The use of mobilized peripheral blood stem cells (PBSCs) has largely replaced the use of bone marrow as a source of stem cells for both allogeneic and autologous stem cell transplantation. G-CSF with or without chemotherapy is the most commonly used regimen for stem cell mobilization. Some donors or patients, especially the heavily pretreated patients, fail to mobilize the targeted number of stem cells with this regimen. A better understanding of the mechanisms involved in hematopoietic stem cell (HSC) trafficking could lead to the development of newer mobilizing agents and therapeutic approaches. This review will cover the current methods for stem cell mobilization and recent developments in the understanding of the biology of stem cells and the bone marrow microenvironment.

Wide ranges i n cell recovery and purity may be observed following CD34(+) cell selection of mobilized HPC componetns. Characteristics of the mobilized HPC, associated with isolation of a high CD34(+) cell yield and purity following cell selection, have yet to be defined.

Cell number and purities were determined before and after 56 CD34(+) cell-selection procedures, performed using the CellPro Ceprate SC system from April 1997 to February 1998. HPC were collected from 28 patients with multiple myeloma, following cyclophosphamide (60mg/kg) and G-CSF (10microg/kg) mobilization.

A medium of 47.9% (range 1.5-109.6%) CD34(+) cells were recovered in the enriched (ENR) fraction. A linear correlation existed between total CD34(+) cells in the ENR fraction and total CD34(+) cells in the START fraction (R2=0.93); there was a logarithmic correlation between CD34 ENR fraction purity and START fraction purity (R2=0.73). A START CD34(+) cell purity > 0.42% improved purity in the ENR fraction. A median of one (range one to nine) procedure was required to isolate 2 x 10 6 CD34(+) cells/kg. Three patients pretreated with alkylating agents failed to mobilized adequate numbers of HPC.

Isolation of highly purified CD34(+) cell-selected components using the Ceprate SC system in dependent on the CD34(+) purity of the lekapheresis component collected. Mobilization regimens should be used to maximize CD34(+) cell purity in stem cell authografts if CD34(+) cell selection is to be performed. Similar strategies should be used to evaluate other cell-selection devices as they become available.

During inflammation and cytopenia, increased levels of hematopoietic growth factors (HPGFs) induce mobilization and proliferation of hematopoietic stem cells and hematopoietic progenitor cells (HPCs), resulting in spatial and quantitative in vivo expansion of the hematopoietic tissue. Exogenous administration of recombinant HPGFs, particularly granulocyte colony-stimulating factor (G-CSF), is routine for mobilization of stem cells, followed by collection and transplantation of autologous or allogeneic stem cells. In this review, we summarize experience using different HPGFs and HPGF combinations for stem cell mobilization, such as G-CSF, granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), stem cell factor (SCF), and others. Preclinical and clinical studies of so-called early- and late-acting HPGFs for ex vivo expansion of HPCs are discussed, also with respect to the unresolved question whether expansion of repopulating stem cells can be achieved in vitro.

In recent years, endothelial progenitor cells (EPCs), gave rise to increasing interest because of their possible use as a therapeutic tool in the treatment of vascular lesions in ischemic tissues or as a target for anti neoplastic therapy. It has been shown that several drugs can increase the number of EPCs into the peripheral blood (PB). However, there is insufficient data concerning the mobilization and collection of EPCs during CD34+ cell mobilization. In this study, we have evaluated EPC mobilization and collection in a series of 47 patients affected by lymphoid neoplasms [31 non Hodgkin lymphoma and 16 multiple myeloma] undergoing CD34+ cell mobilization with cyclophosphamide (4000 mg/m2) and Filgrastim (5 microg/kg). PB EPCs identified by flow cytometry as CD34+/VEGFR2+/CD133+ cells showed a peak on day +10. This peak paralleled that of PB CD34+/CD45+ cells. A direct correlation was observed between CD34+ and CD34+/VEGFR2+/CD133+ cells (r = 0.99 P < 0.0001). An average of 23.7 x 10e6 CD34+/VEGFR2+ CD133+ cells have been collected (range 12.1-41.76 x 10e6). These findings showed that in hematological diseases, cyclophosphamide in combination with filgrastim allows the mobilization and collection of large numbers of EPCs which may be used for reparative medicine studies in these patients.

Successful stem cell mobilization is a prerequisite for autologous blood cell transplantation. We analyzed factors that may predict the success of stem cell mobilization in patients with multiple myeloma (MM).

We analyzed 124 consecutive patients and compared those who failed to mobilize a sufficient amount of CD34(+) cells (peak blood CD34(+) cell count <20x10(6)/L) (n=20) with those with successful mobilization (n=104). The peak blood CD34(+) cell count after mobilization was used as the marker of mobilization success against which the various predictive factors were tested.

In univariate analysis the best predictive factors for mobilization failure were the number of different chemotherapy regimens (P<0.001), number of chemotherapy cycles (P<0.001), time from diagnosis to mobilization (P<0.001) and previous use of IFN (P<0.001). The distributions of treatment responses at mobilization were similar in the groups with successful and unsuccessful mobilization, and were CR or VGPR in 10% of all patients, PR in 54% and stable or progressive disease in 36%. Regarding the mobilization-related factors, lower leukocyte nadir (P<0.001), longer duration of leukocyte counts <1x10(9)/L (P<0.001), lower platelet nadir (P=0.001), longer duration of platelet counts <20x10(9)/L (P<0.001) and the occurrence of sepsis after the mobilization therapy (P=0.001) were significantly associated with mobilization failure. In multivariate analysis, the amount of earlier chemotherapy cycles (P=0.002), low platelet nadir (P=0.020), occurrence of sepsis at mobilization (P=0.040) and previous use of IFN (P=0.052) remained as significant predictive factors for mobilization failure.

Predicting the success of stem cell mobilization beforehand may have important practical consequences. By identifying those patients who will fail to mobilize stem cells, unnecessary mobilization and collection attempts can be avoided.

Intentional recruitment of hematopoietic stem cells from bone marrow to peripheral blood is a clinical process termed peripheral blood stem cell (PSBC) mobilization. Mobilized PSBC has replaced bone marrow as the preferred source of stem cells for patients undergoing high-dose chemotherapy because of rapid and durable engraftment and reconstitution of functional bone marrow. Although the mechanism involved in the process of PBSC mobilization by cytokines is largely unknown, granulocyte colony-stimulating factor (G-CSF) alone or chemotherapy combined with GCSF is used as a mobilizing agent in current clinical practice. To date, G-CSF is the best cytokine for PBSC mobilization. However, there are some controversies in its efficacy (poor mobilizer) and safety (in allogeneic donors). Recent research progress has revealed some part of the mechanistic scenarios of PBSC mobilization and found promising candidates for the agents for PBSC mobilization. Until the research at molecular and cellular levels elucidates the precise mechanisms, collecting and comparing clinical observations is the best way to find more optimal condition for PBSC mobilization.

Failure to mobilize PBPCs for auto-logous transplantation has mostly been attributed to previous therapy and poses therapeutic problems.

The role of underlying disease was analyzed in 17 of 73 (23%) patients with PBPC mobilization failure, and secondary mobilization with high-dose filgrastim was attempted.

Of 16 patients with acute leukemia, 13 (81%) mobilized poorly. In contrast, of 57 patients with non-Hodgkin's lymphoma, Hodgkin's lymphoma, multiple myeloma, and solid tumor, 53 (93%, p < 0.001) showed good PBPC mobilization. Relapsed disease did not predispose to poor mobilization. As secondary mobilization attempt, 7 patients received 25 micro g per kg per day filgrastim without chemotherapy leading to a 3.7 +/- 2.8-fold (SD) increase in the maximum number of circulating CD34+ cells (p = 0.104). PBPC apheresis yielded 3.3 (+/-0.5) x 10(6) CD34+ cells per kg of body weight in 5 patients. Four poor mobilizers received 50 micro g per kg per day filgrastim as second or third mobilization attempt. Circulating CD34+ cells in these patients increased by 1.5 (+/-0.7) compared with the primary G-CSF application.

Selective PBPC mobilization failure was seen in patients with acute leukemia whereas remarkably good mobilization was seen in other malignancies. Increasing the filgrastim dose to 25 micro g per kg per day may allow PBPC collection in patients failing PBPC mobilization.

Gene transfer experiments in nonhuman primates have been shown to be predictive of success in human clinical gene therapy trials. In most nonhuman primate studies, hematopoietic stem cells (HSCs) collected from the peripheral blood or bone marrow after administration of granulocyte colony-stimulating factor (G-CSF) + stem cell factor (SCF) have been used as targets, but this cytokine combination is not generally available for clinical use, and the optimum target cell population has not been systematically studied. In our current study we tested the retroviral transduction efficiency of rhesus macaque peripheral blood CD34(+) cells collected after administration of different cytokine mobilization regimens, directly comparing G-CSF+SCF versus G-CSF alone or G-CSF+Flt3-L in competitive repopulation assays. Vector supernatant was added daily for 96 hours in the presence of stimulatory cytokines. The transduction efficiency of HSCs as assessed by in vitro colony-forming assays was equivalent in all 5 animals tested, but the in vivo levels of mononuclear cell and granulocyte marking was higher at all time points derived from target CD34(+) cells collected after G-CSF+SCF mobilization compared with target cells collected after G-CSF (n = 3) or G-CSF+Flt3-L (n = 2) mobilization. In 3 of the animals long-term marking levels of 5% to 25% were achieved, but originating only from the G-CSF+SCF-mobilized target cells. Transduction efficiency of HSCs collected by different mobilization regimens can vary significantly and is superior with G-CSF+SCF administration. The difference in transduction efficiency of HSCs collected from different sources should be considered whenever planning clinical gene therapy trials and should preferably be tested directly in comparative studies.

This study assessed the ability of recombinant human stem cell factor (rHuSCF) to mobilize stem cells in 44 patients who had failed a prior mobilization (CD34(+) yield 0.5-1.9 x 10(6)/kg BW) with filgrastim-alone or chemotherapy-plus-filgrastim. The same mobilization regimen was used with the addition of rHuSCF. In the filgrastim-alone group (n=13), rHuSCF 20 microg/kg was started 3 days before filgrastim and continued for the duration of filgrastim. In the chemotherapy-plus-filgrastim group (n=31), rHuSCF 20 microg/kg/day plus filgrastim 5-10 microg/kg/day were administered concurrently. Leukaphereses were continued to a maximum of four procedures or a target of >or=3 x 10(6) CD34(+) cells/kg. In both groups, CD34(+) yield (x 10(6)/kg BW) of the study mobilization was higher than that of the prior mobilization (median: 2.42 vs 0.84 P=0.002 and 1.64 vs 0.99 P=<0.001, respectively). In all 54 and 45% of patients in the filgrastim-alone group and chemotherapy-plus-filgrastim group, respectively, reached the threshold yield of 2 x 10(6)/kg. The probability of a successful mobilization was the same in those with a CD34+ yield of 0.5-0.75 x 10(6)/kg BW in the prior mobilization as in those with 0.76-1.99 x 10(6)/kg BW. Downmodulation of c-kit expression and a lower percentage of Thy-1 positivity in the mobilized CD34(+) cells were noted in the successful mobilizers compared with those in the poor mobilizers. This study shows that rhuSCF is effective in approximately half the patients who had failed a prior mobilization and allows them to proceed to transplant. It also points to the likely role of the SCF/c-kit ligand pair in mobilization.

The objective of our study was to determine the effect of adding r-metHuSCF to Filgrastim and cyclophosphamide for mobilization of peripheral blood progenitor cells (PBPC), on collection of CD34(+) cells and engraftment after autologous stem cell transplant. Twenty-three patients with previously treated stage II-IV breast cancer received cyclophosphamide (3 g/m(2)), Filgrastim 5 microg/kg daily and r-metHuSCF 20 microg/kg daily. Two PBPC collections were performed on consecutive days starting the day the WBC count was above 7.5 x 10(3)/microl. Collection was performed between days +9 and +12 and the median number of CD34(+) cells collected was 9.9 x 10(6)/kg (1.1-53.1) and 6.6 x 10(6)/kg (1.4-33.8) for the first and second apheresis, respectively. Despite being previously treated patients, the target CD34(+) cell dose required for SCT was obtained in all patients. SCT was associated with rapid neutrophil and platelet engraftment and a highly significant correlation was observed between the number of CD34(+) cells infused and engraftment. Treatment with SCF plus filgrastim was well tolerated, with mild to moderate local skin rash being the most frequently reported adverse event. In conclusion, addition of r-metHuSCF induces mobilization of a large number of CD34(+) cells which results in shortening of time to engraftment and hospitalization.

It is not known whether increasing the dose of filgrastim after mobilizing chemotherapy improves collection of peripheral blood progenitor cells (PBPC) and leads to faster hematopoietic engraftment after autologous transplantation.

A randomized, open-label, multicenter trial was carried out in patients with breast cancer, multiple myeloma, and lymphoma, in which patients were randomized to receive 5 or 10 microg per kg per day of filgrastim after standard chemotherapy to mobilize PBPCs. After high-dose chemotherapy, the components from the first two leukapheresis procedures were returned, and all patients received 5 microg per kg day of filgrastim after transplantation.

A total of 131 patients were randomized, of whom 128 were mobilized (Group A, 5 microg/kg, n = 66; Group B, 10 microg/kg, n = 62) and 112 were transplanted. Only six patients were not transplanted because of insufficient CD34+ cell numbers. The median number of CD34+ cells collected in the first two leukapheresis procedures tended to be higher in Group B than in Group A (12.0 vs. 7.2 x 10(6)/kg, NS), but after transplantation there was no significant difference in median times to platelet (9 days in both groups) or neutrophil (8 days in both groups) engraftment or the number of platelet transfusions (three in both groups). A subsequent subgroup analysis separating patients transplanted after first- or second-line chemotherapy also showed no measurable impact of filgrastim dose on the median CD34+ cell yield or on platelet engraftment in either subgroup.

PBPC mobilization with chemotherapy and 5 microg per kg of filgrastim is very efficient, and 10 microg per kg of filgrastim does not provide additional clinical benefit.

A high-dose (HD) chemotherapy scheme was designed for the collection of large numbers of peripheral blood progenitor cells (PBPC) in lymphoma patients who were candidates for myeloablative therapy with autograft. The scheme included the sequential administration of HD cyclophosphamide (CY) (7 g/m(2)) and HD ara-C (2 g/m(2) twice a day for 6 consecutive days), followed by final consolidation with PBPC autograft. PBPC harvests were scheduled following both HD CY and HD ara-C. To minimize hematologic toxicity, small aliquots of PBPC (<or=3 x 10(6) CD34(+) cells/kg) collected following HD CY were reinfused following HD ara-C. The treatment was delivered to 112 patients (median age: 43 years) with lymphoid malignancies (107 non-Hodgkin's lymphoma, four Hodgkin's lymphoma, one amyloidosis); 75 patients were at disease onset, whereas 37 had relapsed or were refractory after first-line conventional therapy. PBPC mobilization was assessed in terms of peak values of circulating CD34(+) cells/microl, as well as total CD34(+) cells/kg collected. In a few patients CFU-GM/kg were also evaluated. At the time of maximal mobilization following HD CY, 93 'high-mobilizer' patients had >20 circulating CD34(+) cells/microl, whereas the remaining 19 'low-mobilizer' patients did not reach this cut-off value. In spite of poor mobilization after HD CY, 16 out of 19 low mobilizers provided good harvests following HD ara-C; overall, median collected CD34(+) cells x 10(6)/kg were 1.4 (0-3.1) and 10.2 (0-37) after HD CY and HD ara-C, respectively (P = 0.00007). Similar patterns were observed when PBPC were evaluated by CFU-GM/kg. Complete and durable hemopoietic reconstitution followed autograft with post HD ara-C PBPC. Within the high-mobilizer group, 88 patients received HD ara-C and 79 (90%) still showed high mobilization; overall, median collected CD34(+)cells x 10(6)/kg were 17.8 (range 3-94) and 19 (range 0-107) after HD CY and HD ara-C respectively (P = NS). Thus, the scheme allowed sufficient PBPC collections for autografting in low mobilizer patients; in addition, the scheme could be considered whenever extensive chemotherapy debulking is needed prior to PBPC collection.

Patients (n = 69) with multiple myeloma undergoing peripheral blood stem cell collection (PBSC) were treated with cyclophosphamide and a combination of recombinant methionyl human granulocyte colony-stimulating factor (r-metHuG-CSF, filgrastim) and recombinant methionyl human stem cell factor (r-metHuSCF, ancestim). The objectives of this study were to determine: (1) The proportion of patients reaching a target yield of >or=5 x 10(6) CD34(+) cells/kg in one or two successive large-volume (20 liter) leukapheresis procedures; (2) the optimal collection time for leukapheresis; (3) mobilization kinetics of CD34(+) subsets in response to G-CSF/SCF. All patients were mobilized with cyclophosphamide (2.5 g/m(2)) on day 0 followed by filgrastim (10 microg/kg ) plus ancestim (20 microg/kg) commencing day 1 and continuing to day 11 or 12. Of the 65 evaluable patients, 57 were considered not heavily pretreated and 96.5% obtained a target of >or=5 x 10(6)/kg in one collection. The median CD34(+) cells/kg was 39.5 x 10(6) (range: 5.2-221.2 x 10(6)). Subset analysis demonstrated the number of CD38(-), CD33(-), and CD133(+) peaked at day 11; and CD34(+), CD90(+) cells peaked at day 10. The optimum day for leukapheresis was determined to be day 11. The median absolute peripheral blood CD34(+) cell numbers on day 11 was 665 x 10(6)/l (range: 76-1481 x 10(6)/l). Eight of the 10 heavily pretreated patients were evaluable: three achieved the target dose in one leukapheresis (37.5%) and three (37.5%) achieved the target dose with two leukaphereses. Use of this mobilization strategy allowed the collection of high numbers of CD34(+) cells and early progenitors and the ability to predictably schedule leukapheresis.

Effects of mobilization regimen on the composition of leukapheresis products (LPs) and on hematopoietic reconstitution after autologous peripheral blood progenitor cell transplantation (PBPCT) are not well known.

The effects of three different mobilization regimens--stem cell factor (SCF) plus granulocyte colony stimulating factor (G-CSF) plus cyclophosphamide (CCP), G-CSF alone, and G-CSF plus CCP--on the composition of LPs from patients with nonhematologic PBPC malignancies compared to LPs from G-CSF-mobilized healthy donors and normal marrow (BM) samples were analyzed. The impact of LP composition on both short- and long-term engraftment after autologous PBPCT was also evaluated.

The most effective regimen for mobilization of CD34+ hematopoietic progenitor cells (HPCs) into peripheral blood was SCF, G-CSF, and CCP, providing the highest numbers of all CD34+ HPCs subsets analyzed. Patients mobilized with SCF plus G-CSF plus CCP showed the highest numbers of neutrophils and monocytes, whereas the highest numbers of lymphocytes and NK cells were observed in LPs from G-CSF-mobilized patients. The overall number of CD34+ HPCs was the strongest factor for predicting recovery of platelets, whereas the number of myelomonocytic-committed CD34+ precursors was the most powerful independent prognostic factor for WBC and neutrophil recovery. The overall number of CD4+ T cells returned showed an independent prognostic value for predicting the occurrence of infections, during the first year after transplant.

The use of different mobilization regimens modifies the overall number of CD34+ HPCs obtained during leukapheresis procedures, and also affects both the absolute and the relative composition of the LPs in different CD34+ and CD34- cell subsets.

Stem cell doses necessary for engraftment after myelo-ablative therapy as defined for fresh transplants vary largely. Loss of CD34+ cell quality after cryopreservation might contribute to this variation. With a new early apoptosis assay including the vital stain Syto16, together with the permeability marker 7-AAD, CD34+ cell viability in leucapheresis samples of 49 lymphoma patients receiving a BEAM regimen was analysed. After freeze-thawing large numbers of non-viable, early apoptotic cells appeared, leading to only 42% viability compared to 72% using 7-AAD only. Based on this Syto16 staining in the frozen-thawed grafts, threshold numbers for adequate haematological recovery of 2.8-3.0 x 10(6) CD34+ cells/kg body weight determined for fresh grafts, now decreased to 1.2-1.3 x 10(6) CD34+ cells/kg. In whole blood transplantation of lymphoma patients (n = 45) receiving a BEAM-like regimen, low doses of CD34+ cells were sufficient for recovery (0.3-0.4 x 10(6)CD34+ cells/kg). In contrast to freeze-thawing of leucapheresis material, a high viability of CD34+ cells was preserved during storage for 3 days at 4 degrees C, leaving threshold doses for recovery unchanged. In conclusion, the Syto16 assay reveals the presence of many more non-functional stem cells in frozen-thawed transplants than presumed thus far. This led to a factor 2.3-fold adjustment downward of viable CD34+ threshold doses for haematological recovery.

Defining the optimum regimen and time for repeat peripheral blood progenitor cell mobilization would have important clinical applications.

Remobilization with SCF and G-CSF at 2 weeks after an initial mobilization in mice and at 2 or 4 weeks after an initial mobilization in nonhuman primates was examined. In mice, competitive repopulation assays were used to measure long-term progenitor cell-repopulating activity. In monkeys, mobilization of hematopoietic progenitor CFUs was used as a surrogate marker for progenitor cell-repopulating ability.

Efficacy of progenitor cell remobilization differed in the two animal species. In mice, peripheral blood progenitor cell-repopulating ability with repeat mobilization at 2 weeks was 70 percent of that with the initial mobilization. In monkeys, there was no significant difference in peripheral blood progenitor cell mobilization between the initial and the repeat mobilizations at 2 weeks. In mobilizations separated by 4 weeks, however, peripheral blood progenitor cell mobilization was higher than that with initial mobilizations.

In animal models, mobilization of peripheral blood progenitor cells with remobilization after a 2-week interval is similar to or moderately decreased from that with the initial mobilization. Progenitor cell collection at this time point may be useful in certain clinical circumstances. A 4-week interval between remobilizations may be preferable. Clinical trials in humans would be useful to clarify these issues.

Administration of stem cell factor (SCF) has been proven to enhance cytokine-induced mobilization of CD34+ hematopoietic progenitor cells (HPC) into the peripheral blood (PB). The aim of the present study was to explore in a homogeneous group of 22 uniformly treated breast cancer patients: (1) the kinetics of mobilization into PB of both CD34+ and CD34- cell subsets, including dendritic cells, in sequential samples obtained from day +7 up to day +12 after mobilization; and (2) the composition of the CD34+ and CD34- cell subsets present in the two leukapheresis products obtained for each patient. The following CD34+ and CD34- subsets were analyzed: early CD34+ HPC, erythroid-, myeloid- and B-lymphoid-committed CD34+ precursor cells, mature T, B and NK cells, monocytes, neutrophils, eosinophils, basophils, and dendritic cells (DC) including three subsets of lin-/HLADR+DC (CD16+, CD33high and CD123high). Our results show that the absolute number of PB CD34+ HPC progressively increases from day +7 onwards. As far as the CD34- PB leukocyte subsets are concerned, monocytes (CD14+) displayed the earliest recovery after mobilization predicting neutrophil recovery 1 day in advance. The number of CD34+ HPC collected in a single leukapheresis product was always > or = 1.4 x 10(6) cells/kg body weight. No significant changes were observed between the two leukapheresis sessions either as regards their composition in CD34+ HPC subsets or their CD34- leukocyte populations except for a higher ratio of both CD34+ erythroid/CD34+ myeloid HPC (0.35 +/- 0.13 vs 0.30 +/- 0.13; P = 0.04) and neutrophils/monocytes (1.58 +/- 2.1 vs 0.69 +/- 0.27; P = 0.009) found for the first leukapheresis. Interestingly, the overall number of dendritic cells (DC) was higher in the second leukapheresis (1.06 +/- 0.56 vs 1.9 +/- 0.46; P = 0.02) due to a selective increase of the CD16+ antigen-presenting cells. In summary, our results show that the combination of cyclophosphamide, G-CSF and SCF is highly effective for stem cell mobilization, with differences observed in the mobilization kinetics of the different hematopoietic cell subsets analyzed.

Hematopoietic stem cell transplantation has been extensively exploited as a therapeutic and research modality and has revolutionized current patient care. At present, more and more medical centers use peripheral blood progenitor cells for transplantation by mobilizing hematopoietic stem cells from bone marrow to peripheral blood because of potential advantages of peripheral blood stem cell transplantation over bone-marrow transplantation. Different effective mobilization regimens have been developed recently with chemotherapeutic agents, hematopoietic growth factors or their combination. This article reviews current developments related to hematopoietic stem cell mobilization including the biology of hematopoietic stem cells, strategies for mobilization, management for mobilization failure, mechanisms of mobilization, and side effects during mobilization. Finally, the Initiation-Amplification-Emigration-Adaptation Model is proposed to help aid understanding of the mechanisms of hematopoietic stem cell mobilization and to stimulate development of novel and optimal mobilization strategies for patient care.

This randomized, controlled study compared the ability to mobilize and collect an optimal target yield of 5 x 10(6) CD34+ cells/kg using stem cell factor (SCF; 20 microg/kg/day) plus filgrastim (G-CSF; 10 microg/kg/day) vs filgrastim alone (10 microg/kg/day) in 102 patients diagnosed with non-Hodgkin's lymphoma (NHL) or Hodgkin's disease (HD), who were prospectively defined as being heavily pretreated. Leukapheresis began on day 5 of cytokine administration and continued daily until the target yield was reached, or until a maximum of five leukaphereses had been performed. Compared with the filgrastim-alone group (n = 54), the SCF plus filgrastim group (n = 48) showed an increase in the proportion of patients reaching the target yield within five leukaphereses (44% vs 17%, P = 0.002); reduction in the number of leukaphereses required to reach the target yield (P = 0.003); reduction in the proportion of patients failing to reach a minimum yield of 1 x 10(6) CD34+ cells/kg to proceed to transplant (16% vs 26%, P = NS); increase in the median yield of CD34+ cells per leukapheresis (0.73 x 10(6)/kg vs 0.48 x 10(6)/kg, P = 0.04); and an increase in the median total CD34+ cells collected within five leukaphereses (3.6 x 10(6)/kg vs 2.4 x 10(6)/kg, P = 0.05). All patients receiving SCF were premedicated (antihistamines and albuterol), and treatment was generally well tolerated. Five patients experienced severe mast cell-mediated reactions, none of which were life-threatening. In this study of heavily pretreated lymphoma patients, SCF plus filgrastim was more effective than filgrastim alone for mobilizing PBPC for harvesting and transplantation after high-dose chemotherapy.

To explore the influence of dose and schedule on the ability of pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF) to abrogate thrombocytopenia after multiple cycles of chemotherapy and to mobilize peripheral-blood progenitor cells (PBPC).

In this open-label study, 68 patients with advanced cancer were randomized to receive PEG-rHuMGDF subcutaneously at different doses and durations before administration of carboplatin 600 mg/m(2), cyclophosphamide 1,200 mg/m(2), and filgrastim 5 microgram/kg/d. PEG-rHuMGDF was not given after the first cycle of chemotherapy but was given after the second and subsequent cycles. Chemotherapy was given every 28 days for up to six cycles.

In patients who received the same dose of chemotherapy for at least two cycles, the platelet nadir was significantly higher (47.5 x 10(9)/L v 35.5 x 10(9)/L; P =.003) and duration of grade 3 or 4 thrombocytopenia significantly shorter (0 v 3 days; P =.004) when PEG-rHuMGDF was administered after chemotherapy. There was no evidence of an effect of PEG-rHuMGDF when it was given before chemotherapy. Platelet recovery after the first cycle of chemotherapy was no different for different PEG-rHuMGDF regimens, and there was no difference between patients treated with PEG-rHuMGDF and historical controls treated with identical chemotherapy. There was a modest dose-related increase in progenitor cell levels after administration of PEG-rHuMGDF alone. Peak levels of PBPC occurred later in cycle 2 than in cycle 1 but were not different in magnitude.

PEG-rHuMGDF abrogated severe thrombocytopenia after dose-intensive chemotherapy. However, it had only a modest effect on progenitor cell levels and did not enhance progenitor cell mobilization after chemotherapy and filgrastim.

In order to determine the effect of GM-CSF plus G-CSF in combination in breast cancer patients receiving an effective induction regimen, we compared hematological recovery and peripheral blood progenitor cell (PBPC) mobilization according to colony-stimulating factor (CSF) support. Forty-three breast cancer patients were treated by TNCF (THP-doxorubicin, vinorelbine, cyclophosphamide, fluorouracil, D1 to D4) with CSF support: 11 patients received GM-CSF (D5 to D14); 16 patients G-CSF (D5 to D14) and 16 patients GM-CSF (D5-D14) plus G-CSF (D10-D14). Between two subsequent cycles, progenitor cells were assessed daily, from D13 to D17. The WBC count was similar for patients receiving G-CSF alone or GM-CSF plus G-CSF, but significantly greater than that of patients receiving GM-CSF alone (P<0.001). The GM-CSF plus G-CSF combination led to better PBPC mobilization, with significantly different kinetics (P<0.001) and optimal mean values of CFU-GM, CD34+ cells and cells in cycle, at D15 compared to those obtained with G-CSF or GM-CSF alone. The significantly greater PBPC mobilization obtained with a CSF combination by D15 could be of value for PBPC collection and therapeutic reinjection after high-dose chemotherapies.

Fifty-six patients with chemosensitive NHL were studied to assess factors affecting mobilization and peripheral blood stem cell (PBSC) collection: all were mobilized with high-dose cyclophosphamide and etoposide and G-CSF 5 microg/kg/day. None of them had bone marrow involvement at the time of mobilization or a history of extended field irradiation. Previous chemotherapy regimens were divided into two groups: moderately myelotoxic chemotherapy (MMC) and highly myelotoxic chemotherapy (HMC). The adequacy of the PBSC harvest was not associated with age, gender, a past history of bone marrow involvement or disease status. In contrast, the number of MMC cycles (n(MMC)) and the number of HMC cycles (n(HMC)) were both significant (P = 0.009 and P = 0.0004, respectively) and were used to compute a score predictive of a successful PBSC harvest: SCORE = n(MMC) + 4 n(HMC). The estimated successful PBSC collection rate was greater than 80% in patients with a score ranging from 0 to 15 and dropped rapidly to below 20% in patients with a score exceeding 25. This scoring system may help to determine the timing of PBSC mobilization in patients with a score below 15 and suggests that new PBSC mobilization procedures should be investigated in other patients. Bone Marrow Transplantation (2000) 25, 495-499.

To review recent advances in peripheral-blood progenitor-cell (PBPC) transplantation in order to define the optimal cell dose required for autologous and allogeneic transplantation.

A search of MEDLINE was conducted to identify relevant publications. Their bibliographies were also used to identify further articles and abstracts for critical review.

The CD34(+) cell content of a graft is regarded as an accurate predictor of engraftment success. Postchemotherapy autologous PBPC transplantation with >/= 5 x 10(6) CD34(+) cells/kg body weight leads to more rapid engraftment than does transplantation of lower cell doses. Further increases in transplant cell dose further accelerate platelet but not neutrophil engraftment. Evidence that long-term hematopoietic recovery may be more accurately predicted by the subpopulation of primitive progenitors transplanted suggests that the content of CD34(+)CD33(-) and long-term culture-initiating cells in cell collection samples may be important for predicting successful engraftment, particularly in patients with poor mobilization. Allogeneic transplantation has been limited by concerns regarding graft-versus-host disease and the use of hematopoietic growth factors in donors. The risk of graft rejection and engraftment failure after HLA-mismatched allogeneic transplantation may be overcome by intensive chemoradiotherapy and the infusion of large numbers of T cell-depleted hematopoietic stem cells.

An optimal cell dose of >/= 8 x 10(6) CD34(+) cells/kg seems to be recommended for autologous PBPC transplantation. This dose facilitates the administration of scheduled chemotherapy on time and reduces the demand for other supportive therapies. A combination of growth factors may enable patients with poor mobilization to achieve a collection sufficient to allow transplantation. The optimum PBPC dose for allogeneic transplantation remains to be defined.

The CXC chemokine interleukin-8 induces rapid mobilization of hematopoietic progenitor cells in mice and monkeys. Antibodies against the beta 2-integrin leukocyte function-associated antigen-1 completely blocked interleukin-8-induced mobilization. This was not due to a direct effect on the hematopoietic progenitor cells, as leukocyte function-associated antigen-1 was found not to be expressed on hematopoietic progenitor cells. Additional experiments showed that interleukin-8 induces the rapid release of the metalloproteinase gelatinase B, concurrent with the mobilization of hematopoietic progenitor cells. Mobilization could be completely prevented by anti-gelatinase B antibodies. Because neutrophils express leukocyte function-associated antigen-1 and high affinity interleukin-8 receptors, and release gelatinase B upon stimulation with interleukin-8, we hypothesized that neutrophils are key mediators in interleukin-8-induced stem cell mobilization. Further studies showed that mobilization by interleukin-8 was completely absent in mice rendered neutropenic with anti-granulocytic antibodies. Taken together, these data are consistent with an essential role for neutrophils in interleukin-8-induced stem cell mobilization.