A Small Animal Model for Viscerotropic Disease to Improve Yellow Fever Vaccine

描述(申请人提供)：黄热病病毒(YFV)引起蚊媒疾病黄热病(YF)，这是一种嗜内脏疾病，即它以灵长类动物的肝脏为目标。这种疾病是由一种非常有效的减毒活疫苗17D株控制的，这种疫苗来自野生型菌株Asibi，在过去70年里已经为5.4亿人接种了疫苗。在过去的10年里，有报道称一种罕见但致命的疾病是由YF疫苗相关的嗜内脏疾病(Yel-AVD)疫苗引起的。这种情况与病毒在初级疫苗接种者中的不受控制的复制有关，导致了全身性感染和与野生型YFV非常相似的疾病图景。最初，据报道，耶尔-AVD的发病率为每10万名疫苗接种者中有0.3人。然而，2007年10月，秘鲁报告的发病率为每100,000人中有9人。这种令人震惊的严重不良事件正在导致监管当局重新评估17D疫苗的禁忌症和使用情况，一些人正在呼吁开发一种新的YF疫苗。然而，人们认识到，开发一种新疫苗至少需要15年时间。因此，迫切需要对目前的疫苗进行研究，以了解耶尔-AVD以及如何改进现有的疫苗。使用17D疫苗病毒产生嵌合病毒，在17D疫苗病毒主干中包含一种黄病毒(如乙型脑炎)的结构蛋白基因，强调了这一紧迫性。这种嵌合疫苗正在进行第二阶段的临床试验。令人惊讶的是，人们对野生型YFV毒力或YFV 17D减毒活疫苗的减毒和免疫原性的分子机制知之甚少。这在一定程度上是因为缺乏一种嗜内脏的小动物。PI已经开发出一种新的YFV感染模型，可以很容易地区分野生型Asibi毒株和17D疫苗毒株。我们的长期目标是使用这个模型来理解嗜内脏和减毒的免疫学基础。我们的具体目标是：i)研究与强毒Asibi病毒相比，弱毒17D病毒感染被阻断的致病序列中的步骤，从而识别可能对Yel-AVD的发展重要的先天免疫反应中的潜在异常；以及ii)通过在本项目开发的新的小鼠模型中检测Yel-AVD分离株的嗜内脏表型，鉴定Yel-AVD分离株中存在的YFV编码的嗜内脏分子决定因素。 公共卫生意义：由蚊媒黄热病病毒引起的高致命性病毒性出血热一直是非洲、欧洲和美洲最可怕的疾病之一，直到20世纪30年代S开发出17D减毒活疫苗。即使在今天，每年仍有20多万西非人感染黄热病，导致数万人死亡。减毒17D疫苗株是通过在培养细胞中反复培养野生型YFV分离株(Asibi株)而产生的。尽管17D被认为是有史以来最有效的减毒活疫苗之一，但控制这种减毒活疫苗的减毒和免疫原性的免疫学机制仍然是一个谜。我们的长期目标是确定宿主如何能够控制17D感染，并调查疫苗相关嗜内脏疾病(YEL-AVD)的发生机制。为了实现这一目标，莱曼博士和巴雷特博士提出了一项联盟协议，根据该协议，巴雷特博士的实验室将向莱曼博士的实验室提供病毒，在那里，将使用新开发的YFV致病机制和疾病模型来评估它们的毒力。我们对宿主-病原体相互作用的了解已经足够多，可以合理设计减毒活病毒株，并且存在在基因工程载体系统中引入和测试突变的技术。预计我们的发现将提高YFV疫苗的安全性和有效性，并进一步促进其他减毒活疫苗的合理设计，特别是针对其他致病性黄病毒(例如西尼罗河病毒和登革热病毒)以及与之密切相关的甲型病毒(例如东部马脑炎病毒)，这些病毒大多既是新发传染病的病原体，也是生物恐怖主义/生物战的病原体。

DESCRIPTION (provided by applicant): Yellow fever virus (YFV) causes the mosquito-borne disease yellow fever (YF), a viscerotropic disease, i.e., it targets the liver, of primates. The disease is controlled by a very efficacious live attenuated vaccine, strain 17D, which was derived from wild-type strain Asibi and has been administered to over 540 million people in the last 70 years. In the last 10 years a rare, but fatal, condition has been reported due to the vaccine, termed YF vaccine associated viscerotropic disease (YEL-AVD). This condition is associated with uncontrolled replication of the virus in primary vaccinees resulting in pansystemic infection and a disease picture very similar to wild-type YFV. Originally, YEL-AVD was reported to have an incidence of 0.3 per 100,000 vaccinees. However, in October 2007, an incidence of 9 per 100,000 was reported in Peru. This alarming rate of serious adverse events is causing regulatory authorities to re-evaluate the contraindications and use of the 17D vaccine, and a number of individuals are calling for the development of a new YF vaccine. Nonetheless, it is recognized that development of a new vaccine takes at least 15 years. Thus, there is an urgent need to undertake research on the current vaccine to understand YEL-AVD and how the current vaccine could be improved. This urgency is emphasized by the use of 17D vaccine virus to generate chimeric viruses containing the structural protein genes of one flavivirus (e.g. Japanese encephalitis) in a 17D vaccine virus backbone. Such chimeric vaccines are in phase II clinical trials. Surprisingly, little is known about the molecular mechanisms that govern the virulence of wild-type YFV or the attenuation and immunogenicity of the live- attenuated YFV 17D vaccine. This is, in part, due to the lack of a small animal of viscerotropism. The PI has developed a new YFV infection model that readily distinguishes wild-type Asibi strain from the 17D vaccine strain. Our long-term goals are to use this model to understand the immunologic basis of viscerotropism and attenuation. Our specific aims are: i) investigate the steps in the pathogenic sequence at which attenuated 17D virus infection is blocked compared with virulent Asibi virus thereby identifying potential anomalies in the innate immune response that might be important to the development of YEL-AVD; and ii) identify YFV-encoded molecular determinants of viscerotropism present in YEL-AVD isolates by examining their viscerotropic phenotype in the new mouse model developed in this project. PUBLIC HEALTH RELEVANCE: The highly-lethal viral hemorrhagic fever caused by the mosquito-borne yellow fever virus (YFV) was one of the most feared diseases in Africa, Europe and the Americas until the live-attenuated 17D vaccine was developed in the 1930's. Even today, over 200,000 West Africans contract YF annually, with tens of thousands of fatalities. The attenuated 17D vaccine strain was derived by repeatedly growing a wild- type YFV isolate (strain Asibi) in cultured cells. Although 17D is considered to be one of the most effective live-attenuated virus vaccines ever developed, the immunologic mechanisms that control the attenuation and immunogenicity of this live-attenuated vaccine remain a mystery. Our long-term goal is to determine how the host is able to control the 17D infection and investigate mechanisms by which vaccine-associated viscerotropic disease (YEL-AVD) occurs. To achieve this goal, Drs. Ryman and Barrett have proposed a consortium agreement in which Dr. Barrett's laboratory will provide viruses to Dr. Ryman's laboratory, where their virulence will be assessed using a newly developed model of YFV pathogenesis and disease. Our understanding of host- pathogen interactions has increased sufficiently to allow rational design of live- attenuated virus strains and the technology exists to introduce and test mutations in genetically-engineered vector systems. It is anticipated that our findings will improve the safety and efficacy of the YFV vaccine, and additionally facilitate the rational design of other live-attenuated virus vaccines, particularly against other pathogenic flaviviruses (e.g., West Nile and dengue viruses) and the closely-related alphaviruses (e.g., eastern equine encephalitis virus), most of which are agents of both emerging infectious disease and bioterrorism/biowarfare.