General and individualized changes in T cell immunity during aging.

Functional alterations with age are observed in all human systems, but the aging of the adaptive immune system displays both general changes affecting all individuals, and idiosyncratic changes that are unique to individuals. In the T cell compartment, general aging manifests in three ways: (1) the reduction of naïve T cells, (2) the accumulation of differentiated memory T cells, and (3) a reduced overall T cell receptor (TCR) repertoire. Idiosyncratic impacts of aging, such as changes in the TCR repertoires of altered memory and naïve T cells are shaped by each person's life exposures. Recent advancements in single-cell sequencing provide new information including the identification of new subpopulations of T cells, characteristics of transcriptome changes in T cells and their TCR clonotype with age, and measurement of individual cell age. Here, we focus on the changes in T cell subpopulations, transcriptomes and TCR repertoires in overall and antigen-specific T cell population with aging.