A French single-center experience on allogeneic stem cell transplant cryopreservation during severe acute respiratory syndrome coronavirus 2 pandemic.

Background Aims: Allogeneic hematopoietic stem cell transplantation (allo-SCT) is a curative treatment for chemo-resistant hematological malignancies. Because of transport restriction imposed by the coronavirus disease 2019 pandemic, regulatory bodies and societies recommended graft cryopreservation before recipient conditioning. However, the freezing and thawing processes, including washing steps, might impair CD34+ cell recovery and viability, thereby impacting the recipient engraftment. Over 1 year (between March 2020 and May 2021), we aimed to analyze the results of frozen/thawed peripheral blood stem cell allografts in terms of stem cell quality and clinical outcomes.

Methods: Transplant quality was evaluated by comparing total nucleated cells (TNCs), CD34+ cells and colony-forming unit-granulocyte/macrophage (CFU-GM)/kg numbers as well as TNC and CD34+ cell viabilities before and after thawing. Intrinsic biological parameters such as granulocyte, platelet and CD34+ cell concentrations were analyzed, as they might be responsible for a quality loss. The impact of the CD34+ cell richness of the graft on TNC and CD34 yields was evaluated by designing three groups of transplants based on their CD34 /kg value at collection: >8 × 10 /kg, between 6 and 8 × 10/kg and <6 × 10/kg. The consequences of cryopreservation were compared in the fresh and thawed group by evaluating the main transplant outcomes.

Results: Over 1 year, 76 recipients were included in the study; 57 patients received a thawed and 19 patients a fresh allo-SCT. None received allo-SCT from a severe acute respiratory syndrome coronavirus 2-positive donor. The freezing of 57 transplants led to the storage of 309 bags, for a mean storage time (between freezing and thawing) of 14 days. For the fresh transplant group, only 41 bags were stored for potential future donor lymphocyte infusions. Regarding the graft characteristics at collection, median number of cryopreserved TNC and CD34+ cells/kg were greater than those for fresh infusions. After thawing, median yields were 74.0%, 69.0% and 48.0% for TNC, CD34+ cells and CFU-GM, respectively. The median TNC dose/kg obtained after thawing was 5.8 × 10, with a median viability of 76%. The median CD34+ cells/kg was 5 × 10, with a median viability of 87%. In the fresh transplant group, the median TNC/kg was 5.9 × 10/kg, and the median CD34+ cells/kg and CFU-GM/kg were 6 × 10/kg and 276.5 × 10/kg, respectively. Sixty-one percent of the thawed transplants were out of specifications regarding the CD34+ cells/ kg requested cell dose (6 × 10/kg) and 85% of them would have had this dose if their hematopoietic stem cell transplant had been infused fresh. Regarding fresh grafts, 15.8% contained less than 6 × 10 CD34+ cells /kg and came from peripheral blood stem cells that did not reach 6 × 10 CD34+ cells /kg at collection. Regarding the factor that impaired CD34 and TNC yield after thawing, no significant impact of the granulocyte count, the platelet count or the CD34+ cells concentration/µL was observed. However, grafts containing more than 8 × 10 /kg at collection showed a significantly lower TNC and CD34 yield.

Conclusions: Transplant outcomes (engraftment, graft-versus-host disease, infections, relapse or death) were not significantly different between the two groups.