Tenofovir Alafenamide in HBV Related Decompensated Liver

Inclusion Criteria: * Male or non-pregnant female, age ≥20 years * Chronic HBV infection with positive hepatitis B surface antigen (HBsAg) for at least 6 months at screening. * Hepatic decompensation, defined as Child-Turcotte-Pugh (CTP) score ≥7, or the presence of portal hypertension related complications including ascites, hepatic encephalopathy (\<grade 2) at screening. * HBV NUC treatment naïve or experienced (except prior TAF) for Arm A or currently under HBV NUC treatment (except TAF) with HBV DNA \< 20 IU/mL within 6 months prior screening for Arm B. * Patients with either liver cirrhosis or non-cirrhosis (defined by histology, non-invasive assessments, or imaging/clinical based diagnosis). * Estimated creatinine clearance ≥30 ml/min (using the Cockcroft-Gault method) at screening. (Note: multiply estimated rate by 0.85 for women). * Willing and able to provide informed consent * Able to comply with dosing instructions for study drug administration and able to complete the study schedule of assessments Exclusion Criteria: * Pregnant women, women who are breast feeding or who believe they may wish to become pregnant during the course of the study. * Previous recipient of a solid organ (including liver), or bone marrow transplant. * Severe or uncontrolled comorbidities determined by the Investigator. * Currently ≥grade 2 hepatic encephalopathy, currently or history (within 60 days) of variceal bleeding, hepatorenal syndrome, refractory ascites or spontaneous bacterial peritonitis; cytopenia of absolute neutrophil count \< 750/mm3, or hemoglobin \< 8 g/dL, or platelet \<30000/mm3; or MELD score ≥30 at screening. * Malignancy history including hepatocellular carcinoma, except basal cell skin cancer without recurrence for more than 5 years. * Acute exacerbation of HBV, defined as an elevation of alanine aminotransferase (ALT) activity to more than 10 times the upper limit of normal and more than twice the baseline value. * On any of the disallowed concomitant medications listed in the prior and concomitant medications list (pg. 16). Subjects on prohibited medications who are otherwise eligible will need a wash out period of at least 30 days prior to the Screening. * Males and females of reproductive potential who are unwilling to use "effective" protocol-specified method(s) of contraception during the study.