Assessing the toxic effects of DMSO on cord blood to determine exposure time limits and the optimum concentration for cryopreservation

Background and Objectives Advantages of using cord blood (CB) over other sources of haematopoietic progenitor cells, such as bone marrow, include the ability to cryopreserveand bank the samples until requested for a transplant. Cryopreservationrequires the addition of a cryoprotectantto prevent the formation of intracellular ice during freezing. Dimethyl sulphoxide (DMSO) is commonly used at a concentration of 10% (v/v); however, there is evidence to suggest this chemical is toxic to cells as well as to patients after infusion. Materials and Methods The toxic effects of DMSO were assessed through cell viability and in vitro functional assays in fresh and post-thaw CB samples before determining the maximum exposure time and optimal concentration for cryopreservation. Results A dose-dependent toxicity of DMSO was observed in fresh samples with 40% removing all viable and functional haematopoietic progenitor cells (HPC). In fresh and post-thaw analysis, minimal toxic effect was observed when cryopreservationwas delayed for up to 1 h after 10% DMSO addition. After thawing, DMSO washout was superior to dilution or unmanipulated when maintained for long periods (advantage observed 1 h after thawing). Finally, the optimum concentration for cryopreservingCB was found to be 7·5 to 10% with detrimental effects observed outside of this range. Conclusion These results support the use of 7·5–10% as the optimal DMSO concentration and the maximum exposure time should be limited to <1 h prior to freezing and 30 min post-thaw.