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Somatic mutations associate with clonal expansion of CD8+ T cells

ABSTRACT: Somatic mutations in T cells can cause cancer but also have implications for immunological diseases and cell therapies. The mutation spectrum in non-malignant T cells is unclear. Here, we examined somatic mutations in CD4+ and CD8+ T cells from 90 patients with hematological and immunological disorders and used T cell receptor (TCR) and single-cell sequencing to link mutations with T cell expansions and phenotypes. CD8+ cells had higher mutation burden than CD4+ cells. Notably, the biggest variant allele frequency (VAF) of non-synonymous variants was higher than synonymous variants in CD8+ T cells, indicating non-random distribution. The non-synonymous VAF in CD8+ T cells strongly correlated with the TCR frequency, but not age. We identified mutated pathways essential for T cell function or recurrently mutated in lymphoid neoplasia. Single-cell sequencing revealed cytotoxic Temra phenotypes of mutated T cells. Our findings suggest that somatic mutations contribute to CD8+ T cell expansions without malignant transformation.

PROVIDER: EGAS00001007606 | EGA |

REPOSITORIES: EGA

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Project description:Many aged individuals develop monoclonal expansions of CD8 T cells. These expansions are derived from a CD8 memory T cell that outcompetes neighboring CD8 T cells. The molecular alterations within clonal expansions that confer this competitive advantage relative to other CD8 T cells remains unknown. These microarray experiments were designed to identify genes differentially expressed in age-associated expansions of CD8 memory T cells relative to polyclonal CD8 memory T cells found in the same aged mice. Subsequent analysis of these data identified two major types of clonal expansions, distinguished by expression level of integrin a4 mRNA and protein. Based on this classification, Expansion_rep1 belongs to the integrin a4 high subtype of clonal expansions. In contrast, reps 2, 4, and 5 belong to the integrin a4 low subtype of clonal expansions. Given the divergent biological properties of these two subtypes of clonal expansions, we have focused genes differentially expressed between Expansion_rep 2, 4, and 5 and their paired PolyclonalAged samples. Experiment Overall Design: A total of 8 samples were analyzed for gene expression using the Affymetrix mouse genome 430 2.0 microarray platform. The experimental samples of interest were age-associated clonal expansions of CD8 memory T cells. We purified four clonal expansions from four independent, aged mice (indicated as "Expansion" rep1 2, 3, 4). For each clonal expansion of CD8 memory T cells that was purified, there was a paired control in which polyclonal CD8 memory T cells were harvested from the same aged mouse (denoted as "PolyclonalAged" rep1, 2, 3, 4). These paired samples allow one to consider gene expression changes from mice which have undergone the same age-associated changes in biology. The predominant comparison this study focused on was changes in gene expression between age-associated clonal expansions of CD8 memory T cells and their paired, polyclonal CD8 memory T cells. A total of 4 of these pairs were collected.

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Somatic mutations associate with clonal expansion of CD8+ T cells

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