Intranasal immunization with CPAF combined with ADU-S100 induces an effector CD4 T cell response and reduces bacterial burden following intravaginal infection with Chlamydia muridarum

Chlamydia trachomatis (Ct) is the most common bacterial sexually transmitted infection globally, and a vaccine is urgently needed to stop transmission and disease. Chlamydial Protease Activity Factor (CPAF) is an immunoprevalent and immunodominant antigen for CD4 T cells and B cells, which makes it a strong vaccine candidate. Due to the tolerogenic nature of the female genital tract (FGT) and its lack of secondary lymphoid tissue, effective induction of protective cell-mediated immunity will likely require potent and safe mucosal adjuvants. To address this need, we produced CPAF in a cell-free protein synthesis platform and adjuvanted it with the TLR9-agonist CpG1826, a synthetic cyclic-di-AMP (CDA) STING (stimulator of interferon genes) agonist ADU-S100, and/or the squalene oil-in-water nanoemulsion, AddaS03. We determined that intranasal immunization with CPAF plus ADU-S100 was well tolerated in female mice, induced CD4 T cells characterized by TNFα production alone or in combination with IL-17 A or IFNγ, significantly reduced bacterial shedding, and shortened the duration of infection in mice intravaginally challenged with Chlamydia muridarum. These data demonstrate the potential for CDA as a mucosal adjuvant for vaccines against Chlamydia genital tract infection.