Combined CD34+ cell frequency and S100A8/A9 profiling improves biological risk stratification in peripheral and carotid atherosclerosis

Background Atherosclerosis is a chronic inflammatory disorder and a leading cause of cardiovascular morbidity and mortality. Despite advances in imaging and risk stratification, current tools do not detect biologically unstable and silent plaques. CD34+ haematopoietic stem/progenitor cells (HSPCs) contribute to vascular homeostasis, but their circulating levels and functional capacity are impaired in cardiovascular disease. However, their distribution between peripheral blood and arteries, and correlation with systemic inflammation, remain insufficiently characterised. Purpose Study whether circulating CD34+HSPCs are reduced in patients with advanced peripheral atherosclerosis and differ with carotid plaque stability and symptoms. Based on our previous work, showing upregulation of S100A8/A9, a key mediator of vascular inflammation, in both CD34+HSPCs and plasma of individuals at high cardiovascular risk, we measured plasma S100A8/A9. We hypothesised that CD34+ depletion, vascular tissue accumulation, and elevated S100A8/A9 identify patients at higher biological risk. Methods In this pilot observational study, 246 patients with significant atherosclerosis (mean age 74.3 years±7.6 SD, 75% male) undergoing carotid or femoral endarterectomy were compared with 68 controls without vascular disease (mean age 57 years±4.8 SD, 85.3% male). Clinical data, imaging, and biological samples (blood and vascular tissue, including plaque) were collected. Carotid plaques were classified as stable or unstable, and patients categorised as asymptomatic or symptomatic according to SICVE/ESVS guidelines. Mononuclear cells from blood and vascular tissue were analysed by flow cytometry, and plasma S100A8/A9 by ELISA. Results Compared with controls, the frequency of circulating CD45dimCD34+HSPCs was significantly reduced in patients with femoral and carotid plaques (p<0.01). In particular, patients with unstable plaques and asymptomatic individuals exhibited lower circulating CD45dimCD34+HSPCs (p<0.0001), whereas no significant differences were observed compared with patients with stable plaques or symptomatic disease. Of note, CD45+CD34+CD31- cells found within tissue (4.8%). Plasma S100A8/A9 levels (ug/mL) were elevated across all atherosclerosis patient groups [p<0.001 for femoral and p<0.0001 for carotid plaques, unstable plaques, and asymptomatic patients vs controls; p<0.001 for stable plaques and p<0.05 for symptomatic patients vs controls]. S100A8/A9 levels correlated with circulating CD34+ cells, particularly in patients with stable plaques (r=0.86, p<0.05). Age was not associated with CD34+HSPC frequency or S100A8/A9 levels. Conclusions Advanced atherosclerosis is characterised by CD34+ depletion in asymptomatic or unstable disease and vascular tissue accumulation. Elevated S100A8/A9 reflects systemic inflammation, and combining these biomarkers may improve early risk detection. Prospective studies are needed to confirm the prognostic value.