Oral, intrarectal and intranasal immunizations using CpG and non-CpG oligodeoxynucleotides as adjuvants

We have previously demonstrated that synthetic oligodeoxynucleotides (ODN) containing immunostimulatory CpG motifs (CpG ODN) are potent adjuvants in mice when delivered by intramuscular, intranasal and subcutaneous routes. Herein, using tetanus toxoid (TT) as a model antigen in BALB/c mice, we compared the ability of CpG ODN to induce mucosal and systemic humoral immune responses when antigen was delivered by three different routes: intrarectal, intranasal and oral. Results showed differences in immune responses with the three routes and also revealed that non-CpG "control" ODN had adjuvant effects when used at mucosal sites. This was unexpected since non-CpG ODN do not have such immunostimulatory effects in vitro or after parenteral immunization. These findings were further investigated after oral delivery of a killed influenza vaccine on its own as well as combined with TT and hepatitis B surface antigen. Our findings demonstrate that with mucosal delivery, there is a Th2 immunostimulatory effect associated with the phosphorothioate ODN backbone, and that the presence of CpG motifs shifts this towards a Th1 response.