[1, 4, 10] Taken together these data indicate that the duration/strength of TCR ligation check details results in a progressive reinforcement of expression programmes that are downstream of the TCR signal. Fixation of epigenetic modifications and or the expression of unique transcription factors are a likely mechanism for preserving the exhausted state in the absence of antigen (Fig. 1b). Indeed, gene expression profiling studies demonstrate the preservation of many effector transcriptional programmes including persistent down-regulation of several on-off-on genes (Fig. 1b). Consistent with this idea, we have recently reported on preservation of acquired epigenetic modifications at the PD-1 locus

regulatory regions in virus-specific

CD8 T cells during chronic viral infection.[27] Our data demonstrated that the transient up-regulation of PD-1 expression in functional virus-specific CD8 T cells Selleckchem GSK2118436 was coupled to chromatin accessibility, permissive histone modifications, and acquisition of an unmethylated transcriptional regulatory region at the peak of acute viraemia. Following clearance of the acute viral infection, the PD-1 transcriptional regulatory region regained the DNA methylation programme and became less sensitive to DNase challenge. Importantly, the repressive transcriptional programme was not reacquired in virus-specific CD8 T cells during chronic infection of mice and humans.[27] To our surprise, the permissive epigenetic transcriptional programme at the PD-1 locus was retained in PD-1lo cells following reduction in chronic viral load. Preservation of the permissive transcriptional programme facilitated enhanced re-expression of PD-1 relative to functional memory cells that contained the repressive programme at the PD-1 locus.[27] The kinetic analysis of epigenetic regulation of PD-1 during acute and chronic infections as well as analysis of effector molecule regulation during CD4 and CD8 T-cell memory cell differentiation

have set the stage for further analysis of the enzymes that catalyse the epigenetic modifications Niclosamide and their specificity determinates. Further scrutiny of gene regulatory mechanisms related to the identification and function of phenotypically distinct effector and memory T-cell subsets is necessary. Undoubtedly such studies will further clarify when memory cells are generated and how progressive changes in phenotype and function are obtained. Specifically, analysis of epigenetic modifications will provide a snapshot of the differentiation status of effector and memory T cells. Epigenetic profiling of antigen-specific CD4 and CD8 memory T cells will immediately benefit vaccine development as it will provide a novel parameter for identifying poised expression programmes aiding in the assessment of T-cell memory quality.