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动PfSEA-1作为恶性疟疾疫苗候选。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，每年感染数亿人，并导致撒哈拉以南非洲100多万儿童死亡。在之前的R01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，使用来自坦桑尼亚儿童出生队列的血浆和流行病学数据来识别与两岁儿童耐药性相关的新的恶性疟原虫抗原。这项工作最终在《科学》杂志上发表了一篇全面的、全文的研究文章。我们发现裂殖体出口抗原-1(PfSEA-1)是一种244 kDa的寄生虫抗原，定位于裂殖体感染红细胞的裂殖体/寄生虫空泡膜、毛雷氏裂隙和红细胞膜内叶。针对PfSEA-1中心高度不变的274AA区的抗体(rPfSEA-1A，AA810-1083)通过阻止裂殖体断裂，使三种寄生虫株之间的寄生虫复制减少58%-75%。在遗传不稳定实验中，带有不稳定PfSEA-1的寄生虫在寄生虫复制方面有显著的4.9倍缺陷(P&lt；0.001)。主动接种rPbSEA-1可使伯氏疟原虫攻击后小鼠的寄生虫血症降低3.9%，存活时间延长2倍(P=0.001)。我们坦桑尼亚队列中的儿童在抗PfSEA-1抗体水平无法检测到的时期(45例/23,806儿童周)与可检测到抗体水平的时期(0例/1,688儿童周；调整后OR 4.4；III型固定效应P&lt；0.01)相比，严重疟疾的发病率显著增加。在我们的肯尼亚队列中，与没有检测到抗PfSEA-1抗体的人相比，携带可检测到的抗PfSEA-1抗体的青少年和年轻人的寄生虫血症降低了50%。这些结果首次表明，特异性阻断裂殖体出口的抗体可以在人类中预防严重疟疾，并表明PfSEA-1可能与针对肝细胞和红细胞入侵的疫苗协同作用。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，这是一种以前未被识别的候选疫苗，仅在恶性疟原虫中发现。在体外实验中，多克隆抗MSP-4对寄生虫生长的抑制率为22%(P&lt；0.001)，与抗PfSEA-1单抗联合使用时，抑制率增加到67%(P&lt；0.001)。针对PfGARP高度不变的羧基末端的抗体(PfGARP-A，AA411-673)通过阻止滋养体的发育，在体外抑制了寄生虫的生长，与对照组(P&lt；0.001)相比，抑制了99%。在这项应用中，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，并将在非人类灵长类动物中进一步评估领先组合。这项研究的成果将是一种针对寄生虫进入、细胞内发育和离开单一关键寄生虫阶段的佐剂优化三价疫苗。

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.