Prime-boost immunization with DNA vaccine: Mucosal route of administration changes the rules

In this study we assessed prime-boost immunization strategies with a DNA vaccine (gB DNA) and attenuated recombinant vaccinia virus vector (rvacgB), both encoding the gB protein of HSV, for their effectiveness at inducing mucosal as well as systemic immunity to HSV. Confirming the reports of others, systemic priming with gB DNA and systemic boosting with rvacgB were the most effective means of inducing serum Ab and splenic T cell responses. Nevertheless, the systemic prime-boost approach failed to induce detectable humoral or T cell responses at mucosal sites. However, such responses, at both proximal and distal locations, were induced if immunizations, especially the priming dose, were administered mucosally. Curiously, whereas optimal immunity with systemic priming and boosting occurred when gB DNA was used to prime and rvacgB was used as a boost, mucosal responses were optimal when animals were mucosally primed with rvacgB and boosted with gB DNA given mucosally. Furthermore, notable mucosal responses also occurred in animals mucosally primed with rvacgB and subsequently boosted systemically with gB DNA. Because the mucosal prime-boost immunization protocol also induced excellent systemic immune responses, the approach should be useful to vaccinate against agents for which both mucosal and systemic immunity are important for protection.