mAb-RC3 inhibits the enhanced platelet procoagulant response elicited by the Thr120-PAR4 variant. Production of procoagulant (annexin V-binding) platelets in human isolated platelet preparations from donors subsequently genotyped as homozygous at rs773902 for Thr120 or Ala120, or as heterozygous. Shown are concentration-response curves to (A) PAR4-AP and (B) thrombin. (C) Also shown are concentration-inhibition curves to mAb-RC3 on responses to thrombin (1 U/mL), indicating antibody-mediated PAR4 inhibition is equally effective across all genotypes. All data are mean ± standard error of the mean from n = 3 to 6 experiments per genotype. *P < .05 (1-way ANOVA with Dunnett’s test for multiple comparisons between each genotype).