The effect of processing and cryopreservation on nucleated umbilical cord blood cells

Recovery of nucleated cord blood cells after storage in liquid nitrogen was evaluated. Red cells were depleted using Ficoll-Paque or Puregene® red cell lyses. Freeze Medium contained 10% dimethylsulfoxide and 20% serum for cryoprotection. Recovery of the original cell population remaining serviceable for fluorescence activated cell sorting (FACS) was 12±10% (average ± standard deviation), with a range of 1% to 55%. Viability measured by FACS analysis after freezing was significantly lower than that of the same specimens prior to freezing, 62±20% compared to 91±11% (p<0.001). Percentage CD45+34+ cells were the same for fresh and frozen cells. Gestational age at which specimens were collected had no effect on the percent cells carrying the CD45+34+ markers. We conclude that better cryo-protective supplements are needed to insure consistent high recovery of viable nucleated umbilical cord blood cells after preservation in liquid nitrogen.