This is a fully human IgG1 monoclonal antibody using the same sequences as the therapeutic antibody belimumab. It functions as a specific inhibitor of B-lymphocyte stimulator protein (BlyS), also known as BAFF and TNFSF13B, and is employed as an add-on therapy for treating systemic lupus erythematosus (SLE) and active lupus nephritis. Belimumab works by effectively inhibiting autoreactive, pro-inflammatory B cells that cause chronic inflammation and tissue damage. In patients with SLE, it significantly reduces circulating B (CD20+) cell levels. Belimumab selectively binds BLyS with high affinity, neutralizes it, and blocks its interaction with various B cell receptors, such as transmembrane activator and calcium-modulator and cyclophilin ligand interactor (TACI), B-cell maturation antigen (BCMA), and BLyS receptor 3 (BR3). Ultimately, it impedes the survival of B cells, promotes apoptosis, and diminishes the differentiation and maturation of B cells into immunoglobulin-producing plasma cells.