Functional analysis of CD8 T cell immune control in Toxoplasma gondii infection

描述(申请人提供)：弓形虫是艾滋病患者的一种重要的机会性感染。迫切需要改进战略和方法，以便更有效地预防和治疗艾滋病复发感染。尽管对弓形虫感染的宿主免疫反应有广泛的了解，但目前还没有针对这种寄生虫或任何其他引起艾滋病机会性感染的原虫的疫苗被批准用于人类。在急性原发感染后，在中枢神经系统/脑内建立了一种长期的慢性弓形虫感染，这种慢性感染的特征是持续存在含有缓慢复制的慢速殖子寄生虫形式的包囊。慢性感染中脑囊肿破裂引起的活动性感染重新激活是导致艾滋病难治性和危及生命的弓形体脑炎的主要机制。我们对控制急性感染和慢性感染的抗原特异性免疫因素的理解存在重大差距。我们的初步数据显示，CD8+T细胞控制了急性感染，并防止了慢性感染中的囊肿破裂。CD8+T细胞和干扰素-3的产生是急性、原发和慢性弓形虫感染免疫控制的关键介质。我们假设，急性和慢性感染的免疫控制高度依赖于抗原特异性CD8+T细胞群，这些T细胞群识别感染期间呈递给MHC I类的特定寄生虫衍生表位。这一假设将通过使用突变毒力株和缺乏已知内源性寄生虫来源的CD8+T细胞表位的突变减毒疫苗株的实验来研究确定的CD8+T细胞表位在介导急性和慢性感染控制中的功能重要性来验证(S)。将确定确定的CD8+T细胞表位在激发对致死性急性感染的保护性免疫中的功能重要性，以及正常预先建立的疫苗诱导免疫对缺乏特定寄生虫来源的CD8+T细胞表位的毒力突变株的保护能力(S)。这项创新和探索性的研究将从功能上揭示最近发现的四个潜在免疫优势寄生虫来源的CD8+T细胞表位和它们对应的CD8+T细胞群中是否有任何一个决定了急性和慢性弓形虫感染的免疫控制。该项目具有重大影响，因为它与理解急性和慢性感染的免疫控制有关，这将使未来的研究集中在最关键的寄生虫抗原及其抗原特异性CD8+T细胞反应上。该项目对改进疫苗设计和确定应对艾滋病慢性感染的新干预措施也具有重要意义。 公共卫生相关性：该项目与了解艾滋病条件致病菌弓形虫急性和慢性感染的免疫控制相关。目前没有疫苗可以预防感染，也没有治疗方法可以根除感染者的慢性感染。通过在这个项目中探讨弓形虫感染免疫控制的基本和功能方面，我们希望揭示可直接应用于疫苗开发以预防感染的新信息，以及确定潜在的干预措施，以消除特别有可能严重反复感染风险的已感染人群的慢性感染(S)。

DESCRIPTION (provided by applicant): Toxoplasma gondii is an important opportunistic infection of AIDS patients. Improved strategies and approaches are urgently needed to more effectively prevent and treat recurrent infections in AIDS. Despite extensive knowledge of host immune response to T. gondii infection, no vaccine is yet approved for use in humans for this parasite or any other protozoan parasite causing opportunistic infection in AIDS. Following an acute primary infection, a chronic life-long T. gondii infection is established in CNS/brain and this chronic infection is characterized by the persisting presence of cysts containing slowly replicating bradyzoite parasite forms. Reactivation of active infection due to rupture of brain cysts in chronic infection is the major mechanism causing difficult to treat and life-threatening Toxoplasmic encephalitis in AIDS. A major gap exists in our understanding of the antigen-specific immune factors that control acute infection and chronic infection. Our preliminary data shows that CD8+ T cells control acute infection and prevent cyst rupture in chronic infection. CD8+ T cells and IFN-3 production are critical mediators of immune control in acute primary and chronic T. gondii infection. We hypothesize that immune control of acute and chronic infection is highly dependent on antigen-specific CD8+ T cell populations that recognize specific parasite-derived epitopes presented to MHC class I during infection. This hypothesis will be tested by investigating the functional importance of defined CD8+ T cell epitopes in mediating control of acute and chronic infection in experiments using mutant virulent strains as well as mutant attenuated vaccine strains that lack known endogenous parasite-derived CD8+ T cell epitope(s). The functional importance of defined CD8+ T cell epitopes in eliciting protective immunity to lethal acute infection will be determined, as well as the ability of a normally pre-established vaccine-induced immunity to protect against a virulent mutant strain lacking specific parasite-derived CD8+ T cell epitope(s). This innovative and exploratory study will functionally reveal whether any of the four recently identified and potentially immunodominant parasite-derived CD8+ T cell epitopes and their corresponding CD8+ T cell populations determine the immune control of acute and chronic T. gondii infection. This project offers significant impact as it is relevant to the understanding of immune control of acute and chronic infection, which will allow future studies to focus on the most critical parasite antigens and their antigen-specific CD8+ T cell responses. This project is also is relevant for the improvement of vaccine design and to identify new interventions to address chronic infection in AIDS. PUBLIC HEALTH RELEVANCE: This project is relevant to understanding immune control of acute and chronic infection in the AIDS opportunistic pathogen Toxoplasma gondii. No vaccine is currently available to prevent infection, and no treatment is available to eradicate chronic infection in infected individuals. By addressing fundamental and functional aspects of immune control in T. gondii infection in this project, we expect to reveal new information that can be directly applied to vaccine development to prevent infection, as well as to identify potential interventions to eliminate chronic infection in already infected people who are particularly at risk of serious recurrent infection(s).