Phenotypic Correction of von Willebrand Disease Type 3 Blood-Derived Endothelial Cells with Lentiviral Vectors Expressing von Willebrand Factor.

Von Willebrand disease (VWD) is the most common inherited bleeding disorder, caused by quantitative (type 1 and 3 VWD) or qualitative (type 2 VWD) defects in von Willebrand factor (VWF). Gene therapy is an appealing strategy for treatment of type 3 VWD since it is caused by a single gene defect and since VWF is secreted into the circulation, obviating the need for targeting specific organs or tissues. However, development of gene therapy for VWD has been hampered by the considerable length of the VWF cDNA (8.4 kb) and the inherent complexicity of the VWF protein which requires extensive post-translational processing. The objective of this study consisted of developing a gene-based approach for VWD using lentiviral transduction of blood-outgrowth endothelial cells (BOECs) to express functional VWF. A lentiviral vector encoding the complete human VWF protein was used to transduce BOECs isolated from type 3 VWD dogs resulting in high transduction efficiencies (95.6 ± 2.2 %). These BOECs are completely deficient in VWF due to a point mutation in the VWF gene responsible for impaired VWF synthesis. Transduced VWD BOECs efficiently expressed fully functional vector-encoded VWF (4.6 ± 0.4 U/24hr per 10⁶ cells, figure 1), with normal binding to GPIbα and collagen and normal multimeric pattern resulting in phenotypic correction of these cells, which had not been shown previously. These results indicate that BOECs are attractive target cells for gene therapy of type 3 VWD.