Mechanisms for SIV evasion of vaccine immunity: Role of FasL-mediated cell death

描述(申请人提供)：急性HIV感染伴随一波淋巴细胞活化和耗竭，可能包括感染和未感染的细胞。淋巴细胞激活的机制和细胞丢失的机制没有得到很好的解释，但它们是病毒发病的核心。HIV感染促使淋巴细胞耗尽的能力可能是未能控制初始病毒血症的重要原因，并可能导致慢性疾病持续感染的建立。我们认为，FasL在病毒感染过程中表达增加，是淋巴细胞耗竭的主要介质，特别是在表达Fas受体的记忆细胞群体中，并可能通过促进促炎细胞因子的表达而影响急性感染，从而增加病毒的复制水平。在这项提案中，我们假设，我们在急性SIV感染的发病机制中所涉及的相同机制，也可能会削弱通过接种疫苗获得的先前存在的免疫。如果FasL在克服疫苗接种的保护作用方面发挥重要作用，它将是逃避宿主免疫的重要机制，应该与序列变异和其他可能导致疫苗失败的机制一起考虑。我们的实验方法是通过注射抗FasL蛋白的单抗来阻断猕猴急性SIV感染过程中FasL的活性。在初步研究中，我们提供了猕猴抗FasL活性的证据，表明只有在急性感染期间对猕猴进行治疗，才能增强对病毒的细胞和体液免疫反应，并延长SIV攻击后的生存时间。在这项拟议的研究中，我们首先对SIV和参考抗原免疫猕猴，然后用SIV感染或不用抗FasL治疗来挑战它们。该实验计划还包括对伽马/德尔塔T细胞和B细胞的研究，这些细胞对SIV感染有反应，但不容易受到病毒感染。这些研究提供了一种方法来确定感染和FasL对未直接感染SIV的细胞的影响。对血液和淋巴组织中的免疫反应、细胞因子的产生和病毒载量的分析的综合计划可以检验关于FasL介导的细胞死亡的主要假说，还将显示阻断FasL对病毒传播和细胞因子产生的影响，这可能是替代作用机制的信号。在未来，有可能设计疫苗抗原，在不驱动FasL产生的情况下引发保护性免疫反应。这些抗原本身可能会引起更强的反应，并在自然暴露于艾滋病毒后为宿主提供重要的动力优势。总结：艾滋病毒感染可能通过触发一种破坏免疫细胞的机制和失去对艾滋病毒疾病的保护而逃避疫苗的保护活性。疫苗逃避的其他机制包括突变，改变病毒蛋白质的化学结构，以及干扰免疫细胞识别。通过定义免疫细胞破坏在疫苗逃避中的作用，我们有助于全面了解疫苗失败的潜在机制，这些机制将用于改进候选艾滋病毒疫苗的设计和测试。

DESCRIPTION (provided by applicant): Acute HIV infection is accompanied by a wave of lymphocyte activation and depletion that likely includes both infected and uninfected cells. The mechanisms for lymphocyte activation and the mechanisms for cell loss are not well explained, but are at the core of viral pathogenesis. The ability of HIV infection to drive the depletion of lymphocytes that are mounting anti-viral immune responses may be important in the failure to contain the initial viremia, and may ead to the establishment of persistent infection with chronic disease. We believe that FasL, whose expression increases during viral infection, is a principal mediator of lymphocyte depletion, especially within the Fas receptor expressing memory cell population, and may also influence the acute infection by promoting the expression of pro- inflammatory cytokines that increase the level of virus replication. In this proposal, we postulate that these same mechanisms we have implicated in the pathogenesis of acute SIV infection, may also work to blunt pre-existing immunity that was achieved through vaccination. Should FasL have a major role in overcoming the protective effect of vaccination, it will be an important mechanism for evading host immunity and should be considered alongside sequence variation and other mechanisms that may account for potential vaccine failures. Our experimental approach is to block the activity of FasL during acute SIV infection of macaques, by injecting a monoclonal antibody against this protein. In Preliminary Studies, we provide evidence for the activity of anti-FasL in macaques, showing that treatment of monkeys only during the interval of acute infection, increased cellular and humoral immune responses to virus and extended the survival times after SIV challenge. In the proposed research, we start by immunizing macaques against SIV and reference antigens, then challenging them with SIV infection with or without anti-FasL treatment. The experimental plan also includes studies on gamma/delta T cells and B cells, population that respond to SIV infection but are not susceptible to virus infection. These studies provide a way to define the impact of infection and FasL on cells that are not directly infected by SIV. A comprehensive plan for assays of immune responses, cytokine production and virus burden in blood and lymphoid tissues allows for testing of the main hypothesis about FasL-mediated cell death and will also show the impact of blocking FasL on virus dissemination and cytokine production that might signal alternate mechanisms of action. In future, it may be possible to design vaccine antigens that elicit protective immune responses without driving the production of FasL. These antigens may in and of themselves, elicit stronger responses and provide the host with an important kinetic advantage after natural exposure to HIV. LAY SUMMARY: HIV infection might evade the protective activity of vaccines, by triggering a mechanism for immune cell destruction and loss of protection against HIV disease. Other mechanisms for vaccine evasion include mutation, that changes the chemical structure of viral proteins, and interference with immune cell recognition. By defining the role for immune cell destruction in vaccine evasion, we contribute to a complete understanding of potential mechanisms for vaccine failure that will be used to improve the design and testing of candidate HIV vaccines.