A bivalent multi-adjuvant Chlamydia vaccine targeting secreted and outer membrane antigens reduces genital infection and pathology in mice 2257258

Introduction Chlamydia trachomatis is the most common bacterial STI and a major cause of hydrosalpinx and infertility, making a vaccine urgently needed. We developed a vaccine by conjugating the secreted Chlamydial Protease-like Activity Factor (CPAF) to the STING agonist CL1151 (CPAF-CL1151). Although intramuscular (i.m.) immunization elicited strong Th1 responses, it did not prevent oviduct pathology following C. muridarum infection. We hypothesized that co-delivery of CPAF-CL1151 with the Major Outer Membrane Protein (MOMP) and additional adjuvants (CpG1826 and QS-21) via combined i.m./intranasal (i.n.) routes would enhance mucosal and systemic Th1 immunity and protection. Methods Female C57BL/6 mice were immunized with CPAF-CL1151 ± QS-21 (i.m.) or CPAF-CL1151 + QS-21 ± MOMP ± CpG1826 (i.m.+i.n.). Antigen-specific T-cell responses were assessed by IFNγ/IL-17A ELISpot and flow cytometry, and serum IgG by ELISA. After challenge, cervical chlamydia burden was quantified by inclusion forming unit assay, and oviduct hydrosalpinx was assessed macroscopically. Results CPAF-CL1151 + QS-21 i.m. immunization increased IFNγTNFα CD4+ T cells 2.4-fold compared to CPAF-CL1151 alone. The combined i.m.+i.n. CPAF-CL1151 + MOMP + CpG + QS-21 regimen further doubled this population. MOMP-specific CD4+ T-cell responses were modest (0.75% of CD4+ cells) compared to CPAF (28.7%), but high anti-Chlamydia IgG titers (∼106 endpoint) were generated. The bivalent triple-adjuvant vaccine reduced cervical burden by 1.3 log10 (P < 0.0001) and shortened infection by 11 days compared to PBS controls (P = 0.0002), and decreased hydrosalpinx by ∼50% relative to CPAF-CL1151 + QS-21. Conclusion Thus, a bivalent CPAF-MOMP vaccine delivered via i.m.+i.n. routes induces robust Th1 immunity, accelerates clearance, and reduces oviduct pathology. Ongoing studies aim to define the minimal antigen, adjuvant, and route combinations required for optimal protection.