Recombinant human thrombopoietin augments mobilization of peripheral blood progenitor cells for autologous transplantation

Efficacy of hematopoietic stem cell mobilization regimens in patients with hematological malignancies: a systematic review and network meta-analysis of randomized controlled trials

BACKGROUND

Efficient mobilization of hematopoietic stem cells (HSCs) from bone marrow niche into circulation is the key to successful collection and transplantation in patients with hematological malignancies. The efficacy of various HSCs mobilization regimens has been widely investigated, but the results are inconsistent.

METHODS

We performed comprehensive databases searching for eligible randomized controlled trials (RCTs) that comparing the efficacy of HSCs mobilization regimens in patients with hematological malignancies. Bayesian network meta-analyses were performed with WinBUGS. Standard dose of granulocyte colony-stimulating factor (G-CSF SD) was chosen as the common comparator. Estimates of relative treatment effects for other regimens were reported as mean differences (MD) or odds ratio (OR) with associated 95% credibility interval (95% CrI). The surface under the cumulative ranking curve (SUCRA) were obtained to present rank probabilities of all included regimens.

RESULTS

Databases searching and study selection identified 44 eligible RCTs, of which the mobilization results are summarized. Then we compared the efficacy of mobilization regimens separately for patients with multiple myeloma (MM) and non-Hodgkin lymphoma (NHL) by including 13 eligible trials for network meta-analysis, involving 638 patients with MM and 592 patients with NHL. For patients with MM, data are pooled from 8 trials for 6 regimens, including G-CSF in standard dose (SD) or reduced dose (RD) combined with cyclophosphamide (CY), intermediate-dose cytarabine (ID-AraC) or plerixafor. The results show that compared with G-CSF SD alone, 3 regimens including ID-AraC + G-CSF SD (MD 14.29, 95% CrI 9.99-18.53; SUCRA 1.00), G-CSF SD + Plerixafor SD (MD 4.15, 95% CrI 2.92-5.39; SUCRA 0.80), and CY + G-CSF RD (MD 1.18, 95% CrI 0.29-2.07; SUCRA 0.60) are associated with significantly increased total number of collected CD34+ cells (× 106/kg), among which ID-AraC + G-CSF SD ranked first with a probability of being best regimen of 100%. Moreover, ID-AraC + G-CSF SD and G-CSF SD + Plerixafor SD are associated with significantly higher successful rate of achieving optimal target (collecting ≥ 4-6 × 106 CD34+ cells/kg). For patients with NHL, data are pooled from 5 trials for 4 regimens, the results show that compared with G-CSF SD alone, G-CSF SD + Plerixafor SD (MD 3.62, 95% CrI 2.86-4.38; SUCRA 0.81) and G-CSF SD plus the new CXC chemokine receptor-4 (CXCR-4) antagonist YF-H-2015005 (MD 3.43, 95% CrI 2.51-4.35; SUCRA 0.69) are associated with significantly higher number of total CD34+ cells collected. These 2 regimens are also associated with significantly higher successful rate of achieving optimal target. There are no significant differences in rate of achieving optimal target between G-CSF SD + Plerixafor SD and G-CSF + YF-H-2015005.

CONCLUSIONS

In conclusion, ID-AraC plus G-CSF is associated with the highest probability of being best mobilization regimen in patients with MM. For patients with NHL, G-CSF in combination with plerixafor or YF-H-2015005 showed similar improvements in HSCs mobilization efficacy. The relative effects of other chemotherapy-based mobilization regimens still require to be determined with further investigations.

Recombinant Human Thrombopoietin Accelerates the Recovery of Platelet in Patients With Lower-Risk Myelodysplastic Syndrome: A Proof-of-Concept Study

Aim

The effect of recombinant human thrombopoietin (rhTPO) is largely unknown in lower-risk myelodysplastic syndrome (LR-MDS). This study aimed at investigating the safety and efficacy of rhTPO in patients with LR-MDS.

Methods

LR-MDS patients receiving stanozolol (2 mg, t.i.d.) and supportive care alone (non-rhTPO) or additional rhTPO were enrolled in this study prospectively. rhTPO was given at 15,000 U (q.d.) for 7 days/month for at least 3 months. Patients stopped rhTPO if the platelet count was higher than 50 × 10⁹/L or had no effects after 3 months of treatment. The overall response (OR), complete response (CR), platelet response, side effects, clone evolution, and clinical outcome were evaluated.

Result

Thirty-five patients were enrolled: 20 (57.1%) patients in the rhTPO group and 15 (42.9%) patients in the non-rhTPO group. The demographic and baseline characteristics were balanced between the two groups. Platelet response was higher at 1 and 2 months as compared with that in the non-rhTPO group (p = 0.006 and p = 0.001, respectively). Meanwhile, the rhTPO group had a shorter time to achieve a platelet transfusion-free state compared with the non-rhTPO group (p = 0.034). Hematologic response was higher at 1 and 2 months compared with that in the non-rhTPO group (p = 0.006 and p = 0.001, respectively). There was no significant difference in the overall response or complete response at 1, 2, 3, 6, and 12 months between the two groups. One patient in the rhTPO group evolved into higher-risk MDS at 9 months. No significant difference in disease progression, infection, gastrointestinal disorders, or drug-related liver/renal injuries was found between the two groups (p > 0.05).

Conclusion

Adding short-term rhTPO can accelerate the early platelet response and decrease platelet transfusion, with no obvious side effects.

Clinical Trial Registration

https://clinicaltrials.gov/ct2/show/NCT04324060?cond=NCT04324060&draw=2, identifier NCT04324060

Recombinant human thrombopoietin prior to mobilization chemotherapy facilitates platelet recovery in autologous transplantation in patients with lymphoma: Results of a prospective randomized study

Background

Chemotherapy plus granulocyte colony-stimulating factor (GCSF) regimen is one of the available approaches to mobilize peripheral blood progenitor cells (PBPCs). It causes thrombocytopenia and delays leukapheresis. This study aimed to evaluate the role of recombinant human thrombopoietin (rhTPO) before mobilization chemotherapy in facilitating leukapheresis in patients with lymphoma.

Methods

In this randomized open-label phase 2 trial, patients were randomly assigned in a 1:2 ratio to receive mobilization with rhTPO plus GCSF in combination with chemotherapy (the rhTPO plus GCSF arm) or GCSF alone in combination with chemotherapy (the GCSF alone arm). The recovery of neutrophils and platelets and the amount of platelet transfusion were monitored.

Results

Thirty patients were enrolled in this study between March 2016 and August 2018. Patients in the rhTPO plus GCSF arm (n = 10) had similar platelet nadir after mobilization chemotherapy (P=0.878) and similar amount of platelet transfusion (median 0 vs. 1 unit, P=0.735) when compared with the GCSF alone arm (n = 20). On the day of leukapheresis, the median platelet count was 86 × 10⁹/L (range 18–219) among patients who received rhTPO and 73 × 10⁹/L (range 42–197) among those who received GCSF alone (P=0.982). After the use of rhTPO, the incidence of platelet count <75 × 10⁹/L on the day of leukapheresis did not decrease significantly (30.0% vs. 50.0%, P=0.297). Platelet recovery after PBPC transfusion was more rapid in the rhTPO plus GCSF arm (median 8.0 days [95% confidence interval 2.9–13.1] to platelets ≥50 × 10⁹/L vs. 11.0 days [95% confidence interval 8.6–13.4], P=0.011). The estimated total cost of the mobilization and reconstitution phases per patient was similar between the two treatmtent groups (P=0.362 and P=0.067, respectively).

Conclusions

Our findings indicate that there was no significant clinical benefit of rhTPO use in facilitating mobilization of progenitor cells, but it may promote platelet recovery in the reconstitution phase after high-dose therapy.

Trial registration

This trial has been registered in Clinicaltrials.gov as NCT03014102.

Recombinant human thrombopoietin combined with interleukin-2 improves the effects of chemosensitivity and thrombocytopenia on a basic gemcitabine and carboplatin combination therapy for non-small cell lung cancer in a nude mouse model

Background

To investigate the effects of recombinant human thrombopoietin (rhTPO) and interleukin-2 (IL-2) on a basic gemcitabine (GEM) plus carboplatin (GC) treatment regimen in a murine lung carcinoma model.

Methods

Fifty nude mice with subcutaneous tumors derived from human lung cancer cells were divided into 5 groups, each comprised of 10 mice: A blank group (intraperitoneal injection of saline), a control group (GC) (intraperitoneal injections of GC), a rhTPO group (same as the control group plus subcutaneous injection of rhTPO), an IL-2 group (same as the control group plus subcutaneous injection of IL-2) and a rhTPO + IL-2 group (same as the rhTPO group plus subcutaneous injection of IL-2). Tumor development and histology as well as CD4+, phosphorylated-adenosine monophosphate-activated protein kinase (p-AMPK), phosphorylated-protein kinase B (p-AKT), phosphorylated-extracellular signal-regulated kinase (p-ERK), phosphorylated-phosphoinositide 3-kinase (p-pI3K) and GTPase RAS1 expression in tumor tissues were measured and blood analyses performed.

Results

Tumor sizes from all treated mice were significant smaller than the controls, as were the tumors of IL-2 plus GC treated mice compared to other treated groups. CD4+ expressing cells were increased in tumors after IL-2 and rhTPO treatment and the application of rhTPO significantly restored the blood platelet count. The expression of p-AMPK, p-AKT, p-ERK, p-pI3K and RAS1 in tumor cells were all significantly diminished after the addition of rhTPO and IL-2 to the GC regimen.

Conclusions

The supplementation of rhTPO and IL-2 to a GC regime effectively reduced tumor sizes and restored the platelet count in a human lung cancer mouse model.

rhTPO combined with chemotherapy and G-CSF for autologous peripheral blood stem cells in patients with refractory/relapsed non-Hodgkin's lymphoma

Objective

The mobilization and collection of sufficient autologous peripheral blood stem cells (APBSCs) are important for the fast and sustained reconstruction of hematopoietic function after autologous transplantation. This study aims to evaluate the mobilization effect and safety of thrombopoietin (TPO) combined with chemotherapy + G-CSF for APBSCs in patients with refractory/relapsed non-Hodgkin’s lymphoma.

Methods

A total of 78 patients were included in the present study. After receiving mobilization chemotherapy, all patients were randomly divided into two groups: TPO group (n=40), patients were given subcutaneous injection of rhTPO + G-CSF, and control group (n=38), patients were given subcutaneous injection of G-CSF. The primary endpoint was the total number of obtained CD34+ cells. The secondary endpoints were the mononuclear cell count, the proportion of target and minimum mobilization, the engraftment time of neutrophils and platelets after APBSCT, the number of platelet and red blood cell infusions, the incidence of infectious fever and fever duration, and TPO-related side effects in patients.

Results

TPO participation significantly increased the total CD34+ cell count. A higher proportion of patients in the TPO group achieved the minimum and target CD34+ cells, when compared to the control group. TPO-related adverse events were not observed in either of these groups. In addition, there were no significant differences in engraftment time, the number of platelet and red blood cell transfusions, the incidence of infectious fever, and fever duration between these two groups.

Conclusion

TPO combined with chemotherapy + G-CSF can safely and effectively enhance the mobilization effect for APBSCs in patients with refractory/relapsed non-Hodgkin’s lymphoma.

Recombinant human thrombopoietin improves the efficacy of intermediate-dose cyclophosphamide plus granulocyte colony-stimulating factor in mobilizing peripheral blood stem cells in patients with multiple myeloma: A cohort study

The combination of intermediate-dose cyclophosphamide (ID-CTX) and granulocyte colony-stimulating factor (G-CSF) fails to mobilize peripheral blood stem cells (PBSCs) in approximately 20% of treated patients with multiple myeloma (MM).In this cohort study, patients with MM underwent PBSC mobilization with either an ID-CTX plus G-CSF plus recombinant human thrombopoietin (rhTPO) regimen (72 patients; TPO group), or an ID-CTX plus G-CSF regimen (70 patients; non-TPO group).In the TPO group, the median CD34+ harvest was 5.36 × 10 per kg of body weight (0.50-22.39 × 10 per kg of body weight), with a harvest success rate of 91.7% (66/72), and an excellence rate of 55.6% (40/72). In the non-TPO group, the median CD34+ harvest was 3.30 × 10 per kg of body weight (0.20-21.14 × 10 per kg of body weight), with a harvest success rate of 75.7% (53/70), and an excellence rate of 25.7% (18/70). The median count of the CD34+ cells collected, success rate of collection, and excellence rate of collection were significantly higher in the TPO group than in the non-TPO group (P=.0001, P=.01, and P = .0001, respectively). Time to granulocyte and platelet engraftment was faster among patients in the TPO group than that in those from the non-TPO group. No platelet engraftment delay (>21 days) was observed among patients in the TPO group, while 3 patients in the non-TPO group displayed delayed platelet engraftment.Adding rhTPO to the ID-CTX chemotherapy plus G-CSF regimen improved treatment efficacy in mobilizing PBSCs for autologous hematopoietic stem cell transplantation.

Management of mobilization failure in 2017

In contemporary clinical practice, almost all allogeneic transplantations and autologous transplantations now capitalize on peripheral blood stem cells (PBSCs) as opposed to bone marrow (BM) for the source of stem cells. In this context, granulocyte colony-stimulating factor (G-CSF) plays a pivotal role as the most frequently applied frontline agent for stem cell mobilization. For patients classified as high-risk, chemotherapy based mobilization regimens can be preferred as a first choice and it is notable that this also used for remobilization. Mobilization failure occurs at a rate of 10%-40% with traditional strategies and it typically leads to low-efficiency practices, resource wastage, and delayed in treatment intervention. Notably, however, several factors can impact the effectiveness of CD34⁺ progenitor cell mobilization, including patient age and medical history (prior chemotherapy or radiotherapy, disease and marrow infiltration at the time of mobilization). In recent years, main (yet largely ineffective) approach was to increase G-CSF dose and add SCF, but novel and promising pathways have been opened up by the synergistic impact of a reversible inhibitor of CXCR4, plerixafor, with G-CSF. The literature shows to its favorable results in upfront and failed mobilizers, and it is necessary to use plerixafor (or equivalent agents) to optimize HSC harvest in poor mobilizers. Different CXCR4 inhibitors, growth hormone, VLA4 inhibitors, and parathormone, have been cited as new agents for mobilization failure in recent years. In view of the above considerations, the purpose of this paper is to examine the mobilization of PBSC while focusing specifically on poor mobilizers.

New agents in HSC mobilization

Mobilized peripheral blood (PB) is the most common source of hematopoietic stem cells (HSC) for autologous transplantation. Granulocyte colony stimulating factor (G-CSF) is the most commonly used mobilization agent, yet despite its widespread use, a considerable number of patients still fail to mobilize. Recently, a greater understanding of the interactions that regulate HSC homeostasis in the bone marrow (BM) microenvironment has enabled the development of new molecules that mobilize HSC through specific inhibition, modulation or perturbation of these interactions. AMD3100 (plerixafor), a small molecule that selectively inhibits the chemokine receptor CXCR4 is approved for mobilization in combination with G-CSF in patients with Non-Hodgkin's lymphoma and multiple myeloma. Nevertheless, identifying mobilization strategies that not only enhance HSC number, but are rapid and generate an optimal "mobilized product" for improved transplant outcomes remains an area of clinical importance. In recent times, new agents based on recombinant proteins, peptides and small molecules have been identified as potential candidates for therapeutic HSC mobilization. In this review, we describe the most recent developments in HSC mobilization agents and their potential impact in HSC transplantation.

The current status in hematopoietic stem cell mobilization

Hemotopoietic stem cell mobilization with cytokines alone, has still been widely accepted as the initial attempt for stem cell mobilization. Chemotherapy based mobilization can be preferred as first choice in high risk patients or for remobilization. But mobilization failure still remains to be a problem in one third of patients. Salvage mobilization strategies have been composed to give one more chance to 'poor mobilizers'. Synergistic effect of a reversible inhibitor of CXCR4, plerixafor, with G-CSF has opened a new era for these patients. Preemptive approach in predicted poor mobilizers, immediate salvage approach for patients with suboptimal mobilization or remobilization approach of plerixafor in failed mobilizers have all been demonstrated convincing results in various studies. Alternative CXCR4 inhibitors, VLA4 inhibitors, bortezomib, parathormone have also been emerged as novel agents for mobilization failure.

Thrombopoietic cytokine and P-selectin levels in patients with multiple myeloma undergoing autologous stem cell transplantation: decrease in posttransplantation P-selectin levels might predict the degree of maximum response

PURPOSE

This study was designed to determine the pretransplantation levels of thrombopoietic cytokines, which have a fundamental role in both megakaryopoiesis and myeloma pathogenesis and P-selectin in patients with multiple myeloma undergoing autologous hematopoietic stem cell transplantation (AHSCT) and to correlate the cytokine levels with time to platelet recovery. The effect of AHSCT on the levels of the cytokines and its correlation with maximum disease response was also investigated.

PATIENTS AND METHODS

The levels of thrombopoietin, interleukin (IL)-6, IL-11, IL-1beta, and P-selectin was measured before and 30 days after AHSCT in 32 patients with a median age of 55 years. The median time to platelet recovery was day +11 (range, 0-14 days) without any significant correlation with pretransplantation cytokine levels.

RESULTS

No significant change was observed in thrombopoietic cytokines after AHSCT, whereas serum P-selectin levels showed a significant decrease after AHSCT (P = .001). The decrease in P-selectin was found to be significant in patients who achieved complete remission (P1 = .008) and partial remission (P2 = .018) early after AHSCT. Our data suggest that the level of thrombopoietic cytokines does not have a role in time to platelet recovery.

CONCLUSION

The change in P-selectin levels early after transplantation could be a surrogate marker in determining the maximum posttransplantation response.

Lesion-targeted thrombopoietin potentiates vasculogenesis by enhancing motility and enlivenment of transplanted endothelial progenitor cells via activation of Akt/mTOR/p70S6kinase signaling pathway

Thrombopoietin (TPO), a physiological regulator of megakaryocyte and platelet development, is a multifunctional positive regulator in early hematopoiesis by hematopoietic stem cells. In this study, we investigated the effect of TPO on endothelial progenitor cells (EPCs) for therapeutic vasculogenesis in vitro and in vivo, and the intracellular signaling mechanism exerting the activity of EPCs. 7-day culture-expanded EPCs derived from human peripheral blood mononuclear cells were applied to each assay. Flow cytometry demonstrated the expression of c-Mpl, the receptor of TPO, in cultured EPCs. In vitro experiments revealed enhanced migration and survival of cultured EPCs by TPO. In vivo, TPO was intramuscularly administered into the foci of ischemic hindlimbs in athymic nude mice, immediately followed by intravenous injection of cultured EPCs, to assess the booster effect of TPO on vascular regeneration. At day 4 post-transplantation, transplanted EPCs were 1.7-fold higher in TPO-treated animals compared to control. At day 28, blood perfusion was recovered in the TPO-treated group, accompanied by an increase in microvascular density. The signaling transduction pathway underlying TPO-mediated activities of cultured EPCs was assessed by Western blotting. TPO induced sequential phosphorylations of Akt to p70S6kinase through mTOR. Inhibition of the PI3-kinase/Akt/mTOR/p70S6kinase signaling pathway negated the biological functions of cultured EPCs, either migration (by LY294002 for PI3-kinase and Rapamycin for mTOR) or survival and tubulogenesis (by Rapamycin). These findings provide evidence that TPO possesses booster potential for therapeutic vasculogenesis, by activating the PI3-kinase/Akt/mTOR/p70S6kinase pathway crucial to the biological activities of EPCs.

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

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

Human thrombopoietin reduces myocardial infarct size, apoptosis, and stunning following ischaemia/reperfusion in rats

AIMS

Thrombopoietin (Tpo) is known for its ability to stimulate platelet production. However, it is currently unknown whether Tpo plays a physiological function in the heart.

METHODS AND RESULTS

We assessed the potential protective role of Tpo in vitro and in vivo in two rat models of myocardial ischaemia/reperfusion. Tpo receptor (c-mpl) message was detected in the heart using RT-PCR, and the Tpo receptor protein was detected using western blotting and immunohistochemistry. Tpo treatment immediately before ischaemia reduced myocardial necrosis, apoptosis, and decline in ventricular function following ischaemia/reperfusion in the rat in a concentration- and dose-dependent manner with an optimal concentration of 1.0 ng/mL in vitro and an optimal dose of 0.05 microg/kg iv in vivo. Tpo also reduced infarct size when given after the onset of ischaemia or at reperfusion. Tpo activated JAK-2 (Janus kinase-2) and p44 MAPK (mitogen-activated protein kinase) during reperfusion but not prior to ischaemia. Inhibition of JAK-2 (AG-490), p42/44 MAPK (PD98059), mitochondrial K(ATP) channels (5-HD), and sarcolemmal K(ATP) channels (HMR 1098) abolished Tpo-induced resistance to injury from myocardial ischaemia/reperfusion. AG-490, PD98059, 5-HD, and HMR1098 alone had no effect on cardioprotection. Treatment with a single dose of Tpo (0.05 or 1.0 microg/kg iv) did not result in the elevation of platelet count or haematocrit over a 16-day period.

CONCLUSION

A single treatment of Tpo confers cardioprotection through JAK-2, p42/44 MAPK, and K(ATP) channels, suggesting a potential therapeutic role of Tpo in the treatment of injury resulting from myocardial ischaemia and reperfusion.

Mobilization, collection, and immunomagnetic selection of peripheral blood CD34 cells in recovered aplastic anemia patients

BACKGROUND

Most patients with severe aplastic anemia (sAA) respond to immunosuppression, but a significant number relapse or develop clonal abnormalities such as paroxysmal nocturnal hemoglobinuria, myelodysplasia, or leukemia. In principle, patients without matched sibling donors and older patients might benefit from transplantation of autologous hematopoietic peripheral blood progenitor cells (PBPCs) obtained during remission. Even patients who have clinically recovered from aplastic anemia have diminished hematopoietic progenitor cells, so the practicability of PBPC mobilization in these individuals is unknown.

STUDY DESIGN AND METHODS

The feasibility of PBPC mobilization in nine patients with a history of sAA was evaluated. Granulocyte-colony-stimulating factor (10 microg/kg) was administered subcutaneously for 5 days and followed by a 12-L leukapheresis procedure.

RESULTS

Only two of the nine patients had sufficient mobilization of CD34 cells to merit collection; in these cases sufficient CD34 cells were obtained for autologous transplantation should the need arise.

CONCLUSION

PBPC collection is feasible only in a fraction of recovered AA patients.

Hematopoietic growth factors for hematopoietic stem cell mobilization and expansion

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.

Mobilizing stem cells from normal donors: is it possible to improve upon G-CSF?

Currently, granulocyte colony stimulating factor (G-CSF) remains the standard mobilizing agent for peripheral blood stem cell (PBSC) donors, allowing the safe collection of adequate PBSCs from the vast majority of donors. However, G-CSF mobilization can be associated with some significant side effects and requires a multi-day dosing regimen. The other cytokine approved for stem cell mobilization, granulocyte-macrophage colony stimulating factor (GM-CSF), alters graft composition and may reduce the development of graft-versus-host disease, but a significant minority of donors fails to provide sufficient CD34+ cells with GM-CSF and some experience unacceptable toxicity. AMD3100 is a promising new mobilizing agent, which may have several advantages over G-CSF for donor mobilization. As it is a direct antagonist of the interaction between the chemokine stromal-derived factor-1 and its receptor CXCR4, AMD3100 mobilizes PBSCs within hours rather than days. It is also well tolerated, with no significant side effects reported in any of the clinical trials to date. Studies of autologous and allogeneic transplantation of AMD3100 mobilized grafts have demonstrated prompt and stable engraftment. Here, we review the current state of stem cell mobilization in normal donors and discuss novel strategies for donor stem cell mobilization.

Clinical approaches involving thrombopoietin to shorten the period of thrombocytopenia after high-dose chemotherapy

High-dose chemotherapy followed by a peripheral blood stem cell transplant is successfully used for a wide variety of malignancies. A major drawback, however, is the delay in platelet recovery. Several clinical strategies using thrombopoietin (Tpo) have been developed in an attempt to speed up platelet repopulation. In contrast to its success in immune thrombocytopenia and in low-dose toxic chemotherapeutic regimens, Tpo appears less effective in the case of high-dose chemotherapy and peripheral blood stem cell transplant. To develop a successful therapeutic approach, more knowledge is needed on several aspects of megakaryocyte (progenitor) biology, such as homing to the bone marrow, endomitosis, and platelet formation. Interactions of the megakaryocytes with the marrow vasculature and the microvascular microenvironment are other key factors for optimal thrombocytopoiesis. The present report reviews the background of the inefficiency of Tpo after intensive chemotherapy and describes possible strategies that might lead to successful therapies to treat chemotherapy-induced thrombocytopenia.