Cold storage, warm outcomes: Viability of Haematopoietic stem cells after extended cryopreservation

Hematopoietic progenitor stem cells (HPSCs) are essential for restoring hematopoiesis following high-dose chemotherapy in patients with hematological malignancies, and cryopreservation enables flexibility in transplantation timing. This study evaluated the long-term viability of HPSCs processed and stored under South African National Blood Service protocols. Fifty cryopreserved products stored for 12-156 months (mean: 38.1 months) were analysed post-thaw using flow cytometry with a modified ISHAGE protocol, assessing CD34⁺ and CD45⁺ cells with 7-AAD staining. Products were considered viable if ≥ 80 % CD34⁺ and ≥ 50% CD45⁺ cells were 7-AAD-negative. All products met viability thresholds, with mean CD34⁺ viability of 98.96% (range: 87-100%) and CD45⁺ viability of 66.58% (range: 50-87%). The longest-stored product (13 years) retained 99% CD34⁺ and 59% CD45⁺ viability, and no correlation was observed between storage duration and viability. These findings confirm that HPSCs maintain high viability for up to 13 years, supporting the robustness of cryopreservation protocols and reinforcing the feasibility of long-term stem cell banking for clinical use.