Interleukin 21-activated B cells can kill tumor cells in a granzyme B-dependent manner (66.5)

Abstract

Abstract Interleukin 21 (IL-21) is a promising cytokine for the treatment of tumors and infections. Recently, IL-21 was identified as an inducer of plasma cells when combined with CD40 ligand (CD40L). Using various immunological methods including FACS analysis, ELISA, ELISpot and fluorescence microscopy, we demonstrate here that in the absence of CD40L B cells (BC) rather differentiate into granzyme B (GzmB)-secreting cytotoxic cells instead of plasma cells. GzmB induction in BC requires IL-21 and BC receptor cross-linking, and is associated with phosphorylation of SYK, JAK1/3 and STAT1/3, signaling molecules which are also involved in the activation of CTL and NK cells. CD40L effectively suppresses GzmB in BC, suggesting that GzmB-secreting BC play a role early during inflammatory responses, before CD40L-expressing T cells are present. BC-derived GzmB is enzymatically active and induces apoptosis in tumor cell lines including HeLa cells and PC3 cells. Importantly, induction of apoptosis by GzmB-secreting B cells can be suppressed by neutralization of GzmB using the substrate inhibitor Ac-IEPD-CHO as well as a novel small molecule inhibitor of GzmB identified in our laboratory. Our data reveal a novel role of IL-21-activated BC, which involves GzmB secretion and cytotoxicity. Our findings may have implications for the understanding of tumor immunosurveillance and early anti-viral immune responses, and may open novel approaches for the immunotherapy of neoplastic and viral diseases.