Vaccine for Epidemic Typhus

描述（由申请人提供）：由普氏立克次体引起的流行性斑疹伤寒是过去500年来人类最大的灾难之一。它目前发生在社会混乱和/或经济条件差的地区。proproazekii是B类潜在的生物恐怖病原体。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，预防流行性斑疹伤寒。流行性斑疹伤寒可通过接种减毒E型毒株（也称为马德里E型毒株）来预防。然而，E型毒株没有用于疫苗接种，因为它在14%的免疫者中引起轻度流行性斑疹伤寒，显然是由于毒力强的Evir毒株的逆转。我们假设在Evir毒株中发生了反向突变，这是Evir毒株毒力的决定因素，并且在Evir毒株中更大幅度地敲除突变基因将减弱Evir毒株并使其成为安全的疫苗。该项目的目标是研制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。提出了三个具体目标来评估我们的假设并提供稳定的减毒活疫苗。具体目标1。用基因组测序方法鉴定了在反毒Evir毒株中，无毒E毒株向野生型转化的突变2. 同源基因重组对Evir株反向突变基因失活的研究3. 确定候选减毒疫苗在小鼠、豚鼠和恒河猴中的安全性、免疫原性和保护性免疫。Evir毒株的敲除毒株有望被减毒，并能像E毒株一样在动物体内激发保护性免疫。然而，Evir菌株的基因敲除应防止毒力状态的恢复，因为毒力决定因素被永久删除。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的疫苗。由于立克次体抗原的交叉反应性，这种有效的流行性斑疹伤寒疫苗对其他立克次体疾病也可能有效。

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.