The impact of GPI GPI b α α on platelet‐targeted FVIII FVIII gene therapy in hemophilia A mice with pre‐existing anti‐ FVIII FVIII immunity

摘要

Essentials Platelet‐specific FVIII gene therapy is effective in hemophilia A mice even with inhibitors. The impact of platelet adherence via VWF/GPIb α binding on platelet gene therapy was investigated. GPIb α does not significantly affect platelet gene therapy of hemophilia A with inhibitors. Platelet gene therapy induces immune tolerance in hemophilia A mice with pre‐existing immunity. Summary Background We have previously demonstrated that von Willebrand factor ( VWF) is essential in platelet‐specific FVIII (2bF8) gene therapy of hemophilia A ( HA ) with inhibitory antibodies (inhibitors). At the site of injury, platelet adherence is initiated by VWF binding to the platelet GPI b complex. Objective To investigate the impact of GPI b α on platelet gene therapy of HA with inhibitors. Methods Platelet‐ FVIII expression was introduced by 2bF8 lentivirus (2bF8 LV ) transduction of hematopoietic stem cells ( HSC s) from GPI b α null (Ib null ) mice or rhF8‐primed FVIII null (F8 null ) mice followed by transplantation into lethally irradiated rhF8‐primed F8 null recipients. Animals were analyzed by flow cytometry, FVIII assays and the tail bleeding test. Results After transplantation, 99% of platelets were derived from donors. The macrothrombocytopenia phenotype was maintained in F8 null mice that received 2bF8 LV ‐transduced Ib null HSC s (2bF8‐Ib null /F8 null ). The platelet‐ FVIII expression level in 2bF8‐Ib null /F8 null recipients was similar to that obtained from F8 null mice that received 2bF8 LV ‐transduced F8 null HSC s (2bF8‐F8 null /F8 null ). The tail bleeding test showed that the remaining hemoglobin level in the 2bF8‐Ib null /F8 null group was significantly higher than in the F8 null control group, but there was no significant difference between the 2bF8‐Ib null /F8 null and 2bF8‐F8 null /F8 null groups. The half‐life of inhibitor disappearance time was comparable between the 2bF8‐Ib null /F8 null and 2bF8‐F8 null /F8 null groups. The rhF8 re‐challenge did not elicit a memory immune response once inhibitor titers dropped to undetectable levels after 2bF8 gene therapy. Conclusion GPI b α does not significantly impact platelet gene therapy of HA with inhibitors. 2bF8 gene therapy restores hemostasis and promotes immune tolerance in HA mice with pre‐existing immunity.