PfSEA-1 based vaccines for falciparum malaria

描述（由申请人提供）：本申请的总体目标是推进PfSEA-1作为恶性疟疾的候选疫苗。恶性疟原虫疟疾是发展中国家发病率和死亡率的主要原因，每年在撒哈拉以南非洲感染数亿人并杀死100多万儿童。 在以前的R 01资助的研究中，我们确定了自然获得的保护性人类抗体的寄生虫靶标。我们应用我们的差异，全蛋白质组筛选方法，使用来自坦桑尼亚出生队列儿童的血浆和流行病学数据，以确定与2岁儿童耐药相关的新型恶性疟原虫抗原。这项工作最终形成了一个全面的，完整的科学研究文章。 我们发现裂殖体出口抗原-1（PfSEA-1），一种244-kDa的寄生虫抗原，其定位于裂殖体/寄生虫空泡膜、Maurer裂和裂殖体感染的RBC中的RBC膜的内小叶。与对照相比，PfSEA-1（rPfSEA-1A，aa 810- 1083）的中心高度不变的274 aa区域的抗体通过阻止鞭毛破裂而使三种寄生虫菌株中的寄生虫复制降低58-75%（所有P < 0.009）。在遗传不稳定实验中，具有不稳定PfSEA- 1的寄生虫在寄生虫复制中具有显著的4.9倍缺陷（P < 0.001）。用rPbSEA-1主动接种导致寄生虫血症减少3.9倍，并且在用伯氏疟原虫ANKA寄生虫攻击后存活延长2倍（P = 0.001）。在我们的坦桑尼亚队列中，与可检测到抗体水平的时期（0例/1，688儿童周;调整OR 4.4; III型固定效应P < 0.01）相比，在不可检测到抗PfSEA-1抗体水平的时期（45例/23，806儿童周），严重疟疾的发病率急剧增加。在我们的肯尼亚队列中，具有可检测的抗PfSEA-1抗体的青少年和年轻人与没有可检测的抗PfSEA-1抗体的个体相比，寄生虫血症降低50%。这些结果代表了第一次证明，特异性地阻断嗜酸性粒细胞外出的抗体可以保护人类免受严重疟疾的侵害，并表明PfSEA-1可能与靶向肝细胞和红细胞侵袭的疫苗协同作用。 我们的疫苗发现计划还确定了几个已知的入侵配体（MSP-4和MSP-7 3-统称为MSP）和PfGARP，以前未被识别的候选疫苗只在恶性疟原虫中发现。在体外测定中，多克隆抗MSP-4抑制寄生虫生长22%（P < 0.001），并且当与抗PfSEA-1 mAb组合时，这种抑制增加到67%（P < 0.001）。PfGARP的高度不变的羧基末端的抗体（PfGARP-A，aa 411-673）通过阻止滋养体发育，与对照相比在体外抑制寄生虫生长达99%（P < 0.001）。 在本申请中，我们将在小鼠疫苗试验中评估这些候选疫苗在多种佐剂中的组合，并将在非人灵长类动物中进一步评估先导组合。本研究的可交付成果将是一种佐剂优化的三价疫苗，其靶向寄生虫从单个关键寄生虫阶段进入、细胞内发育和退出。

DESCRIPTION (provided by applicant): The overall aim of this application is to advance PfSEA-1 as a vaccine candidate for falciparum malaria. P. falciparum malaria is a leading cause of morbidity and mortality in developing countries, infecting hundreds of millions of individuals and killing over one million children in sub-Saharan Africa each year. In previous R01 funded studies, we identified the parasite targets of naturally acquired protective human antibodies. We applied our differential, whole proteome screening method using plasma and epidemiologic data from a birth cohort of children living in Tanzania to identify novel Plasmodium falciparum antigens associated with resistance in two-year old children. This work has culminated in a comprehensive, full length Research Article in Science. We discovered Schizont Egress Antigen-1 (PfSEA-1), a 244-kDa parasite antigen which localizes to the schizont/parasitophorous vacuole membrane, Maurer's clefts and the inner leaflet of the RBC membrane in schizont infected RBCs. Antibodies to a central, highly invariant 274 aa region of PfSEA-1 (rPfSEA-1A, aa 810- 1083) decrease parasite replication by 58-75% across three parasite strains compared to controls (all P < 0.009) by arresting schizont rupture. In genetic destabilization experiments, parasites with destabilized PfSEA- 1 had a marked, 4.9 fold defect in parasite replication (P < 0.001). Active vaccination with rPbSEA-1 results in a 3.9 fold reduction in parasitemia and 2 fold longer survival after challenge with P. berghei ANKA parasites (P = 0.001). Children in our Tanzanian cohort experienced a dramatically increased incidence of severe malaria during periods with undetectable anti-PfSEA-1 antibody levels (45 cases/23,806 child weeks) compared to periods with detectable antibody levels (0 cases/1,688 child weeks; adjusted OR 4.4; Type III fixed effects P < 0.01). Adolescents and young adults in our Kenyan cohort with detectible anti-PfSEA-1 antibodies had 50% lower parasitemia compared to individuals without detectible anti-PfSEA-1 antibodies. These results represent the first demonstration that antibodies that specifically block schizont egress can protect against severe malaria in humans and suggest that PfSEA-1 may synergize with vaccines targeting hepatocyte and red cell invasion. Our vaccine discovery program has also identified several known invasion ligands (MSP-4 and MSP-7 3- collectively referred to as MSPs) and PfGARP, a previously unrecognized vaccine candidate found only in falciparum. In in vitro assays, polyclonal anti-MSP-4 inhibited parasite growth by 22% (P < 0.001) and this inhibition increased to 67% when combined with anti-PfSEA-1 mAb (P < 0.001). Antibodies to the highly invariant carboxyl terminal of PfGARP (PfGARP-A, aa 411-673) inhibited parasite growth in vitro by 99% compared to controls (P < 0.001) by arresting trophozoite development. In this application, we will evaluate combinations of these vaccine candidates in multiple adjuvants in murine vaccine trials and the lead combination will be further evaluated in non-human primates. The deliverables from this study will be an adjuvant optimized tri-valent vaccine that targets the entry, intracellular development, and the exit of the parasite from a single, critical parasite stae.