Evaluation of Cell Mimics as Potential Quality Controls for Human Leukocyte Immunophenotyping

Background. Routine lymphocyte counting requires quality assurance validation using quality controls (QCs) that closely resemble fresh human blood leukocytes. This study aimed to evaluate a novel artificial product designed to mimic leukocyte light scatters and marker expression. Methods. FlowCytes and TruCytes, "artificial cell mimics" (Slingshot Biosciences, Emeryville, CA, USA), were tested on CE-IVD-certified systems, namely FACSCanto, FACSLyric (BD Biosciences), Navios, and DxFlex (Beckman Coulter), using routine staining, lysing, fixation, and no-wash procedures for T, B, and NK counting. Results. FlowCytes and TruCytes provided forward and side scatter profiles comparable to human leukocytes on the FACSCanto, FACSLyric, and DxFlex systems but not on Navios despite adapting the process to be slightly different from the manufacturer's recommendations. TruCytes demonstrated robust immunolabeling of CD3, CD4, CD8, and CD19 on the FACSCanto, FACSLyric, and DxFlex systems, with fluorescence intensities and subset distributions being similar to those usually observed in fresh human blood. However, CD16 and CD56 labeling was inconsistent and depended on the antibody clones used. Regrettably, monocyte and granulocyte mimics lacked expression of CD4, CD16, and CD14. TruCytes also displayed significantly lower concentrations of TBNK lymphocyte subsets compared to healthy human blood. Conclusions. FlowCytes and TruCytes show promises as internal quality controls for T cell and B cell immunophenotyping, but not NK cells. They are compatible with most CE-IVD cytometers, even when using lysis/fixation/no-wash routine diagnosis procedures. Further multicentric studies are warranted to assess their performance relative to existing products, such as stabilized human blood.