Comparison of stem cell viability of bone marrow cryopreserved by two different methods.

Two different cryogenic methods were used to study the preservation of murine bone marrow cells. Compared to the classical methods, in which separated mononuclear marrow cells in 10% dimethyl sulfoxide (DMSO) were cryopreserved in liquid nitrogen (-196 degrees C), a modified technique was carried out by cryopreservation of unfractionated marrow cells in a mixed protectant of 5% DMSO and 6% hydroxyethyl starch (HES) at -80 degrees C. Samples that were separately thawed after storage for 1, 4, 8, and 12 weeks were assayed for cell viability and recovery of CFU-GM and CFU-S. No macroscopic clumping of cells was noted either in fractionated or in unfractionated marrow cell cryopreservations. A mild damage, about 25% reduction of stem cells, was found at 1 week and did not deepen further. It seems that the greatest loss of stem cells occurred in the process of cryopreservation itself. Compared to prefreeze values, both a high number of cells that excluded trypan blue (87 +/- 3.4%) and a high recovery of CFU-GM (75 +/- 9.8%) and CFU-S (74 +/- 11.2) were observed in unfractionated marrow samples cryopreserved with the DMSO/HES mixture at -80 degrees C for 3 months and these results were very similar to those obtained from fractionated mononuclear marrow cells cryopreserved at -196 degrees C. The DMSO/HES protectant provides a simplified bone marrow cryopreservation technique that should be favorable to clinical application because of its high stem cell recovery and avoidance of cell-separation manipulation.