Peripheral blood stem cell transplantation in young children: experience with harvesting, mobilization and engraftment.

The purpose of this study was to determine the feasibility and assess optimal timing of harvesting peripheral blood stem cells (PBSC) for transplantation in young children. Thirteen children with body weight less than 25 kg, mean age of 3.9 years (1-9 yrs) who had recurrent solid tumors and leukemia were given tumor specific chemotherapy followed by i.v. rhG-CSF (5 microg/kg/d) for stem cell mobilization. Cytaphereses were done through a central venous line (CVL) during the marrow recovery phase (WBC >0.5 x 10(9)/l). The phereses were analyzed separately and assigned to three groups depending on the WBC at the time of the pheresis: Group I (WBC <1.0 x 10(9)/l), Group II [WBC in the range 1.0-3.0 x 10(9)/l] and Group III (WBC >3.0 x 10(9)/l). Samples from each harvest were assayed for cell count, CFU-GM, BFU-E, CD34+ cell count, and tumor cell immunocytology in patients with neuroblastoma (NBL). A median of 3.2 x 10(8) mononuclear cells per kg (MNC/kg), [mean 2.8 x 10(8) MNC/kg, standard error of the mean (SEM) +/- 0.74 (1.1-4.7)] were infused following myeloablative therapy. 78 phereses were performed in 13 children with a median weight of 18 kg (10-25 kg). A median of 5 phereses were performed per patient. There were no significant differences in the percentage and number of CD34+ cells, CFU-GM or BFU-E colonies assayed by plating 0.5 x 10(5) cells. Differences could be found in the total number of MNC (p<0.008) and the number of MNC/kg (p<0.001) between Groups II and III. No tumor cell contamination was detected in the NBL patients by immunocytology. All patients were rescued with PBSC and achieved sustained white cell engraftment (ANC >0.5 x 10(9)/l) at a median of 13.5 d (10-25 d) and platelet engraftment (untransfused platelet count >20.0 x 10(9)/l) at a median of 29 d (12-63 d). The only toxicity encountered during the phereses was thrombocytopenia in 4 patients whose median post-pheresis platelet count was 6.0 x 10(9)/l (3.0-9.01). It is concluded that collection of PBSC in young children is feasible and safe and can be performed through a cuffed CVL at the time of WBC recovery post mobilization with chemotherapy and G-CSF. Cytopheresis can be effectively performed when the peripheral WBC count approaches 1.0 x 10(9)/l. Following stem cell infusion, engraftment was prompt and durable.