Pathogenic Autoimmunity in Atherosclerosis Evolves From Initially Protective Apolipoprotein B 100 -Reactive CD4 + T-Regulatory Cells

Throughout the inflammatory response that accompanies atherosclerosis, autoreactive CD4 T-helper cells accumulate in the atherosclerotic plaque. Apolipoprotein B (apoB), the core protein of low-density lipoprotein, is an autoantigen that drives the generation of pathogenic T-helper type 1 (T 1) cells with proinflammatory cytokine secretion. Clinical data suggest the existence of apoB-specific CD4 T cells with an atheroprotective, regulatory T cell (T ) phenotype in healthy individuals. Yet, the function of apoB-reactive T and their relationship with pathogenic T 1 cells remain unknown. To interrogate the function of autoreactive CD4 T cells in atherosclerosis, we used a novel tetramer of major histocompatibility complex II to track T cells reactive to the mouse self-peptide apo B (apoB ) at the single-cell level. We found that apoB T cells build an oligoclonal population in lymph nodes of healthy mice that exhibit a T -like transcriptome, although only 21% of all apoB T cells expressed the T transcription factor FoxP3 (Forkhead Box P3) protein as detected by flow cytometry. In single-cell RNA sequencing, apoB T cells formed several clusters with mixed T signatures that suggested overlapping multilineage phenotypes with pro- and anti-inflammatory transcripts of T 1, T helper cell type 2 (T 2), and T helper cell type 17 (T 17), and of follicular-helper T cells. ApoB T cells were increased in mice and humans with atherosclerosis and progressively converted into pathogenic T 1/T 17-like cells with proinflammatory properties and only a residual T transcriptome. Plaque T cells that expanded during progression of atherosclerosis consistently showed a mixed T 1/T 17 phenotype in single-cell RNA sequencing. In addition, we observed a loss of FoxP3 in a fraction of apoB T in lineage tracing of hyperlipidemic mice. In adoptive transfer experiments, converting apoB T failed to protect from atherosclerosis. Our results demonstrate an unexpected mixed phenotype of apoB-reactive autoimmune T cells in atherosclerosis and suggest an initially protective autoimmune response against apoB with a progressive derangement in clinical disease. These findings identify apoB autoreactive T as a novel cellular target in atherosclerosis.