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

描述（由申请人提供）：黄热病病毒（YFV）引起蚊子传播的疾病黄热病（YF），一种亲内脏性疾病，即，靶向灵长类动物的肝脏。该疾病由非常有效的减毒活疫苗菌株17 D控制，该菌株源自野生型菌株Asibi，并且在过去70年中已向超过5.4亿人施用。在过去10年中，报告了一种罕见但致命的疫苗引起的疾病，称为YF疫苗相关内脏嗜性疾病（YEL-AVD）。这种情况与初次接种者中病毒的不受控制的复制有关，导致全系统感染和与野生型YFV非常相似的疾病情况。最初，YEL-AVD的报告发病率为每10万名接种者0.3例。然而，2007年10月，秘鲁报告的发病率为每10万人9人。严重不良事件的惊人发生率促使监管机构重新评估17 D疫苗的禁忌症和使用，一些人呼吁开发新的YF疫苗。尽管如此，人们认识到新疫苗的开发至少需要15年的时间。因此，迫切需要对现有疫苗进行研究，以了解YEL-AVD以及如何改进现有疫苗。通过使用17 D疫苗病毒来产生在17 D疫苗病毒骨架中含有一种黄病毒（例如日本脑炎）的结构蛋白基因的嵌合病毒，强调了这种紧迫性。这种嵌合疫苗正在进行II期临床试验。令人惊讶的是，关于控制野生型YFV的毒力或减毒活YFV 17 D疫苗的减毒和免疫原性的分子机制知之甚少。这部分是由于缺乏向内脏性的小动物。PI开发了一种新的YFV感染模型，该模型易于区分野生型Asibi毒株和17 D疫苗毒株。我们的长期目标是利用这个模型来了解向内脏性和减毒的免疫学基础。我们的具体目标是：i）研究与毒性Asibi病毒相比，减毒17 D病毒感染被阻断的致病序列中的步骤，从而鉴定可能对YEL-AVD的发展重要的先天免疫应答中的潜在异常;和ii）通过在本项目开发的新小鼠模型中检查YEL-AVD分离株的亲内脏表型，鉴定YFV编码的YEL-AVD分离株中存在的亲内脏性分子决定簇。 公共卫生相关性：由蚊子传播的黄热病病毒（YFV）引起的高致死性病毒性出血热是非洲、欧洲和美洲最可怕的疾病之一，直到20世纪30年代开发出减毒活17 D疫苗。即使在今天，每年仍有20多万西非人感染YF，造成数万人死亡。通过在培养细胞中重复生长野生型YFV分离株（Asibi株）来获得减毒的17 D疫苗株.尽管17 D被认为是迄今为止开发的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17 D感染，并研究疫苗相关亲内脏性疾病（YEL-AVD）发生的机制。为了实现这一目标，Ryman博士和Barrett博士提出了一项联盟协议，其中Barrett博士的实验室将向Ryman博士的实验室提供病毒，在那里将使用新开发的YFV发病机制和疾病模型评估其毒力。我们对宿主-病原体相互作用的理解已经充分增加，以允许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。预期我们的发现将提高YFV疫苗的安全性和有效性，并且另外促进其他减毒活病毒疫苗的合理设计，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）和密切相关的甲病毒（例如，东部马脑炎病毒），其中大多数是新出现的传染病和生物恐怖主义/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.