RLYB211 and RLYB212 induce clearance of circulating HPA-1a⁺ murine platelets. Platelets isolated from APLDQ⁺ C56BL/6 mice were labeled with the cell tracker dye CMFDA and were transfused (1 × 10⁸ CMFDA-labeled platelets per mouse) into WT Balb/c female mice. One hour after transfusion, an irrelevant human control mAb (1.34 μg), normal human total IgG (2 mg), RLYB211, or RLYB212 at the indicated concentrations were introduced by tail vein injection. Blood samples were collected from the submandibular vein of the recipients following platelet transfusion but before antibody injection and at 5 and 24 hours post–antibody injection. The percentage of CMFDA-labeled platelets remaining in the circulation was determined by flow cytometry. (A,C) Representative flow-cytometric dot plots showing the presence of CMFDA-labeled APLDQ platelets remaining in circulation (box) over time. (B-D) The survival of transfused CMFDA-labeled APLDQ platelets in WT Balb/c female mice at 5 and 24 hours post–antibody injection. The survival of the transfused labeled platelets was calculated by the percentage of the remaining CMFDA⁺ platelets divided by the beginning percentage of CMFDA⁺ platelets. Data in panels B and D are the quantification of 5 separate experiments, shown as mean plus or minus standard error of the mean. N = 5 per group. ∗P < .05; ∗∗P < .01 vs normal human IgG as analyzed by the Mann-Whitney U test. nhIgG, normal human IgG; ns, not significant.