Use of Plerixafor for Stem Cell Mobilization in the Setting of Autologous and Allogeneic Stem Cell Transplantations: An Update

Scoping review of factors associated with stem cell mobilization and collection in allogeneic stem cell donors

BACKGROUND

There is a large inter-individual variation in the efficacy of CD34+ cell mobilization and collection in healthy allogenic hematopoietic stem cell donors. Donor characteristics, blood cell counts, and factors related to mobilization and collection have previously been associated with blood CD34+ cell count or CD34+ cell yield after G-CSF mobilization and collection. Since the literature reporting associations is heterogeneous, we clarify the determinants of CD34+ count and yield in a scoping review.

MATERIALS AND METHODS

Studies published between 2000 and 2023 were evaluated if they reported allogeneic donors undergoing G-CSF mobilization and peripheral blood stem cell collection (PBSC). Eligible studies assessed blood CD34+ cell count or CD34+ cell yield in the first PBSC collection after mobilization with 4 or 5 days of G-CSF treatment. Associations were recorded between these outcomes and donor factors (age, gender, weight, ethnicity), mobilization factors (G-CSF scheduling or dose), collection factors (venous access, processed blood volume) or laboratory factors (blood cell counts at baseline or after mobilization).

RESULTS

The 52 studies each evaluated between 15 and 20,884 donors. 43 studies were retrospective, 33 assessed blood CD34+ cell counts and 39 assessed CD34+ cell yield from PBSC. Blood CD34+ cell counts consistently predicted CD34+ cell yield. Younger donors usually had higher blood CD34+ cell counts and CD34+ cell yield. Most studies that investigated the effect of donor ancestry found that non-European ancestry donors had higher blood CD34+ cell counts after mobilization and CD34+ cell yields from collection.

CONCLUSIONS

There remains poor consensus about the best predictors of blood CD34+ cell counts and yield that requires further prospective study, particularly of the role of donor ancestry. The current focus on donor gender as a major predictor requires re-evaluation.

CXCR4: From Signaling to Clinical Applications in Neuroendocrine Neoplasms

There are several well-described molecular mechanisms that influence cell growth and are related to the development of cancer. Chemokines constitute a fundamental element that is not only involved in local growth but also affects angiogenesis, tumor spread, and metastatic disease. Among them, the C-X-C motif chemokine ligand 12 (CXCL12) and its specific receptor the chemokine C-X-C motif receptor 4 (CXCR4) have been widely studied. The overexpression in cell membranes of CXCR4 has been shown to be associated with the development of different kinds of histological malignancies, such as adenocarcinomas, epidermoid carcinomas, mesenchymal tumors, or neuroendocrine neoplasms (NENs). The molecular synapsis between CXCL12 and CXCR4 leads to the interaction of G proteins and the activation of different intracellular signaling pathways in both gastroenteropancreatic (GEP) and bronchopulmonary (BP) NENs, conferring greater capacity for locoregional aggressiveness, the epithelial-mesenchymal transition (EMT), and the appearance of metastases. Therefore, it has been hypothesized as to how to design tools that target this receptor. The aim of this review is to focus on current knowledge of the relationship between CXCR4 and NENs, with a special emphasis on diagnostic and therapeutic molecular targets.

An evidence-based and risk-adapted GSF versus GSF plus plerixafor mobilization strategy to obtain a sufficient CD34+ cell yield in the harvest for autologous stem cell transplants

BACKGROUND

Plerixafor is a bicyclam molecule with the ability to reversibly bind to receptor CXCR-4 thus leading to an increased release of stem cells (SC) into the circulation. This study aims to evaluate the efficacy of G-CSF plus plerixafor versus G-CSF alone mobilizing regimens on the basis of CD34+ cell yield and engraftment kinetics following hematopoietic SC transplants.

METHODS

The study incorporated 173 patients with plasma cell neoplasms (PCN), Hodgkin's lymphoma (HL) and non-Hodgkin's lymphoma (NHL), undergoing mobilization and following autologous SC-transplant. For patients with mobilization failure and those predicted to be at risk of harvesting inadequate CD34+ yields (poor-responders), plerixafor was administered. Data was collected and compared in relation to the harvesting protocols used, cell quantification, cell-engraftment potential and overall clinical outcome.

RESULTS

A total of 101 patients received plerixafor (58.4 %) and the median CD34+increase was 312 %. Chemotherapy-mobilized PCN-patients required less plerixafor administration (p = 0.01), no difference was observed in lymphoma groups (p = 0.46). The median CD34+cell yield was 7.8 × 106/kg bm. Patients requiring plerixafor achieved lower, but still comparable cell yields. Total cell dose infused was in correlation with engraftment kinetics. Patients requiring plerixafor had delayed platelet engraftment (p = 0.029).

CONCLUSIONS

Adequately selected plerixafor administration reduces "mobilization-related-failure" rate and assure a high-level cell dose for SC transplants, with superior "therapeutic-potential" and safety profile. The mobilization strategy that incorporates "just-in-time" plerixafor administration, also leads to a reduction of hospitalization days and healthcare resource utilization. For definitive conclusions, further controlled/larger clinical trials concerning correlation of CD34+ cell count/yield, with hematopoietic reconstitution are required.

Stem Cells mobilization and collection in allogeneic related and unrelated donors: a single center experience with focus on plerixafor

INTRODUCTION

Poor CD34 + cells mobilization in allogeneic donors could affect transplant outcome. In a subgroup of patient mobilization with granulocyte colony-stimulating factor (G-CSF) alone is unsatisfactory, and Plerixafor could be used to enhance CD34 + cells release from bone marrow niche.

MATERIALS AND METHODS

We conducted a retrospective single-center, cohort study on healthy allogeneic donors both related and unrelated, treated by Udine Transfusion Center over the last 10 years (2012-2022). In the 195 allogeneic donors treated we analyzed age, sex, body weight, BMI, comorbidities, G-CSF dosage and even baseline white blood cell count as possible predictor of insufficient CD34 + cells mobilization on day 5. In the subgroup of related donors we evaluated even baseline CD34 + cells (measured before mobilization start). Processed donor blood volume, collection efficiency and apheresis product were examined. Additionally a comparative analysis was conducted between G-CSF alone treated donors and poor mobilizing ones, in which Plerixafor was administered at a dose of 0.24 mg/kg as a pre-emptive or rescue agent.

RESULTS

In 9 donors, due to poor mobilization (defined as CD34 + < 20/µL or estimated yield < 1 ×106 kg/recipient body weight), the use of plerixafor was necessary. PLX at a dose of 0.24 mg/kg was administered 5 h before collection, inducing an average increase of 5.1 (1.7-12.6) in CD34 + circulating cells. In this subgroup of patients, BMI and weight were significantly lower (p = 0.03). Interestingly, baseline CD34 + cells (measured before the onset of mobilization) also seems to predict poor mobilization (p = 0.003). In donors additionally treated with Plerixafor compared to those who received G-CSF alone, collection efficiency was higher (p = 0.02) and CD34 + cells collected were comparable (p = 0.2). Side effects related to the administration of plerixafor, if they occurred, were well tolerated.

CONCLUSIONS

Plerixafor is a safe and effective drug in the rescue and prevention of poor mobilization. New prospective studies on allogeneic donors should be performed to increase the treatable population to avoid inadequate collection and mobilization. New laboratory predictors such as baseline CD34 + cells should be investigated in larger cohorts and then used as early screening.

Plerixafor in autologous stem cell transplantation: Does it affect engraftment kinetics?

Plerixafor increases stem cell mobilization by reversibly binding to the chemokine receptor CXCR4. In our study, we examined the results of mobilization with plerixafor and granulocyte colony-stimulating factor (G-CSF) and revealed their effects on autologous stem cell transplantation (ASCT) engraftment kinetics. The study included all cases of ASCT performed in the Adult Bone Marrow Transplantation Unit of xxx University between January 2014 and January 2022. It included a total of 300 patients. The total number of CD34 + cells collected was 7.44 ± 4.19 in patients with plerixafor and 9.53 ± 6.09 in patients without plerixafor. The mean neutrophil and platelet engraftment took longer in plerixafor-mobilized patients (neutrophil: 12 ± 4.1 vs. 10.2 ± 2.7 days; platelet: 21.6 ± 13.9 vs. 14.2 ± 5.9 days; p = 0.008 and p = 0.002). The number of febrile neutropenia attacks was significantly higher in plerixafor-mobilized patients (p = 0.04). In the chemo-mobilized patient subgroup, plerixafor-mobilized patients experienced more febrile neutropenia attacks (p = 0.04). The mean time to both neutrophil and platelet engraftment was longer in patients mobilized with plerixafor. In the subgroup of patients with MM, the mean time to platelet engraftment was longer in patients mobilized with plerixafor. Plerixafor and its effect on engraftment kinetics should be evaluated with further studies in a larger population with survival analysis.

A comparison of peripheral blood stem cell collection outcomes for multiple myeloma; mobilization matters in the era of IMiD induction

Collection of peripheral blood stem cells (PBSCs) for autologous stem cell transplant (ASCT) requires mobilization from the bone marrow. There is variation in mobilization choice; during the COVID-19 pandemic BSBMT&CT guidelines recommended using granulocyte-colony stimulating factor (G-CSF) alone to minimize the use of chemotherapy. We report on the impact of mobilization regimen on stem cell collection, and whether IMiD-containing induction therapy impacts on mobilization and consequently transplant engraftment times for 83 patients undergoing ASCT at Leeds Teaching Hospitals. Cyclophosphamide plus G-CSF (cyclo-G) mobilization yielded more CD34+ cells (8.94 vs. 4.88 ×106/kg, p = < 0.0001) over fewer days (1.6 vs. 2.4 days, p = 0.007), and required fewer doses of salvage Plerixafor than G-CSF only (13.6% vs. 35%, p = 0.0407). IMiD-containing induction impaired all of these factors. CD34+ doses > 8×106/kg were more frequent with Cyclo-G (62% vs. 11%, p = 0.0001), including for those receiving IMiD 1st line induction (50% vs. 13.3%, p = 0.0381). Note that 92.6% of those receiving IMiD-free inductions were mobilized with Cyclo-G. The novel agents used in modern induction regimens (e.g Daratumumab) have been shown to impair yields, increasing the importance of optimizing mobilization regimens in the first instance. Furthermore, as cellular therapies become established in the management of multiple myeloma emerging data highlights the potential benefits of stem cell top up in the management of the haematological toxicities of these therapies. Our findings support re-adoption of Cyclo-G as the gold standard for mobilization to optimize PBSC harvesting and ensure sufficient cells for subsequent ASCTs.

Host Cell Targets for Unconventional Antivirals against RNA Viruses

The recent COVID-19 crisis has highlighted the importance of RNA-based viruses. The most prominent members of this group are SARS-CoV-2 (coronavirus), HIV (human immunodeficiency virus), EBOV (Ebola virus), DENV (dengue virus), HCV (hepatitis C virus), ZIKV (Zika virus), CHIKV (chikungunya virus), and influenza A virus. With the exception of retroviruses which produce reverse transcriptase, the majority of RNA viruses encode RNA-dependent RNA polymerases which do not include molecular proofreading tools, underlying the high mutation capacity of these viruses as they multiply in the host cells. Together with their ability to manipulate the immune system of the host in different ways, their high mutation frequency poses a challenge to develop effective and durable vaccination and/or treatments. Consequently, the use of antiviral targeting agents, while an important part of the therapeutic strategy against infection, may lead to the selection of drug-resistant variants. The crucial role of the host cell replicative and processing machinery is essential for the replicative cycle of the viruses and has driven attention to the potential use of drugs directed to the host machinery as therapeutic alternatives to treat viral infections. In this review, we discuss small molecules with antiviral effects that target cellular factors in different steps of the infectious cycle of many RNA viruses. We emphasize the repurposing of FDA-approved drugs with broad-spectrum antiviral activity. Finally, we postulate that the ferruginol analog (18-(phthalimide-2-yl) ferruginol) is a potential host-targeted antiviral.

Stem Cell Mobilization Yields with Daratumumab- and Lenalidomide-Containing Quadruplet Induction Therapy in Newly Diagnosed Multiple Myeloma: Findings from the MASTER and GRIFFIN Trials

For eligible patients with newly diagnosed multiple myeloma (NDMM), standard of care includes induction therapy followed by autologous stem cell transplantation (ASCT). Daratumumab as monotherapy and in combination treatment is approved across multiple lines of therapy for multiple myeloma (MM), and lenalidomide is an effective and commonly used agent for induction and maintenance therapy in MM. However, there is concern that lenalidomide and daratumumab given as induction therapy might impair mobilization of stem cells for ASCT. Therefore, we assessed stem cell mobilization in patients following frontline induction therapy in the MASTER and GRIFFIN phase 2 clinical studies by examining stem cell mobilization yields, apheresis attempts, and engraftment outcomes for patients from each study. Adult transplantation-eligible patients with NDMM received induction therapy consisting of daratumumab plus carfilzomib/lenalidomide/dexamethasone (D-KRd) for four 28-day cycles in the single-arm MASTER trial or lenalidomide/bortezomib/dexamethasone (RVd) with or without daratumumab (D) for four 21-day cycles in the randomized GRIFFIN trial, followed by stem cell mobilization and ASCT in both studies. Institutional practice differed regarding plerixafor use for stem cell mobilization; the strategies were upfront (ie, planned plerixafor use) or rescue (ie, plerixafor use only after mobilization parameters indicated failure with granulocyte colony-stimulating factor [G-CSF] alone). Descriptive analyses were used to summarize patient characteristics, stem cell mobilization yields, and engraftment outcomes. In MASTER, 116 D-KRd recipients underwent stem cell mobilization and collection at a median of 24 days after completing induction therapy. In GRIFFIN, 175 patients (D-RVd, n = 95; RVd, n = 80) underwent mobilization at a median of 27 days after completing D-RVd induction therapy and 24 days after completing RVd induction therapy. Among those who underwent mobilization and collection, 7% (8 of 116) of D-KRd recipients, 2% (2 of 95) of D-RVd recipients, and 6% (5 of 80) of RVd recipients did not meet the center-specific minimally required CD34⁺ cell yield in the first mobilization attempt; however, nearly all collected sufficient stem cells for ASCT on remobilization. Among patients who underwent mobilization, plerixafor use, either upfront or as a rescue strategy, was higher in patients receiving D-KRd (97%; 112 of 116) and D-RVd (72%; 68 of 95) compared with those receiving RVd (55%; 44 of 80). The median total CD34⁺ cell collection was 6.0 × 10⁶/kg (range, 2.2 to 13.9 × 10⁶/kg) after D-KRd induction, 8.3 × 10⁶/kg (range, 2.6 to 33.0 × 10⁶/kg) after D-RVd induction, and 9.4 × 10⁶/kg (range, 4.1 to 28.7 × 10⁶/kg) after RVd induction; the median days for collection were 2, 2, and 1, respectively. Among patients who underwent mobilization, 98% (114 of 116) of D-KRd patients, 99% (94 of 95) of D-RVd patients, and 98% (78 of 80) of RVd patients underwent ASCT using median CD34⁺ cell doses of 3.2 × 10⁶/kg, 4.2 × 10⁶/kg, and 4.8 × 10⁶/kg, respectively. The median time to neutrophil recovery was 12 days in all 3 treatment groups across the 2 trials. Because both trials used different criteria to define platelet recovery, data on platelet engraftment using the same criteria are not available. Four cycles of daratumumab- and lenalidomide-based quadruplet induction therapy had a minimal impact on stem cell mobilization and allowed predictable stem cell harvesting and engraftment in all patients who underwent ASCT. Upfront plerixafor strategy may be considered, but many patients were successfully collected with the use of G-CSF alone or rescue plerixafor.

Day -1 CD34+ Cells and Platelet Count Predict the Number of Apheresis in Poor-Mobilizer Patients Rescued by Plerixafor

Plerixafor is widely used as up-front treatment with G-CSF to enhance peripheral blood hematopoietic stem cell output in patients failing previous mobilizations. Less frequently, plerixafor is used to rescue an unsatisfactory mobilization following chemotherapy (CT) and G-CSF. This study investigates if pre-collection factors affect the CD34+ cell harvest in chemotherapy and G-CSF mobilizations rescued by plerixafor. Clinical and hematological data relative to patients, mobilization, and apheresis products were retrospectively examined. The outcome was completing a target cell dose ≥ 2 × 10⁶ CD34+ cells/kg at first apheresis. The effect exerted on the outcome by patient- and disease-related factors was investigated by univariate and multivariate logistic regression analysis. The analysis included data from 42 patients affected by hematological (39 patients) and non-hematological malignancies (three patients). Twenty-nine patients (69%) attained the target cell dose at first apheresis. Twelve out of the remaining 13 patients received an additional plerixafor administration, and all accomplished the transplant dose at a second apheresis procedure. Day -1 CD34+ PB count (OR1.46, 95% CI 1.1-1.9, p = 0.008) and platelet count (OR1.0, 95% CI 1.0-1.0, p = 0.033) predicted the achievement of the target dose at first apheresis, independently of pre-mobilization CT, radiation therapy, and disease status at mobilization. At ROC curve analysis, the best cut-off value predicting the successful collection at first apheresis was 7.5/µL for Day -1 CD34+ cell count (AUC 0.830, 0.69 sensitivity, and 0.92 specificity) and 75 × 10⁹/L for Day -1 platelet count (AUC = 0.736, 0.65 sensitivity and 0.85 specificity). In conclusion, on-demand plerixafor rescue allows a successful stem cell collection, irrespectively of disease type and status, prior CT lines, and radiation exposure. Pre-apheresis CD34+ cells and platelet count predict the need for one or two aphereses.

Development and clinical translation considerations for the next wave of gene modified hematopoietic stem and progenitor cells therapies

INTRODUCTION

Consistent and reliable manufacture of gene modified hematopoietic stem and progenitor cell (HPSC) therapies will be of the utmost importance as they become more mainstream and address larger populations. Robust development campaigns will be needed to ensure that these products will be delivered to patients with the highest quality standards.

AREAS COVERED

Through publicly available manuscripts, press releases, and news articles - this review touches on aspects related to HSPC therapy, development, and manufacturing.

EXPERT OPINION

Recent advances in genome modification technology coupled with the longstanding clinical success of HSPCs warrants great optimism for the next generation of engineered HSPC-based therapies. Treatments for some diseases that have thus far been intractable now appear within reach. Reproducible manufacturing will be of critical importance in delivering these therapies but will be challenging due to the need for bespoke materials and methods in combination with the lack of off-the-shelf solutions. Continued progress in the field will manifest in the form of industrialization which currently requires attention and resources directed toward the custom reagents, a focus on closed and automated processes, and safer and more precise genome modification technologies that will enable broader, faster, and safer access to these life-changing therapies.