During the study, the sponsor adjusted the overall clinical development strategy, decided to terminate the enrollment in advance after discussion with the lead investigator.

This is an open-label phase IIa study of HH-003 to evaluate its antiviral activity and safety in subjects with chronic hepatitis B and hepatitis D co-infection. HH-003 is a human monoclonal antibody targeting the pre-S1 domain of the HBV large envelope protein. It blocks engagement of preS1 with sodium taurocholate co-transporting polypeptide (NTCP), the cellular receptor for HBV/HDV.

Inclusion Criteria:

• Signed informed consent form;
• Male or female subjects aged from 18 to 70 years inclusively;
• 18 kg/m2≤BMI≤32 kg/m2, body weight ≥45 kg for men and ≥40 kg for women;
• Positive HBsAg, anti-HDV IgG antibody and HDV RNA at screening;
• Women of childbearing potential or male subjects with female partners of childbearing potential should agree to use an adequate and highly effective contraceptions from screening to the end of study or until 12 weeks after last dose of the study drug (whichever is longer).

Exclusion Criteria:

• Be pregnant or lactating at screening;
• Subjects with decompensated liver cirrhosis;
• Subjects with liver dysfunction (including but not limited to ascites, hepatic encephalopathy and upper gastrointestinal bleeding) within 3 months prior to screening;
• Average daily alcohol consumption >40g for men and >20g for women or drug abuse within 6 months prior to screening;
• Subjects with other serious diseases that is inappropriate for study participation per the Investigator's or the Sponsor's discretion (including but not limited to serious cardiac or pulmonary disease, chronic or recurrent urinary disorders, uncontrolled diabetes and autoimmune diseases, epilepsy requiring treatment);
• History of hepatocellular carcinoma (HCC) or hepatocellular carcinoma suggested by liver histopathology or liver imaging;
• Interferon antiviral therapy within 1 year prior to screening.