A Phase 2, Randomized, Double-Blind, Placebo-Controlled, Multi-center Study to Evaluate the Safety and Efficacy of GS-9620 for the Treatment of Virally-Suppressed Subjects with Chronic Hepatitis B

INTERVENTION: Arm 1: OAV + 1mg GS‐9620 Arm 2: OAV + 2mg GS‐9620 Arm 3: OAV + 4mg GS‐9620 Arm 4: OAV + Placebo OAV = Oral Antiviral (must be commercially available) OAV type, dose and duration will continue as previously prescribed by the patient’s clinician. For all Arms (1, 2, 3 and 4) GS‐9620/placebo will be taken once a week (every 7th day) as an oral tablet. Participants will be randomised into 3 sequential cohorts: ‐ Cohort A participants will be treated with GS‐9620 (1mg, 2mg or 4mg)/placebo once a week for 4 doses ‐ Cohort B participants will be treated with GS‐9620 (1mg, 2mg or 4mg)/placebo once a week for 8 doses ‐ Cohort C participants will be treated with GS‐9620 (1mg, 2mg or 4mg)/placebo once a week for 12 doses All unused study drug and used study drug kits which are dispensed to participants must be returned to the investigative site for accountability. CONDITION: Chronic Hepatitis B PRIMARY OUTCOME: To evaluate the efficacy of GS‐9620 at Week 24 measured by the change from Baseline in serum hepatitis B surface antigen (HBsAg) ( log10 IU/ml) levels To evaluate the safety and tolerability of GS‐9620 in subjects with chronic hepatitis B infection (CHB) currently being treated with oral antivirals (OAV). ; ; This outcome will be assessed through monitoring of Adverse Events/Serious Adverse Events, physical examinations, monitoring of vital signs and blood tests. SECONDARY OUTCOME: To evaluate the change in log10 IU/ml serum HBsAg from Baseline to Week 4, 8, 12 and 48 To evaluate the incidence of drug resistance mutations. ; ; This outcome will be measured using plasma sample testing. To evaluate the proportion of subjects experiencing HBV virological breakthrough. ; ; This outcome will be measured using serum blood tests. To evaluate the proportion of subjects with serum HBsAg decline greater than or equal to 1 log10 IU/ml decline at Weeks 4, 8, 12, 24 and 48 To evaluate the rates of HBsAg loss and seroconversion at Weeks 24 and 48. ; ; This outcome will be measured using serum blood tests. To evaluate the rates of hepatitis B early antigen (HBeAg) loss and seroconversion at Weeks 24 and 48. ; ; This outcome will be measured using serum blood tests. INCLUSION CRITERIA: Patients must meet all of the following inclusion criteria to be eligible to participate in the study. 1. Must have the ability to understand and sign a written informed consent form; consent must be obtained prior to initiation of study procedures 2. Adult male and non‐pregnant, non‐lactating female subjects, (lactating females must agree to discontinue nursing before the study drug is administered), 18–65 years of age inclusive based on the date of the screening visit 3. A negative serum pregnancy test is required for female subjects (unless surgically sterile or greater than two years post‐menopausal). 4. Male subjects and female subjects of childbearing potential who engage in heterosexual intercourse must agree to use protocol specified method(s) of contraception. 5. Documented evidence of chronic HBV infection (e.g. HBsAg positive for more than 6 months) with detectable HBsAg levels at screening 6. Have been on approved HBV OAV tr