Hematopoietic, Immune Recovery and Outcomes after Autologous Stem Cell Transplantation Following Plerixafor Plus G-CSF Versus Chemotherapy and G-CSF Based Mobilization in Pediatric Patients

Background: High-dose chemotherapy (HDC) and autologous stem-cell transplantation (ASCT) has shown survival benefits for chemo-sensitive high risk pediatric solid tumors. Collection of sufficient hematopoietic stem cells is required for ASCT. Plerixafor, a CXCR4 receptor antagonist, has been used when granulocyte colony-stimulating factor (G-CSF) and chemotherapy based (conventional) mobilization may not enable us to collect enough cells, especially in recurred or heavily treated patients. The experiences of plerixafor in pediatric patients are lacking as compared with adults, and immune reconstitution and outcomes in pediatric patients after ASCT with plerixafor based mobilization have not been reported in the literature as far as we have known. Therefore, we aimed to compare engraftment, hematopoietic and immune recovery and transplantation outcomes after ASCT between plerixafor plus G-CSF based and conventional mobilization group in pediatric patients.

Methods: Propensity score matching (PSM) by optimal method with 1:1 ratio was performed to determine the control group. Age, sex, diagnosis, transplantation year, conditioning regimen, and number of transplantation were used as matching variables. We evaluated available parameters such as the day of neutrophil and platelet engraftment, absolute neutrophil counts (ANCs), absolute lymphocyte counts (ALCs), platelet and hemoglobin counts and lymphocyte subsets (CD3, CD4, CD8 [T cell] counts). Mann-Whitney U test was used to compare between two groups.

Results: There were a total of 233 (21 plerixafor plus G-CSF based and 212 conventional mobilization group) patients who underwent HDC and ASCT in Seoul National University Children's Hospital between 2009 and 2016. By creating matched samples using PSM, 42 (21 plerixafor plus G-CSF based and 21 conventional mobilization group) patients were analyzed. The diagnoses were osteosarcoma in 14, brain tumor in 10, lymphoma in 6, neuroblastoma in 5, Ewing sarcoma in 4 and retinoblastoma in 3 patients. We used plerixafor plus G-CSF in patients who previously failed peripheral blood stem cell mobilization by chemotherapy and G-CSF. Patients received G-CSF (10 μg/kg) for 4 days, without prior chemotherapy. Then plerixafor (240 ug/kg) and G-CSF (10 ug/kg) were administered subcutaneously, at 10 and 2 hours before each apheresis. All 21 patients using plerixafor were mobilized successfully, and the median number of CD34+ cells were 10.65 (range 2.35-28.97) × 10⁶/kg after 1 to 4 cycles of apheresis without serious complications. Fifty six ASCTs were performed, including 14 tandem transplantation. The median age at ASCT was 6 (range 3.7-22.4) years. All patients in conventional mobilization group achieved engraftment, but 2 patients in plerixafor plus G-CSF based mobilization group died due to acute respiratory distress syndrome before platelet engraftment and 1 patient died of sudden cardiac arrest before neutrophil and platelet engraftment. The engraftment tended to be faster in conventional mobilization group, but there was no statistically significant difference except for the day of ANC more than 0.5 × 10⁹/L for 3 consecutive days (p=0.040). The ALC was lower in plerixafor plus G-CSF based mobilization group at one and six months after ASCT, respectively (p <0.001, p=0.041). The CD3, CD4 and CD8 count was lower in plerixafor plus G-CSF based mobilization group at one month after ASCT, respectively (p <0.001, p=0.007, p<0.001). The CD8 count was lower in plerixafor plus G-CSF based mobilization group (p=0.016), but the CD3 and CD4 count showed no statistical significant between-group differences at one year after ASCT, respectively (p=0.098, p=0.473). There was no significant between-group differences of overall survival (85.2% in plerixafor plus G-CSF based and 68.8% in conventional mobilization group, p=0.496) with a median follow-up duration of 22.7 (range 0.1-90.2) months.

Conclusion: Hematopoietic and immune recovery tended to be slower in plerixafor plus G-CSF based mobilization group, but was done to a similar extent over time. In addition, transplant outcomes are similar between two groups. Our study suggests that plerixafor could be used safely and enabled more patients to procced to successful ASCT in pediatric patients.