CD34+ cell content before freezing represents the hematopoietic stem cell content of thawed and washed cord blood units

Quality of long-term cryopreserved umbilical cord blood units for hematopoietic cell transplantation

The aim of this study was to evaluate the quality of long-term cryopreserved umbilical cord blood (CB) units for hematopoietic cell transplantation (HCT). The recovery of the number of total nucleated cell (TNC), hematopoietic progenitor cells (HPCs; CD34+ cells, colony-forming units-granulocyte/macrophages [CFU-GMs]), and the percentage of viable cells, CD34+ CD38- cells, and CD34+ CXCR4+ cells of CB units cryopreserved for 10 years for HCT were examined. Eighteen CB units cryopreserved for 10 years (as the study group) and for 1 month (as the control group), respectively, were analyzed. The recovery rate of TNC, CD34+ cells and CFU-GMs were 88.72 ± 16.40, 68.39 ± 18.37 and 42.28 ± 38.16% for the study group and 80.17 ± 14.46, 72.67 ± 20.38 and 49.61 ± 36.39% for the control group (p = 0.106, p = 0.513 and p = 0.559, respectively). There were no significant differences in the recovery rate of TNC, CD34+ cells and CFU-GMs between the study group and the control group. The mean basal percentage of viable cells, CD34+ CD38- cells, and CD34+ CXCR4+ cells after thawing were 83.69 ± 9.45, 9.11 ± 4.13 and 81.65 ± 10.82% for the study group. These results indicate that long-term cryopreservation does not negatively affect the quality of CB units for HCT.

Consistency of the initial cell acquisition procedure is critical to the standardization of CD34+ cell enumeration by flow cytometry: results of a pairwise analysis of umbilical cord blood units and cryopreserved aliquots

BACKGROUND

The CD34+ cell content is a predictive factor for engraftment and survival after umbilical cord blood (UCB) transplantation. The high variability in the CD34 assay results in different recommended cell doses for infusion across transplant centers and also limits the clinical utility of the CD34+ cell counts provided by cord blood banks (CBBs). This bi-institutional study was intended to understand the sources of this variability.

STUDY DESIGN AND METHODS

The level of CD34 agreement between the University of Minnesota (UM) and the Madrid CBB (MCBB) was evaluated on 50 UCB units before and after cryopreservation. Two cryopreserved vials per unit were thawed and processed at both laboratories. Dual-platform ISHAGE-based flow cytometry was used for CD34 enumeration.

RESULTS

Postthaw nucleated cell recoveries were similar. However, whereas CD34+ cell enumeration before freezing was 0.35 +/- 0.22 percent, the results after thawing were 0.98 +/- 0.65 and 0.57 +/- 0.39 percent at UM and MCBB, respectively. Bland-Altman plots analysis ruled out the interchangeability of MCBB and UM CD34 values. Differences in the initial cell acquisition settings accounted for most of the CD34 discrepancy, which was no longer present after normalization of the forward scatter threshold for cell acquisition.

CONCLUSIONS

The standardization of CD34+ cell enumeration by flow cytometry is strongly reliant on a consistent initial cell acquisition procedure. The interlaboratory variation can be minimized by using frozen cell aliquots as reference samples. Both requisites should be considered for CD34 testing and UCB unit selection by regulatory institutions involved with cord blood banking and transplantation.

CD34+ progenitors are reproducibly recovered in thawed umbilical grafts, and positively influence haematopoietic reconstitution after transplantation

Cord blood (CB) units are increasingly used for allogeneic transplantation. Cell dose, a major factor for CB selection, is evaluated before freezing by each CB bank, using various techniques. This may introduce variability and affect the prediction of cell recovery after thawing, or haematopoietic reconstitution. Forty-two children were transplanted at the same institution with unrelated CB units. All units were thawed and evaluated at the same cell therapy facility, using standard procedures. We investigated: (i) factors that affect cell loss after thawing, and (ii) the importance of CD34(+) cell doses. Prefreeze and post-thaw CD34(+) cell doses were statistically correlated, thus suggesting that variability in numeration techniques used by different CB banks does not compromise the biological and clinical value of these figures. CD34(+) cell recovery appeared to be correlated with the absolute number of CD34(+) cells per frozen bag. Infused CD34(+) is the cell dose that better correlates with platelet reconstitution delay; in addition, when using a quartile comparison, haematopoietic recovery appeared to be related with prefreeze and post-thaw CD34(+) cell doses. We conclude that enumeration of CD34(+) cells in CB units is of biological significance, and may help select CB units and identify patients at risk of delayed recovery.