IHBDH-GTHA-2020 is an open- label, non- randomized study to evaluate the safety, tolerability and kinetics of a single intravenous infusion of GS001 in hemophilia A subjects with <1 IU/dl residual FVIII levels.

IHBDH-GTHA-2020 is a open- label, non- randomized study to evaluate the safety, tolerability and kinetics of GS001 in hemophilia A subjects with residual FVIII levels<1 IU/dl. The first patient will receive a single intravenous infusion of GS001 at a dose level of 2 x 10^12 vg/kg body weight. After three weeks of follow-up for the first patient post infusion of GS001, the dose of GS001 can be adjusted for the other two patients based on the activity level of FVIII:C and safety assessment. Following completion of the first 3 patients received GS001 infusion at 2 x 10^12 vg/kg dose level , the following 3 patients will continue to be enrolled to this dose group if there isn't any unexpected safety risk based on the assessments of FVIII expression and safety profile. The safety data and the activity level of FVIII:C from the first 6 subjects at 2 x 10^12 vg/kg dose level will undergo review by an independent DMC prior to dosing the first subject in the next dose level, DMC may recommend dose escalation to 6 x 10^12 vg/kg body weight or other recommended dose levels.

If the DMC recommends dose escalation to 6 x 10 ^12 vg/kg body weight or other recommended doses, at least 10 weeks of safety data and the activity level of FVIII:C post GS001 infusion from the first 3 subjects in this given dose level will undergo review by an independent DMC prior to dosing the following subjects. Based on the data from the first 3 subjects, DMC may recommend the dose adjustments for subsequent enrolled subjects, and expand the number of subject enrolled. Based on the safety, preliminary efficacy and vector kinetics profile of single intravenous infusions of GS001 at different dose levels in severe hemophilia A patients with endogenous factor FVIII activity levels ≤ 1% in this study, and based on the benefit-risk assessment of the subjects, the dose level to be administered for future larger clinical trial in patients with severe hemophilia A will be determined.

After all enrolled subjects have been followed for at least 12 weeks after intravenous infusion GS001, periodic analysis will be performed. Primary analysis of safety and efficacy will be performed 52 (± 2) weeks after intravenous infusion GS001, and all subjects will receive 52 (± 2) weeks of comprehensive safety and efficacy assessments. After completing the 52 (± 2) week visit (end-of-study visit), subjects will continue to be followed in this study for up to an additional 4 years for long-term safety and efficacy assessment to evaluate the long-term safety and efficacy of GS001 treatment.

A total of 12 to 15 subjects are expected to be enrolled in this study. Subjects will provide informed consent and then undergo screening assessments up to 4-8 weeks prior administration of GS001. All subjects will undergo 260 weeks (5 years) safety observation.

Inclusion Criteria:

1. Be able to understand the purpose and risks of the study and provide informed consent according to national and local privacy laws;
2. Male subjects and ≥ 18 years of age;
3. Have hemophilia A with ≤1 IU/dL (≤1%) endogenous FVIII activity levels at the time of screening. If the screening result is >1% due to previous treatment with FVIII product, then it may be confirmed by documented historical evidence from a certified clinical laboratory demonstrating ≤1% FVIII activity levels ;
4. No history of hypersensitivity or anaphylaxis associated with FVIII product administration;
5. Have no measurable FVII inhibitor as assessed by laboratory two times that were at least one week apart; or documented no prior history of FVIII inhibitor after 150 EDs and no clinical signs or symptoms of decreased response to FVIII infusion ;
6. Have acceptable laboratory values sampled at screening and repeated prior to Day 0; A. Hemoglobin ≥ 11 g/dL; B. Platelets ≥ 100 x 10^9/L; C. AST, ALT, alkaline phosphatase ≤ 1.25 upper limit of normal (ULN); D. Bilirubin ≤ 1.25 ULN; E. Creatinine ≤ 2 mg/dL.
7. Agree to use reliable barrier contraception until the end of the 52 weeks observation period, and three consecutive semen samples are negative for vector sequences after GS001 infusion.

Exclusion Criteria:

1. Have Hepatitis B, hepatitis C or HBsAg, HCVAb, HBV-DNA, HCV-RNA are positive and have clinical significance. Both natural clearers and those who have cleared HCV on antiviral therapy are deemed eligible;
2. Currently Receiving antiviral therapy for hepatitis B and C;
3. Have history of chronic infections or other chronic diseases that may pose a risk to the study participation;
4. Have participated in a previous gene therapy research trial within the last 52 weeks or in a clinical study with an investigational drug within the past 30 days;
5. The subject has any concurrent diseases that cannot tolerate treatments of prednisone or prednisolone as judged by the investigator;
6. History of arterial or venous thromboembolic events (e.g., deep vein thrombosis, non-hemorrhagic stroke, pulmonary embolism, myocardial infarction, arterial embolism);
7. Known inherited or acquired thrombophilia, including conditions associated with increased risk of thromboembolism, such as atrial fibrillation;
8. Major surgery planned in 1 year period following the infusion with GS001;
9. Hypersensitivity to the study vector;
10. Have clinically major diseases or any other unspecified conditions that, in the opinion of the Investigator, makes the subject unsuitable for participating in the study;
11. Patients who are unable or unwilling to comply with the schedule of visits and study assessments described in the clinical protocol;
12. Evidence of other bleeding disorders not associated with hemophilia A.