Single-cell atlas of healthy human blood unveils age-related loss of NKG2C⁺GZMB⁻CD8⁺ memory T cells and accumulation of type 2 memory T cells

Extensive, large-scale single-cell profiling of healthy human blood at different ages is one of the critical pending tasks required to establish a framework for the systematic understanding of human aging. Here, using single-cell RNA/T cell receptor (TCR)/BCR-seq with protein feature barcoding, we profiled 317 samples from 166 healthy individuals aged 25-85 years old. From this, we generated a dataset from ∼2 million cells that described 55 subpopulations of blood immune cells. Twelve subpopulations changed with age, including the accumulation of GZMK⁺CD8⁺ T cells and HLA-DR⁺CD4⁺ T cells. In contrast to other T cell memory subsets, transcriptionally distinct NKG2C⁺GZMB⁻CD8⁺ T cells counterintuitively decreased with age. Furthermore, we found a concerted age-associated increase in type 2/interleukin (IL)4-expressing memory subpopulations across CD4⁺ and CD8⁺ T cell compartments (CCR4⁺CD8⁺ Tcm and Th2 CD4⁺ Tmem), suggesting a systematic functional shift in immune homeostasis with age. Our work provides novel insights into healthy human aging and a comprehensive annotated resource.