Safety and Antiviral Activity of a Monoclonal Hepatitis B Antibody: a Phase 1b, Open-label Trial in Individuals With Chronic Hepatitis D Infection

Inclusion Criteria: * HDV infection confirmed by positive anti-HDV antibody and detectable HDV RNA * HBs antibody negative during screening period * Both HBeAg positive and negative participants are included * Ability and willingness to provide informed consent * Participants who can become pregnant must agree to use two methods of contraception: * Participants who can impregnate a partner and who are engaging in sexual activity that could lead to pregnancy must agree to use condoms 10 days prior to study entry and during study follow up to avoid impregnating a partner who can get pregnant. Exclusion Criteria: * Child-Turcotte-Pugh \>9 points * Severe clinical hepatic decompensation-such as hepatic encephalopathy or variceal hemorrhage-occurring currently or within the past 12 months. * Any confirmed significant allergic reactions (urticaria or anaphylaxis) against monoclonal antibody or vaccine, or multiple drug allergies (non-active hay fever is acceptable) * Pregnancy or lactation * Any vaccination 2 weeks prior to entry * Prior receipt of HepB mAb19 therapy * Any significant acute infection (e.g. influenza, COVID-19) or any other clinically significant illness 2 weeks prior to entry * Active hepatitis C infection * Untreated HIV disease * Individuals with HIV receiving antiretroviral therapy who have had a measurement of plasma HIV RNA (viral load) \>50 copies/mL within the past 6 months are excluded. However, a single viral load measurement between \>50 and \<500 copies/mL during this period is acceptable. * Participation in another clinical study of an investigational product currently or 12 weeks prior to entry, or expected participation during this study Laboratory abnormalities in the parameters listed below: * Alpha fetoprotein \>100 ng/mL * Hemoglobin \<10 gm/dL (6.21 mmol/L) * Platelet count \<25,000 /mm3 * Estimated glomerular filtration rate (eGFR) \<60 mL/min * ALT ≥ x10 upper limit of normal (ULN) Current, or history of: * Clinical cardiovascular disease (e.g., cardiac insufficiency, coronary artery disease, cardiomyopathy, congestive heart failure. * Presence of clinically significant ECG abnormalities based on the average of the triplicate ECG recordings (e.g., PR interval \>210 ms (1st degree AV block only if clinical symptoms are present), QT corrected for heart rate using the Fridericia's correction factor \[QTcF\] \> 450 ms for males and QTcF \>470 ms for females); * Chronic liver disease from another cause, ICD, or autoimmune diseases that in the opinion of the investigator would preclude participation * History of hematopoietic stem cell transplant or solid organ transplant