Exploiting cross-reactive, conserved epitopes in Plasmodium vivax to develop a vaccine against falciparum placental malaria.

项目概要/摘要 迫切需要一种疫苗来保护孕妇免受疟疾感染和破坏性影响 对母婴健康的影响。两种疫苗处于早期临床试验阶段， VAR 2CSA是疟原虫表达的主要表面抗原， 胎盘恶性疟原虫分离株。这种蛋白质与胎盘中的受体结合，并介导 感染的红细胞（iRBC），支持胎盘疟疾的发病机制。然而，VAR 2CSA 在强免疫选择下是高度多态的;这通过限制 对不同等位基因的保护范围。多态性抗原是一个普遍存在的挑战， 疟疾亚单位疫苗的开发。这个项目的长期目标是开发一种替代品 针对高度保守、亚优势的妊娠相关疟疾疫苗的研究方法 (even隐蔽的）表位。这种方法的独特之处在于，它利用了一种交叉机制， 种免疫，其中来自一个疟原虫种的表位引起稳健的、广泛中和的 针对来自另一物种的结构相关抗原的抗体。这一机制被发现 最近，在哥伦比亚和巴西人群中，可以在体外获得VAR 2CSA抗体， 在感染间日疟原虫后的妊娠中，这些抗体阻断了iRBC的隔离， 胎盘疟疾的体外相关性。将间日疟原虫的交叉反应表位定位于SD 1亚结构域， 在PvDBP和人SD 1中，纯化的抗体阻断寄生虫粘附。该项目的目标是 开发一种疫苗，保护孕妇免受恶性胎盘疟疾的侵害，这种疫苗是基于交叉- 间日疟原虫SD 1中的反应性表位。这将通过合成三个互补的具体 目标。引发功能性交叉反应性抗体所需的表位将在目标1至目标2中鉴定。 用小鼠单克隆抗体（mAb）筛选构象收缩的肽微阵列， 从哥伦比亚研究人群中分离的针对SD 1的人mAb。表位将被合成为肽- 在目的2中，免疫原性将被优化， 产生具有抗表达var 2csa的不同等位基因的寄生虫的功能活性的抗体。在 第三个目的是，将对这些抗体识别的VAR 2CSA中的隐蔽表位进行定位，以鉴定 SD 1衍生疫苗引发的抗体的靶点。这些发现的整合将提供 跨物种表位识别机制的重要见解，这将作为基础 一种对抗恶性胎盘疟疾的间日疟疫苗， 其他疟疾抗原。

PROJECT SUMMARY/ABSTRACT A vaccine is urgently needed to protect pregnant women from malaria infection and the devastating effects of this disease on maternal and child health. Two vaccines are in early stage clinical trials and both target domains within the protein VAR2CSA, which is the major surface antigen expressed by Plasmodium falciparum placental isolates. This protein binds to receptors in the placenta and mediates sequestration of infected red blood cells (iRBCs), underpinning the pathogenesis of placental malaria. However, VAR2CSA is under strong immune selection and is highly polymorphic; this compromises vaccine efficacy by limiting the breadth of protection against diverse alleles. Polymorphic antigens present a ubiquitous challenge in the development of malaria subunit vaccines. The long-term goal of this project is to develop an alternative approach to a vaccine against pregnancy-associated malaria that targets highly conserved, subdominant (even cryptic) epitopes. What is unique about this approach is that it exploits a mechanism of cross- species immunity, where epitopes from one Plasmodium species elicit robust, broadly neutralizing antibodies against structurally related antigens from another species. This mechanism was discovered recently in Colombian and Brazilian populations where VAR2CSA antibodies can be acquired outside of pregnancy following infection with P. vivax, and these antibodies blocked sequestration of iRBCs using in vitro correlates of placental malaria. The cross-reactive epitope in P. vivax was mapped to subdomain (SD1) in PvDBP and human SD1-purified antibodies blocked parasite adhesion. The objective of this project is to develop a vaccine to protect pregnant women from falciparum placental malaria that is based on the cross- reactive epitope in vivax SD1. This will be achieved through synthesis of three complementary Specific Aims. Epitopes required to elicit functional, cross-reactive antibodies will be identified in Aim 1 through conformationally constricted peptide microarrays screened with mouse monoclonal antibodies (mAbs) and human mAbs to SD1 isolated from Colombian study populations. Epitopes will be synthesized as peptide- conjugates or within engineered recombinant domains, and immunogenicity will be optimized in Aim 2 to produce antibodies with functional activity against parasites that express diverse alleles of var2csa. In the third Aim, the cryptic epitopes in VAR2CSA recognized by these antibodies will be mapped to identify the targets of antibodies elicited by an SD1-derived vaccine. The integration of these findings will provide important insight into the mechanism of cross-species epitope recognition, which will serve as the basis for a vivax vaccine against falciparum placental malaria and could be applied more broadly to vaccines against other malaria antigens.