Vaccine for Epidemic Typhus

描述(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年来人类最大的祸害之一。它目前发生在社会混乱和/或经济状况不佳的地区。普罗瓦泽克杆菌是一种B类潜在生物恐怖病原体。目前还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疾病的发病机制，并预防流行性斑疹伤寒。流行性斑疹伤寒可以通过接种减毒的E株(也称为马德里E株)来预防。然而，E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，显然是由于回复到强毒力的Evir株。我们假设在Evir株中发生了反向突变，这是Evir株毒力的决定因素，并且Evir株中突变基因的更实质性的敲除将使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疫苗，用于流行性斑疹伤寒，并可能用于其他立克次体疾病。我们提出了三个具体目标来评估我们的假设，并提供稳定的减毒活疫苗。具体目的：1.用基因组测序方法鉴定E株弱毒株回复为野生型的突变；2.通过同源基因重组使Evir株反向突变基因(S)基因失活；3.检测候选减毒活疫苗在小鼠、豚鼠和恒河猴中的安全性、免疫原性和保护性。Evir基因敲除株预计会减弱，它应该能够像E株那样激发动物的保护性免疫。然而，由于毒力决定簇被永久删除，因此应防止Evir株的基因敲除恢复到毒力状态。因此，Evir基因敲除株可作为预防流行性斑疹伤寒的安全有效疫苗。这种有效的流行性斑疹伤寒疫苗可能对其他立克次体疾病有效，因为立克次体之间存在交叉反应的抗原。

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.