Study to Evaluate Efficacy and Safety of Switching From TDF to TAF in Adults With Chronic Hepatitis B Who Are Virologically Suppressed

Key Inclusion Criteria:

• Must have the ability to understand and sign a written informed consent form; consentmust be obtained prior to initiation of study procedures

• Adult male and non-pregnant, non-lactating females

• Documented evidence of chronic hepatitis B virus (HBV) infection previously

• Maintained on tenofovir disoproxil fumarate (TDF) 300 mg once daily for at least 48weeks, and as monotherapy for chronic hepatitis B for at least 24 weeks with viralsuppression (HBV DNA < lower limit of quantitation) for a minimum of 12 weeks prior toscreening

• Adequate renal function

• Normal Electrocardiogram

Key Exclusion Criteria:

• Pregnant women or women who are breastfeeding

• Males and females of reproductive potential who are unwilling to use an "effective",protocol-specified method(s) of contraception during the study.

• Co-infection with hepatitis C virus (HCV), hepatitis D virus (HDV), or humanimmunodeficiency virus (HIV)

• Evidence of hepatocellular carcinoma

• Current evidence of, or recent (≤ 5 year) history of clinical hepatic decompensation

• Abnormal hematological and biochemical parameters, including:

• Hemoglobin < 10 g/dL

• Absolute neutrophil count < 750/mm^3

• Platelets ≤ 50,000/mm^3

• Aspartate aminotransferase (AST) or alanine aminotransferase (ALT) > 5 × upperlimit of the normal (ULN)

• Albumin < 3.0 mg/ dL

• International normalized ratio (INR) > 1.5 × ULN (unless stable on anticoagulantregimen)

• Total bilirubin > 2.5 × ULN

• Received solid organ or bone marrow transplant

• Malignancy within 5 years prior to screening, with the exception of specific cancersthat are cured by surgical resection (eg, basal cell skin cancer). Individuals underevaluation for possible malignancy are not eligible.

• Currently receiving therapy with immunomodulators (eg, corticosteroids), nephrotoxicagents, or agents capable of modifying renal excretion

• Individuals receiving ongoing therapy with drugs not to be used with TAF or TDF orindividuals with a known hypersensitivity to study drugs, metabolites, or formulationexcipients

• Current alcohol or substance abuse judged by the investigator to potentially interferewith compliance

• Any other clinical condition or prior therapy that, in the opinion of theinvestigator, would make the individual unsuitable for the study or unable to complywith dosing requirements.

• Use of investigational agents within 3 months of screening, unless allowed by thesponsor Note: Other protocol defined Inclusion/Exclusion criteria may apply.