T follicular helper (T_FH) cells play a crucial role in the development of long-lived, quality-improved B cell responses after infection and vaccination. However, little is known about their clonal evolution. Here we assessed the cell phenotype, clonal dynamics, and TCR specificity of human circulating T_FH (cT_FH) cells at monoclonal level during successive malaria immunizations with radiation-attenuated Plasmodium falciparum (Pf) sporozoites. Repeated parasite exposures induced a dynamic, polyclonal cT_FH response with high frequency of cells specific to the Pf circumsporozoite protein (PfCSP), the main surface protein of sporozoites and a validated vaccine target. Repeated immunizations were required to induce detectable PfCSP-reactive cT_FH cell responses to a small number of epitopes. HLA-restrictions and differences in TCR generation probability explain the high targeting frequency of the polymorphic Th2R/T* region over the conserved T1 epitope. The vast majority of anti-Th2R/T* TCRs failed to tolerate natural polymorphisms in their target peptide sequence suggesting that parasite diversity limits natural boosting of the cT_FH cell response in endemic areas and protection from non-vaccine strains. Among convergent anti-Th2R/T* TCRs with high sequence similarity, subtle differences in CDR3 composition discriminated cross-reactive from non-cross-reactive cT_FH cells. Thus, our study provides deep molecular and cellular insights into the kinetics, fine specificity and HLA-restrictions of the anti-cT_FH cell response that are of direct relevance for the design of PfCSP-based malaria vaccines by guiding the selection of PfCSP peptides that induce optimal B cell help.

中文翻译：

---

人 T 滤泡辅助细胞对恶性疟原虫环子孢子蛋白反应的克隆进化和特异性

T 滤泡辅助 (T _FH ) 细胞在感染和疫苗接种后长寿命、质量改善的 B 细胞反应的发展中起着至关重要的作用。然而，人们对它们的克隆进化知之甚少。在这里，我们评估了单克隆水平的人类循环 T _FH (cT _FH ) 细胞在使用辐射减毒恶性疟原虫( Pf ) 子孢子进行连续疟疾免疫期间的细胞表型、克隆动力学和 TCR 特异性。重复的寄生虫暴露诱导了动态的多克隆 cT _FH响应，具有高频率的Pf特异性细胞环子孢子蛋白 (PfCSP)，子孢子的主要表面蛋白和经过验证的疫苗靶点。需要重复免疫以诱导可检测的 PfCSP 反应性 cT _FH细胞对少量表位的反应。HLA 限制和 TCR 生成概率的差异解释了多态性 Th2R/T* 区域在保守 T1 表位上的高靶向频率。绝大多数抗 Th2R/T* TCR 无法耐受其靶肽序列中的天然多态性，这表明寄生虫多样性限制了 cT _{FH 的}自然增强流行地区的细胞反应和对非疫苗菌株的保护。在具有高序列相似性的收敛性抗 Th2R/T* TCR 中，CDR3 组成的细微差异区分了交叉反应性和非交叉反应性 cT _FH细胞。因此，我们的研究通过指导 PfCSP 肽的选择，为抗 cT _FH细胞反应的动力学、精细特异性和 HLA 限制提供了深入的分子和细胞见解，这些反应与基于 PfCSP 的疟疾疫苗的设计直接相关。诱导最佳 B 细胞帮助。