3100 enhances donor cell reconstitution in part by modulating the levels and constitution of soluble factors in the niche microenvironment. In the current study, the effects of the BM extracellular fluid (supernatant) from AMD3100-treated transplant recipient mice on colony-forming units (CFUs) were examined. A semiquantitative, mass spectrometry-based proteomics approach was used to screen for differentially expressed proteins between the BM supernatants of PBS-treated transplant mice and AMD3100-treated transplant mice. A total of 178 proteins were identified in the BM supernatants. Thioredoxin was among the 32 proteins that displayed greater than a twofold increase in spectral counts in the BM supernatant of AMD3100-treated transplant mice. We found that thioredoxin increased CFUs in a dose-dependent manner. Thioredoxin improved hematopoiesis in irradiated mice and protected mice from radiation-related death. Furthermore, ex vivo exposure to thioredoxin for 24 hours enhanced the long-term repopulation of hematopoietic stem cells. Additionally, combined posttransplant administration of thioredoxin and AMD3100 improved hematologic recovery in primary and secondary transplant recipient mice. Our studies demonstrated that factors in the BM niche microenvironment play a critical role in hematopoiesis. Identifying these factors provides clues on potential novel targets that can be used to enhance hematologic recovery in hematopoietic stem cell transplan`tation.

Sequential administration of the high affinity CXCR4 antagonist BKT140 promotes megakaryopoiesis and platelet production

Platelets are the terminal differentiation product of megakaryocytes (MKs). Cytokines, such as thrombopoietin (TPO), are known to influence different steps in MK development; however, the complex differentiation and platelet localization processes are not fully understood. MKs express the receptor CXCR4 and have been shown to migrate in response to CXCL12 and to increase their platelet production. In this study, we studied the role of CXCR4 in platelet production with the high affinity CXCR4 antagonist, BKT140. Single and sequential administration of BKT140 significantly increased the number of MKs and haematopoietic progenitors (HPCs) within the bone marrow (BM). Increased megakaryopoiesis was associated with increased platelet production. Single and sequential administration of BKT140 also increased the number of HPCs in the blood. In a model of 5-fluorouracil-induced thrombocytopenia, BKT140 significantly reduced the severity and duration of thrombocytopenia and cytopenia when administered before and after chemotherapy. Our results demonstrated that the CXCR4 antagonist, BKT140, mediated unique beneficial effects by stimulating megakaryopoiesis and platelet production. These results provide evidence for the possible therapeutic use of BKT140 for modulating platelet numbers in thrombocytopenic conditions.

Chemokines and adult bone marrow stem cells

The adult bone contains a number of distinct populations of stem cells, including haematopoietic stem cells, mesenchymal stem cells, endothelial progenitor cells and fibrocytes. While haematopoietic stem cells are required to provide a lifelong supply of blood cells it is thought that the other populations of stem cells play a role in tissue regeneration and potentially disease. The chemokine CXCL12 is produced constitutively in the bone marrow and, acting via CXCR4, is critical in maintaining HSPCs in a quiescent state and retaining all subsets of stem and progenitor cells in the bone marrow environment. The cytokine G-CSF, used clinically to mobilize haematopoietic stem cells for bone marrow transplants, activates the sympathetic nervous system and bone marrow macrophages to reduce the expression of CXCL12 by bone marrow stromal cells, thereby promoting the exit of haematopoietic stem cells from the bone marrow. Understanding the molecular mechanisms underlying G-CSF stimulated mobilization has led to development of CXCR4 antagonists as fast acting mobilizing agents for haematopoietic stem cells. Evidence now suggests that CXCR4 antagonists can similarly mobilize distinct subsets of progenitor cells, namely the endothelial progenitor cells and mesenchymal stem cells, but this requires conditioning of the bone marrow with VEGF rather than G-CSF.

Homeostatic and tissue reparation defaults in mice carrying selective genetic invalidation of CXCL12/proteoglycan interactions

BACKGROUND

Interaction with heparan sulfate proteoglycans is supposed to provide chemokines with the capacity to immobilize on cell surface and extracellular matrix for accomplishing both tissue homing and signaling of attracted cells. However, the consequences of the exclusive invalidation of such interaction on the roles played by endogenous chemokines in vivo remain unascertained.

METHODS AND RESULTS

We engineered a mouse carrying a Cxcl12 gene (Cxcl12(Gagtm)) mutation that precludes interactions with heparan sulfate structures while not affecting CXCR4-dependent cell signaling of CXCL12 isoforms (α, β, γ). Cxcl12(Gagtm/Gagtm) mice develop normally, express normal levels of total and isoform-specific Cxcl12 mRNA, and show increased counting of circulating CD34(+) hematopoietic precursor cells. After induced acute ischemia, a marked impaired capacity to support revascularization was observed in Cxcl12(Gagtm/Gagtm) animals associated with a reduced number of infiltrating cells in the ischemic tissue despite the massive expression of CXCL12 isoforms. Importantly, exogenous administration of CXCL12γ, which binds heparan sulfate with the highest affinity ever reported for a cytokine, fully restores vascular growth, whereas heparan sulfate-binding CXCL12γ mutants failed to promote revascularization in Cxcl12(Gagtm/Gagtm) animals.

CONCLUSION

These findings prove the role played by heparan sulfate interactions in the functions of CXCL12 in both homeostasis and physiopathological settings and document for the first time the paradigm of chemokine immobilization in vivo.

SDF-1/CXCR4 signal is involved in decreased expression of p57kip2 in de novo MDS patients

p57kip2 is considered as a candidate tumor suppressor gene involvement in cell cycle control. In this study, we explored the expression of p57kip2 in various myelodysplastic syndrome (MDS) subsets by real-time quantitative PCR, as well as the relationship between p57kip2 and CXC receptor 4 (CXCR4). We also searched the role of stromal cell-derived factor-1 (SDF-1)/CXCR4 signal in p57kip2 expression in vitro. The expression of p57kip2 decreased in MDS cases (low grade MDS, P<0.001, n = 46; high grade MDS, P<0.001, n = 21), compared with that in control group. Patients with poor karyotype (according to IPSS) had lower p57kip2 than that in the normal group (P<0.05). p57kip2 expression increased after treatment with decitabine in the cases that had achieved response (P = 0.009, n = 7). Additionally, a positive correlation between p57kip2 and CXCR4 was investigated (r = 0.652, P<0.001, n = 67). p57kip2 expression in bone marrow mononuclear cells of normal controls increased significantly when co-cultured with SDF-1 in vitro, which could be blocked by AMD3100, whereas SDF-1 only induced a mild increase in p57kip2 in MDS. In conclusion, low expression of p57kip2 is common in MDS, which may play an important role in MDS pathogenesis. Reduced response to SDF-1 contributed to low expression of p57kip2 in MDS cases.

Altered microenvironmental regulation of leukemic and normal stem cells in chronic myelogenous leukemia

We characterized leukemia stem cells (LSC) in chronic phase chronic myelogenous leukemia (CML) using a transgenic mouse model. LSC were restricted to cells with long-term hematopoietic stem cell (LTHSC) phenotype. CML LTHSC demonstrated reduced homing and retention in the bone marrow (BM), related to decreased CXCL12 expression in CML BM, resulting from increased G-CSF production by leukemia cells. Altered cytokine expression in CML BM was associated with selective impairment of normal LTHSC growth and a growth advantage to CML LTHSC. Imatinib (IM) treatment partially corrected abnormalities in cytokine levels and LTHSC growth. These results were validated using human CML samples and provide improved understanding of microenvironmental regulation of normal and leukemic LTHSC and their response to IM in CML.

Cellular therapies supplement: strategies for improving transplant efficiency in the context of cellular therapeutics

The field of hematopoietic stem cell transplantation (HSCT) has overcome many obstacles that have led to our current clinical ability to utilize cells collected from marrow, mobilized peripheral blood, or umbilical cord blood for the treatment of malignant and nonmalignant hematologic diseases. It is in this context that it becomes evident that future progress will lie in our development of an understanding of the biology by which the process of HSCT is regulated. By understanding the cellular components and the mechanisms by which HSCT is either enhanced or suppressed it will then be possible to design therapeutic strategies to improve rates of engraftment that will have a positive impact on immune reconstitution post-HSCT. In this review we focus primarily on allogeneic hematopoietic stem cell transplantation (allo-HSCT), the current challenges associated with allo-HSCT, and some developing strategies to improve engraftment in this setting.

Differential effects of CXCR4 antagonists on the survival and proliferation of myeloid leukemia cells in vitro

Background

Antagonists of CXC chemokine receptor 4 (CXCR4), including AMD3100, induce peripheral mobilization of hematopoietic stem cells and have been approved for clinical use. We explored whether the CXCR4 antagonists affected the survival and proliferation of myeloid leukemia cells in vitro.

Methods

The effects of CXCR4 antagonists AMD3100 and T140 on the survival and proliferation of myeloid leukemia cell lines (U937, HL-60, MO7e, KG1a, and K562) as well as CD34⁺ cells obtained from patients with AML and CML were analyzed by flow cytometry by using annexin V and a colorimetric cell proliferation assay.

Results

AMD3100, but not T140, stimulated the proliferation of leukemia cells in vitro in a dose-dependent manner for up to 5 days (~2-fold increase at a concentration of 10^-5 M), which was not abrogated by pretreatment of the cells with pertussis toxin, but was attenuated by RNAi knockdown of CXCR7 transcripts. In contrast, AMD3100 induced a marked decrease in the cell numbers after 5-7 days. AMD3100, but not T140, induced phosphorylation of MAPK p44/p42. AMD3100 increased the number and size of leukemia cell colonies and reduced cell apoptosis during the first 5-7 days of incubation, but the phenomena were reversed during the later period of incubation.

Conclusion

The effects of CXCR4 antagonists on the proliferation of myeloid leukemia cells are not uniform. AMD3100, but not T140, exerts dual effects, initially enhancing and subsequently inhibiting the survival and proliferation of the cells in vitro.

Niche competition and cancer metastasis to bone

The molecular basis for the preferential metastases of certain cancers to bone is not well understood. In this issue of the JCI, Shiozawa et al. provide compelling evidence that prostate cancer cells preferentially home to the osteoblastic niche in the bone marrow, where they compete with normal HSCs for niche support. Because signals from the niche may regulate tumor quiescence and sensitivity to chemotherapy, these observations have important implications for the treatment of metastatic prostate cancer in bone.

Stromal-derived factor-1/CXCR4 signaling: indispensable role in homing and engraftment of hematopoietic stem cells in bone marrow

Homing and engraftment of hematopoietic stem/progenitor cells (HSPCs) in bone marrow is the major determining factor in success of hematopoietic stem cell transplantation. This is a complex, multistep process orchestrated by the coordinated interplay between adhesion molecules, cytokines, growth factors, and regulatory cofactors, many of which remain to be defined. Recent studies have highlighted the pivotal role of unique stromal-derived factor-1 (SDF-1)/CXCR4 signaling in the regulation of HSPC homing and subsequent engraftment. In addition, studies suggest that SDF-1/CXCR4 signaling acts as an essential survival-promoting factor of transplanted HSPCs as well as maintenance of quiescent HSCs in bone marrow niche. These pleiotropic effects exerted by SDF-1/CXCR4 axis make this unique signaling initiator very promising, not only for optimal hematopoietic reconstitution but also for the development of innovative approaches to achieve restoration, regeneration, or repair of other damaged tissues potentially amendable to reversal by stem cell transplantation. This goal can only be achieved when the role of SDF-1/CXCR4 axis in hematopoietic transplantation is clearly defined. Hence, this review presents current knowledge of the mechanisms through which SDF-1/CXCR4 signaling promotes restoration of hematopoiesis by regulating the homing and engraftment of HSPCs.

Mechanisms of G-CSF-mediated hematopoietic stem and progenitor mobilization

Under normal conditions, the great majority of hematopoietic stem/progenitors cells (HSPCs) reside in the bone marrow. The number of HSPCs in the circulation can be markedly increased in response to a number of stimuli, including hematopoietic growth factors, myeloablative agents and environmental stresses such as infection. The ability to 'mobilize' HSPCs from the bone marrow to the blood has been exploited clinically to obtain HSPCs for stem cell transplantation and, more recently, to stimulate therapeutic angiogenesis at sites of tissue ischemia. Moreover, there is recent interest in the use of mobilizing agents to sensitize leukemia and other hematopoietic malignancies to cytotoxic agents. Key to optimizing clinical mobilizing regimens is an understanding of the fundamental mechanisms of HSPC mobilization. In this review, we discuss recent advances in our understanding of the mechanisms by which granulocyte colony-stimulating factor (G-CSF), the prototypical mobilizing agent, induces HSPC mobilization.

Inhibition of class II phosphoinositide 3-kinase gamma expression by p185(Bcr-Abl) contributes to impaired chemotaxis and aberrant homing of leukemic cells

The expression of p185(Bcr-Abl) in Ba/F3 cells inhibits the chemotactic response of these cells to SDF1alpha. A mutant p185(Bcr-Abl) with deletion of amino acids from 176 to 426 (p185(Delta176-426)) is deficient in suppressing SDF1alpha-stimulated chemotaxis. Comparison of the gene expression profiles among parental Ba/F3 cells and cells transformed by p185(Bcr-Abl) and p185(Delta176-426) reveals that class II phosphoinositide 3-kinase gamma (PI3KC2gamma) expression is markedly down-regulated by p185(Bcr-Abl) but not p185(Delta176-426). Furthermore, knockdown of PI3KC2gamma expression in p185(Delta176-426) cells is sufficient to suppress SDF1alpha-stimulated chemotaxis and to promote infiltration of these cells into the liver. Together, these studies suggest that inhibition of PI3KC2gamma expression may represent a mechanism by which Bcr-Abl suppresses SDF1alpha-induced chemotaxis and induces abnormal homing of leukemic cells.

Insights into the stem cells of chronic myeloid leukemia

Chronic myeloid leukemia (CML) has long served as a paradigm for generating new insights into the cellular origin, pathogenesis and improved approaches to treating many types of human cancer. Early studies of the cellular phenotypes and genotypes represented in leukemic populations obtained from CML patients established the concept of an evolving clonal disorder originating in and initially sustained by a rare, multipotent, self-maintaining hematopoietic stem cell (HSC). More recent investigations continue to support this model, while also revealing new insights into the cellular and molecular mechanisms that explain how knowledge of CML stem cells and their early differentiating progeny can predict the differing and variable features of chronic phase and blast crisis. In particular, these emphasize the need for new agents that effectively and specifically target CML stem cells to produce non-toxic, but curative therapies that do not require lifelong treatments.

A major role of TGF-β1 in the homing capacities of murine hematopoietic stem cell/progenitors

Transforming growth factor-β1 (TGF-β1) is a pleiotropic cytokine with major in vitro effects on hematopoietic stem cells (HSCs) and lymphocyte development. Little is known about hematopoiesis from mice with constitutive TGF-β1 inactivation largely because of important embryonic lethality and development of a lethal inflammatory disorder in TGF-β1−/− pups, making these studies difficult. Here, we show that no sign of the inflammatory disorder was detectable in 8- to 10-day-old TGF-β1−/− neonates as judged by both the number of T-activated and T-regulator cells in secondary lymphoid organs and the level of inflammatory cytokines in sera. After T-cell depletion, the inflammatory disease was not transplantable in recipient mice. Bone marrow cells from 8- to 10-day-old TGF-β1−/− neonates showed strikingly impaired short- and long-term reconstitutive activity associated with a parallel decreased in vivo homing capacity of lineage negative (Lin−) cells. In addition an in vitro–reduced survival of immature progenitors (Lin− Kit+ Sca+) was observed. Similar defects were found in liver cells from TGF-β1−/− embryos on day 14 after vaginal plug. These data indicate that TGF-β1 is a critical regulator for in vivo homeostasis of the HSCs, especially for their homing potential.

Selective enhancement of donor hematopoietic cell engraftment by the CXCR4 antagonist AMD3100 in a mouse transplantation model

The interaction between stromal cell-derived factor-1 (SDF-1) with CXCR4 chemokine receptors plays an important role in hematopoiesis following hematopoietic stem cell transplantation. We examined the efficacy of post transplant administration of a specific CXCR4 antagonist (AMD3100) in improving animal survival and in enhancing donor hematopoietic cell engraftment using a congeneic mouse transplantation model. AMD3100 was administered subcutaneously at 5 mg/kg body weight 3 times a week beginning at day +2 post-transplant. Post-transplant administration of AMD3100 significantly improves animal survival. AMD3100 reduces pro-inflammatory cytokine/chemokine production. Furthermore, post transplant administration of AMD3100 selectively enhances donor cell engraftment and promotes recovery of all donor cell lineages (myeloid cells, T and B lymphocytes, erythrocytes and platelets). This enhancement results from a combined effect of increased marrow niche availability and greater cell division induced by AMD3100. Our studies shed new lights into the biological roles of SDF-1/CXCR4 interaction in hematopoietic stem cell engraftment following transplantation and in transplant-related mortality. Our results indicate that AMD3100 provides a novel approach for enhancing hematological recovery following transplantation, and will likely benefit patients undergoing transplantation.

Disruption of neuronal CXCR4 function by opioids: preliminary evidence of ferritin heavy chain as a potential etiological agent in neuroAIDS

The chemokine CXCL12 and its receptor, CXCR4, regulate neuronal migration, differentiation, and survival. Alterations of CXCL12/CXCR4 signaling are implicated in different neuropathologies, including the neurological complications of HIV infection. Opiates are important co-factors for progression to neuroAIDS and can disrupt the CXCL12/CXCR4 axis in vitro and in vivo. This paper will review recently identified mechanisms of opiate-induced CXCR4 impairment in neurons and introduce results from pilot studies in human brain tissue, which highlight the role of the protein ferritin heavy chain in HIV neuropathology in patients with history of drug abuse.

Cotransplantation with MSCs improves engraftment of HSCs after autologous intra-bone marrow transplantation in nonhuman primates

OBJECTIVE

Hematopoietic stem cells (HSCs) reside in the osteoblastic niche, which consists of osteoblasts. Mesenchymal stromal cells (MSCs) have an ability to differentiate into osteoblasts. Here, using nonhuman primates, we investigated the effects of cotransplantation with MSCs on the engraftment of HSCs after autologous intra-bone marrow transplantation.

MATERIALS AND METHODS

From three cynomolgus monkeys, CD34-positive cells (as HSCs) and MSCs were obtained. The former were divided into two equal aliquots and each aliquot was genetically marked with a distinctive retroviral vector to track the in vivo fate. Each HSC aliquot with or without MSCs was autologously injected into the bone marrow (BM) cavity of right or left side, enabling the comparison of in vivo fates of the two HSC grafts in the same body.

RESULTS

In the three monkeys, CD34(+) cells transplanted with MSCs engrafted 4.4, 6.0, and 1.6 times more efficiently than CD34(+) cells alone, as assessed by BM colony polymerase chain reaction. In addition, virtually all marked cells detected in the peripheral blood were derived from the cotransplantation aliquots. Notably, colony-forming units derived from the cotransplantation aliquots were frequently detected in BM distant sites from the injection site, implying that cotransplantation with MSCs also restored the ability of gene-marked HSCs to migrate and achieve homing in the distant BM.

CONCLUSION

Cotransplantation with MSCs would improve the efficacy of transplantation of gene-modified HSCs in primates, with enhanced engraftment in BM as well as increased chimerism in peripheral blood through migration and homing.

The hematopoietic stem cell in chronic phase CML is characterized by a transcriptional profile resembling normal myeloid progenitor cells and reflecting loss of quiescence

We found that composition of cell subsets within the CD34+ cell population is markedly altered in chronic phase (CP) chronic myeloid leukemia (CML). Specifically, proportions and absolute cell counts of common myeloid progenitors (CMP) and megakaryocyte-erythrocyte progenitors (MEP) are significantly greater in comparison to normal bone marrow whereas absolute numbers of hematopoietic stem cells (HSC) are equal. To understand the basis for this, we performed gene expression profiling (Affymetrix HU-133A 2.0) of the distinct CD34+ cell subsets from six patients with CP CML and five healthy donors. Euclidean distance analysis revealed a remarkable transcriptional similarity between the CML patients' HSC and normal progenitors, especially CMP. CP CML HSC were transcriptionally more similar to their progeny than normal HSC to theirs, suggesting a more mature phenotype. Hence, the greatest differences between CP CML patients and normal donors were apparent in HSC including downregulation of genes encoding adhesion molecules, transcription factors, regulators of stem-cell fate and inhibitors of cell proliferation in CP CML. Impaired adhesive and migratory capacities were functionally corroborated by fibronectin detachment analysis and transwell assays, respectively. Based on our findings we propose a loss of quiescence of the CML HSC on detachment from the niche leading to expansion of myeloid progenitors.

Ex vivo expansion of hematopoietic progenitor cells is associated with downregulation of alpha4 integrin- and CXCR4-mediated engraftment in NOD/SCID beta2-microglobulin-null mice

BACKGROUND

Several studies indicate that ex vivo cytokine-supported expansion induces defective hematopoietic stem cell engraftment. We investigated the role of alpha4 integrin, alpha5 integrin and CXCR4 in engraftment of unmanipulated and cytokine-treated human cord blood CD34(+) cells.

DESIGN AND METHODS

Uncultured or expanded CD34(+) cells were infused in NOD/SCID-beta(2)microglobulin-null mice. The function of alpha4, and alpha5 integrins and CXCR4 was assessed by incubating cells with specific neutralizing antibodies, prior to transplant. The activation state of alpha4 integrin was further tested by adhesion and migration assays.

RESULTS

Neutralization of either alpha4 integrin or CXCR4 abolished engraftment of uncultured CD34(+) cells at 6 week spost-transplant, while alpha5 integrin neutralization had no significant effect. However, after short-term ex vivo culture, blocking alpha4 integrin or CXCR4 did not affect repopulating activity whereas neutralization of alpha5 integrin inhibited engraftment. Using soluble vascular cell adhesion molecule-1 binding assays, we observed that alpha4 integrin affinity in fresh CD34(+) cells was low and susceptible to stimulation while in cultured CD34(+) cells, it was high and insensitive to further activation. In addition, stromal cell-derived factor-1 stimulated migration across vascular cell adhesion molecule-1 in fresh CD34(+) cells but not in cultured CD34(+) cells.

CONCLUSIONS

Our data show that ex vivo culture of hematopoietic progenitor cells is associated with downregulation of both alpha4 integrin- and CXCR4-mediated engraftment. Further investigations suggest that this is caused by supraphysiological increase of alpha4 integrin affinity, which impairs directional migration across vascular cell adhesion molecule-1 in response to stromal cell-derived factor-1. Such changes may underlie the engraftment defect of cytokine-stimulated CD34(+) cells.

Chemokine receptor CXCR4 as a therapeutic target for neuroectodermal tumors

Chemokines (chemotactic cytokines) are a family of proteins associated with the trafficking and activation of leukocytes and other cell types in immune surveillance and inflammatory response. Besides their roles in the immune system, they play pleiotropic roles in tumor initiation, promotion, and progression. Chemokines can be classified into four subfamilies of chemokines, CXC, CC, C, or CX3C, based on their number and spacing of conserved cysteine residues near the N-terminus. This CXC subfamily can be further subclassified into two groups, depending on the presence or absence of a tripeptide motif glutamic acid-leucine-arginine (ELR) in the N-terminal domain. ELR(-)CXCL12, which binds to CXCR4 has been frequently implicated in various cancers. Over the past several years, studies have increasingly shown that the CXCR4/CXCL12 axis plays critical roles in tumor progression, such as invasion, angiogenesis, survival, homing to metastatic sites. This review focuses on involvement of CXCR4/CXCL12 interaction in neuroectodermal cancers and their therapeutic potentials. As an attractive therapeutic target of CXCR4/CXCL12 axis for cancer chemotherapy, development history and application of CXCR4 antagonists are described.

The critical role of SDF-1/CXCR4 axis in cancer and cancer stem cells metastasis

Chemokines exert their multifunctional role in several physiologic and pathologic processes through interaction with their specific receptors. Much evidence have revealed that metastatic spread tumor cells may use chemokine-mediated mechanisms. In particular, an involvement of stromal cell-derived factor-1 (SDF-1) in growth of primary tumors and in metastatic process has been demonstrated. Indeed, it has been suggested that CXCR4 expression by tumor cells, plays a critical role in cell metastasis by a chemotactic gradient to organs expressing the ligand SDF-1. Moreover, CXCR4 overexpression correlated with poor prognosis in many types of cancer. In physiologic condition, SDF-1 also plays an essential role modulating stem cell proliferation, survival, and homing through its canonical receptor CXCR4. Recently, several studies have demonstrated the existence of a small subset of cancer cells which share many characteristics with stem cells and named cancer stem cells (CSC). They constitute a reservoir of self-sustaining cells with the ability to maintain the tumor growth. In particular, most of them express CXCR4 receptor and respond to a chemotactic gradient of its specific ligand SDF-1, suggesting that CSC probably represent a subpopulation capable of initiating metastasis. This review focuses on the role of SDF-1/CXCR4 axis in cancer and in the metastatic progression by tumoral cells, as well as the role of CSC in tumor pathogenesis and in metastatic process. A better understanding of migratory mechanism involving cancer cells and CSC provides a powerful tool for developing novel therapies reducing both local and distant recurrences.

Humanizing bone marrow in immune-deficient mice

Humanized mice are useful for studying human hematopoietic stem cells (HSCs) and their niche. In particular, clonal study of human HSC enables precise comparison of in vivo behavior between murine and human HSCs. A single HSC is able to reconstitute hematopoiesis even after serial transplantations in mice. While the life span of somatic cells is over that of individual in mice, this is not the case in humans. Clonal studies of human HSCs clearly demonstrated their aging in hosts. Since murine studies have demonstrated that HSCs are protected from aging by their niche in bone marrow, the humanizing niche model will reveal the precise mechanism by which human HSCs are protected from exhaustion in vivo. Direct transplantation of human mesenchymal stem cells into mouse bone marrow results in reconstitution of the functional human hematopoietic microenvironment comprised of pericytes, myofibroblasts, reticular cells, osteocytes in bone, bone-lining osteoblasts, and endothelial cells. These humanized mouse models are essential for testing whether the insights on hematopoiesis from mouse studies are applicable to humans before clinical application.

CD26 inhibition on CD34+ or lineage- human umbilical cord blood donor hematopoietic stem cells/hematopoietic progenitor cells improves long-term engraftment into NOD/SCID/Beta2null immunodeficient mice

Given the tremendous need for and potential of umbilical cord blood (CB) to be utilized as a donor source for hematopoietic stem cell (HSC) transplantation in adults, there is a strong push to overcome the constraints created by the limited volumes and subsequent limited HSC and hematopoietic progenitor cell (HPC) numbers available for HSC transplantation from a single collection. We have previously described the use of CD26 inhibitor treatment of donor cells as a method to increase the transplant efficiency of mouse HSCs and HPCs into a mouse recipient. To study the use of CD26 inhibitors as a method of improving the transplantation of human CB HSCs and HPCs, we utilized the nonobese diabetic/severe combined immunodeficient/beta 2 microglobulin null (NOD/SCID/B2m(null)) immunodeficient mouse model of HSC transplantation. We report here significant improvements in the engraftment of long-term repopulating cells following the treatment of either CD34(+) or lineage negative (lin()) donor CB with the CD26 inhibitor, Diprotin A, prior to transplant. These results establish a basis on which to propose the use of CD26 inhibitor treatment of donor CB units prior to transplantation for the purpose of improving transplant efficiency and subsequently patient outcome.

The central role of the chemokine receptor, CXCR4, in haemopoietic stem cell transplantation: will CXCR4 antagonists contribute to the treatment of blood disorders?

Recent clinical trials have used CXCR4 antagonists for the rapid mobilization of CD34(+) haemopoietic stem/progenitor cells (HSC/HPC) from the bone marrow to the blood in patients refractory to granulocyte-colony-stimulating factor (G-CSF). These antagonists not only mobilize non-cycling cells with a higher proportion of repopulating cells, but also enhance CD34(+) cell mobilization when used in combination with G-CSF. Here, we review the importance of CXCR4 and its ligand CXCL12 in haemopoiesis, and the potential roles of CXCR4 antagonists in the clinical HSC transplant setting.

The challenges of targeting chronic myeloid leukemia stem cells

Chronic myeloid leukemia (CML) is sustained by a clonally amplified population of Bcr Abl-positive pluripotent stem cells. Persistence of a large, functionally intact yet suppressed residual normal hematopoietic stem cell population in most patients with CML has made it possible to aim at the development of curative therapies. However, achieving this goal requires the identification of agents that will eradicate the leukemic stem cell population. Several potent Bcr-Abl-targeted drugs have now been introduced into clinical practice with remarkable effects. Nevertheless, accumulating data indicate that the leukemic CML stem cells in patients with chronic phase CML are less responsive to these agents than the bulk of the neoplastic cells. In this article, we review emerging evidence that CML stem cells have a number of unusual properties that underlie their relative insensitivity to treatment, including those that specifically target the Bcr-Abl oncoprotein. The biology of the neoplastic stem cells in patients with CML is clearly important to the future attainment of cures and might also prove a paradigm relevant to other types of malignancies that are sustained by transformed stem cell populations.

CXCR4 antagonists mobilize childhood acute lymphoblastic leukemia cells into the peripheral blood and inhibit engraftment

The role of CXCL12 in the bone marrow (BM) homing and growth of B-cell progenitor acute lymphoblastic leukemia (ALL) has been established. However, the effect of modulating CXCL12/CXCR4 interactions on the retention of ALL cells within the supportive BM microenvironment and the expansion and dissemination of ALL cells in vivo has not been examined. We used mouse models of human childhood and murine leukemia and specific peptide and small molecule CXCR4 antagonists to examine the importance of CXCL12/CXCR4 in the development of leukemia in vivo. CXCR4 antagonists mobilized ALL cells into the peripheral blood (PB). Extended administration of CXCR4 antagonists to mice with leukemia resulted in a reduction in the number of leukemic cells in the PB and spleens of animals compared to control treated animals in three of the five cases tested. There was also a marked reduction in the dissemination of ALL cells to extramedullary sites including liver and kidney in all cases where this occurred. Considering the inhibitory effect of stromal layers on the activity of chemotherapeutic agents and the interactive effect of CXCL12 antagonists with chemotherapeutic agents in vitro, this raises the possibility of using these agents to potentiate the effects of current chemotherapy regimens.

Differential requirements for hematopoietic commitment between human and rhesus embryonic stem cells

Progress toward clinical application of ESC-derived hematopoietic cellular transplantation will require rigorous evaluation in a large animal allogeneic model. However, in contrast to human ESCs (hESCs), efforts to induce conclusive hematopoietic differentiation from rhesus macaque ESCs (rESCs) have been unsuccessful. Characterizing these poorly understood functional differences will facilitate progress in this area and likely clarify the critical steps involved in the hematopoietic differentiation of ESCs. To accomplish this goal, we compared the hematopoietic differentiation of hESCs with that of rESCs in both EB culture and stroma coculture. Initially, undifferentiated rESCs and hESCs were adapted to growth on Matrigel without a change in their phenotype or karyotype. Subsequent differentiation of rESCs in OP9 stroma led to the development of CD34(+)CD45(-) cells that gave rise to endothelial cell networks in methylcellulose culture. In the same conditions, hESCs exhibited convincing hematopoietic differentiation. In cytokine-supplemented EB culture, rESCs demonstrated improved hematopoietic differentiation with higher levels of CD34(+) and detectable levels of CD45(+) cells. However, these levels remained dramatically lower than those for hESCs in identical culture conditions. Subsequent plating of cytokine-supplemented rhesus EBs in methylcellulose culture led to the formation of mixed colonies of erythroid, myeloid, and endothelial cells, confirming the existence of bipotential hematoendothelial progenitors in the cytokine-supplemented EB cultures. Evaluation of four different rESC lines confirmed the validity of these disparities. Although rESCs have the potential for hematopoietic differentiation, they exhibit a pause at the hemangioblast stage of hematopoietic development in culture conditions developed for hESCs.