PRAGUE – AMT-061, a gene therapy consisting of an adeno-associated virus serotype 5 (AAV5) vector and a Padua variant human factor IX (hFIX) gene, provides clinically meaningful FIX activity, based on early results from an ongoing, phase 2b study.
Will Pass/ MDedge News
Dr. Annette Von Drygalski
The findings provide traction for a phase 3 trial (HOPE-B; NCT03569891) which is currently enrolling, according to lead author Annette Von Drygalski, MD, PharmD, director of the Hemophilia and Thrombosis Treatment Center at the University of California, San Diego.
Dr. Von Drygalski said that the results also demonstrate the positive impact of switching from a wild-type hFIX gene in AMT-060 to a Padua hFIX variant in AMT-061, achieved by replacing arginine with leucine at R338L.
Speaking at the annual congress of the European Association for Haemophilia and Allied Disorders, Dr. Von Drygalski referred to AMT-061 as the “enhanced version” of AMT-060. Prior to human trials, nonhuman primate studies comparing AMT-060 with AMT-061 demonstrated a 550% increase in factor IX activity, similar to previous reports of 600%-800% boosts from the Padua variant.
The current findings revealed early outcomes for three men with severe hemophilia B who were given AMT-061. The patients were between 43 years and 50 years of age and had been taking clotting factors prophylactically. Among them, annualized bleed rates ranged from one to five events per year. Two of the three men were HIV-positive, one had IgM antibodies against AAV5, and all three had neutralizing antibodies against AAV5.
“Of note,” Dr. Von Drygalski said, “two of the participants had previously been excluded from participation in gene therapy due to preexisting antibodies against AAV.”
Each man was given a single dose of 2 x 1013 gene copies/kg of AMT-061 intravenously. The primary endpoint was efficacy at 6 weeks after administration. Ongoing secondary endpoints include patient-reported bleeding and FIX concentrate use, joint health, patient-reported quality of life, and laboratory parameters. Patients will be followed for 1 year.
Within 2 weeks, all three men achieved meaningful levels of FIX. Two of three patients demonstrated an upward trend of FIX activity that peaked at about 50% of normal. The third patient’s levels plateaued sooner, with the most recent reading at week 14 showing 25%. Mean factor IX activity level was 38% of normal 12 weeks after gene therapy.
“These clotting factor activity levels translated into complete control [of bleeding] with no requirement for factor IX replacement after infusion,” Dr. Von Drygalski said. For comparison, AMT-060, the wild-type version, only achieved levels of 3%-13%, which are less clinically meaningful.
Along with demonstrating efficacy, AMT-061 was well tolerated. One patient had two adverse events that resolved without treatment: very mild C-reactive protein elevation and transient headache. One patient had a very mild and transient AST elevation (week 2, 43 U/L; week 4, 48 U/L) that resolved without treatment. No patients had ALT elevations and immunosuppression was not needed.
These findings provide a strong foundation for the phase 3 HOPE-B trial, which will include about 50 patients with FIX activity no greater than 2%. Dr. Von Drygalski noted that patients with AAV5-neutralizing antibodies will not be excluded.
The investigators reported financial relationships with Bayer, UniQure, Pfizer, Novo Nordisk, Shire, and others.
SOURCE: Von Drygalski A et al. EAHAD 2019, Abstract OR10.