Interleukin-21 (IL-21) is a pleiotropic cytokine belonging to the common γ-chain receptor family, primarily produced by activated CD4+ T cells, particularly follicular helper T (Tfh) and Th17 cells. It plays critical roles in modulating immune responses, including promoting B cell differentiation, enhancing cytotoxic activity of CD8+ T cells and NK cells, and regulating immunoglobulin production. Dysregulation of IL-21 signaling is implicated in autoimmune diseases (e.g., rheumatoid arthritis, lupus), inflammatory disorders, and cancers, making it a therapeutic target.
IL-21 antibodies are engineered molecules designed to either block IL-21 interaction with its receptor (neutralizing antibodies) or target IL-21-producing cells. Therapeutic monoclonal antibodies against IL-21 or its receptor (IL-21R) aim to suppress pathogenic immune activation in autoimmune conditions. Conversely, agonist antibodies may enhance IL-21-mediated antitumor immunity in cancer immunotherapy.
Research tools like anti-IL-21 antibodies are widely used to study IL-21 expression patterns and signaling pathways. Challenges include balancing therapeutic efficacy with potential immunosuppressive risks and optimizing tissue-specific targeting. Several preclinical and early clinical trials are exploring IL-21 antibodies, though none have yet reached widespread clinical use, reflecting the cytokine's complex dual role in immunity.