Inclusion Criteria: * Male ≥18 years of age * Severe or moderately severe hemophilia A (FVIII activity ≤ 2 IU/dL) as evidenced by * medical history * Received FVIII prophylactic or on-demand replacement therapy for ≥ 150 accumulated * days (exposure days) * ≥12 bleeding episodes if receiving on-demand therapy over the preceding 12 months * BMI ≤ 30 * Agree to use double-barrier contraceptive until at least 3 consecutive semen samples are negative after ASC-618 infusion Exclusion Criteria: * Pre-existing immunity to AAV8 vector as defined by AAV8 total antibodies and neutralizing antibodies qualified tests. * Current inhibitors, or history of high titer FVIII inhibitors * Presence of \> Grade 2 liver fibrosis on elastography/Fibroscan or comparable imaging methodology * History of chronic renal disease * Active infection or any immunosuppressive disorder * History of cardiac surgery and need anticoagulant therapy * Any cardiovascular / genetic risk factors for thromboembolic disorders * Evidence of active Hepatitis B, Hepatitis C, Human Immunodeficiency Virus (HIV)-1/2 or syphilis infection. * Receipt of any vector or gene transfer agent * Current antiviral therapy for hepatitis B or C