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(100) (apoB), the core protein of low-density lipoprotein, is an autoantigen that drives the generation of pathogenic T-helper type 1 (T(H)1) cells with proinflammatory cytokine secretion. Clinical data suggest the existence of apoB-specific CD4(+) T cells with an atheroprotective, regulatory T cell (T(reg)) phenotype in healthy individuals. Yet, the function of apoB-reactive T(regs) and their relationship with pathogenic T(H)1 cells remain unknown. METHODS: 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(978-993) (apoB(+)) at the single-cell level. RESULTS: We found that apoB(+) T cells build an oligoclonal population in lymph nodes of healthy mice that exhibit a T(reg)-like transcriptome, although only 21% of all apoB(+) T cells expressed the T(reg) 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(H) signatures that suggested overlapping multilineage phenotypes with pro- and anti-inflammatory transcripts of T(H)1, T helper cell type 2 (T(H)2), and T helper cell type 17 (T(H)17), and of follicular-helper T cells. ApoB(+) T cells were increased in mice and humans with atherosclerosis and progressively converted into pathogenic T(H)1/T(H)17-like cells with proinflammatory properties and only a residual T(reg) transcriptome. Plaque T cells that expanded during progression of atherosclerosis consistently showed a mixed T(H)1/T(H)17 phenotype in single-cell RNA sequencing. In addition, we observed a loss of FoxP3 in a fraction of apoB(+) T(regs) in lineage tracing of hyperlipidemic Apoe(–/–) mice. In adoptive transfer experiments, converting apoB(+) T(regs) failed to protect from atherosclerosis. CONCLUSIONS: 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(regs) as a novel cellular target in atherosclerosis.