Meeting the COVID challenge: Optimizing vCD34⁺ in cryopreserved HPC samples for implementation of an external QA...

The COVID-19 pandemic has forced a fundamental change in the global procurement of allogeneic hematopoietic progenitor cells (HPCs) for transplantation. To better meet the emergent challenges of transporting cryopreserved allogeneic HPC during pandemics, there is an urgent need for External Quality Assurance (EQA) programs to evaluate reproducibility and harmonization of viable CD34⁺ cell (vCD34⁺) HPC enumeration, as the current EQA programs are unsuitable for analysis of vCD34⁺. The cost-effective distribution of HPC cryopreserved reference samples (CRSs) with acceptable reproducibility and specificity is key to the success of a vCD34⁺ EQA program.

Cryopreserved HPC samples (n = 11) were either stored on dry ice for 1 to 4 days or for 1 day followed by liquid nitrogen (LN) storage for 1 to 3 days to assess optimal conditions for vCD34⁺ EQA. Flow cytometric enumeration of vCD34⁺ HPCs was performed using a single platform assay combined with 7-AAD viability dye exclusion. The optimum transportation condition was validated in pilot and multicenter national studies (n = 12).

A combination of 1 day on dry ice followed by LN storage stabilized viability compared with continuous storage on dry ice. This study demonstrates that dispatch of CRSs on dry ice to recipient centers across a distance of ≤4000 km within 26 h, followed by LN storage, resulted in reproducible intercenter vCD34⁺ enumeration. The estimated cost of safer and more convenient dry ice delivery is >20-fold lower than that of LN.

This approach can form the basis for economically and scientifically acceptable distribution of CRSs for external vCD34⁺ EQA.