Factor VIII ectopically targeted to platelets is therapeutic in hemophilia A with high-titer inhibitory antibodies
Qizhen Shi, … , Jack Gorski, Robert R. Montgomery
Qizhen Shi, … , Jack Gorski, Robert R. Montgomery
Published July 3, 2006
Citation Information: J Clin Invest. 2006;116(7):1974-1982. https://doi.org/10.1172/JCI28416.
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Research Article Hematology

Factor VIII ectopically targeted to platelets is therapeutic in hemophilia A with high-titer inhibitory antibodies

Abstract

Inhibitory immune response to exogenously infused factor VIII (FVIII) is a major complication in the treatment of hemophilia A. Generation of such inhibitors has the potential to disrupt gene therapy for hemophilia A. We explore what we believe to be a novel approach to overcome this shortcoming. Human B-domain–deleted FVIII (hBDDFVIII) was expressed under the control of the platelet-specific αIIb promoter in platelets of hemophilic (FVIIInull) mice to create 2bF8trans mice. The FVIII transgene product was stored in platelets and released at the site of platelet activation. In spite of the lack of FVIII in the plasma of 2bF8trans mice, the bleeding phenotype of FVIIInull mice was corrected. More importantly, the bleeding phenotype was corrected in the presence of high inhibitory antibody titers introduced into the mice by infusion or by spleen cell transfer from recombinant hBDDFVIII–immunized mice. Our results demonstrate that this approach to the targeted expression of FVIII in platelets has the potential to correct hemophilia A, even in the presence of inhibitory immune responses to infused FVIII.

Authors

Qizhen Shi, David A. Wilcox, Scot A. Fahs, Hartmut Weiler, Clive W. Wells, Brian C. Cooley, Drashti Desai, Patricia A. Morateck, Jack Gorski, Robert R. Montgomery

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Figure 3

Platelet-derived FVIII can function in hemostasis.

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Platelet-derived FVIII can function in hemostasis. (A) Quantitative eval...
(A) Quantitative evaluation of FVIII:C levels in mouse plasma by chromogenic assay. No FVIII:C was detected in the plasma of FVIIInull and 2bF8trans mice. (B) Platelet lysate added to dilutions of FVIII did not alter level of FVIII:C as measured by chromogenic assay. (C) Quantitative evaluation of FVIII:C levels in mouse platelet lysates. Platelets were isolated and lysed in 0.5% CHAPS. FVIII:C in lysates was quantitated by chromogenic assay. FVIII:C was detected in platelet lysates from 2bF8trans mice and bone marrow recipients from 2bF8tg+/– mice. Platelet FVIII:C was significantly increased in 2bF8tg+/+ mice compared with 2bF8tg+/– mice. FVIII:C was significantly decreased in 2bF8transVWFnull mice. *P < 0.001. (D) Tail clip survival test assessing phenotypic correction of hemophilia A mice. All 2bF8trans mice and their bone marrow recipients survived tail clipping. (E) Tail clip survival test assessing the beneficial effect of transgenic platelets. Different proportions of washed platelets were transfused into FVIIInull mice, which was followed by tail clipping. All FVIIInull mice that were infused with 2bF8tg+/– platelets to a final level of 30% of total platelets survived tail clipping.