Newborn and child-like molecular signatures in older adults stem from TCR shifts across human lifespan

CD8+ T-cells provide robust anti-viral immunity, yet how epitope-specific T-cells evolve across the human lifespan is unknown. We defined CD8+ T-cell immunity directed at the prominent influenza epitope, HLA-A*02:01-M158-66 (A2/M158) across four age groups (newborns, children, adults and elderly) ex vivo at phenotypic, single cell sequence (transcriptomic), clonal and functional levels. We identified a linear differentiation trajectory from newborns to children then adults, followed by divergence and a clonal reset in older adults. Gene profiles in older adults closely resembled those observed in newborns and children, despite being clonally-different. However, only child- and adult-derived A2/M158+CD8+ T-cells had the potential to differentiate into highly cytotoxic epitope-specific CD8+ T-cells, which was linked to highly functional public TCRab-signatures. Suboptimal TCRab-signatures detected in older adults led to poorer proliferation, polyfunctionality, avidity and recognition of peptide mutants, although displayed no signs of exhaustion. Our study suggests that priming T-cells at different stages of life might greatly affect CD8+ T-cell responses towards viral infections. Overall design: human PBMCs derived from newborns, children adults and older adults were stained using the A2/M158 tetramer followed by tetramer associated magnetic enrichment (TAME) and further stained with a larger phenotypic panel. A2/M158-specific cells were isolated based on their tetramer fluorescence using FACS index-sorting and further analyzed using scRNAseq