Summary
A multicentre phase 1 trial in China tested the AAV gene therapy BBM-H901 in 11 adolescents with severe or moderately severe hemophilia B. At 52 weeks, mean factor IX activity was 41.8 IU/dl and the mean annualized bleeding rate had fallen from 13.9 to 0.5.
A phase 1 clinical trial in China found that an adeno-associated virus (AAV) gene therapy produced measurable factor IX activity and fewer bleeding episodes in 11 adolescents with hemophilia B. The multicentre, single-arm study followed participants for 52 weeks after a single treatment with BBM-H901.
The study, published in Nature Medicine on 16 September 2026, included patients aged 12 to 18 with severe or moderately severe hemophilia B, defined as baseline factor IX coagulant activity (FIX:C) of no more than 2 IU/dl. All participants received the same dose: 5 × 10¹² vector genomes per kilogram of body weight.
At week 52, the mean FIX:C was 41.8 IU/dl, with a standard deviation of 30.1, measured using the one-stage SynthASil method. The mean annualized bleeding rate fell from 13.9 to 0.5 during the study period.
How the gene therapy is intended to work
Hemophilia B is an inherited bleeding disorder caused by insufficient functional factor IX, a protein needed for normal blood clotting. Conventional treatment replaces factor IX through repeated infusions. Gene therapy instead uses an AAV vector as a delivery vehicle for genetic instructions that enable the body to produce factor IX.
BBM-H901 delivers the Factor IX Padua form. This engineered form is designed to provide high clotting activity when produced in the body. The treatment is intended to establish factor IX production after one administration, although the duration of that production is a question that requires longer follow-up.
Trial results and safety
Safety was the primary endpoint. The researchers reported no dose-limiting toxicity during the 52-week follow-up. The most frequently reported adverse events were increased white blood cell and neutrophil counts, along with rash associated with corticosteroid treatment.
One serious adverse event and two grade 3 adverse events occurred. One participant developed abnormal liver function, with alanine aminotransferase reaching 197.0 U/l and aspartate aminotransferase reaching 75.0 U/l. The levels returned to normal four weeks after immunosuppression therapy.
The bleeding result provides the study's main initial evidence of clinical activity. The mean annualized bleeding rate is an estimate of the number of bleeding episodes expected over a year based on the observation period; in this trial, the group average changed from 13.9 before treatment to 0.5 after treatment.
What the adolescent data add
AAV-mediated Factor IX Padua therapy had previously been studied in adults, while its safety and activity in adolescents had been less established. This trial supplies early clinical data for the 12–18 age group and indicates that the treatment produced factor IX activity alongside a lower bleeding rate during the first year after administration.
The evidence remains an early phase 1 result. The study enrolled only 11 participants, had no control group and used a single-arm design, so its findings describe outcomes in this treated group rather than a comparative estimate against prophylactic factor IX treatment. The 52-week follow-up also provides an initial one-year assessment; longer observation will be needed to assess the persistence of factor IX production and safety over time.
The paper reports that Belief Biomed supplied the investigational drug and participated in study design. Five authors were employees of the company. The trial is registered at ClinicalTrials.gov under NCT05709288.