Dual Immunization with Lipoprotein Tp0663 and Flagellin FlaB3 Offers Augmented Protection against <i>Treponema pallidum</i> in Mice

Syphilis is a significant multistage sexually transmitted infection caused by the bacterium <i>Treponema pallidum</i>. The pathogenesis of this pathogen remains inadequately understood, impeding the progress of syphilis vaccine development. Our prior study has demonstrated the potential of the Tp0663 protein as a viable candidate for a vaccine against <i>T. pallidum</i>. In the present study, we sought to explore the protective response of dual immunization using two different antigenic entities (i.e., flagellin FlaB3 and lipoprotein Tp0663) against <i>T. pallidum</i> in a murine model. Our investigation revealed that FlaB3 + Tp0663 can elicit robust humoral and cellular immune responses. In addition, the FlaB3 + Tp0663 vaccine demonstrated a notable reduction in the Treponemal burden within various anatomical sites of infected mice, including the blood, brain, liver, lymph nodes, spleen, and testicles. It is worth noting that the FlaB3 + Tp0663 vaccine suppressed the dissemination of <i>T. pallidum</i> in C57BL/6 mice. The findings demonstrate that <i>T. pallidum</i> flagellin FlaB3 may augment the immunoprotection of Tp0663. This represents a valuable practical perspective and offers insights into developing a syphilis vaccine.