Pre-clinical evaluation of an enhanced-function factor VIII variant for durable hemophilia A gene therapy in male mice

• Published in: Nature communications Vol. 15; no. 1; pp. 7193 - 14
• Main Authors: Sternberg, Anna R., Martos-Rus, Cristina, Davidson, Robert J., Liu, Xueyuan, George, Lindsey A.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 21.08.2024; Nature Publishing Group; Nature Portfolio
• Subjects: 38/39; 38/44; 42; 631/45; 631/45/612; 64/60; 692/308; 82/80; Activated protein C; Animals; Clinical trials; Coagulation factors; Copy number; Dependovirus - genetics; Disease Models, Animal; Durability; Factor VIII - genetics; Factor VIII - metabolism; Factor VIII deficiency; Gene expression; Gene therapy; Genetic Therapy - methods; Genetic Vectors - administration & dosage; Genetic Vectors - genetics; Hemophilia; Hemophilia A - genetics; Hemophilia A - therapy; Hemostasis; Hemostatics; Humanities and Social Sciences; Humans; Inactivation; Male; Males; Mice; Mice, Inbred C57BL; multidisciplinary; Recovery of function; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-024-51296-8

Durable factor VIII expression that normalizes hemostasis is an unrealized goal of hemophilia A adeno-associated virus-mediated gene therapy. Trials with initially normal factor VIII activity observed unexplained year-over-year declines in expression while others reported low-level, stable expression inadequate to restore normal hemostasis. Here we demonstrate that male mice recapitulate expression-level-dependent loss of factor VIII levels due to declines in vector copy number. We show that an enhanced function factor VIII variant (factor VIII-R336Q/R562Q), resistant to activated protein C-mediated inactivation, normalizes hemostasis at below-normal expression without evidence of prothrombotic risk in male hemophilia A mice. These data support that factor VIII-R336Q/R562Q may restore normal factor VIII function at low levels of expression to permit durability using low vector doses to minimize dose-dependent adeno-associated virus toxicities. This work informs the mechanism of factor VIII durability after gene transfer and supports that factor VIII-R336Q/R562Q may safely overcome current hemophilia A gene therapy limitations. A major limitation in hemophilia A gene therapy is the progressive loss of factor VIII expression. Here, the authors demonstrate that low-level expression of a gain-of-function factor VIII variant may safely restore normal hemostasis and permit durability of expression.