Restoring mitochondrial function promotes hematopoietic reconstitution from cord blood following cryopreservation-related functional decline.

Umbilical cord blood (UCB) plays substantial roles in hematopoietic stem cell (HSC) transplantation and regenerative medicine. UCB is usually cryopreserved for years before use. It remains unclear whether and how cryopreservation affects UCB function. We constructed a single-cell transcriptomics profile of CD34+ hematopoietic stem and progenitor cells (HSPCs) and mononuclear cells (MNCs) from fresh and cryopreserved UCB stored for 1, 5, 10, and 19 years. Compared with fresh UCB, cryopreserved HSCs and multipotent progenitors (MPPs) exhibited more active cell-cycle and lower expression levels of HSC and multipotent progenitor signature genes. Hematopoietic reconstitution of cryopreserved HSPCs gradually decreased during the first 5 years but stabilized thereafter, aligning with the negative correlation between clinical neutrophil engraftment and cryopreservation duration of UCB. Cryopreserved HSPCs also showed reduced megakaryocyte generation. In contrast, cryopreserved NK cells and T cells maintained a capacity for cytokine production and cytotoxicity comparable to that of fresh cells. Mechanistically, cryopreserved HSPCs exhibited elevated ROS, reduced ATP synthesis, and abnormal mitochondrial distribution, which collectively led to attenuated hematopoietic reconstitution. These effects could be ameliorated by sulforaphane (SF). Together, we elucidate the negative effect of cryopreservation on UCB HSPCs and identify SF as a mitigation strategy, broadening the temporal window and scope for clinical applications of cryopreserved UCB.