Identification of vaccine candidates against severe malaria

描述(由申请人提供)：这项工作的长期目标是通过了解自然保护性免疫反应来确定预防严重疟疾综合征的候选疫苗。恶性疟原虫感染红细胞(IE)黏附于宿主血管内皮细胞和红细胞。这种黏附是由一个称为PfEMP1的寄生虫多结构域变异蛋白大家族(约60个成员)介导的。它们在IE的表面上以一种相互排斥的方式表达。IE粘连可能导致严重并发症，包括脑型疟疾、妊娠疟疾、严重贫血和呼吸窘迫，这些都是疟疾死亡的主要原因。严重疟疾发作很罕见，一生中几乎从来不会超过1到2次。这一流行病学支持了我们的第一个假设，即只有数量有限的寄生虫株可能是严重疾病的来源，这些寄生虫株可能表达决定特定寄生虫黏附的PfEMP1特定变体。免疫分析血清对不同抗原的反应性是评估获得性免疫和识别潜在候选疫苗的重要方法。然而，将免疫反应与疟疾耐药性联系起来并不简单，因为暴露于疟疾的人通常在一生中反复感染，并对多种抗原产生多样化的免疫反应，在许多情况下与疾病严重程度没有可理解的相关性。我们的第二个假设是，抑制IE与宿主受体黏附的功能性抗体反应可能与预防严重疟疾有更强的关联。对孕期疟疾的广泛研究有力地支持了我们的两个假设。在我们之前的工作中，我们收集了数千份血清样本，这些样本是对生活在非洲疟疾流行区的儿童进行的纵向队列研究中获得的。我们还构建了具有功能的全基因组PfEMP1结构域阵列，并用它们来识别与疟疾中两个主要黏附宿主受体(ICAM1和CD36)特异结合的结构域。我们进一步证明，使用我们的多路高通量样本保留平台，可以在血浆样本中定量总抗结构域抗体和功能性抗体(阻断PfEMP1结构域与其受体的粘连)。为了更好地了解严重疟疾中的保护性体液免疫反应，我们提出了以下具体目标：1)测定血清对PfEMP1结构域的总IgG反应性，并测定抑制CD36和ICAM1受体与相关PfEMP1结构域结合的功能性血清活性。我们将检测大约5000份儿童血清，其中包括大约200-400例严重疟疾病例。2)确定的针对PfEMP1结构域的抗体反应(总的和功能的)与疾病参数和对严重疾病的保护相关联。我们将使用目标1中获得的纵向数据进行广泛的统计分析。这将是第一次全基因组范围的血清反应性研究和针对PfEMP1蛋白的功能性免疫反应的全面研究。这项研究可能为开发针对严重疟疾的疫苗提供候选方案。 公共卫生相关性：这项工作的长期目标是确定候选疫苗，以预防由恶性疟原虫引起的严重疟疾综合征。这些综合症每年导致100多万非洲儿童死亡。寄生虫在血管系统中的特异性黏附介导了这些严重的并发症。在受感染的红细胞表面表达的各种宿主内皮受体和寄生虫PfEMP1蛋白的结构域负责这种粘连。在大多数儿童中，自然形成的免疫力可以预防严重的疾病。天然免疫球蛋白抑制黏附可能是其保护因素之一。在这项建议中，我们将使用在东非流行地区收集的5000份儿童血清，测量针对一组全基因组PfEMP1蛋白的宿主免疫反应(免疫球蛋白G反应性和对两个主要宿主受体的粘附性的抑制)。这些测量的免疫反应将与各种疾病参数相关联，以了解保护和识别PfEMP1结构域，这些结构域可以进一步开发成针对严重疟疾的疫苗。

DESCRIPTION (provided by applicant): The long-term aim of this work is to identify vaccine candidates to prevent severe malaria syndromes through understanding natural protective immune response. Plasmodium falciparum parasite-infected erythrocytes (IE) adhere to the host endothelium and to red blood cells. The adhesion is mediated by a large family (~60 members) of parasite multidomain variant proteins called PfEMP1. They express on the surface of IE in a mutually-exclusive manner. IE adhesion may result in severe complications including cerebral malaria, pregnancy malaria, severe anemia and respiratory distress, major contributors to malaria mortality. Severe malaria episodes are rare and almost never occur more than 1 or 2 times in a lifetime. This epidemiology supports our first hypothesis that only a limited number of parasite lines, possibly expressing particular variants of PfEMP1 that determine specific parasite adhesion, may be the source of severe disease. Immunological profiling of sera for reactivity against different antigens is an important method for assessing acquired immunity and identifying potential vaccine candidates. However, relating immune responses to malaria resistance is not straightforward since exposed individuals are typically infected repeatedly throughout life, and develop diversified immune responses against multiple antigens, in many cases without comprehensible relevance to disease severity. Our second hypothesis is that functional antibody responses that inhibit adhesion of IE to host receptors are likely to have a stronger association to protection from severe malaria. Extensive studies in pregnancy malaria strongly support both our hypotheses. During our previous work we collected thousands of serum samples obtained in longitudinal cohort studies of children living in malaria endemic areas of Africa. We also constructed functional genome-wide PfEMP1 domain arrays and used them to identify domains that bind specifically to the two main adhesion host receptors in malaria (ICAM1 and CD36). We further demonstrated that total anti-domain IgG and functional antibodies (that block adhesion of PfEMP1 domain to its receptor) can be quantified in the plasma samples using our multiplexed high throughput sample-sparing platform. To better understand the protective humoral immune responses in severe malaria, we propose the following specific aims: 1) Measure serum total IgG reactivity against a genome-wide array of PFEMP1 domains, and measure functional serum activity that inhibits CD36 and ICAM1 receptor binding to relevant PFEMP1 domains. We will test about 5000 children's sera including ~200-400 severe malaria cases. 2) Associate defined antibody responses (total and functional) against PfEMP1 domains with disease parameters and protection against severe disease. We will perform a broad range of statistical analyses using the longitudinal data obtained in Aim 1. This would be the first genome-wide study of seroreactivity and a comprehensive study of functional immune responses against PfEMP1 proteins. This study may provide candidates for development of vaccines against severe malaria. PUBLIC HEALTH RELEVANCE: The long-term aim of this work is to identify vaccine candidates to prevent severe malaria syndromes caused by Plasmodium falciparum. These syndromes kill over 1 million African children each year. Specific adhesion of parasites in vasculature mediates these severe complications. Various host endothelial receptors and domains of parasite PfEMP1 proteins that express on the surface of infected red blood cells are responsible for this adhesion. In most children naturally developed immunity prevents severe disease. Inhibition of adhesion by natural IgG might be one of the protective factors. In this proposal we will measure host immune responses (IgG reactivity and inhibition of adhesion to the two main host receptors) against a genome-wide array of PfEMP1 proteins using 5000 children's sera collected in endemic areas in East Africa. These measured immune responses will be associated with various disease parameters to understand protection and to identify PfEMP1 domains that can be developed further into vaccines directed against severe malaria.