[Freezing of umbilical blood cells in mechanical freezers (-80 degrees C)]

Umbilical cord blood (UCB) contains hematopoietic stem cells capable of reconstituting hematopoiesis in the recipient. This property has prompted search for methods to store such cells in liquid nitrogen (-196 degrees C) and offer them for future use in HLA-matched patients. UCB cells are often collected in hospitals remote from storage facilities. Immediate freezing is important to prevent apoptosis which develops relatively quickly after isolation from cord blood. Investigations into the freezing of bone marrow cells have corroborated the feasibility of uncontrolled rate freezing and storage of cells in a mechanical freezer at -80 degrees C. The aim of the present study was to apply this approach to UCB cells and to determine optimal freezing conditions as measured by progenitor cell survival. The highest survival rate among UCB cell species subjected to mechanical freezing was demonstrated by mononuclear cells enriched for the CD34+ subpopulation. The presence of CD34- mononuclear cells (monocytes, lymphocytes) and erythrocytes in the cell suspension reduced progenitor cell survival and proliferation potential. Moreover, it was found that CD34+ cells from UCB can be frozen in an uncontrolled manner. Optimal results were achieved with 10% DMSO and 70% serum. The results were unaffected by the type of medium used (RPMI, Dulbecco, Iscove). In conclusion, uncontrolled rate freezing of UCB cells is an acceptable method prior to transport of the cells in dry ice to a central banking station and storage in liquid nitrogen until needed.