Gene therapy for reducing bleeding in hemophilia patients: HOPE B Trial

USA: A recent study has shown the role of gene therapy in reducing bleeding rate among hemophilia patients. The findings of the study were presented at the American Society of Hematology virtual meeting.

According to the study, a single dose of a viral-mediated gene therapy vector was shown to reduce the bleeding rate among patients with Factor IX-related hemophilia B (HB) by 91% in  months.

"This is the first report of a Phase 3 study in HB and the largest gene therapy trial cohort to date," wrote the authors.

The gene therapy used is etranacogene dezaparvovec comprising an adeno-associated virus serotype 5 (AAV5) vector containing a codon-optimized Padua variant human factor IX (FIX) gene with a liver specific promoter. 

A phase 2b study showed a single dose of etranacogene dezaparvovec to provide mean FIX activity of 41.0% sustained at 1yr post-dose in 3 participants. Although most gene therapy clinical studies exclude pts with pre-existing neutralizing antibodies (NAbs) to the capsid serotype, early clinical studies and nonhuman primate data suggest that generally prevalent titers of anti-AAV5 NAbs may not preclude successful transduction with etranacogene dezaparvovec.

Steven W. Pipe, University of Michigan, Ann Arbor, MO, and colleagues conducted a Phase 3, Health Outcomes with Padua gene; Evaluation in Hemophilia B (HOPE-B) trial was established for further assessing safety and efficacy of etranacogene dezaparvovec in adults with HB with a wide range of pre-existing NAbs to AAV5. In the study, the researchers reported outcomes at 26 weeks. 

HOPE-B is a Phase 3, open-label, single-dose, single-arm, multi-national trial in adult males with severe or moderate-severe HB (FIX≤2%). All patients received routine FIX prophylaxis prior to study. Patients were not excluded based on pre-existing NAbs to AAV5. Patients entered a prospective lead-in period of at least 6 months during which bleeding/factor use was monitored, then received a single intravenous dose of etranacogene dezaparvovec (2x1013 gc/kg). Pts will be followed for 5yrs.

Primary endpoints comprised FIX activity (one stage) at 26 and 52wks after dosing and 52wk annualized bleeding rate. For pts with no clean post-treatment FIX samples (≥10d post exogenous FIX), factor activity was imputed as baseline value based on historic disease severity. Secondary endpoints include factor replacement use, adverse events (AEs), and reactive use of corticosteroids.

75 pts were screened, of whom 67 entered lead-in. 54 pts were dosed (44 severe, 10 moderately severe HB) and completed 26wks of follow-up. 

"Following a single dose of etranacogene dezaparvovec, FIX activity increased, without the need for prophylactic immunosuppression, into the mild-to-normal range at 26wks in pts with severe/moderately severe HB. Importantly, this included pts with titers of pre-existing anti-AAV5 NAbs. Pts were able to discontinue prophylaxis and bleeding was abolished in the majority." wrote the researchers.

"The safety profile was consistent with early phase AAV5 studies and together these data support a favorable safety and efficacy profile for etranacogene dezaparvovec," they concluded.

"LBA-6 First Data from the Phase 3 HOPE-B Gene Therapy Trial: Efficacy and Safety of Etranacogene Dezaparvovec (AAV5-Padua hFIX variant; AMT-061) in Adults with Severe or Moderate-Severe Hemophilia B Treated Irrespective of Pre-Existing Anti-Capsid Neutralizing Antibodies," was presented at the 62nd ASH Annual Meeting and Exposition.