Use and Efficacy of Stem Cells Cryopreserved for More Than One Year.

Adequate viability after cryostorage is essential to allow engraftment of autologous haematopoietic progenitor cells (HPC). Information on the effect of prolonged cryopreservation on HPC viability in humans is limited although donations are routinely stored for over a year. Long-term storage is expensive and demonstration of clinical efficacy of HPC after long-term cryopreservation is important in order to justify the use of resources. Available reports describe only isolated cases in which old cells have been infused. We have conducted a retrospective survey of transplants using HPC stored >1 year within the National Blood Service in England. In total 75 patients received HPC that had been frozen for >1yr in NBS Laboratories. Patients had AML (21), NHL (21), myeloma (18), CML (5), Hodgkins disease (6) and other diseases (4). Fifty seven patients received PBSCs cryopreserved for >1 yr with median time in storage of 23 (12.1–65) months and median infused CD34 dose of 4.6 (1.2–85) ×10⁶/kg. Neutrophil recovery to >0.5 × 10⁹/l was 12 (4–49) days and platelets to > 20 × 10⁹/l was 13 (3–43) days. Thirteen patients received bone marrow that had been cryopreserved for >1 year (median 32 (13–67) months) with infused TNC dose of 1.7 (0.91 – 3.64) × 10⁸/kg. Time to neutrophils >0.5 × 10⁹/l was 17 (12–95) days and platelets > 20 × 10⁹/l 16 (12–66) days. A further 5 patients received a mixture of PBSCs and BM products all of which had been stored for > 1 year. Delayed neutrophil engraftment (neutrophils <0.5 × 10⁹/l at 21 days) occurred in 2/55 PBSC transplants and 2/8 BM transplants. Delayed platelet engraftment (platelets <20 × 10⁹/l at 28 days) occurred in 4/48 PBSC transplants and 4/8 BM transplants. In this survey, although the use of HPC cryopreserved for more than one year was infrequent, satisfactory engraftment was achieved in most patients. The rate of delayed engraftment was higher in BM as compared to PBSC transplants but numbers are too small for statistical analysis. In vitro viability assays were not available in this study but may help inform decisions on the use of cells stored for long periods.