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.
