Flow check pro

At CDL determination of rWBC levels was performed using a flow cytometer (FACSCalibur, BD Biosciences) with QC performed with Calibrite beads, (BD Biosciences). QM‐Manchester used Navios analyzers with QC performed using Flow‐Check Pro and Flow‐Set Pro beads (Beckman Coulter). Both sites used WBC enumeration kits (Leucocount, BD Biosciences) for staining rWBCs before flow cytometric analysis. At QM‐Manchester, flow cytometry results were recorded in a QM database, with results of 1 WBC/μL or less being recorded as 1 WBC/μL.

The samples were acquired on a three-laser, 10-color Gallios flow cytometer (Beckman Coulter), which was calibrated and optimized for sensitivity as described in detail previously.^{20 (link),25 (link)} The daily quality assurance routine consisted of running Flow-Check Pro (Beckman Coulter) beads to verify the optical and fluidic function and then set the fluorescent signal in each channel to ±2% of the previously established target median fluorescence intensity (MFI), using single-peak Rainbow beads (Spherotech), which resulted in a high instrument precision with a coefficient of variation of the single-peak MFI of 0.3–0.7%. Sample handling and data acquisition were performed blinded by two trained research engineers.