ABSTRACT
Clinical evidence of hematopoietic restoration with umbilical cord blood (UCB) grafts indicates the UCB can be a useful source of hematopoietic stem cells for routine bone marrow reconstitution. Considering (10 +/- 5) x 10(8) nucleared cells per cord blood unit, there is a potential limitation for the use of cord blood in adults, which, however, can be overcome by ex vivo expansion of cells. A prerequisite for expansion is the significantly higher recovery of MNC, CD34+ cells and colony-forming cells (CFC) by thawing cryopreserved MNC. Cooling rate always acts as a critical factor that can affect the recovery of cells. Although the rate of - 1 degrees C/min is adopted in most of the cryopreservations, no data has been reported about the detailed effects of different cooling rates. The aim of the study was to reveal the different effects of cooling rates on cryopreservation of hematopoietic stem cells from cord blood. UCB samples were collected, and cryopreserved as mononuclear cells (MNC) with different cooling rates of - 0.5 degrees C/min, - 1 degrees C/min, - 5 degrees C/min, and the recovery and viability of MNC and CD34+ cells, the clonogenic capacity and the ex vivo expansion potential of UCB progenitor cells were evaluated after thawing. With - 1 degrees C/min cooling rate, the recovery of MNC reached 93.3% +/- 1.8% , viability 95.0% +/- 3.9% , recovery of CD34+ cells 80.0% +/- 17.9% , and clonogenic recovery were 87.1% +/- 5.5%, 88.5% +/- 8.9%, 86.2% +/- 7.4% for BFU-E CFU-GM CFU-MK, respectively. After 14 days of liquid culture, no significant difference was detected in CFC expansion between fresh and cryopreserved MNC cells with - 1 degrees C/min cooling rate, but this was not the case with - 0.5 degreesC/min and - 5 degrees C/min. In conclusion, it was demonstrated that controlling the rate at - 1 degrees C/min is more suitable for cryopreservation of hematopoietic stem cells than - 0.5 degrees C/min and - 5 degrees C/min.