Blood stem cell mobilization and collection in patients with lymphoproliferative diseases: practical issues

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.

Optimizing autologous stem cell mobilization strategies to improve patient outcomes: consensus guidelines and recommendations

Autologous hematopoietic stem cell transplantation (aHSCT) is a well-established treatment for malignancies such as multiple myeloma (MM) and lymphomas. Various changes in the field over the past decade, including the frequent use of tandem aHSCT in MM, the advent of novel therapies for the treatment of MM and lymphoma, and the addition of new stem cell mobilization techniques, have led to the need to reassess current stem cell mobilization strategies. Mobilization failures with traditional strategies are common and result in delays in treatment and increased cost and resource utilization. Recently, plerixafor-containing strategies have been shown to significantly reduce mobilization failure rates, but the ideal method to maximize stem cell yields and minimize costs associated with collection has not yet been determined. A panel of experts convened to discuss the currently available data on autologous hematopoietic stem cell mobilization and transplantation and to devise guidelines to optimize mobilization strategies. Herein is a summary of their discussion and consensus.

Risk factors for a poor hematopoietic stem cell mobilization

Poor mobilization is an important problem in autologous stem cell transplantation. We retrospectively reviewed the data of 165 mobilized patients to identify possible risk factors for a poor stem cell mobilization. 27 patients (16.4%) were categorized as poorly mobilized. The poor mobilization ratio differed according to diagnosis (lymphoma: 25.4%, acute leukemia: 15.4%, amyloidosis: 14.3%, and multiple myeloma: 9.6%). Being diagnosed as lymphoma (odds ratio [OR]=6.02, p=0.001), advanced age (OR=1.05, p=0.007) and increased weight (OR=1.03, p=0.03) were found as possible risk factors. Being diagnosed as lymphoma was shown to be the most important risk factor for a poor mobilization. Leukapheresis staff should be aware of the increased risk of a poor mobilization in lymphoma patients and remobilization methods should be considered from the beginning.

Novel strategies for blood stem cell mobilization: special focus on plerixafor

INTRODUCTION

More than 98% of autologous stem cell transplants are now performed with the support of mobilized blood stem cells, and the proportion of allogeneic blood stem cell transplants has risen to more than 70%. Blood stem cell mobilization strategies are therefore important components of all transplant programs.

AREAS COVERED

Stem cell mobilization strategies are evaluated based on current literature, with special focus on the use of plerixafor, a CXCR4 chemokine receptor antagonist. Mobilization methods in autologous settings include the use of G-CSF alone or following chemotherapy (chemomobilization), and the use of G-CSF alone in allogeneic transplants. A combination of G-CSF + plerixafor has been shown to be effective in patients who have failed a previous mobilization. This combination has also been found to be superior to G-CSF alone in Phase III studies in myeloma and non-Hodgkin lymphoma patients as the first-line mobilization.

EXPERT OPINION

Addition of plerixafor to chemomobilization or G-CSF mobilization may be more cost-effective than its routine use, and it is worth considering in predicted or proven poor mobilizers. Novel mobilization strategies have allowed more successful stem cell collection in autologous setting, although the effect of plerixafor on graft content and long-term patient outcomes needs further investigation.

Proposed definition of 'poor mobilizer' in lymphoma and multiple myeloma: an analytic hierarchy process by ad hoc working group Gruppo ItalianoTrapianto di Midollo Osseo

Many lymphoma and myeloma patients fail to undergo ASCT owing to poor mobilization. Identification of poor mobilizers (PMs) would provide a tool for early intervention with new mobilization agents. The Gruppo italianoTrapianto di Midollo Osseo working group proposed a definition of PMs applicable to clinical trials and clinical practice. The analytic hierarchy process, a method for group decision making, was used in setting prioritized criteria. Lymphoma or myeloma patients were defined as ‘proven PM' when: (1) after adequate mobilization (G-CSF 10 μg/kg if used alone or ⩾5 μg/kg after chemotherapy) circulating CD34⁺ cell peak is <20/μL up to 6 days after mobilization with G-CSF or up to 20 days after chemotherapy and G-CSF or (2) they yielded <2.0 × 10⁶ CD34⁺ cells per kg in ⩽3 apheresis. Patients were defined as predicted PMs if: (1) they failed a previous collection attempt (not otherwise specified); (2) they previously received extensive radiotherapy or full courses of therapy affecting SC mobilization; and (3) they met two of the following criteria: advanced disease (⩾2 lines of chemotherapy), refractory disease, extensive BM involvement or cellularity <30% at the time of mobilization; age ⩾65 years. This definition of proven and predicted PMs should be validated in clinical trials and common clinical practice.

Factors affecting stem cell mobilization for autologous hematopoietic stem cell transplantation

High-dose chemotherapy with autologous stem cell transplantation (ASCT) is curative treatment in various hematologic malignancies. Mobilization and collection of peripheral blood stem cell is the essential part of ASCT. The aim of this study was to evaluate the effectiveness of various mobilization regimens, determine the risk factors associated with mobilization failure (MF). We also investigated whether iron overload, which has an adverse impact on various aspects of HSCT including overall survival had any impact on mobilization kinetics. A total of 118 consecutive patients were included in this study. The rate of MF was 11.8 % with the first mobilization regimen. Frequency of MF was higher in lymphoma (P < 0.001) patients and in those receiving G-CSF alone (P= 0.01). Peripheral CD34+ cell count (P < 0.001), bone marrow cellularity (P < 0.001), reticulin fibrosis (P < 0.05) were significantly lower whereas serum ferritin levels (P = 0.06) tended to be higher in patients with MF. CD34+ cell count of the first apheresis product was positively correlated with the white blood cell count (P < 0.05; r = 0.232), platelet count (P = 0.01; r = 0.233), peripheral CD34+ cell count (P < 0.001; r = 0.704) and the grade of bone marrow reticulin fibrosis (P < 0.001; r = 0.366). Serum ferritin levels were negatively correlated with maximum peripheral CD34+ cell count (P = 0.02; r = -0.216) and the CD34+ cell count in the first product (P = 0.05; r = -0.183). Platelet count (P = 0.03; β = 0.262), peripheral CD34+ cell count (P = 0.02; β=0.279) were the two variables which remained to be significant in multivariate analysis. Predicting the poor mobilizers with the platelet count for instance may reduce the risk of MF by using more effective regimens in advance.

Mobilization strategies in hard-to-mobilize patients with lymphoid malignancies

Depending on definitions and patient characteristics, 5-40% of patients with lymphoid malignancies are hard-to-mobilize. Several premobilization factors such as previous chemotherapy (CT), disease, marrow infiltration and platelet count at the time of mobilization influence the efficacy of CD34(+) cell mobilization. In general, however, prediction of hard-to-mobilize patient is difficult. Postmobilization factors especially low blood CD34(+) counts are important in clinical practice as we have now ways to enhance mobilization at this point. Plerixafor combined with granulocyte-colony stimulating factor (G-CSF) has significantly increased efficacy of remobilization in patients who have failed a previous mobilization attempt with a success rate of about 70%. Addition of plerixafor to G-CSF or more recently to a mobilization regimen consisting of CT + G-CSF is promising as blood CD34(+) counts can be increased three to fivefold to facilitate effective collection with less aphaeresis sessions. As plerixafor is expensive, development of practical algorithms for its use is important to make blood stem cell mobilization and collection more efficient in a cost-effective way. This review attempts to summarize current treatment strategies in hard-to-mobilize patients with lymphoid malignancies.

Peripheral blood stem cell collection in multiple myeloma: a retrospective analysis of 6 years leukapheresis activity in 109 patients treated at the Istituto Nazionale dei Tumori of Milan

Double autologous stem cell transplantation is the standard treatment in newly diagnosed multiple myeloma (MM) patients younger than 65 years; therefore, optimization of leukapheresis is crucial. We performed a retrospective analysis of 297 leukaphereses comparing semiautomated (V4.7 in 20% of collections) versus automated (V6.0 in 80%) Caridian (COBE) Spectra versions and analyzing the influence of M-protein on the outcome. Both methods gave comparable collection efficiencies (CE%) (53.4% vs. 55.7% in V6.0 and V4.7, respectively) with similar leukapheresis time and processed volume. Harvest volume was higher in V4.7 (P < 0.0001) with similar contamination of red blood cells (RBCs) (P = 0.77) and platelets (P = 0.09) when compared with V6.0. In patients with higher peripheral white blood cells (WBCs), V6.0 with adjusted harvest volume (<700 mL), achieved similar CD34(+) CE% (P = 0.39) and better enrichment of nucleated cells (P < 0.0,002) but higher RBCs (P < 0.0,001) and platelets contamination (P = 0.001), when compared with a larger cycle volume in patients with lower WBCs. In hard to mobilize patients, CD34(+) CE% was significantly more efficient with V4.7 than V6.0 (P < 0.0,001). CD34(+) CE% was unaffected by serologic M-protein, but platelet CE% was higher in the absence of M-protein (P = 0.0,003), without any reduction in peripheral patients platelets. We, therefore, conclude that in the setting of MM patients with a high WBCs count and/or low percentage of peripheral CD34(+) cells, collections with V4.7 or adjusted cycle volume V6.0 gave comparable result in CD34(+) CE%. RBCs and platelets contamination is higher if low cycle volume is chosen. In hard to mobilize patients, V4.7 is advisable.

Mobilized hematopoietic stem cell yield depends on species-specific circadian timing

Endogenous rhythmicity likely evolved as a mechanism allowing organisms to anticipate predictable daily changes in the environment (Rutter et al., 2002). Under homeostasis, murine hematopoietic stem cell (HSC) egress is orchestrated by rhythmic beta 3 adrenergic signals delivered by the sympathetic nervous system (SNS) that regulate Cxcl12 expression in stromal cells (Mendez-Ferrer et al., 2008). Here, we show that CXCR4 is also regulated under circadian control whose rhythm is synchronized with its ligand, CXCL12, to optimize HSC trafficking. These circadian oscillations are inverted in humans compared to the mouse and continue to influence the yield even when stem cell mobilization is enforced. Our results suggest that the human HSC yield for clinical transplantation might be significantly greater if patients were harvested during the evening compared to the morning.

Host CD4+CD25+ T cells can expand and comprise a major component of the Treg compartment after experimental HCT

Reconstitution of the recipient lymphoid compartment following hematopoietic cell transplantation (HCT) is typically delayed. The present studies investigated the residual host CD4(+)CD25(+)Foxp3(+) (Treg) compartment after several conditioning regimens, including T cell-depleted and T cell-replete HCT and observed (1) a small number of recipient Treg cells survived aggressive conditioning; (2) the surviving, that is, residual Tregs underwent marked expansion; and (3) recipient CD4(+)FoxP3(+) cells composed the majority of the Treg compartment for several months post-syngeneic HCT. Notably, residual Tregs also dominated the compartment post-HCT with T cell-depleted (TCD) major histocompatibility complex-matched allogeneic bone marrow but not following T cell-replete transplantations. The residual Treg cell compartment was functionally competent as assessed by in vitro lymphoid suppression and in vivo autoimmune disease transfer assay. These observations support the notion that functional host Tregs initially occupy a niche in lymphopenic transplantation recipients, undergo significant expansion, and contribute to the compartment for an extended period before donor-derived CD4(+)FoxP3(+) T cells eventually compose the majority of the compartment. In total, the findings suggest that the presence of host Tregs may be important to consider regarding elicitation of immune (eg, antitumor, vaccine) responses in recipients during the early post-transplant period involving autologous and certain allogeneic HCT regimens.