Intra-apheresis recruitment of blood progenitor cells in children.

Background: Determination of the optimal duration of apheresis requires a careful examination of blood progenitor cell (BPC) kinetics during apheresis. Intra-apheresis recruitment of BPCs should be evaluated.

Study Design And Methods: Twenty-six apheresis procedures were performed in 13 children with various malignant disorders (ages, 10 months to 17 years; median, 7 years) to collect BPCs for autologous transplant, using a blood cell separator with 2 to 5.2 blood volumes processed. The subjects were divided into three groups according to age: below 1 year (n = 4), 2 to 10 years (n = 5), and 11 to 20 years (n = 4). BPCs were mobilized by a combination of chemotherapy and granulocyte-colony-stimulating factor (G-CSF; 2-7.5 micrograms/kg/day intravenous drip). The levels of circulating CD34+ cells and colony-forming units-granulocyte-macrophage (CFU-GM) were monitored to examine intra-apheresis recruitment. For every 50 mL per kg or 2 L of processed blood, 5-mL blood samples were collected via a central line.

Results: In the first apheresis procedure, more CD34+ cells were mobilized by the procedure itself in the infant group than in the older groups, and the number of cells decreased with the subject's age. When the same analysis was made during the second apheresis procedure, performed 1 day later, the levels of both CD34+ cells and CFU-GM had decreased to below the preapheresis values in all of the populations. Cell yields in the second apheresis procedure were significantly lower than those in the first.

Conclusion: Although several factors prevent a reliable analysis, the data suggest that the intra-apheresis recruitment of BPCs may be age-specific; the continuous and prolonged supply of cells from the bone marrow to peripheral blood that occurs during apheresis is more predominant in infants, which leads to the collection of proportionately more BPCs in younger children than in their older counterparts.