Stable FIX Expression and Durable Reductions in Bleeding and Factor IX Consumption for up to 4 Years Following AMT-060 Gene Therapy in Adults with Severe or Moderate-Severe Hemophilia B
Authors: Miesbach Wolfgang , Meijer Karina , Coppens Michiel , Kampmann Peter , Klamroth Dr. , Schutgens Roger , Castaman Giancarlo , Seifried Erhard , Schwaeble Joachim , Bönig Halvard , Sawyer Eileen K , Leebeek Frank W.G. 
Published: November 2019

Background: The aim of gene therapy is to provide long-term therapeutic effect from a single administration, yet information on response durability is currently limited. AMT-060 is an adeno-associated virus serotype 5 (AAV5) vector with a codon-optimized wildtype human factor IX (FIX) gene and liver-specific promoter. AMT-060 is being analyzed in an ongoing study of 10 participants with severe/moderate-severe hemophilia B (Phase 1/2 study, NCT02396342).
Aim: To describe efficacy and safety outcomes from a planned interim analysis at up to 4-years post-AMT-060.
Methods: Adult males with FIX activity ≤2% and a severe bleeding phenotype received a single intravenous infusion of AMT-060 (5x1012gc/kg, Cohort 1, n=5) or (2×1013 gc/kg, Cohort 2, n=5). Assessments included FIX activity, FIX replacement use, annualized bleeding rate (ABR), treatment-related adverse events (TRAE), immunological and inflammatory biomarkers up to 4 years (Cohort 1) and 3.5 years (Cohort 2).
Results: As of 8 May 2019, for Cohort 1 the mean yearly FIX activity (annualized to 4 years) was 6.0 as compared to 4.4% in the first year, 6.8% in the second year and 7.3% in the third year. Mean yearly FIX activity for Cohort 2 at 3 years was 7.9% as compared to 7.1% in the first year and 8.4% in the second year. Factor IX activity for each patient over the length of follow up is shown in Figure 1. Eight of 9 participants using prophylaxis at baseline were able to discontinue use. During the last 12 months of observation, the mean annualized bleed rate (ABR) was 1.7 for Cohort 1 and 0.7 for Cohort 2. Respectively, these represent a reduction in mean ABR to the year prior to treatment of 88% and 83%. During this same period the consumption of FIX replacement therapy declined 93% and 96% relative to pre-treatment respectively for Cohort 1 and Cohort 2. No participants developed FIX inhibitors or signs of sustained AAV5 capsid-specific T-cell activation. TRAE were mainly reported in the first 3.5-months after treatment, including three participants who experienced transient mild elevations in alanine aminotransferase as previously described. One new TRAE (joint swelling post-exercise) was observed during the last 12 months of observation post-treatment. Updated data, up to 4-years of observation, will be presented for the first time.
Conclusions: Long-term stable endogenous FIX activity and reductions in ABR and FIX replacement use were observed following a single treatment with AMT-060. There were no additional safety concerns with longer term follow-up. These findings support the ongoing Phase III study of the enhanced construct, AMT-061, which encodes the highly active Padua FIX variant.
Figure 1

Disclosures
Miesbach: Bayer, BioMarin, CSL Behring, Chugai, Freeline, Novo Nordisk, Octapharma, Pfizer, Roche, Takeda/Shire, UniQure: Consultancy; Bayer, Novo Nordisk, Octapharma, Pfizer, Takeda/Shire: Research Funding; Bayer, Chugai, Novo Nordisk, Octapharma, Pfizer, Takeda/Shire, UniQure: Speakers Bureau. Meijer:Pfizer, Sanquin, Uniqure: Research Funding; Uniqure, BMS, Aspen, Boehringer Ingelheim, Sanquin, Bayer: Consultancy, Honoraria; Sanquin: Research Funding; Bayer: Research Funding. Coppens:Pfizer: Honoraria; Portola Pharmaceuticals, Inc: Honoraria; Daiichi Sankyo: Honoraria, Research Funding; Uniqure: Research Funding; Boehringer Ingelheim: Research Funding; Sanquin Blood Supply: Research Funding; Bayer: Honoraria, Research Funding; CSL Behring: Honoraria, Research Funding; Bristol-Myers Squibb: Honoraria. Kampmann:Uniqure BV: Research Funding. Klamroth:Bayer, Biomarin, CSL Behring, Novo Nordisk, Octapharma, Pfizer, Roche, SOBI, Takeda: Consultancy; Bayer, Novo Nordisk, SOBI: Research Funding. Schutgens:Baxalta Shire, Novo Nordisk, Bayer, CSL Behring, Pfizer, UniQure BV: Research Funding. Castaman:Bayer: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novo Nordisk: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Sobi: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; CSL Behring: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Takeda (SHIRE): Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Kedrion: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Roche: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Werfen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Research Funding; Uniqure: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Sanofi: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Seifried:Medac: Other: BSD owns IP and is contract manufacturer; Uniqure BV: Research Funding. Schwaeble:Uniqure BV: Research Funding. Bönig:Celgene, Novartis, Sandoz Hexal: Consultancy; Kiadis Pharma: Other: Contract manufacturing of ATIR101; Sandoz Hexal, Uniqure: Research Funding; Miletenyi: Speakers Bureau. Sawyer:Uniqure BV: Employment. Leebeek:CSL Behring: Research Funding; UniQure: Consultancy; Shire/Takeda: Research Funding; Novo Nordisk: Consultancy; Sobi: Other: Travel grant; Shire/Takeda: Consultancy.