Mechanisms of measles virus CNS adaptation

 描述(申请人提供)：麻疹病毒(MV)是发展中国家儿童死亡的主要原因，尽管有40多人可获得减毒活疫苗 好几年了。免疫功能严重受损的人患MV的风险尤其大。MV在世界各地引起周期性暴发；在美国，我们正处于全国范围的暴发之中。虽然自然感染MV会引起持久的免疫力，但接种疫苗的人的保护力会减弱。最严重的MV感染表现，包括脑炎，发生在细胞免疫受损的人身上。MV在多达一半的常规病例中影响中枢神经系统(CNS)；有了足够的细胞免疫，感染就会被根除，但个人 细胞免疫受损的患者处于不利地位。即使是疫苗毒株也可能导致这些人发生致命的脑炎。在最近在南非爆发的MV疫情中，有几人死于MV CNS感染。我们分析了来自这些患者的病毒，发现MV融合机制-受体结合蛋白(H)+融合蛋白(F)-的特定宿主内进化已经发生。“中枢神经系统适应”病毒F的突变使其能够促进融合，而较少依赖H与两个已知的MV细胞受体的相互作用；该F是独立于H或受体激活的。我们推测，在缺乏有效的细胞免疫的情况下，携带能够在中枢神经系统有效传播的融合机制的MV变体经历了积极的选择。我们建议确定MV在宿主体内入侵CNS的分子决定因素，并确定这些“CNS适应的”病毒是否可以在个体之间传播。在目标1中，我们将鉴定野生型(Wt)MV和CNS适应病毒的H/F融合机制之间的遗传和功能差异，以将临床模式与特定的融合特性联系起来。在目标2中，我们将确定CNS分离株的H/F改变是否允许通过正常的感染途径传播给完整的或免疫抑制的宿主。需要采取预防麻疹感染的战略，以保护免疫力不足或没有免疫力而无法接种疫苗的人。我们建议预防MV感染-免疫受损的人必须在早期阶段停止感染，以避免致命的后果。目的评价融合抑制肽在体外、体外和体内对MV感染的抑制作用。一种针对MV的特异性抗病毒疗法将在棉鼠身上进行测试，以确定其对wt MV和他“中枢神经系统适应”临床分离株病毒的疗效。该计划的长期目标是开发一种安全高效的鼻腔融合蛋白(F)抑制剂，用于预防暴发 情况。目前在美国爆发的MV凸显了这项工作的紧迫性。该项目将导致充分了解MV适应中枢神经系统趋向性的机制和风险，并获得稳定、易于运输的鼻腔抗病毒药物，以保护MV暴发期间的高危人群。

 DESCRIPTION (provided by applicant): Measles virus (MV) is a leading cause of child mortality in developing countries despite the availability of a live attenuated vaccine for over 40 years. Severely immune-compromised people are particularly at risk for MV. MV causes periodic outbreaks all over the world; in the U.S., we are in the midst of a nation-wide outbreak. While natural infection with MV elicits long-lasting immunity, protection wanes in vaccinated persons. The most serious manifestations of MV infection, including encephalitis, occur in people with impaired cellular immunity. MV affects the central nervous system (CNS) in up to half of routine cases; with adequate cellular immunity the infection is eradicated, but individuals with impaired cellular immunity are at a disadvantage. Even the vaccine strain can lead to fatal encephalitis in such persons. In a recent MV outbreak in South Africa several people died of MV CNS infection. We analyzed the viruses from these patients and found that specific intra-host evolution of the MV fusion machinery -- receptor binding protein (H) + fusion protein (F) -- had occurred. A mutation in F of the "CNS-adapted" viruses allows it to promote fusion with less dependence on interaction of H with the two known MV cellular receptors; this F is activated independently of H or receptor. We hypothesize that in the absence of effective cellular immunity, MV variants bearing fusion machinery that enabled efficient spread in the CNS underwent positive selection. We propose to identify the molecular determinants of CNS invasion by MV in the host, and determine whether these "CNS-adapted" viruses can spread between individuals. In aim 1 we will identify the genetic and functional differences between the H/F fusion machinery of wild-type (wt) MV and the CNS-adapted viruses, to correlate clinical pattern with specific fusion properties. In aim 2 we will determine whether the H/F alterations in the CNS isolates permit transmission to intact or immune-suppressed hosts via normal routes of infection. Strategies to prevent measles infection are needed to protect people with inadequate or no immunity who cannot be vaccinated. We propose that prevention of MV infection immune-compromised individuals must halt infection at an early stage to avoid fatal consequences. Aim 3 will evaluate fusion inhibitor peptides against MV infection in vitro, ex vivo, and in vivo. A specific antiviral therapy for MV will be tested in cotton rats for its efficacy against wt MV and he "CNS-adapted" clinical isolate viruses. The long-term objective of this plan is to develop a safe and highly effective intranasal fusion protein (F) inhibitor as prophylaxis for use during outbreak situations. The current MV outbreak in the US highlights the urgency of this work. The project will lead to a full understanding of the mechanism and risks of MV adaptation to CNS tropism, and to a stable, easily transported intranasal antiviral to protect people at risk during MV outbreaks.