A Humanized Mouse Model of Typhoid Fever

描述（申请人提供）：肠沙门氏菌sv。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。目前的伤寒疫苗仅具有适度的免疫原性和保护性。由于缺乏小动物模型，疫苗技术的改进受到了限制。斑疹伤寒沙门氏菌对人类具有高度适应性，不能在正常小鼠中引起进行性感染。鼠伤寒沙门氏菌与鼠的相互作用被用来模拟鼠伤寒沙门氏菌与人的相互作用，但鼠伤寒和人伤寒在病原体和宿主决定因素上都表现出重大差异。在应用程序中，我们报告了用于研究人类伤寒的小动物模型的开发方面的突破，使用NOD-scid IL2rgamma缺失的小鼠植入来自t细胞枯竭的脐带血的CD34+人造血干细胞。在初步研究中，我们已经表明，伤寒沙门氏菌Ty2可以在腹腔内接种后在植入小鼠体内复制，引起致命感染，这概括了人类伤寒的关键特征。相比之下，斑疹伤寒沙门氏菌在未移植的NOD-scid il - 2rgamma缺失的动物或具有免疫能力的NOD对照中不能引起生产性感染。本申请描述了一个试点项目，以评估这个新模型，并严格测试伤寒沙门氏菌需要人类单核细胞在体内复制的假设。该项目的具体目标是：

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.