Multidimensional single-cell analysis of human peripheral blood reveals characteristic features of the immune system landscape in aging and frailty

Frailty is an intermediate status of human ageing process, associated with decompensated homeostasis and death. The immune phenotype of frailty and its underlying cellular and molecular processes remain poorly understood. Here we profiled 114,467 immune cells from cord blood, young adults, healthy and frail elderly using single-cell RNA and TCR V(D)J sequencing. An age-dependent accumulation of cell heterogeneity and transcriptome variability in defined immune cell types was observed. With the specific expression of gene sets, characteristic transcription factors were identified in given immune cell types of certain age group. Trajectory analysis revealed cells from non-frail and frail elderly often fall into distinct trajectories, despite similar chronological age. Numerous TCR clonotypes were shared among T cell subtypes in aged and frail samples, indicating differential pluripotency and resilience capability of aged T cells. Finally, a frailty-specific monocyte subset was identified with exclusively high expression of lncRNAs NEAT1 and MALAT1. Our results discover human frailty-specific immune cell characteristics based on the comprehensive dimensions in immune landscape of ageing and frailty. Overall design: Three cord blood samples, PBMC samples from 3 healthy young, 6 healthy old and 5 frail donors were used for single-cell RNA, TCR and cell surface protein (CCR7, CD45RA, CD4 and CD8) antibody barcoded sequencing to create a single-cell transcriptome and TCR atlas from newborns to frailty.

衰弱（frailty）是人类衰老进程中的中间状态，与稳态失代偿及死亡密切相关。目前对于衰弱的免疫表型及其潜在的细胞与分子机制，仍知之甚少。本研究采用单细胞RNA测序与T细胞受体（TCR）V(D)J测序技术，对脐带血、健康青年、健康老年及衰弱老年个体的114467个免疫细胞进行了表征分析。研究观察到，在特定免疫细胞亚群中，细胞异质性与转录组差异随年龄增长呈现累积态势。通过基因集的特异性表达特征，在特定年龄组的特定免疫细胞亚群中，鉴定得到了特征性转录因子。轨迹分析显示，尽管实际年龄相近，但非衰弱老年与衰弱老年个体的免疫细胞往往处于不同的分化轨迹之中。老年及衰弱样本的T细胞亚群间共享大量TCR克隆型，提示衰老T细胞的增殖潜能与恢复能力存在差异。最终，研究鉴定出一个衰弱特异性单核细胞亚群，该亚群特异性高表达长链非编码RNA（long non-coding RNA，lncRNA）NEAT1与MALAT1。本研究通过全面解析衰老与衰弱的免疫景观多维度特征，揭示了人类衰弱特异性的免疫细胞特征。实验设计：本研究共纳入3份脐带血样本、3份健康青年外周血单个核细胞（peripheral blood mononuclear cell，PBMC）样本、6份健康老年PBMC样本以及5份衰弱老年供者的PBMC样本，通过单细胞RNA测序、TCR测序以及针对细胞表面蛋白CCR7、CD45RA、CD4与CD8的抗体条形码测序，构建了从新生儿到衰弱个体的单细胞转录组与TCR图谱。