Single-cell multiomics reveals the distinct properties of neonatal and adult recent thymic emigrants

Following thymic egress, CD8+ T cells must undergo a post-thymic maturation process to transition from a recent thymic emigrant (RTE) to a mature naïve T cell. Since the neonatal T cell pool is comprised of significantly more RTEs, the prevailing notion is that neonatal CD8+ T cells behave differently than their adult counterparts simply because they have undergone less post-thymic maturation. To test this theory, we leveraged a fate mapping mouse model and paired single cell transcriptome and TCR sequencing to compare neonatal and adult CD8+ RTEs that have undergone the same amount of post-thymic maturation. Interestingly, we found that neonatal and adult CD8+ RTEs exhibit distinct phenotypes, gene expression profiles, TCR usage, and functions. These data suggest that neonatal CD8+ T cells are not simply immature adult CD8+ T cells and that age-related changes in CD8+ T cell functions in early life cannot be attributed solely to differences in the amount of post-thymic maturation.