COMPARATIVE EVALUATION OF CORD BLOOD HEMATOPOIETIC CELL FUNCTIONS BEFORE FREEZING AND AFTER THAWING, AND ANALYSIS BASED ON SAMPLE TYPE AND FREEZING PERIOD

Abstract

Background: Since CBT is performed using frozen cells, it is important to evaluate the hematopoietic function of frozen cells. However, it is not yet clearly known how long this hematopoietic stem cell function can be maintained in liquid nitrogen.
Study design and Methods:
First, we evaluated the hematopoietic function of 617 cord blood units, including 23 validation units, which were frozen between 1997 and 2006 and thawed one month to eight years after freezing. Nucleated cell numbers, viability, CD34 positive cell numbers and CFU-GM numbers were measured in the bigger and smaller compartments of the freezing bags, and values from segment samples of each cord blood unit were compared with those before freezing. Second, hematopoietic cell function was evaluated according to freezing period.
Results:
1. Comparison according to sample type
Viability, total nucleated cell numbers, CD34 positive cell numbers and total CFU-GM numbers of segments appeared lower than those of pre-freezing samples or those of the bigger and smaller compartments of the bag. However, significant correlation was found among samples.
2. Comparison according to freezing period
The viability of samples frozen for more than five years was significantly lower than those less than five years. CD34-positive cell numbers and CFU-GM numbers did not differ based on each freezing period.
Conclusion:
This study proves the validity of predicting hematopoietic cell number and function of frozen cord blood cells in a freezing bag by segment sampling. Although hematopoietic stem cells have not been reduced during freezing periods of up to eight years, follow-up examination is required.