Quantitative, functional, morphological and ultrastructural recovery of platelets as predictor for cryopreservation.

Cryopreservation of platelets is of great interest, since it could extend the shelf life of therapeutic platelet concentrates and facilitate stockpiling and inventory control in blood banking. Despite the use of many cryopreservation procedures the optimal cryopreservation procedure is not defined yet. We have compared the cryopreservation of human platelets by various protocols employing controlled-rate and non-controlled-rate freezing procedures in combination with different concentrations of DMSO (6% and 10%) or 5% DMSO + 6% HES combination. After storage for 1 to 3 months, samples were thawed and analyzed. Measurements included cell recovery, platelet viability according to hypotonic shock response (HSR), platelet aggregation with ADP, morphological and ultrastructural properties of defrozen platelets. Our findings show that the application of our original procedure for controlled-rate freezing consisting of six cooling steps (cooling rate 1 degree C/min) with compensation of released heat of fusion (cooling rate 2 degrees C/min) has significantly influenced the quality of thawed platelets. At the same time, a concentration of 6% DMSO proved to be the most effective. In summary, cryopreservation of human platelets using controlled-rate freezing procedure in combination with lower (6%) DMSO concentration resulted in less damage from freezing and higher recovered function of platelets.