Rapid potency assessment of autologous peripheral blood stem cells by intracellular flow cytometry: the PBSC-IL-3-pSTAT5 assay.

Abstract

The current gold standard for stem cell product potency assessment, the colony-forming unit (CFU) assay, delivers results that are difficult to standardize and requires a substantial amount of time (up to 14 days) for cellular growth. Recently, the authors developed a rapid (<24 h) flow cytometry assay based on the measurement of intracellular phosphorylated STAT5 (pSTAT5) in CD34+ cord blood stem and progenitor cells in response to IL-3 stimulation. The present work presents a novel adaptation of the protocol for use with autologous peripheral blood stem cells (PBSCs) and a performance comparison with the CFU assay. The flow cytometry intracellular staining assay was optimized for PBSCs, and patient samples were analyzed using the PBSC-IL-3-pSTAT5 and CFU assays. Warming events were also simulated to emulate impaired potency products. Optimization led to minor protocol adjustments, such as removal of the red blood cell lysis step, the addition of a formaldehyde fixation step and an increase in anticoagulant concentration. The PBSC-IL-3-pSTAT5 assay discriminated between normal and impaired samples and identified 100% (18 of 18) of the impaired samples, thus showing better specificity than the CFU assay. The updated IL-3-pSTAT5 potency assay has several important advantages, such as accelerating the release of autologous stem cell products and enabling the detection of potentially impaired products. The assay could also be used to rapidly assess the potency of any cryopreserved allogeneic stem cell product, such as those processed during the coronavirus disease 2019 pandemic.