A STING-agonist Conjugate Vaccine Potently Synergizes with admixed QS-21 liposomes and CpG to Elicit Robust Th1 Immunity against Chlamydia in mice 2257260

Abstract Introduction Chlamydia trachomatis (CT) is the most common bacterial sexually transmitted infection and can cause pelvic inflammatory disease and infertility in women. CT vaccine development has been hindered by a lack of safe adjuvants that elicit high frequencies of IFNγ memory CD4 T cells (Th1) required for protection. Our lab developed a novel subunit vaccine consisting of the immunodominant Chlamydia protease-like activity factor (CPAF) antigen conjugated to a novel STING agonist CL1151 (CPAF-CL1151), that induces a protective Th1 response in mice. We hypothesized the addition of QS-21 liposomes and/or a TLR9 agonist (CpG1826) with CPAF-CL1151 would synergistically enhance Th1 immunity against Chlamydia. Methods C57BL/6 mice were immunized intramuscularly (i.m.) or via combined i.m. and intranasal (i.n.) route with different adjuvant combinations (-CL1151+QS-21+CpG). CPAF-specific T cell responses were determined by IFNγ ELISpot, ELISA, and ICS. THP-1 derived macrophages were stimulated with CPAF-CL1151, QS-21, or both and cytokine secretion quantified by ELISA. Results ELISpot showed mice vaccinated i.m with -CL1151+QS-21 had a 2-fold increase in splenic IFNγ CD4 T cells compared to -CL1151 (p < 0.001), and an 8-fold increase compared to QS-21 (p < 0.0001). The triple-adjuvant vaccine (-CL1151+QS-21+CpG) delivered i.m + i.n enhanced the frequency of IFNγ CD4 T cells by 2-fold (p < 0.01) and induced a 6-fold increase in IFNγ secretion by splenocytes upon CPAF restimulation (p < 0.01) over -CL1151 + QS-21. In THP-1 macrophages, -CL1151 + QS-21 had >10-fold increases in IFNβ, IL-6, and IL-1β secretion relative to individual adjuvants, indicating activation of interferon and inflammasome pathways. Conclusion These data highlight the Th1 synergy of TLR, saponin, and STING adjuvants and demonstrates the potential of multi-adjuvant vaccines against intracellular bacterial pathogens. Future studies will define the synergistic molecular and cellular pathways underlying this protective CD4 T cell immunity. Funding Source UO1AI182180 Topic Categories Vaccines and Immunotherapy (VAC)