Refined methods to evaluate the in vivo hemostatic function and viability of transfused human platelets in rabbit models

BACKGROUND: To bridge the gap between in vitro function and clinical efficacy of platelet (PLT) transfusion products, reliable in vivo PLT functional assays for hemostasis and survival in animal models are required. However, there are no standardized methods for assessing the in vivo quality of transfused human PLTs. STUDY DESIGN AND METHODS: Plasma-depleted human PLT concentrates (PCs; Day 3, Day 5, Day 7, Day 10, and damaged) were transfused into busulfan-induced rabbits with thrombocytopenia with prolonged bleeding times 1 day after treatment with ethyl palmitate (EP) to block their reticuloendothelial systems. The hemostatic effect of PC transfusion was evaluated by the ear fine vein bleeding time. For the in vivo survival assay, splenectomized EP-treated rabbits were transfused with human PCs, and viability of the human PLTs in the rabbits was determined by flow cytometry using human PLT-specific antibodies and Trucount tubes. RESULTS: The hemostatic effect of PCs was slightly reduced with increasing storage periods for early time points, but more dramatically reduced for later time points. PLT survival was similar after 3 and 7 days of storage, but PLTs stored for 10 days showed significantly poorer survival than those stored only 3 days. CONCLUSION: Our new and improved protocol for in vivo assessment of transfused PLTs is sufficiently sensitive to detect subtle changes in hemostatic function and viability of human PLTs transfused into rabbit models. This protocol could contribute to preclinical in vivo functional assessment and clinical quality assurance of emerging novel PLT products such as cultured cell–derived human PLTs.