Background: Gene therapy for hemophilia offers the possibility to ameliorate disease severity to a mild or functionally curative state through a single administration. Etranacogene dezaparvovec (AMT-061) is an investigational gene therapy for hemophilia B comprising an adeno associated virus serotype 5 (AAV5) vector containing a codon-optimized Padua variant human factor IX (FIX) gene with liver specific promoter.

Aims: We have previously shown a single dose of etranacogene dezaparvovec to provide sustained FIX activity into the mild-to normal range for up to 52 weeks post-dose in participants with severe or moderate-severe hemophilia B. This time, 2 years of follow-up data will be presented for the first time.

Methods: A Phase 2b, open-label, single-dose, single-arm, multi-center trial (NCT03489291) in adult hemophilia B subjects. Interestingly, participants were not excluded based on neutralizing antibodies to AAV5. All subjects received a single intravenous dose of etranacogene dezaparvovec (2x1013 gc/kg) and will be followed for 5-years. The primary endpoint was FIX activity at Week 6. Secondary endpoints include e-diary recordings of bleeds and FIX concentrate use, laboratory parameters, joint health, patient reported outcomes, and adverse events (AEs).

Results: All participants had FIX ≤1% (severe or moderately-severe FIX deficiency), required routine FIX prophylaxis, and had neutralizing activity to AAV5 at baseline. Following AMT-061 treatment, FIX activity increased rapidly to a mean of 31% at Week 6. At Week 52, mean FIX activity increased further to 41% with FIX activity levels of 50%, 31% and 41% in participants 1-3 respectively. There was no relationship between the presence of anti-AAV5 NAbs and response to etranacogene dezaparvovec. As of 52 weeks, there were no bleeds post-treatment and no requirement for FIX replacement aside from protocol-specified use for perioperative management in participant 3. There were no clinically significant elevations in liver enzymes and no participants required steroids related to the treatment. One participant experienced 2 mild AEs possibly related to treatment shortly after dosing (self-limiting headache and slightly elevated CRP). One patient had hip surgery due to worsening of pre-existing avascular necrosis deemed unrelated by investigator to etranacogene dezaparvovec and received FIX per protocol according to standard clinical practice. No participant developed inhibitors to FIX. Updated results to 2 years of follow-up will be presented with the main focus on FIX activity, FIX replacement therapy use and reported bleeds.

Conclusions: Patients with AAV5 NAbs were included in the Phase 2b etranacogene dezaparvovec trial and have shown sustained FIX activity into the mild-to normal range. All participants were able to discontinue routine prophylaxis, and there have been no bleeds post-treatment with etranacogene dezaparvovec.

Disclosures

Giermasz:BioMarin: Consultancy, Research Funding, Speakers Bureau; Genentech/Roche: Consultancy, Research Funding, Speakers Bureau; uniQure: Consultancy, Research Funding; Sangamo Therapeutics: Research Funding; Bioverativ/Sanofi: Consultancy, Research Funding, Speakers Bureau. Castaman:Alexion: Honoraria; Roche: Consultancy, Honoraria, Speakers Bureau; CSL Behring: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding; Ablynx: Honoraria; Baxalta/Shire: Honoraria; Bayer: Honoraria; Uniqure: Honoraria, Membership on an entity's Board of Directors or advisory committees; Kedrion: Speakers Bureau; Werfen: Speakers Bureau; Sobi: Honoraria, Research Funding, Speakers Bureau; Novo Nordisk: Honoraria, Speakers Bureau. Key:Novo Nordisk: Other: Chair of Grants Committee; Takeda: Research Funding; Grifols: Research Funding; Uniqure: Consultancy. Miesbach:Bayer: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; BioMarin Pharmaceutical Inc: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; UniQure: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Recht:Spark: Research Funding; Novo Nordisk: Consultancy, Other: personal fees, Research Funding; uniQure: Consultancy, Other: personal fees, Research Funding; Takeda: Consultancy, Other: personal fees, Research Funding; BioMarin: Research Funding; Pfizer: Consultancy, Other: personal fees; Genentech: Consultancy, Other: personal fees, Research Funding; CSL Behring: Consultancy, Other: personal fees. Gomez:Global Blood Therapeutics: Speakers Bureau. Gut:uniQure: Current Employment. Pipe:Siemens: Research Funding; Medical and Scientific Advisory Council to the National Hemophilia Foundation; Medical Advisory Board to World Federation of Hemophilia: Membership on an entity's Board of Directors or advisory committees; Apcintex, Bayer, BioMarin, Catalyst Biosciences, CSL Behring, HEMA Biologics, Freeline, Novo Nordisk, Pfizer, F. Hoffmann-La Roche Ltd/Genentech, Inc., Sangamo Therapeutics, Sanofi, Takeda, Spark Therapeutics, uniQure: Consultancy.

OffLabel Disclosure:

Etranacogene dezaparvovec (AMT-061) is an investigational gene therapy for hemophilia B comprising an adeno associated virus serotype 5 (AAV5) vector containing a codon-optimized Padua variant human factor IX (FIX) gene with liver specific promoter.

Author notes

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Asterisk with author names denotes non-ASH members.