Aging and IL-7-Mediated CD8+ T Cell Survival

Yale University, New Haven CT

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Abstract

DESCRIPTION (provided by applicant): Alterations in the immune system, including T cells, occur with aging, likely contributing to the development of infections and malignancies. Although the latter finding suggests an age-associated decline of the immune system, aging could be regarded as a condition with dysregulated inflammation (inflammaging). In T cell immunity, probably, the most prominent change with aging is the expansion of memory CD8+ T cells in peripheral blood although its exact mechanism(s) and significance are yet to be determined. My lab investigated whether the expansion of human memory CD8+ T cells with aging was secondary to increased expression of IL-7 receptor alpha chain (IL-7R?) which dictates the response to the pro-survival cytokine IL- 7. This study found two cell populations which expressed high and low levels of IL-7R? (IL-7R?high and low) in effector memory (EM) CD8+ T cells in human peripheral blood. Of interest, older adults (age ? 65) had expansion of IL-7R?low EM CD8+ T cells (up to 80% of total CD8+ T cells), which are largely cytotoxic and inflammatory cytokine producing cells, compared to young adults (age ? 40). We have found that such cell expansion is associated with cytomegalovirus (CMV) infection, which persists for lifetime, as well as with enhanced production of and response to the cytokine IL-15 which promotes the maintenance of memory CD8+ T cells. However, the significance of the expansion of IL-7R?low EM CD8+ T cells in older adults remains largely unknown, especially in the context of inflammation. To address this critical question, we performed a genome-wide DNA methylation analysis in IL-7R?high and low EM CD8+ T cells in that DNA methylation modulates gene expression. This analysis shows that IL-7R?low EM CD8+ T cells have hypomethylation of DNA in a group of chemotaxis-associated genes with enhanced expression. These include CX3CR1 (receptor for fractalkine), CXCR1 (IL-8 receptor A), chemokine ligand 3 (CCL3) and CCL4. Plus, we noticed increased CX3CR1 expression by IL-7R?low EM CD8+ T cells in older adults compared to young adults. Thus, we hypothesize that 1) IL-7R?low EM CD8+ T cells are potent inflammatory cells with an increased capacity to migrate to inflamed sites and produce chemokines, cytokines and cytotoxic molecules; 2) such increased capacity is related to altered DNA methylation with aging; and 3) the expansion of this cell subset and enhanced IL-15-mediated inflammatory response with aging can contribute to inflammation. These hypotheses will be tested with: Aim 1. Elucidate whether and how aging affects DNA methylation- mediated gene expression in human IL-7R?low EM CD8+ T cells; Aim 2. Elucidate whether and how aging enhances IL-15-mediated inflammatory response in human IL-7R?low EM CD8+ T cells; and Aim 3. Investigate the significance of IL-7R?low EM CD8+ T cells in the development of inflammation with aging. The results of this proposal will shed light on the biological significanc of expanded memory CD8+ T cells with aging, especially in the aspect of inflammaging, as well as on the possible role of DNA methylation in driving this process.