Recovery and post-thaw assessment of human umbilical cord blood cryopreserved as quality control segments and bulk samples.

Abstract Quality control (QC) segments conjoined to a bulk sample container are used to evaluate the viability and quality of cryopreserved UCB. Such QC segments are, typically, attached lengths of sealed tubing that are cooled concurrently with the bulk sample, both containing material from the same donor. QC segments are thawed independently of the bulk sample to assess quality of the cryopreserved product. In current practice there is, typically, post-thaw variation between the QC segment and the bulk sample which, if suggesting inadequate performance, may lead to material being needlessly discarded. In this study these performance differences have been quantified. Two cooling protocols in common use, one with and one without a ‘plunge' step to induce ice nucleation, gave equivalent results that maintained the QC segment versus bulk sample differences. Ice nucleated at significantly lower temperatures in the QC segments compared to the bulk samples, a consequence of their lower volume, thus enhancing damaging osmotic stress. A reduction in total viable cells of approximately 10% was recorded in the QC segments compared to comparable bulk samples. It has been shown that CD45+ cells are more adversely impacted by this lower ice nucleation temperature than CD34+ cells, which can result in an altered composition of the post-thaw cell population.