Positive Selection and Transplantation of Peripheral CD34+ Progenitor Cells: Feasibility and Purging Efficacy in Pediatric Patients with Neuroblastoma

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Abstract
Peripheral stem cells were mobilized and collected in 20 children with stage 4 neuroblastoma. A total of 37 leukaphereses were performed in the 20 patients. The mean number of collected cells was 5.6 ± 2.4 × 108/kg (range 1.9–10.5), and the number of collected CD34+ progenitors was 6.1 ± 6.3 × 106/kg (range 0.75–21.7). CD34-positive selection was performed using the CellPro method. Of the adsorbed cells, 42 ± 20% (range 4.3–76.6) stained positively for CD34, and the number of positively selected CD34+ cells was 2.0 ± 1.9 × 106/kg (range 0.09–7.1). The mean recovery of CD34+ cells was 36 ± 20% (range 6–67). For detection of contaminating neuroblastoma cells before and after CD34-positive selection, a murine antidisialoganglioside GD2 antibody (14.G2a) was used, followed by the alkaline phosphatase antialkaline phosphatase (APAAP) method. Before the positive selection, various numbers of contaminating neuroblastoma cells were found in the leukaphereses of 7 patients. After positive selection, neuroblastoma cells were still detectable in all 7 patients, with a mean log depletion of tumor cells of 1.41 ± 0.45 (range 0.69–2.13). In 1 patient, contaminating neuroblastoma cells were found only after CD34-positive selection. In 15 of the 20 patients, high-dose chemotherapy was performed, and positively selected CD34+ cells were reinfused in 12 patients. In 10 of these, the mean time to reach >0.5 × 109/L granulocytes was 12.3 ± 1.7 days (range 10–16). One patient died at day 7 due to sepsis, and in 1 patient the backup was given at day 15. Because of the low number of collected CD34+ cells, 3 patients were grafted with a combination of unmanipulated PBSC and CD34+ progenitors. In summary, we have shown that positive selection of peripheral CD34+ progenitors is feasible in pediatric patients. However, strategies to improve the recovery of the CD34+ cells and the purging efficacy of this method (i.e., higher enrichment of CD34+ cells, combination of positive and negative selection methods) should be evaluated further.