Impact of plerixafor use in the mobilization of blood grafts for autologous hematopoietic cell transplantation

Plerixafor (PLER), a reversible antagonist of the CXC chemokine receptor type 4, has been in clinical use for mobilization of blood grafts for autologous hematopoietic cell transplantation (AHCT) for about 15 years. Initially PLER was investigated in placebo-controlled trials with the granulocyte colony-stimulating factor (G-CSF) filgrastim. It has also been used in combination with chemotherapy plus G-CSF in patients who had failed a previous mobilization attempt or appeared to mobilize poorly with current mobilization (preemptive use). This review summarizes what is known regarding addition of PLER to standard mobilization regimens. PLER increases mobilization of CD34+ cells, decreases the number of apheresis sessions needed to achieve collection targets and increases the proportion of patients who can proceed to AHCT. It appears also to increase the amount of various lymphocyte subsets in the grafts collected. In general, hematologic recovery after AHCT has been comparable to patients mobilized without PLER, although slower platelet recovery has been observed in some studies of patients who mobilize poorly. In phase III studies, long-term outcome has been comparable to patients mobilized without PLER. This also appears to be the case in patients receiving plerixafor for poor or suboptimal mobilization of CD34+ cells. In practice, PLER is safe and has not been shown to increase tumor cell mobilization.

Stem cell mobilizating effect of heparin in patients undergoing autologous stem cell transplantation

BACKGROUND

Adequate stem cell collection is essential for successful stem cell transplantation. Heparin enhances stem cell mobilization by competing with heparin sulfate proteoglycans. Heparin is also used as an anticoagulant before leukapheresis. Here, we evaluated the effects of heparin on stem cell mobilization in patients who underwent autologous stem cell transplantation (ASCT).

METHODS

We evaluated patients who underwent ASCT. Patients were divided into two groups: those who received heparin plus citrate (heparinized patients) and those who received citrate only (nonheparinized patients) for anticoagulation. Univariate and multivariate analyses were also performed. The collection efficiency 2 (CE2) for CD34+ cells was calculated and compared between heparinized and nonheparinized patients.

RESULTS

This study included 1017 patients. There were 478 (47%) heparinized and 539 (53%) nonheparinized patients. The number of collected CD34+ cells was significantly higher in heparinized patients (P < .00001). The multivariate analyses showed that using heparin was an independent positive factor for collected CD34+ cells (adj-R2  = 0.744; F = 369.331, P < .00001). CE2 was significantly higher in heparinized patients than in nonheparinized patients (66.8% vs 52.1%; P < .00001). The rate of collecting at least 2 × 106 /kg CD34+ cells was 3.3 times higher for heparinized patients in poor mobilizers (P < .00001). Heparinized patients had significantly higher total nucleated and mononuclear cell counts (P < .00001 and <.00001, respectively).

CONCLUSION

Heparin enhances stem cell collection and increases CE2. The use of heparin may reduce the need for other strategies to increase stem cell mobilization.

Mobilization Strategies in Myeloma Patients Intended for Autologous Hematopoietic Cell Transplantation

Background

Multiple myeloma is currently the leading indication for autologous hematopoietic cell transplantation (AHCT). A prerequisite for AHCT is mobilization and collection of adequate blood graft to support high-dose therapy. Current mobilization strategies include granulocyte colony-stimulating factor (G-CSF) alone or in combination with chemotherapy most commonly cyclophosphamide (CY). More recently, plerixafor has become into agenda especially in patients who mobilize poorly. In the selection of a mobilization method, several factors should be considered.

Summary

Preplanned collection target is important as G-CSF plus plerixafor is more effective in the mobilization of CD34+ cells than G-CSF alone. On the other hand, CY plus G-CSF is superior to G-CSF only mobilization. Previous therapy and age of the patients are important considerations as G-CSF alone may not be effective enough in patients with risk factors for poor mobilization. These factors include extensive lenalidomide exposure, irradiation to bone marrow-bearing sites, higher age, or a previous mobilization failure. Also, local preferences and experiences as well as the number of apheresis needed are important issues as well as cost-effectiveness considerations. Mobilization method used may have implication for cellular composition of collected grafts, which might have an impact on posttransplant events such as hematologic and immune recovery in addition to also potential long-term outcomes.

Key Message

Currently, G-CSF alone and preemptive plerixafor if needed might be considered as a standard mobilization strategy in MM patients intended for AHCT.

Flow Cytometric Characterization of Hematopoietic Stem and Progenitor Cell Subpopulations in Autologous Peripheral Blood Stem Cell Preparations after Cryopreservation

Introduction

Autologous stem cell transplantation is a successful routine procedure with only a small number of non-engraftment cases, although the time to hematopoietic recovery may vary considerably across patients. While CD34 has been the decisive marker for enumerating hematopoietic stem and progenitor cells (HSPCs) for more than 30 years, the impact of CD34-positive cellular subpopulations in autologous HSPC grafts on hematopoietic reconstitution remains unclear.

Methods

The two-color ISHAGE protocol represents the current gold standard for CD34+ cell enumeration but includes only the number of viable CD45+/CD34+ cells relative to the body weight of the recipient. We adapted a multicolor flow cytometry marker panel for advanced characterization of CD34 subpopulations in retained samples of autologous peripheral blood stem cell products (n = 49), which had been cryostored for a wide range from 4 to 15 years. The flow cytometric analysis included CD10, CD34, CD38, CD45, CD45RA, CD133, and viability staining with 7AAD. The findings were correlated with clinical engraftment data, including reconstitution of leukocytes, neutrophils, and platelets after transplantation (TPL).

Results

We demonstrated that the identification of autologous HSPC subpopulations by flow cytometry after cryopreservation is feasible. Regarding the distribution of HSPC subpopulations, a markedly different pattern was observed in comparison to previously published data obtained using fresh autologous material. Our data revealed the largest ratio of lympho-myeloid progenitors (LMPPs) after freezing and thawing, followed by multipotent progenitors and erythroid-myeloid progenitors. A high ratio of LMPPs, representing an immature stage of differentiation, correlated significantly with early neutrophilic granulocyte and leukocyte engraftment (p = 0.025 and p = 0.003). Conversely, a large ratio of differentiated cells correlated with late engraftment of neutrophilic granulocytes (p = 0.024). Overall, successful engraftment was documented for all patients.

Conclusion

We established an advanced flow cytometry panel to assess the differentiation ability of cryostored autologous peripheral blood stem cell grafts and correlated it with timely hematopoietic reconstitution. This approach represents a novel and comprehensive way to identify hematopoietic stem and progenitor subpopulations. It is a feasible way to indicate the engraftment capacity of stem cell products.

Innovations in hematopoietic stem-cell mobilization: a review of the novel CXCR4 inhibitor motixafortide

Hematopoietic stem-cell transplantation (HCT) and stem-cell-based gene therapies rely on the ability to collect sufficient CD34+ hematopoietic stem and progenitor cells (HSPCs), typically via peripheral blood mobilization. Commonly used HSPC mobilization regimens include single-agent granulocyte colony-stimulating factor (G-CSF), plerixafor, chemotherapy, or a combination of these agents. These regimens, however, frequently require multiple days of injections and leukapheresis procedures to collect adequate HSPCs for HCT (minimum = >2 × 106 CD34+ cells/kg; optimal = 5-6 × 106 CD34+ cells/kg). In addition, these regimens frequently yield suboptimal CD34+ HSPC numbers for HSPC-based gene-edited therapies, given the significantly higher HSPC number needed for successful gene-editing and manufacturing. Meanwhile, G-CSF is associated with common adverse events such as bone pain as well as an increased risk of rare but potentially life-threatening splenic rupture. Moreover, G-CSF is unsafe in patients with sickle-cell disease, a key patient population that may benefit from autologous HSPC-based gene-edited therapies, where it has been associated with unacceptable rates of serious vaso-occlusive and thrombotic events. Motixafortide is a novel CXCR4 inhibitor with extended in vivo activity (>48 h) that has been shown in preclinical and clinical trials to rapidly mobilize robust numbers of HSPCs in preparation for HCT, while preferentially mobilizing increased numbers of more primitive HSPCs by immunophenotyping and single-cell RNA expression profiling. In this review, we present a history of stem-cell mobilization and update of recent innovations in novel mobilization strategies with a specific focus on the development of motixafortide, a long-acting CXCR4 inhibitor, as a novel HSPC mobilizing agent.

Evaluation of CD34+ Cell Count at Different Time Points Following Plerixafor Administration in Autologous Hematopoietic Stem Cell Transplantation

Background: In apheresis, collecting an adequate number of CD34+ cells is required for successful autologous hematopoietic stem cell transplantation (auto-HSCT) procedure. It is difficult to harvest a sufficient number of stem cells in certain patients due to their old age and history of intensive chemotherapy. Plerixafor could mobilize stem cells and facilitate peripheral blood hematopoietic stem cell collection. However, not enough information is available on the appropriate time intervals from plerixafor administration to apheresis. Objectives: In this study, we aimed at evaluating the level of peripheral blood CD34+ cells at plerixafor administration time and every three hours to identify the peak time of circulating CD34+ cells. Methods: Circulating CD34+ cells were enumerated by flow cytometry on day 4 post mobilization. Plerixafor was administered to patients with poor mobilization based on the count of peripheral blood hematopoietic stem cells. The number of circulating CD34+ cells was evaluated before and 3, 6, 9, and 12 hours after plerixafor administration to assess the time it takes for stem cells to reach their peak level. Results: The highest level of stem cell concentration was found in 9 hours after plerixafor administration with an increasing trend. A statistically significant relationship was also observed between factors including platelet count on the first day of GCSF injection and the day of stem cell infusion, leukocyte count on admission, and basal levels of CD34+ cells in peripheral blood and the amount of harvested stem cells. Conclusions: We demonstrated that plerixafor causes an incremental trend in CD34+ cells mobilization, reaching its peak after 9 hours. Further research should be performed to provide insights into graft cells’ population and hematologic and immunological recovery.

Development of a quantitative prediction model for peripheral blood stem cell collection yield in the plerixafor era

BACKGROUND AIMS

Predicting autologous peripheral blood stem cell (PBSC) collection yield before leukapheresis is important for optimizing PBSC mobilization and autologous stem cell transplantation (ASCT) for treating hematological malignancies. Although guidelines for plerixafor usage based on peripheral blood CD34⁺ (PB-CD34⁺) cell count are available, their predictive performance in the real world remains unclear.

METHODS

This study retrospectively analyzed 55 mobilization procedures for patients with non-Hodgkin lymphoma or multiple myeloma and developed a novel quantitative prediction model for CD34⁺ cell collection yield that incorporated four clinical parameters available the day before leukapheresis; namely, PB-CD34⁺ cell count the day before apheresis (day -1 PB-CD34⁺), number of prior chemotherapy regimens, disease status at apheresis and mobilization protocol.

RESULTS

The effects of PB-CD34⁺ cell counts on CD34⁺ cell collection yield varied widely per patient characteristics, and plerixafor usage was recommended in patients with poorly controlled disease or those with a history of heavy pre-treatments even with abundant day -1 PB-CD34⁺ cell count. This model suggested a more proactive use of plerixafor than that recommended by the guidelines for patients with poor pre-collection condition or those with a higher target number of CD34⁺ cells. Further, the authors analyzed the clinical outcomes of ASCT and found that plerixafor use for stem cell mobilization did not affect short- or long-term outcomes after ASCT.

CONCLUSIONS

Although external validations are necessary, the results can be beneficial for establishing more effective and safer mobilization strategies.

Use of plerixafor to mobilize haematopoietic progenitor cells in healthy donors

Increased transplant activity calls for improved stem cell collection, especially when peripheral blood is the preferred source of haematopoietic progenitor cells (HPCs). Plerixafor is a bicyclam molecule that mobilizes CD34+ cells by reversibly disrupting CXCR4-CXCL12-supported HPC retention. Plerixafor is given with granulocyte colony-stimulating factor (G-CSF) to help harvest autologous CD34+ cells for transplantation when mobilization with G-CSF fails. Mobilization protocols with the same doses of plerixafor and G-CSF have been used off-label in healthy allogeneic donors, with equal success and scarce side effects, both in adult and paediatric patients. Plerixafor has also been used as a sole mobilization agent. Plerixafor alone or coupled with G-CSF might lead to harvesting distinct cellular populations conferring improved engraftment properties and increased survival. Those characteristics might make plerixafor an especially attractive mobilization agent, particularly for non-related donations. However, available data are limited, and long-term follow-up is needed to clarify the best scenario for using plerixafor with or without G-CSF in healthy donors. In this review, we will summarize the evidence supporting this practice, highlighting the practical aspects and providing clues for an expanded use of plerixafor.

Optimizing leukapheresis product yield and purity for blood cell-based gene and immune effector cell therapy

PURPOSE OF REVIEW

A critical common step for blood-based ex-vivo gene and immune effector cell (IEC) therapies is the collection of target cells for further processing and manufacturing, often accomplished through a leukapheresis procedure to collect mononuclear cells (MNCs). The purpose of this review is to describe strategies to optimize the apheresis product cell yield and purity for gene and IEC therapies. Relevant data from the conventional bone marrow transplant literature is described where applicable.

RECENT FINDINGS

Product yield is affected by three main factors: the peripheral blood concentration of the target cell, optimized by mobilizing agents, donor interventions or donor selection; the volume of peripheral blood processed, tailored to the desired product yield using prediction algorithms; and target cell collection efficiency, optimized by a variety of device and donor-specific considerations. Factors affecting product purity include characteristics of the donor, mobilizing agent, device, and device settings.

SUMMARY

Strategies to optimize product yield and purity for gene and IEC therapies are important to consider because of loss of target cell numbers or function with downstream steps and detrimental effects of nontarget cells on further manufacturing and patient outcome.

Engraftment after autologous hematopoietic stem cell transplantation in patients mobilized with Plerixafor: A retrospective, multicenter study of a large series of patients

Plerixafor (PLX) appears to effectively enhance hematopoietic stem-cell mobilization prior to autologous hematopoietic stem cell transplantation (auto-HCT). However, the quality of engraftment following auto-HCT has been little explored. Here, engraftment following auto-HCT was assessed in patients mobilized with PLX through a retrospective, multicenter study of 285 consecutive patients. Information on early and 100-day post-transplant engraftment was gathered from the 245 patients that underwent auto-HCT. The median number of PLX days to reach the stem cell collection goal (≥2 × 10⁶ CD34⁺ cells/kg) was 1 (range 1-4) and the median PLX administration time before apheresis was 11 h (range 1-18). The median number of apheresis sessions to achieve the collection goal was 2 (range 1-5) and the mean number of CD34⁺ cells collected was 2.95 × 10⁶/kg (range 0-30.5). PLX administration was safe, with only 2 mild and transient gastrointestinal adverse events reported. The median time to achieve an absolute neutrophil count (ANC) >500/μL was 11 days (range 3-31) and the median time to platelet recovery >20 × 10³/μL was 13 days (range 5-69). At 100 days after auto-HCT, the platelet count was 137 × 10⁹/L (range 7-340), the ANC was 2.3 × 10⁹/L (range 0.1-13.0), and the hemoglobin concentration was 123 g/L (range 79-165). PLX use allowed auto-HCT to be performed in a high percentage of poorly mobilized patients, resulting in optimal medium-term engraftment in the majority of patients in whom mobilization failed, in this case mainly due to suboptimal peripheral blood CD34⁺ cell concentration on day +4 or low CD34⁺ cell yield on apheresis.

Granulocyte Colony-Stimulating Factor Effectively Mobilizes TCR γδ and NK Cells Providing an Allograft Potentially Enhanced for the Graft-Versus-Leukemia Effect for Allogeneic Stem Cell Transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) is a potential cure for patients with hematological malignancies but substantial risks of recurrence of the malignant disease remain. TCR γδ and NK cells are perceived as potent innate effector cells in HSCT and have been associated with post-transplant protection from relapse in clinical studies. Immunocompetent cells from the donor are crucial for patient outcomes and peripheral blood stem cells (PBSC) are being increasingly applied as graft source. G-CSF is the preferential mobilizing agent in healthy donors for PBSC grafts, yet effects of G-CSF on TCR γδ and NK cells are scarcely uncovered and could influence the graft composition and potency of these cells. Therefore, we analyzed T and NK cell subsets and activation markers in peripheral blood samples of 49 donors before and after G-CSF mobilization and—for a subset of donors—also in the corresponding graft samples using multicolor flowcytometry with staining for CD3, CD4, CD8, TCRαβ, TCRγδ, Vδ1, Vδ2, HLA-DR, CD45RA, CD197, CD45RO, HLA-DR, CD16, CD56, and CD314. We found that TCR γδ cells were mobilized and harvested with an efficiency corresponding that of TCR αβ cells. For TCR γδ as well as for TCR αβ cells, G-CSF preferentially mobilized naïve and terminally differentiated effector (TEMRA) cells over memory cells. In the TCR γδ cell compartment, G-CSF preferentially mobilized cells of the nonVδ2 types and increased the fraction of HLA-DR positive TCR γδ cells. For NK cells, mobilization by G-CSF was increased compared to that of T cells, yet NK cells appeared to be less efficiently harvested than T cells. In the NK cell compartment, G-CSF-stimulation preserved the proportion of CD56dim NK effector cells which have been associated with relapse protection. The expression of the activating receptor NKG2D implied in anti-leukemic responses, was significantly increased in both CD56dim and CD56bright NK cells after G-CSF stimulation. These results indicate differentiated mobilization and altering properties of G-CSF which could improve the effects of donor TCR γδ and NK cells in the processes of graft-versus-leukemia for relapse prevention after HSCT.

Blood graft composition and post-transplant recovery in myeloma patients mobilized with plerixafor: a prospective multicenter study

The composition of autologous blood grafts after cryopreservation, post-transplant hematological recovery up to 1 year and immune recovery up to 6 months as well as outcome was analyzed in 87 patients with multiple myeloma (MM). The patients receiving added plerixafor due to poor mobilization (11%) were compared to those mobilized with G-CSF or cyclophosphamide (CY) plus G-CSF. The use of plerixafor was found to significantly affect the graft composition as there was a significantly higher proportion of the more primitive CD34⁺ cells, higher number of T and B lymphocytes as well as NK cells in the grafts of patients who received also plerixafor. The hematological recovery after auto-SCT was comparable between the groups. The recovery of CD3⁺CD4⁺ T cells was faster in plerixafor mobilized patients at 1 and 3 months post-transplant. There were no significant differences in progression-free (PFS) or overall survival (OS) according to the plerixafor use.

Safety and efficacy of plerixafor dose escalation for the mobilization of CD34+ hematopoietic progenitor cells in patients with sickle cell disease: interim results

Gene therapy for sickle cell disease is limited by the yield of hematopoietic progenitor cells that can be harvested for transduction or gene editing. We therefore performed a phase I dose-escalation study of the hematopoietic progenitor cell mobilizing agent plerixafor to evaluate the efficacy and safety of standard dosing on peripheral blood CD34⁺ cell mobilization. Of 15 patients enrolled to date, only one was chronically transfused and ten were on hydroxyurea. Of eight patients who achieved a CD34⁺ cell concentration >30 cells/μL, six were on hydroxyurea. There was no clear dose response to increasing plerixafor dosage. There was a low rate of serious adverse events; two patients developed vaso-occlusive crises, at the doses of 80 μg/kg and 240 μg/kg. Hydroxyurea may have contributed to the limited CD34⁺ mobilization by affecting baseline peripheral blood CD34 counts, which correlated strongly with peak peripheral blood CD34 counts. Plerixafor administration did not induce significant increases in the fraction of activated neutrophils, monocytes, or platelets. However, increased neutrophils positive for activated β2 integrin and Mac-1 were associated with serious adverse events. In summary, plerixafor was well tolerated but did not achieve consistent CD34⁺ cell mobilization in this cohort of patients, most of whom were being actively treated with hydroxyurea and only one was chronically transfused. The study will continue with escalation of the dose of plerixafor and modification of hydroxyurea administration. Clinicaltrials.gov identifier: NCT02193191.

Preemptive plerixafor injection added to pegfilgrastim after chemotherapy in non-Hodgkin lymphoma patients mobilizing poorly

Filgrastim is usually combined with chemotherapy to mobilize hematopoietic progenitor cells in non-Hodgkin lymphoma (NHL) patients. Limited information is available on the efficacy of a preemptive plerixafor (PLER) injection in poor mobilizers after chemotherapy and pegfilgrastim. In this prospective study, 72 patients with NHL received chemotherapy plus pegfilgrastim, and 25 hard-to-mobilize patients received also PLER. The usefulness and efficacy of our previously developed algorithm for PLER use in pegfilgrastim-containing mobilization regimen were evaluated as well as the graft cellular composition, hematological recovery, and outcome after autologous stem cell transplantation (auto-SCT) according to the PLER use. A median 3.4-fold increase in blood CD34⁺ cell counts was achieved after the first PLER dose. The minimum collection target was achieved in the first mobilization attempt in 66/72 patients (92%) and 68 patients (94%) proceeded to auto-SCT. An algorithm for PLER use was fulfilled in 76% of the poor mobilizers. Absolute numbers of T-lymphocytes and NK cells were significantly higher in the PLER group, whereas the number of CD34⁺ cells collected was significantly lower. Early neutrophil engraftment was slower in the PLER group, otherwise hematological recovery was comparable within 12 months from auto-SCT. No difference was observed in survival according to the PLER use. Chemotherapy plus pegfilgrastim combined with preemptive PLER injection is an effective and convenient approach to minimize collection failures in NHL patients intended for auto-SCT. A significant effect of PLER on the graft cellular composition was observed, but no difference in outcome after auto-SCT was detected.