Comparison of young and aged mouse CD8 TN, TVM and TMEM cells directly ex vivo and after polyclonal stimulation

The overall study (Quinn et al. Cell Reports, 2018) aimed to understand why CD8 virtual memory T (TVM) cells become markedly less proliferative in response to TCR-driven signals with increasing age, whereas CD8 true naive (TN) cells maintain their proliferative capacity. Age-associated decreases in primary CD8+ T cell responses occur, in part, due to direct effects on naïve CD8++ T cells to reduce intrinsic functionality, but the precise nature of this defect remains undefined. Ageing also causes accumulation of antigen-naïve but semi-differentiated “virtual memory” (TVM) cells but their contribution to age-related functional decline is unclear. Here, we show that TVM cells are poorly proliferative in aged mice and humans, despite being highly proliferative in young individuals, while conventional naïve T cells (TN cells) retain proliferative capacity in both aged mice and humans. Adoptive transfer experiments in mice illustrated that naïve CD8 T cells can acquire a proliferative defect imposed by the aged environment but age-related proliferative dysfunction could not be rescued by a young environment. Molecular analyses demonstrate that aged TVM cells exhibit a profile consistent with senescence, marking the first description of senescence in an antigenically naïve T cell population.