Effect of cell concentration on bone marrow and peripheral blood stem cell cryopreservation

The effects of cell concentration during cryopreservation on bone marrow (BM) or peripheral blood (PB)-derived hematopoietic progenitor cells have not been described. The much greater numbers of cells harvested for autologous PB stem cell (PBSC) transplantation requires that the cells be frozen at higher cell concentrations, or in much greater volumes, compared with BM. We cryopreserved 108 PBSC collections from 30 patients at an average (+/- SD) cell concentration of 3.7 +/- 1.9 x 10(8) nucleated cells per mL in 127 +/- 45 mL. The proportion of mononuclear cells was 52.9% +/- 27.2%. The products also contained 2.9 +/- 2.1 x 10(9) platelets/mL and an average red cell proportion of 12.9% +/- 7.2%. The nucleated cell recovery after thawing was 75.4% +/- 13.0%. The nucleated cell concentration during freezing was not predictive for the postthaw recoveries of nucleated cells (P = .38), granulocyte-macrophage colony-forming unit (P = .06) or CD34+ cells (P = .54), or for the viability of mononuclear cells (P = .81). The platelet and red cell concentrations similarly were not predictive for these endpoints. Samples (3 BM, 7 PBSC) from 10 patients were simultaneously cryopreserved at two-fold, and from 5 additional patients (PBSC) at 6- to 24-fold differing cell concentrations. A lower recovery of erythroid burst forming unit was found for samples frozen at higher cell concentrations (P = .04), but no significant differences were found in the other endpoints listed above. The average cell concentration during freezing for each patient's PBSC collections (n = 34 patients) did not predict time to achieve a PB count of > 500 granulocytes/microL (P = .51) or platelet transfusion independence (P = .39). Patients achieved these endpoints of engraftment at medians of 12 and 13 days, respectively. The infusion of these products was generally well tolerated. Similarly, the cell concentration at which BM cells were frozen did not predict for the duration of granulocyte (P = .63) or platelet (P = .36) aplasias for 54 patients undergoing autologous BM transplantation. These data suggest that PBSC or BM cells collected for transplantation may be cryopreserved at very high cell concentrations without loss of engraftment potential or undue infusion-related toxicity.