Sublingual Administration of an Adenovirus Serotype 5 (Ad5)-Based Vaccine Confirms Toll-Like Receptor Agonist Activity in the Oral Cavity and Elicits Improved Mucosal and Systemic Cell-Mediated Responses against HIV Antigens despite Preexisting Ad5 Immunity

HIV/AIDS continue to devastate populations worldwide. Recent studies suggest that vaccines that induce beneficial immune responses in the mucosal compartment may improve the efficacy of HIV vaccines. Adenovirus serotype 5 (Ad5)-based vectors remain a promising platform for the development of effective vaccines. In an effort to improve the efficacy of Ad5-based vaccines, even in the presence of preexisting Ad5 immunity, we evaluated the potential for an Ad5-based HIV vaccine to induce antigen-specific immune responses following sublingual (s.l.) administration, a route not previously tested in regard to Ad-based vaccines. s.l. vaccination with an Ad5-based HIV-Gag vaccine resulted in a significant induction of Gag-specific cytotoxic T-lymphocyte (CTL) responses in both the systemic and the mucosal compartment. We also show that s.l. immunization not only avoided preexisting Ad5 immunity but also elicited a broad repertoire of antigen-specific CTL clones. Additionally, we confirm for the first time that oral delivery of a vaccine expressing a potent Toll-like receptor (TLR) agonist can stimulate innate immune responses through induction of cytokines and chemokines and activation of NK cells, NKT cells, and macrophages in vivo. These results positively correlated with improved antigen-specific CTL responses. These results could be achieved both in Ad5-naive mice and in mice with preexisting immunity to Ad5. The simplicity of the s.l. vaccination regimen coupled with augmentation of TLR-dependent pathways active in the oral cavity makes s.l. delivery a promising method for HIV vaccine development specifically, as well as for many other vaccine applications in general.