Clinical use of AMD3100 to mobilize CD34+ cells in patients affected by non-Hodgkin's lymphoma or multiple myeloma

Role and Therapeutic Targeting of SDF-1α/CXCR4 Axis in Multiple Myeloma

Simple Summary

The SDF-1α/CXCR4 axis plays crucial roles in proliferation, survival, invasion, dissemination, and drug resistance in multiple myeloma. This review summarizes the pleiotropic role of the SDF-1α/CXCR4 axis in multiple myeloma and introduces the SDF-1α/CXCR4 axis-targeted therapies in multiple myeloma.

Abstract

The C-X-C chemokine receptor type 4 (CXCR4) is a pleiotropic chemokine receptor that is expressed in not only normal hematopoietic cells but also multiple myeloma cells. Its ligand, stromal cell-derived factor 1α (SDF-1α) is produced in the bone marrow microenvironment. The SDF-1α/CXCR4 axis plays a pivotal role in the major physiological processes associated with tumor proliferation, survival, invasion, dissemination, and drug resistance in myeloma cells. This review summarizes the pleiotropic role of the SDF-1α/CXCR4 axis in multiple myeloma and discusses the future perspective in the SDF-1α/CXCR4 axis-targeted therapies in multiple myeloma.

Parameters affecting successful stem cell collections for genetic therapies in sickle cell disease

Emerging cellular therapies require the collection of peripheral blood hematopoietic stem cells (HSC) by apheresis for in vitro manipulation to accomplish gene addition or gene editing. These therapies require relatively large numbers of HSCs within a short time frame to generate an efficacious therapeutic product. This review focuses on the principal factors that affect collection outcomes, especially relevant to gene therapy for sickle cell disease.

A Pilot, Exploratory, Randomized, Phase II Safety Study Evaluating Tumor Cell Mobilization and Apheresis Product Contamination in Patients Treated with Granulocyte Colony-Stimulating Factor Alone or Plus Plerixafor

Because of the potential risk of tumor cell mobilization with granulocyte colony-stimulating factor (G-CSF), it is crucial to evaluate any potential effect of plerixafor treatment in the presence of G-CSF on multiple myeloma (MM) cell mobilization. This was an open-label, multicenter, randomized, exploratory, safety study (NCT01753453) that investigated the extent of MM cell mobilization after treatment with G-CSF + plerixafor in patients who were deemed poor mobilizers of hematopoietic stem cells. The primary efficacy outcome was the number of MM cells in peripheral blood and apheresis product after G-CSF + plerixafor treatment versus G-CSF alone. Key secondary efficacy outcomes included overall survival and disease status up to 2 years after the first G-CSF dose. Twenty patients were randomized and received at least 1 dose of study treatment. There were no patients with MM cells in peripheral blood up to day 8 G-CSF administration in either treatment group. Up to day 8 no patient in the G-CSF + plerixafor arm and only 1 patient in the G-CSF arm mobilized at least 4.5 × 10⁵ MM cells in the apheresis product. Nine of 10 patients from each treatment arm proceeded to transplantation. MM cells were detected in 5 patients from each treatment arm before and after transplantation. Adverse events observed in the G-CSF + plerixafor arm were consistent with the known safety profile of plerixafor. No MM cells were detected in peripheral blood of either treatment group up to day 8 of mobilization. Only 1 patient in the G-CSF alone group mobilized at least 4.5 × 10⁵ MM tumor cells in apheresis product up to day 8. However, 50% of patients in both treatment arms had detectable amounts of MM cells in their peripheral blood pre- and post-transplantation. There were no new safety concerns with plerixafor.

ROS-Induced CXCR4 Signaling Regulates Mantle Cell Lymphoma (MCL) Cell Survival and Drug Resistance in the Bone Marrow Microenvironment via Autophagy

PURPOSE

Patients with advanced stages of mantle cell lymphoma (MCL) have a poor prognosis after standard therapies. MCL cells in those patients often spread into tissues other than lymph nodes, such as the bone marrow. Apart from directed migration and homing, there is little understanding of the function of the CXCR4/SDF-1 signaling axis in MCL. In this report, we aim to understand mechanisms of MCL cell survival in the bone marrow.

EXPERIMENTAL DESIGN

For comprehensive analyses of MCL interactions with bone marrow stromal cells, we have generated gene knockout cells using CRISPR-CAS9 system and gene knockdown cells to reveal novel roles of the CXCR4/SDF-1 signaling.

RESULTS

CXCR4 silencing in MCL cells led to a significant reduction in proliferation, cell adhesion to bone marrow stromal cells, and colony formation in PHA-LCM methylcellulose medium, which were reversed upon the addition of SDF-1-neutralizing antibodies. In addition, tracking MCL cell engraftment in vivo revealed that quiescent MCL cells are significantly reduced in the bone marrow upon CXCR4 silencing, indicating that CXCR4/SDF-1 signaling is required for the survival and maintenance of the quiescent MCL cells. Further analysis revealed novel mechanisms of ROS-induced CXCR4/SDF-1 signaling that stimulate autophagy formation in MCL cells for their survival.

CONCLUSIONS

Our data, for the first time, revealed new roles of the CXCR/SDF-1 signaling axis on autophagy formation in MCL, which further promoted their survival within the bone marrow microenvironment. Targeting the CXCR4/SDF-1/autophagy signaling axis may contribute to an enhanced efficacy of current therapies.

Plerixafor plus pegfilgrastim is a safe, effective mobilization regimen for poor or adequate mobilizers of hematopoietic stem and progenitor cells: a phase I clinical trial

The safety, kinetics and efficacy of plerixafor+pegfilgrastim for hematopoietic stem and progenitor cell (HSPC) mobilization are poorly understood. We treated 12 study patients (SP; lymphoma n=10 or myeloma n=2) with pegfilgrastim (6 mg SC stat D1) and plerixafor (0.24 mg/kg SC nocte from D3). Six SP were 'predicted poor-mobilizers' and six were 'predicted adequate-mobilizers'. Peripheral blood (PB) CD34(+) monitoring commenced on D3. Apheresis commenced on D4. Comparison was with 22 historical controls (HC; lymphoma n=18, myeloma n=4; poor mobilizers n=4), mobilized with pegfilgrastim alone. Eight (67%) SP had PB CD34(+) count ⩽5 × 10(6)/L D3 post pegfilgrastim; all SP surpassed this threshold the morning after plerixafor. In SP, PBCD34(+) counts peaked D4 6/12 (50%), remaining ⩾5 × 10(6)/L for 4 days in 8/12 (67%). All SP successfully yielded target cell numbers (⩾2 × 10(6)/kg) within four aphereses. After maximum four aphereses, median total CD34+ yield was higher in SP than HC; 8.0 (range 2.4-12.9) vs 4.8 (0.4-14.0) × 10(6)/kg (P=0.04). Seven of twelve (58%) SP achieved target yield after one apheresis. Flow cytometry revealed no tumor cells in PB or apheresis product of SP. Plerixafor+pegfilgrastim was well tolerated with bone pain (n=2), diarrhoea (n=2) and facial paraesthesiae (n=3). Plerixafor+pegfilgrastim is a simple, safe and effective HSPC mobilization regimen in myeloma and lymphoma, in both poor and good mobilizers, and is superior to pegfilgrastim alone.

Hematopoietic, CNS and skeletal muscle stem cells as drug targets: opportunities, progress and challenges

Lineage-committed stem and progenitor cells are currently targeted by a handful of medicines, mainly to treat conditions involving the immune and hematopoietic systems. Knowledge of new stem and progenitor cell populations in the body is accumulating at a rapid pace and a new era of targeting resident stem cell populations for therapeutic ends is coming into focus. Small-molecule regulators of body-resident stem and progenitor cell assess are now a reality both in the clinic and as promising new drugs in the development pipeline. This review will explore the current state of the art with an emphasis on emerging concepts and experimental systems in the therapeutic regulation of endogenous stem and progenitor cell populations.

The effective use of plerixafor as a real-time rescue strategy for patients poorly mobilizing autologous CD34(+) cells

Plerixafor enhances CD34(+) cell mobilization, however, its optimal use is unknown. We hypothesized that plerixafor could "rescue" patients in the midst of mobilization when factors indicated a poor CD34(+) yield. Of 295 consecutive autologous peripheral blood mobilization attempts at our center, 39 (13%) used plerixafor as rescue strategy due to a CD34(+) cell concentration <10/μl (median 5.95/μl, n = 30), low CD34(+) cell yield from prior apheresis day (median 1.06 × 10(6) CD34(+) cells/kg, n = 7), or other (n = 2). Patients received a median of one plerixafor dose (range: 1-4). Thirty-four (87%) collected =2 × 10 (6) CD34(+) cells/kg and 26 (67%) collected =4 × 10 (6) CD34(+) cells/kg. Median collections for lymphoma (n = 24) and myeloma (n = 15) patients were 4.1 × 10(6) and 8.3 × 10(6) CD34/kg, respectively. A single dose of plerixafor was associated with an increase in the mean peripheral blood CD34(+) concentration of 17.2 cells/μl (P < 0.001) and mean increased CD34(+) cell yield following a single apheresis of 5.11 × 10(6) /kg (P < 0.03). A real-time rescue use of plerixafor is feasible and may allow targeted use of this agent. J. Clin. Apheresis, 2012. © 2012 Wiley Periodicals, Inc.

Emerging strategies for targeting cell adhesion in multiple myeloma

Multiple myeloma (MM) is an incurable hematological cancer involving proliferation of abnormal plasma cells that infiltrate the bone marrow (BM) and secrete monoclonal antibodies. The disease is clinically characterized by bone lesions, anemia, hypercalcemia, and renal failure. MM is presently treated with conventional therapies like melphalan, doxorubicin, and prednisone; or novel therapies like thalidomide, lenalidomide, and bortezomib; or with procedures like autologous stem cell transplantation. Unfortunately, these therapies fail to eliminate the minimal residual disease that remains persistent within the confines of the BM of MM patients. Mounting evidence indicates that components of the BM-including extracellular matrix, cytokines, chemokines, and growth factors-provide a sanctuary for subpopulations of MM. This co-dependent development of the disease in the context of the BM not only ensures the survival and growth of the plasma cells but contributes to de novo drug resistance. In addition, by fostering homing, angiogenesis, and osteolysis, this crosstalk plays a critical role in the progression of the disease. Not surprisingly then, over the past decade, several strategies have been developed to disrupt this communication between the plasma cells and the BM components including antibodies, peptides, and inhibitors of signaling pathways. Ultimately, the goal is to use these therapies in combination with the existing antimyeloma agents in order to further reduce or abolish minimal residual disease and improve patient outcomes.

G-CSF supplementation with chemotherapy can promote revascularization and subsequent tumor regrowth: prevention by a CXCR4 antagonist

Recombinant granulocyte colony-stimulating factor (G-CSF) is used to accelerate recovery from chemotherapy-induced myelosuppression. G-CSF has been recently shown to stimulate angiogenesis mediated by several types of bone marrow-derived cell populations. To investigate whether G-CSF may alter tumor response to therapy, we studied Lewis lung and EMT/6 breast carcinomas in mice treated with paclitaxel (PTX) chemotherapy in combination with G-CSF. We compared the results obtained to mice treated with PTX and AMD3100, a small-molecule drug antagonist of CXCR4 which, like G-CSF, can be used to mobilize hematopoietic cells. We show that PTX combined with G-CSF treatment facilitates revascularization, leading to an improvement in blood perfusion in LLC tumors, and a decrease in hypoxia in EMT/6 tumors, thus enhancing tumor growth in comparison to PTX or PTX and AMD3100 therapies. We found that hemangiocytes but not Gr-1(+) CD11b(+) cells colonize EMT/6 tumors after treatment with PTX and G-CSF, but not PTX and AMD3100, and therefore may contribute to angiogenesis. However, increases in hemangiocyte colonization were not observed in LLC PTX and G-CSF-treated tumors, suggesting distinct mechanisms of tumor revascularization after G-CSF. Overall, our observations suggest that despite its known considerable clinical benefits, G-CSF might contribute to tumor revascularization by various mechanisms, and diminish the antitumor activity of chemotherapy, an effect that can be prevented by AMD3100.

Increased mobilization and yield of stem cells using plerixafor in combination with granulocyte-colony stimulating factor for the treatment of non-Hodgkin's lymphoma and multiple myeloma

Multiple myeloma and non-Hodgkin’s lymphoma remain the most common indications for high-dose chemotherapy and autologous peripheral blood stem cell rescue. While a CD34+ cell dose of 1 × 10⁶/kg is considered the minimum required for engraftment, higher CD34+ doses correlate with improved outcome. Numerous studies, however, support targeting a minimum CD34+ cell dose of 2.0 × 10⁶/kg, and an “optimal” dose of 4 to 6 × 10⁶/kg for a single transplant. Unfortunately, up to 40% of patients fail to mobilize an optimal CD34+ cell dose using myeloid growth factors alone. Plerixafor is a novel reversible inhibitor of CXCR4 that significantly increases the mobilization and collection of higher numbers of hematopoietic progenitor cells. Two randomized multi-center clinical trials in patients with non-Hodgkin’s lymphoma and multiple myeloma have demonstrated that the addition of plerixafor to granulocyte-colony stimulating factor increases the mobilization and yield of CD34+ cells in fewer apheresis days, which results in durable engraftment. This review summarizes the pharmacology and evidence for the clinical efficacy of plerixafor in mobilizing hematopoietic stem and progenitor cells, and discusses potential ways to utilize plerixafor in a cost-effective manner in patients with these diseases.

The CXCR4 Antagonist AMD3100 Has Dual Effects on Survival and Proliferation of Myeloma Cells In Vitro

Purpose

AMD3100, an antagonist of the CXCR4 chemokine receptor is soon to be used clinically for the peripheral mobilization of hematopoietic stem cells (HSCs) in patients with multiple myeloma. AMD3100 has been shown to activate a G protein coupled with CXCR4 and thus acts as a partial CXCR4 agonist in vitro. Thus, we explored whether AMD3100 affected the survival and proliferation of myeloma cells in vitro.

Materials and Methods

The effects of AMD3100 on survival and proliferation of two myeloma cell lines (RPMI8226 and U266) as well as CD138+ cells obtained from several patients with multiple myeloma were analyzed by flow cytometry using annexin V and a colorimetric cell proliferation assay (CCK-8 assay).

Results

AMD3100, but not T140, another CXCR4 antagonist, stimulated the proliferation of myeloma cell lines and CD138+ primary human myeloma cells (-2-fold increase) in a dose-dependent manner in serum-free culture for up to 5 days, which was inhibited by pretreating the cells with pertussis toxin. AMD3100 enhanced the proliferation of U266 cells induced by interleukin-6 and partially reversed AG490-mediated growth inhibition and apoptosis induced by serum deprivation in RPMI8226 cells. AMD3100 induced the phosphorylation of Akt and MAPK p44/p42 in U266 cells and MAPK p44/p42 in RPMI8226 cells. In contrast, AMD3100 markedly increased the cell apoptosis and reduced the number of RPMI8226 cells after 5 to 7 days of culture under serum-free conditions.

Conclusion

AMD3100 exerts dual effects, initially enhancing and subsequently inhibiting the survival and proliferation of myeloma cells, signaling via CXCR4 in vitro.

The Belgian 2010 consensus recommendations for the treatment of multiple myeloma

Since the introduction of novel therapeutic agents including thalidomide, lenalidomide and bortezomib, the prognosis of multiple myeloma (MM) has significantly improved. These agents have been incorporated into numerous treatment schedules for newly diagnosed as well as more advanced MM patients. Hence, the therapeutic options for MM have become more complex and subject to rapid changes. The multiple myeloma study group (MMSG) of the Belgian Hematological Society has established recommendations for the treatment of MM as based on an extensive review of the literature which is also summarized in this paper. The recommendations are the result of a consensus opinion between haematologists with experience in the field and representing most haematology centres in Belgium. Where applicable, reimbursement criteria are also taken into account. The consensus recommendations should be a reference for use by clinical haematologists in daily practice.

International myeloma working group (IMWG) consensus statement and guidelines regarding the current status of stem cell collection and high-dose therapy for multiple myeloma and the role of plerixafor (AMD 3100)

Multiple myeloma is the most common indication for high-dose chemotherapy with autologous stem cell support (ASCT) in North America today. Stem cell procurement for ASCT has most commonly been performed with stem cell mobilization using colony-stimulating factors with or without prior chemotherapy. The target CD34+ cell dose to be collected as well as the number of apheresis performed varies throughout the country, but a minimum of 2 million CD34+ cells/kg has been traditionally used for the support of one cycle of high-dose therapy. With the advent of plerixafor (AMD3100) (a novel stem cell mobilization agent), it is pertinent to review the current status of stem cell mobilization for myeloma as well as the role of autologous stem cell transplantation in this disease. On June 1, 2008, a panel of experts was convened by the International Myeloma Foundation to address issues regarding stem cell mobilization and autologous transplantation in myeloma in the context of new therapies. The panel was asked to discuss a variety of issues regarding stem cell collection and transplantation in myeloma especially with the arrival of plerixafor. Herein, is a summary of their deliberations and conclusions.

CXCR4 inhibitor AMD3100 disrupts the interaction of multiple myeloma cells with the bone marrow microenvironment and enhances their sensitivity to therapy

The interaction of multiple myeloma (MM) cells with their microenvironment in the bone marrow (BM) provides a protective environment and resistance to therapeutic agents. We hypothesized that disruption of the interaction of MM cells with their BM milieu would lead to their sensitization to therapeutic agents such as bortezomib, melphalan, doxorubicin, and dexamethasone. We report that the CXCR4 inhibitor AMD3100 induces disruption of the interaction of MM cells with the BM reflected by mobilization of MM cells into the circulation in vivo, with kinetics that differed from that of hematopoietic stem cells. AMD3100 enhanced sensitivity of MM cell to multiple therapeutic agents in vitro by disrupting adhesion of MM cells to bone marrow stromal cells (BMSCs). Moreover, AMD3100 increased mobilization of MM cells to the circulation in vivo, increased the ratio of apoptotic circulating MM cells, and enhanced the tumor reduction induced by bortezomib. Mechanistically, AMD3100 significantly inhibited Akt phosphorylation and enhanced poly(ADP-ribose) polymerase (PARP) cleavage as a result of bortezomib, in the presence of BMSCs in coculture. These experiments provide a proof of concept for the use of agents that disrupt interaction with the microenvironment for enhancement of efficacy of cytotoxic agents in cancer therapy.

CD34+ cell responsiveness to stromal cell-derived factor-1alpha underlies rate of engraftment after peripheral blood stem cell transplantation

BACKGROUND

Stromal cell-derived factor (SDF)-1, a chemokine produced in the bone marrow (BM), is essential for the homing of hematopoietic stem/progenitor cells (HSPCs) to the BM after transplantation. This study examines whether there is a correlation between the in vitro chemotaxis of CD34+ HSPC toward an SDF-1 gradient and in vivo hematopoietic engraftment.

STUDY DESIGN AND METHODS

Thirty-five patients underwent granulocyte-colony-stimulating factor HSPC collection and autologous transplant with a median dose of 7.7 (range, 3.9-41.5) x 10(6) CD34+ cells per kg body weight. The chemotactic index (CI) of CD34+ cells isolated from leukapheresis products collected from these patients was calculated as the ratio of the percentages of cells migrating toward an SDF-1 gradient to cells migrating to media alone. Expression of the SDF-1 receptor CXCR4 on CD34+ cells was measured by flow cytometry.

RESULTS

Spontaneous cell migration (range, 3.1 +/- 0.6 to 26.5 +/- 7.7%) and SDF-1-directed chemotaxis (11.1 +/- 0.7 to 54.9 +/- 8.3%) of CD34+ cells did not correlate with time to neutrophil engraftment, which occurred at a median of 10 days (range, 8-16 days). Nonparametric tests showed a negative correlation (r = -0.434) between CI and CD34+ cell dose such that neutrophil recovery occurred within the same period in patients transplanted with a lower dose of CD34+ cells but having a high CI as in those transplanted with a higher dose of CD34+ cells but having a low CI. Moreover, CI correlated (r = 0.8) with surface CXCR4 expression on CD34+ cells.

CONCLUSION

In patients transplanted with a relatively lower CD34+ cell dose who achieved fast engraftment, a higher responsiveness to SDF-1 and high CI could have compensated for the lower cell dose. However, to apply the CI as a prognostic factor of the rate of engraftment requires validation in a larger number of patients.

Peripheral blood stem cell mobilization: new regimens, new cells, where do we stand

PURPOSE OF REVIEW

Granulocyte colony-stimulating factor-mobilized peripheral blood stem cells are widely used to reconstitute hematopoiesis; however, preclinical and clinical studies show that improvements to this mobilization can be achieved. We discuss the development of new mobilizing regimens and evaluation of new findings on mobilized stem cell populations that may improve the utility and convenience of peripheral blood stem cell transplant.

RECENT FINDINGS

Chemokines and their receptors regulate leukocyte trafficking, and altering chemokine signaling pathways mobilizes stem cells. In recent trials, combination use of the chemokine (C-X-C motif) receptor 4 antagonist AMD3100 and granulocyte colony-stimulating factor mobilized more CD34 cells in fewer days than granulocyte colony-stimulating factor alone and allowed more patients to proceed to autotransplant. In preclinical studies the chemokine GRObeta synergizes with granulocyte colony-stimulating factor and when used alone or with granulocyte colony-stimulating factor mobilizes more primitive hematopoietic stem cells with less apoptosis, higher integrin activation, lower CD26 expression and enhanced marrow homing compared with granulocyte colony-stimulating factor. Hematopoietic stem cells mobilized by GRObeta or AMD3100 demonstrate superior engraftment and contribution to chimerism in primary and secondary transplant studies in mice, and peripheral blood stem cells mobilized by AMD3100 and granulocyte colony-stimulating factor in patients demonstrate enhanced engraftment capabilities in immunodeficient mice.

SUMMARY

Alternate regimens differentially mobilize stem cell populations with unique intrinsic properties with the potential to expand the utility of hematopoietic transplantation. Continued mechanistic evaluation will be critical to our understanding of mechanisms of mobilization and their use in regenerative medicine.

Renal repair: role of bone marrow stem cells

Acute kidney injury carries severe consequences and has limited treatment options. Bone marrow stem cells may offer the potential for treatment of acute kidney injury. The purpose of this review is twofold. The first purpose is to provide a concise overview of the biology of bone marrow stem cells, including hematopoietic stem cells and mesenchymal stem cells, for clinical nephrologists and renal researchers. The second purpose is to summarize published data regarding the role of bone marrow stem cells in renal repair after acute kidney injury. Currently, much of our knowledge of renal protective effect of bone marrow stem cells is obtained through animal research. Our goal is to understand the mechanism of renal protection by bone marrow stem cells and to develop strategies utilizing these stem cells for the eventual treatment of humans with kidney disease.

Mechanisms of regulation of CXCR4/SDF-1 (CXCL12)-dependent migration and homing in multiple myeloma

The mechanisms by which multiple myeloma (MM) cells migrate and home to the bone marrow are not well understood. In this study, we sought to determine the effect of the chemokine SDF-1 (CXCL12) and its receptor CXCR4 on the migration and homing of MM cells. We demonstrated that CXCR4 is differentially expressed at high levels in the peripheral blood and is down-regulated in the bone marrow in response to high levels of SDF-1. SDF-1 induced motility, internalization, and cytoskeletal rearrangement in MM cells evidenced by confocal microscopy. The specific CXCR4 inhibitor AMD3100 and the anti-CXCR4 antibody MAB171 inhibited the migration of MM cells in vitro. CXCR4 knockdown experiments demonstrated that SDF-1-dependent migration was regulated by the P13K and ERK/ MAPK pathways but not by p38 MAPK. In addition, we demonstrated that AMD3100 inhibited the homing of MM cells to the bone marrow niches using in vivo flow cytometry, in vivo confocal microscopy, and whole body bioluminescence imaging. This study, therefore, demonstrates that SDF-1/CXCR4 is a critical regulator of MM homing and that it provides the framework for inhibitors of this pathway to be used in future clinical trials to abrogate MM trafficking.

Difficult stem cell mobilization despite adequate CD34+ cell dose predicts shortened progression free and overall survival after autologous HSCT for lymphoma

Hematopoietic growth factors alone or in combination with myelosuppressive chemotherapy are used to mobilize peripheral blood stem cells for autologous transplantation. To identify characteristics of successful mobilization with granulocyte colony-stimulating factor (G-CSF) alone and to study the impact of immediate chemotherapy mobilization following G-CSF mobilization, we treated 175 chemotherapy sensitive lymphoma patients with G-CSF (G) mobilization and leukapheresis followed by chemotherapy plus G-CSF (CG) mobilization and leukapheresis and then autologous transplantation. Patients with stage I/II disease at diagnosis and < or =5 years from diagnosis were more likely to mobilize successfully with G-CSF alone (G). CG mobilization led to superior stem cell yields compared to the preceding mobilization with G (median 2.37 vs 1.37 ( x 10(6)CD34+ cells/kg); P<0.0001). Patients (n=58, 33%) with successful G-CSF mobilization (> or =2 x 10(6) CD34+ cells/kg) had quicker platelet recovery and improved progression free and overall survival compared to patients who had adequate collection only after chemotherapy mobilization or to those who failed to collect an adequate graft with either type of mobilization. The poor clinical outcome of patients with difficult mobilization using either method identifies them as a high-risk group who might benefit from alternative therapies.

Enhanced unique pattern of hematopoietic cell mobilization induced by the CXCR4 antagonist 4F-benzoyl-TN14003

An increase in the number of stem cells in blood following mobilization is required to enhance engraftment after high-dose chemotherapy and improve transplantation outcome. Therefore, an approach that improves stem cell mobilization is essential. The interaction between CXCL12 and its receptor, CXCR4, is involved in the retention of stem cells in the bone marrow. Therefore, blocking CXCR4 may result in mobilization of hematopoietic progenitor and stem cells. We have found that the CXCR4 antagonist known as 4F-benzoyl-TN14003 (T-140) can induce mobilization of hematopoietic stem cells and progenitors within a few hours post-treatment in a dose-dependent manner. Furthermore, although T-140 can also increase the number of white blood cells (WBC) in blood, including monocytes, B cells, and T cells, it had no effect on mobilizing natural killer cells. T-140 was found to efficiently synergize with granulocyte colony-stimulating factor (G-CSF) in its ability to mobilize WBC and progenitors, as well as to induce a 660-fold increase in the number of erythroblasts in peripheral blood. Comparison between the CXCR4 antagonists T-140 and AMD3100 showed that T-140 with or without G-CSF was significantly more potent in its ability to mobilize hematopoietic stem cells and progenitors into blood. These results demonstrate that different CXCR4 antagonists may have different therapeutic potentials.

Stem cell homing

PURPOSE OF REVIEW

Transplantation of hematopoietic stem cells is dependent upon the successful homing, engraftment and repopulation of stem cells in the bone marrow. Stem cell homing through the circulation to the bone marrow is the critical first step in this process. This review discusses the latest progress in defining the molecular processes underlying stem cell homing and the specialized niches where stem cells reside.

RECENT FINDINGS

Over the past decade, remarkable advances have been made in characterizing the complex sequence of events involved in stem cell homing to the bone marrow. Specifically, the molecular basis of stem cell adhesion and rolling along bone marrow sinusoidal endothelial cells has been defined, and mechanisms underlying endothelial transmigration and enlodgement in bone marrow niches have now been identified. The processes governing hematopoietic stem cell homing to the bone marrow also regulate hematopoietic stem cell migration to extramedullary tissues and the metastasis of cancer stem cells. Improved understanding of these processes has catalyzed the development of therapies to facilitate stem cell mobilization for clinical purposes.

SUMMARY

Several components of the essential process of stem cell homing have now been characterized. Cell adhesion molecules and their ligands, extracellular matrix components, chemokines, and specialized bone marrow niches all participate in the precise regulation of this process.