By using the hepatitis B core (HBc) protein gene as a carrier, HIV-1 env V3 gene was inserted into the carrier gene, and the HIV gene was expressed inside a chimeric HIV-HBc particle (HIV-HBc), which was a unique candidate for induction of HIV-specific CTL activity. This was seen significantly in mice without the need of an adjuvant, because other responses specific for the HIV peptide such as T-cell proliferation and antibody production were not induced. However, when hemagglutinating virus of Japan (HVJ) protein was incorporated into an anionic liposome containing HIV peptide (HIV-HVJ-liposome) and was used as a booster immunization in HIV-HBc primed animals, the HIV-specific T-cell response and enhanced CTL activity were clearly induced in consecutively immunized animals. Furthermore, the HIV-specific humoral immune response was also induced and a neutralization activity was detected in the immune sera. Thus, when an HIV peptide antigen is expressed inside the virus like a particle of HBc, it can induce both cellular and humoral immunities when an HVJ-HIV-liposome, but not an HIV-liposome, is inoculated as the booster antigen. The HVJ-stimulated splenocytes secreted IL-18 and IL-12 to synergistically enhance the secretion of IFN-gamma in vitro. These findings suggest that the HVJ protein is effective at inducing the HIV-specific immunities, if used as part of a booster antigen in the consecutive immunization regimen.