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The purpose of this study was to explore methods of selectively enriching CD34 + haematopoietic progenitor cells (HPC) in mononuclear cell (MNC) preparations, and to outline a procedure for cryopreservation and thawing of manufactured material. Density gradient centrifugation of umbilical cord blood was achieved using Ficoll-Paque™ media at 1.077 g/mL and 1.065 g/mL densities and Leucosep preparation tubes. Post-process samples were analysed for CD34 + and MNC content. Finally, MNCs were frozen down at a concentration of 8.5 × 10 6 cells/mL in CryoStor CS10 using an Asymptote VIAFreeze controlled rate freezer at a rate of - 2 °C per minute, then thawed and analysed for viability and recovery. Processing with 1.065 g/mL media selectively depleted non-HPC cell types, producing an approximately fourfold increase in CD34 + frequency (M ± 1SD = 1.4 ± 1.3%, P < 0.01) relative to the pre-process sample (M ± 1SD = 0.4 ± 0.3%), whereas 1.077 g/mL media produced only a twofold enrichment (0.7 ± 0.6, P < 0.01). This was not accompanied by any significant forfeit of CD34 + recovery (79 ± 32% vs. 78 ± 32% respectively; P = 0.87). The MNCs generated by the 1.065 g/mL procedure were of greater purity (96 ± 2%) than in the 1.077 g/mL procedure (80 ± 7%, P < 0.01). Post-thaw, MNC viability was 95 ± 1% and CD34 + viability was 98 ± 1%. Ultra-pure MNCs rich in CD34 + HPCs can be generated with a simple, inexpensive modification to Ficoll-Paque™ media. These products can be easily cryopreserved using a simple controlled rate freezing procedure., (© 2023. The Author(s), under exclusive licence to Springer Nature B.V.)

Quality control (QC) segments conjoined to a bulk sample container are used to evaluate the viability and quality of cryopreserved umbilical cord blood (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 the quality of the cryopreserved product. In current practice, there is typically post-thaw variation between the QC segment and the bulk sample which if suggestive of inadequate performance, could lead to material being needlessly discarded. In this study, these performance differences were quantified. Two cooling protocols in common use, 1 with and 1 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 with the bulk samples, a consequence of their lower volume, thereby enhancing damaging osmotic stress. A reduction in total viable cells of approximately 10% was recorded in the QC segments compared with 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 altered composition of the post-thaw cell population., (Copyright © 2019 American Society for Transplantation and Cellular Therapy. Published by Elsevier Inc. All rights reserved.)