A Recombinant Attenuated Vaccine Delivering a YopE-LcrV Fusion Elicits Broad Protection against Plague and Yersiniosis in Mice.

In this study, a novel recombinant attenuated PB1+ strain (χ10069) engineered with Δ Δ Δ triple mutations was used to deliver a fusion protein, YopE amino acid 1 to 138-LcrV (YopE-LcrV), to Swiss Webster mice as a protective antigen against infections by yersiniae. χ10069 bacteria harboring the pYA5199 plasmid constitutively synthesized the YopE-LcrV fusion protein and secreted it via the type 3 secretion system (T3SS) at 37°C under calcium-deprived conditions. The attenuated strain χ10069(pYA5199) was manifested by the establishment of controlled infection in different tissues without developing conspicuous signs of disease in histopathological analysis of microtome sections. A single-dose oral immunization of χ10069(pYA5199) induced strong serum antibody titers (log mean value, 4.2), secretory IgA in bronchoalveolar lavage (BAL) fluid from immunized mice, and -specific CD4 and CD8 T cells producing high levels of tumor necrosis factor alpha (TNF-α), gamma interferon (IFN-γ), and interleukin 2 (IL-2), as well as IL-17, in both lungs and spleens of immunized mice, conferring comprehensive Th1- and Th2-mediated immune responses and protection against bubonic and pneumonic plague challenges, with 80% and 90% survival, respectively. Mice immunized with χ10069(pYA5199) also exhibited complete protection against lethal oral infections by WA and PB1+. These findings indicated that χ10069(pYA5199) as an oral vaccine induces protective immunity to prevent bubonic and pneumonic plague, as well as yersiniosis, in mice and would be a promising oral vaccine candidate for protection against plague and yersiniosis for human and veterinary applications.