Effects of long-term cryopreservation at −80 °C on the viability and recovery of peripheral blood stem cells

Objectives Ensuring the long-term stability of cryopreserved peripheral blood stem cells (PBSCs) is critical for optimal patient outcomes. However, it remains unclear how long-term cryopreservation at −80 °C without controlled-rate freezing in a mechanical freezer affects these cells. Temperature changes may damage cells, reducing their viability. Therefore, in this study, we investigated the effects of long-term storage and the presence of other cells on the viability and recovery of cryopreserved PBSCs.Methods Autologous and allogeneic PBSC samples (n = 115) were cryopreserved at −80 °C in a mechanical freezer without controlled-rate freezing. Subsequently, CD34+ cell viability and recovery were evaluated after storage for up to 60 months using flow cytometry. The effects of co-existing blood cells on the cryopreservation of CD34+ cells were also examined.Results Cryopreservation for <24 months did not significantly reduce the viability and recovery of CD34+ cells, while decreases were observed following storage for >24 months. Further, cryopreservation with ≥10% granulocytes decreased CD34+ cell viability and recovery.Discussion The present findings suggest that storage beyond 24 months and containing a high proportion of granulocytes may have a negative impact on CD34⁺ cell viability and recovery. Attention to storage duration and contaminating cell populations could help support more stable outcomes during cryopreservation at −80 °C.Conclusions The cryopreservation conditions employed in this study did not significantly reduce CD34+ cell viability and recovery during storage for up to 24 months. A higher granulocyte content was associated with lower post-thaw CD34+ viability and recovery.