Tfh responses to novel vaccine candidates and protection from pediatric falciparum malaria

摘要 我们的总体目标是通过鉴定PfSEA-1， 广泛反应性的PfSEA-1特异性T滤泡辅助（Tfh）表位，其对于长寿命抗体至关重要 应答 在之前的R 01资助的研究中，我们发现了裂殖体出口抗原-1（PfSEA-1），一种244-kDa的寄生虫 抗体的目标抗原，抗体能将寄生虫捕获在前体阶段。主动接种， rPbSEA-1导致寄生虫血症减少3倍，并且在用P. 伯氏ANKA寄生虫（P = 0.001）。我们坦桑尼亚出生队列中的儿童（N=785）经历了 在检测不到抗PfSEA-1抗体期间，严重疟疾的发病率急剧增加 与可检测抗体水平的时期（0例/1 688名儿童）相比， 3周;调整OR 4.4; III型固定效应P < 0.01）。在我们的肯尼亚男性队列（12-35岁，N= 138）中， 具有可检测的抗PfSEA-1 IgG抗体的个体与具有可检测的抗PfSEA-1 IgG抗体的个体相比， 在18周的高传播中，未检测到抗PfSEA-1 IgG抗体的个体（P < 0.04） 赛季这项工作最终在《科学1》上发表了一篇全面的、完整的研究文章。 疟疾疫苗开发的一个主要障碍是用免疫球蛋白产生高滴度的功能性抗体。 诱导长寿命血浆和记忆B细胞。在过去的10年里，Tfh细胞被认为是 对体细胞超变、同种型转换、生发中心形成、长寿浆细胞至关重要 形成以及存储器B单元形成2.有趣的是，在人类疟疾中唯一的Tfh细胞报告中 感染，在急性疟疾感染期间观察到Tfh细胞的CXCR 3亚群的无效激活 这种缺陷可能是造成早期抗疟抗体反应不良的原因。 童年3.基于Tfh细胞的已知功能及其在产生保护性抗体中的作用， 针对疫苗抗原4、5的应答，鉴定Tfh表位对于疟疾疫苗优化是必要的。 在本申请中，我们提出使用以下方法来定位PfSEA-1中的Tfh刺激性MHC II类T细胞表位： 重组蛋白以及重叠肽方法。我们将初步确定所有可能的 肽特异性表位在半免疫成人的横截面样品。然后我们将抗体， 细胞因子和T细胞亚群对这些表位的反应，在纵向队列中对感染具有抗性 在生活在肯尼亚西部完全流行地区的2-7岁儿童中进行的研究。 本研究的可交付成果将是新的出口阻断中经验证的T细胞表位列表。 候选疫苗PfSEA-1和抗体之间关系的全面、前瞻性分析， 细胞因子和T细胞亚群对这些表位的应答以及对恶性疟原虫感染的抗性。这些 数据将使我们能够通过以下方法增强第二代基于rPfSEA-1A的疫苗的免疫原性 广泛反应性T细胞表位从侧翼区，或增加T细胞表位的拷贝数 在AA 810-1083区域内。此外，这些结果将大大增加我们对角色的理解 和小儿疟疾感染期间Tfh细胞反应的动力学。

ABSTRACT Our overall aim is to advance PfSEA-1 as a vaccine candidate for pediatric falciparum malaria by identifying broadly reactive, PfSEA-1 specific T follicular helper (Tfh) epitopes, which are critical for long-lived antibody responses. In previous R01 funded studies, We discovered Schizont Egress Antigen-1 (PfSEA-1), a 244-kDa parasite antigen that is the target of antibodies which arrest parasites at the schizont stage. Active vaccination with rPbSEA-1 results in a 3-fold reduction in parasitemia and a 2 fold longer survival time after challenge with P. berghei ANKA parasites (P = 0.001). Children in our Tanzanian birth cohort (N=785) 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). In our cohort of Kenyan males (12-35 yrs old, N= 138), individuals with detectable anti-PfSEA-1 IgG antibodies had 50% decreased parasite density compared to individuals with undetectable anti-PfSEA-1 IgG antibodies (P < 0.04) over an 18-week high transmission season. This work has culminated in a comprehensive, full length Research Article in Science 1. A major obstacle to malaria vaccine development is the generation of high-titer functional antibodies with the induction of long-lived plasma and memory B-cells. In the past 10 yrs, Tfh cells have been recognized as essential for somatic hypermutation, isotype switching, germinal center formation, long lived plasma cell formation as well as memory B cell formation 2. Intriguingly, in the only report of Tfh cells in human malaria infection, inefficient activation of the CXCR3- subset of Tfh cells was observed during acute malaria infections in children, and this defect may be responsible for the poor anti-malarial antibody responses seen in early childhood 3. Based on the known function of Tfh cells and their role in generating protective antibody responses to vaccine antigens 4, 5, identifying Tfh epitopes is essential for malaria vaccine optimization. In the current application, we propose to map Tfh stimulating, MHC Class II T cell epitopes in PfSEA-1 using both recombinant protein as well as overlapping peptide approaches. We will initially identify all possible peptide specific epitopes in a cross-sectional sample of semi-immune adults. We will then relate antibody, cytokine, and T-cell subset responses to these epitopes with resistance to infection in a longitudinal cohort study conducted in 2-7 yr old children living in a holoendemic region of western Kenya. The deliverables from this study will be a list of validated T cell epitopes within the novel egress blocking vaccine candidate PfSEA-1 and a comprehensive, prospective analysis of the relationship between antibody, cytokine and T-cell subset responses to these epitopes and resistance to infection with P. falciparum. These data will allow us to enhance the immunogenicity of second generation rPfSEA-1A based vaccines by including broadly reactive T cell epitopes from the flanking regions, or increasing the copy number of T-cell epitopes within the aa 810-1083 region. In addition, these results will significantly increase our understanding of the role and kinetics of Tfh cell responses during pediatric malaria infections.