Clonal structure and dynamics of human memory B cells and circulating plasmablasts

Using single cell sequencing of multi-year serial blood samples from two healthy donors we found that the memory B cell repertoire was dominated by large clonal families producing IgM, IgG2 and IgA, of which 0.2% share nearly identical VH/VL sequences in different individuals. In contrast, IgG1 families, including those encoding antibodies to T-dependent antigens, were of small size. Longitudinal samples collected over a period of several years showed the overall stability of the memory B cell pool in all its subsets. Surprisingly, clonotype stability was also found in serial samples of circulating plasma cells that largely overlapped with long-term memory B cells and contained recurrent clonotypes of IgA and IgG2 and, at lower frequency, IgG1 specific for recall antigens. Collectively, this study provides a global view of the structure, stability and dynamics of the human memory B cell pool and reveal that a large fraction of the clonal families is active at any time point in the generation of plasma cells involving both T independent and T dependent responses. Overall design: Single cell immune profiling (gene expression) of plasma cells from healthy human donor

本研究针对两名健康供体的多年系列血液样本开展单B细胞测序（single cell sequencing），结果显示记忆B细胞库（memory B cell repertoire）以产生IgM、IgG2与IgA的大型克隆家族（clonal families）为主要构成；其中0.2%的克隆家族在不同个体中拥有几乎完全一致的VH/VL（可变重链/可变轻链）序列。与之形成鲜明对比的是，包括编码T细胞依赖性抗原抗体家族在内的IgG1克隆家族，其规模普遍偏小。通过对多年间收集的纵向样本进行分析，我们发现所有亚群的记忆B细胞池（memory B cell pool）整体保持稳定。令人意外的是，循环浆细胞（circulating plasma cells）的系列样本中同样存在克隆型（clonotype）稳定性；这类浆细胞在很大程度上与长期记忆B细胞存在重叠，且包含IgA与IgG2的复发性克隆型，以及频率较低的、针对回忆抗原（recall antigens）的IgG1克隆型。综上，本研究全面呈现了人类记忆B细胞池的结构、稳定性与动态变化特征，并揭示：在同时涉及T细胞非依赖性与T细胞依赖性应答的浆细胞生成过程中，绝大多数克隆家族在任意时间点均处于活跃状态。整体实验设计：针对健康人类供体浆细胞的单细胞免疫谱分析（gene expression）。