One-stage assay factor VIII activity reflects AAV-derived factor VIII-enhanced thrombin activation and predicts phenotype.

One-stage assay FVIII activity accurately reflects AAV-FVIII-SQ function and better predicts bleeding outcomes in hemophilia A gene therapy than chromogenic assays.

• Why it matters: Accurate assessment of FVIII activity is crucial for predicting hemophilia A severity and treatment success, yet current assays may not fully capture the functional activity of AAV-derived FVIII variants.
• What they did: The study compared AAV-FVIII-SQ and recombinant FVIII-SQ in mice and clinical trial participants using both one-stage and chromogenic assays, analyzing activation, stability, and correlation with bleeding rates across 99 patient-years.
• The result: Findings show that OSA better detects enhanced thrombin activation of AAV-FVIII-SQ, correlates with in vivo hemostatic function, and improves prediction of bleeding risk, guiding more accurate clinical assessments.