Effector and regulatory T cell responses and protection from clinical malaria

描述(申请人提供)：迫切需要一种有效的疟疾疫苗，但由于我们对疟疾免疫的潜在机制了解有限，以及缺乏可靠的体外保护相关因素，阻碍了实现这一目标的进展。最近的研究表明，对疟疾的保护性免疫可以通过在抗疟疾药物的“覆盖”下实验感染活的子孢子来实现，这种药物根除了血液期的寄生虫，但允许红细胞前寄生虫期的发展。该方案诱导CD4T细胞产生IL-2、肿瘤坏死因子α和干扰素γ，并导致无菌保护，使其免受持续至少两年的同源挑战。在之前的资助期，我们测试了这一假设 这种化学预防加上自然暴露于疟疾，在高地方性环境下给儿童提供类似的保护，利用乌干达对幼儿每月给予双氢青蒿素-哌喹(DP)化学预防的随机试验。我们发现，在干预结束后的一年随访中，高度坚持每月DP的儿童对自然发生的疟疾病毒株表现出持续的保护作用。被随机分配到DP组的儿童出现了较高的疟疾特异性CD4T细胞共产生IL-2/肿瘤坏死因子α的频率，这与预期的保护有关，而CD4细胞共产生IL10/干扰素γ的频率较低，与增加风险有关。这些数据表明，CD4T细胞反应的功能质量受到化学预防的影响，是保护性免疫的关键决定因素。在更新期，我们希望通过利用目前正在进行的一项新试验的样本和数据，更全面地表征与保护相关的T细胞反应的功能、表型和转录差异。在该试验中，孕妇和她们的婴儿被随机分配，在怀孕期间和生命的前两年每月接受DP化学预防。我们将评估慢性疟疾抗原暴露如何影响CD4T细胞和Vδ2+γδT细胞，这是一种对疟疾抗原具有内在反应性的半天然淋巴细胞群体。在第一个目标中，我们将表征每月接受DP化学预防的儿童中与预防疟疾相关的CD4T细胞反应，并确定疟疾特异性CD4细胞的表型、功能和转录程序如何受到慢性疟疾抗原暴露的影响。在第二个目标中，我们将确定疟疾暴露对Vγ9Vδ2T细胞群的影响，包括它们的频率、分化状态、克隆型组成以及激活和抑制NK受体(NKR)的表达。我们还将研究NKR表达对疟疾抗原功能反应性的影响。在第三个目标中，我们将测量疟疾特异性T细胞反应(CD4和Vγ9Vδ2)与对恶性疟原虫寄生虫病和症状性疟疾的保护之间的关系。这些研究将解决我们对疟疾保护性免疫潜在的细胞和分子机制理解上的根本差距，并可能为在怀孕或早期婴儿期间实施疟疾化学预防提供强有力的公共卫生理由。

DESCRIPTION (provided by applicant): An effective malaria vaccine is urgently needed, but progress toward this goal has been hindered by our limited understanding of the mechanisms underlying immunity to malaria and a lack of reliable in vitro correlates of protection. It has recently been shown that protective immunity to malaria can be achieved by experimental infection with viable sporozoites under "cover" of antimalarial drugs that eradicate blood-stage parasites but allow the pre-erythrocytic parasite stages to develop. This regimen induces CD4 T cells that produce IL-2, TNFα, and IFNγ and results in sterile protection from homologous challenge that persists for at least 2 years. In the prior funding period, we tested the hypothesis that chemoprevention coupled with natural exposure to malaria could yield similar protection when given to children in a high endemnicity setting, leveraging a randomized trial of monthly dihydroartemisinin-piperaquine (DP) chemoprevention given to young children in Uganda. We found that children highly adherent to monthly DP exhibited sustained protection against naturally occurring malaria strains during one year of follow-up after the intervention ended. Children randomized to DP developed higher frequencies of malaria-specific CD4 T cells co-producing IL-2/TNFα, which were associated with prospective protection, and lower frequencies of CD4 cells co-producing IL10/IFNγ, which were associated with increased risk. These data suggest that the functional quality of the CD4 T cell response is influenced by chemoprevention and is a critical determinant of protective immunity. In the renewal period, we wish to more fully characterize the functional, phenotypic, and transcriptional differences in T cell responses associated with protection by leveraging samples and data from a new trial, currently underway, in which pregnant women and their infants are randomized to receive monthly DP chemoprevention during pregnancy and the first 2 years of life. We will assess how chronic malaria antigen exposure impacts both CD4 T cells and Vδ2+ γδ T cells, a semi-innate lymphocyte population with intrinsic reactivity to malaria antigens. In the first aim, we will characterize CD4 T cell responses associated with protection from malaria in children receiving monthly DP chemoprevention, and determine how the phenotype, function, and transcriptional program of malaria-specific CD4 cells is impacted by chronic malaria antigen exposure. In the second aim, we will determine how malaria exposure impacts the Vγ9Vδ2 T cell population, including their frequency, differentiation status, clonotype composition, and expression of activating and inhibitory NK receptors (NKRs). We will also examine the impact of NKR expression on functional responsiveness to malaria antigens. In the third aim, we will measure associations between malaria-specific T cell responses (CD4 and Vγ9Vδ2) and protection from P. falciparum parasitemia and symptomatic malaria. These studies will address fundamental gaps in our understanding of the cellular and molecular mechanisms underlying protective immunity to malaria, and could provide a strong public health rationale for implementing malaria chemoprevention during pregnancy or early infancy.