{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,2]],"date-time":"2026-10-02T03:35:53Z","timestamp":1790912153655,"version":"4.1.0"},"reference-count":23,"publisher":"American Society of Hematology","issue":"14","content-domain":{"domain":["ashpublications.org"],"crossmark-restriction":true},"short-container-title":[],"published-print":{"date-parts":[[2026,10,1]]},"abstract":"<jats:sec>\n                    <jats:title>Abstract<\/jats:title>\n                    <jats:p>Hemophilia A (HA) phenotype is predicted by factor VIII (FVIII) activity. Most HA adeno-associated virus (AAV) trials incorporate the B-domain\u2013deleted FVIII-SQ variant, and 1-stage assay (OSA) FVIII activity exceeds chromogenic substrate assay (CSA) values by 1.5-fold to twofold. This contrasts with recombinant FVIII-SQ (rFVIII-SQ), suggests altered biochemical properties, and highlights the need to determine which assay reflects hemostatic function. In gene therapy\u2013treated mice and SPK-8011 trial participants, AAV-derived FVIII-SQ (AAV-FVIII-SQ) activation and function within the intrinsic tenase enzyme complex was compared with rFVIII-SQ. In both species, AAV-FVIII-SQ demonstrated normal cofactor function and A2-domain stability. In mice, the assay discrepancy persisted without von Willebrand factor (VWF), indicating it is not driven by altered VWF interactions. Both species demonstrated enhanced thrombin-mediated activation of AAV-FVIII-SQ, detectable by OSA but not CSA. Negative binomial regression analysis of 23 SPK-8011 participants, representing 99 cumulative patient-years, trended toward better prediction of annualized bleeding rate with OSA than CSA. In vivo evaluation of AAV-FVIII-SQ in mice demonstrated that OSA activity better correlated with hemostatic function and corresponded to rFVIII-SQ function. These findings support that OSA FVIII activity reflects AAV-FVIII-SQ function within the intrinsic tenase complex, captures enhanced activation not detected by CSA, and best predicts clinical outcome.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1182\/blood.2025032890","type":"journal-article","created":{"date-parts":[[2026,6,29]],"date-time":"2026-06-29T16:57:47Z","timestamp":1782752267000},"page":"1848-1853","update-policy":"https:\/\/doi.org\/10.1182\/blood.2019cm0000","source":"Crossref","is-referenced-by-count":1,"title":["One-stage assay factor VIII activity reflects AAV-derived factor VIII\u2013enhanced thrombin activation and predicts phenotype"],"prefix":"10.1182","volume":"148","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-1564-7870","authenticated-orcid":false,"given":"Anna R.","family":"Sternberg","sequence":"first","affiliation":[{"name":"1Division of Hematology, Children\u2019s Hospital of Philadelphia, Philadelphia, PA"},{"name":"2Raymond G. Perelman Center for Cellular and Molecular Therapeutics, Children\u2019s Hospital of Philadelphia, Philadelphia, PA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7766-7880","authenticated-orcid":false,"given":"Connor T.","family":"Watson","sequence":"additional","affiliation":[{"name":"1Division of Hematology, Children\u2019s Hospital of Philadelphia, Philadelphia, PA"},{"name":"2Raymond G. Perelman Center for Cellular and Molecular Therapeutics, Children\u2019s Hospital of Philadelphia, Philadelphia, PA"},{"name":"3Department of Pediatrics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Robert J.","family":"Davidson","sequence":"additional","affiliation":[{"name":"1Division of Hematology, Children\u2019s Hospital of Philadelphia, Philadelphia, PA"},{"name":"2Raymond G. 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