Vaccine for Epidemic Typhus

描述（由申请人提供）：流行性斑疹伤寒，由普氏立克次体引起，是过去500年来人类最大的疾病之一。目前这种情况发生在社会混乱和/或经济条件差的地区。R.普氏菌是B类优先级潜在生物恐怖病原体。没有预防流行性斑疹伤寒的安全疫苗。该项目的长期目标是了解立克次体病的发病机制和预防流行性斑疹伤寒。流行性斑疹伤寒可以通过接种减毒E株（也称为马德里E株）来预防。然而，E菌株不用于疫苗接种，因为它在14%的免疫者中引起轻度流行性斑疹伤寒，显然是由于回复到毒性Evir菌株。我们推测Evir株中发生了回复突变，是Evir株毒力的决定因素，进一步敲除Evir株中的突变基因将使Evir株减毒，使其成为安全的疫苗。该项目的目标是开发一种有效和安全的流行性斑疹伤寒疫苗，并可能用于其他立克次体疾病。提出了三个具体的目标来评估我们的假设，并提供一个稳定的减毒活疫苗。具体目标1.通过基因组测序鉴定无毒力E菌株中的突变，所述突变在回复突变的毒性Evir菌株中回复为野生型; 2.通过同源基因重组使Evir株中具有回复突变的基因遗传失活; 3.在小鼠、豚鼠和恒河猴中测定候选减毒疫苗的安全性、免疫原性和保护性免疫。Evir株的基因敲除株有望获得减毒，并能像E株一样激发动物的保护性免疫。然而，应防止基因敲除的Evir株回复到强毒状态，因为毒力决定因子被永久删除。因此，该基因敲除株可作为一种安全有效的斑疹伤寒疫苗。由于立克次体间存在交叉反应抗原，因此该疫苗对其它立克次体疾病也有一定的治疗作用。

DESCRIPTION (provided by applicant): Epidemic typhus, caused by Rickettsia prowazekii, is one of humankind's greatest scourges in the last 500 years. It occurs currently in areas with social disorder and/or poor economic conditions. R. prowazekii is a category B priority potential bioterror pathogen. There is no safe vaccine for preventing epidemic typhus. The long term goal of this project is to understand the pathogenesis of rickettsial diseases and to prevent epidemic typhus. Epidemic typhus can be prevented by vaccination with the attenuated E strain (also called Madrid E strain). However, E strain is not used for vaccination because it causes mild epidemic typhus in 14% of immunized persons, apparently due to reversion to the virulent Evir strain. We hypothesize that a reverse mutation occurred in Evir strain and is the determinant for the virulence of Evir strain and that a more substantial knockout of the mutated gene in Evir strain will attenuate Evir strain and make it a safe vaccine. The objective of this project is to develop an effective and safe vaccine for epidemic typhus and possibly for other rickettsial diseases. Three specific aims are proposed to evaluate our hypothesis and provide a stable live attenuated vaccine. Specific aim 1. Identification of the mutations in the avirulent E strain that revert to wild type in the revertant virulent Evir strain by genomic sequencing; 2. Genetic inactivation of the gene(s) with reverse mutation in Evir strain by homologous gene recombination; 3. Determining safety, immunogenicity, and protective immunity of the candidate attenuated vaccine in mice, guinea pigs and rhesus monkeys. The knockout strain of Evir strain is expected to be attenuated, and it should be able to stimulate protective immunity in animals like E strain does. However, the gene knockout of Evir strain should be prevented from reversion to the virulent state because the virulence determinant is permanently deleted. Thus, the knockout Evir strain can be a safe and effective vaccine for preventing epidemic typhus. This effective epidemic typhus vaccine may be effective for other rickettsial diseases because of the cross-reactive antigens among the rickettsiae.