Cryopreserved umbilical cord blood (CB) is increasingly used as a cell source to reconstitute marrow in hematopoietic stem cell transplant patients. Delays in cryopreservation may adversely affect cell viability, thereby reducing their potential for engraftment after transplantation.STUDY DESIGN AND METHODS:
The impact of delayed cryopreservation for up to 3 days on the viability of both CD45+ and CD34+ cell populations in 28 CB donations with volumes of 58.40 ± 15.4 mL (range, 39.4-107.4 mL) was investigated to establish whether precryopreservation storage time could be extended from our current time of 24 to 48 hours in line with other CB banks. Viability was assessed on 3 consecutive days, both before and after cryopreservation, by flow cytometry using 7-aminoactinomycin D (7-AAD) and annexin V methods.RESULTS:
The results using 7-AAD and annexin V indicated the viability of CD34+ cells before cryopreservation remained high (>92.33 ± 4.11%) over 3 days, whereas the viability of CD45+ cells decreased from 86.36 ± 4.97% to 66.24 ± 7.78% (p < 0.0001) by Day 3. Storage time significantly affected the viability of CD34+ cells after cryopreservation. Using 7-AAD, the mean CD34+ cell viability decreased by approximately 5% per extra day in storage from 84.30 ± 6.27% on Day 1 to 79.01 ± 7.44% (p < 0.0057) on Day 2 and to 73.95 ± 7.54% (p < 0.0001) on Day 3. With annexin V staining CD34+ cell viability fell by approximately 7% per extra day in storage from 77.17 ± 8.47% on Day 1 to 69.56 ± 13.30% (p < 0.0194) on Day 2 and to 62.89 ± 15.22% (p < 0.0002) on Day 3.CONCLUSION:
This study demonstrates that extended precryopreservation storage adversely affects viability and should be avoided.