Genetic platelet depletion is superior in platelet transfusion compared to current models

Abstract

Genetically modified mice have advanced our knowledge on platelets in hemostasis and beyond tremendously. However, mouse models harbor certain limitations, including availability of platelet specific transgenic strains, and off-target effects on other cell types. Transfusion of genetically modified platelets into thrombocytopenic mice circumvents these problems. Additionally, ex vivo treatment of platelets prior to transfusion eliminates putative side effects on other cell types. Thrombocytopenia is commonly induced by administration of anti-platelet antibodies, which opsonize platelets to cause rapid clearance. However, antibodies do not differentiate between endogenous or exogenous platelets, impeding transfusion efficacy. In contrast, genetic depletion with the inducible diphtheria toxin receptor (iDTR) system induces thrombocytopenia via megakaryocyte ablation without direct effects on circulating platelets. We compared the iDTR system with antibody-based depletion methods regarding their utility in platelet transfusion experiments, outlining advantages and disadvantages of both approaches. Antibodies led to thrombocytopenia within two hours and allowed the dose-dependent adjustment of the platelet count. The iDTR model caused complete thrombocytopenia within four days, which could be sustained for up to 11 days. Neither platelet depletion approach caused platelet activation. Only the iDTR model allowed efficient platelet transfusion by keeping endogenous platelet levels low and maintaining exogenous platelet levels over longer time periods, thus providing clear advantages over antibody-based methods. Transfused platelets were fully functional in vivo, and our model allowed examination of transgenic platelets. Using donor platelets from already available genetically modified mice or ex vivo treated platelets, may decrease the necessity of platelet-specific mouse strains, diminishing off-target effects and thereby reducing animal numbers.