Cross-Protective Immunity to African Trypanosomes

描述（由申请方提供）：所有成功的微生物病原体均逃避或改变宿主免疫应答。可以说，寄生虫免疫逃避的最著名的例子是非洲锥虫的变体表面糖蛋白（VSG）外壳的抗原变异，这阻止了生物体从血管和血管外组织感染部位的免疫消除。VSG特异性B细胞应答与血液中寄生虫的控制相关，并且在很大程度上限于血液中寄生虫的控制，但是VSG特异性Th 1细胞应答在功能上和遗传上与针对锥虫的相对抗性相关。这种耐药性是介导的干扰素-？活化巨噬细胞以在血管外组织中产生杀锥虫因子RNI、ROS和TNF α。因此，IFN-？产生对于宿主存活是关键的，但在很大程度上依赖于VSG特异性表位的Th 1细胞识别。然而，最终，VSG外壳的抗原变异导致免疫逃逸，锥虫感染对其宿主总是致命的。我们实验室最近的两项成就为非洲锥虫病的免疫控制或治愈打开了一扇机会之窗。第一个发现是时间保护性VSG特异性T细胞应答仅针对VSG分子内的高度可变的N-末端微结构域，而不针对高度保守的N-末端结构域内的残基。 因此，VSG特异性T细胞应答是变体特异性的，并且不与表达同源C末端结构域序列的其他VSG交叉反应。这一信息提供了一个独特的机会，人工指导Th 1细胞反应保守的VSG序列，并促进控制或治愈感染。第二个发现是，通过从锥虫DNA中的稳定转录位点表达外源eGFP基因，我们能够第一次可视化血管外组织内的活锥虫，并监测免疫治疗对宿主抗性的功效。这些新的要素构成了本提案的基础结构。待测试的中心假设是T细胞对锥虫变体表面糖蛋白（VSG）分子的保守C末端残基的应答的激活将促进对感染的变体交叉保护性免疫，导致疾病的控制或治愈。目的1包括天然的、改变的天然的、重组的和合成的保守的C-末端VSG毒力将用于在未处理小鼠中激发变体交叉特异性Th 1细胞应答的实验。免疫动物随后将被表达保守VSG残基的不同锥虫变体感染。这一目标将为中心假设提供“原理证明”。目标2将工作计划扩展到具有临床转化潜力的实验。已经感染非洲锥虫的小鼠的治疗将通过用目的1中鉴定的不变VSG交叉保护性蛋白序列免疫来完成。将监测动物的感染消退以及对变体交叉保护序列具有特异性的适当T细胞的活化。这一目标为中心假设提供了一个假设性的“真实的世界检验”，在这个检验中，被诊断患有这种疾病的患者可以通过干预治疗来挽救。在已经感染的个体中诱导交叉变异特异性T细胞应答和寄生虫消除的能力将对非洲的临床疾病产生巨大影响。因此，这里提出的实验首次提供了一种控制或治愈第三世界疾病的新方法，迄今为止，这种疾病已被证明是任何形式的预防或临床治疗都难以治愈的。 公共卫生相关性：非洲锥虫病（人类昏睡病）是一种毁灭性的第三世界疾病，在整个撒哈拉以南非洲地区流行。感染没有自然治愈，主要是由于寄生虫变体表面糖蛋白（VSG）外壳的广泛抗原变异。此外，迄今为止，旨在控制该疾病的所有预防和治疗策略都不成功。因此，本提案测试了一种新的方法，并使用了创新的新工具，旨在诱导和监测非洲锥虫的变异交叉保护性免疫，与VSG结构/功能相关的发现将适用于其他微生物感染，其中受感染的宿主优先响应保护性抗原的变异残基，而不是不变残基。

DESCRIPTION (provided by applicant): All successful microbial pathogens evade or alter host immune responses. Arguably the most well-known example of immune evasion by parasites is antigenic variation of the variant surface glycoprotein (VSG) coat by the African trypanosomes, which prevents immune elimination of the organisms from vascular and- extra vascular tissue sites of infection. VSG-specific B cell responses are associated with, and largely limited to, control of Parasites in the blood, but are VSG-specific Th1 cell responses that are functionally and genetically linked to relative resistance against trypanosomes. This resistance is mediated by IFN-? activation of macrophages for production of the trypanocidal factors RNI, ROS and TNFa In the extra vascular tissues. Thus, IFN-? production is critical for host survival but is largely dependent on Th1 cell recognition of VSG-specific epitomes. Ultimately, however, antigenic variation of the VSG coat leads to immune escape and trypanosome infections are invariably fatal for their hosts. Two recent achievements in our laboratory have opened a window of opportunity for immunological control or cure of African trypanosomiasis. The first is a discovery that temporally protective VSG-specific T cell responses are directed exclusively at highly variable N-terminal micro domains within the VSG molecule, and are not directed at residues within the highly conserved -terminal domain. Thus, VSG specific T cell responses are variant specific and do not cross-react with other VSGs that express homologous C-terminal domain sequences. This information provides a unique opportunity to artificially direct Th1 cell responses to conserved VSG sequences and to promote control or cure of infection. The second discovery is that by expressing an exogenous eGFP gene from a stable transcription site in trypanosome DNA, we are able for the first time to visualize viable trypanosomes within the extra vascular tissues and to monitor the efficacy of immunotherapeutic treatments for host resistance. These novel elements form the infrastructure for this proposal. The central hypothesis to be tested is that activation of T cell responses to conserved C-terminal residues of the trypanosome variant surface glycoprotein (VSG) molecule will promote variant cross- protective immunity to infection, leading to control or cure of disease. Aim 1 encompasses experiments in which natural, altered natural, recombinant and synthetic conserved C-terminal VSG subsequences will be used to provoke variant cross-specific Th1 cell responses in na¿ve mice. Immunized animals subsequently will be infected with different trypanosome variants expressing the conserved VSG residues. This aim will provide "proof of principle" for the central hypothesis. Aim 2 extends the work plan to experiments that have clinical translational potential. Treatment of mice already infected with African trypanosomes will be accomplished by immunization with invariant VSG cross- protective protein sequences identified in Aim 1. Animals will be monitored for resolution of infection coupled with activation of appropriate T cells with specificity for variant cross-protective sequences. This aim provides a hypothetical "real world test" for the central hypothesis, in which patients diagnosed with the disease could be rescued by intervention therapy. The ability to induce cross-variant specific T cell responses and parasite elimination in individuals already infected would have tremendous impact on clinical disease in Africa. Thus, the experiments proposed here provide, for the first time, a novel approach to the control or cure of a Third World disease that has proven intractable to every form of preventive or clinical therapy to date. PUBLIC HEALTH RELEVANCE: African trypanosomiasis (Human Sleeping Sickness) is a devastating Third World disease that is endemic throughout Sub-Saharan Africa. There is no natural cure for infection, primarily due to extensive antigenic variation of the parasite variant surface glycoprotein (VSG) coat. Further, all preventive and therapeutic strategies aimed at controlling the disease have been unsuccessful to date. Therefore the present proposal tests a novel approach and uses innovative new tools aimed at the induction and monitoring of variant cross-protective immunity to African trypanosomiasis, and findings relative to VSG structure/function will be applicable to other microbial infections in which infected hosts preferentially respond to variant rather than invariant residues of protective antigens.