Therapeutic Immune Reprogramming by Rapamycin Attenuates Plaque Inflammation and Lymphoid Immune Responses in Aged Atherosclerotic Mice

Aging is a major risk factor for atherosclerosis and is accompanied by profound changes in the immune system, including effector T cell expansion, senescent cell accumulation, and increased pro‐inflammatory signaling. Rapamycin, a promising rejuvenation therapeutic that inhibits mTORC1 and modulates immune aging, was investigated for its potential to attenuate pro‐atherogenic immune responses in aged atherosclerotic mice. 80‐ to 90‐week‐old male Ldlr −/− mice with established atherosclerotic lesions were treated intraperitoneally with rapamycin or control triweekly for 8 weeks. Systemic and plaque immunity was assessed by flow cytometry or single‐cell RNA‐sequencing. Plaque morphology was evaluated by histology. Rapamycin treatment reduced plaque macrophage content (0.73 ± 0.07 × 10 5 μm 2 ) compared to control (ctrl: 0.95 ± 0.09 × 10 5 μm 2 , p < 0.05) and decreased total T cell numbers in vascular and lymphoid tissues. This was accompanied by a shift from effector to central memory phenotypes, particularly within the CD8 + compartment, and a relative enrichment of regulatory CD4 + T cells (Tregs). Single‐cell transcriptomics of aortic Tregs revealed increased expression of suppressive genes ( Foxp3 , Tgfb1 ) upon rapamycin. Rapamycin also reduced T follicular helper cells, IL‐21 expression, germinal center B cells, plasma cells, and total and oxidation‐specific epitope‐specific immunoglobulin levels. Additionally, age‐associated B cells were diminished in spleen and lymph nodes, reflecting a broader anti‐inflammatory effect on B cell immunity. Finally, aortic leukocytes displayed profoundly reduced senescent enrichment scores. Rapamycin remodels the immune landscape in aged atherosclerotic mice, promoting regulatory lymphocyte subsets and suppressing antigen‐driven and inflammatory immune responses. These findings highlight the potential of immune‐targeted rejuvenation to mitigate age‐related atherogenic inflammation.