Cord (placental) blood storage: extent and functional aspects

In 2010, two articles were published in TRANSFUSION dealing with the storage of umbilical (placental) cord blood cell units (UCB). Both articles studied the influence of temperature on maintenance of viable total nucleated cells, CD34+ cells, and committed progenitors (colony forming cells [CFCs]). They used, as a control group, the UCB stored at a temperature of 4°C, that is, the temperature employed in routine storage and transportation. With that respect, the first article showed that there were no significant differences during storage of 84 to 88 hours comparing to time zero values (n = 10) in the recoveries of total nucleated cells, CD34+ cells, and CFCs. However, in the second article, there was evidence of a difference for these three aspects of cells over time. However, this result was based on only three samples. Since this issue is of great importance for practice (the dilemma: could the storage of UCB be extended or not), we studied the storage of 12 UCB units for 72 hours to evaluate if there were any significant decrease for each of these cell populations. Cord blood was collected using Macopharma UCB collection and storage bags (Macopharma, Tourcoing, France) and maintained at 4°C. The viable cell count was obtained using an automatic counter (Cell-Dyn 3500R, Abbott, Ramsey, MN). The number of viable CD34+ cells was obtained using simultaneous staining with anti-CD34 and anti-CD45 as well as 7-aminoactinomycin-D (FACSCalibur flow cytometer, Becton Dickinson, San Jose, CA). CFC detection was made by a methylcellulose ready-touse kit (Stem Alpha ID, Stem Alpha, St Clément les Places, France; 150 ¥ 10 cells per dish; Nunc, Roskilde, Denmark) cultured for 14 days in water-saturated atmosphere at 37°C with 5% CO2. The number of total cells, CD34+ cells, and CFCs decreased for each individual sample after 72 hours of storage (Fig. 1). This series, limited in the number of samples, did not exhibit “Gaussian” distribution, and only two time points (0 and 72 hr) were compared. Thus we used a nonparametric Wilcoxon test for paired (dependent) samples. We found a significant decrease in the recovery for each of these three cell categories (Fig. 2). Concerning CFCs, which is the only functional variable in this study, it should be stressed that the mean recovery was below 80% at 72 hours, which represents an obvious detrimental effect of prolonged storage. In addition, in real use, these UCB cells would be volume reduced, frozen, and thawed. Each of these steps is associated with a cellular loss to some extent that could be increased by cell vulnerability that might be potentiated by length of storage (our experimental observations). Accordingly, to evaluate the possibility to extend the storage period to 72 hours, these variables (including CFCs) should be tested throughout the usual complete process through to the postthawing period. Furthermore, no data are available concerning the maintenance of stem cell populations