Bone Marrow Transplantation (2009) 43, 181–195 & 2009 Macmillan Publishers Limited All rights reserved 0268-3369/09 $32.00 www.nature.com/bmt

REVIEW Improving stem cell mobilization strategies: future directions

W Bensinger1, JF DiPersio2 and JM McCarty3

1Department of Medicine, Division of Oncology, University of Washington School of Medicine, Seattle, WA, USA; 2Department of Medicine, Oncology Division, Washington University in St Louis School of Medicine, St Louis, MO, USA and 3Department of Internal Medicine, Division of Hematology/Oncology and Palliative Care, Virginia Commonwealth University Medical Center, Richmond, VA, USA

Autologous hematopoietic SCT (auto-HSCT) provides chemosensitive relapsed high- or intermediate-grade non- hematopoietic support after high-dose chemotherapy and Hodgkin’s lymphoma (NHL), providing essential hemato- is the standard of care for patients with multiple myeloma poietic support after the administration of high-dose (MM) or chemosensitive relapsed high-or intermediate- therapy (HDT).1–5 Although MM is an incurable malig- grade non-Hodgkin’s lymphoma (NHL). However, yields nancy, auto-HSCT used in conjunction with HDT has been of hematopoietic stem cells vary greatly between patients, shown to prolong survival.5,6 The rates of complete and the optimal strategy to mobilize hematopoietic stem response to conventional therapy without auto-HSCT in cells into peripheral blood for collection has not been patients with MM are B5–15%.5–7 Auto-HSCT in defined. Current mobilization strategies consist of cyto- combination with HDT can increase the rates of complete kines alone or in combination with chemotherapeutic response to B20–44% and is associated with a very low agents. Cytokine-only mobilization regimens are well incidence of treatment-related mortality.5,7–9 The most tolerated, but their utility is limited by suboptimal PBSC common NHL, diffuse large B-cell lymphoma, has a cure yields. When a myelosuppressive chemotherapeutic agent rate of B40–50% with conventional chemotherapy, but is added to a cytokine mobilization regimen, PBSC patients who relapse have a worse prognosis.1,2 Auto- collections improve two-to five-fold.This benefit is HSCT combined with HDT administered after relapse has tempered by increased toxicity, morbidity and resource been shown to prolong the duration of remission in patients utilization. All current regimens fail to mobilize sufficient with diffuse large B-cell lymphoma and provides these patients hematopoietic stem cells to proceed to transplantation in with approximately a 45% probability of long-term disease- 5–30% of patients, necessitating additional mobilization free survival.3 Auto-HSCT is also used in conjunction with attempts or precluding transplantation, which may nega- high-dose myeloablative therapy as a salvage treatment for tively affect patient outcomes and survival. Improved follicular lymphoma. Although controversial, recent data strategies to mobilize stem cells would increase the suggest that more than 10-year disease-free survival is possible availability of auto-HSCT and optimize engraftment and after salvage auto-HSCT for patients with follicular lympho- outcomes in patients with MM or NHL. Novel agents used ma.10 In addition, auto-HSCT may improve the prognosis in in conjunction with cytokines have the potential to increase patients with mantle cell lymphoma, specifically when it is used PBSC collections without introducing additional morbi- as part of first-line treatment.2 dity, thereby improving patient outcomes. The success of auto-HSCT is influenced by a number of Bone Marrow Transplantation (2009) 43, 181–195; factors, with the dose of reinfused stem cells being a key doi:10.1038/bmt.2008.410;published online 12 January 2009 factor.11 Higher stem cell doses are associated with faster Keywords: autologous;stem cell;mobilization;G-CSF; plt engraftment (generally defined as plt count 420 Â 109/l), chemotherapy;plerixafor faster neutrophil engraftment (generally defined as ANC 40.5 Â 109/l)11–16 and reduction in the need for supportive measures such as transfusions of packed RBCs and plts and administration of prophylactic antibiotics.12,15 In some studies, higher stem cell doses have been associated with Introduction higher rates of survival for patients.17,18 Other factors that affect collection efficiency and, therefore, the success of Autologous hematopoietic SCT (auto-HSCT) is the stan- auto-HSCT include patient age, gender, exposure to previous dard of care for patients with multiple myeloma (MM) or irradiation and chemotherapy, previous mobilization attempts and disease characteristics such as the involvement of BM.19–21 Unsuccessful initial stem cell mobilization leads to Correspondence: Dr W Bensinger, Clinical Research Division, Fred costly additional mobilization attempts and may prohibit Hutchinson Cancer Research Center, 1100 Fairview Avenue North, auto-HSCT altogether.14,22–24 D5-390, PO Box 19024, Seattle, WA 98109-1024, USA. E-mail: [email protected] Current regimens to mobilize PBSC for auto-HSCT have Received 1 April 2008;revised 3 November 2008;accepted 11 November differing stem cell yields, safety considerations, resource 2008;published online 12 January 2009 utilization, and levels of contamination of the apheresis Improving stem cell mobilization strategies W Bensinger et al 182 Table 1 Mobilization agents currently used in auto-HSCT31 are estimated to be from 5 to 30%, regardless of the approach.26,45–47 The question of whether failure rates after Mobilization agent Mechanism chemomobilization are lower than failure rates after Cytokines approved for mobilization cytokine-only mobilization has not been adequately stu- GM-CSF Stimulates production of granulocytes died. There remains a significant controversy over the and macrophages question of which method of PBSC mobilization is the G-CSF Granulocyte expansion/activation, protease release and cleavage of adhesion molecules safest and most predictable. This paper reviews current strategies for stem cell Chemotherapeutic agents commonly used for mobilization mobilization for auto-HSCT in patients with MM or CY Expansion and activation of granulocytes relapsed NHL and focuses on peripheral blood as a source Paclitaxel after bone marrow suppression Etoposide of stem cells. The benefits of mobilization either with cytokines alone or with chemomobilization are compared, and the limitations of each approach are described. Lastly, Investigational mobilization agents alternative approaches to mobilization that could improve Pegylated G-CSF Granulocyte expansion/activation, protease the outcomes of autologous stem cell collection and release and cleavage of adhesion molecules EPO Stimulates erythropoiesis transplantation are examined. Stem cell factor G-CSF potentiation Plerixafor Disrupts CXCR4/SDF-1a interactions SB-251353 GRO-b analog involved in directing the The biology of stem cell mobilization movement of stem cells and other leukocytes32,33 TPO Regulates megakaryocyte development, Recent advances in stem cell mobilization techniques have G-CSF synergism exploited the interactions between stem cells and the BM Parathyroid hormone Activates osteoblasts, which produce microenvironment. Composed of stromal cells, endothelial hematopoietic growth factors in the stem cells, osteoblasts and other matrix components (for cell niche example, collagens, fibronectins and proteoglycans), the Abbreviations: auto-HSCT ¼ autologous hematopoietic SCT; BM microenvironment anchors hematopoietic stem cells 21 CXCR4 ¼ chemokine receptor 4;GRO- b ¼ a human CXC chemokine; through a wide range of adhesive interactions. Hemato- SDF-1 ¼ stromal cell-derived-factor-1. poietic stem cells express a broad array of cell surface receptors, namely the adhesion molecules lymphocyte product with tumor cells.20,25–30 The two most common function-associated Ag-1, very late Ag-4 and Mac-1;the mobilization strategies today use cytokines alone or chemokine receptors CXCR4 and CXCR2;the cell surface cytokines after chemotherapy (chemomobilization). Table 1 glycoproteins CD44 and CD62L;and the tyrosine kinase lists the agents that are approved by the United States (US) receptor c-kit.21,31,48 The BM stroma contains stromal cell- Food and Drug Administration (FDA) for stem cell derived factor-1 (SDF-1), CXC chemokine GRO-b, vas- mobilization and the agents that are in development or cular cell adhesion molecule-1, kit ligand, P-selectin used off-label for this purpose. Mobilization using FDA- glycoprotein ligand-1 and hyaluronic acid, all of which approved cytokines alone is generally well tolerated;34,35 are cognate ligands for the stem cell adhesion mole- however, yields are often suboptimal, and collection of cules.21,31,48 Data from a number of preclinical models sufficient numbers of stem cells to support transplantation showed that inhibition of these receptor–ligand interactions can be difficult, particularly in patients who have pre- resulted in enhanced progenitor cell mobilization.49–51 viously been treated with multiple rounds of intensive Although hematopoietic cells mobilized to peripheral chemotherapy.22,36 The addition of a myelosuppressive blood for collection contain distinct populations of true chemotherapeutic agent to a cytokine mobilization regimen stem cells and differentiated progenitor cells, they are often improves collections by a factor of B2.5 (Bensinger et al.25) referred to collectively as stem cells.52 In the BM and and can reduce the number of apheresis sessions needed for peripheral blood, stem cells are characterized by Ags cell collection.37,38 Although national trends in mobiliz- specific to various lineages of hematopoietic cell differ- ation practices have not been studied to a large extent, in entiation.53 Many human hematopoietic progenitor cells our experience, chemomobilization is the standard of care and their precursors, including the majority of true stem in many transplant centers in Europe and the United cells, express the CD34 Ag. As such, the CD34 surface States. Although treatment-related mortality is rare, the use marker is commonly used as a marker for mobilization of chemotherapy agents in a mobilization regimen is efficiency, despite indications that CD34À cells may also associated with variable rates of treatment-related complic- exhibit multilineage reconstitution capacity.52–54 ations and can increase morbidity, particularly from The ultimate goal of SCT is to repopulate the BM niche neutropenia and infections.29,39 As a result, this mobiliz- with a complete lineage of hematopoietic stem cells,21,55 with ation strategy requires increased resource use, hospitaliz- minimal burden to the patient. Although a small number of ations, transfusions and the use of antibiotic therapy.29,39–42 hematopoietic stem cells circulate in the peripheral blood at Furthermore, variation among individual responses to all times, mobilization is necessary to drive sufficient chemomobilization can result in irregular collection sched- numbers of hematopoietic stem cells from the BM to the ules that can increase resource utilization and potentially peripheral circulation, where they can be harvested by delay transplantation.43,44 The utility of all current mobi- apheresis. Peripheral blood has been shown to be superior to lization regimens is limited by their high failure rates, which BM as a source of hematopoietic stem cells for autologous

Bone Marrow Transplantation Improving stem cell mobilization strategies W Bensinger et al 183 transplantation34,56 because collection is easier, morbidity is G-CSF reduced and the tempo of engraftment is quicker.34,56,57 Administration of G-CSF induces functional changes The target dose of infused CD34 þ cells varies from a within the BM microenvironment, as enzymes released minimum of 2.0 Â 106 CD34 þ cells/kg31,58,59 to an optimal from myeloid cells cleave adhesion molecules and disrupt level of 5.0 Â 106 CD34 þ cells/kg.24,26,55 Within this range, the interactions between chemokines, their receptors and higher doses of infused CD34 þ cells are more beneficial the extracellular matrix.73,74.In the presence of G-CSF, the for patients with MM and NHL.8,18,60,61 The quantity of number of myeloid cells committed to the granulocytic CD34 þ cells infused is positively correlated with the lineage increases, which causes the release of active tempo of plt and neutrophil engraftment after PBSC neutrophil serine proteases cathepsin G and neutrophil transplantation.13,14,24 Toor et al.18 and O’Shea et al.8 elastase, along with matrix metalloproteinase-9, into the reported improved OS in myeloma patients who received extracellular fluid of the BM.75,76 This results in enhanced transplants of higher doses of CD34 þ cells. Univariate cleavage of the adhesion molecules vascular cell adhesion and multivariate analyses of patients with MM who molecule-1, c-kit, CXCR4 and SDF-1.74,76–78 Several underwent chemomobilization with CY and G-CSF re- studies have shown that G-CSF and other cytokines can vealed that patients with higher CD34 þ cell harvest yields mobilize stem cells in protease-deficient mice, suggesting a had higher OS rates, independent of the cell dose more complex model in which both protease-dependent transplanted.62 Several studies have also reported a positive and protease-independent pathways contribute to G-CSF- association between CD34 þ cell count and survival in induced mobilization of stem cells.77,79,80 Recent data lymphoma patients.60,61 For patients with MM or NHL, show that G-CSF reduces osteoblast activity and decreases the number of CD34 þ cells collected is heavily influenced SDF-1a mRNA expression, suggesting a protease-indepen- by the mobilization regimen employed.25,28,29,63 dent mechanism through which G-CSF could regulate stem cell mobilization.81 Thus, the biological mechanisms through which cytokines induce PBSC mobilization are 77 Cytokine-induced mobilization complex and not completely understood. However, it is known that CD34 þ cell levels peak on the 5th day after 65 The hematopoietic growth factors GM-CSF (sargramostim, administration of G-CSF. Temporally, the initial neu- Leukine, Bayer Healthcare Pharmaceuticals, Seattle, WA, tropenia is brief and occurs soon after administration, USA) and G-CSF (filgrastim, Neupogen, Amgen Inc., whereas the ensuing neutrophilic state takes several days to Thousand Oaks, CA, USA) are the only agents currently achieve. Subsequent degranulation of neutrophils and approved by the FDA for the mobilization of stem cells for release of elastase and cathepsin D into the BM micro- auto-HSCT.64,65 These agents were developed concurrently 20 environment occur quickly, resulting in adhesion molecule 35 years ago.66,67 degradation and release of CD34 þ cells. G-CSF is the most frequently used stem cell mobilizing agent.72,82 When G-CSF alone is used for stem cell GM-CSF mobilization, it is administered at doses ranging from GM-CSF induces mobilization by stimulating proliferation 10 mg/kg s.c. daily to 32 mg/kg s.c. daily, beginning at least 4 and differentiation of hematopoietic progenitor cells, days before the first apheresis session and continued until particularly CD14 þ monocytes and CD80 þ DCs, in the last apheresis session.65,83 After transplantation, the patients with NHL.35,68.Although historically approved for median time to granulocyte engraftment has been reported mobilization, GM-CSF is little used for that purpose today. to be 11 days, and plt engraftment has been reported to An early analysis of GM-CSF activity69 in 13 patients with be B11–14 days.27,28 Mobilization with G-CSF is sarcoma showed that 3–7 days of treatment administered at generally well tolerated;common AEs are bone pain, a wide range of doses (4–64 mg/kg daily by continuous headache, anemia and decreased plt counts.65 Other AEs infusion) elevated WBC counts by a factor of 4.3 and reported by healthy donors include fatigue, muscle increased the numbers of blood mononuclear cells by a aches, nausea, vomiting and stomach pain.65 In addition, factor of 9.2. However, in subsequent analyses, mobiliz- rare but serious AEs have been reported. Myocardial ation with GM-CSF alone has been reported to lead to infarction and cerebral ischemia have occurred in high-risk relatively low yields of CD34 þ cells.35 Administration of patients with cancer who received G-CSF for a variety of GM-CSF with chemotherapy has been reported to mobilize indications.65 Splenic rupture, sickle cell disease with crisis fewer or a similar number of CD34 þ cells than has been and acute respiratory distress syndrome have also been reported with administration of G-CSF with chemothe- described.65 rapy.68,70,71 In addition, a higher incidence of both mild and The efficacy of G-CSF alone for mobilization of PBSCs serious adverse events (AEs) is associated with GM-CSF for auto-HSCT was established in a phase 3 trial conducted than with G-CSF.64,65,68,70,71 Mild AEs reported in healthy by Schmitz et al.,34 in which 58 patients with NHL or donors who receive GM-CSF include skin-associated Hodgkin’s disease (HD) received either PBSCs mobilized events, arthralgia, bone pain, myalgia and fever with with G-CSF 10 mg/kg s.c. daily for 6 consecutive days chills.35,64 Severe AEs include supraventricular arrhythmia, (n ¼ 27) or BM (n ¼ 31) for hematopoietic reconstitution immune hypersensitivity reactions, hypotension, tachyca- after HDT. A median value of 2.8 Â 106 CD34 þ cells/kg rdia, dyspnea and renal or hepatic dysfunction in predis- was collected after G-CSF mobilization. Furthermore, posed patients.35,64 Consequently, the use of GM-CSF as a when compared with BMT, reinfusion of G-CSF-mobilized single agent for mobilization is comparatively rare.72 PBSCs was found to reduce the number of plt infusions

Bone Marrow Transplantation Improving stem cell mobilization strategies W Bensinger et al 184 Table 2 Mobilization regimens and corresponding CD34+ cell yields in patients with MM or NHLa

Study Disease state Mobilization regimen N Median total Median apheresis No. of collected CD34+ sessions (range) mobilization cells  106/kg failures (range)

Bensinger et al.25 MM, L, BC, O Chemo+G-CSF or GM-CSF 124 10.75 (0.01–178.33) 3 (1–9) 9 G-CSF 119 5.21 (0.08–65.27) 3 (2–8) 6

Alegre et al.27 MM G-CSF 22 4.85 (2.1–10.05) 3 (2–6) NR CY+GM-CSF 18 6.8 (1.8–34.8) 5 (4–12) NR

Desikan et al.29 MM G-CSF 22 5.8 (range NR) 5 23%b CY+G-CSF 22 33.4 (range NR) 7 18%b

Dazzi et al.63 NHL G-CSF 12 2.89 (1.7–5.6) 16 totalc NR CY+G-CSF 12 6.41 (2.2–25.9) 15 totalc NR

Narayanasami et al.28 NHL, HD G-CSF 22 2.5 (0.3–12.4) NR (1–3) 1 CY+G-CSF 24 7.2 (0.3–44.8) NR (1–3) 1

Pavone et al.85 NHL DHAP+G-CSF 38 5.9d (range NR) 2 (1–3) 5 CY+G-CSF 34 7.06d (range NR) 2 (1–3) 4

Kanteti et al.86 NHL, HD G-CSF (randomized) 17 3.48 (0.15–11.06) NR 0 G-CSF (nonrandomized) 16 1.92 (0.96–3.98) NR 0

Schiller et al.87 MM CY+G-CSF+prednisone 37 4.65 (1.2–23.3) 3 (2–5) 0

Pusic et al.47 NHL, HD, MM G-CSF 976 3.36 (range NR) 2 (1–5) 182 Chemo+G-CSF 64 5.43 (range NR) 1.5 (1–5) 12

Abbreviations: BC ¼ breast cancer;chemo ¼ various chemotherapeutic agents;HD ¼ Hodgkin’s disease;L ¼ lymphoma;MM ¼ multiple myeloma; NHL ¼ non-Hodgkin’s lymphoma;NR ¼ not reported;O ¼ other. aReports included in Table 2 were from randomized controlled trials and other studies involving X24 patients with MM or NHL that reported CD34+ cell yields stratified according to mobilization regimen. bPercentage is reported instead of number. cTotal number of apheresis sessions for all patients in the group. dMean value reported instead of median.

needed (6 vs 10, Po0.001) and the time to plt and G-CSF alone (10 mg/kg daily) yielded significantly fewer neutrophil engraftment (16 days vs 23 days, P ¼ 0.02;11 CD34 þ cells and was inferior to mobilization with days vs 14 days, P ¼ 0.005, respectively). Nademanee chemotherapeutic agents plus G-CSF (1.5 Â 106/kg vs et al.84 harvested stem cells in 95 patients with lymphoma 6.7 Â 106/kg, P ¼ 0.0002). Previous cycles of chemotherapy after the s.c. or i.v. administration of regimens of G-CSF increased the risk of poor mobilization.88 In a study of 52 10 mg/kg daily for a median of 12 days (range: 4–23; n ¼ 39), patients with NHL, Micallef et al.89 reported that G-CSF 5 mg/kg daily for a median of 12 days (range: 8–27; mobilization with G-CSF alone (16 mg/kg s.c. daily for n ¼ 26) or no mobilizing therapy (n ¼ 30). The authors 4–6 days) failed to yield adequate numbers of CD34 þ cells reported median CD34 þ cell yields of 6.2 Â 106 cells/kg, in 35% of patients. The authors identified previous 3.4 Â 106 cells/kg and 1.2 Â 106 cells/kg in the respective treatment with fludarabine and BM involvement as risk treatment groups.84 Narayanasami et al.28 mobilized stem factors for poor mobilization. Sugrue et al.22 followed the cells in 22 patients with NHL or HD by using G-CSF outcome of PBSC collection in 21 patients who were 10 mg/kg s.c. daily for 4 days before the start of apheresis termed ‘poor mobilizers’ because an initial mobilization and reported a median CD34 þ cell collection of 2.5 Â 106/ attempt yielded o1 Â 106 CD34 þ cells/kg in two con- kg;approximately 50% of these patients required only one secutive large-volume leukaphereses. Protocols for initial apheresis session, whereas 4% of patients required three mobilization consisted of G-CSF alone in 20 of these sessions. patients (10 mg/kg s.c. daily for 4 days before the start of In many patients with MM or NHL, mobilization with apheresis and continuing throughout the apheresis period) G-CSF as a single agent results in suboptimal CD34 þ cell and G-CSF (5 mg/kg daily) with CY and etoposide in yields (Table 2). These studies show that CD34 þ cell yields 1 patient. Of these 21 patients, 11 did not reach the target are generally lower when a cytokine-only mobilization dose of 2.5 Â 106 CD34 þ cells/kg and required a second regimen is used than when cytokine mobilization is used mobilization, BM harvesting or both. Of the 21 patients, with chemotherapy. In addition, mobilization ‘failures’ 19 proceeded to transplantation. Engraftment of plts took (defined as CD34 þ cell yields of o2.0 Â 106/kg) were much longer in this group (median, 31 days) than in a highly variable throughout these studies, ranging from 0 to group of 23 similar patients who had been termed ‘good 23%. In a study of 58 patients with NHL or HD, mobilizers’ (median, 13 days). All five patients who received Moskowitz et al.88 reported that mobilization with transplants of o1 Â 106 CD34 þ cells/kg relapsed.

Bone Marrow Transplantation Improving stem cell mobilization strategies W Bensinger et al 185 After an initial mobilization attempt, if too few CD34 þ in vitro.96 Mobilization regimens combining GM-CSF with cells are collected to ensure prompt engraftment, patients G-CSF have consisted of sequential or concurrent admini- often undergo additional mobilization attempts, which stration of these agents at a range of doses (G-CSF, increase the risks associated with treatment.83 Several 5–10 mg/kg;GM-CSF, 5 mg/kg–250 mg/m2), with or without salvage regimens have been developed to improve mobili- chemotherapeutic agents.35,71,97,98 These combination regi- zation in patients in whom a first mobilization attempt with mens have not been shown to have substantial benefits over G-CSF alone fails to result in collection of an adequate cell regimens that use G-CSF alone;therefore, GM-CSF and dose. These salvage regimens include high-dose G-CSF G-CSF are not commonly administered together for and combinations of G-CSF with other cytokines, such as primary mobilization. However, the combination of GM-CSF. G-CSF and GM-CSF is used as a salvage mobilization regimen when mobilization with G-CSF alone has been unsuccessful.23,47,99 Boeve et al.23 remobilized stem cells in High-dose G-CSF 86 patients in whom a previous mobilization attempt with High-dose G-CSF was investigated as a primary mobiliz- G-CSF alone had failed. Nineteen patients received a daily ation regimen throughout the 1990s.90–92.Although seldom regimen of G-CSF 10 mg/kg plus GM-CSF 5 mg/kg from 4 used today for primary mobilization, high-dose G-CSF days before apheresis until the end of PBSC collection, regimens are occasionally used for remobilization.23,93 and the remaining 67 patients received high-dose G-CSF Although there is no standard protocol for high-dose (16 mg/kg twice daily).23 Among the patients who received G-CSF administration, doses ranging from 16 to 32 mg/kg s.c. G-CSF plus GM-CSF, a median yield of 1.6 Â 106 CD34 þ daily to 12–16 mg/kg s.c. twice daily have been considered cells/kg was collected during a median of three apheresis high-dose regimens even though some of the available data sessions.23 This result was similar to the average CD34 þ apply to patients with aplastic anemia, solid tumors or cell yield obtained in patients who received high-dose hematological malignancies other than NHL.23,83,91 Early G-CSF.23 The authors concluded that, in comparison with published studies of G-CSF for primary mobilization remobilization with high-dose G-CSF, remobilization with presented opposing viewpoints.91,92 Zeller et al.91 reported G-CSF plus GM-CSF was equally efficacious and entailed that compared to a lower dose regimen (G-CSF 10 mg/kg fewer costs.23 In general, the AEs seen when GM-CSF and s.c. daily beginning 4 days before apheresis, n ¼ 33), high- G-CSF are combined are similar to those seen with the use dose G-CSF (12 mg/kg s.c. twice daily beginning 4 days of either agent alone.35,100 before apheresis, n ¼ 34) resulted in higher CD34 þ cell yields per apheresis session (4.82 Â 108/kg vs 1.13 Â 108/kg and 4.04 Â 108/kg vs 0.93 Â 108/kg) and fewer mean EPO apheresis sessions (2 vs 3) in patients with NHL, HD or EPO, which is commonly used to preserve blood hemo- cancer of the testis. Only minor side effects were noted in globin concentrations in patients undergoing chemotherapy, each group. Conversely, Sheridan et al.92 reported that for has also been shown to potentiate the mobilization effect of patients with NHL, HD or acute lymphoblastic anemia, G-CSF or GM-CSF.101 Although the mechanism of this apheresis yields did not differ significantly between groups cooperative effect is unknown, it is thought that expression who received one of three different regimens of G-CSF of EPO receptors on CD34 þ progenitor cells primed with (12 mg/kg s.c. daily for 7 days, 24 mg/kg s.c. daily for 6 days G-CSF or GM-CSF may promote survival of these cells.102 or 12 mg/kg s.c. daily for 6 days plus an additional 12 mg/kg However, EPO use is generally regarded as inefficient and, i.v. on days 4, 5 and 6). as such, has not become a standard of care. Studies Positive results historically reported for high-dose evaluating the mobilization efficacy of EPO plus G-CSF or G-CSF remobilization regimens83,90 have not been notably G-CSF alone in various doses have generated mixed strengthened or refuted by recent research.23,93 Gazitt results. Perillo et al.103 found that 3–4 daily concomitant et al.83 reported that the administration of G-CSF 32 mg/kg doses of EPO 150 IU/kg s.c. plus G-CSF 5 mg/kg (n ¼ 5 s.c. daily for 4 days before apheresis and continuing until patients) or 10 mg/kg (n ¼ 10 patients) s.c. conferred no the last day of apheresis resulted in successful remobi- mobilization benefit over administration of G-CSF alone lization in 88% of 18 patients whose first mobilization (n ¼ 10 patients) in patients with advanced gynecological attempt was unsuccessful;most of these patients had cancers. Olivieri et al.101 noted that CD34 þ cell yields NHL. However, the use of high-dose G-CSF has been obtained from 16 patients with NHL or other malignancies linked to neutrophil toxicity in patients with aplastic who received daily doses of EPO (50 U/kg s.c.) plus G-CSF anemia.94 Furthermore, mobilization with high-dose (5 mg/kg s.c.) were 2.8 times greater than the yields G-CSF (12 mg/kg s.c. twice daily, beginning 4 days before obtained in 18 similar patients who received daily s.c. apheresis and continuing until the end of apheresis) has doses of 5 mg/kg G-CSF alone. Further investigation is been reported to increase the risk for development of required to ascertain the clinical benefits of EPO combined engraftment syndrome in children who are undergoing with G-CSF.104 mobilization for auto-HSCT to treat hematological malig- nancies or solid tumors.95 SCF The c-kit ligand SCF is produced in BM stromal cells and GM-CSFplus G-CSF acts as a potent co-mitogen for many hematopoietic growth Significant synergism has been reported between GM-CSF factors.105 Recombinant methionyl human SCF (ancestim, and G-CSF in the formation of granulocytic colonies Stemgen, Amgen Inc.) administered s.c. in combination

Bone Marrow Transplantation Improving stem cell mobilization strategies W Bensinger et al 186 with G-CSF has been shown to enhance mobilization and and CY each increase the release of granulocytic proteases may hasten recovery in transplant recipients.105,106 The that cleave the adhesion molecules SDF-1, CXCR4 and combination of SCF and G-CSF exerts a sustained c-kit.38 However, there are conflicting reports on whether a mobilization effect that persists longer than does the effect mobilization regimen consisting of sequential administr- of G-CSF alone, which persists for up to 7 days, as shown ation of chemotherapy followed by G-CSF causes down- by an increase in the numbers of circulating CD34 þ cells regulation of these adhesion molecules.38,118 Increases in for up to 13 days in patients with breast cancer (BC) who matrix metalloproteinase-9 concentrations after mobiliza- received the combination treatment.105 Escalations in doses tion with chemotherapy plus G-CSF have been noted to of SCF (5-30 mg/kg s.c.) used with G-CSF 10 mg/kg s.c. correlate with mobilization efficiency.38 In addition, the revealed a dose–response relationship in patients with toxicity of chemotherapeutic agents to the BM stroma BC105 that was not seen in a similar trial of heavily could prompt the release of hematopoietic stem cells by pretreated lymphoma patients.107 However, subsequent damaging the functional ability of stromal cells to support reports indicated that SCF may have a role in the treatment stem cells.38 of patients with lymphoma and other malignancies who A variety of chemotherapeutic agents are used with have undergone multiple rounds of intensive chemother- G-CSF or GM-CSF to mobilize hematopoietic stem cells apy.108,109 Stiff et al.108 reported that a combination of for autologous transplantation. Administration of CY with G-CSF 10 mg/kg s.c. and SCF 20 mg/kg s.c. administered daily G-CSF is widespread, as this regimen mobilizes hemato- for 5–9 days resulted in significantly higher CD34 þ cell poietic stem cells effectively and is highly active against yields (3.6 Â 106/kg) than did treatment with G-CSF alone tumor cells.55 Successful chemomobilization regimens used (2.4 Â 106/kg; P ¼ 0.05) in a randomized trial of 102 heavily in combination with G-CSF are often disease oriented. pretreated patients who had NHL or HD.108 Dawson Some of the most frequently used chemotherapeutic regi- et al.110 studied remobilization after X5 daily doses of SCF mens in lymphoma patients include IEV (ifosfamide, 20 mg/kg plus twice daily administration of G-CSF 10 mg/ epirubicin and etoposide), DHAP and ESHAP (etoposide, kg, with or without CY, in 48 patients who had been Ara-C, methylprednisolone and cisplatin).85,119 Patients heavily pretreated for a hematological malignancy and in with other hematologic malignancies are frequently treated whom a previous mobilization with G-CSF alone or with with ICE (ifosfamide, carboplatin and etoposide) plus chemotherapy had failed. The authors reported that the G-CSF for mobilization.120 Mobilization that follows an minimum CD34 þ cell dose of 42 Â 106/kg was achieved induction or a salvage regimen can eliminate separate in 38% of these patients. Despite the efficacy of SCF, its use mobilization chemotherapy.119 Pavone et al.85 compared is hindered by the infrequent occurrence of severe anaphy- mobilization with CY or the DHAP regimen followed by lactoid reactions and the resultant need to closely monitor G-CSF in patients with relapsed NHL. As similar cell yields patients after SCF administration.111 Although approved for were collected after each regimen, DHAP, an excellent use in Canada and New Zealand, ancestim is not currently salvage chemotherapy for NHL, could be scheduled into available in the United States,21 and it is seldom used in the treatment for patients proceeding to transplantation. In Europe because of the relatively high risk of side effects. large studies of patients with lymphoma, MM and other malignancies (including many with BC) who received chemotherapy and growth factors for mobilization, the G-CSF in conjunction with chemotherapy median time to neutrophil engraftment was 9–11 days, and the median time to plt engraftment was 9–10 days, which Before the development of hematopoietic cytokines as was slightly faster than occurred with G-CSF alone.25,26 mobilization agents, transient increases in the number of Chemomobilization is widely used in clinical practice hematopoietic stem cells in peripheral blood had been because the addition of a myelosuppressive chemotherapy noted after the administration of myelosuppressive chemo- agent to a cytokine mobilization regimen results in higher therapy.112,113 Thus, the earliest protocols to mobilize CD34 þ cell yields, which may promise better outcomes for hematopoietic stem cells into the peripheral blood used patients. In particular, mobilization with CY and G-CSF chemotherapy alone.114 When G-CSF and GM-CSF rather than with G-CSF alone improves CD34 þ cell became available, daily administration of either agent after collection significantly in patients with either MM27,29 or administration of a chemotherapeutic agent was found to NHL.28,63 Table 2 compares yields of CD34 þ cells enhance collection of hematopoietic stem cells.69,115 achieved with chemomobilization to CD34 þ cell yields The addition of a chemotherapeutic agent to a cytokine obtained using G-CSF alone in patients with either MM or mobilization regimen exerts complex effects on the NHL. Benefits of the relatively higher CD34 þ cell yields mobilization process that have yet to be fully eluci- that result from chemomobilization include faster engraft- dated.31,38 Myelosuppressive chemotherapeutic agents, ment of plts and neutrophils and improved rates of such as CY and paclitaxel, induce aplasia, which stimulates survival.8,18,60,61 Dose-dependent increases in CD34 þ cell hematopoietic recovery.116 The mobilization effect is highly counts have been noted when regimens containing CY plus variable and peaks 10–18 days after administration of G-CSF are used for mobilization.121 However, it has been chemotherapy and generally correlates with neutrophil noted that the use of CY plus G-CSF severely depletes count rebound after a chemotherapy-induced nadir.117 T cells and spares regulatory T cells, which could negatively Researchers have speculated that mobilization with CY affect immune reconstitution.122 plus G-CSF may have a synergistic effect on protease Mobilization with CY and G-CSF requires fewer apher- release in the BM because, when given individually, G-CSF esis sessions to collect sufficient numbers of hematopoietic

Bone Marrow Transplantation Improving stem cell mobilization strategies W Bensinger et al 187 stem cells for auto-SCT than does mobilization with hospitalization has been described, and many reports point G-CSF alone.37,38 In a recent retrospective analysis, Dingli to greater resource utilization with chemomobilization than et al.37 compared the characteristics of 74 patients with with cytokine-alone mobilization.29,37,39 Koc et al.39 found MM who received a hematopoietic growth factor alone for that although treatment with CY plus G-CSF resulted in mobilization to the characteristics of 127 patients with MM greater stem cell yield than did treatment with GM-CSF who received a growth factor plus CY. The authors found plus G-CSF, it also caused greater morbidity. In this study, no difference in the total numbers of cells collected. 30% of patients who underwent mobilization with G-CSF However, the addition of CY significantly reduced the plus CY developed febrile neutropenia that required median number of apheresis sessions, from 4 to 2 hospitalization. In the same study, transfusion support (Po0.0001). Owing to the increased CD34 þ cell yields was required by 39% of patients who underwent mobiliz- per apheresis session, mobilization with chemotherapy plus ation with G-CSF plus CY, but by only 4% of patients who G-CSF can be useful in tandem autologous transplant- underwent mobilization with GM-CSF plus G-CSF. ation, which is considered to be superior to single Desikan et al.29 reported increased hospitalization and autologous transplantation for patients with MM who do transfusions in patients who underwent mobilization with not experience CR after a first transplantation.123 G-CSF plus high-dose CY than with G-CSF alone. In As well as increasing stem cell yields, the addition of addition, Jantunen et al.41 and Fitoussi et al.40 reported chemotherapy to a G-CSF mobilization regimen is thought more hospital days, more days of i.v. antibiotics and more to improve the outcome of SCT by reducing the in vivo blood transfusions in patients who underwent mobilization tumor load and subsequently reducing tumor cell contam- with higher doses of chemotherapy than in those who ination in the apheresis product.55 Dose-dependent de- received lower doses. creases in potentially malignant CD19 þ cells have been Variable responses to mobilization with chemotherapy noted when both CY and G-CSF are used for mobiliza- plus cytokines25 result in unpredictable collection schedules tion.121 Although mobilization regimens that include that could delay transplantation.43,44 After chemomobi- chemotherapy have been noted to reduce the risk of lization, the lapse of time before the number of CD34 þ tumor-contaminated cell collections in patients with MM cells peaks varies substantially between patients.25,43,44 or lymphoma,20,30 there is considerable debate as to WBC counts and CD34 þ cell counts must be monitored whether the cytoreductive effects of mobilization with CY over the course of several days to determine when to begin and growth factors confer any survival benefit to the apheresis.44 Algorithms intended to reduce the incidence of patient. Dingli et al.37 showed that the addition of CY to a unanticipated PBSC collections and to streamline care by G-CSF mobilization regimen did not significantly improve predicting the timing of apheresis after chemomobilization response rates or prolong the time to disease progression. have been used with limited success.39 Hence, patients who In addition, it is thought that patients whose tumor load undergo mobilization with chemotherapy plus cytokines has already been maximally reduced are not likely to often require unscheduled apheresis sessions on weekends, benefit from any additional chemotherapy. Data from the a practice that necessitates inefficient allocation of hospital Center for International Bone Marrow Transplant resources and staff.43 Research (CIBMTR) indicate that disease relapse remains Toxicity from chemotherapeutic agents is an important the primary cause of death after SCT in patients with MM limitation of chemomobilization regimens. Serious AEs are or NHL, and relapse has been traditionally thought pervasive with the use of chemotherapeutic agents and to be associated with high levels of tumor cell contamin- include the development of hemorrhagic cystitis, cardiac ation from both the autograft and the presence of minimal toxicity, infections and anaphylactic reactions.126 Patients residual disease.124 However, results from a recent undergoing auto-HSCT are already at considerable risk of study by Bourhis et al.125 suggested that reinfused tumor serious chemotherapy-related AEs, and avoidance of cells may not be the primary cause of relapse in patients additional risk is prudent. Whether an additional course with myeloma. The authors found no difference in relapse of chemotherapy given solely for mobilization carries rates between a group of patients with MM who were sufficient therapeutic benefit to offset the increased risk reinfused with grafts containing detectable tumor cells and posed by the use of chemotherapeutic agents is unclear. another group reinfused with grafts free of detectable Exposure to chemotherapy for as less as 6 months has been tumor cells.125 Collectively, these data suggest that adding shown to significantly delay post transplantation plt and, to chemotherapy to the mobilization regimen may decrease a lesser extent, neutrophil engraftments.13 One might tumor contamination of the autograft, but that this may speculate that chemotherapy may exert long-term detri- not translate into decreased relapse rates or improved mental effects on the BM or the marrow microenviron- patient survival. ment. Kalaycio et al.127 reported an increased long-term The benefits of adding chemotherapeutic agents to a risk of treatment-related myelodysplastic syndrome or G-CSF mobilization regimen may be offset by the increased AML after auto-HSCT in patients whose marrow had risk of complications to the patients. Compared with been damaged by prior chemotherapy and radiation. It is mobilization regimens using G-CSF alone, chemomobiliz- possible that minimizing the use of chemotherapy agents ation is associated with increased morbidity, greater risk of for mobilization may leave more options available for infection, more hospital admissions, transfusions, antibiotic future treatment. In a recent study, Holtan et al.128 reported therapy and considerably greater cost overall.29,39–42 that the length of time between the last administration of Although treatment-related mortality is rare, significant chemotherapy and the start of apheresis is predictive of a morbidity related to neutropenia that can often require patient’s immune status at the start of apheresis. This result

Bone Marrow Transplantation Improving stem cell mobilization strategies W Bensinger et al 188 may reflect long-term damage to the BM caused by the understanding of stem cell interactions with the BM chemotherapeutic agents in patients with NHL. microenvironment grows, new mobilizing agents will Disease-specific factors such as previous treatment with emerge. chemotherapeutic agents or disease state can affect the success of a chemomobilization regimen.13,30,129 Although Pegfilgrastim mobilization with chemotherapy results in successful stem Pegylated G-CSF (pegfilgrastim, Neulasta, Amgen Inc.) is a cell collections in the majority of patients, obtaining longer-lasting variant of G-CSF;its plasma half-life of 33 h adequate CD34 þ cells may be more difficult in patients is substantially longer than the 4- to 6-h half-life of with low-grade lymphoma than in most other patients who G-CSF.132 A slow rate of renal elimination allows a single are candidates for auto-HSCT.30,129 In addition, previous dose of pegfilgrastim to result in clinically effective serum courses of chemotherapy and radiotherapy can adversely levels from administration until neutrophil recovery.132 influence CD34 þ cell yields.20,30,129 Tricot et al.13 studied This agent has been approved by the FDA for prevention 225 patients with MM;of these, 215 patients received GM- of prolonged neutropenia after chemotherapy for non- CSF 250 mg/m2 daily plus CY for mobilization and 49 hematological malignancies.133 Its potential as a mobilizing patients received G-CSF 5 mg/kg daily plus CY. The agent is currently being explored.132,134 Owing to its authors reported that the target yield of 5 Â 106 CD34 þ pharmacologic efficiency, pegfilgrastim has the potential cells/kg was obtained in only 28% of patients with 424 to reduce resource use by decreasing both the amount of months of previous chemotherapy, whereas 91% of product necessary to induce mobilization and the length of patients with shorter exposures to chemotherapeutic agents time between the initiation of mobilization and the achieved this target. Watts et al.119 reported that in 9 of 78 collection of PBSCs.132 A 12-mg s.c. dose of pegfilgrastim patients with lymphoma who received CY plus G-CSF administered after CY mobilized a median of 7.4 Â 106 10 mg/kg s.c. daily, the regimen failed to generate collections CD34 þ cells/kg after a median of one apheresis session in of 41 Â 106 CD34 þ cells/kg. Patients with MM who patients with MM.134 In a recent phase 2 study involving 26 receive initial therapy with lenalidomide are also at risk of patients with MM, pegfilgrastim (12 mg s.c., single dose) low CD34 þ cell yields.130 Kumar et al.130 noted significant administered after CAD (CY, Adriamycin (doxorubicin), decreases in the total number of CD34 þ cells collected dexamethasone) chemotherapy mobilized X7.5 Â 106 (Po0.001), the average number of CD34 þ cells collected CD34 þ cells/kg in 88% of patients.132 Results from this each day (P 0.001) and the total number of CD34 þ cells o study indicated that peak CD34 þ cell counts were collected on apheresis day 1 (P 0.001) among 135 patients o achieved at a median of 13 days (range: 11–22) after with MM who underwent initial treatment with lenalido- pegfilgrastim administration, slightly quicker than the 15 mide–dexamethasone, as compared with 241 similar days seen with G-CSF, which may affect the timing of patients who underwent initial therapy with either apheresis collections. Pegfilgrastim is well tolerated, with an dexamethasone, thalidomide–dexamethasone or VAD AE profile similar to that of G-CSF. Thoracic pain and (vincristine, Adriamycin (doxorubicin), dexamethasone). nausea were reported in a study by Fruehauf et al.,132 and a Furthermore, a trend was noted toward decreased PBSC case of splenic rupture that may not have been related to yield with increased duration of lenalidomide therapy.130 the study drug was reported in another trial.135 This effect was observed primarily among patients with G-CSF alone mobilization and was not significant when mobilization with CY plus G-CSF was used. Plerixafor In those patients with lymphoma or myeloma for whom Plerixafor (AMD3100, Genzyme Corporation, Cambridge, initial mobilization with CY and growth factors has failed, MA, USA) is a selective and reversible antagonist of regimens combining high-dose etoposide and cytokines CXCR4 and disrupts its interaction with SDF-1, thereby have been shown to be effective strategies for remobiliz- releasing hematopoietic stem cells into the circulation.136–138 ation.131 Incorporation of mobilization into the salvage Plerixafor used in conjunction with G-CSF has been therapy by using G-CSF (10 mg/kg) after the second or shown in a phase 2 study to quickly and predictably third cycle of therapy has been an increasing trend.120 enhance the numbers of CD34 þ cells circulating in the Although the use of G-CSF plus chemotherapy is generally peripheral blood.139 In this study, patients with NHL more effective than the use of G-CSF alone for second mobilized more CD34 þ cells per day of apheresis after mobilization attempts, the repeated administration of administration of plerixafor plus G-CSF than after admini- chemotherapeutic agents for mobilization introduces addi- stration of G-CSF alone (median increase of 4.4-fold tional toxicity and may not be the preferred approach for (range: 1.1- to 54.4-fold)). Similar results were seen in patients in whom chemomobilization has already failed.24 patients with MM (median increase of 3- to 3.5-fold (range: However, no single factor can predict the success of 1.3- to 10-fold)).139 In patients in whom mobilization with mobilization in a patient. G-CSF either alone or in combination with chemotherapy has previously failed, CD34 þ cell yields have been noted to increase by 5- to 100-fold in response to administration Novel agents of plerixafor plus G-CSF.139,140 A cohort of 115 patients termed poor mobilizers who received plerixafor as part of a In recent years, several investigational agents have been compassionate use protocol was assessed by Calandra developed that may prove useful for amplifying yields of et al.140 Collections of X2 Â 106 CD34 þ cells/kg after CD34 þ cells without introducing additional toxicity. As administration of plerixafor plus G-CSF for mobilization

Bone Marrow Transplantation Improving stem cell mobilization strategies W Bensinger et al 189 were achieved in 60.3% of patients with NHL, 71.4% of high success rate seen with plerixafor and G-CSF in patients patients with MM and 76.5% of patients with HD;these with NHL in whom initial mobilization with G-CSF alone rates were similar for patients who had previously failed had failed is consistent with results from the compassionate mobilization with chemotherapy plus cytokines or cyto- use protocol.140 kines alone.140 Preliminary results of two phase 3 multicenter random- SB-251353 ized placebo-controlled studies indicated that the addition SB-251353 is another investigational mobilization agent of plerixafor to a G-CSF regimen resulted in greater currently in preclinical studies.32,33 SB-251353 is an analog efficacy than was seen with a regimen of G-CSF of GRO-b, a human CXC chemokine involved in directing 141,142 alone. All patients in both studies received G-CSF the movement of stem cells and leukocytes.32,33 Although 10 mg/kg s.c. daily for 4 days. On the evening of day 4, human data are lacking, this agent, when combined with patients received either placebo or plerixafor (240 mg/kg G-CSF in rhesus monkeys, was shown to greatly increase s.c.). Patients underwent apheresis on day 5 and continued mobilization of stem cells and progenitor cells in compar- to receive the evening dose of either placebo or plerixafor ison with G-CSF alone.32 Further research is necessary to followed by the morning dose of G-CSF for up to a total of determine the efficacy and potential toxicities of this X 6 four apheresis sessions or until 5 Â 10 CD34 þ cells/kg treatment in humans.32,33 were collected. In one study that examined mobilization with plerixafor in patients with MM, the percentage of patients from whom X6 Â 106 CD34 þ cells/kg were TPO collected in p2 days of apheresis served as the primary Endogenous TPO is the primary regulator of megaka- end point.141 In the other study, which evaluated plerixafor ryocyte development. Recombinant human TPO (rhTPO) for mobilization in patients with NHL, the percentage of has been shown to act synergistically with G-CSF to 144 patients from whom X5 Â 106 CD34 þ cells/kg were enhance stem cell mobilization. This regimen has not collected in p4 days of apheresis was the primary end been shown to be more efficacious or safer than existing point.142 In the phase 3 study that was conducted in mobilization regimens;however, a few studies document patients with MM, it was reported that X6 Â 106 CD34 þ encouraging results. In one such study of 134 patients cells/kg were collected from 72% of patients in the undergoing HDT and auto-HSCT, the target yield of X 6 plerixafor group in p2 days of apheresis, whereas only 5 Â 10 CD34 þ cells/kg was reached in 73% of patients 34% of patients in the placebo group had reached this goal when rhTPO was added to G-CSF, whereas the target yield (P 0.0001). In the phase 3 study conducted in patients was reached in only 46% of patients whose stem cells were o 145 with NHL, the target yield of X5 Â 106 CD34 þ cells/kg mobilized with G-CSF plus a placebo. AEs associated collected in 4 apheresis days was reached by 59% of with the use of rhTPO plus G-CSF appear to be similar to p 144,145 patients in the plerixafor group but by only 20% of patients those seen with the use of G-CSF alone; however, in the placebo group (Po0.0001). Furthermore, the cytopenias owing to neutralizing antibodies to TPO have minimum yield of X2 Â 106 CD34 þ cells/kg collected in been reported in a small number of patients who were given 4 apheresis days was reached by 87% of patients in the rhTPO to treat chemotherapy-induced thrombocyto- p 146,147 plerixafor group but by only 47% of patients in the placebo penia. Currently, no TPOs have been approved by 148 group (Po0.0001). More patients proceeded to transplant- the FDA for mobilization. ation in the plerixafor group (90%) than in the placebo Parathyroid hormone group (55%). In general, treatment with plerixafor and Parathyroid hormone (PTH) activates osteoblasts, which G-CSF was associated with side effects similar to those seen produce hematopoietic growth factors in the stem cell niche, with treatment with G-CSF alone. Most treatment-related thereby increasing the numbers of circulating stem cells.149,150 AEs appeared to be mild and transient. The most common The efficacy and safety of PTH have yet to be established. In AEs were gastrointestinal tract effects, such as diarrhea, a recent phase 1 study, 20 patients with MM, NHL, HD or nausea and vomiting, and injection-site reactions, such as AML, in whom one or two previous mobilization attempts erythema or edema.141,142 had failed, received escalating doses of 40, 60, 80 and 100 mg Patients with NHL who did not mobilize the minimum of PTH (s.c.) for 14 days;PTH doses were combined with yield of X2 Â 106 CD34 þ cells/kg in the phase 3 trial of G-CSF 10 mg/kg on the last 4 days of treatment.150 Overall, plerixafor were enrolled in a follow-up study in which rescue 47% of patients in whom one previous mobilization attempt mobilization therapy with plerixafor plus G-CSF was had failed reached the mobilization criterion of 45CD34þ administered.143 All patients received G-CSF (10 mg/kg) s.c. cells/ml in the peripheral blood, and 40% of patients daily for 4 days;on the evening of the fourth day, patients who had previously experienced two failed mobilization received plerixafor (240 mg/kg s.c.). Apheresis commenced on attempts reached the mobilization criterion. No dose-limiting day 5, after a morning dose of G-CSF. Patients continued to toxicity was evident, and PTH was well tolerated;AEs included receive plerixafor in the evening and G-CSF in the morning headache, muscle pain, back pain, fatigue and hypothermia.150 for up to 4 days of apheresis or until 5 Â 106 CD34 þ cells/kg had been collected. This rescue therapy resulted in collections of X2 Â 106 CD34 þ cells/kg in 33 of 52 patients (63%) in Conclusions whom initial mobilization with placebo and G-CSF had failed and in 4 of 10 patients (40%) in whom initial Current stem cell mobilization regimens for auto-HSCT in mobilization with plerixafor and G-CSF had failed.143 The patients with NHL or MM vary with regard to CD34 þ cell

Bone Marrow Transplantation Improving stem cell mobilization strategies W Bensinger et al 190 yield and toxicity. Mobilization with cytokines alone, most ation as compared with salvage chemotherapy in relapses of commonly G-CSF, is generally well tolerated;however, this chemotherapy-sensitive non-Hodgkin’s lymphoma. N Engl J approach is limited by suboptimal yields and the need for Med 1995; 333: 1540–1545. repeated apheresis sessions to collect sufficient cells for 4 Harousseau JL, Moreau P. Role of bone marrow transplant- transplantation. Mobilization regimens that combine a ation in the disease pathway of myeloma. J Natl Compr Canc Netw chemotherapeutic agent with a cytokine enhance the collec- 2007; 5: 163–169. 5 Child JA, Morgan GJ, Davies FE, Owen RG, Bell SE, tion of CD34 þ cells. However, the higher CD34 þ cell Hawkins K et al. High-dose chemotherapy with hematopoie- collection may be offset by increased toxicities and resource tic stem-cell rescue for multiple myeloma. N Engl J Med 2003; utilization. Importantly, the optimal time to collect CD34 þ 348: 1875–1883. cells after chemotherapy is highly variable and unpredictable, 6 Hari P, Pasquini MC, Vesole DH. Cure of multiple which potentially increases resource utilization. myeloma—more hype, less reality. Bone Marrow Transplant Although chemomobilization is widely used in Europe 2006; 37: 1–18. and the United States, no strategy for mobilization can be 7 Attal M, Harousseau JL, Stoppa AM, Sotto JJ, Fuzibet JG, considered standard, and there are no published guidelines Rossi JF et al. A prospective, randomized trial of autologous regarding PBSC mobilization. For patients with MM who bone marrow transplantation and chemotherapy in multiple N Engl J Med undergo transplantation and who have not received initial myeloma. Intergroupe Francais du Myelome. 1996; 335: 91–97. therapy with lenalidomide, mobilization with G-CSF alone 8 O’Shea D, Giles C, Terpos E, Perz J, Politou M, Sana V et al. is often sufficient for a single transplant and should be Predictive factors for survival in myeloma patients who considered. However, CD34 þ cell yields resulting from undergo autologous stem cell transplantation: a single-centre mobilization with G-CSF alone may not be high enough to experience in 211 patients. Bone Marrow Transplant 2006; 37: support tandem transplantation. Furthermore, G-CSF 731–737. alone is insufficient up to 23% of the time for mobilization 9 Dingli D, Pacheco JM, Dispenzieri A, Hayman SR, in patients with NHL or HD. For these patients, it may be Kumar SK, Lacy MQ et al. Serum M-spike and transplant necessary for mobilization regimens to include chemother- outcome in patients with multiple myeloma. Cancer Sci 2007; apeutic or novel agents. It is our opinion that effective- 98: 1035–1040. ness will be the main driver for the use of any novel 10 Rohatiner AZ, Nadler L, Davies AJ, Apostolidis J, Neuberg D, Matthews J et al. Myeloablative therapy with autologous mobilization strategy. The addition of plerixafor to a G- bone marrow transplantation for follicular lymphoma at the CSF regimen has led to substantial improvements in time of second or subsequent remission: long-term follow-up. efficacy in clinical trials;this strategy shows great potential J Clin Oncol 2007; 25: 2554–2559. for future use in patients with NHL, HD or MM who 11 Jillella AP, Ustun C. What is the optimum number of undergo transplantation. CD34+ peripheral blood stem cells for an autologous Collectively, all regimens in current use fail to mobilize transplant? Stem Cells Dev 2004; 13: 598–606. adequate numbers of CD34 þ cells in 5–30% of patients. 12 Siena S, Schiavo R, Pedrazzoli P, Carlo-Stella C. High failure rates can adversely affect patient outcomes, Therapeutic relevance of CD34 cell dose in blood cell because these patients cannot proceed to transplantation transplantation for cancer therapy. J Clin Oncol 2000; 18: without a repeat of mobilization and apheresis, which is 1360–1377. 13 Tricot G, Jagannath S, Vesole D, Nelson J, Tindle S, Miller L associated with increased morbidity and resource utiliza- et al. Peripheral blood stem cell transplants for multiple tion. Thus, advances in mobilization strategies are needed myeloma: identification of favorable variables for rapid to improve patient outcomes. Novel agents used in engraftment in 225 patients. Blood 1995; 85: 588–596. conjunction with existing therapies have the potential to 14 Stiff PJ. Management strategies for the hard-to-mobilize amplify CD34 þ cell yields without introducing additional patient. 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