Fig 2: Resazurin‐based cell viability assay reaffirms a dose‐dependent cell viability loss in leukaemia cells after NK‐EV correlating with levels of cytotoxic factors. (a) Leukaemia K562 cells were treated for 5 hours with various E: T ratios of NK‐EVs or negative control 293F‐EVs, followed by endpoint resazurin‐based cell viability assay. The results are presented in (i) RFU (Relative Fluorescence Units) readouts (black dashed line represents lysed K562 cell control; detergent‐treated) and (ii) EC50 curve analysis with variable slope for NK‐EV treatment with 95% confidence interval/prediction bands (red dashed line represents 50% response). Data are shown as mean ± S.E.M. from seven independent experiments, each with technical quadruplets. (b) Spearman correlations of selected NK‐EV's corona cytotoxic factors (GzmB, GNLY, PFN, FasL and IFN‐γ) detected by ELISA in relation to cell viability assay using leukaemia K562 cells (n = 14 correlations pairs where one pair (a dot in the figure) represents the correlation between the level of a cytotoxic factor and the cell viability assay readout for a given NK‐EV dose). (c) NK‐EVs corona cytotoxic factors (schematically shown) were assessed by ELISA and presented as the protein‐normalised levels (ng/mg of protein) of a given cytotoxic factor (GzmB, GNLY, PFN, FasL and IFN‐γ) using total protein levels (mg) detected by Qubit Protein Assay. Data are shown as mean ± S.D. from three independent experiments, each with technical duplicates.