When parents choose to bank umbilical cord blood (UCB), they do so with the expectation that this stem cell–rich product will be available to treat conditions like leukemia, lymphoma and anemia, should the need arise. The number of stem cells that persist in each UCB unit is limited, rendering the maintenance of cell viability a critical issue for the biobanking industry.
Dulugiac et al.1 recently evaluated endogenous (e.g., total nucleated cell count [TNCC], CD34+ cell count) and exogenous (e.g., elapsed time from collection to processing, collected UCB volume) factors. Using this data, they drew correlations between these factors and cell viability within a standardized biobanking protocol.
To do this, the team collected 3,000 UCB units via umbilical vein puncture and stored these in 35 mL bags containing an anticoagulant. They processed these samples using hydroxyethyl starch sedimentation within a 48-hour window before applying flow cytometry to assess total cell viability, TNCC and CD34+ cell count.
The overall range for pre-freeze cell viability was 61.86% to 99.5%, with a mean value of 94.37 ± 4.67%. Of the evaluated UCB units, 95.14% presented cell viability above 85%.
The team reported a significant negative correlation between cell viability and elapsed processing time; cell viability decreased when collection-to-processing time increased. They indicated 19.79 ± 8.71 hours to be the mean processing time, with 99.86% of the samples processed within the expected 48-hour timeframe.
Mean cell viability per timeframe
|
0–12 hours (548 units) |
12–24 hours (1,535 units) |
24–36 hours (808 units) |
36–48 hours (105 units) |
48–75 hours (4 units) |
|
98.12% |
94.97% |
92.06% |
84.54% |
75.32% |
The authors found a positive correlation between cell viability and increasing sample volume. The range of collected volume for the UCB samples was 15.2 mL to 202 mL, with a mean of 80.23 ± 28.52 mL. Samples with <80 mL volume had lower cell viability, while samples with >80 mL volume showed no significant differences.
Mean cell viability per volume collected
|
<40 mL (172 units) |
40–80 mL (1,400 units) |
80–120 mL (1,155 units) |
120–160 mL (246 units) |
160–202 mL (27 units) |
|
89.26% |
94.04% |
95.31% |
95.32% |
94.81% |
When examining the impact of the exogenous factors combined, the team found that regardless of collected volume, units processed within 12 hours showed similar cell viability. As elapsed time from collection to processing increased from 12 hours to 48 hours, cell viability decreased, with the most marked drop evident in samples with low volume (<80 mL).
Decrease in cell viability per volume over time, when samples processed within 12 hours are compared to samples processed at 48 hours
|
<40 mL |
40–80 mL |
>80 mL |
|
20.54% decrease |
15.18% decrease |
3–10% decrease |
On the other hand, the team found that the endogenous factors they evaluated did not significantly impact cell viability. The TNCC values ranged from 4.72×107 to 538.7×107, with a mean value of 73.17 ± 36.73×107. They report no correlation between elapsed time and TNCC counts. They note only a very minor positive correlation between TNCC values and cell viability. The range of CD34+ counts was 0.09×106 to 35.89×106, with a mean value of 2.61 ± 2.29×106. They report no correlation between elapsed time and CD34+ values. They found only a very low positive correlation between CD34+ counts and cell viability, particularly at the lower end of the CD34+ values (<0.5×106).
Overall, Dulugiac et al. report that the exogenous factors—elapsed time and collected volume—impact cell viability significantly. When it comes to optimizing industry standards for biobanking of UCB, these findings may help focus control parameters for maximum cell viability.
1 Dulugiac, M., et al. (2014) “Factors which can influence the quality related to cell viability of the umbilical cord blood units,” Transfusion and Apheresis Science, doi: 10.1016/j.transci.2014.08.019.
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