Michael Verneris at the University of Minnesota and his coworkers have systematically analyzed the quality of transplanted umbilical cord blood units from 1992 to 2013 and then compared the quality of the cord blood with the length of time the cord blood had been frozen. Umbilical cord blood (UCB) has the advantage of being collected and frozen (cryopreserved) for years prior to use, but the length of time for which the cord blood has been frozen has not been examined. Verneris and his research group set out to do just that.
Work from mice has shown that length of time umbilical cord blood is frozen has little to no effect on the performance of that blood when it is used in a transplant. Is this the case for human UCB?
Verneris and his colleagues analyzed 288 single UCB units used for transplantation from 1992-2013. The length of time these UCB units were frozen ranged from 0.08 to 11.07 years. Once the UCB units were thawed, the percentage of recovered, nucleated cells (so-called total nucleated cells or TNCs) were determined.
Verneris and others showed that the number of years the UCB unit spent in cryopreservation had no impact on TNC recovery nor number of viable cells available in the UCB after thawing. Duration of cryopreservation also had no impact on how well the cells in the UBC unit engrafted in single UCB transplant patients.
These results show that UCB units can undergo cryopreservation for at least 10 years with no impact on clinical outcomes. Does freezing UBC for longer periods make a difference? Without further work, it is hard to say, but it seems that freezing cord blood for ten years does not affect its efficacy.