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DNA Methylation Regulates the Differential Expression of CX3CR1 on Human IL-7Rαlow and IL-7Rαhigh Effector Memory CD8+ T Cells with Distinct Migratory Capacities to the Fractalkine

DNA methylation is an epigenetic mechanism that modulates gene expression in mammalian cells including T cells. Memory T cells are heterogeneous populations. Human effector memory (EM) CD8+ T cells in peripheral blood contain two cell subsets with distinct traits that express low and high levels of the IL-7Rα. However, epigenetic mechanisms involved in defining such cellular traits are largely unknown. In this study, we use genome-wide DNA methylation and individual gene expression to show the possible role of DNA methylation in conferring distinct traits of chemotaxis and inflammatory responses in human IL-7Rαlow and IL-7Rαhigh EM CD8+ T cells. In particular, IL-7Rαlow EM CD8+ T cells had increased expression of CX3CR1 along with decreased DNA methylation in the CX3CR1 gene promoter compared with IL-7Rαhigh EM CD8+ T cells. Altering the DNA methylation status of the CX3CR1 gene promoter changed its activity and gene expression. IL-7Rαlow EM CD8+ T cells had an increased migratory capacity to the CX3CR1 ligand fractalkine compared with IL-7Rαhigh EM CD8+ T cells, suggesting an important biological outcome of the differential expression of CX3CR1. Moreover, IL-7Rαlow EM CD8+ T cells induced fractalkine expression on endothelial cells by producing IFN-γ and TNF-α, forming an autocrine amplification loop. Overall, our study shows the role of DNA methylation in generating unique cellular traits in human IL-7Rαlow and IL-7Rαhigh EM CD8+ T cells, including differential expression of CX3CR1, as well as potential biological implications of this differential expression.