Cryopreservation of unrelated donor (UD) hematopoietic stem cells (HSCs) does not appear to affect clinical or survival outcomes among patients have undergone hematopoietic stem cell transplantation (HSCT) since the COVID-19 pandemic began, according to research published in Bone Marrow Transplantation.

Prior to the COVID-19 pandemic, UD HSCs were collected and transported in fresh condition, without cryopreservation. Transport within and between countries was supported by the World Marrow Donor Association, and cross-border regulations were generally well defined.

The advent of COVID-19, however, led to barriers in delivery and necessitated cryopreservation of UD HSCs that could not immediately be used. There were, however, previously little data evaluating whether cryopreserved UD HSCs affect the outcomes of patients undergoing HSCT.

Continue Reading

For this study, researchers compared the clinical and survival outcomes of patients who underwent HSCT with cryopreserved UD HSCs with those of patients who had received fresh UD HSCs in the period preceding the COVID-19 pandemic. The researchers also evaluated the reasons that some cryopreserved UD HSCs were not used at all.

Overall, data from 64 patients were included, 32 of which were in the cryopreserved UD HSC group and 32 were in the fresh UD HSC group. In the fresh and cryopreservation groups, the median age at transplantation was 50.5 vs 52 years, respectively, 34.4% vs 28.1% of patients were female, and the most common diagnosis was acute myeloid leukemia in both groups (53.1% and 50%, respectively). The baseline characteristics were balanced between the 2 groups, though patients in the fresh UD HSC group had lower CD34-positive cell counts (median, 5.1 vs 6 in the cryopreservation group; P =.016).

Overall, the median neutrophil engraftment was 17.5 days in the cryopreservation group vs 17 days in the fresh UD HSC group. Length to platelet recovery (25.5 days in the cryopreservation group vs 19 days in the fresh group; P =.192) and full donor chimerism (35 days vs 31.5 days, respectively; P =.872) were not significantly different between the 2 groups. Patients in the cryopreservation group had a non-significantly higher risk of acute graft-vs-host disease (41% vs 31% in the fresh UD HSC group; P =.380). Survival outcomes, similarly, showed no significant difference.

The authors noted that 6 cryopreserved UD donations were not transfused because of logistical and clinical problems, including preservation procedure, packaging, and transportation.

“Importantly, wasting donations raises ethical issues, and logistic incidents that could affect product quality or timely delivery must be avoided,” the authors wrote. “For this purpose, improvements in disaster plans led by international guidelines and harmonization in cryopreservation requirements are urgently needed in these complex scenarios.”


Fernandez-Sojo J, Azqueta C, Valdivia E, et al. Cryopreservation of unrelated donor hematopoietic stem cells: the right answer for transplantations during the COVID-19 pandemic? Bone Marrow Transplant. Published online June 14, 2021. doi:10.1038/s41409-021-01367-x