Enhancing hemophilia A gene therapy by strategic F8 deletions in AAV vectors

Hemophilia A, caused by a deficiency in factor VIII (F8), is a promising target for gene therapy. This study aims to enhance the efficacy of adeno-associated virus serotype 8 (AAV8) vectors, specifically those encoding B-domain-deleted F8 (BDDF8), to treat the condition. We focused on improving therapeutic outcomes by strategically deleting amino acids at the furin cleavage site (RHQR), a modification that is crucial for increasing F8 expression and reducing capsid stress during vector packaging. Using computational modeling with AlphaFold2, combined with western blotting and in vivo clotting assays, we developed and tested several AAV8-BDDF8 variants in a hemophilia A mouse model. The AAV8-BDDF8-ΔRHQR10 variant, which includes a 10-amino acid deletion at the RHQR site, demonstrated a 2- to 3-fold increase in F8 activity, with sustained expression and no hepatotoxicity. This variant also showed reduced capsid stress and enhanced protein expression. However, the observed decline in long-term efficacy highlights the ongoing challenges in AAV-F8 gene therapy, emphasizing the need for continuous improvements. Our findings offer valuable insights for refining AAV-mediated gene therapy in hemophilia A, showing that targeted molecular modifications can significantly enhance therapeutic performance while ensuring safety.