THU0291 Endothelial Progenitor Cells in Systemic Lupus Erythematosus: Effect of B Lymphocyte Stimulator and Its Inhibition

BackgroundCardiovascualar disease is the main comorbidity in Systemic Lupus Erythematosus (SLE). Circulating endothelial progenitor cells (EPCs) are bone marrow-derived cells, able to differentiate into mature endothelial cells. Several studies demonstrated a reduction and functional impairment of EPCs in SLE patients, contributing to the endothelial dysfunction characterizing these patients. Belimumab (BLM), a human monoclonal antibody anti-B Lymphocyte Stimulator (BLyS) is the first biological drug approved for the treatment of SLE patients. In murine models of atherosclerosis, treatment with a BLyS inhibitor slowed the progression and reduced the size of atherosclerotic plaque.Objectivesto evaluate the effect of BLyS inhibition on EPCs both ex vivo – in SLE patients receiving BLM– and in vitro.MethodsWe enrolled consecutive patients with SLE diagnosed according to 1997 ACR criteria. Patients with known cardiovascular disease were excluded. As control, we studied age and sex-matched healthy subjects.SLE disease activity was evaluated by SLEDAI 2K at baseline and after 4 and 12 weeks of BLM; blood samples were collected at the same time-point. Peripheral blood mononuclear cells (PBMC) isolated by Ficoll density-gradient centrifugation were incubated with fluorescein isothiocyanate-labeled anti-CD34 monoclonal antibodies and phycoerythrin-labeled anti VEGF-R2/KDR; acquisition was performed by flow cytometry: EPCs were defined as CD34/KDR double-positive cells.For in vitro studies, recovered cells isolated from healthy donors' PBMC were plated on dishes coated with human fibronectin. Apoptosis was investigated after 6, 12, 24 and 48 hours of incubation with BLyS at different concentration – 5, 20 and 100 ng/ml – and re-evaluated after 6 hours of co-incubation with BLM at 173 and 300 μg/ml.Kolmogorov-Smirnov showed the normal distribution of EPCs; data were expressed as mean±standard deviation. To test the hypothesis that BLM may increase EPCs number we used one-tailed T-test. A p value