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作为儿童恶性疟疾的候选疫苗 广泛反应的PfSEA-1特异性T滤泡辅助分子(TFH)表位，这对长寿抗体至关重要 回应。 在之前的R01资助的研究中，我们发现了Schizont Eress抗原-1(PfSEA-1)，一种244 kDa的寄生虫 在裂殖体阶段阻止寄生虫的抗体的靶标的抗原。主动接种疫苗 RPbSEA-1可使寄生虫血症减少3倍，感染P。 Berghei 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 在抗PfSEA-1抗体检测不到的时期，严重疟疾的发病率显著增加 抗体水平(45例/23806儿童周)与可检测到抗体水平的时期(0例/1,688名儿童 周；调整后OR 4.4；III型固定效应P&lt；0.01)。在我们的肯尼亚男性队列中(12-35岁，N=138)， 可检测到的抗PfSEA-1抗体的个体的寄生虫密度比 在18周的高传播期内未检测到抗PfSEA-1抗体(P&lt；0.04)的个人 赛季到了。这项工作在《科学1》杂志上发表了一篇全面、完整的研究文章。 疟疾疫苗开发的一个主要障碍是产生高效价功能性抗体 诱导长寿的血浆和记忆B细胞。在过去的10年里，TFH细胞被认为是 体细胞高度突变、同型转换、生发中心形成、浆细胞长寿所必需的 以及记忆B细胞的形成2.有趣的是，在人类疟疾中唯一的TFH细胞报告中 在急性疟疾感染期间，观察到TFH细胞CXCR3亚群的低效激活 这种缺陷可能是早期出现的抗疟疾抗体反应差的原因 儿童时期3.基于已知的TFH细胞的功能及其在产生保护性抗体中的作用 对疫苗抗原4、5的反应，识别TFH表位对于疟疾疫苗的优化至关重要。 在目前的应用中，我们建议使用以下方法来映射PfSEA-1中的TfH刺激的MHC II类T细胞表位 重组蛋白和重叠多肽的方法。我们将初步确定所有可能的 半免疫成人横断面样本中的多肽特异性表位。然后我们将关联抗体， 纵向队列中对这些对感染有抵抗力的表位的细胞因子和T细胞亚群反应 对生活在肯尼亚西部全流行病地区的2-7岁儿童进行了研究。 这项研究的成果将是新的出口阻断内有效的T细胞表位的清单 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反应和对恶性疟原虫感染的抵抗力。这些 数据将允许我们通过包括以下内容来增强基于第二代rPfSEA-1A的疫苗的免疫原性 来自侧翼区域的广泛反应的T细胞表位，或增加T细胞表位的拷贝数 在AA 810-1083区域内。此外，这些结果将显著增加我们对这一角色的理解 以及儿童疟疾感染期间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.