Effect of cryopreservation on the immunogenicity of umbilical cord blood cells.

Cryopreservation is the accepted method for long-term storage of cord blood (CB) cells. We evaluated the effects of using different cooling rates (1, 5, 7.5 and 10 degrees C/min) on CB cell allostimulatory and alloproliferative function, antigen expression and clonogenic potential. Significant decreases (P<0.001-0.003) in viable cell recovery observed between fresh CB cells and CB cells cryopreserved at each cooling rate tested. Reductions in clonogenic potential of CB cells cryopreserved at cooling rates of 1, 5, 7.5 and 10 degrees C/min were 44%, 76%, 88% and 93% respectively, compared to fresh controls. FACS analysis indicated no changes in percentages CD34+ cells or lymphocytes. Two sets of mixed lymphocyte reactions were carried out for each CB sample. It was observed that allostimulatory and alloproliferative function varied following cryopreservation at different cooling rates (1 and 5 degrees C/min). Interestingly, there was a significant decrease (P<0.001-0.04) in the alloproliferative function of six of the seven CB samples following cryopreservation using a cooling rate of 5 degrees C/min. Cooling rates between 1 and 5 degrees C/min may provide immunomodulation of CB with maintenance of haematopoietic progenitor cells function.