Primitive hematopoietic progenitors within mobilized blood are spared by uncontrolled rate freezing

Uncontrolled-rate freezing techniques represent an attractive alternative to controlled-rate cryopreservation procedures which are time-consuming and require high-level technical expertise. In this study, we report our experience using uncontrolled-rate cryopreservation and mechanical freezer storage at -140 degrees C. Twenty-eight PBPC samples (10 cryovials, 18 freezing bags) from 23 patients were cryopreserved in a cryoprotectant solution composed of phosphate-buffered saline (80%, v/v) supplemented with human serum albumin (10%, v/v) and dimethylsulfoxide (10%, v/v). The cryopreservation procedure required on average 1.5 h. The mean (+/- s.e.m.) storage time of cryovials and bags was 344 +/- 40 and 299 +/- 57 days, respectively. Although cell thawing was associated with a statistically significant reduction of the absolute number of nucleated cells (vials: 0.3 x 10(9) vs 0.2 x 10(9), P less than or equal to 0.02; bags: 14 x 10(9) vs 11 x 10(9), P < 0.0003), the growth of committed progenitors was substantially unaffected by the freezing-thawing procedure, with mean recoveries of CFU-Mix, BFU-E, and CFU-GM ranging from 60 +/- 29% to 134 +/- 15%. Mean recoveries of LTC-IC from cryovials and bags were 262 +/- 101% and 155 +/- 27% (P less than or equal to 0.2), respectively. In 14 out of 23 patients who underwent high-dose chemotherapy and PBPC reinfusion, the pre- and post-freezing absolute numbers of hematopoietic progenitors cryopreserved in bags were compared. A significant reduction aas detected for CFU-Mix (11 vs 7.4 x 10(5)), but no significant loss of BFU-E (180 vs 150 x 10(5)), CFU-GM (400 vs 290 x 10(5)) and LTC-IC (15 vs 16 x 10(5)) could be demonstrated. When these patients were reinfused with uncontrolled-rate cryopreserved PBPC, the mean number of days to reach 1 x 10(9)/l white blood cells and 50 x 10(9)/l platelets were 9 and 13, respectively. In conclusion, the procedure described here is characterized by short execution time, allows a substantial recovery of primitive and committed progenitors and is associated with prompt hematopoietic recovery following myeloablative therapy even after long-term storage.