Hepatitis B virus (HBV) infection can be treated, but therapy is usually lifelong and has side effects, so a cure for HBV is a critical endpoint. This study examines the key steps to HBV cure in the setting of HIV-HBV co-infection, where rates of development of antibodies against HBV after starting HBV treatment are higher than in people with HBV alone starting treatment. In Asia both HBV and HIV are common so this provides a unique opportunity to study HBV. We will investigate how an effective immune response against the two main HBV proteins is developed. If we can understand how the immune response works against HBV, this could be used to develop new therapies towards a cure for HBV.