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

土拉菌是一种a类选择剂，如果吸入含有10-100 CFU的气溶胶，可引起人类严重和致命的疾病。它是a类特工，是开发对策的优先对象。B型衍生活疫苗株（LVS）对男性气溶胶型A型攻击提供部分保护的能力，证明了土拉菌减毒活疫苗可以提供部分保护的原理。然而，LVS没有获得FDA的许可，并且存在一些缺陷，使其成为一种次优的土拉菌病疫苗。一种最佳的活疫苗将基于在a型亲本菌株中引入精确定义的减毒突变，并将提供强大的保护，防止暴露于雾化的毒性a型土拉菌。我们已经开发了基因工具，促进了A型土拉菌特异性靶向突变的工程。到目前为止，该系列的6个候选菌株在小鼠和/或巨噬细胞存活试验中表现出衰减。我们最先进的候选药物之一FTT1103在严格的C57BL/6小鼠模型中显示出对野生型A型挑战的保护作用。文献中没有其他疫苗显示出这种保护能力。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，将有希望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。使用兔和小鼠模型的平行研究将加速确定主要候选疫苗的进展。这些研究将证实使用这两种动物物种作为评价弗朗西斯菌活疫苗株的相关模型，这些信息尚未得到证实。此外，在体外评估疫苗株相互作用和细胞因子诱导感染巨噬细胞将进行。我们之前的研究表明，A型菌株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与动物模型免疫原性/功效之间存在相关性，这可能表明保护或至少是必要的体外反应之间存在相关性。最后，在兔模型中显示出保护能力的候选疫苗将进行扩大的安全性研究，调查剂量范围，这将是重要的进展。与会专家的共同努力将有助于确定一种有希望的弗朗西斯菌减毒活疫苗株。

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.