(P-BT-1) What To Expect When You Request Post-Thaw Segment QC Testing On A Cord Blood Unit?

Background/Case Studies: The selection process of cord blood units (CBU) requires post-thaw (PT) quality control (QC) testing to verify the quality/potency of stored cells. CBU are manufactured with attached segments that can be cut from the CBU without compromising the bag.
Heterogeneity of data between labs can make interpretation of the QC results difficult for transplant centers (TC).
Here we present the PT segment QC results for 2,249 consecutive segments, in order to create a benchmark of what is to be expected when interpreting segment testing.

Study

Design/Methods: During the period 4/2016 – 2/2023, 1828 clinical CBU from a single cord blood bank had a segment cut for confirmatory HLA typing and QC testing. Of those, 421 were split into two bags. A total of 2249 segments were analyzed.
The following QC parameters were measured:
- Total nucleated cells (TNC), using a Sysmex XE-2100 analyzer;
- Viable CD34 cells (vCD34), by flow cytometry (single platform flow cytometry using ISHAGE strategy and 7-AAD for viability);
- Colony forming units (CFU).
Cell concentrations from the segment were extrapolated to reflect the expected content of the full CBU. Recoveries were calculated using pre-freeze (PF) and PT results and expressed as percentages.

Results/Findings: Mean recoveries for TNC, vCD34 and CFU on the segments were 78.4%, 61.85% and 58.99%, respectively (Figure A-1). Mean CD34 viability was 94.3% (Figure A-2). Two segments (0.1%) had viability < 70% (below FACT requirement); both were found to be testing issues (one segment opened during thaw; for the second, another segment was tested with good results).
Correlation between PF and PT vCD34 and CFU was excellent (R2 of 0.89 and 0.65, respectively) (Figure A-3 and A-4). PT vCD34 and CFU were also strongly correlated (R2 = 0.66) (Figure A-5).
Date of collection (ranging from 1999 to 2020) was also evaluated and did not influence PT CD34 viability (Figure A-6).
Of the 1828 CBU tested, 323 were shipped. Engraftment information was available for 81 of them. Two patients failed to engraft (2%), and 4 patients died too early for engraftment to be evaluated. The rest were successfully transplanted.

Conclusions: This analysis confirms that segment QC testing continues to be a reliable indicator of CBU quality for the TC, with strong correlation between PF and segment PT values.
Our data also demonstrates that PT vCD34 and CFU are significantly correlated; segment vCD34 is a reliable predictor of CFU growth and as such, can be used as an indicator of CBU quality before infusion when CFU results are not yet available.
Our results on a large number of segments, from CBU collected over a 20-year period, provide transplant centers with a range of expected recoveries that can be used as a reference to predict the ability of the CBU to be successfully transplanted.

Importance of research: Post-thaw CBU segment QC testing is a crucial part of CBU selection. We report here our 7-year retrospective analysis of testing 2,000+ segments, confirming the relevance of segment testing in CBU evaluation. Our data shows consistently strong correlation of segment post-thaw values with pre-freeze values. The reported recoveries can be used by transplant centers as a benchmark to interpret post-thaw results and understand the correlation between post-thaw viable CD34 and CFU.