{"id":4746,"date":"2025-07-17T13:32:37","date_gmt":"2025-07-17T13:32:37","guid":{"rendered":"https:\/\/medical.biomarin.com\/en-us\/?page_id=4746"},"modified":"2026-01-07T19:45:11","modified_gmt":"2026-01-07T19:45:11","slug":"fviii-inhibitor-development-summary","status":"publish","type":"page","link":"https:\/\/medical.biomarin.com\/en-us\/hemophilia-a\/valoctocogene-roxaparvovec-safety\/fviii-inhibitor-development-summary\/","title":{"rendered":"FVIII Inhibitor Development Summary"},"content":{"rendered":"<div id=\"acf-block-645511272e5db\" class=\"hero hero-no-overlay hero-small-title\">\n            <div class=\"hero-background-image hero-background-image-desktop\" style=\"background-image: url(https:\/\/medical.biomarin.com\/en-us\/wp-content\/uploads\/sites\/2\/2025\/10\/Program-banner-drop.png?v=1.20);\"><\/div>\n\t    <div class=\"hero-background-image hero-background-image-mobile\" style=\"background-image: url(https:\/\/medical.biomarin.com\/en-us\/wp-content\/uploads\/sites\/2\/2025\/10\/Program-banner-drop-Mobile.png?v=1.20);\"><\/div>\n    \t<div class=\"overlay\"><\/div>\n\t<div class=\"wrapper\">\n\t\t<div class=\"inner-wrapper\">\n\t\t\t<div class=\"hero-content\">\n\t\t\t    \t\t\t        <ul class=\"breadcrumb\">\n\t\t\t            \t\t\t                                                                        <li><a href=\"https:\/\/medical.biomarin.com\/en-us\/hemophilia-a\/\">Hemophilia A<\/a><\/li>\n                            \t\t\t                                                                        <li><a href=\"https:\/\/medical.biomarin.com\/en-us\/hemophilia-a\/valoctocogene-roxaparvovec-safety\/\">Valoctocogene roxaparvovec safety<\/a><\/li>\n                            \t\t\t                                                                        <li>FVIII Inhibitor Development Summary<\/li>\n                            \t\t\t            \t\t\t        <\/ul>\n\t\t\t    \t\t\t\t\t\t\t\t\t\t\t\t    <h1>FVIII Inhibitor Development\n<\/h1>\n\t\t\t\t\t\t\t\t\t\t\t\t\n                <p class=\"inline-buttons\">\n                                                        <\/p>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n<\/div>\n\n\n<div id=\"acf-block-645512ae5ba05\" class=\"block wrapped-content bg-band bg-band-primary block-zero-top block-tight-bottom\">\n    <div class=\"wrapper\">\n        <div class=\"inner-wrapper\">\n                \n<div id=\"acf-block-645512ae5bb64\" class=\"block-wysiwyg\">\n            <h2>State of Knowledge Summary<\/h2>\n<ul>\n<li>Patients with prior or active anti-factor VIII neutralizing antibodies (factor VIII [FVIII] inhibitors) were excluded from clinical trials.<sup>1,2<\/sup><\/li>\n<li>No FVIII inhibitor responses have been observed in valoctocogene roxaparvovec clinical trials.<sup>8-10<\/sup><\/li>\n<\/ul>\n    <\/div>\n        <\/div>\n    <\/div>\n<\/div>\n\n<div id=\"acf-block-6489ac6e0b826\" class=\"block wrapped-content\">\n    <div class=\"wrapper\">\n        <div class=\"inner-wrapper\">\n                \n<div id=\"acf-block-6489ac6e0b985\" class=\"block-wysiwyg\">\n            <h2>FVIII Inhibitor Development<\/h2>\n<p>For clinical trial enrollment patients receiving valoctocogene roxaparvovec were required to screen negative for anti-AAV5 antibodies, have no history of FVIII inhibitors, and screen negative (&lt;0.6 BU) for FVIII inhibitors in a Nijmegen modified Bethesda assay with a lifetime minimum of 150 exposure days to FVIII replacement therapy.<sup>1,2<\/sup><\/p>\n    <\/div>\n        <\/div>\n    <\/div>\n<\/div>\n\n<div id=\"acf-block-645513905c507\" class=\"block split-content equal-bias content-reverse bottom-border block-tight-bottom\" data-muted-autoplay=\"false\">\n\t<div class=\"wrapper\">\n\t\t<div class=\"inner-wrapper\">\n\t\t                                                                <div class=\"content-block first-block\">\n                                                                                                                                                                                                                                                                                    \n                                    \n                                                                                                                \n                                    \n                                    <figure>\n                                        <div class=\"image image-rounded\">\n                                                                                            <img decoding=\"async\" class=\"\" src=\"https:\/\/medical.biomarin.com\/en-us\/wp-content\/uploads\/sites\/2\/2025\/07\/FVIII_INHIBITOR_DEVELOPMENT_01-1900x1119.png\" alt=\"Graphic of Factor VIII attaching to antibodies\"\/>                                                                                    <\/div>\n                                                                            <\/figure>\n                                                                                    <\/div>\n                    \n                                            <div class=\"content-block second-block\">\n                                                                                                <p>&#xA0;<\/p>\n<ul>\n<li>No patients have developed a FVIII inhibitor response (Nijmegen modified Bethesda assay)&#x200B;<sup>8-10<\/sup><\/li>\n<li>12 of 134 (9%)&#xA0;GENEr8-1 participants tested positive at one or more time points&#xA0;for FVIII TAb; no association with ALT elevations or FVIII activity measures&#xA0;&#x200B;<sup>7<\/sup>\n<ul>\n<li>A majority of the positive tests were low titer, single positive results that revert to negative at the next &#x200B;time point&#x200B;<sup>7<\/sup><\/li>\n<li>No cellular immune response to FVIII (IFN-&#x3B3;ELISpot) was detected at those &#x200B;time points&#x200B;<sup>7<\/sup><\/li>\n<\/ul>\n<\/li>\n<li>These results are consistent with low titer, transient antibody responses described in the literature for both healthy donors and hemophilia A patients who do not progress to inhibitors<sup>3,4<\/sup><\/li>\n<\/ul>\n                                                                                    <\/div>\n                                                \t\t<\/div>\n\t<\/div>\n<\/div>\n\n<div id=\"acf-block-64871d02606ff\" class=\"block wrapped-content\">\n    <div class=\"wrapper\">\n        <div class=\"inner-wrapper\">\n                \n<div id=\"acf-block-64871d0260839\" class=\"block-wysiwyg\">\n            <p><strong>The use of valoctocogene roxaparvovec in patients with active inhibitors or prior history of FVIII inhibitors is under investigation in a Phase 1\/2 clinical trial.<\/strong><sup>5<\/sup><\/p>\n<ul>\n<li>Study 270-205 is a 2-part Phase 1\/2 open-label, multicenter clinical trial evaluating the safety and efficacy of Valoctocogene roxaparvovec in patients with severe hemophilia A and FVIII inhibitors.<sup>5<\/sup> Patients with active and a prior history of FVIII inhibitors will be included in Parts A and B, respectively.<\/li>\n<li>Safety and efficacy outcomes including, change in FVIII activity level and annualized bleeding rate, will be assessed for up to 5 years.<sup>5<\/sup> Additionally, Part A will assess change in FVIII inhibitor titers and Part B the recurrence of FVIII inhibitors.<\/li>\n<\/ul>\n    <\/div>\n\n<div id=\"acf-block-64871d62776a6\" class=\"block-wysiwyg\">\n            <h2><\/h2>\n<p>&#xA0;<\/p>\n    <\/div>\n\n<figure id=\"acf-block-64871d02623e1\">\n    <div class=\"image image-rounded image-align-left\">\n                    <img decoding=\"async\" class=\"\" src=\"https:\/\/medical.biomarin.com\/en-us\/wp-content\/uploads\/sites\/2\/2025\/07\/FVIII_INHIBITOR_DEVELOPMENT_02.svg\" alt=\"Table including objectives, inclusion criteria, and exlusion criteria\"\/>            <\/div>\n    <\/figure>\n\n<div id=\"acf-block-65f4932d4041e\" class=\"block-wysiwyg\">\n            <p><span class=\"TextRun SCXW23261625 BCX8\"><span class=\"NormalTextRun CommentStart CommentHighlightPipeHovered CommentHighlightHovered SCXW23261625 BCX8\">To <\/span><span class=\"NormalTextRun CommentHighlightPipeHovered SCXW23261625 BCX8\">date, interim data have been collected from 10 patients (3 from Part A and 7 from Part B)<\/span><span class=\"NormalTextRun SCXW23261625 BCX8\">. <\/span><span class=\"NormalTextRun SCXW23261625 BCX8\">Patients have reached 44.7-<\/span><span class=\"NormalTextRun SCXW23261625 BCX8\">122.7 weeks<\/span><span class=\"NormalTextRun SCXW23261625 BCX8\"> of <\/span><span class=\"NormalTextRun ContextualSpellingAndGrammarErrorV2Themed SCXW23261625 BCX8\">follow-up<\/span><span class=\"NormalTextRun SCXW23261625 BCX8\"> and none have <\/span><span class=\"NormalTextRun SCXW23261625 BCX8\">discontinued<\/span><span class=\"NormalTextRun SCXW23261625 BCX8\"> the study.<\/span><\/span><span class=\"EOP SCXW23261625 BCX8\">&#xA0;<\/span><\/p>\n<ul>\n<li>Part A <sup>6<\/sup>\n<ul>\n<li><span class=\"TextRun SCXW126306369 BCX8\"><span class=\"NormalTextRun SCXW126306369 BCX8\">All 3 active inhibitor patients had increased FVIII <\/span><span class=\"NormalTextRun SCXW126306369 BCX8\">inhibitor titers, suggesting that FVIII is still being produced.&#xA0;<\/span><\/span><span class=\"EOP SCXW126306369 BCX8\">&#xA0;<\/span><\/li>\n<li><span class=\"NormalTextRun SCXW211284811 BCX8\">Factor VIII activity was detectable in 1 <\/span><span class=\"NormalTextRun SCXW211284811 BCX8\">patient<\/span><\/li>\n<\/ul>\n<\/li>\n<li>Part B <sup>6<\/sup>\n<ul>\n<li><span class=\"TextRun SCXW263527857 BCX8\"><span class=\"NormalTextRun SCXW263527857 BCX8\">Co<\/span><span class=\"NormalTextRun SCXW263527857 BCX8\">nsistent with those <\/span><span class=\"NormalTextRun SCXW263527857 BCX8\">observed<\/span><span class=\"NormalTextRun SCXW263527857 BCX8\"> in GENEr8-1, with patients having mean (standard deviation) FVIII activity levels via chromogenic substrate assay<\/span><\/span>:\n<ul>\n<li><span class=\"TextRun SCXW17510834 BCX8\"><span class=\"NormalTextRun SCXW17510834 BCX8\"><span class=\"TextRun SCXW254526040 BCX8\"><span class=\"NormalTextRun SCXW254526040 BCX8\">50.1 (43.8)<\/span> <span class=\"EOP SCXW254526040 BCX8\"><span class=\"TextRun SCXW36760222 BCX8\"><span class=\"NormalTextRun SCXW36760222 BCX8\">IU\/dL <\/span><\/span><\/span><span class=\"NormalTextRun SCXW254526040 BCX8\">at Weeks 25-28<\/span><\/span><\/span><\/span><\/li>\n<li><span class=\"TextRun SCXW17510834 BCX8\"><span class=\"NormalTextRun SCXW17510834 BCX8\"><span class=\"EOP SCXW254526040 BCX8\"><span class=\"TextRun SCXW36760222 BCX8\"><span class=\"NormalTextRun SCXW36760222 BCX8\">25.8 (18.2) IU\/dL <\/span><span class=\"NormalTextRun SCXW36760222 BCX8\">at Weeks<\/span><span class=\"NormalTextRun SCXW36760222 BCX8\"> 49-52<\/span><\/span><span class=\"EOP SCXW36760222 BCX8\">&#xA0;<\/span><\/span><\/span><\/span><\/li>\n<\/ul>\n<\/li>\n<li><span class=\"TextRun SCXW17510834 BCX8\"><span class=\"NormalTextRun SCXW17510834 BCX8\">No bleed events or use of FVIII infusions were reported<\/span><\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p><span class=\"TextRun SCXW143553031 BCX8\"><span class=\"NormalTextRun SCXW143553031 BCX8\">The safety profile was <\/span><span class=\"NormalTextRun AdvancedProofingIssueV2Themed SCXW143553031 BCX8\">similar to<\/span><span class=\"NormalTextRun SCXW143553031 BCX8\"> GENEr8-1 with all patients reporting at least 1 adverse event (AE) and most experiencing alanine aminotransferase (ALT) elevations<\/span><span class=\"NormalTextRun SCXW143553031 BCX8\">.<sup>6 <\/sup><\/span><span class=\"NormalTextRun SCXW143553031 BCX8\">There were no reports of FVIII inhibitor recurrence in Part B patients.<\/span><\/span><span class=\"EOP SCXW143553031 BCX8\">&#xA0;<\/span><\/p>\n<p>&#xA0;<\/p>\n    <\/div>\n\n<figure id=\"acf-block-691770fcda6e0\">\n    <div class=\"image image-rounded image-align-left\">\n                    <img decoding=\"async\" class=\"\" src=\"https:\/\/medical.biomarin.com\/en-us\/wp-content\/uploads\/sites\/2\/2025\/11\/Safety-Outcomes-of-GENEr8-INH-FVIII-Table-NOV2025.jpg?v=1.20\" alt=\"Image of Safety-Outcomes-of-GENEr8-INH-FVIII table\"\/>            <\/div>\n            <figcaption><p>AE, adverse event; ALT, alanine aminotransferase; FVIII, factor VIII; NA, not applicable; SAE, serious adverse event<\/p>\n<\/figcaption>\n    <\/figure>\n        <\/div>\n    <\/div>\n<\/div>\n\n<div id=\"acf-block-64882994ea0de\" class=\"block next-previous\">\n    <div class=\"wrapper\">\n\t\t<div class=\"inner-wrapper\">\n            <div class=\"link link-prev\">\n                                    <p><a class=\"button button-text button-arrow button-arrow-left\" href=\"https:\/\/medical.biomarin.com\/en-us\/valoctocogene-roxaparvovec-safety\/thromboembolism\/\" target=\"_self\">Thromboembolism Summary<\/a><\/p>\n                            <\/div>\n            <div class=\"link link-next\">\n                                    <p><a class=\"button button-text button-arrow\" href=\"https:\/\/medical.biomarin.com\/en-us\/valoctocogene-roxaparvovec-safety\/\" target=\"_self\">Valoctocogene roxaparvovec safety<\/a><\/p>\n                            <\/div>\n\t\t<\/div>\n\t<\/div>\n<\/div>\n\n<div id=\"acf-block-6487179ccbcfc\" class=\"block references\">\n    <div class=\"wrapper\">\n\t\t<div class=\"inner-wrapper\">\n\t\t    \t\t\t    <h4>References:\n<\/h4>\n\t\t\t\t\t\t                <ol>\n                                                                                                                        <li><span>Ozelo MC, Mahlangu J, Pasi KJ, et al. Valoctocogene Roxaparvovec Gene Therapy for Hemophilia A. N Engl J Med. 2022;386(11):1013-1025.\n<\/span><\/li>\n                                                                                                                                                <li><span>Pasi KJ, Rangarajan S, Mitchell N, et al. Multiyear Follow-up of AAV5-hFVIII-SQ Gene Therapy for Hemophilia A. N Engl J Med. 2020;382(1):29-40.\n<\/span><\/li>\n                                                                                                                                                <li><span>Reipert BM, Gangadharan B, Hofbauer CJ, et al. The prospective Hemophilia Inhibitor PUP Study reveals distinct antibody signatures prior to FVIII inhibitor development. Blood Adv. 2020;4(22):5785-5796.\n<\/span><\/li>\n                                                                                                                                                <li><span>Whelan SF, Hofbauer CJ, Horling FM, et al. Distinct characteristics of antibody responses against factor VIII in healthy individuals and in different cohorts of hemophilia A patients. Blood. 2013;121(6):1039-1048.\n<\/span><\/li>\n                                                                                                                                                <li><span>BioMarin Pharmaceutical. Safety, Tolerability, and Efficacy Study of Valoctocogene Roxaparvovec in Hemophilia A With Active or Prior Inhibitors.\n<\/span><\/li>\n                                                                                                                                                <li><span>Chavele KM, Chiou S, Chou S, et al. Safety and efficacy of valoctocogene roxaparvovec in participants with active or prior FVIII inhibitors: Results from a phase 1\/2 trial [presentation]. Presented at the Bari 13th International Congress (BIC). September 12-14, 2025; Padua, Italy.\n<\/span><\/li>\n                                                                                                                                                <li><span>Long BR, Robinson TM, Day JRS, et al. Clinical immunogenicity outcomes from GENEr8-1, a phase 3 study of valoctocogene roxaparvovec, an AAV5-vectored gene therapy for hemophilia A. <em>Mol Ther. <\/em>2024;32(7):2052-2063.\n<\/span><\/li>\n                                                                                                                                                <li><span>Symington E, Rangarajan S, Lester W, et al. Valoctocogene roxaparvovec gene therapy provides durable haemostatic control for up to 7 years for haemophilia A. Haemophilia. 2024;30(5):1138-1147.\n<\/span><\/li>\n                                                                                                                                                <li><span>Leavitt AD, Mahlangu J, Raheja P, et al. Efficacy and safety of valoctocogene roxaparvovec 4 years after gene transfer in GENEr8-1 [presentation]. Presented at the International Society on Thrombosis and Haemostasis (ISTH) Congress. June 22-26, 2024; Bangkok, Thailand.\n<\/span><\/li>\n                                                                                                                                                <li><span>Leavitt AD, Mahlangu J, Raheja P, et al. Efficacy, safety, and quality of life 4 years after valoctocogene roxaparvovec gene transfer for severe hemophilia A in the phase 3 GENEr8-1 trial. <em>Res Pract Thromb Haemost. <\/em>2024;8(8):102615.\n<\/span><\/li>\n                                                            <\/ol>\n\t\t\t\t\t<\/div>\n\t<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"","protected":false},"author":2,"featured_media":0,"parent":4754,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":""},"class_list":["post-4746","page","type-page","status-publish","hentry"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.1.1 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>FVIII Inhibitor Development Summary | BioMarin Medical<\/title>\n<meta name=\"description\" content=\"Learn more about FVIII Inhibitor Development\" \/>\n<meta name=\"robots\" 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