Advancement of New Live Attenuated F. Tularensis Type A Vaccine Strains

土拉热弗朗西丝菌是A类选择性病原体，如果吸入含有少至10-100 CFU的气溶胶，可导致人类严重和致命的疾病。它是A类选择剂，是对抗措施开发的优先事项。B型衍生活疫苗株LVS在男性中提供部分保护以抵抗气溶胶A型攻击的能力提供了原理性证据，即活减毒F.土拉热疫苗可以提供部分保护。然而，LVS没有获得FDA的许可，并且存在几个缺点，使其成为次优的兔热病疫苗。最佳的活疫苗将基于将精确定义的减毒突变引入A型亲本菌株，并将赋予针对暴露于气溶胶化的毒性A型F的强保护。土拉热。我们已经开发了遗传工具，促进了A型F中特异性靶向突变的工程化。土拉热。迄今为止，来自该系列测试的六种候选菌株在小鼠和/或巨噬细胞存活测定中显示出减毒。我们最先进的候选物之一，FTT 1103，已被证明在严格的C57 BL/6小鼠模型中提供针对野生型A型攻击的保护。文献中发表的其他疫苗都没有表现出这种保护能力。在这项拨款申请中，我们将利用从最初的中大西洋RCE资助投资中获得的数据和专业知识，将有前途的候选疫苗推进临床前研究，以确认其免疫原性和保护潜力。使用兔和小鼠模型进行的平行研究将加快确定主要候选疫苗的进展。这些研究将验证使用这两种动物种属作为评价活弗朗西斯菌疫苗株的相关模型，这些信息尚未得到验证。此外，还将在感染巨噬细胞中进行疫苗株相互作用和细胞因子诱导的体外评估。我们以前的研究表明，A型菌株中的突变对这些关键过程有显著影响，我们假设巨噬细胞数据和动物模型免疫原性/有效性之间存在相关性，这可能表明保护或至少是必要的体外应答相关。最后，在兔模型中证明保护能力的候选疫苗将进行扩大的安全性研究，调查对发展至关重要的剂量范围。聚集在一起的专家们的共同努力将能够鉴定出一种有希望的减毒弗朗西斯菌活疫苗株。

Francisella tularensis is a Category A select agent that can cause severe and fatal disease in humans if an aerosol containing as few as 10-100 CFU is inhaled. It is a category A select agent and is a priority for countermeasure development. The ability of the Type B derived live vaccine strain, LVS, to confer partial protection against aerosol Type A challenge in men provided proof of principle that a live attenuated F. tularensis vaccine could offer partial protection. However, LVS is not licensed by the FDA and suffers from several drawbacks that render it a sub-optimal tularemia vaccine. An optimal live vaccine will be based on introducing precisely defined attenuating mutations into a Type A parent strain and will confer strong protection against exposure to aerosolized virulent Type A F. tularensis. We have developed genetic tools that facilitated engineering of specifically targeted mutations in Type A F. tularensis. Six of the candidate strains from this series tested thus far, demonstrated attenuation in the mouse and/or macrophage survival assays. One of our most advanced candidates, FTT1103, has been shown to confer protection against wild type, Type A challenge in the stringent C57BL/6 mouse model. No other vaccine published in the literature has shown this protective capacity. In this grant application we will make use of the data produced and expertise acquired from the initial Mid Atlantic RCE funding investment to advance promising vaccine candidates to preclinical studies that will confirm their immunogenic and protective potential. Parallel studies using the rabbit and mouse models will allow accelerated progress towards the identification of lead vaccine candidates. These studies will validate the use of these two animal species as relevant models for evaluation of live Francisella vaccine strains, information that is not yet verified. In addition, in vitro assessment of vaccine strain interaction and cytokine induction in infected macrophages will be performed. Our previous studies demonstrated that mutations in Type A strains had significant effects on these critical processes and we hypothesize that a correlation could be made between macrophage data and animal model immunogenicity/efficacy that could suggest a correlate of protection or at the least, essential in vitro responses. Finally, the vaccine candidate that demonstrates protective capacity in the rabbit model will undergo expanded safety studies investigating dose ranges that will be important for advancement. This concerted effort by the assembled experts will allow identification of a promising live attenuated Francisella vaccine strain.