Impact of uncontrolled freezing and long-term storage of peripheral blood stem cells at - 80 °C on haematopoietic recovery after autologous transplantation. Report from two centres.

Controlled-rate freezing and storage in vapour phase nitrogen are used by most transplantation teams for the cryopreservation and storage of peripheral blood haematopoietic stem cells (PBSC). In this study, we analysed 666 autologous PBSC transplants after uncontrolled freezing and storage of PBSC at -80 °C. Statistical analysis showed that neutrophil recovery was associated with both the infused CD34(+) cell dose (P=0.01) and the post transplantation use of growth factors (P<0.001) and that platelet recovery was associated with the infused CD34(+) cell dose (P<0.001) and with the diagnosis (P=0.02). We analysed three groups according to the duration of the cryopreservation period (less than 6 months, between 6 and 12 months or more than 1 year). Haematopoietic recovery was not found to be adversely affected by longer storage at -80 °C. The haematopoietic recoveries of 50 pairs of sequential transplantations from the same PBSC mobilization were analysed. Despite prolonged cryopreservation, there were no statistically significant differences in neutrophil (P=0.09) or platelet (P=0.22) recovery in the second compared with the first transplant. In conclusion, the long-term storage of PBSC at -80 °C after uncontrolled-rate freezing is an easy and comparatively inexpensive cryopreservation method that leads to successful haematopoietic recovery even after prolonged storage.