Transient warming affects potency of cryopreserved cord blood units

Cryopreserved cord blood units (CBUs) can be exposed to transient warming events (TWEs) during routine banking operations, which may affect their potency. NetCord-FACT guidelines recommend removal of these CBUs from inventory. The objective of this work was to evaluate warming kinetics of frozen CBUs in different settings to determine the optimal working environment and define the impact of different TWE scenarios on CB post-thaw quality and potency.

The warming kinetics of frozen CBUs was influenced by both working surfaces and ambient working temperature, with cold plates providing better protection than vinyl or metal surfaces. Measurement of time for required operational activities revealed that CBUs are probably exposed to core temperatures greater than -150°C even when cold plates are used to reduce warming rates.

On the basis of the warming kinetics and observed operational activities, three TWE causing scenarios (control, typical, worst case) were investigated using a pool-and-split design and cell viability, recovery and potency (colony-forming unit [CFU]) assays were performed. TWEs were found to have little impact on the recovery of total nucleated cells or on the viability of CD34⁺ cells. In contrast, the viability and recovery of CD45⁺ cells in the smaller CBU compartments were reduced by TWEs. Moreover, the worst-case TWE reduced CFU recovery from CBUs, whereas the typical-scenario TWE had little effect.

Our results demonstrate that the distal segment underestimates the viability and potency of CBUs and that TWEs can affect the post-thaw viability and potency of CBUs. Although TWEs are almost inevitable during cord-blood banking operations, their effects must be diminished by reducing exposure time, using cold plates and strict operational protocols, to prevent worst-case TWEs.