Peripheral Blood Progenitor Cell Collection in Low-Weight Infants (36 patients; 69 Large Volume Leukapheresis Procedures)

Peripheral blood progenitor cells (PBPC) have increasingly become the preferred source of stem cells for autologous transplantation due to their easier accessibility, rapid engraftment and higher safety. The harvest of PBPC in paediatric patients assumes critical importance, particularly in low-weight infants, in whom optimizing the procedure allows the collection of sufficient number of cells, with a reduced number of leukapheresis. The published data of these low-weight patients are scarce, and very likely the accumulation of cases will contribute to optimize the procedure.

In this single centre study we retrospectively analyzed data of 69 large volume leukapheresis (LVL) from 36 low weight (< 20Kg) paediatric patients between January 1998 and April 2008. Primary diagnosis included several malignancies: neuroblastomas (21 cases), meduloblastomas (4 cases), acute leukaemia (4 cases), retinoblastoma (2 cases) and other 5 cases with various solid tumours. All the LVL procedures underwent with a continuous flow blood separator (COBE Spectra) after priming the extracorporeal line with red blood cells and acid-citrate-dextrose (ACD) was used as the anticoagulant.

Mean body weight was 15,78kg (ranging 9–19Kg), and a median age of 44 months (ranging 7–88 months). Blood withdrawn at a mean rate of 33,8 mL/min (standard deviation [SD] 8,0), through central vein catheters and using 4 volemias (one case with 3), lasting a mean 133,43 minutes/procedure (ranging 212–101 min). A mean of 4881,78 ml of blood was processed (ranging 2101–7327mL).

Leukapheresis was performed on the fifth day of G-CSF stimulation in most of the procedures (66,7%), while 21 patients were submitted to stimulation for a longer period (18,8% with 6 days, 7,2% with 7 days and 4,3% with eight). The mean G-CSF dose used was 203,06 μg/d (ranging 105–400 μg/d).

The mean number of CD34⁺ cells in peripherical blood, before leukapheresis, was 20,4 ×10⁶ cells (ranging 1–216 ×10⁶ cells), while the PBPC collection yielded 2,73 ×10⁶ CD34⁺/Kg (ranging 0,1–28,94 ×10⁶ CD34⁺/Kg).

The majority of LVL procedures (53,6%) were initiated with a peripherical blood CD34⁺ count inferior to 15×10⁶ cells. Only 33,3% of each LVL procedure harvest sufficient PBPC (> 2,5 ×10⁶ CD34⁺/Kg), most of which from patients with peripherical blood CD34⁺ count superior to 15×10⁶ cells (59,4%). There is a significant correlation between peripherical blood CD34⁺ count, before leukapheresis, and collected PBPC CD34⁺ (Pearson chi-square 18,212; p<0,01).

Every patient underwent a mean of 1,9 apheresis procedures (range 1–5), 20 patients required only a single apheresis to collect the minimum requirement of CD34⁺/Kg, 6 patients underwent leukapheresis on two consecutive days, while 7 patients required a second course of mobilization with G-CSF in the following month, to achieve the necessary amount of CD34⁺ cells.

The leucocyte count variation during the procedure was + 8,12 cells/μL (18,37 [SD 9,0]–26,49 cells/μL [SD 28,6]); the platelet (plt) count variation was negative 63,78 ×10³ plt/μL (145 [SD 78,5]–81,53×10³ plt/μL [SD 39,47]); the haemoglobin count variation was negative 1,45 g/dL (9,79 [SD 1,35]–8,34 g/dL [SD 1,49]). There were no significant differences between heart rate (105,86 [SD 22,9]–113,31 bpm [SD 22,5]) and systolic blood pressure before and after the procedure (114,28 [SD 12,54]–108,38 mmHg [SD 15,72]).

There were adverse events in 14,5% of LVL procedures, most of them related with symptomatic hypocalcaemia (6 cases), corrected with calcium injection. Two cases of catheter malfunctioning were reported, one of them associated with haemodinamic instability. There was also a case of high blood pressure peak with no haemodinamic instability and another case with vomiting. All these patients underwent PBPC collection, in the following days.

Twenty five percent of the cases needed transfusion support, with 9 cases requiring blood transfusion, and 8 cases requiring platelet transfusion (platelet count fell below 50×10³ plt/μL).

Nineteen patients underwent autologous transplantation, using the collected cells. There were no incidents regarding the storage of the PBPC.

In conclusion, harvesting PBPC in small children is effective and safe, as this data shows. Future publications will allow to gather the necessary experience in order to optimize this procedure.