Aim: To explore proper cryopreservative systems for hematopoietic stem cells.
Methods: Peripheral blood mononuclear cells from 20 persons were mixed with different cryopreservative agent, dimethyl suflfoxide (DMSO) or combination of DMSO and hydroxyethyl starch (HES), then cooled in -80 degrees C low temperature refrigerator (Refr) or autocontrolled programmed cryogenic system (PCS), preserved in Refr or in liquid nitrogen. GM-CFU, LTC-IC, CD34+ cells and typeran blue resistance (TBR) were assayed after different period of cryopreservation.
Results: The recovery rates of CFU-GM, LTC-IC, CD34+ cells and TBR in peripheral blood mononuclear cells which were cooled and preserved in Refr with 5% DMSO-6% HES were 82.2% +/- 14.7%, 83.0% +/- 12.2%, 94.2% +/- 4.3% and 97.7% +/- 3.9% respectively, significantly higher than that in Refr with 10% DMSO (P < 0.05). When cells were cryopreservated with the same cryopreservatives, there was no significantly difference of recovery rate in group of Refr and group of Refr with PCS. Meanwhile, there was not significantly difference of recovery rate among all three groups, preserved in Refr ahead of liquid nitrogen, in Refr merely, in liquid nitrogen with PCS within one year (p > 0.05). However, the recovery rate of CFU-GM, LTC- IC, CD34+ cells and TBR decreased dramatically if cells were cooled and preserved in Refr for two years. After cells were thawed, the cell activity declined gradually at room temperature if the cryopreservatives were not removed or diluted. The cell activity of 10% DMSO group was affected more than that of 5% DMSO-6% HES group.
Conclusion: 5% DMSO-6% HES is better than 10% DMSO as cryopreservatives for hematopoietic stem cells. Refr cryopreservation is a simple and effective method if cells would be cryopreserved for less than one year. If cells would be cryopreserved for more than one year, liquid nitrogen cryopreservation should be recommended. The cryopreservatives should be diluted or removed immediately after cells were thawed.