Two distinct durable human switched memory B cell populations are induced by vaccination and infection

The traditional definition of memory lymphocytes encompasses antigen-experienced, durable subsets that persist in the absence of antigen and are capable of responding to the antigen on subsequent encounters. We examined the relative durability of eight different non-overlapping class-switched human B cell sub-populations (excluding plasmablasts) that together encompass 100% of all human class switched B cells and identified only two long-lived B cell populations that persist after vaccination in the relative absence of their cognate antigen. In addition to canonical switched memory B cells (SWM) with an IgD- CD27+ CXCR5+ phenotype, a second, non-canonical but distinct memory population of IgD- CD27- CXCR5+ (double negative 1, DN1) B cells is also durable. Beyond surface phenotyping, DN1 memory B cells intriguingly exhibit lower levels of replacement mutations in complementarity determining as well as framework regions of their B cell receptors and have longer CDRH3 sequences relative to canonical SWM B cells. This non-canonical, human memory B cell subset is distinguished by a distinct TP63 driven transcriptional signature that has been linked to extended cell survival and these B cells persist in the circulation at least as long as canonical SWM B cells. Non-canonical human DN1 memory B cells therefore represent a second, distinct, durable, less somatically hypermutated, class-switched human memory B cell subset defined by a unique transcriptomic signature, that likely arises outside germinal centers and may have evolved to preserve immunological breadth. Overall design: RNA-seq data of 18 samples, comprised of three groups, N, S, and D, representing three types of cells, i.e., "Naive B", "Switched Memory B", and "DN1 B" cells. Each group has 6 biological replicates.

记忆淋巴细胞（memory lymphocytes）的传统定义为：经抗原致敏后可在无抗原环境中持久存活，并能在再次接触同源抗原时触发应答的细胞亚群。本研究针对覆盖人类全部类别转换B细胞（class-switched B cell）的8种互不重叠的亚群（排除浆母细胞（plasmablasts））开展了持久性分析，最终仅鉴定出两种长寿命B细胞亚群，可在同源抗原相对缺失的疫苗接种后持续存在。除具备IgD⁻CD27⁺CXCR5⁺表型的经典类别转换记忆B细胞（switched memory B cells，SWM）外，第二种非经典但特征明确的记忆亚群——IgD⁻CD27⁻CXCR5⁺（双阴性1型，DN1）B细胞——同样具有持久性。除表面表型特征外，值得关注的是，与经典SWM B细胞相比，DN1记忆B细胞的B细胞受体互补决定区（complementarity determining regions）及框架区（framework regions）的置换突变水平更低，且CDRH3序列更长。该非经典人类记忆B细胞亚群以TP63驱动的独特转录特征为标识，该特征与细胞存活时间延长相关，且这类B细胞在循环系统中的存续时长至少与经典SWM B细胞相当。综上，非经典人类DN1记忆B细胞代表了第二种特征明确、持久存在、体细胞超突变程度更低的人类类别转换记忆B细胞亚群，其以独特的转录组特征为定义依据，大概率起源于生发中心（germinal centers）之外，且可能通过演化获得了维持免疫广度的功能。实验设计：本数据集包含18份RNA测序（RNA-seq）样本，分为N、S、D三组，分别对应初始B细胞（Naive B）、类别转换记忆B细胞（Switched Memory B）与DN1 B细胞三种细胞类型，每组设置6个生物学重复（biological replicates）。