Delivery of the Pertactin/P.69 polypeptide of Bordetella pertussis using an attenuated Salmonella typhimurium vaccine strain: expression levels and immune response.
Pertactin/P.69, a surface-associated polypeptide antigen of Bordetella pertussis, was expressed in a Salmonella typhimurium aroA aroD vaccine strain, BRD509, using different expression systems, and the immune response in mice against these constructs was compared. Initially, Pertactin/P.69 was expressed on the surface of BRD509 from a single copy of the gene encoding the antigen localized on the Salmonella chromosome. As previously shown, secretory and humoral antibody responses could not be detected following multiple immunization with this strain (BRD640). However, a strong anti-Pertactin/P.69 proliferative response was observed in murine splenocytes following a single oral dose with BRD640. The stimulated splenocytes secreted interferon-gamma but not interleukin-5, indicating that BRD640 induced a Th1 type T-helper response against Pertactin/P.69. We wished to construct a vaccine strain that might induce secretory and humoral responses against Pertactin/P.69 as well as a cell-mediated immune response. Consequently, Pertactin/P.69 was expressed at high levels in the cytoplasm of BRD509 under the control of the inducible nirB promoter from a ColE1-based replicon. Anti-Pertactin/P.69 immune responses were not observed following immunization of BALB/c mice with this strain (BRD975). Priming of the immune system against Pertactin/P.69 was, however, observed following oral immunization with BRD975 and boosting subcutaneously with purified Pertactin/P.69 antigen. The major anti-Pertactin/P.69 IgG subclass detected in boosted mice was IgG2a; thus, as BRD640, BRD975 appeared to induce a Th1 type T-helper response against Pertactin/P.69.