Comparison of platelet‐derived and plasma factor VIII efficacy using a novel native whole blood thrombin generation assay. (25th November 2015)

• Record Type: Journal Article
• Authors: Baumgartner, C. K.; Zhang, G.; Kuether, E. L.; Weiler, H.; Shi, Q.; Montgomery, R. R.
• Is Part Of: Journal of thrombosis and haemostasis. Volume 13:Number 12(2015:Dec.)
• Page Start: 2210
• Page End: 2219
• Publication Date: 2015-11-25
• Subjects: factor VIII -- gene therapy -- hemophilia A -- platelets -- thrombin; Thrombosis -- Periodicals; Hemostasis -- Periodicals; Blood coagulation disorders -- Periodicals; 616.1
• DOI: 10.1111/jth.13169
• Languages: English
• ISSNs: 1538-7933

Abstract

Summary: Background: We have recently developed a successful gene therapy approach for hemophilia A in which factor VIII (FVIII) expression is targeted to platelets by the αIIb promoter. Levels of platelet‐expressed FVIII (2bF8) achieved by gene therapy may vary between individuals due to differences in ex vivo transduction and gene expression efficiency. Accurate assays to evaluate 2bF8 efficacy are desirable. Objective: To compare the hemostatic efficacy of 2bF8 with replacement therapy over a wide therapeutic dose range. Methods: Efficacy of 2bF8 was assessed using a new transgenic mouse model expressing high 2bF8 levels (LV18 tg ). Blood from LV18 tg mice or FVIII null mice infused with recombinant FVIII was mixed with FVIII null blood at different ratios ex vivo to achieve several concentrations of 2bF8 or plasma FVIII. Samples were evaluated with a novel native whole blood thrombin generation assay that uses recalcified whole blood without the addition of tissue factor to initiate coagulation. Results: FVIII dose dependency was observed in all five thrombin generation parameters. While the total amount of thrombin generated was similar, 2bF8 significantly accelerated thrombin generation compared with plasma FVIII. Remarkably, a 10‐fold lower dose of 2bF8 than plasma FVIII (0.2% vs. 2%) significantly shortened the onset and peak of thrombin generation compared with FVIII null blood. Conclusion: Using a new transgenic mouse model, we showed that the novel native whole blood thrombin generation assay established here can be used to monitor platelet targeted FVIII gene therapy. The higher therapeutic efficacy of 2bF8 compared with factor replacement therapy seemed to be due to acceleration of thrombin generation.