Hepatitis B Virus Core Antigen (HBcAg) is part of the infectious virion containing an inner "core particle" enclosing the viral genome. The icosahedral core particle contains 180 or 240 copies of the core protein. HBcAg is one of the three major clinical antigens of hepatitis B virus but disappears early in the course of infection. The hepatitis B virus core antigen (HBcAg) is a highly immunogenic subviral particle and functions as both a T-cell-dependent and a T-cell-independent antigen. Therefore, HBcAg may be a promising candidate target for therapeutic vaccine control of chronic HBV infection.