Francisella tularensis Vaccines Elicit Concurrent Protective T- and B-Cell Immune Responses in BALB/cByJ Mice

In the last decade several new vaccines against Francisella tularensis, which causes tularemia, have been characterized in animal models. Whereas many of these vaccine candidates showed promise, it remains critical to bridge the preclinical studies to human subjects, ideally by taking advantage of correlates of protection. By combining in vitro intramacrophage LVS replication with gene expression data through multivariate analysis, we previously identified and quantified correlative T cell immune responses that discriminate vaccines of different efficacy. Further, using C57BL/6J mice, we demonstrated that the relative levels of gene expression vary according to vaccination route and between cell types from different organs. Here, we extended our studies to the analysis of T cell functions of BALB/cByJ mice to evaluate whether our approach to identify correlates of protection also applies to a Th2 dominant mouse strain. BALB/cByJ mice had higher survival rates than C57BL/6J mice when they were immunized with suboptimal vaccines and challenged. However, splenocytes derived from differentially vaccinated BALB/cByJ mice controlled LVS intramacrophage replication in vitro in a pattern that reflected the hierarchy of protection observed in C57BL/6J mice. In addition, gene expression of selected potential correlates revealed similar patterns in splenocytes of BALB/cByJ and C57BL/6J mice. The different survival patterns were related to B cell functions, not necessarily to specific antibody production, which played an important protective role in BALB/cByJ mice when vaccinated with suboptimal vaccines. Our studies therefore demonstrate the range of mechanisms that operate in the most common mouse strains used for characterization of vaccines against F. tularensis, and illustrate the complexity necessary to define a comprehensive set of correlates.近十年来，针对引发土拉热（tularemia）的土拉弗朗西斯菌（Francisella tularensis）的多款新型疫苗已在动物模型中完成表征研究。尽管诸多候选疫苗均展现出应用潜力，但将临床前研究成果转化至人体试验仍为关键环节，理想途径是借助保护相关标志物（correlates of protection）实现研究衔接。此前，我们通过多变量分析将体外巨噬细胞内土拉弗朗西斯菌弱毒疫苗株（LVS）增殖实验与基因表达数据相结合，鉴定并量化了可区分不同保护效力疫苗的相关性T细胞免疫应答。进一步研究中，我们以C57BL/6J小鼠为模型，证实基因表达的相对水平会随疫苗接种途径以及不同器官来源的细胞类型而变化。本研究将此前的工作拓展至BALB/cByJ小鼠的T细胞功能分析，以验证我们鉴定保护相关标志物的方法是否同样适用于Th2优势型小鼠品系。当使用亚优化疫苗免疫并攻毒后，BALB/cByJ小鼠的存活率高于C57BL/6J小鼠。然而，从不同方案免疫的BALB/cByJ小鼠体内分离的脾细胞（splenocytes），在体外可通过反映C57BL/6J小鼠中保护效力层级的模式，抑制土拉弗朗西斯菌弱毒疫苗株的巨噬细胞内增殖。此外，对部分候选保护相关标志物的基因表达分析显示，BALB/cByJ与C57BL/6J小鼠的脾细胞中呈现出相似的表达模式。两种小鼠品系的存活率差异与B细胞功能相关，而非特异性抗体产生——后者在亚优化疫苗免疫的BALB/cByJ小鼠中发挥了重要的保护作用。综上，本研究阐明了土拉弗朗西斯菌疫苗表征中最常用的两类小鼠品系所涉及的作用机制范围，并揭示了构建完整保护相关标志物体系所需的复杂性。