Fusion-Expressed CTB Improves Both Systemic and Mucosal T-Cell Responses Elicited by an Intranasal DNA Priming/Intramuscular Recombinant Vaccinia Boosting Regimen

Previous study showed that CTB (Cholera toxin subunit B) can be used as a genetic adjuvant to enhance the systemic immune responses. To further investigate whether it can also be used as a genetic adjuvant to improve mucosal immune responses, we constructed DNA and recombinant Tiantan vaccinia (rTTV) vaccines expressing OVA-CTB fusion antigen. Female C57BL/6 mice were immunized with an intranasal DNA priming/intramuscular rTTV boosting regimen. OVA specific T-cell responses were measured by IFN-γ ELISPOT and specific antibody responses were determined by ELISA. Compared to the nonadjuvant group (pSV-OVA intranasal priming/rTTV-OVA intramuscular boosting), pSV-OVA-CTB intranasal priming/rTTV-OVA-CTB intramuscular boosting group significantly improved the magnitudes of T-cell responses at spleen (1562 ± 567 SFCs/10(6) splenocytes versus 330 ± 182 SFCs/10(6) splenocytes, P < 0.01), mesenteric LN (96 ± 83 SFCs/10(6) lymphocytes versus 1 ± 2 SFCs/10(6) lymphocytes, P < 0.05), draining LNs of respiratory tract (109 ± 60 SFCs/10(6) lymphocytes versus 2 ± 2 SFCs/10(6) lymphocytes, P < 0.01) and female genital tract (89 ± 48 SFCs/10(6) lymphocytes versus 23 ± 21 SFCs/10(6) lymphocytes, P < 0.01). These results collectively demonstrated that fusion-expressed CTB could act as a potent adjuvant to improve both systemic and mucosal T-cell responses.