Mobilization of hematopoietic stem cells by plerixafor alone in children: A sequential Bayesian trial

Mobilization with high-dose granulocyte colony-stimulating factor alone at 12 μg/kg twice a day in high-risk pediatric patients: A retrospective analysis of the experience in a single center

INTRODUCTION

Mobilization regimes in pediatric patients at high risk for poor mobilization are not standardized across different institutions. We present a retrospective analysis of our experience with a high-dose granulocyte colony-stimulating factor (G-CSF) regime of 12 μg/Kg per body weight (BW) twice a day for 4 days used in high-risk patients.

MATERIAL AND METHODS

We report the results of all pediatric patients mobilized with high-dose G-CSF between January 1999 and February 2021 in our center. A successful mobilization was defined as a peripheral blood (PB) CD34⁺ cell count of ≥10 CD34⁺ cells/μl on the fifth day of mobilization immediately before leukapheresis. A minimum cell yield of ≥2 × 10⁶ CD34⁺ cells/Kg of BW was required for a successful collection.

RESULTS

Of the 262 patients included in the analysis, mobilization failure was found in 27 (10.3%). In a univariate analysis, this was associated with age, weight, baseline diagnosis, and having undergone a previous mobilization cycle, the latter being the only factor that remained significantly associated in a multivariate analysis (P = 0.03). The 54 patients (20.6%) did not reach the minimum required CD34⁺ cell yield. 50.4% of the patients reported adverse events (AEs) during the mobilization period, and 23 (9.1%) reported 3 or more concomitant AEs. However, all of them were mild and did not affect the mobilization schedule.

CONCLUSIONS

Although most high-risk pediatric patients are successfully mobilized with the high-dose G-CSF regime, this approach does not salvage all of them and significantly increases the presence of AEs in comparison to standard-dose regimes.

Plerixafor stem cell mobilization in Japanese children: A post-marketing study

BACKGROUND

Plerixafor is approved in Japan for hematopoietic stem cell mobilization prior to autologous transplant, but limited data are available on the use in children. This study evaluates the safety and effectiveness of plerixafor in Japanese children aged <15 years.

METHODS

A multicenter, post-marketing surveillance study was conducted in Japan to evaluate the safety and effectiveness of plerixafor in routine clinical practice. This subgroup analysis examined the safety and effectiveness of plerixafor administered as a once-daily, subcutaneous injection in children aged <15 years. The primary effectiveness outcome was the proportion of patients with 2 × 10⁶ cells CD34+ cells/kg collected via apheresis within 4 days.

RESULTS

Eighteen patients with solid tumors were included in this analysis; (median age 6.0 years, range, 1-13 years). In addition to granulocyte colony-stimulating factor, all patients had received chemotherapy immediately prior to plerixafor administration. The mean (SD) daily dose of plerixafor was 0.24 (0.01) mg/kg. Seven of the 18 patients (38.9%) developed adverse drug reactions (ADRs), all occurring in patients aged ≥6 years and weighing ≥16 kg. The most common ADRs were pyrexia (n = 4), vomiting (n = 3), nausea (n = 2), and abdominal pain (n = 2). Twelve patients (66.7%) achieved a CD34+ cell count ≥2 × 10⁶ cells/kg within 4 days after the start of plerixafor administration.

CONCLUSIONS

The results provide an encouraging sign that plerixafor 0.24 mg/kg may be safe and effective in pediatric patients in routine clinical practice in Japan, but further research in larger studies is needed.

Complete Remission of a Refractory Acute Myeloid Leukemia with Myelodysplastic- and Monosomy 7-Related Changes after a Combined Conditioning Regimen of Plerixafor, Cytarabine and Melphalan in a 4-Year-Old Boy: A Case Report and Review of Literature

Acute myeloid leukemia with myelodysplastic changes and monosomy 7 is a rare form of pediatric leukemia associated with very poor disease-free survival. The refractoriness of the disease is due to the protection offered by the bone marrow niche, making leukemic stem cells impervious to whatever chemotherapy or myeloablative regimen is chosen. Using a mobilizing agent for haematopoietic stem cells, Plerixafor, could sensitise leukemic cells to the myeloablative therapy. This approach was not previously used in a pediatric population, and in adult populations, was used in combination with busulphan with no difference in overall survival. We describe the case of a 4-year-old boy affected by refractory acute myeloid leukemia with myelodysplastic changes and monosomy 7. The child had never achieved a remission. We proposed a combined time-scheduled scheme of therapy with plerixafor and melphalan. Combining pharmacokinetics of plerixafor with pharmacokinetics and rapid and elevated myeloablative potential of melphalan in high dosage (200 mg/m²), we succeeded in mobilizing more than 85% of stem blasts immediately before infusion of Melphalan. The count of residual blasts after 8 h from melphalan infusion was only 1.3 cells/μL. The child achieved an engraftment at day +32 with full donor chimerism. Sixteen months after haematopoietic stem cell transplantation (HSCT), he is well and in complete remission. Our case suggests that the use of plerixafor before a conditioning therapy with melphalan could induce remission in acute myeloid leukemia refractory to the usual conditioning therapy in pediatric patients. This work adds strength to the body of knowledge regarding the “personalized” conditioning regimen for high-risk leukemic patients.

Combined plerixafor and granulocyte colony-stimulating factor for harvesting high-dose hematopoietic stem cells: Possible niche for plerixafor use in pediatric patients

PB is a source of HSC, especially for autologous HCT in solid tumors. However, there is a risk of failing to achieve the target number of SC after mobilization with growth factors alone in patients who were heavily pretreated with chemotherapy or those in need for tandem transplants. SC were harvested from seven pediatric patients with solid tumors who were in need of autologous HCT following combination GCSF and plerixafor. Six of them received plerixafor after failing to achieve enough SC with GCSF only, while the seventh patient received the combined protocol upfront. All seven patients achieved the target number of SC according to their treatment protocol. There were no adverse events. All patients underwent autologous HCT using the harvested HSC and achieved full engraftment. A protocol for harvesting autologous HCT using GCSF and plerixafor is feasible and safe in children with solid tumors who had been heavily pretreated with chemotherapy or needed tandem transplants.

Plerixafor is safe and efficacious for mobilization of peripheral blood stem cells in pediatric patients

BACKGROUND

Chemotherapy followed by filgrastim is the most common strategy used to mobilize autologous peripheral blood stem cells (PBSCs) for high-dose chemotherapy and autologous stem cell transplantation. Unfortunately, this method does not always lead to adequate PBSC collection in heavily treated patients with relapsed malignancies or if multiple transplants are required. Plerixafor, a hematopoietic stem cell mobilizer that inhibits the CXCR4 chemokine receptor and blocks binding of its cognate ligand, stromal cell-derived factor-1α (SDF-1α), has been shown to be safe and efficacious in the mobilization of autologous PBSC in adults. Despite its use in adults, little evidence exists to support its use in children.

STUDY DESIGN AND METHODS

We report a retrospective review of 16 consecutive pediatric patients receiving plerixafor as part of their mobilization regimen at Cincinnati Children's Hospital Medical Center. All patients but one were given 0.24 mg/kg dose of plerixafor and the median number of plerixafor doses received was two (range, one to four doses). One patient received higher doses of plerixafor.

RESULTS

An adequate number of CD34+ cells were obtained in 14 of 16 patients (87.5%). The median number of CD34+ cells collected for patients who reached collection goal was 6 × 10(6) CD34+ cells/kg (range, 1.6 × 10(6) -12.4 × 10(6) /kg). No acute adverse events were noted to be attributable to plerixafor administration.

CONCLUSION

Our findings suggest that plerixafor use in children is safe and efficacious for the mobilization of autologous PBSCs in subjects with relapsed malignancies or requiring stem cells for multiple transplants.

Plerixafor: what we still have to learn

Plerixafor, a hematopoietic stem cell mobilizer, is indicated in combination with G-CSF to mobilize hematopoietic stem cells to the peripheral blood for collection and subsequent autologous transplantation in patients with non-Hodgkin's lymphoma and multiple myeloma. Current evidence suggests that the addition of plerixafor with chemotherapy plus G-CSF is safe and effective in the large majority of the patients with low blood CD34(+) cell count after mobilization and/or poor yield after the first collection. Nevertheless, there are several questions strongly debated, and in this paper, we would like to identify areas of possible future use and development of the drug.