Immune evasion in a humanized mouse model of HHV-6 infection

描述（由申请人提供）：疱疹病毒与其宿主共同进化了数亿年。随着我们的适应性免疫系统的进化，疱疹病毒编码的免疫逃避机制也在进化。 由于疱疹病毒在其宿主体内保持潜伏或持续存在，因此疱疹病毒已经进化出一套独特的策略来帮助它们对抗终身宿主免疫应答。 这一应用的中心前提是疱疹病毒在其进化过程中已经进行了长达1亿年的免疫逃避机制的遗传筛选。我们试图利用它们的进化来发现细胞生物学，免疫学和病毒学的新概念。该项目的长期目标是了解人类疱疹病毒逃避免疫系统检测的机制。本研究的重点是建立人疱疹病毒6型和7型（HHV-6/7）的人源化小鼠模型系统。我们已经发现，一个HHV-6/7编码的ORF，U21，与I类MHC分子从细胞表面，下调，大概是作为逃避细胞毒性T细胞检测的手段。此外，U21还下调NK活化配体云母和MICB从细胞表面，和U21的表达降低NK细胞对U21表达细胞的细胞毒性。HHV-6/7对人类宿主具有高度特异性，因此没有可用的动物模型系统。 此外，一个可遗传操纵的BAC系统一直难以创建。因此，虽然我们已经在体外证明了U21的这些功能，但当U21在组织培养细胞中表达时，我们还不了解这些免疫evasin分子在病毒感染背景下的相对贡献。最近，成功开发了用于HHV-6研究的生物活性炭系统。用一个？U21 HHV 6病毒，我们将能够检查在病毒感染的情况下U21对I类MHC分子和NK活化配体的影响。 然后，为了确定U21对HHV-6感染的发病机制的影响，我们将用重组HHV-6感染人源化“scid-hu”小鼠。拟议的研究也将导致更好地了解急性和长期HHV-6感染。更好地了解这些未充分研究的病毒是必不可少的：不仅更多地了解这些病毒的机制会导致更彻底地理解这些病毒如何在逃避宿主免疫反应方面取得如此巨大的成功，而且更好地了解这些病毒可能在癫痫，移植受体和自身免疫性疾病的治疗中具有未来的临床应用。 本研究与公共卫生的相关性HHV-6感染引起的高热可能是幼儿热性惊厥的最常见原因，在生命的第二年发病率最高。长期以来，人们一直认为儿童癫痫发作与颞叶癫痫的风险大幅增加有关（3）。最近的一项研究表明，HHV- 6和HHV-7感染约占幼儿严重癫痫发作病例的40%（4）。在70%的内侧颞叶癫痫脑组织切除物中发现HHV 6 DNA（5）。总之，这些研究表明儿童感染HHV-6和HHV-7与癫痫的发展之间存在联系。HHV-6也在造血细胞移植受者中重新激活，导致不良的神经认知结果，并可导致急性边缘系统损害。 脑炎（3，4）。

DESCRIPTION (provided by applicant): The herpesviruses have co-evolved with their hosts for hundreds of millions of years. As our adaptive immune systems evolved, so did the mechanisms of immune evasion encoded by herpesviruses. Because herpesviruses remain latent or persistent within their host throughout life, the herpesviruses have evolved a unique set of strategies to help them contend with the lifelong host immune response. This application's central premise is that the herpesviruses, in their evolution, have performed a 100 million year- long genetic screen for mechanisms of immune evasion. We seek to take advantage of their evolution to discover new concepts in cell biology, immunology and virology. The long term goal of this project is to understand the mechanisms by which human herpesviruses evade detection by the immune system. The focus of this proposal is to develop a humanized mouse model system for the study of human herpesviruses-6 and -7 (HHV-6/7). We have found that one HHV-6/7-encoded orf, U21, associates with and downregulates class I MHC molecules from the cell surface, presumably as a means of escaping cytotoxic T cell detection. In addition, U21 also downregulates the NK activating ligands MICA and MICB from the cell surface, and expression of U21 reduces NK cytotoxicity toward U21-expressing cells. HHV-6/7 are highly specific for their human hosts, so there is no animal model system available. Moreover, a genetically manipulable BAC system has been difficult to create. Thus, while we have demonstrated these functions of U21 in vitro, when U21 is expressed in tissue culture cells, we do not yet understand the relative contributions of these immunoevasin molecules in the context of virus infection. Recently, a BAC system for the study of HHV-6 was successfully developed. Using a ?U21 HHV6 virus, we will be able to examine the influence of U21 upon class I MHC molecules and NK activating ligands in the context of virus infection. Then, to determine the impact of U21 on the pathogenesis of HHV-6 infection, we will infect humanized "scid-hu" mice with recombinant HHV-6. The proposed studies will also result in better understanding of acute and long-term HHV-6 infection. A better understanding of these understudied viruses is essential: not only will greater knowledge of these viral mechanisms lead to a more thorough comprehension of how these viruses have such great success in evading the host immune response, but a greater understanding of these viruses may have future clinical application in the treatment of epilepsy, transplant recipients, and autoimmune disorders. RELEVANCE OF THIS RESEARCH TO PUBLIC HEALTH The high fevers resulting from HHV-6 infection are perhaps the most common cause of febrile seizures in young children, with a peak incidence in the second year of life. Childhood seizures have long been known to be associated with a substantially increased risk of temporal epilepsy (3). A recent study has shown that HHV- 6, and HHV-7 infection accounts for ~40% of all cases of severe seizures in young children (4). HHV6 DNA was found in 70% of brain tissue resections from mesial temporal lobe epilepsy (5). Together, these studies suggest a link between childhood infection with HHV-6 and -7, and the development of epilepsy. HHV-6 also reactivates in hematopoietic cell transplant recipients, resulting in poor neurocognitive outcome and can result in acute limbic encephalitis (3,4).