The Effects of Long-Term Freezing on Umbilical Cord Blood

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.

Frozen Stem Cells Taken from a Cadaver Five Years Ago Vigorously Grow

It is incumbent upon regenerative medicine researchers to discover non-controversial sources of stem cells that are safe and abundant. To that end, harvesting stem cells from deceased donors might represent an innovative and potentially unlimited reservoir of different stem cells.

In this present study, tissues from the blood vessels of cadavers were used as a source of human cadaver mesenchymal stromal/stem cells (hC-MSCs). The scientists in this paper successfully isolated cells from arteries after the death of the patient and subjected them to cryogenic storage in a tissue-banking facility for at least 5 years.

After thawing, the hC-MSCs were re-isolated with high-efficiency (12 × 10[6]) and showed all the usual characteristics of mesenchymal stromal cells. They expressed all the proper markers, were able to differentiate into the right cell types, and showed the same immunosuppressive activity as mesenchymal stromal cells from living persons.

Thus the efficient procurement of stem cells from cadavers demonstrates that such cells can survive harsh conditions, low oxygen tensions, and freezing and dehydration. This paves the way for a scientific revolution where cadaver stromal/stem cells could effectively treat patients who need cell therapies.

See Sabrina Valente, and others, Human cadaver multipotent stromal/stem cells isolated from arteries stored in liquid nitrogen for 5 years.  Stem Cell Research & Therapy 2014, 5:8.