Thawing methods do not affect cell viability of CD45+and CD34+cells, but long-term cryopreservation of umbilical cord blood units generally decreases cell viability

Introduction: Umbilical cord blood units (UCBUs) are collected and cryopreserved in biobanks for a future transplant. Hematopoietic stem cells and hematopoietic progenitor cells (HSC/HPC) present in UCB can be damaged due to factors such as the cryopreservation process, the thawing process, and prolonged storage time. Methods: UCBUs (n = 27) were obtained from the Biobank of the National Center of Blood Transfusion (NCBT) from Mexico. They contained three attached segments of UCBU, including 1.0-2.3 x 10(6) CD34+ cells prior to cryopreservation and were stored during the period from 2003 to 2015. Each UCB segment was thawed with three different methods and CD34 cells, CD45 cells, and 7-AAD were identified by flow cytometry. Furthermore, we carried out CFU assays, and trypan blue staining. Results: Viable CD45+ (vCD45+) cells, vCD34+ cells, CFU, and percentage of E-Clone were not statistically significant among three different thawing methods. The number of vCD45+ and vCD34+ cells diminished in the three thawing methods compared with the same cells prior to their cryopreservation (p < 0.0001). vCD45+ and vCD34+ cells diminished in the >= 10-year cryopreservation group (p < 0.001). In addition, percentage of recovery of vCD45+ and vCD34+ cells diminished in this same group (p = 0.013 and p < 0.0001, respectively). Conclusion: The thawing methods did not affect either cell viability (vCD45+ and vCD34+ cells) or pluripotency (CFU, percentage of E-Clone) in attached segments of UCBUs. The 10-year cryopreservation time in attached segments of UCBUs alters the number of vCD45+ and vCD34+ cells; however, it does not affect their pluripotency.