A Humanized Mouse Model of Typhoid Fever

描述(申请人提供)：肠道沙门氏菌。伤寒(S.Typhi)是人类伤寒的病原体，可在正常宿主中引起危及生命的感染。目前的伤寒疫苗只具有中等的免疫原性和保护性。由于缺乏小动物模型，疫苗技术的改进一直受到限制。伤寒沙门氏菌高度适应人类，不会在正常小鼠中引起进行性感染。鼠伤寒沙门氏菌与小鼠的相互作用被用来模拟伤寒沙门氏菌与人的相互作用，但小鼠伤寒和人伤寒在病原体和宿主决定因素上都有很大的不同。在应用中，我们报道了一种用于研究人类伤寒的小动物模型的发展取得了突破，使用NOD-SCID IL2rGamma缺失小鼠植入来自T细胞耗尽的脐带血中的CD34+人造血干细胞。在初步研究中，我们已经证明，伤寒沙门氏菌TY2可以在腹腔接种后在移植小鼠体内复制，导致致命感染，这概括了人类伤寒的关键特征。相反，伤寒沙门氏菌不能在非移植的NOD-SCID IL2rGamma缺失型动物或免疫活性NOD对照组中引起生产性感染。这项申请描述了一个试点项目，以评估这一新模型，并严格测试伤寒沙门氏菌需要人类单个核细胞在体内复制的假设。该项目的具体目标是： 1.人源化小鼠伤寒模型的特征新的模型将使用微生物学、组织病理学和流式细胞术的方法进行表征，以确定感染过程、先天免疫反应和细胞凋亡的重要性。 2.鉴定在人源化小鼠中复制所需的伤寒沙门氏菌基因。一种基于微阵列的方法将被用于识别削弱伤寒沙门氏菌毒力的转座子突变。 我们的模型提供了一个前所未有的机会，以获得对伤寒发病机制的新见解，识别新的伤寒疫苗候选者，并设计出预防伤寒感染的新策略。 公共卫生相关性：这项建议的目标是描述一种新的人源化的人类伤寒小鼠模型，并使用该模型来识别伤寒沙门氏菌毒力的遗传决定因素。一种模仿人类伤寒的小动物模型代表着朝着开发更有效的伤寒疫苗迈出的一大步。公共卫生声明：伤寒沙门氏菌仍然是一种严重的人类病原体，估计每年导致1600万人感染，并导致60多万人死亡。目前可用的两种伤寒疫苗并不完全有效，只能提供短期保护。由于缺乏小动物模型，伤寒疫苗的开发一直受到限制。在这一应用中，我们报告了一种人源化小鼠模型的突破性发展，该模型概括了人类伤寒的关键方面。伤寒沙门氏菌能够在移植了从脐带血中获得的人类免疫细胞的小鼠身上复制，产生进行性致命感染。这首次为分析伤寒临床结局的宿主和微生物决定因素提供了一个实验系统。这项建议中描述的研究将为伤寒沙门氏菌与人类免疫系统的相互作用提供新的见解，并为构建安全有效的伤寒疫苗确定新的战略。

DESCRIPTION (provided by applicant): Salmonella enterica sv. Typhi (S. Typhi) is the etiologic agent of typhoid fever in humans and can cause life-threatening infection in normal hosts. Current typhoid vaccines are only moderately immunogenic and protective. Improvements in vaccine technology have been constrained by the lack of a small animal model. S. Typhi is highly adapted to humans and fails to cause progressive infection in normal mice. S. Typhimurium- murine interactions are used to model S. Typhi-human interactions, but murine typhoid and human typhoid exhibit major differences in both pathogen and host determinants. In the application, we report a breakthrough in the development of a small animal model for the study of human typhoid fever, using NOD-scid IL2rgamma null mice engrafted with CD34+ human hematopoietic stem cells from T-cell depleted umbilical cord blood. In preliminary studies, we have shown that S. Typhi Ty2 can replicate in vivo within engrafted mice following intraperitoneal inoculation to cause lethal infection that recapitulates crucial features of human typhoid. In contrast, S. Typhi is unable to cause productive infection in non-engrafted NOD-scid IL2rgamma null animals or immunocompetent NOD controls. This application describes a pilot project to evaluate this new model and rigorously test the hypothesis that S. Typhi requires human mononuclear cells to replicate in vivo. The specific aims of the project are: 1.Chacterization of the Humanized Mouse Typhoid Model. The novel model will be characterized using microbiologic, histopathologic, and flow cytometric methods to define the course of infection, innate immune response, and importance of apoptosis. 2. Identification of S. Typhi Genes Required for Replication in Humanized Mice. A microarray-based method will be used to identify transposon mutations that impair S. Typhi virulence. Our model provides an unprecedented opportunity to gain new insights into typhoid pathogenesis, identify new S. Typhi vaccine candidates and devise new strategies for the prevention of S. Typhi infections. PUBLIC HEALTH RELEVANCE: The goals of this proposal are to characterize a novel humanized mouse model of human typhoid and to use this model to identify genetic determinants of Salmonella Typhi virulence. A small animal model that mimics human typhoid represents a major advance toward the development of more effective typhoid vaccines. Public Health Statement: Salmonella Typhi remains a serious human pathogen, estimated to cause 16,000,000 infections each year and resulting in more than 600,000 deaths. The two currently available typhoid vaccines are not completely effective and provide only short-term protection. Typhoid vaccine development has been constrained by the lack of a small animal model. In this application, we report the breakthrough development of a humanized mouse model that recapitulates critical aspects of human typhoid. Salmonella Typhi is able to replicate in mice engrafted with human immune cells obtained from umbilical cord blood, producing a progressive lethal infection. For the first time, this provides an experimental system to analyze the host and microbial determinants of clinical outcomes in typhoid fever. The studies described in this proposal will provide new insights into the interaction of S. Typhi with the human immune system and identify new strategies for the construction of safe and effective typhoid vaccines.