Cryopreservation of human hematopoietic cells with membrane stabilizers and bioantioxidants as additives in the conventional freezing medium

Cord blood (CB) and fetal liver (FL) cells are two alternative sources of human hematopoietic stem cells. Optimization of cryopreservation protocols is an important aspect in the banking of these tissues. Out of the multiple factors responsible for cryodamage of cells, membrane leakage and oxygen free-radical generation have been shown to contribute substantially toward the process. We have studied the effect of certain additives, like membrane stabilizers and bioantioxidants, to the conventional freezing medium on viability, nucleated cell recovery, and clonogenic potential of frozen cells. Our results show that trehalose, a membrane stabilizer, when used in combination with 10% dimethyl sulfoxide (DMSO) affords better cryoprotection as evidenced by significantly increased colony formation as compared to 10% DMSO alone. The cryoprotection afforded by trehalose persists at least for 1.5 years and there is no bias toward protection of a particular lineage. We also found that this increased cryoprotective effect of trehalose is seen both at -196 degreesC and -80 degreesC storage temperatures. Addition of taurine, an amino acid, another membrane stabilizer, and a natural cryoprotectant to the traditional freezing medium also results in beneficial effect. Of the three bioantioxidants tested, i.e., ascorbic acid, alpha -tocopherol acetate, and catalase, catalase shows maximum cryoprotective effect both at -196 degreesC and at -80 degreesC. Because the mode of cryoprotective action of catalase and trehalose are totally different, we tried a combination of these two compounds along with 10% DMSO. At -196 degreesC the protection afforded by the combination was significantly better than that afforded by individual components. At -80 degreesC, however, the combination did not give any added protection as compared to the individual single additives, although it was significantly better than 10% DMSO alone. These results indicate that the addition of membrane stabilizers and antioxidants to the conventional freezing medium may help to improve post thaw recovery of hematopoietic cells.