Abstract
For successsful cryopreservation of animal cells, a control of water content in cells during freezing and thawing is critical. Since the finding of cryoprotective effect of glycerol and dimethyl sulfoxide in middle 1940's, numerous animal cells have been successfully cryopreserved. Placental/umbilical cord blood is enriched with hematopoeitic stem/progenitor cells, and that is now considered as a new source of hematopoietic cells to treat leukemia, lymphoma and other congenital diseases. We have cryopreserved cord blood with a mixture of penetrating and nonpenetrating cryoprotectants, i.e., 10% dimethyl sulfoxide, 1 % dextran and 0.8% hydroxyethyl starch with stepwise addition. With the cryoprotectant, the concentrated cord blood stem/progenitor cells were frozen at 2℃/min to -50℃ and plunged in LN_2 in a BioArchive System. This optimal freezing condition was determined by the analyses of differential scanning calorimeter. The cord blood units were transplanted to HLA matched patients and the number of transplantation has increased more than 120. About half of the patients received cord blood units washed out dimethyl sulfoxide after cryopreservation to avoid cell damage caused by rapid entry of water into the cells. The clinical outcome of these patients is as good as that of bone marrow transplantation, which was the major treatment for these difficult diseases.
