Enhancement of mucosal immune response against HIV-1 Gag by DNA immunization

In order to examine the feasibility of Gag-expression DNA as a potential candidate for HIV vaccine using a mouse model, we injected DNA into mice either intramuscularly or by using a gene gun. Both methods induced a low level of antibody production. However, after booster immunization with p24 protein emulsified with complete Freund's adjuvant via a footpad, we found that only the preceding intramuscular DNA immunization induced an anti-Gag Th1-type (IgG_2a) antibody response, in addition to the enhancement of a Th2-type (IgG₁) antibody response. Importantly, when mice were boosted intranasally with p24 and cholera toxin, intramuscular DNA injection was found to enhance both systemic and mucosal Gag-specific immune responses. These results indicate that intramuscular DNA immunization confers the inducibility of memory cells, which circulate around various mucosal tissues. Therefore, intramuscular DNA priming, followed by a mucosal booster immunization, could be considered as a regimen applicable to HIV vaccine.