Difference in Viability of CD34+ Cells in Cryopreserved Cord Blood According to Evaluation Methods

Background: On performing umbilical cord blood (UCB) transplantation, faster engraftment may lead better clinical outcome. Because transplanted viable cell count in UCB is related to the engraftment, accu- rate evaluation of viability of CD34+ cells in cryopreserved UCB has clinical implication. We examined the difference in viability of cells in cryopreserved UCB according to the duration of cryopreservation and different methods. Methods: A total of 60 UCB samples which were cryopreserved for 1 to 4 years were used in this study. Viability of cryopreserved cells were examined with trypan blue exclusion assay, DNA contents analysis, caspase-3 activation test, intracellular esterase activity and Annexin-V/PI staining. Results: After thawing the cryopreserved UCB, 89% of the total MNCs and 84% of CD34+ cells were viable as identified by trypan blue exclusion assay. In the CD34+ cell population, the cell death rate was found to be 47% by Annexin-V/PI staining and less than 5% by DNA contents analysis. However, cspase-3 activity failed to document apoptosis. The intracellular esterase activity test also showed a cell death rate of about 10 ∼20% at 2, 4, and 6 hours after thawing.