A novel adjuvant system combining STING agonist-antigen conjugation with liposomal QS-21 exhibits potent synergistic Chlamydia vaccine immunogenicity

Chlamydia trachomatis (CT) is the most prevalent bacterial sexually transmitted infection worldwide. Over 70% of infections in women and approximately 50% in are asymptomatic, leading to underdiagnosis and sustained transmission. In women, untreated infection can result in severe reproductive complications, including pelvic inflammatory disease, ectopic pregnancy, and infertility. An effective vaccine is therefore urgently needed. A safe and effective vaccine against Chlamydia trachomatis remains an urgent global health need. Protective immunity requires robust Th1-biased CD4 T cell responses, yet subunit vaccines often fail to elicit sufficient cellular immunity. Here, we describe a next-generation adjuvant strategy based on site-specific conjugation of the chlamydial antigen CPAF to a synthetic cyclic dinucleotide STING agonist (CPAF–STG1151), with and without combination adjuvant formulation including QS-21 liposomes. Intramuscular immunization with CPAF–STG1151 induced potent, CD4-dominant Th1 responses across multiple mouse strains and both sexes while requiring a 100-fold lower agonist dose compared to admixed STING agonist formulation. Addition of QS-21 further amplified innate cytokine production, antibody titers, and polyfunctional Th1 responses in mice and synergistically enhanced interferon and inflammasome-associated cytokine responses in human macrophages in vitro. Notably, CPAF-STG1151 alone elicited robust cellular and humoral immunity, highlighting its potential as a simplified, scalable vaccine platform. Together, these findings demonstrate that antigen–STING agonist conjugation, with optional combined saponin adjuvant formulation, provides a versatile and translatable strategy for inducing Th1 immunity against Chlamydia and other intracellular pathogens.

沙眼衣原体（Chlamydia trachomatis, CT）是全球范围内最为流行的细菌性性传播感染病原体。该病原体引发的感染中，女性感染者无症状比例超70%，男性感染者约为50%，这会导致诊断不足与持续传播。对于女性而言，未经治疗的感染可引发严重生殖系统并发症，包括盆腔炎性疾病、异位妊娠及不孕症。因此，开发有效疫苗的需求极为迫切，针对沙眼衣原体的安全有效疫苗仍是全球亟待满足的公共卫生需求。保护性免疫需要强健的偏向Th1型的CD4阳性T细胞应答，然而亚单位疫苗往往难以诱导足够的细胞免疫。本研究介绍了一种新一代佐剂策略：将衣原体抗原CPAF与合成环状二核苷酸干扰素基因刺激因子（STING）激动剂进行位点特异性偶联，得到CPAF–STG1151，并分别设计不含与包含QS-21脂质体的联合佐剂配方。采用CPAF–STG1151进行肌内免疫，可在多种小鼠品系及雌雄个体中诱导强效的CD4阳性T细胞主导的Th1型应答，且与混合使用STING激动剂的配方相比，所需激动剂剂量仅为其1/100。添加QS-21可进一步增强小鼠体内的先天细胞因子产生、抗体滴度及多功能Th1型应答，并在体外实验中协同增强人巨噬细胞的干扰素及炎症小体相关细胞因子应答。值得注意的是，单独使用CPAF-STG1151即可诱导强效的细胞免疫与体液免疫，凸显其作为简化且可规模化疫苗平台的潜力。综上，本研究结果表明，抗原与STING激动剂偶联（可选择性添加皂苷类佐剂配方），可为诱导针对沙眼衣原体及其他胞内病原体的Th1型免疫提供一种通用且可转化的策略。