LINE1 are spliced in non-canonical transcript variants to regulate T cell quiescence and exhaustion

How gene expression is controlled to preserve human T cell quiescence is poorly understood. Here we show that non-canonical splicing variants containing long interspersed nuclear element 1 (LINE1) enforce naive CD4⁺ T cell quiescence. LINE1-containing transcripts are derived from CD4⁺ T cell-specific genes upregulated during T cell activation. In naive CD4⁺ T cells, LINE1-containing transcripts are regulated by the transcription factor IRF4 and kept at chromatin by nucleolin; these transcripts act in cis, hampering levels of histone 3 (H3) lysine 36 trimethyl (H3K36me3) and stalling gene expression. T cell activation induces LINE1-containing transcript downregulation by the splicing suppressor PTBP1 and promotes expression of the corresponding protein-coding genes by the elongating factor GTF2F1 through mTORC1. Dysfunctional T cells, exhausted in vitro or tumor-infiltrating lymphocytes (TILs), accumulate LINE1-containing transcripts at chromatin. Remarkably, depletion of LINE1-containing transcripts restores TIL effector function. Our study identifies a role for LINE1 elements in maintaining T cell quiescence and suggests that an abundance of LINE1-containing transcripts is critical for T cell effector function and exhaustion.