The case for plerixafor to replace filgrastim as the optimal agent to mobilize peripheral blood donors for allogeneic hematopoietic cell transplantation

Addition of plerixafor in poorly mobilized allogeneic stem cell donors

Background

Peripheral blood stem cells (PBSCs) are the predominant graft source for adult allogeneic hematopoietic stem cell transplantation (HSCT). In poorly mobilized autologous donors, plerixafor improves collection outcomes. We examine plerixafor use in allogeneic donors who mobilize poorly with granulocyte colony‐stimulating factor (G‐CSF) in those who are healthy and those with pre‐existing medical conditions, and determine the optimal threshold to add plerixafor.

Study Design/Methods

We retrospectively examined all allogeneic PBSC collections from January 2013 to October 2020 at our center. Donors received G‐CSF 10 mcg/kg daily for 4 days before undergoing apheresis collection on day 5. Plerixafor was added based on poor CD34+ cell collection yield after the first or second collection day.

Results

Of the 1008 allogeneic donors, 41 (4.1%) received one dose of plerixafor in addition to G‐CSF due to poor collection yield. After starting plerixafor there was a 0.75‐ to 7.74‐fold (median 2.94) increase in CD34+ yield from the previous day. No donors with G‐CSF‐only mobilization who collected <2.0 × 10⁶ CD34+ cells/kg recipient weight on day one achieved the goal of ≥4.0 × 10⁶ CD34+ cells/kg recipient weight total over 2 days but 59.2% of donors who used rescue plerixafor did.

Conclusion

Donors both healthy and those with pre‐existing disease responded well to plerixafor with minimal side effects. If the first‐day collection yield is less than ~63% of the collection goal, addition of plerixafor may be necessary to reach the collection goal and limit the number of collection days in allogeneic donors.

Filgrastim (r-met-hu G-CSF) enhances the efficiency of spermatogenesis in prepubertal Bos indicus bulls

This study aimed to test the effects of the drug r-met-hu-G-CSF (filgrastim) on spermatogenic efficiency in prepubertal Brahman bulls. Twelve intact, healthy prepubertal bulls were administered 0, 1 (LD = low dose) or 4 (HD = high dose) µg/Kg r-met-hu-G-CSF (daily for 4 days), and haematological analysis was performed. Bulls were castrated (D0 or D60). BW (body weight) and SC (scrotal circumference) were recorded. Testis weight and volume were taken at castration with samples for testis histology and stereology: germ cell types, spermatids count and DSP (daily sperm production per gram)/g of testicular parenchyma. Testicular weight, volume, BW, SC and gonadosomatic index (GSI) were NS (LD-HD; p > .05). At D0 (age 11 months), the most advanced germ cell types (maGCt) ranged from intermediate spermatogonia to pachytene spermatocytes. After 2 months, control animals had round spermatids as maGCt, LD animals 75% round spermatids and 25% elongated spermatids, and HD animals round spermatids. Spermatids/testis were higher in LD (1.23 ± 0.2 millions) than in controls (0.65 ± 0.1 millions, p < .05). Spermatogenic efficiency (DSP/g) was higher in LD (5.4 ± 0.4 million) than in controls (3.2 ± 0.2 million, p < .01). In conclusion, r-met-hu-G-CSF raises spermatogenic efficiency in prepubertal Brahman bulls.

CXCR4 blockade reduces the severity of murine heart allograft rejection by plasmacytoid dendritic cell-mediated immune regulation

Allograft-specific regulatory T cells (T_reg cells) are crucial for long-term graft acceptance after transplantation. Although adoptive T_reg cell transfer has been proposed, major challenges include graft-specificity and stability. Thus, there is an unmet need for the direct induction of graft-specific T_reg cells. We hypothesized a synergism of the immunotolerogenic effects of rapamycin (mTOR inhibition) and plerixafor (CXCR4 antagonist) for T_reg cell induction. Thus, we performed fully-mismatched heart transplantations and found combination treatment to result in prolonged allograft survival. Moreover, fibrosis and myocyte lesions were reduced. Although less CD3⁺ T cell infiltrated, higher T_reg cell numbers were observed. Noteworthy, this was accompanied by a plerixafor-dependent plasmacytoid dendritic cells-(pDCs)-mobilization. Furthermore, in vivo pDC-depletion abrogated the plerixafor-mediated T_reg cell number increase and reduced allograft survival. Our pharmacological approach allowed to increase T_reg cell numbers due to pDC-mediated immune regulation. Therefore pDCs can be an attractive immunotherapeutic target in addition to plerixafor treatment.

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.

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

Mobilization failure is an important issue in stem cell transplantations. Stem cells are yielded from the peripheral blood via apheresis. Granulocyte colony-stimulating factor (G-CSF) is the most commonly used mobilization agent among patients and donors. G-CSF is administered subcutaneously for multiple days. However, patients with mobilization failure cannot receive autologous stem cell transplantation and, therefore, cannot be treated adequately. The incidence rate of mobilization failure among patients is about 6–23%. Plerixafor is a molecule that inhibits the binding of chemokine receptor-4 with stromal-cell-derived factor-1, thereby resulting in the release of CD34+ cells in the peripheral blood. Currently, plerixafor is used in patients with mobilization failure with G-CSF and is administered subcutaneously. Several studies conducted on different clinical settings have shown that plerixafor is effective and well tolerated by patients. However, more studies should be conducted to explore the optimal approach for plerixafor in patients with mobilization failure. The incidence of mobilization failure among donors is lower. However, plerixafor is not approved among donors with mobilization failure. Moreover, several clinical studies in donors have shown a beneficial effect of plerixafor. In addition, the adverse events of plerixafor are mild and transient, which can overcome the adverse events due to G-CSF. This review assessed the current role and effects of plerixafor in stem cell mobilization for autologous and allogeneic stem cell transplantations.

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.

Addition of plerixafor to G-CSF in poor mobilizing healthy related donors overcame mobilization failure: An observational case series on behalf of the Grupo Español de Trasplante Hematopoyético (GETH)

Plerixafor (Mozobil, Sanofi) is approved for using in patients with lymphoma and multiple myeloma when steady-state mobilization strategies fail. Although off-label use of plerixafor in healthy related donors (HRD) is known, limited data are available and no recommendations exist to guide its use in this setting. With the aim of collecting data from HRDs who received plerixafor in our country, we designed an observational case series study within the Spanish Group of Hematopoietic Transplant and Cell Therapy (GETH). Plerixafor was administered subcutaneously to 30 HRDs at a median dose of 0.24 mg/Kg (interquartile range (IQR): 0.23-0.25) because mobilization failure after using mobilization with G-CSF (mobilization failure was defined as collection of <4.0 × 10⁶ CD34+ cells/Kg recipient). All HRDs received G-CSF at a median dose of 11 μg/Kg/day (IQR: 10-12) for 4-5 days. Leukocytapheresis after G-CSF mobilization was performed in 23 (77 %) HRDs collecting a median of 1.6 × 10⁶ CD34+ cells/Kg recipient weight (IQR: 0.9-2.5). Addition of plerixafor allowed the collection of a higher median number of CD34 cells (4.98 × 10⁶ CD34+ cells/Kg recipient weight (IQR: 3.5-5.8)) when compared with the collection of CD34+ cells with G-CSF alone (p < 0.01). The final median total number of CD34+ cells collected was 6.1 × 10⁶/Kg recipient weight (IQR: 4.8-7.3). Mild adverse events related with plerixafor administration were reported in 8 (27 %) donors. In conclusion, addition of plerixafor after G-CSF mobilization failure in HRDs allowed collecting higher number of CD34+ cells in comparison with steady-state mobilization.

Characteristics of cells with engraftment capacity within CD34+ cell population upon G-CSF and Plerixafor mobilization

In the context of hematopoietic cell transplantation, hematopoietic stem cells and progenitor cells (HSC and HPC) are usually collected by apheresis following their mobilization by G-CSF alone or in combination with Plerixafor® when patients fail to respond to G-CSF alone. In medical practice, the quality of the hematopoietic graft is based on CD34⁺ cell content that is used to define "Good Mobilizer (GM)" or "Poor Mobilizer (PM)" patients but does not report the real HSC content of grafts. In this study, we assessed the HSC content within the CD34⁺ fraction of graft samples from 3 groups of patients: 1-GM patients receiving G-CSF only (GM^G-CSF), 2-PM patients receiving G-CSF only (PM^G-CSF), 3-PM patients receiving G-CSF + Plerixafor (PM^G-CSF+P). Although HSC from the 3 groups of patients displayed very similar phenotypic profiles, expression of "stemness" genes and metabolic characteristics, their capacity to engraft NSG mice differed revealing differences in terms of HSC between groups. Indeed according to mobilization regimen, we observed differences in migration capacity of HSC, as well as differences in engraftment intensity depending on the initial pathology (myeloma versus lymphoma) of patients. This suggests that mobilization regimen could strongly influence the long term engraftment efficiency of hematopoietic grafts.

Viagra Enables Efficient, Single-Day Hematopoietic Stem Cell Mobilization

Hematopoietic stem cell (HSC) transplantation is a curative treatment for a variety of blood and immune disorders. Currently available methods to obtain donor HSCs are suboptimal, and the limited supply of donor HSCs hampers the success and availability of HSC transplantation therapies. We recently showed that manipulation of vascular integrity can be employed to induce HSC mobilization from the bone marrow to the blood stream, facilitating non-invasive collection of HSCs. Here, we tested whether FDA-approved vasodilators are capable of mobilizing HSCs. We found that a rapid, 2-h regimen of a single oral dose of Viagra (sildenafil citrate) combined with a single injection of the CXCR4 antagonist AMD3100 leads to efficient HSC mobilization at levels rivaling the standard-of-care 5-day regimen of granulocyte-colony stimulating factor (G-CSF/Filgrastim/Neupogen). Our findings solidify vascular integrity as an essential regulator of HSC trafficking and provide an attractive, single-day regimen for HSC mobilization using already FDA-approved drugs.

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Viagra enhances AMD3100-mediated HSC mobilization

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Extremely rapid and efficient HSC mobilization with two FDA-approved drugs

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Vascular integrity regulates HSC trafficking