Determining post-thaw CD34+ cell dose of cryopreserved haematopoietic progenitor cells demonstrates high recovery and confirms their integrity

Background: The acceptable dose of haematopoietic progenitor cells (HPCs) for transplantation is generally based on the number of CD34+ cells determined prior to cryopreservation. Commonly, cryopreservation is associated with total nucleated cell viability loss. Because HPCs have been shown to be more resistant to cryopreservation damage than nucleated cells overall, low viability may not reflect the quality and integrity of the thawed product. Methods: Peripheral blood HPC products from 45 mobilized allogeneic and autologous donors were harvested by continuous flow blood separation and cryopreserved in 7.5% dimethyl sulfoxide. The number of viable CD34+ cells was determined by flow cytometry. Viability was measured by trypan blue (TB) uptake and 7-aminoactinomycin D (7-AAD) flow cytometry. Results: Post-thaw HPC products were analysed for viability, CD34+ cell recovery and engraftment capability. The average post-thaw viable CD34+ cell recovery was 86.4%, while the average post-thaw viability, measured by TB or 7-AAD, was 74.0% and 57.0%, respectively. Most of the cells that did not survive cryopreservation were of the granulocyte series. All of the donors who underwent transplantation engrafted, mostly within 14 days. Conclusions: Our data show that most CD34+ cells survive cryopreservation, regardless of the overall post-thaw total nucleated cell viability. Measuring the number of viable CD34 cells post-thaw might be of importance, and in cases of low viability can confirm the quality of the product issued.