Flow cytometric assay of scFv-CD39 binding to human platelets, detected with an Alexa Fluor 488–coupled anti–Penta-His antibody that binds to the constructs’ 6xHis-tag. (A) Quantitative comparison. Bar graphs depict the median fluorescence intensity values of 3 independent experiments (mean ± standard error of the mean; ***P < .001). These assays were analyzed with 2-way repeated-measures analysis of variance with the Bonferroni posttest. (B and C) Representative fluorescence histograms. Binding of (B) non–targ-CD39 and (C) targ-CD39 to activated platelets vs nonactivated platelets is shown.