Age-Related Decline in Primary CD8+ T Cell Responses Is Associated with the Development of Senescence in Virtual Memory CD8+ T Cells.

Age-associated decreases in primary CD8+ T cell responses occur, in part, due to direct effects on naive CD8+ T cells to reduce intrinsic functionality, but the precise nature of this defect remains undefined. Aging also causes accumulation of antigen-naive 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 naive T cells (TN cells) retain proliferative capacity in both aged mice and humans. Adoptive transfer experiments in mice illustrated that naive 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 an observation of senescence in an antigenically naive T cell population.

Distinct epigenetic signatures delineate transcriptional programs during virus-specific CD8(+) T cell differentiation.

The molecular mechanisms that regulate the rapid transcriptional changes that occur during cytotoxic T lymphocyte (CTL) proliferation and differentiation in response to infection are poorly understood. We have utilized ChIP-seq to assess histone H3 methylation dynamics within naive, effector, and memory virus-specific T cells isolated directly ex vivo after influenza A virus infection. Our results show that within naive T cells, codeposition of the permissive H3K4me3 and repressive H3K27me3 modifications is a signature of gene loci associated with gene transcription, replication, and cellular differentiation. Upon differentiation into effector and/or memory CTLs, the majority of these gene loci lose repressive H3K27me3 while retaining the permissive H3K4me3 modification. In contrast, immune-related effector gene promoters within naive T cells lacked the permissive H3K4me3 modification, with acquisition of this modification occurring upon differentiation into effector/memory CTLs. Thus, coordinate transcriptional regulation of CTL genes with related functions is achieved via distinct epigenetic mechanisms.