Effect of Long-Term Storage on Hematopoietic Progenitor Cell Transplant Product Quality

Abstract

Abstract Hematopoietic progenitor cell (HPC) transplant product quality indicators after prolonged cryopreservation are variable. A recent study in Europe demonstrated wide variability of cryopreservation times, from 1 to >20 years, with most centers storing products for 5 or 10 years. Thawed HPC viability using various ex vivo means and in vivo by studying neutrophil and platelet engraftment has generally supported preservation of CD34+ viability with prolonged storage. However, sample size, methods, and timepoints varied, and clear guidelines currently do not exist regarding how long HPCs can be stored. This study’s objectives include an evaluation of HPC quality indicators over time and if HPC product age and/or viability correlates with HPC engraftment. Retrospective record review was conducted on 837 HPC products thawed between January 1, 2011, and December 31, 2018. HPC products were sampled and characterized at thawing by flow cytometry for total nucleated cell (TNC) recovery, CD34+ recovery, and CD34+ viability (by 7-AAD). Preestablished acceptability criteria for TNC recovery, CD34+ recovery, and CD34+ viability were >80%, >40%, and >60%, respectively. If available, products with ANC engraftment data were further analyzed to correlate data with time to HPC engraftment. HPC products were stored between 3 and 5,943 days; 816 products were infused, ranging from 3 to 5,273 days in storage. Most (81%) HPC transplants occurred within the first year, 47 infusions occurred after storage >5 years, and 4 infusions occurred after storage >10 years. CD34 viability and percent recovery of TNC and CD34 were not significantly different as time in storage increased. Given sample paucity, 19 samples stored for >10 years were analyzed in individual years and grouped. In total, 96.5% samples stored for <1 year and 68% in samples stored >10 years met acceptability criteria for >60% CD34+ recovery; 98.9% samples stored <1 year met the >60% CD34+ viability acceptability threshold versus 90% of samples stored for >10 years. The oldest sample infused after storage of 5,273 days (14.4 years) showed 42% TNC recovery, 19% CD34+ recovery, and 84% CD34 viability; ANC engraftment data were not available. Sixty-five samples containing ANC engraftment data showed that time to ANC engraftment ranged from 9 to 15 days. No clear trend was present for viability or CD34 recovery when compared with days to engraftment based on limited data. Although rare, infusion of HPC products of extended duration occurs. This study suggests that HPC product quality may decrease after extended cryopreservation based on preestablished acceptability criteria. The oldest sample infused had preserved CD34+ viability despite significantly less TNC and CD34+ recovery, suggesting thawing might select for more robust HPCs. More studies with older samples are needed to determine the clinical impact of cryopreservation and if modification of current quality indicators could be useful clinically.