Malaria Group, International Centre for Genetic Engineering and Biotechnology, New Delhi, India.
Infect Immun. 2013 Feb;81(2):441-51. doi: 10.1128/IAI.01107-12. Epub 2012 Nov 26.
Blood-stage malaria vaccines that target single Plasmodium falciparum antigens involved in erythrocyte invasion have not induced optimal protection in field trials. Blood-stage malaria vaccine development has faced two major hurdles, antigenic polymorphisms and molecular redundancy, which have led to an inability to demonstrate potent, strain-transcending, invasion-inhibitory antibodies. Vaccines that target multiple invasion-related parasite proteins may inhibit erythrocyte invasion more efficiently. Our approach is to develop a receptor-blocking blood-stage vaccine against P. falciparum that targets the erythrocyte binding domains of multiple parasite adhesins, blocking their interaction with their receptors and thus inhibiting erythrocyte invasion. However, with numerous invasion ligands, the challenge is to identify combinations that elicit potent strain-transcending invasion inhibition. We evaluated the invasion-inhibitory activities of 20 different triple combinations of antibodies mixed in vitro against a diverse set of six key merozoite ligands, including the novel ligands P. falciparum apical asparagine-rich protein (PfAARP), EBA-175 (PfF2), P. falciparum reticulocyte binding-like homologous protein 1 (PfRH1), PfRH2, PfRH4, and Plasmodium thrombospondin apical merozoite protein (PTRAMP), which are localized in different apical organelles and are translocated to the merozoite surface at different time points during invasion. They bind erythrocytes with different specificities and are thus involved in distinct invasion pathways. The antibody combination of EBA-175 (PfF2), PfRH2, and PfAARP produced the most efficacious strain-transcending inhibition of erythrocyte invasion against diverse P. falciparum clones. This potent antigen combination was selected for coimmunization as a mixture that induced balanced antibody responses against each antigen and inhibited erythrocyte invasion efficiently. We have thus demonstrated a novel two-step screening approach to identify a potent antigen combination that elicits strong strain-transcending invasion inhibition, supporting its development as a receptor-blocking malaria vaccine.
针对红细胞入侵过程中涉及的单一疟原虫抗原的血阶段疟疾疫苗在现场试验中并未诱导出最佳保护效果。血阶段疟疾疫苗的开发面临两个主要障碍,即抗原多态性和分子冗余性,这导致无法证明具有强大、跨株、抑制入侵的抗体。针对多个入侵相关寄生虫蛋白的疫苗可能更有效地抑制红细胞入侵。我们的方法是开发一种针对恶性疟原虫的受体阻断性血阶段疫苗,该疫苗针对多种寄生虫黏附蛋白的红细胞结合域,阻断其与受体的相互作用,从而抑制红细胞入侵。然而,由于存在众多的入侵配体,挑战在于确定能产生强大跨株入侵抑制的组合。我们评估了 20 种不同的三联抗体混合物在体外对一组 6 种关键裂殖子配体的抑制入侵活性,包括新型配体恶性疟原虫顶膜富含天冬氨酸蛋白(PfAARP)、EBA-175(PfF2)、恶性疟原虫网织红细胞结合样同源蛋白 1(PfRH1)、PfRH2、PfRH4 和恶性疟原虫血小板结合蛋白顶膜微线蛋白(PTRAMP),这些配体位于不同的顶质体中,并在入侵过程中不同时间点被转运到裂殖子表面。它们与红细胞的结合具有不同的特异性,因此参与不同的入侵途径。EBA-175(PfF2)、PfRH2 和 PfAARP 的抗体组合对多种恶性疟原虫克隆的红细胞入侵产生了最有效的跨株抑制作用。这种有效的抗原组合被选为共免疫混合物,能诱导针对每种抗原的平衡抗体反应,并有效地抑制红细胞入侵。因此,我们展示了一种新的两步筛选方法来鉴定一种能产生强大跨株入侵抑制作用的有效抗原组合,支持其作为受体阻断性疟疾疫苗的开发。