Gene Therapy for Hemophilia B Patients Aged 12-18 Years Old

Inclusion Criteria: Subjects and statutory guardian must be able to understand the purpose and risks of the study and provide signed and dated informed consent; Be male and 12≤ age <18 years of age, body wight ≥ 50kg; Have hemophilia B with ≤2 IU/dL (≤2 %) endogenous FIX activity levels as documented by a certified clinical laboratory at the time of screening. If the screening result is >2% due to insufficient washout from FIX protein product, then the severity of hemophilia B may be confirmed by documented historical evidence from a certified clinical laboratory demonstrating ≤2% FIX coagulant activity (FIX:C) ; Had had ≥75 prior exposure days (EDs) to any recombinant and/or plasma-derived FIX protein products based on historical data from the subject's record/history; With ≤ 1:4 neutralizing antibodies and ≤1:200 binding antibodies against BBM-H901 capsid; Subjects with bleeding episode and/ or FIX agents infusion events within 12 weeks prior to screening; Have no prior history of hypersensitivity or anaphylaxis associated with any FIX or IV immunoglobulin administration; Have no measurable FIX inhibitor as assessed by laboratory; or documented no prior history of FIX inhibitor (family history of inhibitors will not exclude the subject) and no clinical signs or symptoms of decreased response to FIX administration; Have acceptable laboratory values: Hemoglobin ≥11 g/dL ; Platelets ≥100,000 cells/μL; AST, ALT ≤1.5x upper limit of normal at the testing laboratory; Bilirubin ≤1.5x ULN ; glomerular filtration rate eGFR ≥ 60ml/min. For those subjects with sexual maturity, subject and statutory guardian must know that subjects must agree to use reliable barrier contraception until 52 weeks; with good compliance to the schedule of visit and fill in the subject diary. Exclusion Criteria: Hepatitis B surface antigen antibody (HBSAg-Ab) or HBV-DNA positive; hepatitis C antibody or HCV-RNA positive; Currently on antiviral therapy for hepatitis B or C; With coagulation disorders other than hemophilia B; Had immunosuppressive therapy other than steroid and other suggested IST agents within 30 days prior to screening; Had vaccine 30 days prior to screening or have scheduled vaccination plan during the study (up to 52 weeks); Have significant underlying liver disease, as defined by a preexisting diagnosis of portal hypertension, splenomegaly, encephalopathy, etc; other liver conditions unsuitable to gene therapy judged by investigator; Have surgery plan within 52 weeks after gene therapy; Have history of chronic infection or high rish of infection that the Investigator considers to constitute an unacceptable risk; Had participated in a previous gene therapy research trial within the last 52 weeks or in a clinical study with an investigational drug within the last 12 weeks; Had any herb that may affect the liver function within 4 weeks prior to screening; Have history of fatal bleeding episode, eg intracranial hemorrhage, etc; Any concurrent clinically significant major disease or any other condition that, in the opinion of the Investigator, makes the subject unsuitable for participation in the study;