- At a median 13 years after a single infusion of AAV-mediated gene therapy, factor IX expression remained stable in 10 patients with severe hemophilia B.
- The median annualized bleeding rate decreased from 14 episodes to 1.5 episodes, representing a median rate reduction by a factor of 9.7.
- No late-onset safety concerns were observed.
A single infusion of adeno-associated virus (AAV)-mediated gene therapy led to sustained clinical benefit and no late-onset safety concerns in patients with severe hemophilia B, a longitudinal study showed.
At a median follow-up of 13 years, factor IX expression remained stable in the 10 men across dose groups, with seven not receiving factor IX prophylaxis, reported Amit Nathwani, MBChB, PhD, of University College London, and colleagues.
The median annualized bleeding rate decreased from 14 episodes to 1.5 episodes, representing a median rate reduction by a factor of 9.7, and use of factor IX concentrate decreased by a factor of 12.4, "which considerably alleviated the disease burden," they wrote in the New England Journal of Medicine.
"These findings support the long-term safety and efficacy of AAV gene therapy for hemophilia B, thus offering this group of patients a promising and durable treatment option with recently licensed gene-therapy products," Nathwani and team noted.
In 2014, Nathwani and his group reported on the successful administration of a single intravenous infusion of a self-complementary, serotype 8 pseudotyped AAV vector encoding a codon-optimized factor IX transgene (scAAV2/8-LP1-hFIXco).
Subsequent studies by other investigators confirmed those early results, ultimately leading to the FDA approval of etranacogene dezaparvovec (Hemgenix) and fidanacogene elaparvovec (Beqvez) in adults with severe hemophilia.
"However, uncertainties remain regarding the durability of transgene expression," wrote Nathwani and colleagues. "In addition, the long-term safety of AAV-mediated gene transfer remains unclear, and the effect of the humoral immune response to AAV requires ongoing evaluation."
The 10 men with severe hemophilia B received a single dose of scAAV2/8-LP1-hFIXco vector, administered through a peripheral vein, in three dose cohorts (low dose: 2×1011 vector genomes [vg]/kg of body weight [n=2], intermediate dose: 6×1011 vg/kg [n=2], or high dose: 2×1012 vg/kg [n=6]) between March 2010 and December 2012.
Since 2010, a total of 354 adverse events have been reported; 15 were considered to be associated with AAV gene therapy, including transient elevations in liver aminotransferase levels (of grade 1 or 2) in four of six participants who had been treated with the high vector dose.
There were no cases of factor IX inhibition, thrombosis, recurrent transaminitis, or death. Two cases of cancer developed -- lung adenocarcinoma in a patient with a history of smoking 7 years after receipt of gene therapy, and a case of prostate cancer in a 74-year-old patient 11.6 years after gene therapy was administered. Molecular analysis and a review by an expert multidisciplinary team suggested the cancers were not associated with gene therapy.
At a median of 3.2 years after gene therapy, all participants had dose-dependent increases in factor IX coagulant activity. At 13 years, factor IX activity remained stable, with mean levels of 1.7 IU/dL in the low-dose cohort, 2.3 IU/dL in the intermediate-dose cohort, and 4.8 IU/dL in the high-dose cohort.
Three patients with severe hemophilic arthropathy who had a median of 10 target joints (joints with recurring bleeding episodes) resumed factor IX prophylaxis within 4 years after the receipt of gene therapy due to recurrent spontaneous joint bleeding events.
"Factor IX levels of 1 to 3 IU per deciliter in these participants that had been measured at least 3 days after the infusion proved to be insufficient to prevent such bleeding, a finding that highlights the effect of joint health and other biologic factors on outcomes after the receipt of gene therapy," the authors observed.
Disclosures
This study was supported by grants from the U.K. Medical Research Council, the Katharine Dormandy Trust, the U.K. Department of Health, NHS Blood and Transplant, the National Institute for Health Research (including a Biomedical Research Centres funding award to University College London Hospitals and University College London), the Royal Free Hospital Charity, the Innovative Medicines Initiative, the Assisi Foundation of Memphis, the Hemophilia of Georgia Foundation, the Colburn-Keenan Foundation, the American Lebanese Syrian Associated Charities, and the National Heart, Lung, and Blood Institute.
Nathwani has a patent on an FIX expression cassette.
Several co-authors reported multiple relationships with industry.
Primary Source
New England Journal of Medicine
Source Reference: Reiss UM, et al "Sustained clinical benefit of AAV gene therapy in severe hemophilia B" N Engl J Med 2025; DOI: 10.1056/NEJMoa2414783.
https://www.medpagetoday.com/hematologyoncology/hemophilia/116033
